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Sample records for low-gravity optical spectral

  1. Optical measurements and tests performed in a low-gravity environment

    NASA Technical Reports Server (NTRS)

    Owen, R. B.

    1980-01-01

    Shadowgraph and schlieren techniques have been used on board the NASA KC-135 low-gravity simulation aircraft to measure gravity-related fluid flow occurring in various experimental configurations. These configurations included cooled and solidified ammonium chloride and water, electrodeposited cobalt in CoSO4 solution, and immiscible and crystal melt solutions. Hardware tests have also been performed for such critical optical system components as lasers and spatial filters to determine their performance and operation under low-gravity conditions. These test results will be used in the design of the various future Shuttle experiments which will utilize advanced optical measurement techniques. The design and configuration of the optical systems used to make these measurements and tests are presented, and the performance and operation of these systems and their components under low-gravity conditions are discussed. Some preliminary results are included.

  2. Optical measurements and tests performed in a low-gravity environment

    NASA Technical Reports Server (NTRS)

    Owen, R. B.

    1980-01-01

    Shadowgraph and schlieren techniques have been used on board the NASA KC-135 low-gravity simulation aircraft to measure gravity-related fluid flow occurring in various experimental configurations. These configurations included cooled and solidified ammonium chloride and water, electrodeposited cobalt in CoSO4 solution, and immiscible and crystal melt solutions. Hardware tests have also been performed for such critical optical system components as lasers and spatial filters to determine their performance and operation under low-gravity conditions. These test results will be used in the design of the various future Shuttle experiments which will utilize advanced optical measurement techniques. The design and configuration of the optical systems used to make these measurements and tests are presented, and the performance and operation of these systems and their components under low-gravity conditions are discussed. Some preliminary results are included.

  3. Single Bubble Sonoluminescence in Low Gravity and Optical Radiation Pressure Positioning of the Bubble

    NASA Technical Reports Server (NTRS)

    Thiessen, D. B.; Young, J. E.; Marr-Lyon, M. J.; Richardson, S. L.; Breckon, C. D.; Douthit, S. G.; Jian, P. S.; Torruellas, W. E.; Marston, P. L.

    1999-01-01

    Several groups of researchers have demonstrated that high frequency sound in water may be used to cause the regular repeated compression and luminescence of a small bubble of gas in a flask. The phenomenon is known as single bubble sonoluminescence (SBSL). It is potentially important because light emitted by the bubble appears to be associated with a significant concentration of energy within the volume of the bubble. Unfortunately, the detailed physical mechanisms causing the radiation of light by oscillating bubbles are poorly understood and there is some evidence that carrying out experiments in a weightless environment may provide helpful clues. In addition, the radiation pressure of laser beams on the bubble may provide a way of simulating weightless experiments in the laboratory. The standard model of SBSL attributes the light emission to heating within the bubble by a spherically imploding shock wave to achieve temperatures of 50,000 K or greater. In an alternative model, the emission is attributed to the impact of a jet of water which is required to span the bubble and the formation of the jet is linked to the buoyancy of the bubble. The coupling between buoyancy and jet formation is a consequence of the displacement of the bubble from a velocity node (pressure antinode) of the standing acoustic wave that drives the radial bubble oscillations. One objective of this grant is to understand SBSL emission in reduced buoyancy on KC-135 parabolic flights. To optimize the design of those experiments and for other reasons which will help resolve the role of buoyancy, laboratory experiments are planned in simulated low gravity in which the radiation pressure of laser light will be used to position the bubble at the acoustic velocity node of the ultrasonic standing wave. Laser light will also be used to push the bubble away from the velocity node, increasing the effective buoyancy. The original experiments on the optical levitation and radiation pressure on bubbles

  4. ATHLETE: Low Gravity Testbed

    NASA Technical Reports Server (NTRS)

    Qi, Jay Y.

    2011-01-01

    The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) is a vehicle concept developed at Jet Propulsion Laboratory as a multipurpose robot for exploration. Currently, the ATHLETE team is working on creating a low gravity testbed to physically simulate ATHLETE landing on an asteroid. Several projects were worked on this summer to support the low gravity testbed.

  5. Low Gravity Improves Welds

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Kaukler, William F.; Plaster, Teresa C.

    1993-01-01

    Hardnesses and tensile strengths greater. Welds made under right conditions in low gravity appear superior to those made under high gravity. Conclusion drawn from results of welding experiments conducted during low- and high-gravity-simulating maneuvers of KC-135 airplane. Results have implications not only for welding in outer space but also for repeated rapid welding on Earth or in airplanes under simulated low gravity to obtain unusually strong joints.

  6. Low Gravity Improves Welds

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Kaukler, William F.; Plaster, Teresa C.

    1993-01-01

    Hardnesses and tensile strengths greater. Welds made under right conditions in low gravity appear superior to those made under high gravity. Conclusion drawn from results of welding experiments conducted during low- and high-gravity-simulating maneuvers of KC-135 airplane. Results have implications not only for welding in outer space but also for repeated rapid welding on Earth or in airplanes under simulated low gravity to obtain unusually strong joints.

  7. Adhesion Casting In Low Gravity

    NASA Technical Reports Server (NTRS)

    Noever, David A.; Cronise, Raymond J.

    1996-01-01

    Adhesion casting in low gravity proposed as technique for making new and improved materials. Advantages of low-gravity adhesion casting, in comparison with adhesion casting in normal Earth gravity, comes from better control over, and greater uniformity of, thicknesses of liquid films that form on and adhere to solid surfaces during casting.

  8. Foam formation in low gravity

    NASA Technical Reports Server (NTRS)

    Wessling, Francis C.; Mcmanus, Samuel P.; Matthews, John; Patel, Darayas

    1990-01-01

    An apparatus that produced the first polyurethane foam in low gravity has been described. The chemicals were mixed together in an apparatus designed for operation in low gravity. Mixing was by means of stirring the chemicals with an electric motor and propeller in a mixing chamber. The apparatus was flown on Consort 1, the first low-gravity materials payload launched by a commercial rocket launch team. The sounding rocket flight produced over 7 min of low gravity during which a polyurethane spheroidal foam of approximately 2300 cu cm was formed. Photographs of the formation of the foam during the flight show the development of the spheroidal form. This begins as a small sphere and grows to approximately a 17-cm-diam spheroid. The apparatus will be flown again on subsequent low-gravity flights.

  9. Materials processing in low gravity

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1990-01-01

    Activities of the Materials Processing in Low Gravity Program in which the University of Alabama in Huntsville (UAH) designed, fabricated, and performed various low gravity experiments in materials processing between October 26, 1988 through October 25, 1989 are discussed. Details of low gravity experiments using the Drop Facilities at the Marshall Space Flight Center (MSFC) and the KC-135 aircraft at Ellington Field are discussed. This effort included the defining of experimental requirements and equipment, experiment-facility integration requirements, building/assembling the necessary experiment apparatus, and conducting experiments which will contribute to the knowledge base for commercialization of materials processing in low gravity. UAH also performed logistical support needed to execute the experimentation, the necessary sample preparation, metallography analysis, and physical properties measurements of the processed samples.

  10. Materials processing in low gravity

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1989-01-01

    Work is reported on the Materials Processing Low Gravity Program in which the University of Alabama worked with scientists and engineers at Marshall Space Flight Center to design, implement and perform low gravity experiments with various scientific investigators in materials processing science through March 15, 1989. The facilities used in these short duration low gravity experiments include the Drop Tube and Drop Tower at MSFC, and the KC-135 aircraft at Ellington Field. The utilization of these ground-based low gravity facilities for materials processing was instrumental in determining the feasibility of either performing a particular experiment in the microgravity of Space or continuing on-going activities which may have been delayed due to the absence of shuttle flights during this contractual effort.

  11. REXUS 16 Low Gravity Experiment

    NASA Astrophysics Data System (ADS)

    Manoliu, L.; Ciuca, I.; Lupu, E. S.; Ciobanu, I.; Cherciu, C.; Soare, C.; Murensan, C.; Dragomir, D.; Chitu, C.; Nachila, C.

    2015-09-01

    The REXUS/BEXUS is a programme realized under a bilateral agency agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB) (Source: www.rexusbexus.net) . Within this programme, the experiment proposed by LOW Gravity was given the opportunity to fly on board of REXUS 16 from Kiruna, Sweden, in May 2014. Since space settlements are within our reach and material processing in reduced gravity is a key requirement, we aim to improve this field by investigating the melting and welding processes taking place in milligravity on board of a sounding rocket. Our main objective is to analyze the surface deformation and physical properties of titanium and acid core solder alloys welded/melted under miligravity conditions with a 25W LASER diode. The main components of our experiment are the metal samples, the LASER diode and the control electronics. The metal samples are placed in front of an optical system and are shifted during approximately 120 seconds of milligravity. The optical system is connected via an optic fiber to the LASER diode. The electronics consists of two custom-made boards: the mainboard which is connected to the REXUS interface and controls the LASER diode and the sample shifting and the logboard which has an SD card to log all experiment data (sample position, experiment acceleration and rotation rate, pressure and temperature, battery voltage and LASER diode status). During the flight, due to unexpected vibration levels, the fiber optics was damaged at T+70 and the experiment could not fulfill its main objective. A GoPro camera mounted inside the experiment box recorded the experiment operation. Valuable information regarding temperature and battery voltage was also sent remotely to our Ground Station. This data enabled us to perform a thorough failure analysis. Parallel readings of these parameters taken by other experiments and by the REXUS Service Module corroborate our data and increase the accuracy of our analysis

  12. Low-gravity electrodeposition and growth of polymer thin films with large third-order optical nonlinearities by electrochemical processes for devices: Thiophene-based polymers

    NASA Technical Reports Server (NTRS)

    Penn, Benjamin G.; Riley, Clyde

    1993-01-01

    It has been proposed that NLO thin film properties may be improved by low-gravity processing. Strong candidates for NLO thin film applications are the polythiophenes. Polymeric thiophenes are attractive materials due to their ease of preparation, stability, and high X(exp 3). A simple and convenient method for preparation of polythiophenes is electrochemical oxidation. We will apply some of our experience and lessons learned in low-gravity metal, metal/cermet electrode position to improve the quality of polythiophene(s) thin films. In low gravity electrode position of Ni at a high rate on an Au substrate often results in the production of an x-ray non diffracting surface. Cobalt metal deposition does not give this result nor does Ni when deposited similarly on a glassy carbon substrate. Co/Ni alloy composition produced during electrode position is strongly dependent upon the amount of convection. Code position of neutral inert cermets with metals is influenced significantly by the presence of gravity and the size of the cermets. Tracks left in the 1-g surfaces by unsuccessful particle occlusion indicate suspension of the large particles is not the only reason for poor volume percentages of the larger particles in the deposits. All size particles are more homogeneously distributed in the deposits in low-gravity electrocodeposition than in 1-g. Low gravity gives larger volume percentages for the larger particles in the deposits, while 1-g gives larger volume percentages for the smaller particles. Intermediate size particles give mixed results. The experimental cells were constructed with flat electrode end plates such that 1-g bench reference electrode positions could be carried out at various orientations with respect to gravity. A series of bench studies using similar designed cells are suggested so that convection modification can be applied to electrochemical thin film preparation. Convection effects can then be coupled with other parameter variations in current

  13. Low gravity transfer line chilldown

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.; Collins, Frank G.; Kawaji, Masahiro

    1992-01-01

    The progress to date is presented in providing predictive capabilities for the transfer line chilldown problem in low gravity environment. A low gravity experimental set up was designed and flown onboard the NASA/KC-135 airplane. Some results of this experimental effort are presented. The cooling liquid for these experiments was liquid nitrogen. The boiling phenomenon was investigated in this case using flow visualization techniques as well as recording wall temperatures. The flow field was established by injecting cold liquid in a heated tube whose temperature was set above saturation values. The tubes were vertically supported with the liquid injected from the lower end of the tube. The results indicate substantial differences in the flow patterns established during boiling between the ground based, (1-g), experiments and the flight experiments, (low-g). These differences in the flow patterns will be discussed and some explanations will be offered.

  14. Materials processing in low gravity

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1991-01-01

    Several NASA facilities are available for low gravity experimentation: the Drop Facilities at NASA Marshall and the KC-135 at NASA Johnson. The use of these facilities allows for a rather inexpensive method of determining whether or not particular experiments will be worthwhile candidates for space experiments. Equipment currently available include various furnaces for the Drop Tube, the Drop Tower, and the KC-135. The furnaces for the Drop Tube include both an electron beam and electromagnetic levitation furnace. A vacuum furnace is used for the Drop Tower. Several furnaces used in performing KC-135 solidification experiments include the Automated Directional Solidification Furnace, the Isothermal Casting Furnace, the Rapid Melt/Rapid Quench and the Polymer/Video Furnaces.

  15. Low gravity liquid motions in spacecraft

    NASA Technical Reports Server (NTRS)

    Dodge, Franklin T.

    1987-01-01

    Low gravity liquid motions in a spacecraft are discussed in outline form and on viewgraphs. Free-surface sloshing, liquid draining, liquid reorientation, and sloshing in a bladdered tank are covered. Conclusions and recommendations are given.

  16. Approaches to Validation of Models for Low Gravity Fluid Behavior

    NASA Technical Reports Server (NTRS)

    Chato, David J.; Marchetta, Jeffery; Hochstein, John I.; Kassemi, Mohammad

    2005-01-01

    This paper details the author experiences with the validation of computer models to predict low gravity fluid behavior. It reviews the literature of low gravity fluid behavior as a starting point for developing a baseline set of test cases. It examines authors attempts to validate their models against these cases and the issues they encountered. The main issues seem to be that: Most of the data is described by empirical correlation rather than fundamental relation; Detailed measurements of the flow field have not been made; Free surface shapes are observed but through thick plastic cylinders, and therefore subject to a great deal of optical distortion; and Heat transfer process time constants are on the order of minutes to days but the zero-gravity time available has been only seconds.

  17. Limits of spectral resolution in optical measurements

    NASA Astrophysics Data System (ADS)

    Marques, Manuel B.

    2014-08-01

    Nowadays a growing number of scientists relies on optical spectral measurements for their research. The market is full of new plug-and-play equipment for spectral analysis that take the fuss out of the measurements. As with other instruments (computers, lasers, etc.) the researcher doesńt need any longer to work with someone with a post-graduate formation on the technology to be able to do excellent research. But, as in every instrument, there are limitations on the instrument use that affect its precision and resolution. Currently there is in the market a large variety of equipment for spectral measurements. They range from the huge long focal length double pass monochromators to the small pocket size USB connected array spectrometers. The different configurations have different sensitivities on the light input system, light intensity, coherence, polarization, etc. In this talk we will discuss a few of the limitations in spectral measurements that can be found in experimental setups.

  18. Inhalation risk in low-gravity spacecraft.

    PubMed

    Todd, P; Sklar, V; Ramirez, W F; Smith, G J; Morgenthaler, G W; McKinnon, J T; Oberdorster, G; Schulz, J

    1994-07-01

    Inhalation risks on long-duration manned spaced flight include gasses chronically released by outgassing of materials, gasses released during spills, thermodegradation events (including fires) with their attendant particulates, and fire extinguishment. As an example, an event in which electronic insulation consisting of polytetrafluoroethylene undergoes thermodegradation on the Space Station Freedom was modeled experimentally and theoretically from the initial chemistry and convective transport through pulmonary deposition in humans. The low-gravity environment was found to impact various stages of event simulation. Critical unknowns were identified, and these include the extent of production of ultrafine particles and polymeric products at the source in low gravity, the transport of ultrafine particles in the spacecraft air quality control system, and the biological response of the lung, including alveolar macrophages, to this inhalation risk in low gravity.

  19. Vesta and low gravity impact mixing

    NASA Astrophysics Data System (ADS)

    Hoffmann, Martin; Nathues, Andreas; Vincent, Jean-Baptiste; Sierks, Holger

    2013-04-01

    impacts into granular material lead to anything but a simple crater morphology. Unusual scaling laws (Uehara et al. 2003) and much more diverse phase patterns than in ordinary solid media have to be taken into account, if a consistent interpretation of the formation of a crater in very deep regolith is attempted (e.g. Opsomer et al. 2011). Additional effects are due to the low gravity environment on a small planetary body like Vesta (Tancredi et al. 2012). On Vesta many apparent counterparts to the results of the experiments can be found, as demonstrated by some examples. On a global scale, the multitude of small, unresolved primary and secondary impacts into the granular regolith contributes to the observed maturity on Vesta even after short time scales. References Cook, M. A., Mortensen, K. S. 1967. Impact cratering in granular materials. J. Appl. Phys. 38, 5125-5128. Daniels, K. E., Coppock, J. E., Behringer, R. P. 2004. Dynamics of meteor impacts. Chaos 14, 84. Daraio, C., Nesterenko, V. F., Herbold, E. B., Jin S. 2006. Energy trapping and shock desintegration in a composite granular medium. Phys. Rev. Lett. 96, 058002, 1-4. Opsomer, E., Ludewig, F., Vandewalle, N. 2011. Phase transitions in vibrated granular systems in microgravity. Phys. Rev. E84, 051306, 1-5. Rivas, N., Ponce, S., Gellet, B., Risso, D., Soto, R., Cordero, P. 2011. Sudden chain energy transfer events in vibrated granular media. Phys. Rev. Lett. 106, 088001, 1-4. Tancredi, G., Maciel, A., Heredia, L., Richeri, P., Nesmachnow, S. 2012. Granular physics in low-gravity environments using discrete element method. Monthly Not. Royal Astron. Soc. 420, 3368-3380. Uehara, J. S., Ambroso, M. A., Ojha, R. J., Durian, D. J. 2003. Low-speed impact craters in loose granular media. Phys. Rev. Lett. 90, 194301, 1-4.

  20. Self-spectral calibration for spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Zhang, Xianling; Gao, Wanrong; Bian, Haiyi; Chen, Chaoliang; Liao, Jiuling

    2013-06-01

    A different real-time self-wavelength calibration method for spectral domain optical coherence tomography is presented in which interference spectra measured from two arbitrary points on the tissue surface are used for calibration. The method takes advantages of two favorable conditions of optical coherence tomography (OCT) signal. First, the signal back-scattered from the tissue surface is generally much stronger than that from positions in the tissue interior, so the spectral component of the surface interference could be extracted from the measured spectrum. Second, the tissue surface is not a plane and a phase difference exists between the light reflected from two different points on the surface. Compared with the zero-crossing automatic method, the introduced method has the advantage of removing the error due to dispersion mismatch or the common phase error. The method is tested experimentally to demonstrate the improved signal-to-noise ratio, higher axial resolution, and slower sensitivity degradation with depth when compared to the use of the zero-crossing method and applied to two-dimensional cross-sectional images of human finger skin.

  1. Spectral properties of light in quantum optics

    NASA Astrophysics Data System (ADS)

    Knöll, L.; Vogel, W.; Welsch, D.-G.

    1990-07-01

    The problem of spectral filtering of quantized light fields is studied, based on the recently developed quantum-optical theory of the action of passive, lossless optical systems [L. Knöll, W. Vogel, and D.-G. Welsch, Phys. Rev. A 36, 3803 (1987)]. Expressions for the operator of the electric field strength of the light and the normally and time-ordered field-correlation functions are derived for the case of a Fabry-Pérot interferometer being present. Various kinds of field decomposition that are usually considered in classical optics are studied. The results are compared with the Fourier approach to spectral properties of light. It is shown that, dependent on the experimental scheme used, new quantum effects appear, which may prevent the observation of the Fourier structure of the light as predicted from classical optics. Quantitatively this is demonstrated for the example of spectral squeezing in resonance fluorescence, where significant discrepancies between the measured and the full Fourier spectrum are found.

  2. Passive and Active Stabilization of Liquid Bridges in Low Gravity

    NASA Technical Reports Server (NTRS)

    Marston, Philip L.; Thiessen, David B.; Marr-Lyon, Mark J.; Wei, Wei; Niederhaus, Charles E.; Truong, Duc K.

    2001-01-01

    Tests are planned in the low gravity environment of the International Space Station (ISS) of new methods for the suppression of the capillary instability of liquid bridges. Our suppression methods are unusual in that they are not limited to liquid bridges having very special properties and may impact a variety of low-gravity and earth-based technologies. There are two main approaches to be investigated: (1) Passive Acoustic Stabilization (PAS); and (2) Active Electrostatic Stabilization (AES). In PAS, the suppression of the mode growth is accomplished by placing the bridge in an acoustic field having the appropriate properties such that the acoustic radiation pressure automatically pulls outward on the thinnest portion of the bridge. In AES, the bridge deformation is sensed optically and counteracted by actively adjusting the electrostatic Maxwell stresses via two ring electrodes concentric with the slightly conducting bridge to offset the growth of the unstable mode. While the present work emphasizes cylindrical bridges, the methods need not be restricted to that case. The methods to be explored are relevant to the suppression of capillary instabilities in floating zone crystal growth, breakup of liquid jets and columns, bubbles, and annular films as well as the management of coolants or propellants in low-gravity.

  3. Protein crystal growth in low gravity

    NASA Technical Reports Server (NTRS)

    Feigelson, Robert S.

    1991-01-01

    The objective of this research is to study the effect of low gravity on the growth of protein crystals and those parameters which will affect growth and crystal quality. The application of graphoepitaxy (artificial epitaxy) to proteins is detailed. The development of a method for the control of nucleation is discussed. The factor affecting the morphology of isocitrate lyase crystals is presented.

  4. Femtosecond spectral interferometry of optical activity: Theory

    NASA Astrophysics Data System (ADS)

    Rhee, Hanju; Ha, Jeong-Hyon; Jeon, Seung-Joon; Cho, Minhaeng

    2008-09-01

    Optical activities such as circular dichroism (CD) and optical rotatory dispersion (ORD) are manifested by almost all natural products. However, the CD is an extremely weak effect so that time-resolved CD spectroscopy has been found to be experimentally difficult and even impossible for vibrational CD with current technology. Here, we show that the weak-signal and nonzero background problems can be overcome by heterodyned spectral interferometric detection of the phase and amplitude of optical activity free-induction-decay (OA FID) field. A detailed theoretical description and a cross-polarization scheme for selectively measuring the OA FID are presented and discussed. It is shown that the parallel and perpendicular electric fields when the solution sample contains chiral molecules are coupled to each other. Therefore, simultaneous spectral interferometric measurements of the parallel and perpendicular FID fields can provide the complex susceptibility, which is associated with the circular dichroism and optical rotatory dispersion as its imaginary and real parts, respectively. On the basis of the theoretical results, to examine its experimental possibility, we present numerical simulations for a model system. We anticipate the method discussed here to be a valuable tool for detecting electronic or vibrational optical activity in femtosecond time scale.

  5. Removing autocorrelation in spectral optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Ai, Jun; Wang, Lihong V.

    2006-02-01

    We have developed a new algorithm and configuration for removing the autocorrelation of the object wave in spectral optical coherence tomography. The self-interferogram of the object wave is acquired synchronously with the standard interferogram of the recombined object and reference waves. The former is then subtracted from the latter after Fourier transformation. The algorithm is validated by numerical simulation and by experimental measurement of a USAF target and a feline eye.

  6. Spectrally efficient polymer optical fiber transmission

    NASA Astrophysics Data System (ADS)

    Randel, Sebastian; Bunge, Christian-Alexander

    2011-01-01

    The step-index polymer optical fiber (SI-POF) is an attractive transmission medium for high speed communication links in automotive infotainment networks, in industrial automation, and in home networks. Growing demands for quality of service, e.g., for IPTV distribution in homes and for Ethernet based industrial control networks will necessitate Gigabit speeds in the near future. We present an overview on recent advances in the design of spectrally efficient and robust Gigabit-over-SI-POF transmission systems.

  7. Spectral fusing Gabor domain optical coherence microscopy.

    PubMed

    Meemon, Panomsak; Widjaja, Joewono; Rolland, Jannick P

    2016-02-01

    Gabor domain optical coherence microscopy (GD-OCM) is one of many variations of optical coherence tomography (OCT) techniques that aims for invariant high resolution across a 3D field of view by utilizing the ability to dynamically refocus the imaging optics in the sample arm. GD-OCM acquires multiple cross-sectional images at different focus positions of the objective lens, and then fuses them to obtain an invariant high-resolution 3D image of the sample, which comes with the intrinsic drawback of a longer processing time as compared to conventional Fourier domain OCT. Here, we report on an alternative Gabor fusing algorithm, the spectral-fusion technique, which directly processes each acquired spectrum and combines them prior to the Fourier transformation to obtain a depth profile. The implementation of the spectral-fusion algorithm is presented and its performance is compared to that of the prior GD-OCM spatial-fusion approach. The spectral-fusion approach shows twice the speed of the spatial-fusion approach for a spectrum size of less than 2000 point sampling, which is a commonly used spectrum size in OCT imaging, including GD-OCM.

  8. Thermoacoustic convection of fluids in low gravity

    NASA Technical Reports Server (NTRS)

    Spradley, L. W.

    1974-01-01

    The heat flow in a confined perfect gas in low gravity is investigated, including the effects of conduction and thermal convection. Buoyancy-driven flow is neglected, due to the low-gravity environment, but the effect of thermoacoustic motion due to fluid compressibility is included. One-dimensional mathematical models are constructed from the conservation equations for a compressible, viscous, heat-conducting fluid. A conservative, time-dependent finite-difference method is used to generate numerical solutions on a digital computer. Problems for flat plates and cylindrical segments are solved for specified thermal boundary conditions. Numerical results are given which indicate that thermoacoustic convection can significantly increase the transient heat flow over conduction model predictions for cases where a confined gas is rapidly heated.

  9. Helium 2 slosh in low gravity

    NASA Technical Reports Server (NTRS)

    Ross, Graham O.

    1994-01-01

    This paper describes the status and plans for the work being performed under NASA NRA contract NASW-4803 so that members of the Microgravity Fluid Dynamics Discipline Working Group are aware of this program. The contract is a cross-disciplinary research program and is administered under the Low Temperature Microgravity Research Program at the Jet Propulsion Laboratory. The purpose of the project is to perform low-gravity verification experiments on the slosh behavior of He II to use in the development of a CFD model that incorporates the two-fluid physics of He II. The two-fluid code predicts a different fluid motion response in low-gravity environment from that predicted by a single-fluid model, while the 1g response is identical for the both types of model.

  10. Enhancement of spectral resolution and optical rejection ratio of Brillouin optical spectral analysis using polarization pulling.

    PubMed

    Preussler, Stefan; Zadok, Avi; Wiatrek, Andrzej; Tur, Moshe; Schneider, Thomas

    2012-06-18

    High-resolution, wide-bandwidth optical spectrum analysis is essential to the measuring and monitoring of advanced optical, millimeter-wave, and terahertz communication systems, sensing applications and device characterization. One category of high-resolution spectrum analyzers reconstructs the power spectral density of a signal under test by scanning a Brillouin gain line across its spectral extent. In this work, we enhance both the resolution and the optical rejection ratio of such Brillouin-based spectrometers using a combination of two techniques. First, two Brillouin loss lines are superimposed upon a central Brillouin gain to reduce its bandwidth. Second, the vector attributes of stimulated Brillouin scattering amplification in standard, weakly birefringent fibers are used to change the signal state of polarization, and a judiciously aligned output polarizer discriminates between amplified and un-amplified spectral contents. A frequency resolution of 3 MHz, or eight orders of magnitude below the central optical frequency, is experimentally demonstrated. In addition, a weak spectral component is resolved in the presence of a strong adjacent signal, which is 30 dB stronger and detuned by only 60 MHz. The measurement method involves low-bandwidth direct detection, and does not require heterodyne beating. The measurement range of the proposed method is scalable to cover the C + L bands, depending on the tunable pump source. The accuracy of the measurements requires that the pump frequencies are well calibrated.

  11. Generation of Bubbly Suspensions in Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Hoffmann, Monica I.; Hussey, Sam; Bell, Kimberly R.

    2000-01-01

    Generation of a uniform monodisperse bubbly suspension in low gravity is a rather difficult task because bubbles do not detach as easily as on Earth. Under microgravity, the buoyancy force is not present to detach the bubbles as they are formed from the nozzles. One way to detach the bubbles is to establish a detaching force that helps their detachment from the orifice. The drag force, established by flowing a liquid in a cross or co-flow configuration with respect to the nozzle direction, provides this additional force and helps detach the bubbles as they are being formed. This paper is concerned with studying the generation of a bubbly suspension in low gravity in support of a flight definition experiment titled "Behavior of Rapidly Sheared Bubbly Suspension." Generation of a bubbly suspension, composed of 2 and 3 mm diameter bubbles with a standard deviation <10% of the bubble diameter, was identified as one of the most important engineering/science issues associated with the flight definition experiment. This paper summarizes the low gravity experiments that were conducted to explore various ways of making the suspension. Two approaches were investigated. The first was to generate the suspension via a chemical reaction between the continuous and dispersed phases using effervescent material, whereas the second considered the direct injection of air into the continuous phase. The results showed that the reaction method did not produce the desired bubble size distribution compared to the direct injection of bubbles. However, direct injection of air into the continuous phase (aqueous salt solution) resulted in uniform bubble-diameter distribution with acceptable bubble-diameter standard deviation.

  12. Low-gravity processing of superconducting compounds

    NASA Technical Reports Server (NTRS)

    Otto, G. H.

    1976-01-01

    Low gravity conditions can be sustained on earth for several seconds in an evacuated drop tube. Because radiation cooling is most effective at high temperatures, the refractive metals and alloys are prime candidates for free fall solidification. The results of initial experiments on droplet formation, droplet release, critical size and evaporation losses are given. The time required for free fall solidification of different size droplets is calculated. The materials studied were copper, niobium and vanadium, and a niobium-tin alloys. Improvements in purity, composition, homogeneity and stoichiometry are expected during free fall solidification of niobium based alloys which should become evident in an increase in the superconducting transition temperature.

  13. Low gravity fluid-thermal experiments

    SciTech Connect

    Krotiuk, W.J.; Cuta, J.M.

    1987-06-01

    Pacific Northwest Laboratory (PNL) is the lead laboratory for the thermal-hydraulic research in the US Department of Energy Multimegawatt Space Nuclear Power Program. PNL must provide the tools necessary to analyze proposed space reactor concepts, which include single- and two-phase alkali metal and gas-cooled designs. PNL has divided its activities for this task into three basic areas: computer code development, thermal-hydraulic modeling, and experimentation. The subject of this paper is the low-gravity experimental program currently underway at PNL in support of the MMW Program.

  14. Snapshot Spectral Domain Optical Coherence Tomography

    NASA Astrophysics Data System (ADS)

    Valdez, Ashley

    Optical coherence tomography systems are used to image the retina in 3D to allow ophthalmologists diagnose ocular disease. These systems yield large data sets that are often labor-intensive to analyze and require significant expertise in order to draw conclusions, especially when used over time to monitor disease progression. Spectral Domain Optical Coherence Tomography (SD-OCT) instantly acquires depth profiles at a single location with a broadband source. These systems require mechanical scanning to generate two- or three-dimensional images. Instead of mechanically scanning, a beamlet array was used to permit multiple depth measurements on the retina with a single snapshot using a 3x 3 beamlet array. This multi-channel system was designed, assembled, and tested using a 1 x 2 beamlet lens array instead of a 3 x 3 beamlet array as a proof of concept prototype. The source was a superluminescent diode centered at 840nm with a 45nm bandwidth. Theoretical axial resolution was 6.92um and depth of focus was 3.45mm. Glass samples of varying thickness ranging from 0.18mm to 1.14mm were measured with the system to validate that correct depth profiles can be acquired for each channel. The results demonstrated the prototype system performed as expected, and is ready to be modified for in vivo applicability.

  15. Binary supergratings: Aperiodic optics for spectral engineering

    NASA Astrophysics Data System (ADS)

    Fay, Martin Freestone

    The Binary Supergrating (BSG) is an aperiodic guided-wave optical device which, in parallel to the much-touted Photonic Band Gap, represents the extension of the Bragg grating into frequency space. The result is an easily manufactured two-level refractive index profile offering fully customizable spectral characteristics, including wavelength-dependent control over beam direction, dispersion and power. As a general concept, a BSG can be synthesized using a variety of approaches, ranging from a simple threshold quantization of the emulated ideal analog index profile to more sophisticated delta-sigma modulator (DSM) methods, which preserve diffraction characteristics over a specified band of interest with high fidelity. The comparative advantages of each are explored in the context of their tolerance to manufacturing variances. For most cases, the BSG designs degrade gracefully and retain their functionality under extreme errors in fabrication. However, particular vulnerabilities do emerge, along with strategies to mitigate their effect. The BSG is then demonstrated experimentally, in a first proof-of-concept embodiment employing a lateral satellite grating configuration, which eases fabrication by having both waveguide and grating features defined in the same lithographic sequence. Results from this passive optical device corroborate both the BSG's design flexibility and its particular vulnerabilities, yielding clear directions for subsequent implementations. In the domain of active BSG-enabled devices, the novel self-collimated multi-wavelength laser (SCMWL) outputs low-divergence beams at multiple simultaneous wavelengths. The concept, theory, and design of this invention is presented, followed by experimental results from optically pumped proof-of-concept embodiments. The observed spectra confirm the SCMWL concept, while also revealing the complex dynamics underlying this device. At once simple and subtle, the BSG concept yields itself both for immediate

  16. Functional Spectral Domain Optical Coherence Tomography imaging

    NASA Astrophysics Data System (ADS)

    Bower, Bradley A.

    Spectral Domain Optical Coherence Tomography (SDOCT) is a high-speed, high resolution imaging modality capable of structural and functional characterization of tissue microstructure. SDOCT fills a niche between histology and ultrasound imaging, providing non-contact, non-invasive backscattering amplitude and phase from a sample. Due to the translucent nature of the tissue, ophthalmic imaging is an ideal space for SDOCT imaging. Structural imaging of the retina has provided new insights into ophthalmic disease. The phase component of SDOCT images remains largely underexplored, though. While Doppler SDOCT has been explored in a research setting, it has yet to gain traction in the clinic. Other, functional exploitations of the phase are possible and necessary to expand the utility of SDOCT. Spectral Domain Phase Microscopy (SDPM) is an extension of SDOCT that is capable of resolving sub-wavelength displacements within a focal volume. Application of sub-wavelength displacement measurement imaging could provide a new method for non-invasive optophysiological measurement. This body of work encompasses both hardware and software design and development for implementation of SDOCT. Structural imaging was proven in both the lab and the clinic. Coarse phase changes associated with Doppler flow frequency shifts were recorded and a study was conducted to validate Doppler measurement. Fine phase changes were explored through SDPM applications. Preliminary optophysiology data was acquired to study the potential of sub-wavelength measurements in the retina. To remove the complexity associated with in-vivo human retinal imaging, a first principles approach using isolated nerve samples was applied using standard SDPM and a depthencoded technique for measuring conduction velocity. Results from amplitude as well as both coarse and fine phase processing are presented. In-vivo optophysiology using SDPM is a promising avenue for exploration, and projects furthering or extending this body

  17. Spectral/Fourier Domain Optical Coherence Tomography

    NASA Astrophysics Data System (ADS)

    de Boer, Johannes F.

    Optical coherence tomography is a low-coherence interferometric method for imaging of biological tissue [1, 2]. For more than a decade after its inception between 1988 and 1991, the dominant implementation has been time domain OCT (TD-OCT), in which the length of a reference arm is rapidly scanned. The first spectral or Fourier domain OCT (SD/FD-OCT) implementation was reported in 1995 [3]. In SD-OCT the reference arm is kept stationary, and the depth information is obtained by a Fourier transform of the spectrally resolved interference fringes in the detection arm of a Michelson interferometer. This approach has provided a significant advantage in signal-to-noise ratio (SNR), which despite reports as early as 1997 [4, 5] has taken about half a decade to be recognized fully by the OCT community in 2003 [6-8]. The first demonstration of SD-OCT for in vivo retinal imaging in 2002 [9] was followed by a full realization of the sensitivity advantage by video rate in vivo retinal imaging [10], including high-speed 3-D volumetric imaging [11], ultrahigh-resolution video rate imaging [12, 13], and Doppler blood flow determination in the human retina [14, 15]. The superior sensitivity of SD-OCT, combined with the lack of need for a fast mechanical scanning mechanism, has opened up the possibility of much faster scanning without loss of image quality and provided a paradigm shift from point sampling to volumetric mapping of biological tissue in vivo. The technology has been particularly promising for ophthalmology [16, 17]. In this chapter, the principles and system design considerations of SD-OCT will be discussed in more detail.

  18. Protein crystal growth in low gravity

    NASA Technical Reports Server (NTRS)

    Feigelson, Robert S.

    1990-01-01

    The effect of low gravity on the growth of protein crystals and those parameters which will affect growth and crystal quality was studied. The proper design of the flight hardware and experimental protocols are highly dependent on understanding the factors which influence the nucleation and growth of crystals of biological macromolecules. Thus, those factors are investigated and the body of knowledge which has been built up for small molecule crystallization. These data also provide a basis of comparison for the results obtained from low-g experiments. The flows around growing crystals are detailed. The preliminary study of the growth of isocitrate lyase, the crystal morphologies found and the preliminary x ray results are discussed. The design of two apparatus for protein crystal growth by temperature control are presented along with preliminary results.

  19. Low gravity exothermic heating/cooling apparatus

    NASA Technical Reports Server (NTRS)

    Poorman, R. M. (Inventor)

    1985-01-01

    A low gravity exothermic heating/cooling apparatus is disclosed for processing materials in space which includes an insulated casing and a sample support carried within the casing which support a sample container. An exothermic heat source includes a plurality of segments of exothermic material stacked one upon another to produce a desired temperature profile when ignited. The sample container is arranged within the core of the stacked exothermic heating material. Igniters are spaced vertically along the axis of the heating material to ignite the exothermic material at spaced points to provide total rapid burn and release of heat. To rapidly cool and quench the heat, a source of liquid carbon dixoide is provided which is conveyed through a conduit and a metering orifice into a distribution manifold where the carbon dioxide is gasified and dispersed around the exothermic heating material and the sample container via tubes for rapidly cooling the material sample.

  20. Combustion and fires in low gravity

    NASA Technical Reports Server (NTRS)

    Friedman, Robert

    1994-01-01

    Fire safety always receives priority attention in NASA mission designs and operations, with emphasis on fire prevention and material acceptance standards. Recently, interest in spacecraft fire-safety research and development has increased because improved understanding of the significant differences between low-gravity and normal-gravity combustion suggests that present fire-safety techniques may be inadequate or, at best, non-optimal; and the complex and permanent orbital operations in Space Station Freedom demand a higher level of safety standards and practices. This presentation outlines current practices and problems in fire prevention and detection for spacecraft, specifically the Space Station Freedom's fire protection. Also addressed are current practices and problems in fire extinguishment for spacecraft.

  1. Granular physics in low-gravity enviroments

    NASA Astrophysics Data System (ADS)

    Tancredi, G.; Maciel, A.; Heredia, L.; Richeri, P.; Nesmachnow, S.

    2011-10-01

    The granular media are formed by a set of macroscopic objects (named grains) which interact through temporal or permanent contacts. Several processes has been identified which require a full understanding, like: grain blocking, formation of arcs, size segregation, response to shakes and impacts, etc. These processes has been studied experimentally in the laboratory, and, in the last decades, numerically. The Discrete Element Method (DEM) simulate the mechanical behavior in a media formed by a set of particles which interact through their contact points. We describe the implementation of DEM for the study of several relevant processes in minor bodies of the Solar System. We present the results of simulations of the process of size segregation in low-gravity environments, the so-called Brazil nut effect, in the cases of Eros and Itokawa. The segregation of particles with different densities is also analyzed, with the application to the case of P/Hartley 2. The surface shaking in these different gravity environments could produce the ejection of particles from the surface at very low relative velocities. The shaking that cause the above processes is due to impacts or explosions like the release of energy by the liberation of internal stresses or the reaccommodation of material. We run simulations of the passage of seismic wave produced at impact through a granular media.

  2. Bubbly Suspension Generated in Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.

    2000-01-01

    Bubbly suspensions are crucial for mass and heat transport processes on Earth and in space. These processes are relevant to pharmaceutical, chemical, nuclear, and petroleum industries on Earth. They are also relevant to life support, in situ resource utilization, and propulsion processes for long-duration space missions such as the Human Exploration and Development of Space program. Understanding the behavior of the suspension in low gravity is crucial because of factors such as bubble segregation, which could result in coalescence and affect heat and mass transport. Professors A. Sangani and D. Koch, principal investigators in the Microgravity Fluid Physics Program managed by the NASA Glenn Research Center at Lewis Field, are studying the physics of bubbly suspension. They plan to shear a bubbly suspension in a couette cell in microgravity to study bubble segregation and compare the bubble distribution in the couette gap with the one predicted by the suspension-averaged equations of motion. Prior to the Requirement Definition Review of this flight experiment, a technology for generating a bubbly suspension in microgravity has to be established, tested, and verified.

  3. Low gravity two-phase flow with heat transfer

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.

    1991-01-01

    A realistic model for the transfer line chilldown operation under low-gravity conditions is developed to provide a comprehensive predictive capability on the behavior of liquid vapor, two-phase diabatic flows in pipes. The tasks described involve the development of numerical code and the establishment of the necessary experimental data base for low-gravity simulation.

  4. Spectral separation of optical spin based on antisymmetric Fano resonances

    PubMed Central

    Piao, Xianji; Yu, Sunkyu; Hong, Jiho; Park, Namkyoo

    2015-01-01

    We propose a route to the spectral separation of optical spin angular momentum based on spin-dependent Fano resonances with antisymmetric spectral profiles. By developing a spin-form coupled mode theory for chiral materials, the origin of antisymmetric Fano spectra is clarified in terms of the opposite temporal phase shift for each spin, which is the result of counter-rotating spin eigenvectors. An analytical expression of a spin-density Fano parameter is derived to enable quantitative analysis of the Fano-induced spin separation in the spectral domain. As an application, we demonstrate optical spin switching utilizing the extreme spectral sensitivity of the spin-density reversal. Our result paves a path toward the conservative spectral separation of spins without any need of the magneto-optical effect or circular dichroism, achieving excellent purity in spin density superior to conventional approaches based on circular dichroism. PMID:26561372

  5. Spectral Response of Metallic Optical Antennas Driven by Temperature.

    PubMed

    Cuadrado, Alexander; López-Alonso, José Manuel; González, Francisco Javier; Alda, Javier

    2017-01-01

    When optical antennas are used as light detectors, temperature changes their spectral response. Using this relation, we determine the spectrum of a light beam from an optical antenna's signal. A numerical evaluation of the temperature-spectral response has been completed with a model for the noise of the device. Using both the response and the noise model, we have established the capabilities of the device by quantifying the error in the spectrum determination both for broadband spectrum and monochromatic radiation.

  6. Precision spectral manipulation: A demonstration using a coherent optical memory

    SciTech Connect

    Sparkes, B. M.; Cairns, C.; Hosseini, M.; Higginbottom, D.; Campbell, G. T.; Lam, P. K.; Buchler, B. C.

    2014-12-04

    The ability to coherently spectrally manipulate quantum information has the potential to improve qubit rates across quantum channels and find applications in optical quantum computing. Here we present experiments that use a multi-element solenoid combined with the three-level gradient echo memory scheme to perform precision spectral manipulation of optical pulses. If applied in a quantum information network, these operations would enable frequency-based multiplexing of qubits.

  7. NONLINEAR OPTICAL PHENOMENA: Dispersive regime of spectral compression

    NASA Astrophysics Data System (ADS)

    Kutuzyan, A. A.; Mansuryan, T. G.; Esayan, G. L.; Akopyan, R. S.; Muradyan, Kh

    2008-04-01

    The role of the group velocity dispersion in the spectral compression of subpicosecond laser pulses is analysed based on numerical and experimental studies. It is shown that the group velocity dispersion in an optical fibre can substantially change the physical pattern of the spectral compression process.

  8. Cloud optical properties and phase discrimination using transmitted spectral radiance

    NASA Astrophysics Data System (ADS)

    LeBlanc, S. E.; Pilewskie, P.; Schmidt, S.; Coddington, O.

    2013-12-01

    Cloud optical thickness, effective radius, and thermodynamic phase are commonly retrieved from satellite measurements of reflected light. Reflected light is influenced most strongly by droplets and ice crystals near cloud top, whereas transmitted light has interacted with cloud particles throughout the entire layer. This transmitted spectral radiance is used in a new method to retrieve cloud thermodynamic phase, cloud optical thickness, and effective radius. The method uses 15 regions of the shortwave transmittance spectrum that are modulated by the spectral absorption and scattering by liquid water droplets and ice particles. Spectral features in these regions are characterized by their slope, normalized magnitude, spectral derivatives, spectral curvature, and second derivatives. We use an optimal estimation method to find the most likely set of cloud optical thickness, effective radius, and thermodynamic phase that produces the observed spectral features in transmitted radiance spectra. This retrieval's performance is evaluated using the GEneralized Nonlinear Retrieval Analysis (GENRA) with the Shannon information content. Results showed that the normalized Shannon information content for retrieved ice cloud properties was larger on average (84%) than for liquid water cloud properties (78%) in addition to having a smaller bias. The retrieval was applied to zenith spectral radiance measured with the ground-based Solar Spectral Flux Radiometer (SSFR) located at Boulder, Colorado for 10 cases that occurred between May 2012 and January 2013. Retrieved cloud optical thickness, effective radius, and their uncertainties are compared to those retrieved using two other methods. By using several spectral characterizations in a large number of spectral bands, the average uncertainty in retrieved optical thickness and effective radius is reduced below that of any other retrieval method based on cloud transmittance.

  9. Time-Resolved Spectral Optical Breast Tomography

    DTIC Science & Technology

    2005-06-01

    four- dimensional (4D) data is formed. The spectral information adds an additional dimension of the data. The optimal approach to analyze this huge... dimensional near-infrared tomogra- UK, 2001). phy of the breast: initial simulation, phantom, and clinical 38. J.-F. Cardoso, "Blind signal separation...detector signal acquisition scheme providing a variety of spatial and angular views essential for three- dimensional (3D) object localization. Each

  10. Spectral selectivity in optical fiber capillary dye lasers.

    PubMed

    Mobini, Esmaeil; Abaie, Behnam; Peysokhan, Mostafa; Mafi, Arash

    2017-05-01

    We explore the spectral properties of a capillary dye laser in the highly multimode regime. Our experiments indicate that the spectral behavior of the laser does not conform to a simple Fabry-Perot (FP) analysis; rather, it is strongly dictated by a Vernier resonant mechanism involving multiple modes, which propagate with different group velocities. The laser operates over a very broad spectral range and the Vernier effect gives rise to a free spectral range, which is orders of magnitude larger than that expected from a simple FP mechanism. The theoretical calculations presented confirm the experimental results. Propagating modes of the capillary fiber are calculated using the finite-element method and it is shown that the optical path lengths resulting from simultaneous beatings of these modes are in close agreement with the optical path lengths directly extracted from the Fourier transform of the experimentally measured laser emission spectra.

  11. Demonstration of optical steganography transmission using temporal phase coded optical signals with spectral notch filtering.

    PubMed

    Hong, Xuezhi; Wang, Dawei; Xu, Lei; He, Sailing

    2010-06-07

    A novel approach is proposed and experimentally demonstrated for optical steganography transmission in WDM networks using temporal phase coded optical signals with spectral notch filtering. A temporal phase coded stealth channel is temporally and spectrally overlaid onto a public WDM channel. Direct detection of the public channel is achieved in the presence of the stealth channel. The interference from the public channel is suppressed by spectral notching before the detection of the optical stealth signal. The approach is shown to have good compatibility and robustness to the existing WDM network for optical steganography transmission.

  12. Adaptive spectral window sizes for feature extraction from optical spectra

    NASA Astrophysics Data System (ADS)

    Kan, Chih-Wen; Lee, Andy Y.; Pham, Nhi; Nieman, Linda T.; Sokolov, Konstantin; Markey, Mia K.

    2008-02-01

    We propose an approach to adaptively adjust the spectral window size used to extract features from optical spectra. Previous studies have employed spectral features extracted by dividing the spectra into several spectral windows of a fixed width. However, the choice of spectral window size was arbitrary. We hypothesize that by adaptively adjusting the spectral window sizes, the trends in the data will be captured more accurately. Our method was tested on a diffuse reflectance spectroscopy dataset obtained in a study of oblique polarization reflectance spectroscopy of oral mucosa lesions. The diagnostic task is to classify lesions into one of four histopathology groups: normal, benign, mild dysplasia, or severe dysplasia (including carcinoma). Nine features were extracted from each of the spectral windows. We computed the area (AUC) under Receiver Operating Characteristic curve to select the most discriminatory wavelength intervals. We performed pairwise classifications using Linear Discriminant Analysis (LDA) with leave-one-out cross validation. The results showed that for discriminating benign lesions from mild or severe dysplasia, the adaptive spectral window size features achieved AUC of 0.84, while a fixed spectral window size of 20 nm had AUC of 0.71, and an AUC of 0.64 is achieved with a large window size containing all wavelengths. The AUCs of all feature combinations were also calculated. These results suggest that the new adaptive spectral window size method effectively extracts features that enable accurate classification of oral mucosa lesions.

  13. Spectral signature studies in optical region

    NASA Astrophysics Data System (ADS)

    Sahai, Baldev; Navalgund, R. R.; Patel, N. K.; Singh, T. P.

    Reflectance spectra of a large number of rock, vegetation and soil samples have been measured in the laboratory in the visible and near infrared wavelength regions. Procedures have been evolved to find optimum spectral bands for rock discrimination. `In situ' reflectance measurements on different crops like wheat, paddy, millet, cotton, maize, groundnut etc. during their various growth stages have been carried out using hand-held radiometers. Recently measurements have been conducted over six wheat plots subjected to different irrigation schedules to see the effect of water stress on the signatures. Results show that the best period for monitoring water stress in wheat through remote sensing is 45-80 days after sowing.

  14. Diffractive Optical Elements for Spectral Imaging

    NASA Technical Reports Server (NTRS)

    Wilson, D.; Maker, P.; Muller, R.; Mourolis, P.; Descour, M.; Volin, C.; Dereniak, E.

    2000-01-01

    Diffractive optical elements fabricated on flat and non-flat substrates frequently act as dispersive elements in imaging spectrometers. We describe the design and electron-beam fabrication of blazed and computer-generated-hologram gratings for slit and tomographic imaging spectrometer.

  15. Diffractive Optical Elements for Spectral Imaging

    NASA Technical Reports Server (NTRS)

    Wilson, D.; Maker, P.; Muller, R.; Maker, P.; Mouroulis, P.; Descour, M.; Volin, C.; Dereniak, E.

    2000-01-01

    Diffractive optical elements fabricated on flat and non-flat substrates frequently act as dispersive elements in imaging spectrometers. We describe the design and electron-beam fabrication of blazed and computer-generated-hologram gratings for slit and tomographic imaging spectrometers.

  16. Optical unmixing using programmable spectral source based on DMD

    NASA Astrophysics Data System (ADS)

    Luo, Ding; Bauer, Sebastian; Taphanel, Miro; Längle, Thomas; Puente León, Fernando; Beyerer, Jürgen

    2016-05-01

    Traditional spectral unmixing involves intense signal processing applied on multispectral or hyperspectral data captured from an imaging device, which is highly time-consuming. In this article, a novel method, namely "optical unmixing", is proposed to alleviate the post processing effort by replacing the heavy computation with a spectrally tunable light source. By choosing spectral features of the light source intelligently, the abundance map of each material can be retrieved with minimum computation from gray value images captured by a normal camera. For n unknown endmembers, 3n + 1 measurements are required to retrieve the abundance maps with proposed algorithms.

  17. Polymer integrated waveguide optical biosensor by using spectral splitting effect

    NASA Astrophysics Data System (ADS)

    Han, Xiaonan; Han, Xiuyou; Shao, Yuchen; Wu, Zhenlin; Liang, Yuxin; Teng, Jie; Bo, Shuhui; Morthier, Geert; Zhao, Mingshan

    2017-06-01

    The polymer waveguide optical biosensor based on the Mach-Zehnder interferometer (MZI) by using spectral splitting effect is investigated. The MZI based biosensor has two unequal width sensing arms. With the different mode dispersion responses of the two-arm waveguides to the cladding refractive index change, the spectral splitting effect of the output interference spectrum is obtained, inducing a very high sensitivity. The influence of the different mode dispersions between the two-arm waveguides on the spectral splitting characteristic is analyzed. By choosing different lengths of the two unequal width sensing arms, the initial dip wavelength of the interference spectrum and the spectral splitting range can be controlled flexibly. The polymer waveguide optical biosensor is designed, and its sensing property is analyzed. The results show that the sensitivity of the polymer waveguide optical biosensor by using spectral splitting effect is as high as 104 nm/RIU, with an improvement of 2-3 orders of magnitude compared with the slot waveguide based microring biosensor.

  18. Polymer integrated waveguide optical biosensor by using spectral splitting effect

    NASA Astrophysics Data System (ADS)

    Han, Xiaonan; Han, Xiuyou; Shao, Yuchen; Wu, Zhenlin; Liang, Yuxin; Teng, Jie; Bo, Shuhui; Morthier, Geert; Zhao, Mingshan

    2017-02-01

    The polymer waveguide optical biosensor based on the Mach-Zehnder interferometer (MZI) by using spectral splitting effect is investigated. The MZI based biosensor has two unequal width sensing arms. With the different mode dispersion responses of the two-arm waveguides to the cladding refractive index change, the spectral splitting effect of the output interference spectrum is obtained, inducing a very high sensitivity. The influence of the different mode dispersions between the two-arm waveguides on the spectral splitting characteristic is analyzed. By choosing different lengths of the two unequal width sensing arms, the initial dip wavelength of the interference spectrum and the spectral splitting range can be controlled flexibly. The polymer waveguide optical biosensor is designed, and its sensing property is analyzed. The results show that the sensitivity of the polymer waveguide optical biosensor by using spectral splitting effect is as high as 104 nm/RIU, with an improvement of 2-3 orders of magnitude compared with the slot waveguide based microring biosensor.

  19. Testing ultrafast two-photon spectral amplitudes via optical fibres.

    PubMed

    Brida, G; Caricato, V; Chekhova, M V; Genovese, M; Gramegna, M; Iskhakov, T Sh

    2010-06-07

    We test two-dimensional TPSA of biphoton light emitted via ultrafast spontaneous parametric down-conversion (SPDC) using the effect of group-velocity dispersion in optical fibres. Further, we apply this technique to demonstrate the engineering of biphoton spectral properties by acting on the pump pulse shape.

  20. Optical-based spectral modeling of infrared focal plane arrays

    NASA Astrophysics Data System (ADS)

    Mouzali, Salima; Lefebvre, Sidonie; Rommeluère, Sylvain; Ferrec, Yann; Primot, Jérôme

    2016-07-01

    We adopt an optical approach in order to model and predict the spectral signature of an infrared focal plane array. The modeling is based on a multilayer description of the structure and considers a one-dimensional propagation. It provides a better understanding of the physical phenomena occurring within the pixels, which is useful to perform radiometric measurements, as well as to reliably predict the spectral sensitivity of the detector. An exhaustive model is presented, covering the total spectral range of the pixel response. A heuristic model is also described, depicting a complementary approach that separates the different optical phenomena inside the pixel structure. Promising results are presented, validating the models through comparison with experimental results. Finally, advantages and limitations of this approach are discussed.

  1. Liquid optical phantoms mimicking spectral characteristics of laboratory mouse biotissues

    NASA Astrophysics Data System (ADS)

    Loginova, D. A.; Sergeeva, E. A.; Krainov, A. D.; Agrba, P. D.; Kirillin, M. Yu

    2016-06-01

    Optical phantoms mimicking optical properties of real biotissues in the visible and IR spectral regions are developed based on measurements of the spectral characteristics of ex vivo samples of laboratory mouse biotissues. The phantoms are composed of aqueous solutions of Lipofundin, Indian ink and red ink with different spectral characteristics. The deviations of the measured absorption and scattering coefficients of phantoms in the wavelength range 480 - 580 nm from the corresponding values for real biotissues do not exceed 25% and 2%, respectively. For phantoms in the wavelength region 580 - 880 nm, the deviations of the absorption coefficient do not exceed 40% and the deviations of the scattering coefficient do not exceed 25%. These values, in general, fall within the range of variations for different individual mice of one strain.

  2. The coupled dynamics of fluids and spacecraft in low gravity and low gravity fluid measurement

    NASA Technical Reports Server (NTRS)

    Hansman, R. John; Peterson, Lee D.; Crawley, Edward F.

    1987-01-01

    The very large mass fraction of liquids stored on broad current and future generation spacecraft has made critical the technologies of describing the fluid-spacecraft dynamics and measuring or gauging the fluid. Combined efforts in these areas are described, and preliminary results are presented. The coupled dynamics of fluids and spacecraft in low gravity study is characterizing the parametric behavior of fluid-spacecraft systems in which interaction between the fluid and spacecraft dynamics is encountered. Particular emphasis is given to the importance of nonlinear fluid free surface phenomena to the coupled dynamics. An experimental apparatus has been developed for demonstrating a coupled fluid-spacecraft system. In these experiments, slosh force signals are fed back to a model tank actuator through a tunable analog second order integration circuit. In this manner, the tank motion is coupled to the resulting slosh force. Results are being obtained in 1-g and in low-g (on the NASA KC-135) using dynamic systems nondimensionally identical except for the Bond numbers.

  3. Temperature-dependent spectral generalized magneto-optical ellipsometry

    NASA Astrophysics Data System (ADS)

    Neuber, G.; Rauer, R.; Kunze, J.; Korn, T.; Pels, C.; Meier, G.; Merkt, U.; Bäckström, J.; Rübhausen, M.

    2003-12-01

    We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics.

  4. Acousto-optical tunable filter for combined wideband, spectral, and optical coherence microscopy.

    PubMed

    Machikhin, Alexander S; Pozhar, Vitold E; Viskovatykh, Alexander V; Burmak, Ludmila I

    2015-09-01

    A multimodal technique for inspection of microscopic objects by means of wideband optical microscopy, spectral microscopy, and optical coherence microscopy is described, implemented, and tested. The key feature is the spectral selection of light in the output arm of an interferometer with use of the specialized imaging acousto-optical tunable filter. In this filter, two interfering optical beams are diffracted via the same ultrasound wave without destruction of interference image structure. The basic requirements for the acousto-optical tunable filter are defined, and mathematical formulas for calculation of its parameters are derived. Theoretical estimation of the achievable accuracy of the 3D image reconstruction is presented and experimental proofs are given. It is demonstrated that spectral imaging can also be accompanied by measurement of the quantitative reflectance spectra. Examples of inspection of optically transparent and nontransparent samples demonstrate the applicability of the technique.

  5. Spectral Behavior of Weakly Compressible Aero-Optical Distortions

    NASA Astrophysics Data System (ADS)

    Mathews, Edwin; Wang, Kan; Wang, Meng; Jumper, Eric

    2016-11-01

    In classical theories of optical distortions by atmospheric turbulence, an appropriate and key assumption is that index-of-refraction variations are dominated by fluctuations in temperature and the effects of turbulent pressure fluctuations are negligible. This assumption is, however, not generally valid for aero-optical distortions caused by turbulent flow over an optical aperture, where both temperature and pressures fluctuations may contribute significantly to the index-of-refraction fluctuations. A general expression for weak fluctuations in refractive index is derived using the ideal gas law and Gladstone-Dale relation and applied to describe the spectral behavior of aero-optical distortions. Large-eddy simulations of weakly compressible, temporally evolving shear layers are then used to verify the theoretical results. Computational results support theoretical findings and confirm that if the log slope of the 1-D density spectrum in the inertial range is -mρ , the optical phase distortion spectral slope is given by - (mρ + 1) . The value of mρ is then shown to be dependent on the ratio of shear-layer free-stream densities and bounded by the spectral slopes of temperature and pressure fluctuations. Supported by HEL-JTO through AFOSR Grant FA9550-13-1-0001 and Blue Waters Graduate Fellowship Program.

  6. Spectral diffraction efficiency characterization of broadband diffractive optical elements.

    SciTech Connect

    Choi, Junoh; Cruz-Cabrera, Alvaro Augusto; Tanbakuchi, Anthony

    2013-03-01

    Diffractive optical elements, with their thin profile and unique dispersion properties, have been studied and utilized in a number of optical systems, often yielding smaller and lighter systems. Despite the interest in and study of diffractive elements, the application has been limited to narrow spectral bands. This is due to the etch depths, which are optimized for optical path differences of only a single wavelength, consequently leading to rapid decline in efficiency as the working wavelength shifts away from the design wavelength. Various broadband diffractive design methodologies have recently been developed that improve spectral diffraction efficiency and expand the working bandwidth of diffractive elements. We have developed diffraction efficiency models and utilized the models to design, fabricate, and test two such extended bandwidth diffractive designs.

  7. Determination of the natural convection coefficient in low-gravity

    NASA Technical Reports Server (NTRS)

    Goldmeer, J.; Motevalli, V.; Haghdoust, M.; Jumper, G.

    1992-01-01

    Fire safety is an important issue in the current space program; ignition in low-g needs to be studied. The reduction in the gravitational acceleration causes changes in the ignition process. This paper examines the effect of gravity on natural convection, which is one of the important parameters in the ignition process. The NASA-Lewis 2.2 Second Drop Tower provided the low-gravity environment for the experiments. A series of experiments was conducted to measure the temperature of a small copper plate which was heated by a high intensity lamp. These experiments verified that in low-gravity the plate temperature increased faster than in the corresponding 1-g cases, and that the natural convection coefficient rapidly decreased in the low-gravity environment.

  8. Terahertz wave electro-optic measurements with optical spectral filtering

    SciTech Connect

    Ilyakov, I. E. Shishkin, B. V.; Kitaeva, G. Kh.; Akhmedzhanov, R. A.

    2015-03-23

    We propose electro-optic detection techniques based on variations of the laser pulse spectrum induced during pulse co-propagation with terahertz wave radiation in a nonlinear crystal. Quantitative comparison with two other detection methods is made. Substantial improvement of the sensitivity compared to the standard electro-optic detection technique (at high frequencies) and to the previously shown technique based on laser pulse energy changes is demonstrated in experiment.

  9. Aerosol spectral optical depths: Jet fuel and forest fire smokes

    NASA Astrophysics Data System (ADS)

    Pueschel, R. F.; Livingston, J. M.

    1990-12-01

    The Ames autotracking airborne sun photometer was used to investigate the spectral optical depth between 380 and 1020 nm of smokes from a jet fuel pool fire and a forest fire in May and August 1988, respectively. Results show that the forest fire smoke exhibited a stronger wavelength dependence of optical depths than did the jet fuel fire smoke at optical depths less than unity. At optical depths greater than or equal to 1, both smokes showed neutral wavelength dependence, similar to that of an optically thin stratus deck. These results verify findings of earlier investigations and have implications both on the climatic impact of large-scale smokes and on the wavelength-dependent transmission of electromagnetic signals.

  10. Protein crystal growth in low gravity

    NASA Technical Reports Server (NTRS)

    Feigelson, Robert S.

    1988-01-01

    The solubility and growth of the protein canavalin, and the application of the schlieren technique to study fluid flow in protein crystal growth systems were investigated. These studies have resulted in the proposal of a model to describe protein crystal growth and the preliminary plans for a long-term space flight experiment. Canavalin, which may be crystallized from a basic solution by the addition of hydrogen (H+) ions, was shown to have normal solubility characteristics over the range of temperatures (5 to 25 C) and pH (5 to 7.5) studies. The solubility data combined with growth rate data gathered from the seeded growth of canavalin crystals indicated that the growth rate limiting step is a screw dislocation mechanism. A schlieren apparatus was constructed and flow patterns were observed in Rochelle salt (sodium potassium tartrate), lysozyme, and canavalin. The critical parameters were identified as the change in density with concentration (dp/dc) and the change in index of refraction with concentration (dn/dc). Some of these values were measured for the materials listed. The data for lyrozyme showed non-linearities in plots of optical properties and density vs. concentration. In conjunction with with W. A. Tiller, a model based on colloid stability theory was proposed to describe protein crystallization. The model was used to explain observations made by ourselves and others. The results of this research has lead to the development for a preliminary design for a long-term, low-g experiment. The proposed apparatus is univeral and capable of operation under microprocessor control.

  11. Aerosol spectral optical depths - Jet fuel and forest fire smokes

    NASA Technical Reports Server (NTRS)

    Pueschel, R. F.; Livingston, J. M.

    1990-01-01

    The Ames autotracking airborne sun photometer was used to investigate the spectral depth between 380 and 1020 nm of smokes from a jet fuel pool fire and a forest fire in May and August 1988, respectively. Results show that the forest fire smoke exhibited a stronger wavelength dependence of optical depths than did the jet fuel fire smoke at optical depths less than unity. At optical depths greater than or equal to 1, both smokes showed neutral wavelength dependence, similar to that of an optically thin stratus deck. These results verify findings of earlier investigations and have implications both on the climatic impact of large-scale smokes and on the wavelength-dependent transmission of electromagnetic signals.

  12. Observation of two-phase flow in low gravity environment

    NASA Astrophysics Data System (ADS)

    Yoshimura, Yoshinori; Masuda, Suechika; Morioka, Mikio; Nakao, Keizo; Sugawara, Toshihiro

    A drop tower was used to study two-phase flow composed of liquid and gas in a low gravity enviroment. The effect of gravitational acceleration on the flow pattern is discussed. Two nondimensional correlations were derived to estimate the transition of the flow pattern in a horizontal two-phase flow.

  13. Wire insulation degradation and flammability in low gravity

    NASA Technical Reports Server (NTRS)

    Friedman, Robert

    1994-01-01

    This view-graph presentation covers the following topics: an introduction to spacecraft fire safety, concerns in fire prevention in low gravity, shuttle wire insulation flammability experiment, drop tower risk-based fire safety experiment, and experimental results, conclusions, and proposed studies.

  14. Low gravity on earth by magnetic levitation of biological material.

    PubMed

    Valles, James M; Guevorkian, Karine

    2002-07-01

    The use of a magnetic field gradient levitation apparatus as a tool for investigating gravisensing mechanisms in biological systems and as a low gravity simulator for biological systems is described. The basic principles are described. Differences between its application to pure materials and the heterogeneous materials of biological materials are emphasized.

  15. Dynamic spectral-domain optical coherence elastography for tissue characterization.

    PubMed

    Liang, Xing; Adie, Steven G; John, Renu; Boppart, Stephen A

    2010-06-21

    A dynamic spectral-domain optical coherence elastography (OCE) imaging technique is reported. In this technique, audio-frequency compressive vibrations are generated by a piezoelectric stack as external excitation, and strain rates in the sample are calculated and mapped quantitatively using phase-sensitive spectral-domain optical coherence tomography. At different driving frequencies, this technique provides contrast between sample regions with different mechanical properties, and thus is used to mechanically characterize tissue. We present images of a three-layer silicone tissue phantom and rat tumor tissue ex vivo, based on quantitative strain rate. Both acquisition speed and processing speed are improved dramatically compared with previous OCE imaging techniques. With high resolution, high acquisition speed, and the ability to characterize the mechanical properties of tissue, this OCE technique has potential use in non-destructive volumetric imaging and clinical applications.

  16. Acousto-optic infrared spectral imager for Pluto fast flyby

    NASA Technical Reports Server (NTRS)

    Glenar, D. A.; Hillman, J. J.

    1993-01-01

    Acousto-optic tunable filters (AOTF's) enable the design of compact, two-dimensional imaging spectrometers with high spectral and spatial resolution and with no moving parts. Tellurium dioxide AOTF's operate from about 400 nm to nearly 5 microns, and a single device will tune continuously over one octave by changing the RF acoustic frequency applied to the device. An infrared (1.2-2.5 micron) Acousto-Optic Imaging Spectrometer (AImS) was designed that closely conforms to the surface composition mapping objectives of the Pluto Fast Flyby. It features a 75-cm focal length telescope, infrared AOTF, and 256 x 256 NICMOS-3 focal plane array for acquiring narrowband images with a spectral resolving power (lambda/delta(lambda)) exceeding 250. We summarize the instrument design features and its expected performance at the Pluto-Charon encounter.

  17. Spectral domain optical coherence tomography finding in posterior microphthalmos.

    PubMed

    Kumar, Mukesh; Das, Taraprasad; Kesarwani, Siddharth

    2012-11-01

    An eight-year-old boy presented with decreased vision in both eyes. At presentation, the visual acuity was 6/60 in both eyes with high plus spheres. Anterior segment examination was normal. Fundus examination and spectral domain optical coherence tomography were consistent with posterior microphthalmos and showed an elevated foveal contour and fold in the outer plexiform layer. External limiting membrane, photoreceptor and retinal pigment epithelium were not involved in the fold. To the best of our knowledge this is the first such case report with optical coherence tomography imaging of the retinal layer involved in a case of posterior microphthalmos.

  18. CHOROIDAL IMAGING USING SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY

    PubMed Central

    Regatieri, Caio V.; Branchini, Lauren; Fujimoto, James G.; Duker, Jay S.

    2012-01-01

    Background A structurally and functionally normal choroidal vasculature is essential for retinal function. Therefore, a precise clinical understanding of choroidal morphology should be important for understanding many retinal and choroidal diseases. Methods PUBMED (http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed) was used for most of the literature search for this article. The criterion for inclusion of an article in the references for this review was that it included materials about both the clinical and the basic properties of choroidal imaging using spectral-domain optical coherence tomography. Results Recent reports show successful examination and accurate measurement of choroidal thickness in normal and pathologic states using spectral-domain optical coherence tomography systems. This review focuses on the principles of the new technology that make choroidal imaging using optical coherence tomography possible and on the changes that subsequently have been documented to occur in the choroid in various diseases. Additionally, it outlines future directions in choroidal imaging. Conclusion Optical coherence tomography is now proven to be an effective noninvasive tool to evaluate the choroid and to detect choroidal changes in pathologic states. Additionally, choroidal evaluation using optical coherence tomography can be used as a parameter for diagnosis and follow-up. PMID:22487582

  19. Spectral ellipsometry studying of iron's optical and electronic properties

    NASA Astrophysics Data System (ADS)

    Chernukha, Yevheniia; Stashchuk, Vasyl S.; Polianska, Olena; Oshtuk, Olexsandr

    2014-05-01

    Fe's optical and electronic properties were investigated at room temperature in different structural states. The sample's surface was explored in wide spectral range λ = 0,23-17,0 μm (E = 4,96 - 0,07 еV ) by the Beatty's spectral ellipsometry method. While an experiment was carried out ellipsometry parameters Δ and ψ were measure near the principal angle of incidence. The refraction index R , permittivity Ɛ and optical conductivity σ( hν ) , that is proportional to the interband density of electronic states, were calculated using these parameters. Fe's optical conductivities in liquid, amorphous and crystalline states were compared in this work. The optical conductivity was calculated using the published data of the iron's density of electronic states in crystalline, amorphous and liquid states for the comparison of the experimental and theoretical results. It is shown that, at structural transformations "amorphous, liquid state- crystalline state", the optical properties of metallic iron are determined, in the first turn, by the nearest neighborhood, and the electronic structure is not subjected to significant modifications.

  20. Orthogonal dispersive spectral-domain optical coherence tomography.

    PubMed

    Bao, Wen; Ding, Zhihua; Li, Peng; Chen, Zhiyan; Shen, Yi; Wang, Chuan

    2014-04-21

    Ultrahigh depth range spectral domain optical coherence tomography (SDOCT) can be realized based on the orthogonal dispersive spectrometer consisted by a high spectral resolution virtually-imaged phased array (VIPA) and a low spectral resolution grating. However, two critical issues result in the challenge of obtaining desirable one-dimensional (1-D) spectra from the recorded two-dimensional (2-D) orthogonal spectra for high-quality OD-SDOCT imaging. One is the wavenumber mapping errors and the other is the periodic intensity modulations. The paper proposes a method for desirable reconstruction of 1-D spectra from the recorded 2-D orthogonal spectra. A sample etalon with identical parameters to the dispersive VIPA is used to determine the free spectrum range (FSR) of the VIPA, and spectral phases from two reflecting mirrors are further applied for broadband wavenumber calibration. The cascading of column spectra are performed from interval of four lines of column spectra, and four records of cascaded 1-D spectra are obtained and then averaged to alleviate the periodic intensity modulations. Broadband 1-D spectra are thus reconstructed with an ultrahigh spectral resolution. To demonstrate the feasibility of the proposed method, three typical samples are imaged by the OD-SDOCT system.

  1. Impact of computational methods and spectral models on the retrieval of optical properties via spectral optimization.

    PubMed

    Huang, Shaohui; Li, Yonghong; Shang, Shaoping; Shang, Shaoling

    2013-03-11

    Spectral optimization algorithm (SOA) is a well-accepted scheme for the retrieval of water constituents from the measurement of ocean color radiometry. It defines an error function between the input and output remote sensing reflectance spectrum, with the latter modeled with a few variables that represent the optically active properties, while the variables are solved numerically by minimizing the error function. In this paper, with data from numerical simulations and field measurements as input, we evaluate four computational methods for minimization (optimization) for their efficiency and accuracy on solutions, and illustrate impact of bio-optical models on the retrievals. The four optimization routines are the Levenberg-Marquardt (LM), the Generalized Reduced Gradient (GRG), the Downhill Simplex Method (Amoeba), and the Simulated Annealing-Downhill Simplex (i.e. SA + Amoeba, hereafter abbreviated as SAA). The Garver-Siegel-Maritorena SOA model is used as a base to test these computational methods. It is observed that 1) LM is the fastest method, but SAA has the largest number of valid retrievals; 2) the quality of final solutions are strongly influenced by the forms of spectral models (or eigen functions); and 3) dynamically-varying eigen functions are necessary to obtain smaller errors for both reflectance spectrum and retrievals. Results of this study provide helpful guidance for the selection of a computational method and spectral models if an SOA scheme is to be used to process ocean color images.

  2. Bridgman crystal growth in low gravity - A scaling analysis

    NASA Technical Reports Server (NTRS)

    Alexander, J. I. D.; Rosenberger, Franz

    1990-01-01

    The results of an order-of-magnitude or scaling analysis are compared with those of numerical simulations of the effects of steady low gravity on compositional nonuniformity in crystals grown by the Bridgman-Stockbarger technique. In particular, the results are examined of numerical simulations of the effect of steady residual acceleration on the transport of solute in a gallium-doped germanium melt during directional solidification under low-gravity conditions. The results are interpreted in terms of the relevant dimensionless groups associated with the process, and scaling techniques are evaluated by comparing their predictions with the numerical results. It is demonstrated that, when convective transport is comparable with diffusive transport, some specific knowledge of the behavior of the system is required before scaling arguments can be used to make reasonable predictions.

  3. Flash spectral imaging for optical metrology of solar cells

    NASA Astrophysics Data System (ADS)

    Ho, Jian Wei; Koh, Jessica Li Jian; Wong, Johnson Kai Chi; Raj, Samuel; Janssen, Eric; Aberle, Armin G.

    2017-08-01

    Flash spectral imaging of full area (156 mm by 156 mm) silicon solar wafers and cells is realized in a setup integrating pseudo-monochromatic LEDs over the wavelength range of 370 to 1050 nm and a high-resolution monochrome camera. The captured information allows the computation of sample reflectance as a function of wavelength and coordinates, thereby constituting a spectral reflectance map. The derived values match that obtained from monochromator-based measurements. Optical inspection is then based on the characteristic reflectance of surface features at optimally contrasting wavelengths. The technique reveals otherwise hidden stains and anti-reflection coating (ARC) non-uniformities, and enable more selective visualization of grains in multicrystalline Si wafers. Optical contrast enhancement of metallization significantly improves accuracy of metal detection. The high effective resolution of the monochrome camera also allows fine metallization patterns to be measured. The rapid succession of flash-and-image-capture at each wavelength makes the reported optical metrology technique amenable in photovoltaic manufacturing for solar wafers/cells sorting, monitoring and optimization of processes.

  4. Suppressing spectral diffusion of emitted photons with optical pulses

    SciTech Connect

    Fotso, H. F.; Feiguin, A. E.; Awschalom, D. D.; Dobrovitski, V. V.

    2016-01-22

    In many quantum architectures the solid-state qubits, such as quantum dots or color centers, are interfaced via emitted photons. However, the frequency of photons emitted by solid-state systems exhibits slow uncontrollable fluctuations over time (spectral diffusion), creating a serious problem for implementation of the photon-mediated protocols. Here we show that a sequence of optical pulses applied to the solid-state emitter can stabilize the emission line at the desired frequency. We demonstrate efficiency, robustness, and feasibility of the method analytically and numerically. Taking nitrogen-vacancy center in diamond as an example, we show that only several pulses, with the width of 1 ns, separated by few ns (which is not difficult to achieve) can suppress spectral diffusion. As a result, our method provides a simple and robust way to greatly improve the efficiency of photon-mediated entanglement and/or coupling to photonic cavities for solid-state qubits.

  5. SASER action in optically excited ruby: Angular and spectral distribution

    NASA Astrophysics Data System (ADS)

    Tilstra, L. G.; Arts, A. F. M.; de Wijn, H. W.

    2007-12-01

    Selective pulsed optical excitation is used in 500-at.ppm ruby (Al2O3:Cr3+) at 1.4 K to prepare complete population inversion of the Zeeman-split bar E(2E) doublet in a zone of limited size. The inversion results in prolific stimulated emission of phonons resonant with the one-phonon transition connecting the doublet states. The phonons are detected via the R1 luminescence. The angular and spectral distributions of the associated acoustic wave are measured using a geometry with inverted zones at either end of the crystal, one serving as generator and the other as detector. The divergence appears to be governed by the geometry of the zone, while the spectral distribution is, within errors, in keeping with the inhomogeneously broadened phonon transition.

  6. Influence of flow on interface shape stability in low gravity

    NASA Technical Reports Server (NTRS)

    Steen, Paul H.

    1994-01-01

    The objectives are to: (1) Understand the influence in low gravity of flow on interface shape. For example, document and control the influence of axial flow on the Plateau-Rayleigh instability of a liquid bridge; and (2) Extend the ground-based density-matching technique of low gravity simulation to situations with flow; that is, develop Plateau chamber experiments for which flow can be controlled. Containerless containment of liquid by surface tension has broad importance in low gravity. For space vehicles, the behavior of liquid/gas interfaces is crucial to successful liquid management systems. In microgravity science, free interfaces are exploited in various applications. Examples include float-zone crystal growth, phase separation near the critical point of liquid mixtures (spinoidal decomposition) and quenching of miscibility gap molten metal alloys. In some cases, it is desired to stabilize the capillary instability while in others it is desired to induce capillary breakup. In all cases, understanding the stability of interface shape in the presence of liquid motion is central.

  7. Laser-Induced Incandescence Measurements in Low Gravity

    NASA Technical Reports Server (NTRS)

    VanderWal, R. L.

    1997-01-01

    A low-gravity environment offers advantages to investigations concerned with soot growth or flame radiation by eliminating of buoyancy-induced convection. Basic to each type of study is knowledge of spatially resolved soot volume fraction, (f(sub v). Laser-induced incandescence (LII) has emerged as a diagnostic for soot volume fraction determination because it possesses high temporal and spatial resolution, geometric versatility and high sensitivity. Implementation and system characterization of LII in a drop tower that provides 2.2 sec of low-gravity (micro)g) at the NASA Lewis Research Center are described here. Validation of LII for soot volume fraction determination in (micro)g is performed by comparison between soot volume fraction measurements obtained by light extinction [20] and LII in low-gravity for a 50/50 mixture (by volume) of 0 acetylene/nitrogen issuing into quiescent air. Quantitative soot volume fraction measurements within other laminar flames of ethane and propane and a turbulent diffusion flame in (micro)g via LII are also demonstrated. An analysis of LII images of a turbulent acetylene diffusion flame in 1-g and (micro)g is presented.

  8. Low Gravity Guidance System for Airborne Microgravity Research

    NASA Technical Reports Server (NTRS)

    Rieke, W. J.; Emery, E. F.; Boyer, E. O.; Hegedus, C.; ODonoghue, D. P.

    1996-01-01

    Microgravity research techniques have been established to achieve a greater understanding of the role of gravity in the fundamentals of a variety of physical phenomena and material processing. One technique in use at the NASA Lewis Research Center involves flying Keplarian trajectories with a modified Lear Jet and DC-9 aircraft to achieve a highly accurate Microgravity environment by neutralizing accelerations in all three axis of the aircraft. The Low Gravity Guidance System (LGGS) assists the pilot and copilot in flying the trajectories by displaying the aircraft acceleration data in a graphical display format. The Low Gravity Guidance System is a microprocessor based system that acquires and displays the aircraft acceleration information. This information is presented using an electroluminescent display mounted over the pilot's instrument panel. The pilot can select the Microgravity range that is required for a given research event. This paper describes the characteristics, design, calibration and testing of the Low Gravity Guidance System Phase 3, significant lessons from earlier systems and the developmental work on future systems.

  9. Specification of optical components using the power spectral density function

    SciTech Connect

    Lawson, J.K.; Wolfe, C.R.; Manes, K.R.; Trenholme, J.B.; Aikens, D.M.; English, R.E. Jr.

    1995-06-20

    This paper describes the use of Fourier techniques to characterize the wavefront of optical components, specifically, the use of the power spectral density, (PSD), function. The PSDs of several precision optical components will be shown. Many of the optical components of interest to us have square, rectangular or irregularly shaped apertures with major dimensions up-to 800 mm. The wavefronts of components with non-circular apertures cannot be analyzed with Zernicke polynomials since these functions are an orthogonal set for circular apertures only. Furthermore, Zernicke analysis is limited to treating low frequency wavefront aberrations; mid-spatial scale and high frequency error are expressed only as ``residuals.`` A more complete and powerful representation of the optical wavefront can be obtained by Fourier analysis in 1 or 2 dimensions. The PSD is obtained from the amplitude of frequency components present in the Fourier spectrum. The PSD corresponds to the scattered intensity as a function of scattering angle in the wavefront and can be used to describe the intensity distribution at focus. The shape of a resultant wavefront or the focal spot of a complex multi-component laser system can be calculated and optimized using the PSDs of individual optical components which comprise it.

  10. System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

    DOEpatents

    Skupsky, S.; Kessler, T.J.; Letzring, S.A.

    1993-11-16

    A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse. 10 figures.

  11. System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

    DOEpatents

    Skupsky, Stanley; Kessler, Terrance J.; Letzring, Samuel A.

    1993-01-01

    A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse.

  12. High-Sensitivity Optical Pulse Characterization Using Sagnac Electro-Optic Spectral Shearing Interferometry

    SciTech Connect

    Dorrer, C.; Bromage, J.

    2010-05-04

    An electro-optic spectral shearing interferometer for high-sensitivity optical pulse characterization is described. Two replicas of the test pulse counterpropagate in a Sagnac interferometer with orthogonal polarization states, resulting in two relatively sheared copolarized replicas after temporal phase modulation. The polarization interferometer is intrinsically stable, and its birefringence sets the delay between interfering replicas to reduce the spectrometer resolution requirement. Experimental implementations demonstrate real-time pulse characterization at average powers as low as 1 nWwith spectral shears as high as 280 GHz.

  13. Balanced detection for spectral domain optical coherence tomography.

    PubMed

    Kuo, Wen-Chuan; Lai, Chih-Ming; Huang, Yi-Shiang; Chang, Cheng-Yi; Kuo, Yue-Ming

    2013-08-12

    The use and advantages of applying balanced-detection (BD) operation method to high speed spectral domain optical coherence tomography (SDOCT) are presented in this study, which we believe is the first such demonstration. Compared to conventional SDOCT, BD-SDOCT provides two unique advantages. First, the method can suppress background noise and autocorrelation artifacts in biological tissues. Second, it is a power-efficient method which is particularly helpful for high speed SDOCT to eliminate random intensity noise and to achieve shot noise limited detection. This performance allows in vivo three-dimensional tissue visualization with high imaging quality and high speed.

  14. Optical activity of transparent polymer layers characterized by spectral means

    NASA Astrophysics Data System (ADS)

    Cosutchi, Andreea Irina; Dimitriu, Dan Gheorghe; Zelinschi, Carmen Beatrice; Breaban, Iuliana; Dorohoi, Dana Ortansa

    2015-06-01

    The method based on the channeled spectrum, validated for inorganic optical active layers, is used now to determine the optical activity of some transparent polymer solutions in different solvents. The circular birefringence, the dispersion parameter and the specific rotation were estimated in the visible range by using the measurements of wavelengths in the channeled spectra of Hydroxypropyl cellulose in water, methanol and acetic acid. The experiments showed the specific rotation dependence on the polymer concentration and also on the solvent nature. The decrease of the specific rotation in the visible range with the increase in wavelength was evidenced. The method has some advantages as the rapidity of the experiments and the large spectral range in which it can be applied. One disadvantage is the fact that the channeled spectrum does not allow to establish the rotation sense of the electric field intensity.

  15. Recording digital holograms of optically transparent objects in arbitrary spectral intervals based on acousto-optic filtration of radiation

    NASA Astrophysics Data System (ADS)

    Machikhin, A. S.; Polschikova, O. V.; Ramazanova, A. G.; Pozhar, V. E.

    2015-10-01

    The problem of obtaining digital holographic images of optically transparent objects in arbitrary spectral intervals is considered. A Mach-Zehnder interferometer based optical scheme with acousto-optic spectral filtration of the broadband radiation is presented. The spectral selection allows one to increase the informativeness of digital holograms due to the choice of spectral channels in which elements with different physico-chemical properties have a sufficient contrast. Examples of recorded spectral holographic images of a test object and real objects are presented.

  16. Optical and spectral tunability of multilayer spherical and cylindrical nanoshells

    NASA Astrophysics Data System (ADS)

    Daneshfar, Nader; Bazyari, Khashayar

    2014-08-01

    This theoretical work presents a comparative study of the optical properties and spectral tunability of hybrid multilayer spherical and cylindrical nanoshells based on the quasi-static approximation of classical electrodynamics. The interband transitions have been considered using the Drude-Lorentz model for the complex dielectric function of metallic layers because the optical properties of metals arise from both the optical excitation of interband transitions and the free-electron response. A general formula for N-ayer concentric nanoshells is arranged, and numerical calculations are performed for the four-layer nanoshells as an example. We have analyzed in detail different configurations of nanoshells such as dielectric-metal-dielectric-metal with dielectric core, metal-dielectric-metal-dielectric with metal core and semiconductor-metal-dielectric-metal with semiconductor core because composition of nanoshells have dramatic influence on their optical properties. The absorbance spectrum behavior of the shell thicknesses, surrounding medium, shape and composition of each layer of the nanoshell is numerically investigated.

  17. Tunable acousto-optic spectral imager for atmospheric composition measurements in the visible spectral domain.

    PubMed

    Dekemper, Emmanuel; Loodts, Nicolas; Van Opstal, Bert; Maes, Jeroen; Vanhellemont, Filip; Mateshvili, Nina; Franssens, Ghislain; Pieroux, Didier; Bingen, Christine; Robert, Charles; De Vos, Lieve; Aballea, Ludovic; Fussen, Didier

    2012-09-01

    We describe a new spectral imaging instrument using a TeO(2) acousto-optical tunable filter (AOTF) operating in the visible domain (450-900 nm). It allows for fast (~1 second), monochromatic (FWHM ranges from 0.6 nm at 450 nm to 3.5 nm at 800 nm) picture acquisition with good spatial resolution. This instrument was designed as a breadboard of the visible channel of a new satellite-borne atmospheric limb spectral imager, named the Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS), that is currently being developed. We tested its remote sensing capabilities by observing the dense, turbulent plume exhausted by a waste incinerator stack at two wavelengths sensitive to NO(2). An average value of 6.0±0.4×10(17) molecules cm(-2) has been obtained for the NO(2) slant column density within the plume, close to the stack outlet. Although this result was obtained with a rather low accuracy, it demonstrates the potential of spectral imaging by using AOTFs in remote sensing.

  18. Optimization of spectral band utilization in gridless WDM optical network

    NASA Astrophysics Data System (ADS)

    Martins, Indayara B.; Aldaya, Ivan; Perez-Sanchez, G.; Gallion, Philippe

    2014-02-01

    In this paper, the effects of gridless spectrum allocation in Wavelength Division Multiplexed (WDM) optical networks are examined. The advanced modulation formats and multi-rate transmissions of the signals, which are key parameters in the optical system project, are taken into account. The consumed spectrum, as well as the impact of linear and nonlinear impairments on the signal transmission, are compared to WDM network adopting standard grid and gridless ITU. To analyze the influence of these physical effects, some key network design parameters are monitored and evaluated, such as the guard band size, the signal occupied bandwidth, the laser power and the quality of channels. The applied signal modulation formats were On/Off Keying (OOK), Quadrature Phase Shift keying (QPSK), and Dual Polarization State Phase Modulation (DP-QPSK), whereas the transmission rate per wavelength was varied from 10 Gb/s to 100Ghz. The guard band, signal band, and laser power were swept and the resulted Bit Error Rate (BER) was estimated from the eye-diagram. Analytical calculations and simulations are conducted in order to evaluate the impact of the gridless spectrum allocation on both the spectral consumption and the signal quality of transmission (QoT). Results reveal that a gridless transmission system reduces the spectral consumption while offering an acceptable QoT. This work was carried out with both analytical modeling and numerical calculation using the Optisystem as well as Matlab.

  19. Ultrasensitive plasmonic sensing in air using optical fibre spectral combs

    PubMed Central

    Caucheteur, Christophe; Guo, Tuan; Liu, Fu; Guan, Bai-Ou; Albert, Jacques

    2016-01-01

    Surface plasmon polaritons (SPP) can be excited on metal-coated optical fibres, enabling the accurate monitoring of refractive index changes. Configurations reported so far mainly operate in liquids but not in air because of a mismatch between permittivities of guided light modes and the surrounding medium. Here we demonstrate a plasmonic optical fibre platform that overcomes this limitation. The underpinning of our work is a grating architecture—a gold-coated highly tilted Bragg grating—that excites a spectral comb of narrowband-cladding modes with effective indices near 1.0 and below. Using conventional spectral interrogation, we measure shifts of the SPP-matched resonances in response to static atmospheric pressure changes. A dynamic experiment conducted using a laser lined-up with an SPP-matched resonance demonstrates the ability to detect an acoustic wave with a resolution of 10−8 refractive index unit (RIU). We believe that this configuration opens research directions for highly sensitive plasmonic sensing in gas. PMID:27834366

  20. CCD fiber optic spectrometer for the measurement of spectral irradiance

    NASA Astrophysics Data System (ADS)

    Morley, J. U.; McArthur, L. J. B.; Halliwell, D.; Poissant, Y.; Pelland, S.

    2010-08-01

    Recent technological advancements have made CCD spectrometers an increasingly suitable alternative to traditional monochromator-based instrumentation. The authors have developed instrumentation for the near instantaneous measurement of spectral global, direct, diffuse, reflected and southward-tilted irradiances. The system uses an AvaSpec2048TEC-2 - a dual channel thermo-electric-cooled fiber optic spectrometer from Avantes Inc. Each channel has a 2048-pixel linear array detector and the system achieves a spectral resolution of 0.0007 μm (FWHM) over the range 0.241-1.1 μm. The system also includes sensor heads, fiber optic cables and a multiplexer. Two types of sensor heads have been developed: a pyrheliometer configuration for direct beam, and a pyranometer configuration for global, diffuse, reflected and tilted measurements. Calibration uses a system of standard light sources. Cosine errors inherent to the spectralon diffusers have been characterized and corrections are applied to data from each sensor head. Accuracy of global irradiance is examined by comparing measurements against global photosynthetically active radiation (PAR) (0.395 - 0.695 μm) from Eppley red and green dome pyranometers. PAR daily totals (MJ/m2/day) and one minute averages (W/m2) are compared for 35 days in 2009 and daily totals are within +/- 10% from June to October.

  1. Ultrasensitive plasmonic sensing in air using optical fibre spectral combs

    NASA Astrophysics Data System (ADS)

    Caucheteur, Christophe; Guo, Tuan; Liu, Fu; Guan, Bai-Ou; Albert, Jacques

    2016-11-01

    Surface plasmon polaritons (SPP) can be excited on metal-coated optical fibres, enabling the accurate monitoring of refractive index changes. Configurations reported so far mainly operate in liquids but not in air because of a mismatch between permittivities of guided light modes and the surrounding medium. Here we demonstrate a plasmonic optical fibre platform that overcomes this limitation. The underpinning of our work is a grating architecture--a gold-coated highly tilted Bragg grating--that excites a spectral comb of narrowband-cladding modes with effective indices near 1.0 and below. Using conventional spectral interrogation, we measure shifts of the SPP-matched resonances in response to static atmospheric pressure changes. A dynamic experiment conducted using a laser lined-up with an SPP-matched resonance demonstrates the ability to detect an acoustic wave with a resolution of 10-8 refractive index unit (RIU). We believe that this configuration opens research directions for highly sensitive plasmonic sensing in gas.

  2. Optical Polarization and Spectral Variability in the M87 Jet

    NASA Technical Reports Server (NTRS)

    Perlman, Eric S.; Adams, Steven C.; Cara, Mihai; Bourque, Matthew; Harris, D. E.; Madrid, Juan P.; Simons, Raymond C.; Clausen-Brown, Eric; Cheung, C. C.; Stawarz, Lukasz; Georganopoulos, Markos; Sparks, William B.; Biretta, John A.

    2011-01-01

    During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability was also seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST -1 shows a highly significant correlation between flux and polarization, with P increasing from approx 20% at minimum to > 40% at maximum, while the orientation of its electric vector stayed constant. HST-l's optical-UV spectrum is very hard (alpha(sub uv-0) approx. 0.5, F(sub v) varies as (v(exp -alpha)), and displays "hard lags" during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2alpha upper limits of 0.5 delta parsecs and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet PA, makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and 'looping' in the (I, P) plane. The nucleus has a much steeper spectrum ((alpha(sub uv-0) approx. 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet.

  3. All-optical OFDM demultiplexing by spectral magnification and band-pass filtering.

    PubMed

    Palushani, E; Mulvad, H C Hansen; Kong, D; Guan, P; Galili, M; Oxenløwe, L K

    2014-01-13

    We propose a simple OFDM receiver allowing for the use of standard WDM receivers to receive spectrally advanced OFDM signals. We propose to spectrally magnify the optical-OFDM super-channels using a spectral telescope consisting of two time-lenses, which enables reduced inter-carrier-interference in subcarrier detection by simple band-pass filtering. A demonstration on an emulated 100 Gbit/s DPSK optical-OFDM channel shows improved sensitivities after 4-times spectral magnification.

  4. Atmospheric Optical Properties and Spectral Analysis of Desert Aerosols

    NASA Astrophysics Data System (ADS)

    Yvgeni, D.; Karnieli, A.; Kaufman, Y. J.; Andreae, M. O.; Holben, B. N.; Maenhaut, W.

    2002-05-01

    Scientific background Aerosols can interact directly with solar and terrestrial radiation by scattering as well as absorption. In addition, they can indirectly alter the planetary albedo by modifying the properties of clouds. Objectives Investigations have been devoted to two main areas: (1) Aerosol climatology situation in the Negev desert, investigations of physical and chemical characteristics of aerosols, and study of the local and long-range transport trajectory of polluted air masses over the Negev desert; and (2) An estimation of the optical properties throughout the atmospheric column by surface measurements via performance of spectral and statistical analysis of the data received from two measurement systems. Results and conclusions Analyzed data from the Sede Boker site, in the Negev Desert of Israel, shows an increase in aerosol optical depth during the summer seasons and a decrease during winter. One of the possible reasons for this characteristic is an increase of the precipitable water (reaches 3.0-3.5 cm) due to a constant wind stream from the Mediterranean Sea in same time. The highest probability distribution of the aerosol optical depth is in the range of 0.15-0.20; and of the Angstrom parameter is in range of 0.83 - 1.07. During dust storm events, the scattering coefficient range at 670 nm and 440 nm wavelengths were inverted. It was discovered that the dust particles in this case had non-spherical character. Comparison between optical depth, measured through all atmospheric column, and scattering coefficient from surface measurements provides correlation coefficient (r) equal to 0.64. The Angstrom parameter, calculated via optical depth and via scattering coefficient, provides a correlation coefficient of 0.66. Thus we can obtain an estimate of the influence of the surface aerosol situation on column optical properties. The combined analysis of dust cloud altitude and optical depth as a function of the time indicates long-term transport and

  5. Fire Safety in the Low-Gravity Spacecraft Environment

    NASA Technical Reports Server (NTRS)

    Friedman, Robert

    1999-01-01

    Research in microgravity (low-gravity) combustion promises innovations and improvements in fire prevention and response for human-crew spacecraft. Findings indicate that material flammability and fire spread in microgravity are significantly affected by atmospheric flow rate, oxygen concentration, and diluent composition. This information can lead to modifications and correlations to standard material-assessment tests for prediction of fire resistance in space. Research on smoke-particle changes in microgravity promises future improvements and increased sensitivity of smoke detectors in spacecraft. Research on fire suppression by extinguishing agents and venting can yield new information on effective control of the rare, but serious fire events in spacecraft.

  6. Properties of Smoke from Overheated Materials in Low-Gravity

    NASA Technical Reports Server (NTRS)

    Urban, David L.; Ruff, Gary A.; Sheredy, William; Cleary, Thomas; Yang, Jiann; Mulholland, George; Yuan, Zeng-Guang

    2009-01-01

    Smoke particle size measurements were obtained under low-gravity conditions by overheating several materials typical of those found in spacecraft. The measurements included integral measurements of the smoke particles and physical sample of the particles for Transmission Electron Microscope analysis. The integral moments were combined to obtain geometric mean particle sizes and geometric standard deviations. These results are presented with the details of the instrument calibrations. The experimental results show that, for the materials tested, a substantial portion of the smoke particles are below 500 nm in diameter.

  7. Liquid inflow to initially empty cylindrical tanks in low gravity

    NASA Technical Reports Server (NTRS)

    Spuckler, C. M.

    1972-01-01

    An experimental investigation was performed to determine the characteristics of liquid inflow to initially empty cylindrical tanks in a low gravity environment. The acceleration was varied so that Bond numbers based on the inlet radius varied from 0.059 to 2.80. The liquid entered the tank as a jet that grew to a maximum height and then decreased in height with respect to the bottom of the tank, with the liquid from the jet collecting in the bottom of the tank. The maximum jet heights were correlated in terms of the Weber number and the Bond number.

  8. Sparsity based denoising of spectral domain optical coherence tomography images

    PubMed Central

    Fang, Leyuan; Li, Shutao; Nie, Qing; Izatt, Joseph A.; Toth, Cynthia A.; Farsiu, Sina

    2012-01-01

    In this paper, we make contact with the field of compressive sensing and present a development and generalization of tools and results for reconstructing irregularly sampled tomographic data. In particular, we focus on denoising Spectral-Domain Optical Coherence Tomography (SDOCT) volumetric data. We take advantage of customized scanning patterns, in which, a selected number of B-scans are imaged at higher signal-to-noise ratio (SNR). We learn a sparse representation dictionary for each of these high-SNR images, and utilize such dictionaries to denoise the low-SNR B-scans. We name this method multiscale sparsity based tomographic denoising (MSBTD). We show the qualitative and quantitative superiority of the MSBTD algorithm compared to popular denoising algorithms on images from normal and age-related macular degeneration eyes of a multi-center clinical trial. We have made the corresponding data set and software freely available online. PMID:22567586

  9. Endoscopic probe optics for spectrally encoded confocal microscopy.

    PubMed

    Kang, Dongkyun; Carruth, Robert W; Kim, Minkyu; Schlachter, Simon C; Shishkov, Milen; Woods, Kevin; Tabatabaei, Nima; Wu, Tao; Tearney, Guillermo J

    2013-01-01

    Spectrally encoded confocal microscopy (SECM) is a form of reflectance confocal microscopy that can achieve high imaging speeds using relatively simple probe optics. Previously, the feasibility of conducting large-area SECM imaging of the esophagus in bench top setups has been demonstrated. Challenges remain, however, in translating SECM into a clinically-useable device; the tissue imaging performance should be improved, and the probe size needs to be significantly reduced so that it can fit into luminal organs of interest. In this paper, we report the development of new SECM endoscopic probe optics that addresses these challenges. A custom water-immersion aspheric singlet (NA = 0.5) was developed and used as the objective lens. The water-immersion condition was used to reduce the spherical aberrations and specular reflection from the tissue surface, which enables cellular imaging of the tissue deep below the surface. A custom collimation lens and a small-size grating were used along with the custom aspheric singlet to reduce the probe size. A dual-clad fiber was used to provide both the single- and multi- mode detection modes. The SECM probe optics was made to be 5.85 mm in diameter and 30 mm in length, which is small enough for safe and comfortable endoscopic imaging of the gastrointestinal tract. The lateral resolution was 1.8 and 2.3 µm for the single- and multi- mode detection modes, respectively, and the axial resolution 11 and 17 µm. SECM images of the swine esophageal tissue demonstrated the capability of this device to enable the visualization of characteristic cellular structural features, including basal cell nuclei and papillae, down to the imaging depth of 260 µm. These results suggest that the new SECM endoscopic probe optics will be useful for imaging large areas of the esophagus at the cellular scale in vivo.

  10. Endoscopic probe optics for spectrally encoded confocal microscopy

    PubMed Central

    Kang, DongKyun; Carruth, Robert W.; Kim, Minkyu; Schlachter, Simon C.; Shishkov, Milen; Woods, Kevin; Tabatabaei, Nima; Wu, Tao; Tearney, Guillermo J.

    2013-01-01

    Spectrally encoded confocal microscopy (SECM) is a form of reflectance confocal microscopy that can achieve high imaging speeds using relatively simple probe optics. Previously, the feasibility of conducting large-area SECM imaging of the esophagus in bench top setups has been demonstrated. Challenges remain, however, in translating SECM into a clinically-useable device; the tissue imaging performance should be improved, and the probe size needs to be significantly reduced so that it can fit into luminal organs of interest. In this paper, we report the development of new SECM endoscopic probe optics that addresses these challenges. A custom water-immersion aspheric singlet (NA = 0.5) was developed and used as the objective lens. The water-immersion condition was used to reduce the spherical aberrations and specular reflection from the tissue surface, which enables cellular imaging of the tissue deep below the surface. A custom collimation lens and a small-size grating were used along with the custom aspheric singlet to reduce the probe size. A dual-clad fiber was used to provide both the single- and multi- mode detection modes. The SECM probe optics was made to be 5.85 mm in diameter and 30 mm in length, which is small enough for safe and comfortable endoscopic imaging of the gastrointestinal tract. The lateral resolution was 1.8 and 2.3 µm for the single- and multi- mode detection modes, respectively, and the axial resolution 11 and 17 µm. SECM images of the swine esophageal tissue demonstrated the capability of this device to enable the visualization of characteristic cellular structural features, including basal cell nuclei and papillae, down to the imaging depth of 260 µm. These results suggest that the new SECM endoscopic probe optics will be useful for imaging large areas of the esophagus at the cellular scale in vivo. PMID:24156054

  11. Protein crystallization in low gravity by step gradient diffusion method

    NASA Astrophysics Data System (ADS)

    Sygusch, Jurgen; Coulombe, René; Cassanto, John M.; Sportiello, Michael G.; Todd, Paul

    1996-05-01

    Two-step crystallization experiments were conducted in low gravity employing a liquid-liquid diffusion method in an effort to eliminate problems associated with protein crystal growth under the supersaturating conditions required for nucleation. Experiments were performed in diffusion cells formed by the sliding of blocks on orbit. Step gradient diffusion experiments consisted of first exposing protein solutions in diffusion half-wells for brief periods to initiating buffer solutions of high precipitant concentrations to induce nucleation followed by exposure of the same protein solutions to solutions of lower precipitant concentration to promote growth of induced nuclei into crystals. To avoid convective disturbances that occur when solutions of discrepant densities are interfaced at normal gravity, crystallization of hen egg-white lysozyme and rabbit skeletal muscle aldolase by step gradient diffusion was investigated in low gravity on four NASA space shuttle flights. In general, the largest crystals of both proteins formed at the highest initiating precipitant concentration used, which is consistent with nuclei formation upon brief exposure to high precipitant concentration, and that these nuclei are competent for sustained growth at lower precipitant concentration. The two-step approach dissociates nucleation events from crystal growth allowing parameters affecting nucleation kinetics such as time, precipitant concentration and temperature of nucleation to be varied separately from conditions used for post-nucleation growth.

  12. Low-gravity fluid physics: A program overview

    NASA Astrophysics Data System (ADS)

    1990-08-01

    An overview is presented of the microgravity fluid physics program at Lewis Research Center. One of the main reasons for conducting low gravity research in fluid physics is to study phenomena such as surface tension, interfacial contact angles, and diffusion independent of such gravitationally induced effects as buoyant convection. Fluid physics is at the heart of many space-based technologies including power systems, thermal control systems, and life support systems. Fundamental understanding of fluid physics is a key ingredient to successful space systems design. In addition to describing ground-based and space-based low-gravity facilities, selected experiments are presented which highlight Lewis work in fluid physics. These experiments can be categorized into five theme areas which summarize the work being conducted at Lewis for OSSA: (1) isothermal/iso-solutal capillary phenomena; (2) capillary phenomena with thermal/solutal gradients; (3) thermal-solutal convection; (4) first- and second-order phase transitions in a static fluid; and (5) multiphase flow.

  13. Low-gravity fluid physics: A program overview

    NASA Technical Reports Server (NTRS)

    1990-01-01

    An overview is presented of the microgravity fluid physics program at Lewis Research Center. One of the main reasons for conducting low gravity research in fluid physics is to study phenomena such as surface tension, interfacial contact angles, and diffusion independent of such gravitationally induced effects as buoyant convection. Fluid physics is at the heart of many space-based technologies including power systems, thermal control systems, and life support systems. Fundamental understanding of fluid physics is a key ingredient to successful space systems design. In addition to describing ground-based and space-based low-gravity facilities, selected experiments are presented which highlight Lewis work in fluid physics. These experiments can be categorized into five theme areas which summarize the work being conducted at Lewis for OSSA: (1) isothermal/iso-solutal capillary phenomena; (2) capillary phenomena with thermal/solutal gradients; (3) thermal-solutal convection; (4) first- and second-order phase transitions in a static fluid; and (5) multiphase flow.

  14. Suppressing spectral diffusion of emitted photons with optical pulses

    DOE PAGES

    Fotso, H. F.; Feiguin, A. E.; Awschalom, D. D.; ...

    2016-01-22

    In many quantum architectures the solid-state qubits, such as quantum dots or color centers, are interfaced via emitted photons. However, the frequency of photons emitted by solid-state systems exhibits slow uncontrollable fluctuations over time (spectral diffusion), creating a serious problem for implementation of the photon-mediated protocols. Here we show that a sequence of optical pulses applied to the solid-state emitter can stabilize the emission line at the desired frequency. We demonstrate efficiency, robustness, and feasibility of the method analytically and numerically. Taking nitrogen-vacancy center in diamond as an example, we show that only several pulses, with the width of 1more » ns, separated by few ns (which is not difficult to achieve) can suppress spectral diffusion. As a result, our method provides a simple and robust way to greatly improve the efficiency of photon-mediated entanglement and/or coupling to photonic cavities for solid-state qubits.« less

  15. Spectral optical properties of selected photosynthetic microalgae producing biofuels

    NASA Astrophysics Data System (ADS)

    Lee, Euntaek; Heng, Ri-Liang; Pilon, Laurent

    2013-01-01

    This paper presents the spectral complex index of refraction of biofuel producing photosynthetic microalgae between 400 and 750 nm. They were retrieved from their experimentally measured average absorption and scattering cross-sections. The microalgae were treated as homogeneous polydisperse spheres with equivalent diameter such that their surface area was identical to that of their actual spheroidal shape. An inverse method was developed combining Lorentz-Mie theory as the forward method and genetic algorithm. The unicellular green algae Chlamydomonas reinhardtii strain CC125 and its truncated chlorophyll antenna transformants tla1, tlaX, and tla1-CW+ as well as Botryococcus braunii, Chlorella sp., and Chlorococcum littorale were investigated. These species were selected for their ability to produce either hydrogen gas or lipids for liquid fuel production. Their retrieved real and imaginary parts of the complex index of refraction were continuous functions of wavelength with absorption peaks corresponding to those of in vivo Chlorophylls a and b. The T-matrix method was also found to accurately predict the experimental measurements by treating the microalgae as axisymmetric spheroids with the experimentally measured major and minor diameter distributions and the retrieved spectral complex index of refraction. Finally, pigment mass fractions were also estimated from the retrieved absorption index. The method and/or the reported optical properties can be used in various applications from ocean remote sensing, carbon cycle study, as well as photobiological carbon dioxide mitigation and biofuel production.

  16. Electron Bunch Shape Measurements Using Electro-optical Spectral Decoding

    NASA Astrophysics Data System (ADS)

    Borysenko, A.; Hiller, N.; Müller, A.-S.; Steffen, B.; Peier, P.; Ivanisenko, Y.; Ischebeck, R.; Schlott, V.

    Longitudinal diagnostics of the electron bunch shapes play a crucial role in the operation of linac-based light sources. Electro-optical techniques allow us to measure the longitudinal electron bunch profiles non-destructively on a shot-by-shot basis. Here we present results from measurements of electron bunches with a length of 200-900 fs rms at the Swiss FEL Injector Test Facility. All the measurements were done using an Yb-doped fibre laser system (with a central wavelength of a 1050 nm) and a GaP crystal. The technique of electro-optical spectral decoding (EOSD) was applied and showed great capabilities to measure bunch shapes down to around 370 fs rms. Measurements were performed for different electron energies to study the expected distortions of the measured bunch profile due to the energy-dependent widening of the electric field, which plays a role for low beam energies below and around 40 MeV. The studies provide valuable input for the design of the EOSD monitors for the compact linear accelerator FLUTE that is currently under commissioning at the Karslruhe Institute of Technology (KIT).

  17. Extended depth of focus adaptive optics spectral domain optical coherence tomography

    PubMed Central

    Sasaki, Kazuhiro; Kurokawa, Kazuhiro; Makita, Shuichi; Yasuno, Yoshiaki

    2012-01-01

    We present an adaptive optics spectral domain optical coherence tomography (AO-SDOCT) with a long focal range by active phase modulation of the pupil. A long focal range is achieved by introducing AO-controlled third-order spherical aberration (SA). The property of SA and its effects on focal range are investigated in detail using the Huygens-Fresnel principle, beam profile measurement and OCT imaging of a phantom. The results indicate that the focal range is extended by applying SA, and the direction of extension can be controlled by the sign of applied SA. Finally, we demonstrated in vivo human retinal imaging by altering the applied SA. PMID:23082278

  18. Achromatic registration of quadrature components of the optical spectrum in spectral domain optical coherence tomography

    SciTech Connect

    Shilyagin, P A; Gelikonov, G V; Gelikonov, V M; Moiseev, A A; Terpelov, D A

    2014-07-31

    We have thoroughly investigated the method of simultaneous reception of spectral components with the achromatised quadrature phase shift between two portions of a reference wave, designed for the effective suppression of the 'mirror' artefact in the resulting image obtained by means of spectral domain optical coherence tomography (SD OCT). We have developed and experimentally tested a phase-shifting element consisting of a beam divider, which splits the reference optical beam into the two beams, and of delay lines being individual for each beam, which create a mutual phase difference of π/2 in the double pass of the reference beam. The phase shift achromatism over a wide spectral range is achieved by using in the delay lines the individual elements with different dispersion characteristics. The ranges of admissible adjustment parameters of the achromatised delay line are estimated for exact and inexact conformity of the geometric characteristics of its components to those calculated. A possibility of simultaneous recording of the close-to-quadrature spectral components with a single linear photodetector element is experimentally confirmed. The suppression of the artefact mirror peak in the OCT-signal by an additional 9 dB relative to the level of its suppression is experimentally achieved when the air delay line is used. Two-dimensional images of the surface positioned at an angle to the axis of the probe beam are obtained with the correction of the 'mirror' artefact while maintaining the dynamic range of the image. (laser biophotonics)

  19. Dynamics of Superfluid Helium in Low-Gravity

    NASA Technical Reports Server (NTRS)

    Frank, David J.

    1997-01-01

    This report summarizes the work performed under a contract entitled 'Dynamics of Superfluid Helium in Low Gravity'. This project performed verification tests, over a wide range of accelerations of two Computational Fluid Dynamics (CFD) codes of which one incorporates the two-fluid model of superfluid helium (SFHe). Helium was first liquefied in 1908 and not until the 1930s were the properties of helium below 2.2 K observed sufficiently to realize that it did not obey the ordinary physical laws of physics as applied to ordinary liquids. The term superfluidity became associated with these unique observations. The low temperature of SFHe and it's temperature unifonrmity have made it a significant cryogenic coolant for use in space applications in astronomical observations with infrared sensors and in low temperature physics. Superfluid helium has been used in instruments such as the Shuttle Infrared Astronomy Telescope (IRT), the Infrared Astronomy Satellite (IRAS), the Cosmic Background Observatory (COBE), and the Infrared Satellite Observatory (ISO). It is also used in the Space Infrared Telescope (SIRTF), Relativity Mission Satellite formally called Gravity Probe-B (GP-B), and the Test of the Equivalence Principle (STEP) presently under development. For GP-B and STEP, the use of SFHE is used to cool Superconducting Quantum Interference Detectors (SQUIDS) among other parts of the instruments. The Superfluid Helium On-Orbit Transfer (SHOOT) experiment flown in the Shuttle studied the behavior of SFHE. This experiment attempted to get low-gravity slosh data, however, the main emphasis was to study the low-gravity transfer of SFHE from tank to tank. These instruments carried tanks of SFHE of a few hundred liters to 2500 liters. The capability of modeling the behavior of SFHE is important to spacecraft control engineers who must design systems that can overcome disturbances created by the movement of the fluid. In addition instruments such as GP-B and STEP are very

  20. Singular value decomposition based regularization prior to spectral mixing improves crosstalk in dynamic imaging using spectral diffuse optical tomography

    PubMed Central

    Zhan, Yuxuan; Eggebrecht, Adam T.; Culver, Joseph P.; Dehghani, Hamid

    2012-01-01

    The spectrally constrained diffuse optical tomography (DOT) method relies on incorporating spectral prior information directly into the image reconstruction algorithm, thereby correlating the underlying optical properties across multiple wavelengths. Although this method has been shown to provide a solution that is stable, the use of conventional Tikhonov-type regularization techniques can lead to additional crosstalk between parameters, particularly in linear, single-step dynamic imaging applications. This is due mainly to the suboptimal regularization of the spectral Jacobian matrix, which smoothes not only the image-data space, but also the spectral mapping space. In this work a novel regularization technique based on the singular value decomposition (SVD) is presented that preserves the spectral prior information while regularizing the Jacobian matrix, leading to dramatically reduced crosstalk between the recovered parameters. Using simulated data, images of changes in oxygenated and deoxygenated hemoglobin concentrations are reconstructed via the SVD-based approach and compared with images reconstructed by using non-spectral and conventional spectral methods. In a 2D, two wavelength example, it is shown that the proposed approach provides a 98% reduction in crosstalk between recovered parameters as compared with conventional spectral reconstruction algorithms, and 60% as compared with non-spectrally constrained algorithms. Using a subject specific multilayered model of the human head, a noiseless dynamic simulation of cortical activation is performed to further demonstrate such improvement in crosstalk. However, with the addition of realistic noise in the data, both non-spectral and proposed algorithms perform similarly, indicating that the use of spectrally constrained reconstruction algorithms in dynamic DOT may be limited by the contrast of the signal as well as the noise characteristics of the system. PMID:23024899

  1. High resolution atomic coherent control via spectral phase manipulation of an optical frequency comb.

    PubMed

    Stowe, Matthew C; Cruz, Flavio C; Marian, Adela; Ye, Jun

    2006-04-21

    We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.

  2. High Resolution Atomic Coherent Control via Spectral Phase Manipulation of an Optical Frequency Comb

    SciTech Connect

    Stowe, Matthew C.; Cruz, Flavio C.; Marian, Adela; Ye Jun

    2006-04-21

    We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.

  3. Effect of Group-Velocity Dispersion on Photon-Number Squeezing of Optical Pulses using Optical Fibers and Spectral Filter

    NASA Astrophysics Data System (ADS)

    Nishizawa, Norihiko; Horio, Takeo; Mori, Masakazu; Goto, Toshio; Yamane, Kazuo

    1999-04-01

    Photon-number squeezing of optical pulses using optical fibers and band-pass spectral filters is numerically analyzed. The evolution of the quantum noise in the optical pulse propagation is calculated in both the spectral and time domains. The mechanism of filtering squeezing and the role of the group-velocity dispersion are investigated.It is shown that the squeezing is realized owing to the interaction between the self-phase modulation and the group-velocity dispersion.

  4. Error-corrective optical recall of digital images by photoburning of persistent spectral holes

    NASA Astrophysics Data System (ADS)

    Rebane, A.; Ollikainen, O.

    1991-06-01

    Associative error-corrective recall of spatially- and wavelength (frequency) encoded digital optical signals is carried out by using spectrally highly-selective low-temperature photochromic storage media. It is demonstrated that the technique of photoburning of persistent spectral provides, in addition to usual spatial coordinates, new parallel-accessible degrees of freedom which can be used for ultrafast optical processing.

  5. SWIRL as a means of liquid management in low gravity

    NASA Technical Reports Server (NTRS)

    Steward, W. Gene

    1993-01-01

    Swirling of a liquid in a container may prove to be a more desirable method of managing liquids in low gravity (space) environments than by rotating the entire container. By injecting a relatively high velocity liquid tangentially into the body of the fluid, swirl can best be started rapidly, however an estimate of the quantity and velocity of jetflow, or mechanical power of a pump impeller required to maintain a given radial acceleration (G force) is needed to assess the feasibility of such a method. While the key aspect of the problem is determining the rate of rotational energy dissipation by wall friction in the container, there are other considerations, and the present study investigates the possible additional effects of axial variation of tangential velocity and secondary (radial and axial) flow components within the rotating fluid.

  6. Description of the containerless melting of glass in low gravity

    NASA Technical Reports Server (NTRS)

    Ray, C. S.; Day, D. E.

    1983-01-01

    A brief description is given of a single-axis, acoustic levitator/furnace apparatus used to position, heat, melt, and quench multicomponent oxide, glass-forming compositions in low gravity. This apparatus is capable of processing eight approximately spherical samples (about 6 mm diameter) at temperatures up to 1550 C in a dry air atmosphere. Results are also presented for a containerless melting experiment conducted on SPAR VI where a ternary CaO-Ga2O3-SiO2 composition was levitated and quenched to a glass. Selected properties of the glass prepared on SPAR VI are compared with the properties of glass samples of identical composition prepared on earth.

  7. Containerless low gravity processing of glass forming and immiscible alloys

    NASA Technical Reports Server (NTRS)

    Andrews, J. Barry; Briggs, Craig; Robinson, M. B.

    1990-01-01

    Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix.

  8. Utilization of Low Gravity Environment for Measuring Liquid Viscosity

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.; Ethridge, Edwin

    1998-01-01

    The method of drop coalescence is used for determining the viscosity of highly viscous undercooled liquids. Low gravity environment is necessary in order to allow for examining large volumes affording much higher accuracy for the viscosity calculations than possible for smaller volumes available under 1 - g conditions. The drop coalescence method is preferred over the drop oscillation technique since the latter method can only be applied for liquids with vanishingly small viscosities. The technique developed relies on both the highly accurate solution of the Navier-Stokes equations as well as on data from experiments conducted in near zero gravity environment. Results are presented for method validation experiments recently performed on board the NASA/KC-135 aircraft. While the numerical solution was produced using the Boundary Element Method. In these tests the viscosity of a highly viscous liquid, glycerine at room temperature, was determined using the liquid coalescence method. The results from these experiments will be discussed.

  9. Crystal growth of enzymes in low gravity (L-5)

    NASA Technical Reports Server (NTRS)

    Morita, Yuhei

    1993-01-01

    Recent developments in protein engineering have expanded the possibilities of studies of enzymes and other proteins. Now such studies are not limited to the elucidation of the relationship between the structure and function of the protein. They also aim at the production of proteins with new and practical functions, based on results obtained during investigation of structure and function. For continuing research in this field, investigation of the tertiary structure of proteins is important. X-ray diffraction of single crystals of protein is usually used for this purpose. The main difficulty is the preparation of the crystals. The theme of the research is to prepare such crystals at very low gravity, with the main purpose being to obtain large single crystals of proteins suitable for x-ray diffraction studies.

  10. Low gravity containerless processing of immiscible gold rhodium alloys

    NASA Technical Reports Server (NTRS)

    Andrews, J. Barry

    1986-01-01

    Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedementation of the more dense of the immiscible liquid phases. However, under low-g conditions it should be possible to form a dispersion of the two immiscible liquids and maintain this dispersed structure during solidification. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the Marshall Space Flight Center 105 meter drop tube in order to investigate the influence of low gravity, containerless solidification on their microstructure. Hypermonotectic alloys composed of 65 atomic % rhodium exhibited a tendency for the gold rich liquid to wet the outer surface of the containerless processed samples. This tendency led to extensive segregation in several cases. However, well dispersed microstructures consisting of 2 to 3 micron diameter rhodium-rich spheres in a gold-rich matrix were produced in 23.4 atomic % rhodium alloys. This is one of the best dispersions obtained in research on immiscible alloy-systems to data.

  11. Low-gravity impact experiments: Progress toward a facility definition

    NASA Technical Reports Server (NTRS)

    Cintala, M. J.

    1986-01-01

    Innumerable efforts were made to understand the cratering process and its ramifications in terms of planetary observations, during which the role of gravity has often come into question. Well known facilities and experiments both were devoted in many cases to unraveling the contribution of gravitational acceleration to cratering mechanisms. Included among these are the explosion experiments in low gravity aircraft, the drop platform experiments, and the high gravity centrifuge experiments. Considerable insight into the effects of gravity was gained. Most investigations were confined to terrestrial laboratories. It is in this light that the Space Station is being examined as a vehicle with the potential to support otherwise impractical impact experiments. The results of studies performed by members of the planetary cratering community are summarized.

  12. Undercooling measurement in a low-gravity containerless environment

    NASA Technical Reports Server (NTRS)

    Robinson, M. B.

    1981-01-01

    A technique is described for measuring the amount of undercooling for samples processed in a low-gravity containerless environment. The time of undercooling is determined by measuring the time of cooling before nucleation and recalescence by two infrared detectors. Once the cooling curve for each drop is calculated, the amount of undercooling can then be found. The technique is demonstrated by measuring the amount of undercooling for drops of pure niobium and select compositions of the niobium-germanium alloy system while free falling in a 32 n evacuated drop tube. The total hemispherical emissivities and specific heats for these materials were measured using a high-temperature containerless calorimeter. An overview of the effect of undercooling on drops of niobium and niobium-germanium is given.

  13. Apparatus for mixing solutions in low gravity environments

    NASA Technical Reports Server (NTRS)

    Carter, Daniel C. (Inventor); Broom, Mary B. (Inventor)

    1990-01-01

    An apparatus is disclosed for allowing mixing of solutions in low gravity environments so as to carry out crystallization of proteins and other small molecules or other chemical syntheses, under conditions that maximize crystal growth and minimize disruptive turbulent effects. The apparatus is comprised of a housing, a plurality of chambers, and a cylindrical rotatable valve disposed between at least two of the chambers, said valve having an internal passageway so as to allow fluid movement between the chambers by rotation of the valve. In an alternate embodiment of the invention, a valve is provided having an additional internal passage way so that fluid from a third chamber can be mixed with the fluids of the first two chambers. This alternate embodiment of the invention is particularly desirable when it is necessary to provide a termination step to the crystal growth, or if a second synthetic step is required.

  14. Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2014-01-01

    A low gravity material experiment will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). There are two sections of the flight experiment: (I) crystal growth of ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, by physical vapor transport (PVT) and (II) melt growth of CdZnTe by directional solidification. The main objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the grown crystals as results of buoyancy-driven convection and growth interface fluctuations caused by irregular fluid-flows on Earth. The investigation consists of extensive ground-based experimental and theoretical research efforts and concurrent flight experimentation. This talk will focus on the ground-based studies on the PVT crystal growth of ZnSe and related ternary compounds. The objectives of the ground-based studies are (1) obtain the experimental data and conduct the analyses required to define the optimum growth parameters for the flight experiments, (2) perfect various characterization techniques to establish the standard procedure for material characterization, (3) quantitatively establish the characteristics of the crystals grown on Earth as a basis for subsequent comparative evaluations of the crystals grown in a low-gravity environment and (4) develop theoretical and analytical methods required for such evaluations. ZnSe and related ternary compounds have been grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals have been characterized extensively by various techniques to correlate the grown crystal properties with the growth conditions.

  15. Linear-wavenumber spectrometer for high-speed spectral-domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Gelikonov, V. M.; Gelikonov, G. V.; Shilyagin, P. A.

    2009-03-01

    An equidistant (in the wavenumber) spectrometer based on a diffraction grating, a compensation prism, and a CCD linear array is developed and implemented for spectral-domain optical coherence tomography. A criterion is introduced for estimating the level of residual nonequidistance. This criterion allows one to determine the threshold compensation level necessary for obtaining the spectrally limited spatial resolution. The method is tested in spectral-domain optical coherent tomography systems at wavelengths of 1270 and 830 nm.

  16. Analysis of spectral response of optical switching devices based on chalcogenide bistable fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Scholtz, Lubomír.; Müllerová, Jarmila

    2015-01-01

    Fiber Bragg gratings (FBGs) are novel and promising devices for all-optical switching, ADD/DROP multiplexers, AND gates, switches, all-optical memory elements. Optical switching based on optical Kerr effects induced with high pump laser light incident on the FBGs cause the change of spectral characteristics of grating depending on the incident power. In this paper numerical studies of the nonlinear FBGs are presented. Optical switching based on the optical bistability in nonlinear chalcogenide FBGs is investigated. The spectral response of nonlinear FBGs is discussed from theoretical viewpoint. The simulations are based on the nonlinear coupled mode theory.

  17. Interferometric and nonlinear-optical spectral-imaging techniques for outer space and live cells

    NASA Astrophysics Data System (ADS)

    Itoh, Kazuyoshi

    2015-12-01

    Multidimensional signals such as the spectral images allow us to have deeper insights into the natures of objects. In this paper the spectral imaging techniques that are based on optical interferometry and nonlinear optics are presented. The interferometric imaging technique is based on the unified theory of Van Cittert-Zernike and Wiener-Khintchine theorems and allows us to retrieve a spectral image of an object in the far zone from the 3D spatial coherence function. The retrieval principle is explained using a very simple object. The promising applications to space interferometers for astronomy that are currently in progress will also be briefly touched on. An interesting extension of interferometric spectral imaging is a 3D and spectral imaging technique that records 4D information of objects where the 3D and spectral information is retrieved from the cross-spectral density function of optical field. The 3D imaging is realized via the numerical inverse propagation of the cross-spectral density. A few techniques suggested recently are introduced. The nonlinear optical technique that utilizes stimulated Raman scattering (SRS) for spectral imaging of biomedical targets is presented lastly. The strong signals of SRS permit us to get vibrational information of molecules in the live cell or tissue in real time. The vibrational information of unstained or unlabeled molecules is crucial especially for medical applications. The 3D information due to the optical nonlinearity is also the attractive feature of SRS spectral microscopy.

  18. Materials processing threshold report: 2. Use of low gravity for cast iron process development

    NASA Technical Reports Server (NTRS)

    Frankhouser, W. L.

    1980-01-01

    Potential applications of a low gravity environment of interest to the commercial producers of cast iron were assessed to determine whether low gravity conditions offer potential opportunities to producers for improving cast iron properties and expanding the use of cast irons. The assessment is limited to the gray and nodular types of iron, however, the findings are applicable to all cast irons. The potential advantages accrued through low gravity experiments with cast irons are described.

  19. Improved optical profiling using the spectral phase in spectrally resolved white-light interferometry

    SciTech Connect

    Debnath, Sanjit Kumar; Kothiyal, Mahendra Prasad

    2006-09-20

    In spectrally resolved white-light interferometry (SRWLI), the white-light interferogram is decomposed into its monochromatic constituent. The phase of the monochromatic constituents can be determined using a phase-shifting technique over a range of wavelengths. These phase value shave fringe order ambiguity. However, the variation of the phase with respect to the wavenumber is linear and its slope gives the absolute value of the optical-path difference. Since the path difference is related to the height of the test object at a point, a line profile can be determined without ambiguity. The slope value, though less precise helps us determine the fringe order. The fringe order combined with the monochromatic phase value gives the absolute profile, which has the precision of phase-shifting interferometry. The presence of noise in the phase may lead to the misidentification of fringe order, which in turn gives unnecessary jumps in the precise profile. The experimental details of measurement on standard samples with SRWLI are discussed in this paper.

  20. Frequency interleaving towards spectrally efficient directly detected optical OFDM for next-generation optical access networks.

    PubMed

    Mehedy, Lenin; Bakaul, Masuduzzaman; Nirmalathas, Ampalavanapillai

    2010-10-25

    In this paper, we theoretically analyze and demonstrate that spectral efficiency of a conventional direct detection based optical OFDM system (DDO-OFDM) can be improved significantly using frequency interleaving of adjacent DDO-OFDM channels where OFDM signal band of one channel occupies the spectral gap of other channel and vice versa. We show that, at optimum operating condition, the proposed technique can effectively improve the spectral efficiency of the conventional DDO-OFDM system as much as 50%. We also show that such a frequency interleaved DDO-OFDM system, with a bit rate of 48 Gb/s within 25 GHz bandwidth, achieves sufficient power budget after transmission over 25 km single mode fiber to be used in next-generation time-division-multiplexed passive optical networks (TDM-PON). Moreover, by applying 64- quadrature amplitude modulation (QAM), the system can be further scaled up to 96 Gb/s with a power budget sufficient for 1:16 split TDM-PON.

  1. Long-term optical spectral monitoring of NGC 7469

    NASA Astrophysics Data System (ADS)

    Shapovalova, Alla I.; Popović, L. Č.; Chavushyan, V. H.; Afanasiev, V. L.; Ilić, D.; Kovačević, A.; Burenkov, A. N.; Kollatschny, W.; Spiridonova, O.; Valdes, J. R.; Bochkarev, N. G.; Patino-Alvarez, V.; Carrasco, L.; Zhdanova, V. E.

    2017-01-01

    We present the results of the long-term (20-year period, from 1996 to 2015) optical spectral monitoring of the Seyfert 1 galaxy NGC 7469. The variation in the light-curves of the broad He II λ4686Å Hβ and Hα lines, and the continuum at 5100 Å and 6300 Å have been explored. The maximum of activity was in 1998, and the variability in the continuum and lines seems to have two periods of around 1200 and 2600 days, however these periodicities should be taken with caution because of the red-noise. Beside these periods, there are several short-term (1-5 days) flare-like events in the light-curves. There are good correlations between the continuum fluxes and Hα and Hβ line fluxes, but significantly smaller correlation between the He II and continuum. We found that the time-lags between the continuum and broad lines are different for Hβ (˜20 l.d.) and Hα (˜3 l.d.), and that He II also has a smaller lag (˜2-3 l.d.). The Hα and Hβ line profiles show a slight red asymmetry, and the broad line profiles did not changed in the 20-year period. Using the lags and widths of Hα and Hβ we estimated the central black hole mass and found that it is ˜(1 - 6) · 107 M⊙, which is in agreement with previous reverberation estimates.

  2. Spectral domain optical coherence tomography with dual-balanced detection

    NASA Astrophysics Data System (ADS)

    Bo, En; Liu, Xinyu; Chen, Si; Luo, Yuemei; Wang, Nanshuo; Wang, Xianghong; Liu, Linbo

    2016-03-01

    We developed a spectral domain optical coherence tomography (SD-OCT) system employing dual-balanced detection (DBD) for direct current term suppression and SNR enhancement, especially for auto-autocorrelation artifacts reduction. The DBD was achieved by using a beam splitter to building a free-space Michelson interferometer, which generated two interferometric spectra with a phase difference of π. These two phase-opposed spectra were guided to the spectrometer through two single mode fibers of the 8 fiber v-groove array and acquired by ultizing the upper two lines of a three-line CCD camera. We rotated this fiber v-groove array by 1.35 degrees to focus two spectra onto the first and second line of the CCD camera. Two spectra were aligned by optimum spectrum matching algorithm. By subtracting one spectrum from the other, this dual-balanced detection system achieved a direct current term suppression of ~30 dB, SNR enhancement of ~3 dB, and auto-autocorrelation artifacts reduction of ~10 dB experimentally. Finally we respectively validated the feasibility and performance of dual-balanced detection by imaging a glass plate and swine corneal tissue ex vivo. The quality of images obtained using dual-balanced detection was significantly improved with regard to the conventional single-detection (SD) images.

  3. Characterization of PET preforms using spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Hosseiny, Hamid; Ferreira, Manuel João.; Martins, Teresa; Carmelo Rosa, Carla

    2013-11-01

    Polyethylene terephthalate (PET) preforms are massively produced nowadays with the purpose of producing food and beverages packaging and liquid containers. Some varieties of these preforms are produced as multilayer structures, where very thin inner film(s) act as a barrier for nutrients leakage. The knowledge of the thickness of this thin inner layer is important in the production line. The quality control of preforms production requires a fast approach and normally the thickness control is performed by destructive means out of the production line. A spectral domain optical coherence tomography (SD-OCT) method was proposed to examine the thin layers in real time. This paper describes a nondestructive approach and all required signal processing steps to characterize the thin inner layers and also to improve the imaging speed and the signal to noise ratio. The algorithm was developed by using graphics processing unit (GPU) with computer unified device architecture (CUDA). This GPU-accelerated white light interferometry technique nondestructively assesses the samples and has high imaging speed advantage, overcoming the bottlenecks in PET performs quality control.

  4. Retinal Imaging of Infants on Spectral Domain Optical Coherence Tomography

    PubMed Central

    Vinekar, Anand; Mangalesh, Shwetha; Jayadev, Chaitra; Maldonado, Ramiro S.; Bauer, Noel; Toth, Cynthia A.

    2015-01-01

    Spectral domain coherence tomography (SD OCT) has become an important tool in the management of pediatric retinal diseases. It is a noncontact imaging device that provides detailed assessment of the microanatomy and pathology of the infant retina with a short acquisition time allowing office examination without the requirement of anesthesia. Our understanding of the development and maturation of the infant fovea has been enhanced by SD OCT allowing an in vivo assessment that correlates with histopathology. This has helped us understand the critical correlation of foveal development with visual potential in the first year of life and beyond. In this review, we summarize the recent literature on the clinical applications of SD OCT in studying the pathoanatomy of the infant macula, its ability to detect subclinical features, and its correlation with disease and vision. Retinopathy of prematurity and macular edema have been discussed in detail. The review also summarizes the current status of SD OCT in other infant retinal conditions, imaging the optic nerve, the choroid, and the retinal nerve fibre in infants and children, and suggests future areas of research. PMID:26221606

  5. Corneal topography from spectral optical coherence tomography (sOCT)

    PubMed Central

    Ortiz, Sergio; Siedlecki, Damian; Pérez-Merino, Pablo; Chia, Noelia; de Castro, Alberto; Szkulmowski, Maciej; Wojtkowski, Maciej; Marcos, Susana

    2011-01-01

    We present a method to obtain accurate corneal topography from a spectral optical coherence tomography (sOCT) system. The method includes calibration of the device, compensation of the fan (or field) distortion introduced by the scanning architecture, and image processing analysis for volumetric data extraction, segmentation and fitting. We present examples of three-dimensional (3-D) surface topography measurements on spherical and aspheric lenses, as well as on 10 human corneas in vivo. Results of sOCT surface topography (with and without fan-distortion correction) were compared with non-contact profilometry (taken as reference) on a spherical lens, and with non-contact profilometry and state-of-the art commercial corneal topography instruments on aspheric lenses and on subjects. Corneal elevation maps from all instruments were fitted by quadric surfaces (as well as by tenth-order Zernike polynomials) using custom routines. We found that the discrepancy in the estimated radius of curvature from nominal values in artificial corneas decreased from 4.6% (without fan distortion correction) to 1.6% (after fan distortion correction), and the difference in the asphericity decreased from 130% to 5%. In human corneas, the estimated corneal radius of curvature was not statistically significantly different across instruments. However, a Bland-Altman analysis showed consistent differences in the estimated asphericity and corneal shape between sOCT topographies without fan distortion correction and the rest of the measurements. PMID:22162814

  6. Spectral domain optical coherence tomography imaging with an integrated optics spectrometer.

    PubMed

    Nguyen, V Duc; Akca, B Imran; Wörhoff, Kerstin; de Ridder, René M; Pollnau, Markus; van Leeuwen, Ton G; Kalkman, Jeroen

    2011-04-01

    We designed and fabricated an arrayed-waveguide grating (AWG) in silicon oxynitride as a spectrometer for spectral domain optical coherence tomography (SD-OCT). The AWG has a footprint of only 3.0 cm × 2.5 cm, operates at a center wavelength of 1300 nm, and has 78 nm free spectral range. OCT measurements are performed that demonstrate imaging up to a maximum depth of 1 mm with an axial resolution of 19 μm, both in agreement with the AWG design parameters. Using the AWG spectrometer combined with a fiber-based SD-OCT system, we demonstrate cross-sectional OCT imaging of a multilayered scattering phantom.

  7. Imaging-AOTF-based full-field spectral-domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Machikhin, Alexander; Viskovatykh, Alexander; Pozhar, Vitold; Burmak, Ludmila

    2015-03-01

    A technique for spectral filtration of interference images in full-field optical coherence tomography is proposed, implemented and tested. It is based on the spectral selection of light in the registration channel of the interferometer by imaging acousto-optic tunable filter. It is demonstrated that the diffraction of two interfering optical beams via the same ultrasound wave does not destruct the coherence. This new technique, which can be named tunable-imaging-filter-based full-field spectral-domain optical coherence tomography (TIF FF SD OCT), is applicable for 3D surface and inner structure visualization of optically inhomogeneous biomedical objects with moderate spectral, lateral and axial resolution, however with rather high speed.

  8. Spectral Shearing of Quantum Light Pulses by Electro-Optic Phase Modulation

    NASA Astrophysics Data System (ADS)

    Wright, Laura J.; Karpiński, Michał; Söller, Christoph; Smith, Brian J.

    2017-01-01

    Frequency conversion of nonclassical light enables robust encoding of quantum information based upon spectral multiplexing that is particularly well-suited to integrated-optics platforms. Here we present an intrinsically deterministic linear-optics approach to spectral shearing of quantum light pulses and show it preserves the wave-packet coherence and quantum nature of light. The technique is based upon an electro-optic Doppler shift to implement frequency shear of heralded single-photon wave packets by ±200 GHz , which can be scaled to an arbitrary shift. These results demonstrate a reconfigurable method to controlling the spectral-temporal mode structure of quantum light that could achieve unitary operation.

  9. Macular Surgery Using Intraoperative Spectral Domain Optical Coherence Tomography

    PubMed Central

    Riazi-Esfahani, Mohammad; Khademi, Mohammad Reza; Mazloumi, Mehdi; Khodabandeh, Alireza; Riazi-Esfahani, Hamid

    2015-01-01

    Purpose: To report the use of intraoperative spectral domain optical coherence tomography (SD-OCT) for detecting anatomical changes during macular surgery. Methods: In a consecutive case series, 32 eyes of 32 patients undergoing concurrent pars plana vitrectomy and intraoperative SD-OCT for macular hole (MH), epiretinal membrane (ERM) and vitreomacular traction (VMT) were enrolled. Intraoperative changes in retinal thickness and dimensions of the macular hole were measured in patients with ERM and VMT following surgical manipulation using a hand-held SD-OCT device (iVue, Optovue Inc., Fremont, CA, USA). Results: SD-OCT images of sixteen eyes with macular hole were subjected to quantitative and qualitative analysis. All MH dimensions remained stable during consecutive stages of surgery except for MH apex diameter, which showed a significant decrease after internal limiting membrane (ILM) peeling (P=0.025). Quantitative analysis of ten patients with ERM showed a significant decrease in retinal thickness after membrane removal (P=0.018) which did not remain significant until the end of the procedure (P=0.8). In three cases, subretinal fluid was formed after ILM peeling. Quantitative analysis of five patients with VMT showed a decrease in retinal thickness during consecutive steps of the surgery, although these changes were not significant. In two cases, subretinal fluid was formed after ILM peeling. Conclusion: Intraoperative SD-OCT is a useful imaging technique which provides vitreoretinal surgeons with rapid awareness of changes in macular anatomy during surgery and may therefore result in better anatomical and visual outcomes. PMID:26730318

  10. Spectral singularity in confined PT symmetric optical potential

    SciTech Connect

    Sinha, Anjana; Roychoudhury, R.

    2013-11-15

    We present an analytical study for the scattering amplitudes (Reflection ‖R‖ and Transmission ‖T‖), of the periodic PT symmetric optical potential V(x)=W{sub 0}cos{sup 2}x+iV{sub 0}sin2x confined within the region 0 ⩽x⩽L, embedded in a homogeneous medium having uniform potential W{sub 0}. The confining length L is considered to be some integral multiple of the period π. We give some new and interesting results. Scattering is observed to be normal (‖T‖{sup 2}⩽ 1, ‖R‖{sup 2}⩽ 1) for V{sub 0}⩽ 0.5, when the above potential can be mapped to a Hermitian potential by a similarity transformation. Beyond this point (V{sub 0} > 0.5) scattering is found to be anomalous (‖T‖{sup 2}, ‖R‖{sup 2} not necessarily ⩽1). Additionally, in this parameter regime of V{sub 0}, one observes infinite number of spectral singularities E{sub SS} at different values of V{sub 0}. Furthermore, for L= 2nπ, the transition point V{sub 0}= 0.5 shows unidirectional invisibility with zero reflection when the beam is incident from the absorptive side (Im[V(x)] < 0) but with finite reflection when the beam is incident from the emissive side (Im[V(x)] > 0), transmission being identically unity in both cases. Finally, the scattering coefficients ‖R‖{sup 2} and ‖T‖{sup 2} always obey the generalized unitarity relation : ‖T|{sup 2}−1|=√(|R{sub R}|{sup 2}|R{sub L}|{sup 2}), where subscripts R and L stand for right and left incidence, respectively.

  11. Imaging drusens using Spectral Domain Optical Coherence Tomography.

    PubMed

    Gella, Laxmi; Raman, Rajiv; Sharma, Tarun

    2016-01-01

    The purpose was to evaluate pathological changes of photoreceptor layer and retinal pigment epithelium in eyes with drusens using Spectral Domain Optical Coherence Tomography (SD-OCT). Twenty-nine eyes of 29 patients with (drusens) dry age-related macular degeneration and 43 eyes of 43 controls were included in this study. All subjects underwent complete ophthalmic examination including SD-OCT. Central foveal thickness (CFT), photoreceptor layer (PRL) thickness and retinal pigment epithelial (RPE) thickness were measured and compared between the groups. P value < 0.05 was considered statistically significant. Best corrected visual acuity (BCVA) ranged between 20/20 and 20/200. RPE (36.10 ± 5.48 μm Vs 39.27 ± 4.30) and PRL thickness (53.93 ± 7.36 μm Vs 61.20 ± 4.50 μm) were significantly reduced in patients with drusens compared to controls. Increase in age was a significant risk factor for drusens (OR: 1.22, p < 0.001) and increased PRL thickness was a protective factor (OR: 0.720, p = 0.002). PRL thickness was significantly associated with BCVA (p = 0.019). With an increased resolution of SD-OCT, the involvement of the outer retinal layers was more clearly defined. SD-OCT may allow for the early detection of exudative changes.

  12. Macular thickness measurements using Copernicus Spectral Domain Optical Coherence Tomography.

    PubMed

    Gella, Laxmi; Raman, Rajiv; Sharma, Tarun

    2015-01-01

    To provide normal macular thickness measurements using Spectral Domain Optical Coherence Tomography (SDOCT, Copernicus, Optopol Technologies, Zawierci, Poland). Fifty-eight eyes of 58 healthy subjects were included in this prospective study. All subjects had comprehensive ophthalmic examination including best-corrected visual acuity (BCVA). All the subjects underwent Copernicus SDOCT. Central foveal thickness (CFT) and photoreceptor layer (PRL) thickness were measured and expressed as mean and standard deviation. Mean retinal thickness for each of the 9 regions defined in the Early Treatment Diabetic Retinopathy Study was reported. The data were compared with published literature in Indians using Stratus and Spectralis OCTs to assess variation in instrument measurements. The mean CFT in the study sample was 173.8 ± 18.16 microns (131-215 microns) and the mean PRL thickness was 65.48 ± 4.23 microns (56-74 microns). No significant difference (p = 0.148) was found between CFT measured automated (179.28 ± 22 microns) and manually (173.83 ± 18.1 microns). CFT was significantly lower in women (167.62 ± 16.36 microns) compared to men (180.03 ± 18 microns) (p = 0.008). Mean retinal thickness reported in this study was significantly different from published literature using Stratus OCT and Spectralis OCT. We report the normal mean retinal thickness in central 1 mm area to be between 138 and 242 microns in Indian population using Copernicus SDOCT. We suggest that different OCT instruments cannot be used interchangeably for the measurement of macular thickness as they vary in segmentation algorithms.

  13. Spectral Domain Optical Coherence Tomography for Glaucoma (An AOS Thesis)

    PubMed Central

    Schuman, Joel S.

    2008-01-01

    Purpose Optical coherence tomography (OCT) is a rapidly evolving, robust technology that has profoundly changed the practice of ophthalmology. Spectral domain OCT (SD-OCT) increases axial resolution 2- to 3-fold and scan speed 60- to 110-fold vs time domain OCT (TD-OCT). SD-OCT enables novel scanning, denser sampling, and 3-dimensional imaging. This thesis tests my hypothesis that SD-OCT improves reproducibility, sensitivity, and specificity for glaucoma detection. Methods OCT progress is reviewed from invention onward, and future development is discussed. To test the hypothesis, TD-OCT and SD-OCT reproducibility and glaucoma discrimination are evaluated. Forty-one eyes of 21 subjects (SD-OCT) and 21 eyes of 21 subjects (TD-OCT) are studied to test retinal nerve fiber layer (RNFL) thickness measurement reproducibility. Forty eyes of 20 subjects (SD-OCT) and 21 eyes of 21 subjects (TD-OCT) are investigated to test macular parameter reproducibility. For both TD-OCT and SD-OCT, 83 eyes of 83 subjects are assessed to evaluate RNFL thickness and 74 eyes of 74 subjects to evaluate macular glaucoma discrimination. Results Compared to conventional TD-OCT, SD-OCT had statistically significantly better reproducibility in most sectoral macular thickness and peripapillary RNFL sectoral measurements. There was no statistically significant difference in overall mean macular or RNFL reproducibility, or between TD-OCT and SD-OCT glaucoma discrimination. Surprisingly, TD-OCT macular RNFL thickness showed glaucoma discrimination superior to SD-OCT. Conclusions At its current development state, SD-OCT shows better reproducibility than TD-OCT, but glaucoma discrimination is similar for TD-OCT and SD-OCT. Technological improvements are likely to enhance SD-OCT reproducibility, sensitivity, specificity, and utility, but these will require additional development. PMID:19277249

  14. Feeding Frequency Affects Cultured Rat Pituitary Cells in Low Gravity

    NASA Technical Reports Server (NTRS)

    Hymer, W. C.; Grindeland, R. E.; Salada, T.; Cenci, R.; Krishnan, K.; Mukai, C.; Nagaoka, S.

    1996-01-01

    In this report, we describe the results of a rat pituitary cell culture experiment done on STS-65 in which the effect of cell feeding on the release of the six anterior pituitary hormones was studied. We found complex microgravity related interactions between the frequency of cell feeding and the quantity and quality (i.e. biological activity) of some of the six hormones released in flight. Analyses of growth hormone (GH) released from cells into culture media on different mission days using gel filtration and ion exchange chromatography yielded qualitatively similar results between ground and flight samples. Lack of cell feeding resulted in extensive cell clumping in flight (but not ground) cultures. Vigorous fibroblast growth occurred in both ground and flight cultures fed 4 times. These results are interpreted within the context of autocrine and or paracrine feedback interactions. Finally the payload specialist successfully prepared a fresh trypsin solution in microgravity, detached the cells from their surface and reinserted them back into the culture chamber. These cells reattached and continued to release hormone in microgravity. In summary, this experiment shows that pituitary cells are microgravity sensitive and that coupled operations routinely associated with laboratory cel1 culture can also be accomplished in low gravity.

  15. Critical Transport Phenomena in Fluid Helium Under Low Gravity

    NASA Technical Reports Server (NTRS)

    Meyer, H.; Behringer, R. P.

    1985-01-01

    The feasibility of carrying out measurements of certain critical transport properties of pure fluid under conditions of low gravity was studied. These properties are the thermal conductivity, kappa, the shear viscosity zeta and the diffusive relaxation time tau, which are predicted to diverge (tend to infinity) as the liquid-vapor critical point is approached. However, in this critical region, the Earth's gravity effect becomes very important. As the critical point is approached, the gravity effects increasingly distort the results. The reason for this is that the compressibility of the fluid also diverges and under the influence of gravity causes a vertical density gradient in the fluid, which is significant even when very thin fluid layers (typically 1 mm high) are being used. The result is that the temperature dependence of kappa, zeta, and tau tends to flatten off as T sub c is approached instead of continuing to increase, and therefore the predictions from the renormalization group and mode coupling theories cannot be subjected to a satisfactory test.

  16. Numerical Study of Mixing of Two Fluids Under Low Gravity

    NASA Technical Reports Server (NTRS)

    Duval, Walter M. B.

    1992-01-01

    The mixing characteristics of two fluids inside a cavity due to buoyancy driven flow fields for low gravity conditions is investigated via numerical experiments. The buoyancy driven flow, depending on the parametric region, stretches and deforms the material interface into a wave morphological pattern. The morphological pattern affects the resulting stratification thickness of the mixed region. Three basic mixing regimes occur: convective, diffusive, and chaotic. In the convective regime, an overturning motion occurs which gives rise to a stable wave formation. This wave oscillates and its decay leads to a stable stratification. Whereas, in the diffusive regime, the length of the interface remains constant while mixing occurs. This limiting behavior is very important to materials processing in space, and it admits a closed form solution corresponding to vanishing convective terms which agrees with computational results. Finally, in the chaotic regime, the material interface continuously stretches and folds on itself similar to a horseshoe map. The length of stretch of the interface increases exponentially. Internal wavebreaking occurs for this case. This wavebreaking generates local turbulence, and provides an effective mechanism for mixing.

  17. Tank pressure control in low gravity by jet mixing

    NASA Technical Reports Server (NTRS)

    Bentz, Michael D.

    1993-01-01

    The Tank Pressure Control Experiment (TPCE) is a space experiment developed to help meet the need for a critical aspect of cryogenic fluid management technology: control of storage tank pressures in the absence of gravity by forced convective mixing. The experiment used a 13.7-liter tank filled to a constant 83 percent level with refrigerant 113 at near saturation conditions to simulate the fluid dynamics and thermodynamics of cryogenic fluids in space applications. The objectives of TPCE were to characterize the fluid dynamics of axial jet-induced mixing in low gravity, to evaluate the validity of empirical mixing models, and to provide data for use in developing and validating computational fluid dynamic models of mixing processes. TPCE accomplished all of its objectives in flight on Space Shuttle Mission STS-3 in August of 1991. The range of flow patterns photographed generally confirmed a prior correlation based on drop tower tests. A closed-form equation derived from a simple thermodynamic model was found to provide a first-order prediction of the pressure reduction time as a function of mixer parameters, tank size, and fluid thermophysical properties. Low energy mixing jets were found to be effective and reliable at reducing thermal non-uniformities, promoting heat and mass transfer between the phases, and reducing tank pressure.

  18. Low gravity quenching of hot tubes with cryogens

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.; Collins, Frank G.; Kawaji, M.

    1992-01-01

    An experimental proceedure for examining flow boiling in low gravity environment is presented. The proceedure involves both ground based and KC-135 flight experiments. Two experimental apparati were employed, one for studying subcooled liquid boiling and another for examining saturated liquid boiling. For the saturated flow experiments, liquid nitrogen was used while freon 113 was used for the subcooled flow experiments. The boiling phenomenon was investigated in both cases using flow visualization techniques as well as tube wall temperature measurements. The flow field in both cases was established by injecting cold liquid in a heated tube whose temperature was set above the saturation values. The tubes were both vertically and horizontally supported with the liquid injected from the lower end of the tube. The results indicate substantial differences in the flow patterns established during boiling between the ground based, (1-g), experiments and the flight experiments, (low-g). These differences in the flow patterns will be discussed and some explanations will be offered.

  19. Liquid propellant reorientation in a low-gravity environment

    NASA Technical Reports Server (NTRS)

    Sumner, I. E.

    1978-01-01

    An existing empirical analysis relating to the reorientation of liquids in cylindrical tanks due to propulsive settling in a low gravity environment was extended to include the effects of geyser formation in the Weber number range from 4 to 10. Estimates of the minimum velocity increment required to be imposed on the propellant tank to achieve liquid reorientation were made. The resulting Bond numbers, based on tank radius, were found to be in the range from 3 to 5, depending upon the initial liquid fill level, with higher Bond number required for high initial fill levels. The resulting Weber numbers, based on tank radius and the velocity of the liquid leading edge, were calculated to be in the range from 6.5 to 8.5 for cylindrical tanks having a fineness ratio of 2.0, with Weber numbers of somewhat greater values for longer cylindrical tanks. It, therefore, appeared to be advantageous to allow small geysers to form and then dissipate into the surface of the collected liquid in order to achieve the minimum velocity increment. The Bond numbers which defined the separation between regions in which geyser formation did and did not occur due to propulsive settling in a spherical tank configuration ranged from 2 to 9 depending upon the liquid fill level.

  20. Critical Transport Phenomena in Fluid Helium Under Low Gravity

    NASA Technical Reports Server (NTRS)

    Meyer, H.; Behringer, R. P.

    1985-01-01

    The feasibility of carrying out measurements of certain critical transport properties of pure fluid under conditions of low gravity was studied. These properties are the thermal conductivity, kappa, the shear viscosity zeta and the diffusive relaxation time tau, which are predicted to diverge (tend to infinity) as the liquid-vapor critical point is approached. However, in this critical region, the Earth's gravity effect becomes very important. As the critical point is approached, the gravity effects increasingly distort the results. The reason for this is that the compressibility of the fluid also diverges and under the influence of gravity causes a vertical density gradient in the fluid, which is significant even when very thin fluid layers (typically 1 mm high) are being used. The result is that the temperature dependence of kappa, zeta, and tau tends to flatten off as T sub c is approached instead of continuing to increase, and therefore the predictions from the renormalization group and mode coupling theories cannot be subjected to a satisfactory test.

  1. Hydrodynamics of Packed Bed Reactor in Low Gravity

    NASA Technical Reports Server (NTRS)

    Motil, Brian J.; Nahra, Henry K.; Balakotaiah, Vemuri

    2005-01-01

    Packed bed reactors are well known for their vast and diverse applications in the chemical industry; from gas absorption, to stripping, to catalytic conversion. Use of this type of reactor in terrestrial applications has been rather extensive because of its simplicity and relative ease of operation. Developing similar reactors for use in microgravity is critical to many space-based advanced life support systems. However, the hydrodynamics of two-phase flow packed bed reactors in this new environment and the effects of one physiochemical process on another has not been adequately assessed. Surface tension or capillary forces play a much greater role which results in a shifting in flow regime transitions and pressure drop. Results from low gravity experiments related to flow regimes and two-phase pressure drop models are presented in this paper along with a description of plans for a flight experiment on the International Space Station (ISS). Understanding the packed bed hydrodynamics and its effects on mass transfer processes in microgravity is crucial for the design of packed bed chemical or biological reactors to be used for water reclamation and other life support processes involving water purification.

  2. Stem sap flow in plants under low gravity conditions

    NASA Astrophysics Data System (ADS)

    Tokuda, Ayako; Hirai, Hiroaki; Kitaya, Yoshiaki

    2016-07-01

    A study was conducted to obtain a fundamental knowledge for plant functions in bio-regenerative life support systems in space. Stem sap flow in plants is important indicators for water transport from roots to atmosphere through leaves. In this study, stem sap flow in sweetpotato was assessed at gravity levels from 0.01 to 2 g for about 20 seconds each during parabolic airplane flights. Stem sap flow was monitored with a heat balance method in which heat generated with a tiny heater installed in the stem was transferred upstream and downstream by conduction and upstream by convection with the sap flow through xylems of the vascular tissue. Thermal images of stem surfaces near heated points were captured using infrared thermography and the internal heat convection corresponding to the sap flow was analyzed. In results, the sap flow in stems was suppressed more at lower gravity levels without forced air circulation. No suppression of the stem sap flow was observed with forced air circulation. Suppressed sap flow in stems would be caused by suppression of transpiration in leaves and would cause restriction of water and nutrient uptake in roots. The forced air movement is essential to culture healthy plants at a high growth rate under low gravity conditions in space.

  3. Liquid-Vapor Interface Configurations Investigated in Low Gravity

    NASA Technical Reports Server (NTRS)

    Concus, Paul; Finn, Robert; Weislogel, Mark M.

    1998-01-01

    The Interface Configuration Experiment (ICE) is part of a multifaceted study that is exploring the often striking behavior of liquid-vapor interfaces in low-gravity environments. Although the experiment was posed largely as a test of current mathematical theory, applications of the results should be manifold. In space almost every fluid system is affected, if not dominated, by capillarity (the effects of surface tension). As a result, knowledge of fluid interface behavior, in particular an equilibrium interface shape from which any analysis must begin, is fundamental--from the control of liquid fuels and oxygen in storage tanks to the design and development of inspace thermal systems, such as heat pipes and capillary pumped loops. ICE has increased, and should continue to increase, such knowledge as it probes the specific peculiarities of current theory upon which our present understanding rests. Several versions of ICE have been conducted in the drop towers at the NASA Lewis Research Center, on the space shuttles during the first and second United States Microgravity Laboratory missions (USML-1 and USML-2), and most recently aboard the Russian Mir space station. These studies focused on interfacial problems concerning the existence, uniqueness, configuration, stability, and flow characteristics of liquid-vapor interfaces. Results to date have clearly demonstrated the value of the present theory and the extent to which it can predict the behavior of capillary systems.

  4. Spectrally-resolved optical efficiency using a multi-junction cell as light sensor: Application cases

    NASA Astrophysics Data System (ADS)

    Victoria, Marta; Domínguez, César; Jost, Norman; Vallerotto, Guido; Antón, Ignacio; Sala, Gabriel

    2017-09-01

    The experimental method to determine the spectrally-resolved optical efficiency of concentrating optics is described in this paper. The measurement uses a multi-junction solar cell as light sensor and a series of band-pass filters to isolate the optical performance of different narrow spectral bands throughout the spectrum of interest. Additional bias light is provided to saturate the subcells whose spectral response is out of the transmittance of every band-pass filter. The method allows the characterization of the combined transmittance, reflectance and absorbance of every material composing the optics including optical couplers and thin layers such as antireflective coatings. The two application cases included illustrate the potential of this novel characterization technique. Firstly, a novel refractive concentrator, the Achromatic Doublet on Glass (ADG) Fresnel lens is measured. Secondly, the method is applied to analyze the degradation of outdoor exposed glass molded Secondary Optical Elements (SOE).

  5. High resolution retinal imaging with a compact adaptive optics spectral domain optical coherence tomography system

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Iftimia, Nicusor V.; Bigelow, Chad E.; Ustun, Teoman E.; Bloom, Benjamin; Ferguson, R. Daniel; Burns, Stephen A.

    2007-02-01

    Adaptive optics (AO) is used to correct ocular aberrations primarily in the cornea, lens, and tear film of every eye. Among other applications, AO allows high lateral resolution images to be acquired with scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT). Spectral domain optical coherence tomography (SDOCT) is a high-speed imaging technique that can acquire cross-sectional scans with micron-scale axial resolution at tens to hundreds of kHz line rates. We present a compact clinical AO-SDOCT system that achieves micron-scale axial and lateral resolution of retinal structures. The system includes a line scanning laser ophthalmscope (LSLO) for simultaneous wide-field retinal viewing and selection of regions-of-interest. OCT and LSLO imaging and AO correction performance are characterized. We present a case study of a single subject with hyper-reflective lesions associated with stable, resolved central serous retinopathy to compare and contrast AO as applied to scanning laser ophthalmoscopy and optical coherence tomography. The two imaging modes are found to be complementary in terms of information on structure morphology. Both provide additional information lacking in the other. This preliminary finding points to the power of combining SLO and SDOCT in a single research instrument for exploration of disease mechanisms, retinal cellular architecture, and visual psychophysics.

  6. Imaging patients with glaucoma using spectral-domain optical coherence tomography and optical microangiography

    NASA Astrophysics Data System (ADS)

    Auyeung, Kris; Auyeung, Kelsey; Kono, Rei; Chen, Chieh-Li; Zhang, Qinqin; Wang, Ruikang K.

    2015-03-01

    In ophthalmology, a reliable means of diagnosing glaucoma in its early stages is still an open issue. Past efforts, including forays into fluorescent angiography (FA) and early optical coherence tomography (OCT) systems, to develop a potential biomarker for the disease have been explored. However, this development has been hindered by the inability of the current techniques to provide useful depth and microvasculature information of the optic nerve head (ONH), which have been debated as possible hallmarks of glaucoma progression. We reasoned that a system incorporating a spectral-domain OCT (SD-OCT) based Optical Microangiography (OMAG) system, could allow an effective, non-invasive methodology to evaluate effects on microvasculature by glaucoma. SD-OCT follows the principle of light reflection and interference to produce detailed cross-sectional and 3D images of the eye. OMAG produces imaging contrasts via endogenous light scattering from moving particles, allowing for 3D image productions of dynamic blood perfusion at capillary-level resolution. The purpose of this study was to investigate the optic cup perfusion (flow) differences in glaucomatous and normal eyes. Images from three normal and five glaucomatous subjects were analyzed our OCT based OMAG system for blood perfusion and structural images, allowing for comparisons. Preliminary results from blood flow analysis revealed reduced blood perfusion within the whole-depth region encompassing the Lamina Cribrosa in glaucomatous cases as compared to normal ones. We conclude that our OCT-OMAG system may provide promise and viability for glaucoma screening.

  7. Ultrasound spectral analysis of photoacoustic signals from red blood cell populations at different optical wavelengths

    NASA Astrophysics Data System (ADS)

    Fadhel, Muhannad N.; Kolios, Michael C.

    2017-03-01

    Spectral analysis of photoacoustic (PA) signals in the ultrasound frequency domain is a method that analyzes the power spectrum of PA signals to quantify tissue microstructures. PA spectral analysis has been correlated to changes in the size, morphology and concentration of absorbers that are smaller than the system spatial resolution. However, the calculated spectral parameters are still not system independent due to difficulty in eliminating variations in the light distribution for different optical wavelengths. Changes in spectral parameters for the same absorber geometry but different optical illumination wavelengths needs to be carefully examined. A gelatin vessel phantom is used. The vessels contain red blood cells comprised of oxy, deoxy and methemoglobin induced using oxygen, sodium hydrosulfite and sodium nitrite, respectively. The samples were imaged using the VevoLAZR system at wavelengths 680 - 905 nm in steps of 15 nm. The radiofrequency (RF) signals were analyzed to calculate the spectral slope. The results were compared to simulated RF signals acquired using the mcxyz Monte Carlo package coupled to the solution of the PA wave equation using the Green's function approach. Changes in the spectral slope as a function of optical wavelength were detected. For longer optical wavelengths, the spectral slope increased for deoxyhemoglobin, but decreased for oxyhemoglobin and methemoglobin. The changes in the spectral slope were correlated to changes in the fluence distribution as optical properties change for different wavelengths. The change in the spectral slope as a function of optical wavelength and chromophore content can potentially be used in spectral unmixing for better estimation of hemoglobin content.

  8. The optical properties and spectral features of malignant skin melanocytes in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Goryachuk, A. A.; Begaeva, V. A.; Khodzitsky, M. K.; Truloff, A. S.

    2016-08-01

    The samples of cells of mice's melanocytes have been investigated. Their optical properties and spectral features were investigated by terahertz time-domain spectroscopy (TDS) in transmission mode. It was found that the optical properties of oncological melanocytes and normal cells are different and oncological cells have spectral features of absorption coefficient so it can be concluded that it is easy to discriminate mice's oncological skin melanocytes by using THz TDS.

  9. Differentiating Mild Papilledema and Buried Optic Nerve Head Drusen Using Spectral Domain Optical Coherence Tomography

    PubMed Central

    Kulkarni, Kaushal M.; Pasol, Joshua; Rosa, Potyra R.; Lam, Byron L.

    2013-01-01

    Purpose To evaluate the clinical utility of spectral domain optical coherence tomography (SD-OCT) in differentiating mild papilledema from buried optic nerve head drusen (ONHD). Design Comparative case series. Participants 16 eyes of 9 patients with ultrasound-proven buried ONHD, 12 eyes of 6 patients with less than or equal to Frisén grade 2 papilledema due to idiopathic intracranial hypertension. 2 normal fellow eyes of patients with buried ONHD were included. Methods A raster scan on the optic nerve and retinal nerve fiber layer (RNFL) thickness analysis was performed on each eye using SD-OCT. Eight eyes underwent enhanced depth imaging SD-OCT. Images were assessed qualitatively and quantitatively to identify differentiating features between buried ONHD and papilledema. Five clinicians trained with a tutorial and masked to the underlying diagnosis reviewed the SD-OCT images of each eye independently to determine the diagnosis. Main outcome measures Differences in RNFL thickness in each quadrant between the two groups, and diagnostic accuracy of five independent clinicians based on the SD-OCT images alone. Results We found no statistically significant difference in RNFL thickness between buried ONHD and papilledema in any of the four quadrants. Diagnostic accuracy among the readers was low and ranged from 50–64%. The kappa coefficient of agreement among the readers was 0.35 (95% Confidence interval: 0.19, 0.54). Conclusions SD-OCT is not clinically reliable in differentiating buried ONHD and mild papilledema. PMID:24321144

  10. Characterization of chromatic dispersion of optical filters by high-stability real-time spectral interferometry.

    PubMed

    Ogawa, Kensuke

    2006-09-10

    Chromatic dispersion of optical filters is characterized by what is believed to be novel broadband spectral interferometry, which is based on dual-wavelength heterodyne measurement of spectral phase. High phase stability is achieved by differential phase detection using two lasers for wavelength-swept probe and phase-tracking reference. The technique provides self-tracking interferometry by passive stabilization of optical phase and allows real-time measurement of spectral phase and group delay with a low phase drift of less than 0.04pi. A fiber Bragg grating and a thin-film filter are characterized by this method.

  11. Electroretinography combined with spectral domain optical coherence tomography to detect retinal damage in shaken baby syndrome.

    PubMed

    Nakayama, Yuri; Yokoi, Tadashi; Sachiko, Nishina; Okuyama, Makiko; Azuma, Noriyuki

    2013-08-01

    In order to correlate anatomical changes with visual function in shaken baby syndrome, we performed electroretinography and spectral domain optical coherence tomography on a 2-month-old girl and a 9-month-old girl after the retinal hemorrhages absorbed. Both patients had significant abnormalities in spectral domain optical coherence tomography images of the macular area. The amplitudes of the focal macular electroretinograms were more severely decreased than those of the full-field electroretinograms. Combining spectral domain coherence tomography with focal macular electroretinograms might better estimate the functional damage to the macula in patients with shaken baby syndrome.

  12. Retrieval of the atmospheric compounds using a spectral optical thickness information

    SciTech Connect

    Ioltukhovski, A.A.

    1995-03-01

    A spectral inversion technique for retrieval of the atmospheric gases and aerosols contents is proposed. This technique based upon the preliminary measurement or retrieval of the spectral optical thickness. The existence of a priori information about the spectral cross sections for some of the atmospheric components allows to retrieve the relative contents of these components in the atmosphere. Method of smooth filtration makes possible to estimate contents of atmospheric aerosols with known cross sections and to filter out other aerosols; this is done independently from their relative contribution to the optical thickness.

  13. Deep optical imaging of tissue using the second and third near-infrared spectral windows.

    PubMed

    Sordillo, Laura A; Pu, Yang; Pratavieira, Sebastião; Budansky, Yury; Alfano, Robert R

    2014-05-01

    Light at wavelengths in the near-infrared (NIR) region allows for deep penetration and minimal absorption through high scattering tissue media. NIR light has been conventionally used through the first NIR optical tissue window with wavelengths from 650 to 950 nm. Longer NIR wavelengths had been overlooked due to major water absorption peaks and a lack of NIR-CCD detectors. The second NIR spectral window from 1100 to 1350 nm and a new spectral window from 1600 to 1870 nm, known as the third NIR optical window, were investigated. Optical attenuation measurements from thin tissue slices of normal and malignant breast and prostate tissues, pig brain, and chicken tissue were obtained in the spectral range from 400 to 2500 nm. Optical images of chicken tissue overlying three black wires were also obtained using the second and third spectral windows. Due to a reduction in scattering and minimal absorption, longer attenuation lengths and clearer optical images could be seen in the second and third NIR optical windows compared to the conventional first NIR optical window. A possible fourth optical window centered at 2200 nm was noted.

  14. Optical signal processing for enabling high-speed, highly spectrally efficient and high capacity optical systems

    NASA Astrophysics Data System (ADS)

    Fazal, Muhammad Irfan

    The unabated demand for more capacity due to the ever-increasing internet traffic dictates that the boundaries of the state of the art maybe pushed to send more data through the network. Traditionally, this need has been satisfied by multiple wavelengths (wavelength division multiplexing), higher order modulation formats and coherent communication (either individually or combined together). WDM has the ability to reduce cost by using multiple channels within the same physical fiber, and with EDFA amplifiers, the need for O-E-O regenerators is eliminated. Moreover the availability of multiple colors allows for wavelength-based routing and network planning. Higher order modulation formats increases the capacity of the link by their ability to encode data in both the phase and amplitude of light, thereby increasing the bits/sec/Hz as compared to simple on-off keyed format. Coherent communications has also emerged as a primary means of transmitting and receiving optical data due to its support of formats that utilize both phase and amplitude to further increase the spectral efficiency of the optical channel, including quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK). Polarization multiplexing of channels can double capacity by allowing two channels to share the same wavelength by propagating on orthogonal polarization axis and is easily supported in coherent systems where the polarization tracking can be performed in the digital domain. Furthermore, the forthcoming IEEE 100 Gbit/s Ethernet Standard, 802.3ba, provides greater bandwidth, higher data rates, and supports a mixture of modulation formats. In particular, Pol-MUX QPSK is increasingly becoming the industry's format of choice as the high spectral efficiency allows for 100 Gbit/s transmission while still occupying the current 50 GHz/channel allocation of current 10 Gbit/s OOK fiber systems. In this manner, 100 Gbit/s transfer speeds using current fiber links, amplifiers, and filters

  15. Multiple irradiation sensing of the optical effective attenuation coefficient for spectral correction in handheld OA imaging.

    PubMed

    Held, K Gerrit; Jaeger, Michael; Rička, Jaro; Frenz, Martin; Akarçay, H Günhan

    2016-06-01

    Spectral optoacoustic (OA) imaging enables spatially-resolved measurement of blood oxygenation levels, based on the distinct optical absorption spectra of oxygenated and de-oxygenated blood. Wavelength-dependent optical attenuation in the bulk tissue, however, distorts the acquired OA spectrum and thus makes quantitative oxygenation measurements challenging. We demonstrate a correction for this spectral distortion without requiring a priori knowledge of the tissue optical properties, using the concept of multiple irradiation sensing: recording the OA signal amplitude of an absorbing structure (e.g. blood vessel), which serves as an intrinsic fluence detector, as function of irradiation position. This permits the reconstruction of the bulk effective optical attenuation coefficient μeff,λ . If performed at various irradiation wavelengths, a correction for the wavelength-dependent fluence attenuation is achieved, revealing accurate spectral information on the absorbing structures. Phantom studies were performed to show the potential of this technique for handheld clinical combined OA and ultrasound imaging.

  16. Spatial routing of optical beams through time-domain spatial-spectral filtering

    NASA Astrophysics Data System (ADS)

    Babbitt, W. R.; Mossberg, T. W.

    1995-04-01

    We propose a novel new method of temporal-waveform-controlled high-speed passive spatial routing of optical beams. The method provides for the redirection of optical signals contained within a single input beam into output directions that are specified entirely by temporal information encoded on the waveform of each incident signal. The routing is effected by means of deflection from spectrally structured spatial gratings that may be optically programmed into materials with or without intrinsic frequency selectivity.

  17. Comparisons of spectrally-enhanced asymmetrically-clipped optical OFDM systems.

    PubMed

    Lowery, Arthur James

    2016-02-22

    Asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) is a technique that sacrifices spectral efficiency in order to transmit an orthogonally frequency-division multiplexed signal over a unipolar channel, such as a directly modulated direct-detection fiber or free-space channel. Several methods have been proposed to regain this spectral efficiency, including: asymmetrically clipped DC-biased optical OFDM (ADO-OFDM), enhanced U-OFDM (EU-OFDM), spectral and energy efficient OFDM (SEE-OFDM), Hybrid-ACO-OFDM and Layered-ACO-OFDM. This paper presents simulations up to high-order constellation sizes to show that Layered-ACO-OFDM offers the highest receiver sensitivity for a given optical power at spectral efficiencies above 3 bit/s/Hz. For comparison purposes, white Gaussian noise is added at the receiver, component nonlinearities are not considered, and the fiber is considered to be linear and dispersion-less. The simulations show that LACO-OFDM has a 7-dB sensitivity advantage over DC-biased OFDM (DCO-OFDM) for 1024-QAM at 87.5% of DCO-OFDM's spectral efficiency, at the same bit rate and optical power. This is approximately equivalent to a 4.4-dB advantage at the same spectral efficiency of 87.7% if 896-QAM were to be used for DCO-OFDM.

  18. Optical skin assessment based on spectral reflectance estimation and Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Bauer, Jacob R.; Hardeberg, Jon Y.; Verdaasdonk, Rudolf

    2017-02-01

    Optical non-contact measurements in general, and chromophore concentration estimation in particular, have been identified to be useful tools for skin assessment. Spectral estimation using a low cost hand held device has not been studied adequately as a basis for skin assessment. Spectral measurements on the one hand, which require bulky, expensive and complex devices and direct channel approaches on the other hand, which operate with simple optical devices have been considered and applied for skin assessment. In this study, we analyse the capabilities of spectral estimation for skin assessment in form of chromophore concentration estimation using a prototypical low cost optical non-contact device. A spectral estimation work flow is implemented and combined with pre-simulated Monte Carlo spectra to use estimated spectra based on conventional image sensors for chromophore concentrations estimation and obtain health metrics. To evaluate the proposed approach, we performed a series of occlusion experiments and examined the capabilities of the proposed process. Additionally, the method has been applied to more general skin assessment tasks. The proposed process provides a more general representation in form of a spectral image cube which can be used for more advanced analysis and the comparisons show good agreement with expectations and conventional skin assessment methods. Utilising spectral estimation in conjunction with Monte Carlo simulation could lead to low cost, easy to use, hand held and multifunctional optical skin assessment with the possibility to improve skin assessment and the diagnosis of diseases.

  19. Investigation on landing impact dynamic and low-gravity experiments for deep space lander

    NASA Astrophysics Data System (ADS)

    Chen, JinBao; Nie, Hong; Wan, JunLin; Lin, Qing

    2014-10-01

    Herein symmetrical four-legged suspension lunar lander was used as the research object, the six-degree-of-freedom dynamic model was built and the model of the lunar soil friction coefficient was improved. For the low-gravity simulation on objects outside earth for future work, the law of dynamic similarity for detectors was deduced. A new method was proposed for simulating the low-gravity field on the surface of objects outside earth, which was achieved by changing initial conditions of the landing by the probe and by subsequent treatment of experimental data. The prototype tested the limitation of this method was verified. It is shown that the prototypes of detectors can be used in detectors low-gravity simulation test with this method, and equipments are simple and operationally effective. This method can be used for later lunar exploration, and low-gravity simulations on extraterrestrial objects.

  20. A summary of existing and planned experiment hardware for low-gravity fluids research

    NASA Technical Reports Server (NTRS)

    Hill, Myron E.; Omalley, Terence F.

    1991-01-01

    An overview is presented of (1) existing ground-based, low gravity research facilities, with examples of hardware capabilities, and (2) existing and planned space-based research facilities, with examples of current and past flight hardware. Low-gravity, ground-based facilities, such as drop towers and aircraft, provide the experimenter with quick turnaround time, easy access to equipment, gravity levels ranging from 10(exp -2) to 10(exp -6) G, and low-gravity durations ranging from 2 to 30 sec. Currently, the only operational space-based facility is the Space Shuttle. The Shuttle's payload bay and middeck facilities are described. Existing and planned low-gravity fluids research facilities are also described with examples of experiments and hardware capabilities.

  1. Relationship Between Optic Nerve Appearance and Retinal Nerve Fiber Layer Thickness as Explored with Spectral Domain Optical Coherence Tomography

    PubMed Central

    Aleman, Tomas S.; Huang, Jiayan; Garrity, Sean T.; Carter, Stuart B.; Aleman, Wendy D.; Ying, Gui-shuang; Tamhankar, Madhura A.

    2014-01-01

    Purpose To study the relationship between the appearance of the optic nerve and the retinal nerve fiber layer (RNFL) thickness determined by spectral domain optical coherence tomography (OCT). Methods Records from patients with spectral domain-OCT imaging in a neuro-ophthalmology practice were reviewed. Eyes with glaucoma/glaucoma suspicion, macular/optic nerve edema, pseudophakia, and with refractive errors > 6D were excluded. Optic nerve appearance by slit lamp biomicroscopy was related to the RNFL thickness by spectral domain-OCT and to visual field results. Results Ninety-one patients (176 eyes; mean age: 49 ± 15 years) were included. Eighty-three eyes (47%) showed optic nerve pallor; 89 eyes (50.6%) showed RNFL thinning (sectoral or average peripapillary). Average peripapillary RNFL thickness in eyes with pallor (mean ± SD = 76 ± 17 μm) was thinner compared to eyes without pallor (91 ± 14 μm, P < 0.001). Optic nerve pallor predicted RNFL thinning with a sensitivity of 69% and a specificity of 75%. Optic nerve appearance predicted RNFL thinning (with a sensitivity and specificity of 81%) when RNFL had thinned by ∼ 40%. Most patients with pallor had RNFL thinning with (66%) or without (25%) visual field loss; the remainder had normal RNFL and fields (5%) or with visual field abnormalities (4%). Conclusions Optic nerve pallor as a predictor of RNFL thinning showed fair sensitivity and specificity, although it is optimally sensitive/specific only when substantial RNFL loss has occurred. Translational Relevance Finding an acceptable relationship between the optic nerve appearance by ophthalmoscopy and spectral domain-OCT RNFL measures will help the clinician's interpretation of the information provided by this technology, which is gaining momentum in neuro-ophthalmic research. PMID:25374773

  2. Near-infrared spectral imaging of the female breast for quantitative oximetry in optical mammography

    SciTech Connect

    Yu Yang; Liu Ning; Sassaroli, Angelo; Fantini, Sergio

    2009-04-01

    We present a hybrid continuous-wave, frequency-domain instrument for near-infrared spectral imaging of the female breast based on a tandem, planar scanning of one illumination optical fiber and one collection optical fiber configured in a transmission geometry. The spatial sampling rate of 25 points/cm{sup 2} is increased to 400 points/cm{sup 2} by postprocessing the data with a 2D cubic spline interpolation. We then apply a previously developed spatial second-derivative algorithm to an edge-corrected intensity image (N-image) to enhance the visibility and resolution of optical inhomogeneities in breast tissue such as blood vessels and tumors. The spectral data at each image pixel consist of 515-point spectra over the 650-900 nm wavelength range, thus featuring a spectral density of two data points per nanometer. We process the measured spectra with a paired-wavelength spectral analysis method to quantify the oxygen saturation of detected optical inhomogeneities, under the assumption that they feature a locally higher hemoglobin concentration. Our initial measurements on two healthy human subjects have generated high-resolution optical mammograms displaying a network of blood vessels with values of hemoglobin saturation typically falling within the 60%-95% range, which is physiologically reasonable. This approach to spectral imaging and oximetry of the breast has the potential to efficiently exploit the high intrinsic contrast provided by hemoglobin in breast tissue and to contribute a useful tool in the detection, diagnosis, and monitoring of breast pathologies.

  3. Design and implementation of a low-gravity solidification experiment package for the F-104

    NASA Technical Reports Server (NTRS)

    Smith, G.; Mead, R.; Bond, R.; Workman, G. L.; Curreri, P. A.

    1984-01-01

    The use of the F-104 Interceptor for low gravity materials processing experiments is extended to include alloy solidification studies above 1000 C. The F-104 can provide up to 60 seconds of low gravity, but requires a unique experiment package for integration into the aircraft, both physically and electronically. The current research with the F-104 experimental furnace system which has been used to process cast iron samples is described. Results demonstrate the capability of the facility and its operation.

  4. Spectral imaging as a potential tool for optical sentinel lymph node biopsies

    NASA Astrophysics Data System (ADS)

    O'Sullivan, Jack D.; Hoy, Paul R.; Rutt, Harvey N.

    2011-07-01

    Sentinel Lymph Node Biopsy (SLNB) is an increasingly standard procedure to help oncologists accurately stage cancers. It is performed as an alternative to full axillary lymph node dissection in breast cancer patients, reducing the risk of longterm health problems associated with lymph node removal. Intraoperative analysis is currently performed using touchprint cytology, which can introduce significant delay into the procedure. Spectral imaging is forming a multi-plane image where reflected intensities from a number of spectral bands are recorded at each pixel in the spatial plane. We investigate the possibility of using spectral imaging to assess sentinel lymph nodes of breast cancer patients with a view to eventually developing an optical technique that could significantly reduce the time required to perform this procedure. We investigate previously reported spectra of normal and metastatic tissue in the visible and near infrared region, using them as the basis of dummy spectral images. We analyse these images using the spectral angle map (SAM), a tool routinely used in other fields where spectral imaging is prevalent. We simulate random noise in these images in order to determine whether the SAM can discriminate between normal and metastatic pixels as the quality of the images deteriorates. We show that even in cases where noise levels are up to 20% of the maximum signal, the spectral angle map can distinguish healthy pixels from metastatic. We believe that this makes spectral imaging a good candidate for further study in the development of an optical SLNB.

  5. Observation of the Optical and Spectral Characteristics of Ball Lightning

    NASA Astrophysics Data System (ADS)

    Cen, Jianyong; Yuan, Ping; Xue, Simin

    2014-01-01

    Ball lightning (BL) has been observed with two slitless spectrographs at a distance of 0.9 km. The BL is generated by a cloud-to-ground lightning strike. It moves horizontally during the luminous duration. The evolution of size, color, and light intensity is reported in detail. The spectral analysis indicates that the radiation from soil elements is present for the entire lifetime of the BL.

  6. Spectral structure and decompositions of optical states, and their applications

    NASA Astrophysics Data System (ADS)

    Rohde, Peter P.; Mauerer, Wolfgang; Silberhorn, Christine

    2007-04-01

    We discuss the spectral structure and decomposition of multi-photon states. Ordinarily 'multi-photon states' and 'Fock states' are regarded as synonymous. However, when the spectral degrees of freedom are included this is not the case, and the class of 'multi-photon' states is much broader than the class of 'Fock' states. We discuss the criteria for a state to be considered a Fock state. We then address the decomposition of general multi-photon states into bases of orthogonal eigenmodes, building on existing multi-mode theory, and introduce an occupation number representation that provides an elegant description of such states. This representation allows us to work in bases imposed by experimental constraints, simplifying calculations in many situations. Finally we apply this technique to several example situations, which are highly relevant for state of the art experiments. These include Hong Ou Mandel interference, spectral filtering, finite bandwidth photo-detection, homodyne detection and the conditional preparation of Schrödinger kitten and Fock states. Our techniques allow for very simple descriptions of each of these examples.

  7. Large area conductive nanoaperture arrays with strong optical resonances and spectrally flat terahertz transmission

    NASA Astrophysics Data System (ADS)

    Krewer, K. L.; Jiang, K.; Bley, K.; Jin, Z.; Mics, Z.; Weiss, C. K.; Landfester, K.; Elmers, H.-J.; Bonn, M.; Turchinovich, D.

    2017-07-01

    Using simple and inexpensive nanosphere lithography, we produce large, centimeter-squared sized thin golden films patterned with a hexagonal array of nanoapertures with controllable dimensions on the order of 100-300 nm, spaced by a 350-375 nm pitch distance. The optical transmission spectra of our samples are dominated by the resonant plasmonic features in the spectral range 500-700 nm, caused by the nanostructure in the film. At the same time, the transmission at terahertz (THz) radiation is as high as ˜10% and is spectrally flat. Our measurements are in agreement with finite difference time domain simulations. Such thin metal hole array films allow for very efficient injection of optical energy, while at the same time maintaining reasonably high transparency of THz waves. These structures can be used in any application combining strong optical sensitivity and THz transparency, in optical biomolecular sensing, or as optically transparent electrodes.

  8. Optical spectral signatures of liquids by means of fiber optic technology for product and quality parameter identification

    NASA Astrophysics Data System (ADS)

    Mignani, A. G.; Ciaccheri, L.; Mencaglia, A. A.; Diaz-Herrera, N.; Garcia-Allende, P. B.; Ottevaere, H.; Thienpont, H.; Attilio, C.; Cimato, A.; Francalanci, S.; Paccagnini, A.; Pavone, F. S.

    2009-01-01

    Absorption spectroscopy in the wide 200-1700 nm spectral range is carried out by means of optical fiber instrumentation to achieve a digital mapping of liquids for the prediction of important quality parameters. Extra virgin olive oils from Italy and lubricant oils from turbines with different degrees of degradation were considered as "case studies". The spectral data were processed by means of multivariate analysis so as to obtain a correlation to quality parameters. In practice, the wide range absorption spectra were considered as an optical signature of the liquids from which to extract product quality information. The optical signatures of extra virgin olive oils were used to predict the content of the most important fatty acids. The optical signatures of lubricant oils were used to predict the concentration of the most important parameters for indicating the oil's degree of degradation, such as TAN, JOAP anti-wear index, and water content.

  9. Wide spectral range imaging acousto-optic turnable filter used in outer space probe

    NASA Astrophysics Data System (ADS)

    Zhang, Zehong; Wang, Liangqiu; He, Xiaoliang; Zhou, Yong

    2014-02-01

    This article introduces a wide spectral range imaging acousto-optic turnable filter made of two transducers. "Mismatch rate" was firstly put forward to represent the degree to which the impedance mismatch and a three stage matching circuit was designed for the filter to improve its spectral range and operating bandwidth. Now the spectral range is from 0.4μm to 1.1μm, the overall operating bandwidth reaches 1.14 octave, the diffraction efficiency over 60%, spectral resolution from 1.3nm to 7.5nm. To get rid of " tin pest", alloy material was used to make bonding layer material instead of pure tin, making the storage temperature of the acousto-optic turnable filter ranges from -65 °C to 85 °C, and the operating temperature from -35 °C to 70 °C.

  10. 10 Gbit/s optical wavelength converter with a Brillouin scattering-based spectral filter.

    PubMed

    Granot, Er'el; Sternklar, Shmuel; Chayet, Haim; Ben-Ezra, Shalva; Narkiss, Niv; Shahar, Nir; Sher, Arieh; Tsadka, Sagie

    2005-08-10

    For the first time, to our knowledge, a highly robust, high-bit-rate (10 Gbit/s) wavelength converter that is based on a narrow Brillouin filter is reported. The conversion takes place in a semiconductor optical amplifier (SOA) in a cross-gain-phase process. The SOA operates in a weak-modulation mode, and the exiting signal undergoes a dc reduction with a narrow spectral filter. In our system we perform spectrally narrow filtering by using a long Brillouin grating.

  11. Spectral Shearing of Quantum Light Pulses by Electro-Optic Phase Modulation.

    PubMed

    Wright, Laura J; Karpiński, Michał; Söller, Christoph; Smith, Brian J

    2017-01-13

    Frequency conversion of nonclassical light enables robust encoding of quantum information based upon spectral multiplexing that is particularly well-suited to integrated-optics platforms. Here we present an intrinsically deterministic linear-optics approach to spectral shearing of quantum light pulses and show it preserves the wave-packet coherence and quantum nature of light. The technique is based upon an electro-optic Doppler shift to implement frequency shear of heralded single-photon wave packets by ±200  GHz, which can be scaled to an arbitrary shift. These results demonstrate a reconfigurable method to controlling the spectral-temporal mode structure of quantum light that could achieve unitary operation.

  12. Spectral emissivities and optical constants of electromagnetically levitated liquid metals as functions of temperature and wavelength

    NASA Technical Reports Server (NTRS)

    Krishnan, S.; Hauge, R. H.; Margrave, J. L.

    1989-01-01

    The development of a noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomittant with radiance brightness. Using this approach, the optical properties of electromagnetically levitated liquid metals Cu, Ag, Au, Ni, Pd, Pt, and Zr were measured in situ at four wavelengths and up to 600 K superheat in the liquid. The data suggest an increase in the emissivity of the liquid compared with the incandescent solid. The data also show moderate temperature dependence of the spectral emissivity. A few measurements of the optical properties of undercooled liquid metals were also conducted. The data for both solids and liquids show excellent agreement with available values in the literature for the spectral emissivities as well as the optical constants.

  13. Combined spectral-domain optical coherence tomography and hyperspectral imaging applied for tissue analysis: Preliminary results

    NASA Astrophysics Data System (ADS)

    Dontu, S.; Miclos, S.; Savastru, D.; Tautan, M.

    2017-09-01

    In recent years many optoelectronic techniques have been developed for improvement and the development of devices for tissue analysis. Spectral-Domain Optical Coherence Tomography (SD-OCT) is a new medical interferometric imaging modality that provides depth resolved tissue structure information with resolution in the μm range. However, SD-OCT has its own limitations and cannot offer the biochemical information of the tissue. These data can be obtained with hyperspectral imaging, a non-invasive, sensitive and real time technique. In the present study we have combined Spectral-Domain Optical Coherence Tomography (SD-OCT) with Hyperspectral imaging (HSI) for tissue analysis. The Spectral-Domain Optical Coherence Tomography (SD-OCT) and Hyperspectral imaging (HSI) are two methods that have demonstrated significant potential in this context. Preliminary results using different tissue have highlighted the capabilities of this technique of combinations.

  14. Spectral tailoring of nanoscale EUV and soft x-ray multilayer optics

    NASA Astrophysics Data System (ADS)

    Huang, Qiushi; Medvedev, Viacheslav; van de Kruijs, Robbert; Yakshin, Andrey; Louis, Eric; Bijkerk, Fred

    2017-03-01

    Extreme ultraviolet and soft X-ray (XUV) multilayer optics have experienced significant development over the past few years, particularly on controlling the spectral characteristics of light for advanced applications like EUV photolithography, space observation, and accelerator- or lab-based XUV experiments. Both planar and three dimensional multilayer structures have been developed to tailor the spectral response in a wide wavelength range. For the planar multilayer optics, different layered schemes are explored. Stacks of periodic multilayers and capping layers are demonstrated to achieve multi-channel reflection or suppression of the reflective properties. Aperiodic multilayer structures enable broadband reflection both in angles and wavelengths, with the possibility of polarization control. The broad wavelength band multilayer is also used to shape attosecond pulses for the study of ultrafast phenomena. Narrowband multilayer monochromators are delivered to bridge the resolution gap between crystals and regular multilayers. High spectral purity multilayers with innovated anti-reflection structures are shown to select spectrally clean XUV radiation from broadband X-ray sources, especially the plasma sources for EUV lithography. Significant progress is also made in the three dimensional multilayer optics, i.e., combining micro- and nanostructures with multilayers, in order to provide new freedom to tune the spectral response. Several kinds of multilayer gratings, including multilayer coated gratings, sliced multilayer gratings, and lamellar multilayer gratings are being pursued for high resolution and high efficiency XUV spectrometers/monochromators, with their advantages and disadvantages, respectively. Multilayer diffraction optics are also developed for spectral purity enhancement. New structures like gratings, zone plates, and pyramids that obtain full suppression of the unwanted radiation and high XUV reflectance are reviewed. Based on the present achievement

  15. Real-time characterization of spectral coherence of ultrafast laser based on optical time-stretch

    NASA Astrophysics Data System (ADS)

    Xu, Yiqing; Wei, Xiaoming; Ren, Zhibo; Wong, Kenneth K. Y.; Tsia, Kevin

    2016-03-01

    Nonlinearly generated broadband ultrafast laser have been increasingly utilized in many applications. However, traditional techniques of characterizing these sources lack the ability to observe the instantaneous features and transitory behaviours of both amplitude and phase. With the advent of the optical time stretch techniques, the instantaneous shotto- shot spectral intensity can be directly measured continuously at an unprecedentedly high speed. Meanwhile, the information of the real-time phase variation, which is carried by the frequency-time mapped spectral signal has yet been fully explored. We present a technique of experimentally measuring the spectral coherence dynamics of broadband pulsed sources. Our method relies on a delayed Young's type interferometer combined with optical time-stretch. We perform the proof-of-principle demonstrations of spectral coherence dynamics measurement on two sources: a supercontinuum source and a fiber ring buffered cavity source, both with a repetition rate of MHz. By employing the optical time stretch with a dispersive fiber, we directly map the spectral interference fringes of the delayed neighbouring pulses and obtain a sufficiently large ensemble of spectral interferograms with a real-time oscilloscope (80Gb/s sampling rate). This enables us to directly quantify the spectral coherence dynamics of the ultrafast sources with a temporal resolution down to microseconds. Having the ensemble of single-shot interferograms, we also further calculate the cross spectral coherence correlation matrices of these ultrafast sources. We anticipate that our technique provides a general approach for experimentally evaluating the spectral coherence dynamics of ultrafast laser generated by the nonlinear processes e.g. modulation instability, supercontinuum generation, and Kerr resonator.

  16. Optical detection of explosives: spectral signatures for the explosive bouquet

    NASA Astrophysics Data System (ADS)

    Osborn, Tabetha; Kaimal, Sindhu; Causey, Jason; Burns, William; Reeve, Scott

    2009-05-01

    Research with canines suggests that sniffer dogs alert not on the odor from a pure explosive, but rather on a set of far more volatile species present in an explosive as impurities. Following the explosive trained canine example, we have begun examining the vapor signatures for many of these volatile impurities utilizing high resolution spectroscopic techniques in several molecular fingerprint regions. Here we will describe some of these high resolution measurements and discuss strategies for selecting useful spectral signature regions for individual molecular markers of interest.

  17. Spectral classification of optical transients with du Pont telescope

    NASA Astrophysics Data System (ADS)

    Morrell, Nidia; Shappee, Ben; Drout, Maria; Dong, Subo

    2017-04-01

    We obtained optical spectroscopy (range 370-920 nm) of 11 transients with the 2.5-m du Pont telescope (+WFCCD) at Las Campanas Observatory between March 26 and 29 UT. The data were cross-correlated with a library of supernova spectra via the Supernova Identification tool (Blondin and Tonry, 2007, ApJ, 666, 1024).

  18. Spectral encoding based measurement of x-ray/optical relative delay to ~10 fs rms

    NASA Astrophysics Data System (ADS)

    Bionta, Mina R.; French, Doug; Cryan, James P.; Glownia, James M.; Hartmann, Nick; Nicholson, David J.; Baker, Kevin; Bostedt, Christoph; Cammarrata, Marco; Chollet, Matthieu; Ding, Yuantao; Fritz, David M.; Durbin, Steve M.; Feng, Yiping; Harmand, Marion; Fry, Alan R.; Kane, Daniel J.; Krzywinski, Jacek; Lemke, Henrik T.; Messerschmidt, Marc; Ratner, Daniel F.; Schorb, Sebastian; Toleikis, Sven; Zhu, Diling; White, William E.; Coffee, Ryan N.

    2012-10-01

    A recently demonstrated single-shot measurement of the relative delay between x-ray FEL pulses and optical laser pulses has now been improved to ~10 fs rms error and has successfully been demonstrated for both soft and hard x-ray pulses. It is based on x-ray induced step-like reduction in optical transmissivity of a semiconductor membrane (Si3N4). The transmissivity is probed by an optical continuum spanning 450 - 650 nm where spectral chirp provides a mapping of the step in spectrum to the arrival time of the x-ray pulse relative to the optical laser system.

  19. Adaptive optics for fluorescence wide-field microscopy using spectrally independent guide star and markers.

    PubMed

    Vermeulen, Pierre; Muro, Eleonora; Pons, Thomas; Loriette, Vincent; Fragola, Alexandra

    2011-07-01

    We describe the implementation and use of an adaptive optics loop in the imaging path of a commercial wide field microscope. We show that it is possible to maintain the optical performances of the original microscope when imaging through aberrant biological samples. The sources used for illuminating the adaptive optics loop are spectrally independent, in excitation and emission, from the sample, so they do not appear in the final image, and their use does not contribute to the sample bleaching. Results are compared with equivalent images obtained with an identical microscope devoid of adaptive optics system.

  20. A spectrally tunable microstructured optical fibre Bragg grating utilizing an infiltrated ferrofluid.

    PubMed

    Candiani, A; Konstantaki, M; Margulis, W; Pissadakis, S

    2010-11-22

    The spectral response of a Bragg grating reflector inscribed in a microstructured optical fibre is tuned by employing an infiltrated ferrofluid, while modifying the overlap of the ferrofluidic medium with the grating length. Significant spectral changes in terms of Bragg grating wavelength shift and extinction ratio were obtained under static magnetic field actuation. Spectral measurements revealed non-bidirectional propagation effects dependent upon the relative position between the ferrofluid and the grating. The actuation speed of the device was measured to be of the order of few seconds.

  1. Spectral and spatial dependence of
diffuse optical signals in response to
peripheral nerve stimulation

    PubMed Central

    Chen, Debbie K.; Erb, M. Kelley; Tong, Yunjie; Yu, Yang; Sassaroli, Angelo; Bergethon, Peter R.; Fantini, Sergio

    2010-01-01

    Using non-invasive, near-infrared spectroscopy we have previously reported optical signals measured at or around peripheral nerves in response to their stimulation. Such optical signals featured amplitudes on the order of 0.1% and peaked about 100 ms after peripheral nerve stimulation in human subjects. Here, we report a study of the spatial and spectral dependence of the optical signals induced by stimulation of the human median and sural nerves, and observe that these optical signals are: (1) unlikely due to either dilation or constriction of blood vessels, (2) not associated with capillary bed hemoglobin, (3) likely due to blood vessel(s) displacement, and (4) unlikely due to fiber-skin optical coupling effects. We conclude that the most probable origin of the optical response to peripheral nerve stimulation is from displacement of blood vessels within the optically probed volume, as a result of muscle twitch in adjacent areas. PMID:21258519

  2. Spectral dependence of the efficiency of direct optical excitation of molecular oxygen in tetrachloromethane

    NASA Astrophysics Data System (ADS)

    Kiselev, V. M.; Kislyakov, I. M.; Bagrov, I. V.

    2016-06-01

    The spectral dependence of the efficiency of direct optical excitation of an oxygen molecule in tetrachloromethane using cw LED sources with different wavelengths and an optical parametric oscillator with single-shot output radiation (tuning range of 415-670 nm) has been studied by recording the phosphorescence of singlet oxygen at the O2(1Δg)-O2(3Σg) transition (λ = 1270 nm). The results show that single-shot irradiation of tetrachloromethane in the short-wavelength spectral range leads to efficient quenching of singlet- oxygen phosphorescence by the products of photolytic decomposition of solvent.

  3. Combined optical coherence tomography and hyper-spectral imaging using a double clad fiber coupler

    NASA Astrophysics Data System (ADS)

    Guay-Lord, Robin; Lurie, Kristen L.; Attendu, Xavier; Mageau, Lucas; Godbout, Nicolas; Ellerbee Bowden, Audrey K.; Strupler, Mathias; Boudoux, Caroline

    2016-03-01

    This proceedings shows the combination of Optical Coherence Tomography (OCT) and Hyper-Spectral Imaging (HSI) using a double-clad optical fiber. The single mode core of the fiber is used to transmit OCT signals, while the cladding, with its large collection area, provides an efficient way to capture the reflectance spectrum of the sample. The combination of both methods enables three-dimensional acquisition of sample morphology with OCT, enhanced by the molecular information contained in its hyper-spectral image. We believe that the combination of these techniques could result in endoscopes with enhanced tissue identification capability.

  4. Half-spectral unidirectional invisibility in non-Hermitian periodic optical structures.

    PubMed

    Longhi, Stefano

    2015-12-01

    The phenomenon of half-spectral unidirectional invisibility is introduced for one-dimensional periodic optical structures with tailored real and imaginary refractive index distributions in a non PT-symmetric configuration. The effect refers to the property in which the optical medium appears to be invisible, both in reflection and transmission, below the Bragg frequency when probed from one side and above the Bragg frequency when probed from the opposite side. Half-spectral invisibility is obtained by a combination of in-phase index and gain gratings whose spatial envelopes are related to each other by a Hilbert transform.

  5. Pharmaceutical Film Coating Catalog for Spectral Domain Optical Coherence Tomography.

    PubMed

    Lin, Hungyen; Dong, Yue; Markl, Daniel; Zhang, Zijian; Shen, Yaochun; Zeitler, J Axel

    2017-10-01

    Optical coherence tomography (OCT) has recently been demonstrated to measure the film coating thickness of pharmaceutical tablets and pellets directly. The results enable the analysis of inter- and intra-tablet coating variability at an off-line and in-line setting. To date, only a few coating formulations have been tried and there is very little information on the applicability of OCT to other coatings. As it is well documented that optical methods including OCT are prone to scattering leading to limited penetration, some pharmaceutical coatings may not be measurable altogether. This study presents OCT measurements of 22 different common coatings for the assessment of OCT applicability. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

  6. Is the dependence of spectral index on luminosity real in optically selected AGN samples?

    NASA Astrophysics Data System (ADS)

    Tang, Su Min; Zhang, Shuang Nan; Hopkins, Philip F.

    2007-05-01

    We critically examine the dependence of spectral index on luminosity in optically selected AGN samples. An analysis of optically selected high-z quasars showed an anticorrelation of αOX, the spectral index between the rest-frame 2500 Å and 2 keV, with optical luminosity. We examine this relationship by means of Monte Carlo simulations and conclude that a constant αOX independent of optical luminosity is still consistent with this high-z sample. We further find that contributions of large dispersions and narrow range of optical luminosity are most important for the apparent, yet artificial, αOX-lo correlation reported. We also examine another, but more complete, low-z optical selected AGN sub-sample from Steffen et al., and our analysis shows that a constant αOX independent of optical luminosity is also consistent with the data. By comparing X-ray and optical luminosity functions, we find that a luminosity-independent αOX is in fact more preferred than the luminosity-dependent αOX model. We also discuss the selection effects caused by flux limits, which might systematically bias the lX-lo relation and cause discrepancy in optically selected and X-ray selected AGN samples. To correctly establish a dependence of αOX of AGNs on their luminosity, a larger and more complete sample is needed and consequences of luminosity dispersions and selection effects in flux-limited samples must be taken into account properly.

  7. Optical Power Spectral Analysis for Machine-Readable Factor Maps.

    DTIC Science & Technology

    1980-12-01

    for one- and two-dimensional arrangements respectively, uses glass lenses and galvanometers to move and form a telecentric scanner, with samples in...relayed by the relay optics (RO) to the center of rotation of a second galvanometer mirror Ms,, which scans orthogonal to that of the first. Generally...the galvanometers are moved under computer control so that the sam- pling beam raster discretely scans the transparency, and a matrix of sample points

  8. Investigating the Spectral Dependence of Biomass Burning Aerosol Optical Properties

    NASA Astrophysics Data System (ADS)

    Odwuor, A.; Corr, C.; Pusede, S.

    2016-12-01

    Aerosol optical properties, such as light absorption and scattering, are important for understanding how aerosols affect the global radiation budget and for comparison with data gathered from remote sensing. It has been established that the optical properties of aerosols are wavelength dependent, although some remote sensing measurements do not consider this. Airborne measurements of these optical properties were used to calculate the absorption Angstrom exponent, a parameter that characterizes the wavelength dependence of light absorption by aerosols, and single scattering albedo, which measures the relative magnitude of light scattering to total extinction (scattering and absorption combined). Aerosols produced by biomass burning in Saskatchewan, Canada in July 2008 and a forest fire in Southern California, U.S. in June 2016 were included in this analysis. These wildfires were sampled by the NASA DC-8 aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and NASA Student Airborne Research Program (SARP) missions, respectively. Aerosol absorption was measured using a particle soot photometer (PSAP) at 470, 532 and 660 nm. Scattering was measured using a 3-wavelength (450, 550 and 700 nm) nephelometer. Absorption Angstrom exponents were calculated at 470 and 660 nm and single scattering albedos were calculated at 450 and 550 nm. Results of this study indicate that disregarding the wavelength dependence of organic aerosol can understate the positive radiative forcing (warming) associated with aerosol absorption.

  9. A Review on Spectral Amplitude Coding Optical Code Division Multiple Access

    NASA Astrophysics Data System (ADS)

    Kaur, Navpreet; Goyal, Rakesh; Rani, Monika

    2017-03-01

    This manuscript deals with analysis of Spectral Amplitude Coding Optical Code Division Multiple Access (SACOCDMA) system. The major noise source in optical CDMA is co-channel interference from other users known as multiple access interference (MAI). The system performance in terms of bit error rate (BER) degrades as a result of increased MAI. It is perceived that number of users and type of codes used for optical system directly decide the performance of system. MAI can be restricted by efficient designing of optical codes and implementing them with unique architecture to accommodate more number of users. Hence, it is a necessity to design a technique like spectral direct detection (SDD) technique with modified double weight code, which can provide better cardinality and good correlation property.

  10. The modification of spectral characteristics of cytostatics by optical beams

    NASA Astrophysics Data System (ADS)

    Pascu, Mihail Lucian; Brezeanu, Mihail; Carstocea, Benone D.; Voicu, Letitia; Gazdaru, Doina M.; Smarandache, Adriana A.

    2004-10-01

    Besides the biochemical action of methotrexate (MTX) and 5-fluorouracil (FU) their effect in destroying cancer tumours could be enhanced by exposure to light at different doses. Absorption, excitation and emission spectra of 10-4M - 10-5M MTX solutions in natural saline and sodium hydroxide at pH = 8.4 were measured, while their exposure to coherent and uncoherent light in the visible and near ultraviolet (UV) spectral ranges was made (Hg lamps and Nitrogen pulsed laser radiation were used). Absorption spectra exhibit spectral bands in the range 200 nm - 450 nm. The 200 - 450 nm excitation spectra were measured with emission centered on 470 nm; MTX fluorescence excitation was measured at 390 nm and the emission was detected between 400 nm and 600 nm showing a maximum at 470 nm. Spectra modifications, nonlinearly depending on exposure time (varying from 1 min to 20 min), evidenced MTX photo-dissociation to the fluorescent compound 2,4 diamino-formylpteridine. In the 5-FU case the absorption spectra exhibit bands between 200 nm and 450 nm. The emission fluorescence spectra were measured between 400 nm and 600 nm, with λex = 350 nm for UV Hg lamp and with λex = 360 nm for laser irradiated samples; at irradiation with N2 laser emitted radiation the excitation spectra were measured in the range of 200 nm - 400 nm, with λem = 440 nm. New vascularity rapid destruction was observed for conjunctive impregnated with 5-FU solution whilst exposed to incoherent UV and visible light.

  11. The Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRB 080319B

    NASA Astrophysics Data System (ADS)

    Stamatikos, Michael; Ukwatta, Tilan N.; Sakamoto, Takanori; Dhuga, Kalvir S.; Toma, Kenji; Pe'Er, Asaf; Mészáros, Peter; Band, David L.; Norris, Jay P.; Barthelmy, Scott D.; Gehrels, Neil

    2009-05-01

    We report on observations of correlated behavior between the prompt γ-ray and optical emission from GRB 080319B, which confirm that (i) they occurred within the same astrophysical source region and (ii) their respective radiation mechanisms were dynamically coupled. Our results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt γ-ray photon counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic γ-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15-350 keV γ-rays and the optical emission observed by TORTORA (extrinsic optical/γ-ray spectral lag), thus effectively partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, the rise and decline of prompt optical emission at ~T+10+/-1 sec and ~T+50+/-1 sec, respectively, both coincide with discontinuities in the hard to soft evolution of the photon index for a power law fit to 15-150 keV Swift-BAT data at ~T+8+/-2 sec and ~T+48+/-1 sec. These spectral energy changes also coincide with intervals whose time-resolved spectral lag values are consistent with zero, at ~T+12+/-2 sec and ~T+50+/-2 sec. These results, which are robust across heuristic permutations of Swift-BAT energy channels and varying temporal bin resolution, have also been corroborated via independent analysis of Konus-Wind data. This potential discovery may provide the first observational evidence for an implicit connection between spectral lags and GRB emission mechanisms in the context of canonical fireball phenomenology. Future work includes exploring a subset of bursts with prompt optical emission to probe the unique or ubiquitous nature of this result.

  12. Single-step method for fiber-optic probe-based full-range spectral domain optical coherence tomography.

    PubMed

    Min, Eun Jung; Shin, Jun Geun; Lee, Jae Hwi; Yasuno, Yoshiaki; Lee, Byeong Ha

    2013-07-20

    We propose a single-step method appropriated for a fiber-optic probe-based full-range spectral domain optical coherence tomography (OCT). The fiber-optic probe was scanned over a sample with a magnetically driven actuator. In the reference arm, a phase shift of π/2 was applied during two neighbor axial scanning, from which the complex spectral interferogram was directly reconstructed. Since the complex-conjugate-free OCT image is obtained by doing just one Fourier transform on the complex interferogram, obtaining the full-range image is simple in algorithm and effective in computation time. Some full-range images of biological samples created with the proposed method are presented and the processing time is analyzed.

  13. High-dynamic-range hybrid analog-digital control broadband optical spectral processor using micromirror and acousto-optic devices.

    PubMed

    Riza, Nabeel A; Reza, Syed Azer

    2008-06-01

    For the first time, to the best of our knowledge, the design and demonstration of a programmable spectral filtering processor is presented that simultaneously engages the power of an analog-mode optical device such as an acousto-optic tunable filter and a digital-mode optical device such as the digital micromirror device. The demonstrated processor allows a high 50 dB attenuation dynamic range across the chosen 1530-1565 nm (~C band). The hybrid analog-digital spectral control mechanism enables the processor to operate with greater versatility when compared to analog- or digital-only processor designs. Such a processor can be useful both as a test instrument in biomedical applications and as an equalizer in fiber communication networks.

  14. Two-axes spectral splitting optical concentrator based on single plastic element

    NASA Astrophysics Data System (ADS)

    Stefancich, M.; Maragliano, C.; Apostoleris, Harry; Chiesa, Matteo

    2014-10-01

    High efficiency concentrator photovoltaic systems are currently based on costly III/V cells and, to offset the high cell capital cost, elevated optical concentrations are used, with consequent reduction in acceptance angles and tight tolerance optics. While this allows for spectacular conversion efficiencies, it does not provide cost effectiveness in a market dominated by low efficiency/low cost technologies. An alternative approach, well known in literature, is based on the combined use of an optical concentrator and a spectral splitting element allowing for the use of separate cells with different spectral responses and, thus, opening the way to a much wider range of possible materials and technologies. While many configurations have been presented during the years, optical efficiency has often been an issue due to the separate action of the concentrating and splitting element. We propose here, as substantial evolution of a previous design [1], a single injection molded plastic non-imaging optical element embodying both two axes concentration and spectral splitting functions. Based on the specific dispersion characteristics of polycarbonate and on a constructive analytical design procedure, this element allows for optical efficiencies exceeding 80%. Theory, simulations and preliminary experimental results will be presented.

  15. Spectral dependences of extrinsic optical absorption in sillenite crystals

    SciTech Connect

    Kisteneva, M G; Khudyakova, E S; Shandarov, S M; Akrestina, A S; Dyu, V G; Kargin, Yu F

    2015-07-31

    The influence of laser irradiation at wavelengths of 532 and 655 nm and annealing in air at temperatures from 200 to 370 °C on optical absorption spectra of undoped bismuth silicon oxide and bismuth germanium oxide and aluminium-doped bismuth titanium oxide crystals has been studied experimentally. The experimental data have been interpreted in terms of a model for extrinsic absorption that takes into account not only the contribution of the photoexcitation of electrons from deep donor centres with a normal distribution of their concentration with respect to ionisation energy but also that of intracentre transitions. (laser applications and other topics in quantum electronics)

  16. New white-light spectral interferometric techniques for dispersion characterization of optical samples and fibers

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    2003-04-01

    The application of white-light spectral interferometry with the equalization wavelength determination is extended to propose new techniques for dispersion characterization of optical samples and fibers. First, a configuration of a non-dispersive Michelson interferometer and an optical sample of known thickness is proposed and realized to measure the differential group refractive index dispersion and the group velocity dispersion in the optical sample. Second, a tandem configuration of a non-dispersive Michelson interferometer and a birefringent optical sample of known thickness is proposed to measure the differential group refractive index dispersion in the birefringent optical sample. The latter experimental setup can be effectively modified to measure dispersion in both birefringent and polarization maintaining optical fibers.

  17. Clinical Usefulness of Spectral-Domain Optical Coherence Tomography in Glaucoma and NAION

    PubMed Central

    Lee, Tae Hee; Heo, Hwan

    2016-01-01

    The development of optical coherence tomography (OCT) has changed the clinical management of ophthalmic diseases by furthering the understanding of pathogenesis, as well as improving the monitoring of their progression and assisting in quantifying the response to treatment modalities in ophthalmic diseases. Initially, the two-dimensional configuration of the optic nerve head (ONH) and the thickness of the retinal nerve fiber layer (RNFL) were the main OCT structural parameters used in clinical management of optic nerve diseases. Now, with higher resolution power and faster acquisition times, the details of ONH and the retina including the macular area can be measured using spectral domain OCT (SD-OCT) with high reproducibility and increased diagnostic ability. OCT can provide structural information to improve the understanding and management of optic nerve diseases. In this review, we will briefly summarize the clinical applications of SD-OCT in glaucoma and nonarteritic anterior ischemic optic neuropathy, which are two representative optic nerve diseases. PMID:27689029

  18. Spectral analysis of optical emission of microplasma in sea water

    NASA Astrophysics Data System (ADS)

    Gamaleev, Vladislav; Morita, Hayato; Oh, Jun-Seok; Furuta, Hiroshi; Hatta, Akimitsu

    2016-09-01

    This work presents an analysis of optical emission spectra from microplasma in three types of liquid, namely artificial sea water composed of 10 typical agents (10ASW), reference solutions each containing a single agent (NaCl, MgCl2 + H2O, Na2SO4, CaCl2, KCl, NaHCO3, KBr, NaHCO3, H3BO3, SrCl2 + H2O, NaF) and naturally sampled deep sea water (DSW). Microplasma was operated using a needle(Pd)-to-plate(Pt) electrode system sunk into each liquid in a quartz cuvette. The radius of the tip of the needle was 50 μm and the gap between the electrodes was set at 20 μm. An inpulse generator circuit, consisting of a MOSFET switch, a capacitor, an inductor and the resistance of the liquid between the electrodes, was used as a pulse current source for operation of discharges. In the spectra, the emission peaks for the main components of sea water and contaminants from the electrodes were detected. Spectra for reference solutions were examined to enable the identification of unassigned peaks in the spectra for sea water. Analysis of the Stark broadening of H α peak was carried out to estimate the electron density of the plasma under various conditions. The characteristics of microplasma discharge in sea water and the analysis of the optical emission spectra will be presented. This work was supported by JSPS KAKENHI Grant Number 26600129.

  19. Comparing optic nerve head analysis between confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography.

    PubMed

    Roberti, Gloria; Centofanti, Marco; Oddone, Francesco; Tanga, Lucia; Michelessi, Manuele; Manni, Gianluca

    2014-10-01

    Confocal scanning laser ophthalmoscopy, HRT3, and spectral domain optical coherence tomography (OCT), RTVue-100, are able to give 3-dimensional (3D) topography images of optic nerve head (ONH) and to derive stereometric parameters and sectorial analysis. The purpose of the study is to evaluate the agreement of these two devices and their diagnostic accuracy to discriminate eyes with glaucoma from those without. Glaucoma patients and healthy control subjects were included. All of them underwent a complete ophthalmological examination, including slit lamp evaluation and visual field (VF) test. After pupil dilatation, HRT3 and RTVue-100 were performed. The following stereometric parameters were recorded: disc area, rim area, rim volume, cup volume, cup area, cup/disk ratio, and the following sectors, superotemporal, superonasal, inferotemporal, inferonasal. Forty-six eyes of 46 glaucoma patients and 58 eyes of 58 healthy subjects were included in the study. In both groups, HRT3 rim area and rim volume were statistically higher than RTVue-100 (glaucomas: 0.95 ± 0.38 versus 0.44 ± 0.33 and 0.19 ± 0.13 versus 0.02 ± 0.03, p < 0.01. controls: 1.41 ± 0.30 versus 1.08 ± 0.37 and 0.37 ± 0.13 versus 0.14 ± 0.11, p < 0.01), while cup area was statistically higher by RTVue-100 (glaucomas: 1.42 ± 0.57 versus 1.14 ± 0.58, p < 0.01. controls: 1.05 ± 1.35 versus 0.65 ± 0.48). Bland and Altman plots confirmed the presence of a fixed bias. The parameters with largest AUROC were rim volume, rim area and cup/disk ratio for both instruments. HRT3 inferotemporal sector had the highest sensitivity (80.43%, at 75.9% specificity), while for RTVue-100, the superotemporal sector had the highest sensitivity (76.1%, at 81% specificity). The agreement was moderate for inferotemporal sector and fair for the others. HRT3 and RTVue-100 are not interchangeable for ONH analysis. They both have good diagnostic accuracy, but RTVue

  20. Spectral interferometric fiber optic temperature sensor with enhanced sensitivity

    NASA Astrophysics Data System (ADS)

    Militky, J.; Kadulova, M.; Hlubina, P.

    2016-12-01

    Spectral interferometric techniques utilizing the interference of polarization modes in a highly birefringent (HB) elliptical-core fiber to measure temperature are analyzed experimentally. First, an experimental setup comprising a white-light source, a polarizer, a sensing birefringent fiber, an analyzer and a spectrometer is considered. Temperature sensing by this method is based on the wavelength interrogation. Second, the above setup is extended by a birefringent quartz crystal to increase the sensitivity of the temperature sensing. Third, the above setup is extended by an analyzer, and the combination of a polarizer, a birefringent quartz crystal and an analyzer represents another interferometer, which is used to increase the sensitivity of the temperature sensing. In this case the Vernier effect is present and the resultant spectrum is with an envelope, which is utilized in temperature sensing. We reached a sensitivity of 0.56 nm/K in the third setup, compared to -0.12 nm/K and -0.19 nm/K in the first and the second setup, respectively.

  1. Polarized spectral combs probe optical fiber surface plasmons.

    PubMed

    Caucheteur, Christophe; Voisin, Valérie; Albert, Jacques

    2013-02-11

    The high-order cladding modes of conventional single mode fiber come in semi-degenerate pairs corresponding to mostly radially or mostly azimuthally polarized light. Using tilted fiber Bragg gratings to excite these mode families separately, we show how plasmonic coupling to a thin gold coating on the surface of the fiber modifies the effective indices of the modes differently according to polarization and to mode order. In particular, we show the existence of a single "apolarized" grating resonance, with equal effective index for all input polarization states. This special resonance provides direct evidence of the excitation of a surface plasmon on the metal surface but also an absolute wavelength reference that allows for the precise localization of the most sensitive resonances in refractometric and biochemical sensing applications. Two plasmon interrogation methods are proposed, based on wavelength and amplitude measurements. Finally, we use a biotin-streptavidin biomolecular recognition experiment to demonstrate that differential spectral transmission measurements of a fine comb of cladding mode resonances in the vicinity of the apolarized resonance provide the most accurate method to extract information from plasmon-assisted Tilted fiber Bragg gratings, down to pM concentrations and at least 10(-5) refractive index changes.

  2. Studies of dynamic processes in biomedicine by high-speed spectral optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wojtkowski, M.; Kowalczyk, A.

    2007-02-01

    This contribution demonstrates potential of Spectral Optical Coherence Tomography (SOCT) for studies of dynamic processes in biomedicine occurring at various time scales. Several examples from ophthalmology, optometry, surgery, neurology are given to illustrate the extension of SOCT beyond pure morphological investigations.

  3. Spectral domain optical coherence tomography imaging of subretinal bands associated with chronic retinal detachments

    PubMed Central

    Kothari, Nikisha; Kuriyan, Ajay E; Flynn, Harry W

    2016-01-01

    We report three patients with subretinal bands associated with retinal detachment in chronic retinal detachments who underwent successful retinal reattachment. Subretinal bands before and after surgery can be identified on clinical examination and spectral domain optical coherence tomography. Removal of subretinal bands is not mandatory to achieve retinal reattachment. PMID:27099457

  4. Spectral staining of tumor tissue by fiber optic FTIR spectroscopy

    NASA Astrophysics Data System (ADS)

    Salzer, Reiner; Steiner, Gerald; Kano, Angelique; Richter, Tom; Bergmann, Ralf; Rodig, Heike; Johannsen, Bernd; Kobelke, Jens

    2003-07-01

    Infrared (IR) optical fiber have aroused great interest in recent years because of their potential in in-vivo spectroscopy. This potential includes the ability to be flexible, small and to guide IR light in a very large range of wavelengths. Two types - silver halide and chalcogenide - infrared transmitting fibers are investigated in the detection of a malignant tumor. As a test sample for all types of fibers we used a thin section of an entire rat brain with glioblastoma. The fibers were connected with a common infrared microscope. Maps across the whole tissue section with more than 200 spectra were recorded by moving the sample with an XY stage. Data evaluation was performed using fuzzy c-means cluster analysis (FCM). The silver halide fibers provided excellent results. The tumor was clearly discernible from healthy tissue. Chalcogenide fibers are not suitable to distinguish tumor from normal tissue because the fiber has a very low transmittance in the important fingerprint region.

  5. Fiber-optic-echelle-CCD spectral monitoring of UX Arietis

    SciTech Connect

    Huenemoerder, D.P.; Buzasi, D.L.; Ramsey, L.W. )

    1989-10-01

    Results are presented on 30 fiber-optic-echelle-CCD spectra for the UX Ari system, covering one orbit in the spring and two orbits in the fall of 1987. The spectra obtained have a resolution of about 12,000 over the range of the Ca II H lines in the near UV to the Ca II triplet in the near IR, covering several activity sensitive lines. The most striking features observed were strong H-alpha and H-beta absorption near phase 0.8, which were present at epochs eight months apart. The geometry of the system, as determined from the mass ratio, rotational velocities, and the assumption of synchronous rotation, gives a radius for the K star that is approximately filling its Roche lobe. It is suggested that the excess absorption seen is due to mass-transfer activity resulting from Roche lobe overflow of the K star and accretion onto the G star. 30 refs.

  6. The Effect of Optic Disc Center Displacement on Retinal Nerve Fiber Layer Measurement Determined by Spectral Domain Optical Coherence Tomography

    PubMed Central

    Uhm, Ki Bang; Sung, Kyung Rim; Kang, Min Ho; Cho, Hee Yoon; Seong, Mincheol

    2016-01-01

    Purpose To investigate the effect of optic disc center displacement on retinal nerve fiber layer (RNFL) measurement determined by spectral domain optical coherence tomography (SD-OCT). Methods The optic disc center was manipulated at 1-pixel intervals in horizontal, vertical, and diagonal directions. According to the manipulated optic disc center location, the RNFL thickness data were resampled: (1) at a 3.46-mm diameter circle; and (2) between a 2.5-mm diameter circle and 5.4-mm square. Error was calculated between the original and resampled RNFL measurements. The tolerable error threshold of the optic disc center displacement was determined by considering test-retest variability of SD-OCT. The unreliable zone was defined as an area with 10% or more variability. Results The maximum tolerable error thresholds of optic disc center displacement on the RNFL thickness map were distributed from 0.042 to 0.09 mm in 8 directions. The threshold shape was vertically elongated. Clinically important unreliable zones were located: (1) at superior and inferior region in the vertical displacement; (2) at inferotemporal region in the horizontal displacement, and (3) at superotemporal or inferotemporal region in the diagonal displacement. The unreliable zone pattern and threshold limit varied according to the direction of optic disc displacement. Conclusions Optic disc center displacement had a considerable impact on whole RNFL thickness measurements. Understanding the effect of optic disc center displacement could contribute to reliable RNFL measurements. PMID:27783663

  7. All-Optical Label Swapping Strategies for Spectral Amplitude Code Labels in Packet-Switched Optical Networks

    NASA Astrophysics Data System (ADS)

    Habib, Christian

    There is currently much work focused on developing packet-switched optical networks to overcome the limitations of existing optical networks. Switch design for packet-switched optical networks is particularly challenging, in part due to the lack of a practical optical memory system. As a result, optical labels and all-optical label processing have attracted much attention. This thesis examines a crucial label processing component of an optical packet switch, namely the label swapper. In this thesis, three different tabletop topologies for low-cost all-optical swapping of spectral amplitude code labels for packet-switched networks are examined in a proof-of-concept phase. The first uses cross-absorption modulation in an electro-absorption modulator within a semiconductor fiber ring laser (SFRL), the second uses cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) within an SFRL, and the third makes use of XGM in a SOA as well as injection locking in a Fabry-Perot laser diode for wavelength conversion. The benefits and limitations of each approach as well as future improvements are discussed. Building on these results, a high-performance integrated version of XGM swapper is designed, simulated, and masks are produced for fabrication using indium phosphide technology.

  8. Digital subcarrier multiplexing for flexible spectral allocation in optical transport network.

    PubMed

    Zhang, Yuanyuan; O'Sullivan, Maurice; Hui, Rongqing

    2011-10-24

    We demonstrate a spectrally efficient digital subcarrier multiplexed (DSCM) coherent optical system for optical transport network. In the proposed system, mutually orthogonal subcarrier channels are digitally generated, which allows a high degree of flexibility in bandwidth allocation and scalability in data rate granularity. The receiver can also dynamically change the number of DSCM channels for detection without changing the system configuration. We experimentally investigate the transmission performance of a 22.2 Gb/s DSCM system with 10 subcarrier channels using QPSK modulation. The impacts of channel spacing and time mismatch between subcarrier channels are also explored. © 2011 Optical Society of America

  9. Narrow bandwidth Bragg gratings imprinted in polymer optical fibers for different spectral windows

    NASA Astrophysics Data System (ADS)

    Marques, Carlos A. F.; Bilro, Lúcia B.; Alberto, Nélia J.; Webb, David J.; Nogueira, Rogério N.

    2013-10-01

    The production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in different spectral regions using polymer optical fibers (POFs) is reported. Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 600-nm, 850-nm and 1550-nm in several types of polymer optical fibers were inscribed using a scanning technique with a short optical path. The technique allowed the inscription in relative short periods of time. The obtained 3-dB bandwidth varies from 0.22 down to 0.045 nm considering a Bragg grating length between 10 and 25-mm, respectively.

  10. Paired SSB optical OFDM channels for high spectral efficient signal transmission over DWDM networks

    NASA Astrophysics Data System (ADS)

    Chicharro, Francisco I.; Ortega, Beatriz; Mora, José

    2016-07-01

    A new high spectral efficient SSB-OOFDM DWDM transmission system has been experimentally demonstrated. The proposed transmitter employs paired optical channels consisting of two SSB modulated OFDM signals using opposite sidebands in order to allow an efficient use of the spectrum with optical carriers separation under 10 GHz. Moreover, different paired channels are multiplexed into the 25 GHz grid DWDM fiber transmission link. Optical carrier spacing of 8.75 GHz in paired channels has been demonstrated allowing 40.8 Gb/s signal transmission rate over a 25 GHz paired channel bandwidth.

  11. Constraints on the temperature inhomogeneity in quasar accretion discs from the ultraviolet-optical spectral variability

    NASA Astrophysics Data System (ADS)

    Kokubo, Mitsuru

    2015-05-01

    The physical mechanisms of the quasar ultraviolet (UV)-optical variability are not well understood despite the long history of observations. Recently, Dexter & Agol presented a model of quasar UV-optical variability, which assumes large local temperature fluctuations in the quasar accretion discs. This inhomogeneous accretion disc model is claimed to describe not only the single-band variability amplitude, but also microlensing size constraints and the quasar composite spectral shape. In this work, we examine the validity of the inhomogeneous accretion disc model in the light of quasar UV-optical spectral variability by using five-band multi-epoch light curves for nearly 9 000 quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 region. By comparing the values of the intrinsic scatter σint of the two-band magnitude-magnitude plots for the SDSS quasar light curves and for the simulated light curves, we show that Dexter & Agol's inhomogeneous accretion disc model cannot explain the tight inter-band correlation often observed in the SDSS quasar light curves. This result leads us to conclude that the local temperature fluctuations in the accretion discs are not the main driver of the several years' UV-optical variability of quasars, and consequently, that the assumption that the quasar accretion discs have large localized temperature fluctuations is not preferred from the viewpoint of the UV-optical spectral variability.

  12. Characterizing the spectral signatures and optical properties of dams in Cyprus using field spectroradiometric measurements

    NASA Astrophysics Data System (ADS)

    Papoutsa, Christiana; Hadjimitsis, Diofantos G.; Alexakis, Dimitrios

    2011-11-01

    A field study of optical properties of inland water quality was performed in Asprokremmos Dam in Cyprus. The field campaign last from May 2010 to October 2010. Field spectroradiometric measurements were taken using a handheld spectro-radiometer GER1500 equipped with a fibre optic probe. Spectral range of the instrument is 299-1088nm. Reflectance was calculated as a ratio of the target radiance to the reference radiance. The target radiance value was the measured value taken on the water of the reservoir and the reference radiance value was the measured value taken on the standard Spectralon panel, which represent the sun radiance which rich the earth surface-without atmospheric influence. From this campaign spectral signatures of the water were retrieved in several depths. The appearance of water color can be determined through the analysis of the retrieval spectral signatures, irradiance reflectance R(λ), and the optical properties of the water, backscattering coefficient (bb) and absorption coefficient (a). Constituents and their concentration in the water can directly affect the optical properties of the water so optical properties values can be used in order to evaluate the type of water and to determine water quality parameters such as turbidity.

  13. Use of spectral analogy to evaluate canopy reflectance sensitivity to leaf optical property

    NASA Technical Reports Server (NTRS)

    Baret, Frederic; Vanderbilt, Vern C.; Steven, Michael D.; Jacquemoud, Stephane

    1993-01-01

    The spectral variation of canopy reflectance is mostly governed by the absorption properties of the elements, hence the leaves, since their intrinsic scattering properties show very little spectral variation. The relationship between canopy reflectance and leaf reflectance measured at the red edge over sugar beet canopies was used to simulate canopy reflectance from leaf reflectance spectra measured over the whole spectral domain. The results show that the spectral analogies found allows accurate reconstruction of canopy reflectance spectra. Explicit assumptions about the very low spectral variation of leaf intrinsic scattering properties are thus indirectly justified. The sensitivity of canopy reflectance (rho(sub c)) to leaf optical properties can then be investigated from concurrent spectral variations of canopy (delta rho(sub c)/delta lambda) and leaf reflectance (delta rho(sub l)/delta lambda): (delta rho(sub c))/(delta rho(sub l)) = ((delta rho(sub c))/(delta lambda) ((delta rho( sub l))/(delta lambda))(sup -1)). This expression is strictly valid only when the optical properties of the soil background or the other vegetation elements such as bark are either spectrally flat or do not contribute significantly to canopy reflectance. Simulations using the SAIL and PROSPECT models demonstrate that the sensitivity of canopy reflectance to leaf reflectance is significant for large vegetation cover fractions in spectral domains where absorption is low. In these conditions, multiple, scattering enhances the leaf absorption features by a factor that can be greater than 2.0. To override the limitations of the SAIL model for the description of the canopy architecture, we tested the previous findings on experimental data. Concurrent canopy and leaf reflectance spectra were measured for a range of sugar beet canopies. The results show good agreement with the theoretical findings. Conclusions are drawn about the applicability of these findings, with particular attention to

  14. Use of spectral analogy to evaluate canopy reflectance sensitivity to leaf optical property

    NASA Technical Reports Server (NTRS)

    Baret, Frederic; Vanderbilt, Vern C.; Steven, Michael D.; Jacquemoud, Stephane

    1993-01-01

    The spectral variation of canopy reflectance is mostly governed by the absorption properties of the elements, hence the leaves, since their intrinsic scattering properties show very little spectral variation. The relationship between canopy reflectance and leaf reflectance measured at the red edge over sugar beet canopies was used to simulate canopy reflectance from leaf reflectance spectra measured over the whole spectral domain. The results show that the spectral analogies found allows accurate reconstruction of canopy reflectance spectra. Explicit assumptions about the very low spectral variation of leaf intrinsic scattering properties are thus indirectly justified. The sensitivity of canopy reflectance (rho(sub c)) to leaf optical properties can then be investigated from concurrent spectral variations of canopy (delta rho(sub c)/delta lambda) and leaf reflectance (delta rho(sub l)/delta lambda): (delta rho(sub c))/(delta rho(sub l)) = ((delta rho(sub c))/(delta lambda) ((delta rho( sub l))/(delta lambda))(sup -1)). This expression is strictly valid only when the optical properties of the soil background or the other vegetation elements such as bark are either spectrally flat or do not contribute significantly to canopy reflectance. Simulations using the SAIL and PROSPECT models demonstrate that the sensitivity of canopy reflectance to leaf reflectance is significant for large vegetation cover fractions in spectral domains where absorption is low. In these conditions, multiple, scattering enhances the leaf absorption features by a factor that can be greater than 2.0. To override the limitations of the SAIL model for the description of the canopy architecture, we tested the previous findings on experimental data. Concurrent canopy and leaf reflectance spectra were measured for a range of sugar beet canopies. The results show good agreement with the theoretical findings. Conclusions are drawn about the applicability of these findings, with particular attention to

  15. Short-duration low-gravity experiments - Time scales, challenges and results

    NASA Technical Reports Server (NTRS)

    Rosenberger, F.

    1993-01-01

    Short-duration low-gravity experiments can be conducted either in drop tubes and drop towers, or on sounding rockets and aircraft on ballistic trajectories. While these facilities offer more frequent flight opportunities and higher cost effectiveness than orbiting spacecraft, their relatively short low-gravity times are often perceived as limiting their utility to only a narrow range of applications and research areas. In this review it is shown, based on scaling laws for diffusive transport of momentum, species and heat, radiative heat transfer and capillarity-driven motion, that with proper consideration of the characteristic length scales, a host of phenomena can be meaningfully investigated during a few seconds. This usefulness of short-duration low-gravity facilities is illustrated with numerous results of recent studies of solidification, combustion, transport in multiphase systems, statics and dynamics of liquid surfaces, magnetic Benard convection, fluid management, transport properties and the graviperception in cells.

  16. Short-duration low-gravity experiments - Time scales, challenges and results

    NASA Technical Reports Server (NTRS)

    Rosenberger, F.

    1993-01-01

    Short-duration low-gravity experiments can be conducted either in drop tubes and drop towers, or on sounding rockets and aircraft on ballistic trajectories. While these facilities offer more frequent flight opportunities and higher cost effectiveness than orbiting spacecraft, their relatively short low-gravity times are often perceived as limiting their utility to only a narrow range of applications and research areas. In this review it is shown, based on scaling laws for diffusive transport of momentum, species and heat, radiative heat transfer and capillarity-driven motion, that with proper consideration of the characteristic length scales, a host of phenomena can be meaningfully investigated during a few seconds. This usefulness of short-duration low-gravity facilities is illustrated with numerous results of recent studies of solidification, combustion, transport in multiphase systems, statics and dynamics of liquid surfaces, magnetic Benard convection, fluid management, transport properties and the graviperception in cells.

  17. Spectral domain optical coherence tomography findings in long-term silicone oil-related visual loss.

    PubMed

    Shalchi, Zaid; Mahroo, Omar A; Shunmugam, Manoharan; Mohamed, Moin; Sullivan, Paul M; Williamson, Tom H

    2015-03-01

    To investigate spectral domain optical coherence tomography findings in long-term silicone oil-related visual loss. Four symptomatic patients were reviewed 4 years to 9 years after vitrectomy with silicone oil tamponade for macula-on retinal detachment. Three lost vision with oil in situ, with one at the time of oil removal. Eleven control eyes with good vision were included. Patients underwent assessment of best-corrected visual acuity, contrast sensitivity, Farnsworth-Munsell 100 Hue testing, static perimetry, and spectral domain optical coherence tomography imaging of the macula and disk. Long-term best-corrected visual acuity was significantly reduced in affected eyes (range, 0.44-1.02), as was contrast sensitivity (0.75-1.35) and color discrimination (Farnsworth-Munsell-100 Hue score, 151-390). Static perimetry showed a central scotoma in all affected eyes. Optical coherence tomography revealed microcystic macular changes in the inner nuclear layer of all affected eyes associated with severe loss of the papillofoveal retinal nerve fiber layer. In one patient, serial optical coherence tomography images showed development of microcystic macular changes 18 months after oil removal. Control eyes lacked these features, except two asymptomatic eyes that showed microcystic changes on optical coherence tomography with a corresponding paracentral scotoma. We have demonstrated microcystic macular changes in the inner nuclear layer of affected eyes, as well as focal severe loss of the papillofoveal projection. These changes share significant morphologic features reported in multiple sclerosis-associated optic neuritis and Leber hereditary optic neuropathy.

  18. Generalized spectral method for near-field optical microscopy

    SciTech Connect

    Jiang, B.-Y.; Zhang, L. M.; Basov, D. N.; Fogler, M. M.; Castro Neto, A. H.

    2016-02-07

    Electromagnetic interaction between a sub-wavelength particle (the “probe”) and a material surface (the “sample”) is studied theoretically. The interaction is shown to be governed by a series of resonances corresponding to surface polariton modes localized near the probe. The resonance parameters depend on the dielectric function and geometry of the probe as well as on the surface reflectivity of the material. Calculation of such resonances is carried out for several types of axisymmetric probes: spherical, spheroidal, and pear-shaped. For spheroids, an efficient numerical method is developed, capable of handling cases of large or strongly momentum-dependent surface reflectivity. Application of the method to highly resonant materials, such as aluminum oxide (by itself or covered with graphene), reveals a rich structure of multi-peak spectra and nonmonotonic approach curves, i.e., the probe-sample distance dependence. These features also strongly depend on the probe shape and optical constants of the model. For less resonant materials such as silicon oxide, the dependence is weak, so that the spheroidal model is reliable. The calculations are done within the quasistatic approximation with radiative damping included perturbatively.

  19. Generalized spectral method for near-field optical microscopy

    NASA Astrophysics Data System (ADS)

    Jiang, B.-Y.; Zhang, L. M.; Castro Neto, A. H.; Basov, D. N.; Fogler, M. M.

    2016-02-01

    Electromagnetic interaction between a sub-wavelength particle (the "probe") and a material surface (the "sample") is studied theoretically. The interaction is shown to be governed by a series of resonances corresponding to surface polariton modes localized near the probe. The resonance parameters depend on the dielectric function and geometry of the probe as well as on the surface reflectivity of the material. Calculation of such resonances is carried out for several types of axisymmetric probes: spherical, spheroidal, and pear-shaped. For spheroids, an efficient numerical method is developed, capable of handling cases of large or strongly momentum-dependent surface reflectivity. Application of the method to highly resonant materials, such as aluminum oxide (by itself or covered with graphene), reveals a rich structure of multi-peak spectra and nonmonotonic approach curves, i.e., the probe-sample distance dependence. These features also strongly depend on the probe shape and optical constants of the model. For less resonant materials such as silicon oxide, the dependence is weak, so that the spheroidal model is reliable. The calculations are done within the quasistatic approximation with radiative damping included perturbatively.

  20. Latitudinal variation of spectral optical thickness and columnar size distribution of the El Chichon stratospheric aerosol layer

    NASA Technical Reports Server (NTRS)

    Spinhirne, J. D.; King, M. D.

    1985-01-01

    Measurements are presented for the spectral optical thickness of El Chichon's stratospheric aerosol layer, obtained during an airborne latitudinal survey in April and May of 1983. Columnar aerosol size distributions of the stratosphere are derived by inverting the aerosol optical thickness measurements as a function of wavelength and from spectral aerosol depth measurements obtained during an airborne survey in October and November 1982. Spectral optical thickness data and the derived size distributions from both airborne missions show latitidunal regions with similar characteristics. Airborne solar radiometer measurements are shown to be useful in studies of the latitudinal variations of optical and related particle size characteristics of the stratospheric aerosol layer.

  1. A numerical solution for thermoacoustic convection of fluids in low gravity

    NASA Technical Reports Server (NTRS)

    Spradley, L. W.; Bourgeois, S. V., Jr.; Fan, C.; Grodzka, P. G.

    1973-01-01

    A finite difference numerical technique for solving the differential equations which describe thermal convection of compressible fluids in low gravity are reported. Results of one-dimensional calculations are presented, and comparisons are made to previous solutions. The primary result presented is a one-dimensional radial model of the Apollo 14 heat flow and convection demonstration flight experiment. The numerical calculations show that thermally induced convective motion in a confined fluid can have significant effects on heat transfer in a low gravity environment.

  2. Pressurization and expulsion of cryogenic liquids: Generic requirements for a low gravity experiment

    NASA Technical Reports Server (NTRS)

    Vandresar, Neil T.; Stochl, Robert J.

    1991-01-01

    Requirements are presented for an experiment designed to obtain data for the pressurization and expulsion of a cryogenic supply tank in a low gravity environment. These requirements are of a generic nature and applicable to any cryogenic fluid of interest, condensible or non-condensible pressurants, and various low gravity test platforms such as the Space Shuttle or a free-flyer. Background information, the thermophysical process, preliminary analytical modeling, and experimental requirements are discussed. Key parameters, measurements, hardware requirements, procedures, a test matrix, and data analysis are outlined.

  3. Low-gravity solidification of cast iron and space technology applications

    NASA Technical Reports Server (NTRS)

    Graham, J. A.

    1984-01-01

    Two types of analyses relating to cast iron solidification were conducted. A theoretical analysis using a computer to predict the cooling versus time relationship throughout the test specimen was performed. Tests were also conducted in a ground-based laboratory to generate a cooling time curve for cast iron. In addition, cast iron was cooled through the solidification period on a KC-135 and an F-104 aircraft while these aircraft were going through a period of low gravity. Future subjects for low gravity tests are enumerated.

  4. Experimental study of the use of multiband acousto-optic filters for spectral encoding / decoding the optical signals

    NASA Astrophysics Data System (ADS)

    Proklov, V. V.; Byshevski-Konopko, O. A.; Filatov, A. L.; Lugovskoi, A. V.; Pisarevsky, Yu V.

    2016-08-01

    A prototype of the acousto-optic (AO) decoder of optical signals is created on the base of the multiband AO filter. The joint work of the decoder with the developed previously AO coder has been verified experimentally. The main qualitative and quantitate characteristics of the spectral coding and decoding by Walsh sequences of the industrial LED radiation in the near infrared range are investigated. It is shown, that in the proposed data transmission system realization Signal-to-Interference Ratio (SIR) is not less than 13 dB.

  5. A Simple Optical Model Well Explains Plasmonic-Nanoparticle-Enhanced Spectral Photocurrent in Optically Thin Solar Cells

    NASA Astrophysics Data System (ADS)

    Tanabe, Katsuaki

    2016-05-01

    A simple optical model for photocurrent enhancement by plasmonic metal nanoparticles atop solar cells has been developed. Our model deals with the absorption, reflection, and scattering of incident sunlight as well as radiation efficiencies on metallic nanoparticles. Our calculation results satisfactorily reproduce a series of experimental spectral data for optically thin GaAs solar cells with Ag and Al nanoparticles of various dimensions, demonstrating the validity of our modeling approach. Our model is likely to be a powerful tool for investigations of surface plasmon-enhanced thin-film solar cells.

  6. A Simple Optical Model Well Explains Plasmonic-Nanoparticle-Enhanced Spectral Photocurrent in Optically Thin Solar Cells.

    PubMed

    Tanabe, Katsuaki

    2016-12-01

    A simple optical model for photocurrent enhancement by plasmonic metal nanoparticles atop solar cells has been developed. Our model deals with the absorption, reflection, and scattering of incident sunlight as well as radiation efficiencies on metallic nanoparticles. Our calculation results satisfactorily reproduce a series of experimental spectral data for optically thin GaAs solar cells with Ag and Al nanoparticles of various dimensions, demonstrating the validity of our modeling approach. Our model is likely to be a powerful tool for investigations of surface plasmon-enhanced thin-film solar cells.

  7. Investigation and development of a high spectral resolution coherent optical spectrum analysis system.

    PubMed

    Feng, Kunpeng; Cui, Jiwen; Dang, Hong; Zhao, Shiyuan; Wu, Weidong; Tan, Jiubin

    2016-10-31

    Focusing on high resolution optical spectroscopy, a coherent optical spectrum analysis (COSA) system is investigated in this paper. Principle is built to demonstrate the operation of COSA and its signal processing in both time and frequency domain. According to COSA principle, resolution bandwidth (RBW) filters are found to have significant influence on power accuracy and spectral resolution of the optical spectrum analysis (OSA). Much effort is paid to design RBW filters, including center frequency, bandwidth and type of filters. Two RBW filters are optimized to reduce the power uncertainty of different spectral resolution and satisfy different signal under test. Then, simulations and experiments are conducted to verify COSA principle and results show that the power uncertainty is less than 0.5% and 1.2% for high and medium spectral resolution application, respectively. Finally, experiments on the OSA of actual spectra indicate that COSA system can achieve a 6 MHz spectral resolution and has an excellent capacity in analysis of fine spectrum structures.

  8. Optical spectral evolution of Nova Cygni 1992 = V 1974 Cygni

    NASA Astrophysics Data System (ADS)

    Rafanelli, P.; Rosino, L.; Radovich, M.

    1995-02-01

    We report the results of the optical spectrophotometric observations of N Cyg 1992 = V 1974 Cyg performed at Asiago between 6 and 670 days after its visual maximum (1992 February 22, mv approximately 4.4). On 1992 February 28, during the first decline the spectrum of the nova was characterized by the presence over a strong continuum of wide emission lines of HI (Balmer), FeII, NaI, CaII, flanked by two systems of P Cyg absorptions with mean radial velocities of -1250 and -1900 km/s. The transition phase was reached at the beginning of April with a gradual fading of the lines of lower ionization potential and the emerging of the HeI, NII, NIII lines. P Cygni absorption features with radial velocity higher than in February were still perceptible. The nova entered the nebular stage some weeks later, at the end of April. The presence in the spectrum, besides (OIII) lambda lambda 4959, 5007, of strong forbidden lines of (NeIII) at lambda lambda 3869, 3968, left no doubt of its classification as a 'neon nova' similar to QU Vul. The evolution of the spectrum in the next months was characterized by the progressive growth of the ionization degree. Following the forbidden lines of (NeIII) and (OIII), also those of (NeIV), (FeVI), (FeVII) and (NeV) became outstanding. The highest degree of ionization was attained on 1993 July, about 500 days from visual maximum, when the coronal lines of (FeX), (FeXI), (AX) reached their highest strength. The steadily decline of the degree of ionization began about one-hundred days later, with the rapid disappearance of the coronal lines and the progressive fading of the lines of highest ionization potential. The intensities of the emission lines during the nova evolution are reported. The discussion concerns the determination of: color excess, absolute magnitude and distance (2.8 kpc) of the nova; effective temperature of the contracting photosphere; and abundance in the ejecta of He, O, N, and Ne, relative to H.

  9. Optical system design of multi-spectral and large format color CCD aerial photogrammetric camera

    NASA Astrophysics Data System (ADS)

    Qian, Yixian; Sun, Tianxiang; Gao, Xiaodong; Liang, Wei

    2007-12-01

    Multi-spectrum and high spatial resolution is the vital problem for optical design of aerial photogrammetric camera all the time. It is difficult to obtain an outstanding optical system with high modulation transfer function (MTF) as a result of wide band. At the same time, for acquiring high qualified image, chromatic distortion in optical system must be expected to be controlled below 0.5 pixels; it is a trouble thing because of wide field and multi-spectrum. In this paper, MTF and band of the system are analyzed. A Russar type photogrammetric objective is chosen as the basic optical structure. A novel optical system is presented to solve the problem. The new optical photogrammetric system, which consists of panchromatic optical system and chromatic optical system, is designed. The panchromatic optical system, which can obtain panchromatic image, makes up of a 9k×9k large format CCD and high-accuracy photographic objective len, its focal length is 69.83mm, field angle is 60°×60°, the size of CCD pixels is 8.75um×8.75um, spectral scope is from 0.43um to 0.74um, modulation transfer function is all above 0.4 in whole field when spatial frequency is at 60lp/mm, distortion is less than 0.007%. In a chromatic optical system, three 2k×2k array CCDs combine individually three same photographic objectives, the high resolution chromatic image is acquired by the synthesis of red, green, blue image data information delivered by three CCD sensors. For the chromatic system, their focal length is 24.83mm and they have the same spectral range of 0.39um to 0.74um. A difference is that they are coated in different film on their protect glass. The pixel number is 2048 × 2048; its MTF exceeds 0.4 in full field when spatial frequency is 30lp/mm. The advantages of digital aerial photogrammetric camera comparison with traditional film camera are described. It is considered that the two development trends on digital aerial photogrammetric camera are high-spectral resolution and

  10. Multimodal ophthalmic imaging using swept source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Malone, Joseph D.; El-Haddad, Mohamed T.; Tye, Logan A.; Majeau, Lucas; Godbout, Nicolas; Rollins, Andrew M.; Boudoux, Caroline; Tao, Yuankai K.

    2016-03-01

    Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) benefit clinical diagnostic imaging in ophthalmology by enabling in vivo noninvasive en face and volumetric visualization of retinal structures, respectively. Spectrally encoding methods enable confocal imaging through fiber optics and reduces system complexity. Previous applications in ophthalmic imaging include spectrally encoded confocal scanning laser ophthalmoscopy (SECSLO) and a combined SECSLO-OCT system for image guidance, tracking, and registration. However, spectrally encoded imaging suffers from speckle noise because each spectrally encoded channel is effectively monochromatic. Here, we demonstrate in vivo human retinal imaging using a swept source spectrally encoded scanning laser ophthalmoscope and OCT (SSSESLO- OCT) at 1060 nm. SS-SESLO-OCT uses a shared 100 kHz Axsun swept source, shared scanner and imaging optics, and are detected simultaneously on a shared, dual channel high-speed digitizer. SESLO illumination and detection was performed using the single mode core and multimode inner cladding of a double clad fiber coupler, respectively, to preserve lateral resolution while improving collection efficiency and reducing speckle contrast at the expense of confocality. Concurrent en face SESLO and cross-sectional OCT images were acquired with 1376 x 500 pixels at 200 frames-per-second. Our system design is compact and uses a shared light source, imaging optics, and digitizer, which reduces overall system complexity and ensures inherent co-registration between SESLO and OCT FOVs. En face SESLO images acquired concurrent with OCT cross-sections enables lateral motion tracking and three-dimensional volume registration with broad applications in multivolume OCT averaging, image mosaicking, and intraoperative instrument tracking.

  11. The optical properties of mouse skin in the visible and near infrared spectral regions.

    PubMed

    Sabino, Caetano P; Deana, Alessandro M; Yoshimura, Tania M; da Silva, Daniela F T; França, Cristiane M; Hamblin, Michael R; Ribeiro, Martha S

    2016-07-01

    Visible and near-infrared radiation is now widely employed in health science and technology. Pre-clinical trials are still essential to allow appropriate translation of optical methods into clinical practice. Our results stress the importance of considering the mouse strain and gender when planning pre-clinical experiments that depend on light-skin interactions. Here, we evaluated the optical properties of depilated albino and pigmented mouse skin using reproducible methods to determine parameters that have wide applicability in biomedical optics. Light penetration depth (δ), absorption (μa), reduced scattering (μ's) and reduced attenuation (μ't) coefficients were calculated using the Kubelka-Munk model of photon transport and spectrophotometric measurements. Within a broad wavelength coverage (400-1400nm), the main optical tissue interactions of visible and near infrared radiation could be inferred. Histological analysis was performed to correlate the findings with tissue composition and structure. Disperse melanin granules present in depilated pigmented mouse skin were shown to be irrelevant for light absorption. Gender mostly affected optical properties in the visible range due to variations in blood and abundance of dense connective tissue. On the other hand, mouse strains could produce more variations in the hydration level of skin, leading to changes in absorption in the infrared spectral region. A spectral region of minimal light attenuation, commonly referred as the "optical window", was observed between 600 and 1350nm.

  12. Arbitrary phase modulation for optical spectral control and suppression of stimulated Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Harish, Achar V.; Nilsson, Johan

    2015-05-01

    We investigate the use of external phase modulation to broaden the linewidth of a laser source. We use nonlinear optimization to find phase modulations that create nearly tophat-shaped discrete spectra and thus the highest total power within a limited linewidth and a limited peak spectral power density. Such phase modulations and spectra can be realized with an arbitrary waveform generator (AWG) and are attractive for suppressing stimulated Brillouin scattering in optical fiber. Compared to alternative modulation approaches, the AWG benefits from a large number of degrees of freedom and well-controlled spectral phase in the AWG output.

  13. Spectral triangulation molecular contrast optical coherence tomography with indocyanine green as the contrast agent

    PubMed Central

    Yang, Changhuei; McGuckin, Laura E. L.; Simon, John D.; Choma, Michael A.; Applegate, Brian E.; Izatt, Joseph A.

    2005-01-01

    We report a new molecular contrast optical coherence tomography (MCOCT) implementation that profiles the contrast agent distribution in a sample by measuring the agent’s spectral differential absorption. The method, spectra triangulation MCOCT, can effectively suppress contributions from spectrally dependent scatterings from the sample without a priori knowledge of the scattering properties. We demonstrate molecular imaging with this new MCOCT modality by mapping the distribution of indocyanine green, a FDA-approved infrared red dye, within a stage 54 Xenopus laevis. PMID:15455765

  14. Harmonic spectral modulation of an optical frequency comb to control the ultracold molecules formation

    NASA Astrophysics Data System (ADS)

    Malinovskaya, Svetlana A.; Liu, Gengyuan

    2016-11-01

    A method for creation of ultracold molecules by stepwise adiabatic passage from the Feshbach state to the fundamentally ground state using an optical frequency comb is presented within a semiclassical multilevel model. The sine modulation of the spectral phase of the comb leads to the creation of a quasi-dark dressed state. An insignificant population of the excited state manifold in this dark state provides an efficient way of mitigating decoherence in the system. In contrast, the cosine modulation does not lead to the quasi-dark state formation. The results demonstrate the importance of the parity of the spectral chirp in quantum control.

  15. Spectral fluorescence and scattering of cyanobacteria and diatoms held by optical tweezers

    NASA Astrophysics Data System (ADS)

    Sonek, Gregory J.; Liu, Yagang; Iturriaga, Rodolfo H.

    1994-10-01

    Optical tweezers is a term used to describe the optical force generation and confinement process by a highly focused laser beam. The forces exerted by the tweezer are sufficient to confine and move cells and particles without physical contact. When integrated with fluorescence or scattering detection, the laser tweezer can become a powerful instrument for the rapid characterization of the optical properties of isolated organic marine particulates and phytoplanktonic cells, from which bulk properties may be inferred. This technique offers the advantage of studying planktonic cells and organisms in their natural environment by confinement without immobilization, thereby preserving the spectral absorption and fluorescence properties of the samples under study. Herein, we report, for the first time, on the measurement of the spectral fluorescence and scattering of cyanobacteria and diatoms which have been confined by an optical tweezer. Preliminary data shows the characteristic emission peak from the chlorophyll (alpha) pigment (685 nm) for both samples, as well as spectral features that may be related to other photosynthetic pigments.

  16. A Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRBs?

    NASA Astrophysics Data System (ADS)

    Stamatikos, Michael; Ukwatta, Tilan N.; Sakamoto, Taka; Dhuga, Kalvir S.

    2008-10-01

    We report on observations of correlated behavior between the prompt γ-ray and optical emission from GRB 080319B, which (i) strongly suggest that they occurred within the same astrophysical source region and (ii) indicate that their respective radiation mechanisms were most likely dynamically coupled. Our preliminary results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt γ-ray photon counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic γ-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15-350 keV γ-rays and the optical emission observed by TORTORA (extrinsic γ-ray/optical lag), thus effectively partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, prompt optical emission is nested within intervals of both (a) trivial intrinsic γ-ray spectral lag (~T+12+/-2 and ~T+50+/-2 sec) with (b) discontinuities in the hard to soft evolution of the photon index for a power law fit to 15-150 keV Swift-BAT data (~T+8+/-2 and ~T+48+/-1 sec), both of which coincide with the rise (~T+10+/-1 sec) and decline (~T+50+/-1 sec) of prompt optical emission. This potential discovery, robust across heuristic permutations of BAT energy channels and varying temporal bin resolution, provides the first observational evidence for an implicit connection between spectral lag and the dynamics of shocks in the context of canonical fireball phenomenology.

  17. Comparative spectral analysis between the functionality of the human eye and of the optical part of a digital camera

    NASA Astrophysics Data System (ADS)

    Toadere, Florin

    2015-02-01

    A software that comparatively analysis the spectral functionality of the optical part of the human eye and of the optical image acquisition system of the digital camera, is presented. Comparisons are done using demonstrative images which present the spectral color transformations of an image that is considered the test object. To perform the simulations are presented the spectral models and are computed their effects on the colors of the spectral image, during the propagation of the D48 sun light through the eye and the optics of the digital camera. The simulations are made using a spectral image processing algorithm which converts the spectral image into XYZ color space, CIE CAM02 color appearance model and then into RGB color space.

  18. Pool film boiling experiments on a wire in low gravity: preliminary results.

    PubMed

    Di Marco, P; Grassi, W; Trentavizi, F

    2002-10-01

    This paper reports preliminary results for pool film boiling on a wire immersed in almost saturated FC72 recently obtained during an experimental campaign performed in low gravity on the European Space Agency Zero-G airplane, (reduced gravity level 10(-2)). This is part of a long-term research program on the effect of gravitational and electric forces on boiling. The reported data set refers to experiments performed under the following conditions: (1) Earth gravity without electric field, (2) Earth gravity with electric field, (3) low gravity without electric field, and (4) low gravity with electric field. Although a decrease of gravity causes a heat transfer degradation, the electric field markedly improves heat exchange. This improvement is so effective that, beyond a certain field value, the heat flux is no longer sensitive to gravity. Two main film boiling regimes have been identified, both in normal and in low gravity: one is affected by the electric field and the other is practically insensitive to the field influence.

  19. Effect of low gravity on calcium metabolism and bone formation (L-7)

    NASA Technical Reports Server (NTRS)

    Suda, Tatsuo

    1993-01-01

    Recently, attention has been focused on the disorders of bone and calcium metabolism during space flight. The skeletal system has evolved on the Earth under 1-g. Space flights under low gravity appear to cause substantial changes in bone and calcium homeostasis of the animals adapted to 1-g. A space experiment for the First Materials Processing Test (FMPT) was proposed to examine the effects of low gravity on calcium metabolism and bone formation using chick embryos loaded in a space shuttle. This space experiment was proposed based on the following two experimental findings. First, it has been reported that bone density decreases significantly during prolonged space flight. The data obtained from the US Skylab and the U.S.S.R. Salyut-6 cosmonauts have also documented that the degree of bone loss is related to the duration of space flight. Second, the US-Soviet joints space experiment demonstrated that the decrease in bone density under low gravity appears to be due to the decrease in bone formation rather than the increase in bone resorption. The purpose of our space experiment is, therefore, to investigate further the mechanisms of bone growth under low gravity using fertilized chick embryos.

  20. Predictive simulation of gait at low gravity reveals skipping as the preferred locomotion strategy.

    PubMed

    Ackermann, Marko; van den Bogert, Antonie J

    2012-04-30

    The investigation of gait strategies at low gravity environments gained momentum recently as manned missions to the Moon and to Mars are reconsidered. Although reports by astronauts of the Apollo missions indicate alternative gait strategies might be favored on the Moon, computational simulations and experimental investigations have been almost exclusively limited to the study of either walking or running, the locomotion modes preferred under Earth's gravity. In order to investigate the gait strategies likely to be favored at low gravity a series of predictive, computational simulations of gait are performed using a physiological model of the musculoskeletal system, without assuming any particular type of gait. A computationally efficient optimization strategy is utilized allowing for multiple simulations. The results reveal skipping as more efficient and less fatiguing than walking or running and suggest the existence of a walk-skip rather than a walk-run transition at low gravity. The results are expected to serve as a background to the design of experimental investigations of gait under simulated low gravity.

  1. Advantages of ice crystal growth experiments in a low gravity environment

    NASA Technical Reports Server (NTRS)

    Anderson, B. J.; Keller, V. W.; Hallett, J.

    1979-01-01

    The effects of convective fluid motions and mechanical supports on ice crystal growth in experiments conducted on earth can be inferred from studies conducted in their absence in a low-gravity environment. Current experimental results indicate the effects may be significant.

  2. Secondary arm coarsening and microsegregation in superalloy PWA-1480 single crystals: Effect of low gravity

    NASA Technical Reports Server (NTRS)

    Vijayakumar, M.; Tewari, S. N.; Lee, J. E.; Curreri, P. A.

    1990-01-01

    Single crystal specimens of nickel base superalloy PWA-1480 were directionally solidified on ground and during low gravity (20 sec) and high gravity (90 sec) parabolic maneuver of KC-135 aircraft. Thermal profiles were measured during solidification by two in-situ thermocouples positioned along the sample length. The samples were quenched during either high or low gravity cycles so as to freeze the structures of the mushy zone developing under different gravity levels. Microsegregation was measured by examining the solutal profiles on several transverse cross-sections across primary dendrites along their length in the quenched mushy zone. Effect of gravity level on secondary arm coarsening kinetics and microsegregation have been investigated. The results indicate that there is no appreciable difference in the microsegregation and coarsening kinetics behavior in the specimens grown under high or low gravity. This suggests that short duration changes in gravity/levels (0.02 to 1.7 g) do not influence convection in the interdendritic region. Examination of the role of natural convection, in the melt near the primary dendrite tips, on secondary arm spacings requires low gravity periods longer than presently available on KC-135. Secondary arm coarsening kinetics show a reasonable fit with the predictions from a simple analytical model proposed by Kirkwood for a binary alloy.

  3. A joint estimation detection of Glaucoma progression in 3D spectral domain optical coherence tomography optic nerve head images.

    PubMed

    Belghith, Akram; Bowd, Christopher; Weinreb, Robert N; Zangwill, Linda M

    2014-03-18

    Glaucoma is an ocular disease characterized by distinctive changes in the optic nerve head (ONH) and visual field. Glaucoma can strike without symptoms and causes blindness if it remains without treatment. Therefore, early disease detection is important so that treatment can be initiated and blindness prevented. In this context, important advances in technology for non-invasive imaging of the eye have been made providing quantitative tools to measure structural changes in ONH topography, an essential element for glaucoma detection and monitoring. 3D spectral domain optical coherence tomography (SD-OCT), an optical imaging technique, has been commonly used to discriminate glaucomatous from healthy subjects. In this paper, we present a new framework for detection of glaucoma progression using 3D SD-OCT images. In contrast to previous works that the retinal nerve fiber layer (RNFL) thickness measurement provided by commercially available spectral-domain optical coherence tomograph, we consider the whole 3D volume for change detection. To integrate a priori knowledge and in particular the spatial voxel dependency in the change detection map, we propose the use of the Markov Random Field to handle a such dependency. To accommodate the presence of false positive detection, the estimated change detection map is then used to classify a 3D SDOCT image into the "non-progressing" and "progressing" glaucoma classes, based on a fuzzy logic classifier. We compared the diagnostic performance of the proposed framework to existing methods of progression detection.

  4. A joint estimation detection of Glaucoma progression in 3D spectral domain optical coherence tomography optic nerve head images

    PubMed Central

    Belghith, Akram; Bowd, Christopher; Weinreb, Robert N.; Zangwill, Linda M.

    2014-01-01

    Glaucoma is an ocular disease characterized by distinctive changes in the optic nerve head (ONH) and visual field. Glaucoma can strike without symptoms and causes blindness if it remains without treatment. Therefore, early disease detection is important so that treatment can be initiated and blindness prevented. In this context, important advances in technology for non-invasive imaging of the eye have been made providing quantitative tools to measure structural changes in ONH topography, an essential element for glaucoma detection and monitoring. 3D spectral domain optical coherence tomography (SD-OCT), an optical imaging technique, has been commonly used to discriminate glaucomatous from healthy subjects. In this paper, we present a new framework for detection of glaucoma progression using 3D SD-OCT images. In contrast to previous works that the retinal nerve fiber layer (RNFL) thickness measurement provided by commercially available spectral-domain optical coherence tomograph, we consider the whole 3D volume for change detection. To integrate a priori knowledge and in particular the spatial voxel dependency in the change detection map, we propose the use of the Markov Random Field to handle a such dependency. To accommodate the presence of false positive detection, the estimated change detection map is then used to classify a 3D SDOCT image into the “non-progressing” and “progressing” glaucoma classes, based on a fuzzy logic classifier. We compared the diagnostic performance of the proposed framework to existing methods of progression detection. PMID:25606299

  5. A joint estimation detection of Glaucoma progression in 3D spectral domain optical coherence tomography optic nerve head images

    NASA Astrophysics Data System (ADS)

    Belghith, Akram; Bowd, Christopher; Weinreb, Robert N.; Zangwill, Linda M.

    2014-03-01

    Glaucoma is an ocular disease characterized by distinctive changes in the optic nerve head (ONH) and visual field. Glaucoma can strike without symptoms and causes blindness if it remains without treatment. Therefore, early disease detection is important so that treatment can be initiated and blindness prevented. In this context, important advances in technology for non-invasive imaging of the eye have been made providing quantitative tools to measure structural changes in ONH topography, an essential element for glaucoma detection and monitoring. 3D spectral domain optical coherence tomography (SD-OCT), an optical imaging technique, has been commonly used to discriminate glaucomatous from healthy subjects. In this paper, we present a new framework for detection of glaucoma progression using 3D SD-OCT images. In contrast to previous works that the retinal nerve fiber layer (RNFL) thickness measurement provided by commercially available spectral-domain optical coherence tomograph, we consider the whole 3D volume for change detection. To integrate a priori knowledge and in particular the spatial voxel dependency in the change detection map, we propose the use of the Markov Random Field to handle a such dependency. To accommodate the presence of false positive detection, the estimated change detection map is then used to classify a 3D SDOCT image into the "non-progressing" and "progressing" glaucoma classes, based on a fuzzy logic classifier. We compared the diagnostic performance of the proposed framework to existing methods of progression detection.

  6. Real-time and static in vivo ophthalmic imaging by spectral optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wojtkowski, Maciej; Bajraszewski, Tomasz; Targowski, Piotr; Kowalczyk, Andrzej

    2004-07-01

    Fast Spectral Optical Coherence Tomography (SOCT) technique is used to perform cross sectional and three-dimensional ophthalmic images. Static, real-time and 3-D in vivo images of the human cornea, lens, iris, corneo-scleral junction, retinal layers, optic disc and macula lutea are presented. The ophthalmic application of SOCT is promising because this technique ensures fast acquisition with relatively low optical power of incident light. All demonstrated images are obtained with the aid of SOCT instrument, which was constructed in the optical laboratory of medical physics group at Nicolaus Copernicus University (Torun, Poland). What is to our knowledge there are the first good quality (>90dB sensitivity) ophthalmic OCT images obtained by technique, which is different than time domain OCT.

  7. Polarization maintaining fiber based ultra-high resolution spectral domain polarization sensitive optical coherence tomography

    PubMed Central

    2010-01-01

    We present a new ultra high resolution spectral domain polarization sensitive optical coherence tomography (PS-OCT) system based on polarization maintaining (PM) fibers. The method transfers the principles of our previous bulk optic PS-OCT systems to a fiberized setup. The phase shift between the orthogonal polarization states travelling in the two orthogonal modes of the PM fiber is compensated by software in post processing. Thereby, the main advantage of our bulk optics setups, i.e. the use of only a single input polarization state to simultaneously acquire reflectivity, retardation, optic axis orientation, and Stokes vector, is maintained. The use of a broadband light source of 110 nm bandwidth provides improved depth resolution and smaller speckle size. The latter is important for improved resolution of depolarization imaging. We demonstrate our instrument for high-resolution PS-OCT imaging of the healthy human retina. PMID:20052196

  8. Modeling the spectral optical properties of ammonium sulfate and biomass burning aerosols

    SciTech Connect

    Grant, K.E.; Chuang, C.C.; Grossman, A.S.; Penner, J.E.

    1997-09-01

    The importance of including the global and regional radiative effects of aerosols in climate models has increasingly been realized. Accurate modeling of solar radiative forcing due to aerosols from anthropogenic sulfate and biomass burning emissions requires adequate spectral resolution and treatment of spatial and temporal variability. The variation of aerosol spectral optical properties with local relative humidity and dry aerosol composition must be considered. Because the cost of directly including Mie calculations within a climate model is prohibitive, parameterizations from offline calculations must be used. Starting from a log-normal size distribution of dry ammonium sulfate, we developed optical properties for tropospheric sulfate aerosol at 15 relative humidities up to 99 percent. The resulting aerosol size distributions were then used to calculate bulk optical properties at wavelengths between 0.175 {micro}m and 4 {micro}m. Finally, functional fits of optical properties were made for each of 12 wavelength bands as a function of relative humidity. Significant variations in optical properties occurred across the total solar spectrum. Relative increases in specific extinction and asymmetry factor with increasing relative humidity became larger at longer wavelengths. Significant variation in single-scattering albedo was found only in the longest near-IR band. This is also the band with the lowest albedo. A similar treatment was done for aerosols from biomass burning. In this case, size distributions were taken as having two carbonaceous size modes and a larger dust mode. The two carbonaceous modes were considered to be humidity dependent. Equilibrium size distributions and compositions were calculated for 15 relative humidities and five black carbon fractions. Mie calculations and Chandrasekhar averages of optical properties were done for each of the resulting 75 cases. Finally, fits were made for each of 12 spectral bands as functions of relative humidity

  9. Spectral evolution of soft x-ray emission from optically thin, high electron temperature platinum plasmas

    NASA Astrophysics Data System (ADS)

    Hara, Hiroyuki; Ohashi, Hayato; Li, Bowen; Dunne, Padraig; O'Sullivan, Gerry; Sasaki, Akira; Suzuki, Chihiro; Tamura, Naoki; Sakaue, Hiroyuki A.; Kato, Daiji; Murakami, Izumi; Higashiguchi, Takeshi; LHD Experiment Group

    2017-08-01

    The soft x-ray spectra of heavy element plasmas are frequently dominated by unresolved transition array (UTA) emission. We describe the spectral evolution of an intense UTA under optically thin conditions in platinum plasmas. The UTA was observed to have a peak wavelength around 4.6 nm at line-of-sight averaged electron temperatures less than 1.4 keV at electron densities of (2.5-7.5) × 1013 cm-3. The UTA spectral structure was due to emission from 4d-4f transitions in highly charged ions with average charge states of q = 20-40. A numerical simulation successfully reproduced the observed spectral behavior.

  10. Spectral Talbot phenomena of frequency combs induced by cross-phase modulation in optical fibers.

    PubMed

    Azaña, José

    2005-02-01

    Cross-phase modulation (XPM) of a frequency comb (finite-duration optical pulse sequence) by an intense, long Gaussian pump pulse is theoretically investigated, and new effects, namely, frequency-domain self-imaging phenomena (integer and fractional Talbot effects), are reported. The conditions favorable for observing spectral self-imaging phenomena by XPM are derived and numerically confirmed. The effects of nonidealities in a practical experiment (e.g., group-delay walk-off and dispersion) are also evaluated. One can use spectral self-imaging to tune the free spectral range of a frequency comb (without affecting the shape and bandwidth of the individual passbands) simply by adjusting the pump power in a fiber XPM scheme.

  11. Focusing and spectral characteristics of periodic diffractive optical elements with circular symmetry under femtosecond pulsed illumination.

    PubMed

    Mendoza-Yero, Omel; Mínguez-Vega, Gladys; Lancis, Jesús; Climent, Vicent

    2007-11-01

    The analytical solution is derived, within the Rayleigh-Sommerfeld formulation of diffraction, for the on-axis spectral irradiance of a broadband source after diffracting through a circular symmetric hard aperture. By using this solution, and within the paraxial approximation, we investigate several diffraction-induced effects originated by binary diffractive optical elements made up of a set of annular apertures with equal areas and periodic in the squared radial coordinate. In particular, the ability to focus femtosecond pulses is investigated. In addition, the analysis of the spectral modifier function associated with these elements allows us to simulate spectral shifts at focus positions. Finally, we introduce a relatively simple and low-cost technique to slice the spectrum of a broadband source in order to generate narrow bands or wavelength channels.

  12. Improving image quality in intensity-interferometric spectral-domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Shirai, Tomohiro

    2016-07-01

    Intensity-interferometric spectral-domain optical coherence tomography (I-SD-OCT), devised recently as a classical analog of quantum OCT, enables axially scanless cross-sectional imaging with an immunity to group-velocity dispersion and a factor-of-\\sqrt{2} resolution improvement. However, unwanted artifacts inevitably emerge in the resultant image. In this paper, it is demonstrated theoretically and experimentally that such artifacts can be reduced without any difficulty by means of either a mechanical displacement of the detector for capturing spectral intensity patterns or a numerical displacement of the spectral intensity patterns stored in a computer. Furthermore, it is proved that the I-SD-OCT signal can be extracted from the conventional SD-OCT setup under a certain condition. These two features serve to improve the image quality in I-SD-OCT.

  13. Super-Nyquist shaping and processing technologies for high-spectral-efficiency optical systems

    NASA Astrophysics Data System (ADS)

    Jia, Zhensheng; Chien, Hung-Chang; Zhang, Junwen; Dong, Ze; Cai, Yi; Yu, Jianjun

    2013-12-01

    The implementations of super-Nyquist pulse generation, both in a digital field using a digital-to-analog converter (DAC) or an optical filter at transmitter side, are introduced. Three corresponding signal processing algorithms at receiver are presented and compared for high spectral-efficiency (SE) optical systems employing the spectral prefiltering. Those algorithms are designed for the mitigation towards inter-symbol-interference (ISI) and inter-channel-interference (ICI) impairments by the bandwidth constraint, including 1-tap constant modulus algorithm (CMA) and 3-tap maximum likelihood sequence estimation (MLSE), regular CMA and digital filter with 2-tap MLSE, and constant multi-modulus algorithm (CMMA) with 2-tap MLSE. The principles and prefiltering tolerance are given through numerical and experimental results.

  14. Persistent Spectral Hole Burning Materials for Time-and- Frequency-Domain Optical Memories and Signal Processing

    DTIC Science & Technology

    2007-11-02

    spectral hole burning, optical material, rare earth , photon echo, optical correlator, laser, optical, spectroscopy, coherent transient 17. SECURITY...that determine material performance, emphasizing parameters relevant to device development. Attention was focused on rare earth and transition metal...Er3+ ions and optimized their hole burning and coherent transient properties. Crystal composition and rare earth ion concentration were tailored to

  15. Direct optical imaging of graphene in vitro by nonlinear femtosecond laser spectral reshaping.

    PubMed

    Li, Baolei; Cheng, Yingwen; Liu, Jie; Yi, Congwen; Brown, April S; Yuan, Hsiangkuo; Vo-Dinh, Tuan; Fischer, Martin C; Warren, Warren S

    2012-11-14

    Nonlinear optical microscopy, based on femtosecond laser spectral reshaping, characterized and imaged graphene samples made from different methods, both on slides and in a biological environment. This technique clearly discriminates between graphene flakes with different numbers of layers and reveals the distinct nonlinear optical properties of reduced graphene oxide as compared to mechanically exfoliated or chemical vapor deposition grown graphene. The nonlinearity makes it applicable to scattering samples (such as tissue) as opposed to previous methods, such as transmission. This was demonstrated by high-resolution imaging of breast cancer cells incubated with graphene flakes.

  16. Leaf Optical Properties in Higher Plants: Linking Spectral Characteristics with Plant Stress

    NASA Technical Reports Server (NTRS)

    Carter, Gregory A.; Knapp, Alan K.

    1999-01-01

    A number of studies have addressed responses of leaf spectral reflectance, transmittance, or absorptance to physiological stress. Stressors included dehydration, ozone, herbicides, disease, insufficient mycorrhizae and N fertilization, flooding and insects. Species included conifers, grasses, and broadleaved trees. Increased reflectance with maximum responses near 700 nm wavelength occurred in all cases. Varying the chlorophyll content in leaves or pigment extracts can simulate this effect. Thus, common optical responses to stress result from decreases in leaf chlorophyll contents or the capacity of chloroplasts to absorb light. Leaf optic can be quite sensitive to any stressor that alters soil-plant-atmosphere processes.

  17. Spectrally-efficient all-optical OFDM by WSS and AWG.

    PubMed

    Hoxha, J; Morosi, J; Shimizu, S; Martelli, P; Boffi, P; Wada, N; Cincotti, G

    2015-05-04

    We report on the transmission experiment of seven 12.5-GHz spaced all optical-orthogonal frequency division multiplexed (AO-OFDM) subcarriers over a 35-km fiber link, using differential quadrature phase shift keying (DQPSK) modulation and direct detection. The system does not require chromatic dispersion compensation, optical time gating at the receiver (RX) or cyclic prefix (CP), achieving the maximum spectral efficiency. We use a wavelength selective switch (WSS) at the transmitter (TX) to allow subcarrier assignment flexibility and optimal filter shaping; an arrayed waveguide grating (AWG) AO-OFDM demultiplexer is used at the RX, to reduce the system cost and complexity.

  18. Dual illumination for cornea and retina imaging using spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Shirazi, Muhammad Faizan; Wijesinghe, Ruchire Eranga; Ravichandran, Naresh Kumar; Jeon, Mansik; Kim, Jeehyun

    2017-04-01

    A dual illumination system is proposed for cornea and retina imaging using spectral domain optical coherence tomography (SD-OCT). The system is designed to acquire cornea and retina imaging with dual illumination with limited optics and using a single spectrometer. The beam propagation for cornea and retina imaging in dual illumination enables to acquire the images of different segments. This approach will reduce the imaging time for separate corneal and retinal imaging. The in vivo imaging of both the cornea and retina of a health volunteer shows the feasibility of the system for clinical applications

  19. Human tissue color as viewed in high dynamic range optical spectral transmission measurements.

    PubMed

    Petrov, Georgi I; Doronin, Alexander; Whelan, Harry T; Meglinski, Igor; Yakovlev, Vladislav V

    2012-09-01

    High dynamic range optical-to-near-infrared transmission measurements for different parts of human body in the spectral range from 650 to 950 nm have been performed. Experimentally measured spectra are correlated with Monte Carlo simulations using chromaticity coordinates in CIE 1976 L*a*b* color space. Both a qualitative and a quantitative agreement have been found, paving a new way of characterizing human tissues in vivo. The newly developed experimental and computational platform for assessing tissue transmission spectra is anticipated to have a considerable impact on identifying favorable conditions for laser surgery and optical diagnostics, while providing supplementary information about tissue properties.

  20. A spectral collocation method for a rotating Bose-Einstein condensation in optical lattices

    NASA Astrophysics Data System (ADS)

    Li, Z.-C.; Chen, S.-Y.; Chien, C.-S.; Chen, H.-S.

    2011-06-01

    We extend the study of spectral collocation methods (SCM) in Li et al. (2009) [1] for semilinear elliptic eigenvalue problems to that for a rotating Bose-Einstein condensation (BEC) and a rotating BEC in optical lattices. We apply the Lagrange interpolants using the Legendre-Gauss-Lobatto points to derive error bounds for the SCM. The optimal error bounds are derived for both H-norm and L-norm. Extensive numerical experiments on a rotating Bose-Einstein condensation and a rotating BEC in optical lattices are reported. Our numerical results show that the convergence rate of the SCM is exponential, and is independent of the collocation points we choose.

  1. Photothermal spectral-domain optical coherence reflectometry for direct measurement of hemoglobin concentration of erythrocytes.

    PubMed

    Yim, Jinyeong; Kim, Hun; Ryu, Suho; Song, Sungwook; Kim, Hyun Ok; Hyun, Kyung-A; Jung, Hyo-Il; Joo, Chulmin

    2014-07-15

    A novel optical detection method for hemoglobin concentration is described. The hemoglobin molecules consisting mainly of iron generate heat upon their absorption of light energy at 532 nm, which subsequently changes the refractive index of the blood. We exploit this photothermal effect to determine the hemoglobin concentration of erythrocytes without any preprocessing of blood. Highly sensitive measurement of refractive index alteration of blood samples is enabled by a spectral-domain low coherence reflectometric sensor with subnanometer-level optical path-length sensitivity. The performance and validity of the sensor are presented by comparing the measured results against the reference data acquired from an automatic hematology analyzer.

  2. Spectral optical constants of ethanol and isopropanol from ultraviolet to far infrared

    NASA Astrophysics Data System (ADS)

    Sani, Elisa; Dell'Oro, Aldo

    2016-10-01

    Ethanol and isopropanol are fluids of common use in different branches of materials science. In particular, in the ever growing field of nanoscience, they are dispersing media for nanoparticle suspensions. The knowledge of optical constants of these fluids is required for the characterization of optical properties of nanoparticles, besides providing insights into fundamental properties of fluids themselves. In this work, we calculated the real refractive index n of ethanol and isopropanol applying the Kramers-Kronig theory to the experimentally obtained k spectrum over an extremely wide spectral range, from 181 to ∼ 54000 cm-1.

  3. Leaf Optical Properties in Higher Plants: Linking Spectral Characteristics with Plant Stress

    NASA Technical Reports Server (NTRS)

    Carter, Gregory A.; Knapp, Alan K.

    1999-01-01

    A number of studies have addressed responses of leaf spectral reflectance, transmittance, or absorptance to physiological stress. Stressors included dehydration, ozone, herbicides, disease, insufficient mycorrhizae and N fertilization, flooding and insects. Species included conifers, grasses, and broadleaved trees. Increased reflectance with maximum responses near 700 nm wavelength occurred in all cases. Varying the chlorophyll content in leaves or pigment extracts can simulate this effect. Thus, common optical responses to stress result from decreases in leaf chlorophyll contents or the capacity of chloroplasts to absorb light. Leaf optic can be quite sensitive to any stressor that alters soil-plant-atmosphere processes.

  4. Intrinsic temperature-dependent evolutions in the electron-boson spectral density obtained from optical data.

    PubMed

    Hwang, Jungseek

    2016-03-31

    We investigate temperature smearing effects on the electron-boson spectral density function (I(2)χ(ω)) obtained from optical data using a maximum entropy inversion method. We start with two simple model input I(2)χ(ω), calculate the optical scattering rates at selected temperatures using the model input spectral density functions and a generalized Allen's formula, then extract back I(2)χ(ω) at each temperature from the calculated optical scattering rate using the maximum entropy method (MEM) which has been used for analysis of optical data of high-temperature superconductors including cuprates, and finally compare the resulting I(2)χ(ω) with the input ones. From this approach we find that the inversion process can recover the input I(2)χ(ω) almost perfectly when the quality of fits is good enough and also temperature smearing (or thermal broadening) effects appear in the I(2)χ(ω) when the quality of fits is not good enough. We found that the coupling constant and the logarithmically averaged frequency are robust to the temperature smearing effects and/or the quality of fits. We use these robust properties of the two quantities as criterions to check whether experimental data have intrinsic temperature-dependent evolutions or not. We carefully apply the MEM to two material systems (one optimally doped and the other underdoped cuprates) and conclude that the I(2)χ(ω) extracted from the optical data contain intrinsic temperature-dependent evolutions.

  5. New measurement technique for dispersion characterizing optical fibers using low-coherence spectral interferometry with a Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    1999-08-01

    Low-coherence spectral interferometry with channelled spectrum detection, extensively used for dispersion characterizing optical fibers, utilizes the fact that the spectral interference between two modes of an optical fiber shows up at its output as a periodic modulation of the source spectrum with the period dependent on the group optical path difference (OPD) between modes. However, this measurement technique cannot be used to measure intermodal dispersion in the optical fiber for which the period of modulation is too small to be resolved by a spectrometer. We proposed and realized a new measurement technique utilizing a tandem configuration of a dispersive Michelson interferometer and the two-mode optical fiber in which the intermodal spectral interference can be resolved even if a low-resolution spectrometer is used. In the tandem configuration of the dispersive Michelson interferometer and the two-mode optical fiber, the OPD in the Michelson interferometer is adjusted close to the group OPD between modes of the optical fiber so that the low-frequency spectral modulation that can be processed is produced. Using the Fourier transform method in processing the measured spectral modulations and subtracting the effect of the dispersive Michelson interferometer, the intermodal dispersion of the two-mode optical fiber over a limited spectral region has been obtained.

  6. Optical and X-ray radiation from fast pulsars - Effects of duty cycle and spectral shape

    NASA Technical Reports Server (NTRS)

    Pacini, F.; Salvati, M.

    1987-01-01

    The optical luminosity of PSR 0540 is considerably stronger than what one would have predicted in a simple model developed earlier where the pulses are synchrotron radiation by secondary electrons near the light cylinder. This discrepancy can be eliminated if one incorporates into the model the effects of the large duty cycle and the spectral properties of PSR 0540. It is also shown that the same model can provide a reasonable fit to the observed X-ray fluxes from fast pulsars.

  7. Towards using spectral domain optical coherence tomography for dental wear monitoring

    NASA Astrophysics Data System (ADS)

    Mǎrcǎuteanu, Corina; Bradu, Adrian; Sinescu, Cosmin; Topalǎ, Florin I.; Negrutiu, Meda Lavinia; Podoleanu, Adrian G.

    2014-03-01

    In this paper we demonstrate that fast spectral domain optical coherence tomography imaging systems have the potential to monitor the evolution of pathological dental wear. On 10 caries free teeth, four levels of artificially defects similar to those observed in the clinic were created. After every level of induced defect, OCT scanning was performed. B-scans were acquired and 3D reconstructions were generated.

  8. Optical properties of human colon tissues in the 350 – 2500 nm spectral range

    SciTech Connect

    Bashkatov, A N; Genina, E A; Kochubey, V I; Kolesnikova, E A; Tuchin, V V; Rubtsov, V S

    2014-08-31

    We present the optical characteristics of the mucosa and submucosa of human colon tissue. The experiments are performed in vitro using a LAMBDA 950 spectrophotometer in the 350 – 2500 nm spectral range. The absorption and scattering coefficients and the scattering anisotropy factor are calculated based on the measured diffuse reflectance and total and collimated transmittance spectra using the inverse Monte Carlo method. (laser biophotonics)

  9. Analysis of multimode fiber bundles for endoscopic spectral-domain optical coherence tomography

    PubMed Central

    Risi, Matthew D.; Makhlouf, Houssine; Rouse, Andrew R.; Gmitro, Arthur F.

    2016-01-01

    A theoretical analysis of the use of a fiber bundle in spectral-domain optical coherence tomography (OCT) systems is presented. The fiber bundle enables a flexible endoscopic design and provides fast, parallelized acquisition of the OCT data. However, the multimode characteristic of the fibers in the fiber bundle affects the depth sensitivity of the imaging system. A description of light interference in a multimode fiber is presented along with numerical simulations and experimental studies to illustrate the theoretical analysis. PMID:25967012

  10. Optical Sensing of Ecosystem Carbon Fluxes Combining Spectral Reflectance Indices with Solar Induced Fluorescence

    NASA Astrophysics Data System (ADS)

    Huemmrich, K. F.; Middleton, E.; Corp, L. A.; Campbell, P. K.; Kustas, W. P.

    2014-12-01

    Optical sampling of spectral reflectance and solar induced fluorescence provide information on the physiological status of vegetation that can be used to infer stress responses and estimates of production. Multiple repeated observations are required to observe the effects of changing environmental conditions on vegetation. This study examines the use of optical signals to determine inputs to a light use efficiency (LUE) model describing productivity of a cornfield where repeated observations of carbon flux, spectral reflectance and fluorescence were collected. Data were collected at the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) fields (39.03°N, 76.85°W) at USDA Beltsville Agricultural Research Center. Agricultural Research Service researchers measured CO2 fluxes using eddy covariance methods throughout the growing season. Optical measurements were made from the nearby tower supporting the NASA FUSION sensors. The sensor system consists of two dual channel, upward and downward looking, spectrometers used to simultaneously collect high spectral resolution measurements of reflected and fluoresced light from vegetation canopies. Estimates of chlorophyll fluorescence, combined with measures of vegetation pigment content and the Photosynthetic Reflectance Index (PRI) derived from the spectral reflectance are compared with CO2 fluxes over diurnal periods for multiple days. PRI detects changes in Xanthophyll cycle pigments using reflectance at 531 nm compared to a reference band at 570 nm. The relationships among the different optical measurements indicate that they are providing different types of information on the vegetation and that combinations of these measurements provide improved retrievals of CO2 fluxes than any index alone.

  11. Optical Sensing of Ecosystem Carbon Fluxes Combining Spectral Reflectance Indices with Solar Induced Fluorescence

    NASA Astrophysics Data System (ADS)

    Huemmrich, K. F.; Corp, L.; Campbell, P. K.; Cook, B. D.; Middleton, E.; Cheng, Y.; Zhang, Q.; Russ, A.; Kustas, W. P.

    2013-12-01

    Optical sampling of spectral reflectance and solar induced fluorescence provide information on the physiological status of vegetation that can be used to infer stress responses and estimates of production. Multiple repeated observations can observe the effects of changing environmental conditions on vegetation. This study examines the use of optical signals to determine inputs to a light use efficiency (LUE) model describing productivity of a cornfield where repeated observations of carbon flux, spectral reflectance and fluorescence were collected. Data were collected at the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) fields (39.03°N, 76.85°W) at USDA Beltsville Agricultural Research Center. Agricultural Research Service researchers measured CO2 fluxes using eddy covariance methods throughout the growing season. Optical measurements were made from the nearby tower supporting the NASA FUSION sensors. This sensor system consists of two dual channel, upward and downward looking, spectrometers used to simultaneously collect high spectral resolution measurements of reflected and fluoresced light from vegetation canopies. Estimates of chlorophyll fluorescence, combined with measures of vegetation pigment content and the Photosynthetic Reflectance Index (PRI) derived from the spectral reflectance are compared with CO2 fluxes over diurnal periods for multiple days. PRI detects changes in Xanthophyll cycle pigments using reflectance at 531 nm compared to a reference band at 570 nm. The relationships among the different optical measurements indicate that they are providing different types of information on the vegetation and that combinations of these measurements provide improved retrievals of CO2 fluxes than any index alone.

  12. Spectral shaping for non-Gaussian source spectra in optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Tripathi, Renu; Nassif, Nader; Nelson, J. Stuart; Park, Boris Hyle; de Boer, Johannes F.

    2002-03-01

    We present a digital spectral shaping technique to reduce the sidelobes (ringing) of the axial point-spread function in optical coherence tomography for non-Gaussian-shaped source spectra. The spectra of two superluminescent diodes were combined to generate a spectrum with significant modulation. Images of onion cells demonstrate the improved image quality in a turbid biological sample. A quantitative analysis of the accompanying penalty in signal-to-noise ratio is given.

  13. Non-full-thickness macular holes reassessed with spectral domain optical coherence tomography.

    PubMed

    Michalewska, Zofia; Michalewski, Janusz; Odrobina, Dominik; Nawrocki, Jerzy

    2012-05-01

    The aim of this study was to describe spectral domain optical coherence tomography characteristics and evolution of non-full-thickness macular holes, with a bed of retinal tissue present in the outer retinal layers, which the author will henceforth refer to as non-full-thickness macular holes (NFMHs). Retrospective observational study of 10,239 consecutive spectral domain optical coherence tomographic examinations was conducted, to select patients with idiopathic NFMH. We measured the following parameters: visual acuity, type of NFMH, coexistence of epiretinal membranes, photoreceptor layer defects, central and maximum retinal thickness, and diameters of the fovea defect. Patients with a history of diabetes; previous vein occlusions, with age-related macular degeneration; high and medium myopia; a previous history of retinal detachment; or macular edema were excluded. Four subtypes of NFMH were distinguished among 125 eyes (116 patients): macular pseudohole (21 eyes), paralamellar macular holes (34 eyes), pseudoholes with lamellar defects (25 eyes), and lamellar macular holes (45 eyes). We observed different fovea appearances on consecutive B-scans in 54% of eyes. Epiretinal membranes coexisted in 100% of cases. Photoreceptor layer defects, seen in 29% of cases, were the most important factor correlating with visual acuity. Other factors correlating with visual acuity were maximum retinal thickness and outer diameter of the fovea defect. We noted epiretinal membranes in the second eye in 32 cases. Sixty-six patients were followed up for a mean time of 14 months. Non-full-thickness macular hole formation was documented in five cases. Spectral domain optical coherence tomography images presented of four different morphologic types NFMH, which may change during the natural course of the disease. High resolution of spectral domain optical coherence tomography enabled the visualization of photoreceptor defects, a feature not previously described. Moreover, epiretinal

  14. SPECTRAL OPTICAL MONITORING OF THE NARROW-LINE SEYFERT 1 GALAXY Ark 564

    SciTech Connect

    Shapovalova, A. I.; Burenkov, A. N.; Popovic, L. C.; Kovacevic, J.; Chavushyan, V. H.; Valdes, J. R.; Torrealba, J.; Carrasco, L.; Ilic, D.; Kovacevic, A.; Kollatschny, W.; Bochkarev, N. G.; Leon-Tavares, J.; Mercado, A.; Benitez, E.; Dultzin, D.; De la Fuente, E.

    2012-09-15

    We present the results of a long-term (1999-2010) spectral optical monitoring campaign of the active galactic nucleus (AGN) Ark 564, which shows a strong Fe II line emission in the optical. This AGN is a narrow-line Seyfert 1 (NLS1) galaxy, a group of AGNs with specific spectral characteristics. We analyze the light curves of the permitted H{alpha}, H{beta}, optical Fe II line fluxes, and the continuum flux in order to search for a time lag between them. Additionally, in order to estimate the contribution of iron lines from different multiplets, we fit the H{beta} and Fe II lines with a sum of Gaussian components. We find that during the monitoring period the spectral variation (F{sub max}/F{sub min}) of Ark 564 is between 1.5 for H{alpha} and 1.8 for the Fe II lines. The correlation between the Fe II and H{beta} flux variations is of higher significance than that of H{alpha} and H{beta} (whose correlation is almost absent). The permitted-line profiles are Lorentzian-like and do not change shape during the monitoring period. We investigate, in detail, the optical Fe II emission and find different degrees of correlation between the Fe II emission arising from different spectral multiplets and the continuum flux. The relatively weak and different degrees of correlations between permitted lines and continuum fluxes indicate a rather complex source of ionization of the broad-line emission region.

  15. Molecular Electronics for Frequency Domain Optical Storage. Persistent Spectral Hole-Burning. A Review.

    DTIC Science & Technology

    1985-03-25

    if applicable) Office of Naval Research IBM Almaden Research Center Chemistry Division, Code 1113 6c. ADDRESS (City, State, and ZIP Code) 7b...NOTATION Journal of Molecular Electronics 17. .* COSATI CODES 18. SUBJECT TERMS (Continue on reverse of necessary and identify by block number) FIEL GRUP SB...GOUP Molecular electronics, spectral hole-burning, frequency I I domain. optical storage, solid state photo chemistry , * I photon gating. 19. ABSTRACT

  16. Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry

    NASA Astrophysics Data System (ADS)

    Xu, Yiqing; Wei, Xiaoming; Ren, Zhibo; Wong, Kenneth K. Y.; Tsia, Kevin K.

    2016-06-01

    The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for real- time spectral coherence characterization with microsecond-resolution. Accessing the single-shot interferograms continuously, it further reveals the degree of second-order coherence, defined by the cross-spectral density function, at high speed-a capability absent in any existing spectroscopic measurement tools. As the technique can simultaneously measure both the high-speed variations of spectrally resolved coherence and intensity, time-stretch interferometry could create a new arena for ultrafast pulse characterization, especially favorable for probing and understanding the non-repetitive or stochastic dynamics in real-time.

  17. Sufficient conditions for the avoidance of spectral dispersion in optical prisms.

    PubMed

    Lin, Psang Dain

    2016-07-01

    Prisms are common optical elements consisting of only flat boundary surfaces. Two conditions need to be fulfilled to avoid chromatic aberration for a prism, namely, no mutual image tilt and no mutual image shift for different wavelengths. Mutual image tilt occurs when the unit directional vector of the exit ray varies as a function of the prism's refractive index, resulting in spectral dispersion. In a previous study by the present group [Appl. Opt.45, 3951 (2006)APOPAI0003-693510.1364/AO.45.003951], it was shown that when the rays enter and exit a prism perpendicularly, image reorientation is achieved without spectral dispersion. The present study derives a further sufficient condition to avoid spectral dispersion caused by refraction. The condition explains the ability of Dove prisms and solid glass corner cubes to produce the required image orientation even when the entrance and exit rays are not normal to the respective boundary surfaces. In general, the proposed condition provides a useful analytical guideline for avoiding spectral dispersion in a wide variety of optical systems.

  18. Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry

    PubMed Central

    Xu, Yiqing; Wei, Xiaoming; Ren, Zhibo; Wong, Kenneth K. Y.; Tsia, Kevin K.

    2016-01-01

    The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for real- time spectral coherence characterization with microsecond-resolution. Accessing the single-shot interferograms continuously, it further reveals the degree of second-order coherence, defined by the cross-spectral density function, at high speed-a capability absent in any existing spectroscopic measurement tools. As the technique can simultaneously measure both the high-speed variations of spectrally resolved coherence and intensity, time-stretch interferometry could create a new arena for ultrafast pulse characterization, especially favorable for probing and understanding the non-repetitive or stochastic dynamics in real-time. PMID:27295560

  19. X-ray Spectral and Optical Properties of a ULX in NGC 4258 (M106)

    NASA Astrophysics Data System (ADS)

    Avdan, H.; Avdan, S.; Akyuz, A.; Balman, S.; Aksaker, N.; Akkaya Oralhan, I.

    2016-09-01

    We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton, Chandra, Swift, and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L X ˜ 2 × 1039 erg s-1 in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and the spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST/Advanced Camera for Surveys, three optical sources have been identified as counterpart candidates within the 1σ error radius of 0.″3. The brightest one has an absolute magnitude of M V ≈ -7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M V ≈ -5.8 and -5.3. The possible spectral types of the candidates from brightest to dimmest were determined as B6-A5, B0-A7, and B2-A3. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10-15 M ⊙, indicating that the compact source is most likely a stellar-mass black hole.

  20. On the possibility of developing incoherent fibre-optic data transmission systems based on signal spectral coding with matched acousto-optical filters

    SciTech Connect

    Proklov, Valerii V; Byshevski-Konopko, O A; Grigorievski, V I

    2013-06-30

    The scheme is suggested for developing the optical communication line based on the principle of code division of multiple access with matched acousto-optical filters and a 16-bit long Walsh sequence. Results of modelling show that such a line can operate if adjacent spectral lines are separated by at least double the Rayleigh criterion. (optical information transmission)

  1. Simulation of broad spectral bandwidth emitters at 1060 nm for optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Tooley, I. G.; Childs, D. T. D.; Stevens, B. J.; Groom, K. M.; Hogg, R. A.

    2016-03-01

    The simulation of broad spectral bandwidth light sources (semiconductor optical amplifiers (SOA) and superluminescent diodes (SLD)) for application in ophthalmic optical coherence tomography is reported. The device requirements and origin of key device parameters are outlined, and a range of single and double InGaAs/GaAs quantum well (QW) active elements are simulated with a view to application in different OCT embodiments. We confirm that utilising higher order optical transitions is beneficial for single QW SOAs, but may introduce deleterious spectral modulation in SLDs. We show how an addition QW may be introduced to eliminate this spectral modulation, but that this results in a reduction of the gain spectrum width. We go on to explore double QW structures where the roles of the two QWs are reversed, with the narrow QW providing long wavelength emission and gain. We show how this modification in the density of states results in a significant increase in gain-spectrum width for a given current.

  2. Retrieval of high-spectral-resolution lidar for atmospheric aerosol optical properties profiling

    NASA Astrophysics Data System (ADS)

    Liu, Dong; Luo, Jing; Yang, Yongying; Cheng, Zhongtao; Zhang, Yupeng; Zhou, Yudi; Duan, Lulin; Su, Lin

    2015-10-01

    High-spectral-resolution lidars (HSRLs) are increasingly being developed for atmospheric aerosol remote sensing applications due to the straightforward and independent retrieval of aerosol optical properties without reliance on assumptions about lidar ratio. In HSRL technique, spectral discrimination between scattering from molecules and aerosol particles is one of the most critical processes, which needs to be accomplished by means of a narrowband spectroscopic filter. To ensure a high retrieval accuracy of an HSRL system, the high-quality design of its spectral discrimination filter should be made. This paper reviews the available algorithms that were proposed for HSRLs and makes a general accuracy analysis of the HSRL technique focused on the spectral discrimination, in order to provide heuristic guidelines for the reasonable design of the spectral discrimination filter. We introduce a theoretical model for retrieval error evaluation of an HSRL instrument with general three-channel configuration. Monte Carlo (MC) simulations are performed to validate the correctness of the theoretical model. Results from both the model and MC simulations agree very well, and they illustrate one important, although not well realized fact: a large molecular transmittance and a large spectral discrimination ratio (SDR, i.e., ratio of the molecular transmittance to the aerosol transmittance) are beneficial t o promote the retrieval accuracy. The application of the conclusions obtained in this paper in the designing of a new type of spectroscopic filter, that is, the field-widened Michelson interferometer, is illustrated in detail. These works are with certain universality and expected to be useful guidelines for HSRL community, especially when choosing or designing the spectral discrimination filter.

  3. Field Studies of Broadband Aerosol Optical Extinction in the Ultraviolet Spectral Region

    NASA Astrophysics Data System (ADS)

    Washenfelder, R. A.; Attwood, A.; Brock, C. A.; Brown, S. S.

    2013-12-01

    Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross sections and complex refractive indices. In the case of brown carbon, its wavelength-dependent absorption in the ultraviolet spectral region has been suggested as an important component of aerosol radiative forcing. We describe a new field instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We deployed this instrument during the Fire Lab at Missoula Experiment during Fall 2012 to measure biomass burning aerosol, and again during the Southern Oxidant and Aerosol Study in summer 2013 to measure organic aerosol in the Southeastern U.S. In both field experiments, we determined aerosol optical extinction as a function of wavelength and can interpret this together with size distribution and composition measurements to characterize the aerosol optical properties and radiative forcing.

  4. Cutting Edge of Traumatic Maculopathy with Spectral-domain Optical Coherence Tomography – A Review

    PubMed Central

    Mendes, Sílvia; Campos, António; Campos, Joana; Neves, Arminda; Beselga, Diana; Fernandes, Cristina; Castro Sousa, João Paulo

    2015-01-01

    This article reviews clinically relevant data regarding traumatic maculopathy (TM), frequently observed in clinical practice, especially due to sport or traffic accident injuries. It is characterized by transient gray-whitish retinal coloration and reduction of visual acuity (VA) with closed, blunt object globe trauma of their prior. It may be limited to the posterior pole (Berlin’s edema), or peripheral areas of the retina. Spectral-domain optical coherence tomography (SD-OCT) provides detail insight using high resolution cross-sectional tomographs of the ocular tissue. It is a potent non-invasive tool for the clinician to follow-up. Clinicians are, thereby empowered with a tool that enables evaluation of the retinal status and allows for prediction of the prognosis. Spectral-domain optical coherence tomography supports the idea that the major site of injury is in the photoreceptor and layers of the retinal pigment epithelium (RPE). Depending on the severity of the trauma, SD-OCT may reveal differential optical densities of intraretinal spaces ranging from disappearance of the thin hyporeflective optical space in mild lesions, or areas of disruption of the inner segment/outer segment (IS/OS) junction and hyperreflectivity of the overlying retina, pigment disorders and retinal atrophy, in more severe cases. The prognosis for recovery of vision is generally good, and improvement occurs within 3-4 weeks. PMID:26060831

  5. Comprehensive Optical Coverage of Jupiter for Spectral Comparison with NH4SH

    NASA Astrophysics Data System (ADS)

    Thelen, Alexander E.; Chanover, Nancy; Loeffler, Mark; Hudson, Reggie; Simon, Amy

    2015-11-01

    The distinct regions in Jupiter's atmosphere - comprised of belts, zones, storms, and the Great Red Spot - are thought to be colored by unidentified chemical compounds called chromophores. These molecules, created through Jupiter's complex atmospheric chemistry, may be responsible for the spectral slope and lack of features in the blue (shortwards of 500 nm) portion of Jupiter's optical spectrum. Though many candidate compounds have been proposed - such as ammonium hydrosulfide (NH4SH) - the identity of the coloring agent (or agents) remains elusive due to the sparse history of laboratory experiments conducted at appropriate temperatures and pressures for Jovian conditions. To build on previous ground-based observations of Jupiter in the optical, we have obtained spectra with the Dual Imaging Spectrograph - mounted on the Astrophysical Research Consortium 3.5-meter telescope at Apache Point Observatory - over a wide portion of the visible spectrum (~380-880 nm) by utilizing multiple central wavelength settings. These observations, taken during February, 2013 and April, 2015, cover multiple latitudinal regions on Jupiter, including the Great Red Spot. In this study, we present the spectral comparison of various regions in the Jovian atmosphere with data taken at the Cosmic Ice Laboratory at NASA’s Goddard Space Flight Center. By exposing thin films of NH4SH to varying amounts of ionizing radiation at Jovian temperature conditions, we can analyze the color and spectral changes of the ice. This enables us to evaluate NH4SH as a candidate chromophore through comparisons of spectral slope and features found in ground-based optical spectra of Jupiter. This work was supported by NASA’s Outer Planets Research Program through grant number NNX12AJ14G.

  6. Spectral optical layer properties of cirrus from collocated airborne measurements and simulations

    NASA Astrophysics Data System (ADS)

    Finger, Fanny; Werner, Frank; Klingebiel, Marcus; Ehrlich, André; Jäkel, Evelyn; Voigt, Matthias; Borrmann, Stephan; Spichtinger, Peter; Wendisch, Manfred

    2016-06-01

    Spectral upward and downward solar irradiances from vertically collocated measurements above and below a cirrus layer are used to derive cirrus optical layer properties such as spectral transmissivity, absorptivity, reflectivity, and cloud top albedo. The radiation measurements are complemented by in situ cirrus crystal size distribution measurements and radiative transfer simulations based on the microphysical data. The close collocation of the radiative and microphysical measurements, above, beneath, and inside the cirrus, is accomplished by using a research aircraft (Learjet 35A) in tandem with the towed sensor platform AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected from two field campaigns over the North Sea and the Baltic Sea in spring and late summer 2013. One measurement flight over the North Sea proved to be exemplary, and as such the results are used to illustrate the benefits of collocated sampling. The radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius reff, and optical thickness τ on cirrus spectral optical layer properties. Furthermore, the radiative effects of low-level, liquid water (warm) clouds as frequently observed beneath the cirrus are evaluated. They may cause changes in the radiative forcing of the cirrus by a factor of 2. When low-level clouds below the cirrus are not taken into account, the radiative cooling effect (caused by reflection of solar radiation) due to the cirrus in the solar (shortwave) spectral range is significantly overestimated.

  7. Polarization-based balanced detection for spectral-domain optical coherence tomography.

    PubMed

    Black, Adam J; Akkin, Taner

    2015-08-20

    We present a new design for spectral-domain optical coherence tomography that allows balanced detection using a single camera. The design uses polarization optics to encode the light in reference and sample arms. Two parallel and highly aligned spectra, which carry out-of-phase interference signals, in-phase common noise, and auto-interference terms, are focused on the camera, which performs the digital balanced detection for each wavelength. The optical system is characterized and tested for tissue imaging. Results demonstrate consistent signal gains in depth and suppression of DC and sample auto-interference. The design could be further amended for polarization-sensitive imaging and might demonstrate a market for manufacturing dual-line cameras with analog-balanced detection capability.

  8. Wide free-spectral-range triple ring resonator as optical filter

    NASA Astrophysics Data System (ADS)

    Dey, Sabitabrata; Mandal, S.

    2011-08-01

    A waveguide-based wide free-spectral-range (FSR) triple ring resonator (TRR) as an optical filter has been investigated in this article. The transmittance of the TRR is presented in Z-domain. The delay line signal processing approach and Mason's gain formula have been used to develop the transmittance of the TRR. The TRR in the article is capable of providing an FSR up to 605 GHz with lower crosstalk limited within -10 dB. Another efficacious scheme of TRR with much wider FSR of 1029 GHz and with reduced unit delay length is presented in the article. Here also crosstalk, as well as resonance loss, remains within reasonable limits. The FSRs obtained using the present TRR architectures in this work are until now reported as maximum for a corresponding class of optical ring resonators. The issues of group delay and dispersion, two important parameters associated with high frequency optical communication have been addressed in this article.

  9. Bandwidth-variable tunable optical filter unit for illumination and spectral imaging systems using thin-film optical band-pass filters.

    PubMed

    Hennig, Georg; Brittenham, Gary M; Sroka, Ronald; Kniebühler, Gesa; Vogeser, Michael; Stepp, Herbert

    2013-04-01

    An optical filter unit is demonstrated, which uses two successively arranged tunable thin-film optical band-pass filters and allows for simultaneous adjustment of the central wavelength in the spectral range 522-555 nm and of the spectral bandwidth in the range 3-16 nm with a wavelength switching time of 8 ms∕nm. Different spectral filter combinations can cover the complete visible spectral range. The transmitted intensity was found to decrease only linearly with the spectral bandwidth for bandwidths >6 nm, allowing a high maximum transmission efficiency of >75%. The image of a fiber bundle was spectrally filtered and analyzed in terms of position-dependency of the transmitted bandwidth and central wavelength.

  10. Low-coherence spectral interferometry with a Michelson interferometer applied to dispersion measurement of a two-mode optical fiber

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    1999-12-01

    Intermodal dispersion in a two-mode optical fiber can be measured in the spectral domain when the spectral interference between modes at the output of the optical fiber shows up as a periodic modulation of the source spectrum that can be processed. However, this technique cannot be used to measure intermodal dispersion in the two- mode optical fiber when the period of modulation is too small to be resolved by a spectrometer. Consequently, we proposed a new measuring technique utilizing a tandem configuration of a dispersive Michelson interferometer and the two-mode optical fiber in which the spectral interference can be resolved even if a low-resolution spectrometer is used. In the tandem configuration of the Michelson interferometer and the two-mode optical fiber, the optical path difference (OPD) in the Michelson interferometer is adjusted close to the group OPD between modes of the optical fiber so that the low-frequency spectral modulation that can be processed is produced. Using the Fourier transform method in processing the measured spectral modulations and subtracting the effect of the dispersive Michelson interferometer, the feasibility of this technique has successfully been demonstrated in obtaining the intermodal dispersion in the two-model optical fiber.

  11. Polarization-sensitive spectral-domain optical coherence tomography using a single line scan camera

    NASA Astrophysics Data System (ADS)

    Cense, Barry; Mujat, Mircea; Chen, Teresa C.; Park, B. H.; de Boer, Johannes F.

    2007-03-01

    Polarization-sensitive optical coherence tomography can be used to measure the birefringence of biological tissue such as the human retina. Previous measurements with a time-domain polarization-sensitive optical coherence tomography system revealed that the birefringence of the human retinal nerve fiber layer is not constant, but varies as a function of location around the optic nerve head. Here we present a spectral-domain polarization-sensitive optical coherence tomography system that uses a spectrometer configuration with a single line scan camera and a Wollaston prism in the detection arm. Since only one camera has to be synchronized with other components in the system, the design is simplified considerably. This system is 60 times faster than a time-domain polarization-sensitive optical coherence tomography system. Data was acquired using concentric circular scans around the optic nerve head of a young healthy volunteer and the acquisition time for 12 circular scans was reduced from 72 s to 1.2 s. The acquired data sets demonstrate variations in retinal thickness and double pass phase retardation per unit depth that were similar to data from the same volunteer taken with a time-domain polarization-sensitive system. The double pass phase retardation per unit depth of the retinal nerve fiber layer varied between 0.18 and 0.40 degrees/μm, equivalent to a birefringence of 2.2 • 10-4 and 4.8 • 10-4 respectively, measured at 840 nm.

  12. All-optical swapping of spectral amplitude code labels for packet-switched networks

    NASA Astrophysics Data System (ADS)

    Chen, Lawrence R.

    2008-08-01

    Packet-switched networks have attracted considerable attention as a basis for next-generation optical networks due to their advantages in terms of flexibility and network efficiency over traditional circuit-switched networks. Optical code multi-protocol label switching (OC-MPLS) promises fast, flexible, power-efficient switching by keeping signals in the optical domain and avoiding costly conversions to the electrical domain. In this paper, we review the use of spectral amplitude codes (SACs) for implementing OC-MPLS labels. We discuss the principles and features, as well as key enabling technologies required for their processing. In particular, we compare three different approaches for low cost all-optical swapping of SAC labels. All approaches are based on semiconductor fiber lasers and exploit nonlinearity in a semiconductor device: the first uses cross-absorption modulation in an electroabsorption modulator, the second uses cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA), and the third makes use of XGM in an SOA as well as injection locking in a Fabry-Pérot laser. We present the static and dynamic responses of each for swapping a multi-wavelength input label to a multi-wavelength output label. The benefits and limitations of each approach as well as future improvements are discussed. We also present the results of systems experiments which demonstrate error-free all-optical label swapping, recognition, and switching of multi-rate packets in packet-switched networks using multi-wavelength labels.

  13. Optical design of 400-1000nm spectral imaging system based on a single freeform mirror

    NASA Astrophysics Data System (ADS)

    Hou, Jia; He, Zhiping; Shu, Rong

    2015-10-01

    The imaging spectrometer supplies spectral images in one spectral dimension and two spatial dimensions simultaneously. The Offner spectral imaging system was outstanding because of its small volume, light weight, free spectral smile and little keystone. However, the manufacture of the convex grating is a challenge and the cost is high. Here, an optical design of a compact 400-1000nm spectral imaging system using a planar grating based on a single freeform mirror was proposed. The spectrograph was similar with the Offner structure, only the grating is planar. The multi-spectra was split by the planar diffraction grating, and the collimating mirror and the focusing mirror were the same freeform surface by using it twice. The freeform surface was non-rotational symmetry. Its large degree of freedom can correct kinds of aberration, such as astigmatism, smile and keystone. The system has a compact volume as 120×100×100mm3. The entrance slit was 6mm, and the object NA(numerical aperture) was 0.12. The pixel size of the detector was 16μm×16μm, and its resolution was 375(spatial)×400(spectral). The design result showed that image quality close to the diffraction limit has been obtained. The maximums of the keystone and the smile at all working wavelengths in all fields were respectively 1.6μm and 7.5μm, which were both less than half of the pixel size. At last, the tolerance analysis considering manufacture and alignment of the system was done, the result showed that the manufacturability of the existing diamond turning machining technology can satisfy the accuracy need of the freeform mirror.

  14. Simultaneous dual-band spectral domain optical coherence tomography using a supercontinuum laser light source

    NASA Astrophysics Data System (ADS)

    Cimalla, Peter; Mehner, Mirko; Cuevas, Maximiliano; Walther, Julia; Koch, Edmund

    2009-07-01

    Optical coherence tomography (OCT) is performed in the spectral domain simultaneously at two different wavelength bands centered at 800 nm and 1250 nm. A novel commercial supercontinuum laser is applied as a single light source whose emission spectrum is shaped by optical and spatial filtering to obtain an adequate double peak spectrum. After spectral shaping, the wavelength bands 700 - 900 nm and 1100 - 1400 nm are used for OCT imaging. A fiber-coupled setup optimized for both spectral regions facilitates easy and flexible access to the measurement area. Each wavelength band is analyzed with an individual spectrometer at an A-scan rate of about 12 kHz which allows real-time sample examination. The free-space axial resolutions were measured to be less than 4.5 μm and 7 μm at 800 nm and 1250 nm, respectively. This technique combines the high resolution at 800 nm with the enhanced imaging depth at 1250 nm. Furthermore, spatially resolved spectroscopic sample features are extracted by comparing the backscattering properties at the two different wavelength bands, showing the ability of dual-band OCT to enhance image contrast.

  15. The infrared optical constants of sulfuric acid at 250 K. [spectral reflectance measurement of aqueous solutions

    NASA Technical Reports Server (NTRS)

    Pinkley, L. W.; Williams, D.

    1976-01-01

    Results are presented for measurements of the IR spectral reflectance at near-normal incidence of aqueous solutions of sulfuric acid with acid concentrations of 75% and 95.6% by weight. Kramers-Kronig analyses of the reflectance data are employed to obtain values of the optical constants n(nu) and k(nu) in the spectral range from 400 to 6000 cm to the -1 power. The optical constants of these solutions at 250 K and 300 K are compared. It is found that in spectral regions remote from strong absorption bands, the values of the n(nu) indices obtained at 250 K agree with the values given by Lorentz-Lorenz correction of the same indices at 300 K. All absorption bands observed at 300 K are found to be present at 250 K with slight shifts in frequency and with significant differences in the k(nu) indices at the band maxima. Based on these results, it is concluded that the clouds of Venus probably consist of droplets of aqueous solutions of sulfuric acid with acid concentrations of about 75% by weight.

  16. Spectroradiometer with wedge interference filters (SWIF): measurements of the spectral optical depths at Mauna Loa Observatory.

    PubMed

    Vasilyev, O B; Leyva, A; Muhila, A; Valdes, M; Peralta, R; Kovalenko, A P; Welch, R M; Berendes, T A; Isakov, V Y; Kulikovskiy, Y P; Sokolov, S S; Strepanov, N N; Gulidov, S S; von Hoyningen-Huene, W

    1995-07-20

    A spectroradiometer with wedge interference filters (SWIF) (the filters were produced by Carl Zeiss, Jena, Germany) and a CCD matrix (which was of Russian production) that functions as the sensor has been designed and built for use in ground-based optical sensing of the atmosphere and the Earth's surface in the spectral range of 0.35-1.15 µm. Absolute calibration of this instrument was performed through a series of observations of direct solar radiation at Mauna Loa Observatory (MLO) in Hawaii in May and June 1993. Spectral optical depth (SOD) measurements that were made during these field experiments provided detailed spectral information about both aerosol extinction (scattering plus absorption) and molecular absorption in the atmosphere above the site at MLO. The aerosol-SOD measurements were compared with narrow-band radiometer measurements at wavelengths of 380, 500, and 778 nm The SWIF and narrow-band radiometer measurements are in agreement to within the experimental error. At a wavelength of 500 nm, the aerosol SOD was found to be approximately 0.045. Adescription of the SWIF instrument, its absolute calibration, and the determination of atmospheric SOD's at MLO are presented.

  17. Spectral-Domain Optical Coherence Tomography Staging and Autofluorescence Imaging in Achromatopsia

    PubMed Central

    Greenberg, Jonathan P.; Sherman, Jerome; Zweifel, Sandrine A.; Chen, Royce W. S.; Duncker, Tobias; Kohl, Susanne; Baumann, Britta; Wissinger, Bernd; Yannuzzi, Lawrence A.; Tsang, Stephen H.

    2015-01-01

    Importance Evidence is mounting that achromatopsia is a progressive retinal degeneration, and treatments for this condition are on the horizon. Objectives To categorize achromatopsia into clinically identifiable stages using spectral-domain optical coherence tomography and to describe fundus autofluorescence imaging in this condition. Design, Setting, and Participants A prospective observational study was performed between 2010 and 2012 at the Edward S. Harkness Eye Institute, New York-Presbyterian Hospital. Participants included 17 patients (aged 10-62 years) with full-field electroretinography-confirmed achromatopsia. Main outcomes and Measures Spectral-domain optical coherence tomography features and staging system, fundus autofluorescence and near-infrared reflectance features and their correlation to optical coherence tomography, and genetic mutations served as the outcomes and measures. Results Achromatopsia was categorized into 5 stages on spectral-domain optical coherence tomography: stage 1 (2 patients [12%]), intact outer retina; stage 2 (2 patients [12%]), inner segment ellipsoid line disruption; stage 3 (5 patients [29%]), presence of an optically empty space; stage 4 (5 patients [29%]), optically empty space with partial retinal pigment epithelium disruption; and stage 5 (3 patients [18%]), complete retinal pigment epithelium disruption and/or loss of the outer nuclear layer. Stage 1 patients showed isolated hyperreflectivity of the external limiting membrane in the fovea, and the external limiting membrane was hyperreflective above each optically empty space. On near infrared reflectance imaging, the fovea was normal, hyporeflective, or showed both hyporeflective and hyperreflective features. All patients demonstrated autofluorescence abnormalities in the fovea and/or parafovea: 9 participants (53%) had reduced or absent autofluorescence surrounded by increased autofluorescence, 4 individuals (24%) showed only reduced or absent autofluorescence, 3

  18. Spectral-domain optical coherence tomography staging and autofluorescence imaging in achromatopsia.

    PubMed

    Greenberg, Jonathan P; Sherman, Jerome; Zweifel, Sandrine A; Chen, Royce W S; Duncker, Tobias; Kohl, Susanne; Baumann, Britta; Wissinger, Bernd; Yannuzzi, Lawrence A; Tsang, Stephen H

    2014-04-01

    IMPORTANCE Evidence is mounting that achromatopsia is a progressive retinal degeneration, and treatments for this condition are on the horizon. OBJECTIVES To categorize achromatopsia into clinically identifiable stages using spectral-domain optical coherence tomography and to describe fundus autofluorescence imaging in this condition. DESIGN, SETTING, AND PARTICIPANTS A prospective observational study was performed between 2010 and 2012 at the Edward S. Harkness Eye Institute, New York-Presbyterian Hospital. Participants included 17 patients (aged 10-62 years) with full-field electroretinography-confirmed achromatopsia. MAIN OUTCOMES AND MEASURES Spectral-domain optical coherence tomography features and staging system, fundus autofluorescence and near-infrared reflectance features and their correlation to optical coherence tomography, and genetic mutations served as the outcomes and measures. RESULTS Achromatopsia was categorized into 5 stages on spectral-domain optical coherence tomography: stage 1 (2 patients [12%]), intact outer retina; stage 2 (2 patients [12%]), inner segment ellipsoid line disruption; stage 3 (5 patients [29%]), presence of an optically empty space; stage 4 (5 patients [29%]), optically empty space with partial retinal pigment epithelium disruption; and stage 5 (3 patients [18%]), complete retinal pigment epithelium disruption and/or loss of the outer nuclear layer. Stage 1 patients showed isolated hyperreflectivity of the external limiting membrane in the fovea, and the external limiting membrane was hyperreflective above each optically empty space. On near infrared reflectance imaging, the fovea was normal, hyporeflective, or showed both hyporeflective and hyperreflective features. All patients demonstrated autofluorescence abnormalities in the fovea and/or parafovea: 9 participants (53%) had reduced or absent autofluorescence surrounded by increased autofluorescence, 4 individuals (24%) showed only reduced or absent autofluorescence, 3

  19. The vibro-acoustic mapping of low gravity trajectories on a Learjet aircraft

    NASA Technical Reports Server (NTRS)

    Grodsinsky, C. M.; Sutliff, T. J.

    1990-01-01

    Terrestrial low gravity research techniques have been employed to gain a more thorough understanding of basic science and technology concepts. One technique frequently used involves flying parabolic trajectories aboard the NASA Lewis Research Center Learjet aircraft. A measurement program was developed to support an isolation system conceptual design. This program primarily was intended to measure time correlated high frequency accelerations (up to 100 Hz) present at various locations throughout the Learjet during a series of trajectories and flights. As suspected, the measurements obtained revealed that the environment aboard such an aircraft can not simply be described in terms of the static level low gravity g vector obtained, but that it also must account for both rigid body and high frequency vibro-acoustic dynamics.

  20. Liquid-vapor interface locations in a spheroidal container under low gravity

    NASA Technical Reports Server (NTRS)

    Carney, M. J.

    1986-01-01

    As a part of the general study of liquid behavior in low gravity environments, an experimental investigation was conducted to determine if there are equilibrium liquid-vapor interface configurations that can exist at more than one location in oblate spheroidal containers under reduced gravity conditions. Static contact angles of the test liquids on the spheroid surface were restricted to near 0 deg. The experiments were conducted in a low gravity environment. An oblate spheroidal tank was tested with an eccentricity of 0.68 and a semimajor axis of 2.0 cm. Both quantitative and qualitative data were obtained on the liquid-vapor interface configuration and position inside the container. The results of these data, and their impat on previous work in this area, are discussed. Of particular interest are those equilibrium interface configurations that can exist at multiple locations in the container.

  1. Low-gravity fluid dynamics and transport phenomena. Progress in Astronautics and Aeronautics. Vol. 130

    SciTech Connect

    Koster, J.N.; Sani, R.L. )

    1990-01-01

    Various papers on low-gravity fluid dynamics and transport phenomena are presented. Individual topics addressed include: fluid management in low gravity, nucleate pool boiling in variable gravity, application of energy-stability theory to problems in crystal growth, thermosolutal convection in liquid HgCdTe near the liquidus temperature, capillary surfaces in microgravity, thermohydrodynamic instabilities and capillary flows, interfacial oscillators, effects of gravity jitter on typical fluid science experiments and on natural convection in a vertical cylinder. Also discussed are: double-diffusive convection and its effects under reduced gravity, segregation and convection in dendritic alloys, fluid flow and microstructure development, analysis of convective situations with the Soret effect, complex natural convection in low Prandtl number metals, separation physics, phase partitioning in reduced gravity, separation of binary alloys with miscibility gap in the melt, Ostwald ripening in liquids, particle cloud combustion in reduced gravity, opposed-flow flame spread with implications for combustion at microgravity.

  2. Control of suspended low-gravity simulation system based on self-adaptive fuzzy PID

    NASA Astrophysics Data System (ADS)

    Chen, Zhigang; Qu, Jiangang

    2017-09-01

    In this paper, an active suspended low-gravity simulation system is proposed to follow the vertical motion of the spacecraft. Firstly, working principle and mathematical model of the low-gravity simulation system are shown. In order to establish the balance process and suppress the strong position interference of the system, the idea of self-adaptive fuzzy PID control strategy is proposed. It combines the PID controller with a fuzzy controll strategy, the control system can be automatically adjusted by changing the proportional parameter, integral parameter and differential parameter of the controller in real-time. At last, we use the Simulink tools to verify the performance of the controller. The results show that the system can reach balanced state quickly without overshoot and oscillation by the method of the self-adaptive fuzzy PID, and follow the speed of 3m/s, while simulation degree of accuracy of system can reach to 95.9% or more.

  3. A quantitative analysis of human monocytes motilty in modeled low gravity conditions

    NASA Astrophysics Data System (ADS)

    Cogoli-Greuter, M.; Galleri, G.; Meloni, M. A.; Liuzzo, M. I.; Cogoli, A.; Pippia, P.

    2005-08-01

    Cell-cell interaction between T cells and monocytes as well as aggregate formation are important means of signal transduction in mitogenic activation of lymphocytes. Nearly total loss of T cell activation was discovered in microgravity and confirmed by later experiments. Aggregate formation of lymphocytes in suspension was observed in microgravity but there is still no direct evidence that interactions between monocytes and T lymphocytes are occurring normally in microgravity. In this study we have found that locomotion of adherent monocytes is modified in modelled low gravity conditions, using the Random Positioning Machine as earth based model of low gravity conditions. The experiments were performed in the MIA unit, hardware suitable for Type I containers, the interface to the Kubik incubator flying in the upcoming Soyuz Missions.

  4. Mapping of photoreceptor dysfunction using high resolution three-dimensional spectral optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Sikorski, B. L.; Szkulmowski, M.; Kałużny, J. J.; Bajraszewski, T.; Kowalczyk, A.; Wojtkowski, M.

    2008-02-01

    The ability to obtain reliable information on functional status of photoreceptor layer is essential for assessing vision impairment in patients with macular diseases. The reconstruction of three-dimensional retinal structure in vivo using Spectral Optical Coherence Tomography (Spectral OCT) became possible with a recent progress of the OCT field. Three-dimensional data collected by Spectral OCT devices comprise information on light intensity back-reflected from the junction between photoreceptor outer and inner segments (IS/OS) and thus can be used for evaluating photoreceptors impairment. In this paper, we introduced so called Spectral OCT reflectivity maps - a new method of selecting and displaying the spatial distribution of reflectivity of individual retinal layers. We analyzed the reflectivity of the IS/OS layer in various macular diseases. We have measured eyes of 49 patients with photoreceptor dysfunction in course of age-related macular degeneration, macular holes, central serous chorioretinopathy, acute zonal occult outer retinopathy, multiple evanescent white dot syndrome, acute posterior multifocal placoid pigment epitheliopathy, drug-induced retinopathy and congenital disorders.

  5. Spectral characterization of tracheal and esophageal tissues using a hyperspectral camera and fiber optic sensors

    NASA Astrophysics Data System (ADS)

    Nawn, Corinne D.; Souhan, Brian E.; Carter, Robert; Kneapler, Caitlin; Fell, Nicholas; Ye, Jing Yong

    2016-03-01

    During emergency medical situations where the patient has an obstructed airway or necessitates respiratory support, endotracheal intubation (ETI) is the medical technique of placing a tube into the trachea in order to facilitate adequate ventilation of the lungs. In particular, the anatomical, visual and time-sensitive challenges presented in these scenarios, such as in trauma, require a skilled provider in order to successfully place the tube into the trachea. Complications during ETI such as repeated attempts, failed intubation or accidental intubation of the esophagus can lead to severe consequences or ultimately death. Consequently, a need exists for a feedback mechanism to aid providers in performing successful ETI. To investigate potential characteristics to exploit as a feedback mechanism, our study examined the spectral properties of the trachea tissue to determine whether a unique spectral profile exists. In this work, hyperspectral cameras and fiber optic sensors were used to capture and analyze the reflectance profiles of tracheal and esophageal tissues illuminated with UV and white light. Our results show consistent and specific spectral characteristics of the trachea, providing foundational support for using spectral properties to detect features of the trachea.

  6. Potential of optical spectral transmission measurements for joint inflammation measurements in rheumatoid arthritis patients

    NASA Astrophysics Data System (ADS)

    Meier, A. J. Louise; Rensen, Wouter H. J.; de Bokx, Pieter K.; de Nijs, Ron N. J.

    2012-08-01

    Frequent monitoring of rheumatoid arthritis (RA) patients enables timely treatment adjustments and improved outcomes. Currently this is not feasible due to a shortage of rheumatologists. An optical spectral transmission device is presented for objective assessment of joint inflammation in RA patients, while improving diagnostic accuracy and clinical workflow. A cross-sectional, nonrandomized observational study was performed with this device. In the study, 77 proximal interphalangeal (PIP) joints in 67 patients have been analyzed. Inflammation of these PIP joints was also assessed by a rheumatologist with a score varying from 1 (not inflamed) to 5 (severely inflamed). Out of 77 measurements, 27 were performed in moderate to strongly inflamed PIP joints. Comparison between the clinical assessment and an optical measurement showed a correlation coefficient r=0.63, p<0.001, 95% CI [0.47, 0.75], and a ROC curve (AUC=0.88) that shows a relative good specificity and sensitivity. Optical spectral transmission measurements in a single joint correlate with clinical assessment of joint inflammation, and therefore might be useful in monitoring joint inflammation in RA patients.

  7. Spectral interferometric microscopy reveals absorption by individual optical nanoantennas from extinction phase

    PubMed Central

    Gennaro, Sylvain D.; Sonnefraud, Yannick; Verellen, Niels; Van Dorpe, Pol; Moshchalkov, Victor V.; Maier, Stefan A.; Oulton, Rupert F.

    2014-01-01

    Optical antennas transform light from freely propagating waves into highly localized excitations that interact strongly with matter. Unlike their radio frequency counterparts, optical antennas are nanoscopic and high frequency, making amplitude and phase measurements challenging and leaving some information hidden. Here we report a novel spectral interferometric microscopy technique to expose the amplitude and phase response of individual optical antennas across an octave of the visible to near-infrared spectrum. Although it is a far-field technique, we show that knowledge of the extinction phase allows quantitative estimation of nanoantenna absorption, which is a near-field quantity. To verify our method we characterize gold ring-disk dimers exhibiting Fano interference. Our results reveal that Fano interference only cancels a bright mode’s scattering, leaving residual extinction dominated by absorption. Spectral interference microscopy has the potential for real-time and single-shot phase and amplitude investigations of isolated quantum and classical antennas with applications across the physical and life sciences. PMID:24781663

  8. The spectral shift between near- and far-field resonances of optical nano-antennas.

    PubMed

    Menzel, Christoph; Hebestreit, Erik; Mühlig, Stefan; Rockstuhl, Carsten; Burger, Sven; Lederer, Falk; Pertsch, Thomas

    2014-04-21

    Within the past several years a tremendous progress regarding optical nano-antennas could be witnessed. It is one purpose of optical nano-antennas to resonantly enhance light-matter interactions at the nanoscale, e.g. the interaction of an external illumination with molecules. In this specific, but in almost all schemes that take advantage of resonantly enhanced electromagnetic fields in the vicinity of nano-antennas, the precise knowledge of the spectral position of resonances is of paramount importance to fully exploit their beneficial effects. Thus far, however, many nano-antennas were only optimized with respect to their far-field characteristics, i.e. in terms of their scattering or extinction cross sections. Although being an emerging feature in many numerical simulations, it was only recently fully appreciated that there exists a subtle but very important difference in the spectral position of resonances in the near-and the far-field. With the purpose to quantify this shift, Zuloaga et al. suggested a Lorentzian model to estimate the resonance shift. Here, we devise on fully analytical grounds a strategy to predict the resonance in the near-field directly from that in the far-field and disclose that the issue is involved and multifaceted, in general. We outline the limitations of our theory if more sophisticated optical nano-antennas are considered where higher order multipolar contributions and higher order antenna resonances become increasingly important. Both aspects are highlighted by numerically studying relevant nano-antennas.

  9. Single-shot high-resolution characterization of optical pulses by spectral phase diversity

    SciTech Connect

    Dorrer, C.; Waxer, L. J.; Kalb, A.; Hill, E. M.; Bromage, J.

    2015-12-15

    The concept of spectral phase diversity is proposed and applied to the temporal characterization of optical pulses. The experimental trace is composed of the measured power of a plurality of ancillary optical pulses derived from the pulse under test by adding known amounts of chromatic dispersion. The spectral phase of the pulse under test is retrieved by minimizing the error between the experimental trace and a trace calculated from the optical spectrum using the known diagnostic parameters. An assembly composed of splitters and dispersive delay fibers has been used to generate 64 ancillary pulses whose instantaneous power can be detected in a single shot with a high-bandwidth photodiode and oscilloscope. Pulse-shape reconstruction for pulses shorter than the photodetection impulse response has been demonstrated.The diagnostic is experimentally shown to accurately characterize pulses from a chirped-pulse–amplification system when its stretcher is detuned from the position for optimal recompression. As a result, various investigations of the performance with respect to the number of ancillary pulses and the range of chromatic dispersion generated in the diagnostic are presented.

  10. AIMS: Acousto-optic imaging spectrometer for spectral mapping of solid surfaces

    NASA Astrophysics Data System (ADS)

    Glenar, David A.; Blaney, Diana L.; Hillman, John J.

    2003-01-01

    A compact, two-channel acousto-optic tunable filter (AOTF) camera is being built at GSFC as a candidate payload instrument for future Mars landers or small-body rendezvous missions. This effort is supported by the NASA Mars Instrument Development Program (MIDP), Office of Space Science Advanced Technologies and Mission Studies. Acousto-optic Imaging Spectrometer (AIMS) is electronically programmable and provides arbitrary spatial and spectral selection from 0.48 to 2.4 μm. The geometric throughput of AOTF's are well matched to the requirements for lander mounted cameras since (I) they can be made very compact, (II) "slow" (f/14-f/18) optics required for large depth-of-field fall well within the angular aperture limit of AOTF's, and (III) they operate at low ambient temperatures. A breadboard of the AIMS short-wavelength channel is now being used for spectral imaging of high-interest Mars analog materials (iron oxides, carbonates, sulfates and sedimentary basalts) as part of the initial instrument validation exercises.

  11. Single-shot high-resolution characterization of optical pulses by spectral phase diversity

    DOE PAGES

    Dorrer, C.; Waxer, L. J.; Kalb, A.; ...

    2015-12-15

    The concept of spectral phase diversity is proposed and applied to the temporal characterization of optical pulses. The experimental trace is composed of the measured power of a plurality of ancillary optical pulses derived from the pulse under test by adding known amounts of chromatic dispersion. The spectral phase of the pulse under test is retrieved by minimizing the error between the experimental trace and a trace calculated from the optical spectrum using the known diagnostic parameters. An assembly composed of splitters and dispersive delay fibers has been used to generate 64 ancillary pulses whose instantaneous power can be detectedmore » in a single shot with a high-bandwidth photodiode and oscilloscope. Pulse-shape reconstruction for pulses shorter than the photodetection impulse response has been demonstrated.The diagnostic is experimentally shown to accurately characterize pulses from a chirped-pulse–amplification system when its stretcher is detuned from the position for optimal recompression. As a result, various investigations of the performance with respect to the number of ancillary pulses and the range of chromatic dispersion generated in the diagnostic are presented.« less

  12. High resolution spectral domain optical coherence tomography (OCT) images of Alström Syndrome

    PubMed Central

    Vingolo, EM; Salvatore, S.; Grenga, PL; Maffei, P.; Milan, G.; Marshall, JD

    2010-01-01

    Alström syndrome (ALMS1) is a multisystemic disorder characterized by cone–rod dystrophy, hearing loss, obesity, insulin resistance and hyperinsulinemia, type 2 diabetes mellitus, dilated cardiomyopathy, and progressive hepatic and renal dysfunction.The cone-rod retinal dystrophy usually develops within a few weeks after birth. We examined a young boy with Alstrom by means of microperimetry MP-1 and optical coherence tomography (OCT) Spectral Domain. Instead of the typical alterations observed in cone-rod dystrophies, the characteristics of the central foveal tissue suggest signs of retinal immaturity, with only a single layer of short thick cones and rods as well as immature short outer segments. High- speed/ high- resolution spectral domain OCT allowed for the first time a detailed analysis of retinal layers in a young patient with Alstrom Syndrome. PMID:21158358

  13. Concentric circular ring and nanodisk optical antenna enhanced multispectral quantum dot infrared photodetector with spectral localization

    NASA Astrophysics Data System (ADS)

    Zhang, Yingjie; Kemsri, Thitikorn; Li, Lin; Gu, Guiru; Lu, Xuejun

    2017-10-01

    In this paper, we report a concentric circular ring and nanodisk plasmonic optical antenna (POA) enhanced multispectral quantum dot infrared photodetector (QDIP). The circular ring and the nanodisk POA structures are designed to have plasmonic resonant wavelengths in the longwave infrared (LWIR) and the midwave infrared (MWIR) spectral regimes, respectively. The electric field (E-field) distributions are simulated and show spectral localization due to the distinct plasmonic resonant wavelengths of the POA structures. The circular ring is found to enhance the E-fields in the nanodisk regions due to the mutual coupling. A concentric circular ring and nanodisk POA enhanced multispectral QDIP was fabricated and tested. Multispectral enhancement was observed. The enhancement is compared to that of a QDIP with only the circular ring POA structure. The experiment data agree with the simulation. The concentric circular ring and nanodisk POA provides a compact planar structure for multispectral QDIP enhancement.

  14. Solid optical ring interferometer for high-throughput feedback-free spectral analysis and filtering

    SciTech Connect

    Petrak, B.; Peiris, M.; Muller, A.

    2015-02-15

    We describe a simple and inexpensive optical ring interferometer for use in high-resolution spectral analysis and filtering. It consists of a solid cuboid, reflection-coated on two opposite sides, in which constructive interference occurs for waves in a rhombic trajectory. Due to its monolithic design, the interferometer’s resonance frequencies are insensitive to environmental disturbances over time. Additional advantages are its simplicity of alignment, high-throughput, and feedback-free operation. If desired, it can be stabilized with a secondary laser without disturbance of the primary signal. We illustrate the use of the interferometer for the measurement of the spectral Mollow triplet from a quantum dot and characterize its long-term stability for filtering applications.

  15. Spectral collocation methods using sine functions for a rotating Bose-Einstein condensation in optical lattices

    NASA Astrophysics Data System (ADS)

    Chen, Huei-Shuang; Chang, Shing-Lin; Chien, Cheng-Sheng

    2012-02-01

    We study spectral-Galerkin methods (SGM) and spectral collocation methods (SCM) for parameter-dependent problems, where the Fourier sine functions are used as the basis functions. When the SGM and the SCM are incorporated in the context of a Taylor predictor-inexact Newton corrector continuation algorithm for tracing solution curves of the Gross-Pitaevskii equation (GPE), they can efficiently provide accurate numerical solutions for the GPE. We show how the inexact Newton method outperforms the classical Newton method in the continuation algorithm. In our numerical experiments, the centered difference method (CDM), the SGM and SCM are exploited to compute energy levels and wave functions of a rotating Bose-Einstein condensation (BEC) and a rotating BEC in optical lattices in 2D. Sample numerical results are reported.

  16. Electro-optical parameters in excited states of some spectrally active molecules

    NASA Astrophysics Data System (ADS)

    Benchea, Andreea Celia; Closca, Valentina; Rusu, Cristina Marcela; Morosanu, Cezarina; Dorohoi, Dana Ortansa

    2014-08-01

    The spectral shifts measured in different solvents are expressed as functions of the solvent macroscopic parameters. The value of the correlation coefficient multiplying the functions of electric permittivity was determined by statistical means. The correlation coefficient depends on the electric dipole moment of the spectrally active molecules. The electro-optical parameters in the ground state of the solute molecules can be approximated by molecular modeling. The excited state parameters are usually estimated using the results obtained both by HyperChem Programme and solvatochromic study. The importance of this approximate method is that it offers information about of the excited state of solute molecule for which our measuring possibilities are very restrictive. The information about the excited electronic state is affected by the limits in which the theories of liquid solutions are developed. Our results refer to two molecules of vitamins from B class, namely B3 and B6.

  17. Spectral domain optical coherence tomography findings in CNGB3-associated achromatopsia and therapeutic implications.

    PubMed

    McClintock, Michael; Peden, Marc C; Kay, Christine N

    2014-01-01

    We describe the spectral domain OCT findings in two siblings with CNGB3-associated achromatopsia. A 33-year-old female and her 31-year-old sibling were evaluated for mild nystagmus and decreased visual acuity which had been present since childhood. They were each evaluated with full field Ganzfeld electroretinography which demonstrated flat photopic responses and preserved rod function. Genetic testing performed at Carver lab at the University of Iowa confirmed a diagnosis of achromatopsia with identical mutations in the CNGB3 gene. Spectral domain optical coherence tomography was performed which revealed foveal changes in both siblings, with slight phenotypic variations in these genotypically identical siblings. OCT findings in achromatopsia emphasize the importance of early identification and treatment in this disorder.

  18. Descemet membrane endothelial keratoplasty: intraoperative and postoperative imaging spectral-domain optical coherence tomography.

    PubMed

    Ang, Marcus; Dubis, Adam M; Wilkins, Mark R

    2015-01-01

    We describe a case report of using the same handheld spectral-domain anterior segment optical coherence tomography (ASOCT) for rapid intraoperative and postoperative imaging in a case of Descemet membrane endothelial keratoplasty (DMEK). A 67-year-old woman, with Fuchs dystrophy and corneal decompensation, underwent DMEK with intraoperative ASOCT imaging using the handheld Envisu spectral domain ASOCT system (Bioptigen, Inc., Morrisville, NC, USA). We found that this easy-to-use portable system with handheld probe allowed for rapid imaging of the anterior segment during donor manipulation to visualize the orientation of the DMEK donor, as well as to confirm the initial adhesion of the DMEK donor. Moreover, the same system may be used for postoperative monitoring of graft adhesion, corneal thickness, and stromal remodeling in the clinic with very high-definition images.

  19. Bubble behavior during solidification in low-gravity. [SPAR 1 and SPAR 3 flights

    NASA Technical Reports Server (NTRS)

    Papazian, J. M.; Wilcox, W. R.

    1979-01-01

    The trapping and behavior of gas bubbles were studied during low gravity solidification of carbon tetrabromide. The flight experiments were performed during two sounding rocket flights (SPAR 1 and SPAR 3) and involved gradient freeze solidification of gas saturated melts. Gas bubbles were evolved at the solid-liquid interfaces during the low gravity intervals. No large-scale thermal migration of bubbles, bubble pushing by the solid-liquid interface, or bubble detachment from the interface were observed during the low gravity experiments. During the SPAR 3 experiment, a unique bubble motion-fluid flow event occurred in one specimen: a large bubble moved downward and caused some circulation of the melt. The gas bubbles that were trapped by the solid in commercial purity material formed voids that had a cyclindrical shape in SPAR 3, in contrast to the spherical shape that had been observed in SPAR 1. These shapes were not influenced by the gravity level, but were dependent upon the initial temperature gradient. In higher purity material the shape of the voids changed from cylindrical in one-g to spherical in low-g.

  20. Experimental And Numerical Evaluation Of Gaseous Agents For Suppressing Cup-Burner Flames In Low Gravity

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Linteris, Gregory T.; Katta, Viswanath R.

    2003-01-01

    Longer duration missions to the moon, to Mars, and on the International Space Station (ISS) increase the likelihood of accidental fires. NASA's fire safety program for human-crewed space flight is based largely on removing ignition sources and controlling the flammability of the material on-board. There is ongoing research to improve the flammability characterization of materials in low gravity; however, very little research has been conducted on fire suppression in the low-gravity environment. Although the existing suppression systems aboard the Space Shuttle (halon 1301, CF3Br) and the ISS (CO2 or water-based form) may continue to be used, alternative effective agents or techniques are desirable for long-duration missions. The goal of the present investigation is to: (1) understand the physical and chemical processes of fire suppression in various gravity and O2 levels simulating spacecraft, Mars, and moon missions; (2) provide rigorous testing of analytical models, which include detailed combustion-suppression chemistry and radiation sub-models, so that the model can be used to interpret (and predict) the suppression behavior in low gravity; and (3) provide basic research results useful for advances in space fire safety technology, including new fire-extinguishing agents and approaches.

  1. Extinguishment of a Diffusion Flame Over a PMMA Cylinder by Depressurization in Low-Gravity

    NASA Technical Reports Server (NTRS)

    Goldmeer, Jeffrey S.; Tien, James S.; Urban, David L.

    1997-01-01

    The behavior of flames in low-speed flows in low-gravity is relevant to spacecraft fire safety. Previous work has shown that flames in the presence of low-speed forced flows in low-gravity may be more flammable than in a forced flow of the same magnitude in normal gravity. Additionally, fire suppression plans for the International Space Station include the use of venting (depressurization) as an emergency option for extinguishing fires. This procedure would induce flows in the affected compartment that could temporarily intensify the fire, as was observed in flammability tests of solids conducted on board Skylab. Despite a general Understanding, current knowledge of the combined effects of reduced pressure and forced flow on a burning solid in low-gravity is inadequate for the design of a venting extinguishment system. Previous studies in low-g have examined flammability limits for thermally thin solids. However, there are differences when burning thick materials because the interior solid-phase temperature continuously changes, which affects the percentage of gas-phase heat feedback to the solid-phase. Changes in the heat feedback to the solid-phase can affect the flammability characteristics of the material. In the current work, the extinction of a diffusion flame burning over PMMA (polymethyl methacrylate) cylinders during depressurization with a low-speed cross flow was examined experimentally and via numerical simulations.

  2. Analysis of low gravity tolerance of model experiments for space station: Preliminary results for directional solidification

    NASA Technical Reports Server (NTRS)

    Alexander, J. Iwan D.; Ouazzani, Jalil

    1988-01-01

    It has become clear from measurements of the acceleration environment in the Spacelab that the residual gravity levels on board a spacecraft in low Earth orbit can be significant and should be of concern to experimenters who wish to take advantage of the low gravity conditions on future Spacelab missions and on board the Space Station. The basic goals are to better understand the low gravity tolerance of three classes of materials science experiments: crystal growth from a melt, a vapor, and a solution. The results of the research will provide guidance toward the determination of the sensitivity of the low gravity environment, the design of the laboratory facilites, and the timelining of materials science experiments. To data, analyses of the effects of microgravity environment were, with a few exceptions, restricted to order of magnitude estimates. Preliminary results obtained from numerical models of the effects of residual steady and time dependent acceleration are reported on: heat, mass, and momentum transport during the growth of a dilute alloy by the Bridgman-Stockbarger technique, and the response of a simple fluid physics experiment involving buoyant convection in a square cavity.

  3. Multidimensional optical signal processing using optical coherent transient spatial-spectral holography

    NASA Astrophysics Data System (ADS)

    Anderson, Kenneth Edward

    This thesis presents analysis and experimental demonstrations of several new optical signal processing architectures that are based on optical coherent transient (OCT) technology and investigates many system design issues that must be taken into account when building such systems. OCT materials have the potential to optically process both high bandwidth (>10 GHz) and high time-bandwidth (>106) signals with the ability to potentially store huge amounts of data (up to 1000's of TB/cm3 using spatial-temporal holography. Several OCT system architectures are proposed and discussed including: raster image correlators, scanners, RF spectrum analyzers, time integrating correlators, image sequence correlators, and dynamic optical switches. In addition, some of the first experimental demonstrations of multiple channel spatial-temporal signal processing using OCT materials are shown. Novel system architectures for performing chromatic, polarization mode, and modal dispersion compensation are discussed, analyzed, and initial experimental results are shown demonstrating chromatic dispersion compensation of up to 5 mus of dispersion. A new approach for multiplexing 100's of individual DWDM channels of information down one multimode fiber is proposed and analyzed. In addition, a high bandwidth adaptive phased array beam steering system is also proposed and investigated along with experimental results showing the first demonstration of simultaneous time delay and processing of information with OCT materials. Lastly, results are presented for several stabilized lasers systems that have been built throughout the course of this research. The techniques used for stabilizing these lasers systems included optical feedback from gratings and Fabry-Perot cavities and electronic feedback techniques using Pound-Drever-Hall frequency locking.

  4. Development of a low-cost, 11 µm spectral domain optical coherence tomography surface profilometry prototype

    NASA Astrophysics Data System (ADS)

    Suliali, Nyasha J.; Baricholo, Peter; Neethling, Pieter H.; Rohwer, Erich G.

    2017-06-01

    A spectral-domain Optical Coherence Tomography (OCT) surface profilometry prototype has been developed for the purpose of surface metrology of optical elements. The prototype consists of a light source, spectral interferometer, sample fixture and software currently running on Microsoft® Windows platforms. In this system, a broadband light emitting diode beam is focused into a Michelson interferometer with a plane mirror as its sample fixture. At the interferometer output, spectral interferograms of broadband sources were measured using a Czerny-Turner mount monochromator with a 2048-element complementary metal oxide semiconductor linear array as the detector. The software performs importation and interpolation of interferometer spectra to pre-condition the data for image computation. One dimensional axial OCT images were computed by Fourier transformation of the measured spectra. A first reflection surface profilometry (FRSP) algorithm was then formulated to perform imaging of step-function-surfaced samples. The algorithm re-constructs two dimensional colour-scaled slice images by concatenation of 21 and 13 axial scans to form a 10 mm and 3.0 mm slice respectively. Measured spectral interferograms, computed interference fringe signals and depth reflectivity profiles were comparable to simulations and correlated to displacements of a single reflector linearly translated about the arm null-mismatch point. Surface profile images of a double-step-function-surfaced sample, embedded with inclination and crack detail were plotted with an axial resolution of 11 μm. The surface shape, defects and misalignment relative to the incident beam were detected to the order of a micron, confirming high resolution of the developed system as compared to electro-mechanical surface profilometry techniques.

  5. Measurements of spectral responses for developing fiber-optic pH sensor

    NASA Astrophysics Data System (ADS)

    Yoo, Wook Jae; Heo, Ji Yeon; Jang, Kyoung Won; Seo, Jeong Ki; Moon, Jin Soo; Park, Jang-Yeon; Park, Byung Gi; Cho, Seunghyun; Lee, Bongsoo

    2011-01-01

    In this study, we have fabricated a fiber-optic pH sensor, which is composed of a light source, a pH-sensing probe, plastic optical fibers and a spectrometer, for determining the degree of infection by Helicobacter pylori in the stomach. As pH indicators, phenol red and m-cresol purple are used, and pH liquid solutions are prepared by mixing phenol red or m-cresol purple solutions and various kinds of pH buffer solutions. The light emitted by a light source is guided by plastic optical fibers to the pH liquid solution, and the optical characteristic of a reflected light is changed according to the color variations of the pH indicator in the pH-sensing probe. Therefore, we have measured the intensities and wavelength shifts of the reflected lights, which change according to the color variations of indicators at different pH values, by using a spectrometer for spectral analysis. Also, the relationships between the pH values of liquid solutions and the optical properties of the modulated lights are obtained on the basis of the changes of the colors of indicators.

  6. MODIS Aqua Optical Throughput Degradation Impact on Relative Spectral Response and Calibration on Ocean Color Products

    NASA Technical Reports Server (NTRS)

    Lee, Shihyan; Meister, Gerhard

    2017-01-01

    Since Moderate Resolution Imaging Spectroradiometer Aqua's launch in 2002, the radiometric system gains of the reflective solar bands have been degrading, indicating changes in the systems optical throughput. To estimate the optical throughput degradation, the electronic gain changes were estimated and removed from the measured system gain. The derived optical throughput degradation shows a rate that is much faster in the shorter wavelengths than the longer wavelengths. The wavelength-dependent optical throughput degradation modulated the relative spectral response (RSR) of the bands. In addition, the optical degradation is also scan angle-dependent due to large changes in response versus the scan angle over time. We estimated the modulated RSR as a function of time and scan angles and its impacts on sensor radiometric calibration for the ocean science. Our results show that the calibration bias could be up to 1.8 % for band 8 (412 nm) due to its larger out-of-band response. For the other ocean bands, the calibration biases are much smaller with magnitudes at least one order smaller.

  7. Fiber-optic surface plasmon resonance sensors in the near-infrared spectral region.

    PubMed

    Masson, Jean-Francois; Kim, Yoon-Chang; Obando, Louis A; Peng, Wei; Booksh, Karl S

    2006-11-01

    The sensitivity of fiber-optic surface plasmon resonance (SPR) sensors was improved by a factor of at least thirteen for aqueous solutions by modifying the tip geometry to allow interrogation of the surface plasmon (SP) band in the near-infrared (NIR) region. This was achieved by tuning the angle at the distal end of the SPR sensor to a dual taper of 71 degrees and 19 degrees . Using a low numerical aperture (NA) fiber-optic sensor, NA = 0.12, is necessary to obtain a functional SPR sensor working in the NIR region. Theoretical simulations using the Maxwell equations demonstrated that even higher enhancement is theoretically possible while maintaining a narrow spectral feature upon the excitation of the SP bands on gold surfaces. The manufacture of the SPR sensors yields good agreement between theoretical simulations and experimental observations. To investigate the properties of these fiber-optic SPR-NIR sensors, sucrose solutions ranging from 0 to 15 x 10(-3) in mole fraction were utilized. The increased sensitivity of the fiber-optic SPR sensors, when used to monitor biomarkers, would yield lower detection limits. The smaller sensing area, compared to planar or other fiber-optic SPR sensors, combined with an improvement of the sensitivity, would yield a dramatic reduction of the absolute amount detected by biosensors.

  8. Observation and modelling of dusty, low gravity L, and M dwarfs

    NASA Astrophysics Data System (ADS)

    Seifahrt, Andreas; Helling, Christiane; Burgasser, Adam J.; Allers, Katelyn N.; Cruz, Kelle L.; Cushing, Michael C.; Heiter, Ulrike; Looper, Dagny L.; Witte, Sören

    2009-02-01

    Observational facilities allow now the detection of optical and IR spectra of young M- and L-dwarfs. This enables empirical comparisons with old M- and L- dwarfs, and detailed studies in comparison with synthetic spectra. While classical stellar atmosphere physics seems perfectly appropriate for old M-dwarfs, more physical and chemical processes, cloud formation in particular, needs to be modelled in the substellar regime to allow a detailed spectral interpretation. Not much is known so far about the details of the inset of cloud formation at the spectral transition region between M and L dwarfs. Furthermore there is observational evidence for diversity in the dust properties of objects having the same spectral type. Do we understand these differences? The question is also how young M- and L-dwarfs need to be classified, which stellar parameter do they have and whether degenerations in the stellar parameter space due to the changing atmosphere physics are present, like in the L-T transition region. The Splinter was driven by these questions which we will use to encourage interactions between observation and theory. Given the recent advances, both in observations and spectral modelling, an intensive discussion between observers and theoreticians will create new synergies in our field.

  9. Spectral domain optical coherence tomography imaging of spectacular ecdysis in the royal python (Python regius).

    PubMed

    Tusler, Charlotte A; Maggs, David J; Kass, Philip H; Paul-Murphy, Joanne R; Schwab, Ivan R; Murphy, Christopher J

    2015-01-01

    To describe using spectral domain optical coherence tomography (SD-OCT), digital slit-lamp biomicroscopy, and external photography, changes in the ophidian cuticle, spectacle, and cornea during ecdysis. Four normal royal pythons (Python regius). Snakes were assessed once daily throughout a complete shed cycle using nasal, axial, and temporal SD-OCT images, digital slit-lamp biomicroscopy, and external photography. Spectral domain optical coherence tomography (SD-OCT) images reliably showed the spectacular cuticle and stroma, subcuticular space (SCS), cornea, anterior chamber, iris, and Schlemm's canal. When visible, the subspectacular space (SSS) was more distended peripherally than axially. Ocular surface changes throughout ecdysis were relatively conserved among snakes at all three regions imaged. From baseline (7 days following completion of a full cycle), the spectacle gradually thickened before separating into superficial cuticular and deep, hyper-reflective stromal components, thereby creating the SCS. During spectacular separation, the stroma regained original reflectivity, and multiple hyper-reflective foci (likely fragments from the cuticular-stromal interface) were noted within the SCS. The cornea was relatively unchanged in character or thickness throughout all stages of ecdysis. Slit-lamp images did not permit observation of these changes. Spectral domain optical coherence tomography (SD-OCT) provided excellent high-resolution images of the snake anterior segment, and especially the cuticle, spectacle, and cornea of manually restrained normal snakes at all stages of ecdysis and warrants investigation in snakes with anterior segment disease. The peripheral spectacle may be the preferred entry point for diagnostic or therapeutic injections into the SSS and for initiating spectacular surgery. © 2014 American College of Veterinary Ophthalmologists.

  10. Optical properties of peritoneal biological tissues in the spectral range of 350-2500 nm

    NASA Astrophysics Data System (ADS)

    Bashkatov, A. N.; Genina, E. A.; Kozintseva, M. D.; Kochubei, V. I.; Gorodkov, S. Yu.; Tuchin, V. V.

    2016-01-01

    The optical characteristics of biological tissues sampled from the anterior abdominal wall of laboratory rats are for the first time experimentally studied in a wide wavelength range (350-2500 nm). The experiments have been performed in vitro using a LAMBDA 950 (PerkinElmer, United States) spectrophotometer. Inverse Monte Carlo simulation is used to restore the spectral dependences for scattering and absorption coefficients, as well as the scattering anisotropy factor for biological tissue based on the recorded spectra of diffuse reflection and total and collimated transmissions.

  11. Spectral-Domain Optical Coherence Tomography of Polypoidal Choroidal Vasculopathy Associated With Benign Choroidal Nevus.

    PubMed

    De Salvo, Gabriella; Vaz-Pereira, Sara; Sehmi, Kulwant S; Andrews, Richard M; Sagoo, Mandeep S

    2015-01-01

    Two cases of polypoidal choroidal vasculopathy (PCV) complicating benign choroidal nevus and their tomographic features at spectral-domain optical coherence tomography (SD-OCT) are reported. Two eyes with choroidal nevus and associated subretinal fluid underwent complete ophthalmological examination, SD-OCT, fundus fluorescein angiography, and indocyanine green angiography (ICGA). SD-OCT and ICGA confirmed the diagnosis of PCV in both cases. Ophthalmologists should be aware of this rare combination between choroidal nevus and PCV. If a choroidal nevus presents with subretinal fluid, this does not always herald malignant transformation, and PCV should be ruled out so that the correct treatment can be planned.

  12. Human ex-vivo oral tissue imaging using spectral domain polarization sensitive optical coherence tomography.

    PubMed

    Sharma, Priyanka; Verma, Yogesh; Sahu, Khageswar; Kumar, Sudhir; Varma, Amit V; Kumawat, Jyoti; Gupta, Pradeep Kumar

    2017-01-01

    We report the use of spectral domain polarization sensitive optical coherence tomography for ex-vivo imaging of human oral mandibular tissue samples. Our results show that compared to the changes observed in the epithelium thickness and the decay constant of A-scan intensity profile, a much larger degree of change was observed in the phase retardation for tissue sites progressing from normal to the malignant state. These results suggest that monitoring of tissue retardance can help in better differentiation of normal and cancerous oral tissue sites.

  13. Suppression of image autocorrelation artefacts in spectral domain optical coherence tomography and multiwave digital holography

    SciTech Connect

    Gelikonov, V M; Gelikonov, G V; Terpelov, D A; Shabanov, D V; Shilyagin, P A

    2012-05-31

    An improved method for suppressing image artefacts in spectral domain optical coherence tomography (SD OCT) and multiwave digital holography, caused by the influence of coherent noise in the course of successive registration of an autocorrelation component and informative signal is reported. The method allows complete suppression of all types of coherent noises, provided that the sample of values used to record the autocorrelation component satisfies the conditions of Kotelnikov's theorem: in SD OCT - for the transverse structure of the studied medium, in multiwave digital holography - for the envelop function of the radiation source frequency tuning spectrum.

  14. Multijunction Solar Cell Efficiencies: Effect of Spectral Window, Optical Environment and Radiative Coupling

    DTIC Science & Technology

    2014-09-04

    a high quality GaAs solar cell in the absence of radiative coupling (B¼ 0).6,9 The current–voltage response of the cell was characterized by a solar ...efficiency multijunction cells . Experimental Alta Devices provided thin-lm, exible GaAs solar cells for the experimental portion of this study. The...Multijunction solar cell efficiencies: effect of spectral window, optical environment and radiative coupling† Carissa N. Eisler,a Ze’ev R. Abrams,b

  15. Spectral-domain optical coherence tomography appearance of a retinal nematode.

    PubMed

    Masudi, Ali; Soheilian, Masoud; Nourinia, Ramin; Soheilian, Rasam; Peyman, Gholam A

    2013-11-25

    A 65-year-old man presented with decreased visual acuity in his left eye of 10 days' duration. Ocular examination revealed visual acuity of 20/200 in the left eye caused by a visible retinal nematode (roundworm) located close to the fovea. Spectral-domain optical coherence tomography imaging showed the nematode in the retinal nerve fiber layer. The patient was followed up without treatment, and the nematode disappeared spontaneously after 5 weeks. Visual acuity in the affected eye improved to 20/25.

  16. Spectral engineering by flexible tunings of optical Tamm states and Fabry-Perot cavity resonance.

    PubMed

    Zhang, Xu-Lin; Song, Jun-Feng; Feng, Jing; Sun, Hong-Bo

    2013-11-01

    We present a design for spectral engineering in a metal dual distributed Bragg reflector (DBR)-based structure. Optical Tamm states and Fabry-Perot cavity mode, dual windows for light-matter interaction enhancement, can be excited simultaneously and tuned flexibly, including their respective bandwidth and resonant wavelength, due to the variable reflection phase from the outer DBR's internal surface. The design can find applications in solar cells for light trappings. Via calculations of overall absorptivity, the proposed simpler dual-states-based scheme is demonstrated to be almost as effective as the coherent-light-trapping scheme, owing to the dual-states-induced broader-band absorption enhancement.

  17. Novel technique for measuring intermodal dispersion in optical fibers using the spectral interference in the Michelson interferometer configuration

    NASA Astrophysics Data System (ADS)

    Hlubina, Petr

    1999-07-01

    The spectral interference between two modes of an optical fiber, which shows up as a periodic modulation of the source spectrum at its output, cannot be used to measure intermodal dispersion in the optical fiber when the period of modulation is too small to be resolved by a spectrometer. We proposed a novel measuring technique utilizing a tandem configuration of a dispersive Michelson interferometer and a two-mode optical fiber in which the intermodal interference can be restored, and consequently spectral interference fringes can be resolved, even if a low-resolution spectrometer is used. In the tandem configuration of the Michelson interferometer and the two-mode optical fiber, the optical path difference (OPD) in the Michelson interferometer is adjusted close to the group OPD between modes of the optical fiber so that the low-frequency spectral modulation that can be processed is produced. The feasibility of this technique has successfully been demonstrated in obtaining the wavelength dependence of the group OPD between two modes of the optical fiber. Using the Fourier transform method in processing the measured spectral modulations and subtracting the effect of the dispersive Michelson interferometer, the intermodal dispersion of the two-mode optical fiber has been obtained.

  18. Your Age is Showing: Understanding the Spectral Features of Young Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    DiTomasso, Victoria; Schwab, Ellianna; Rice, Emily L.; Riedel, Adric R.; Cruz, Kelle L.; Faherty, Jackie

    2017-01-01

    Brown dwarfs are substellar objects that continuously cool, shrink, and fade over billions of years. These physical changes lead us to expect that young objects will have spectral indicators of low gravity. We selected 11 brown dwarfs ranging in spectral type from M7-L7 whose optical and/or low resolution NIR spectroscopy suggest that they are low gravity, hence young, objects. Using high-resolution (R~20,000) near-infrared data from the NIRSPEC instrument at the Keck II telescope in Hawaii, we analyzed J-band (1.1-1.4 μm) spectra of these targets. We calculated their radial velocities and combined those values with previously calculated parallax distances and proper motions to determine their likelihood of membership in nearby young moving groups, successfully placing three of them. We also compared our high-resolution spectra to observations of confirmed young (<500 Myr old) and field age (1-5 Gyr old) brown dwarfs. We examined differences in the gravity-sensitive potassium (K I) lines at 1.175 μm and 1.25 μm both qualitatively and quantitatively. By analyzing the high resolution spectroscopy of these candidate young brown dwarfs we can evaluate the consistency of spectral indicators of youth across spectral type, age, resolution, and wavelength regime.

  19. All-optical spectral linewidth reduction of lasers for coherent optical communication.

    PubMed

    Pan, Deng; Ke, Changjian; Fu, Songnian; Liu, Yaping; Liu, Deming; Willner, Alan E

    2013-12-15

    We propose and experimentally demonstrate an effective spectral linewidth suppression scheme for a commercial tunable laser source. By using a long-cavity, narrow-bandwidth stimulated Brillouin scattering filter and multifrequency-selection mechanism simultaneously, a single-longitudinal-mode laser output with linewidth suppression from ~3 MHz to less than 20 kHz is successfully achieved in the whole C-band. Meanwhile, insertion loss of ~5 dB and a side-mode suppression ratio improvement of ~20 dB at a typical output wavelength of 1552.520 nm are obtained. The scheme is experimentally verified to be wavelength independent in the C-band and characterized with good performance of wavelength and power stability.

  20. Discerning Spectral Features in L Dwarfs

    NASA Astrophysics Data System (ADS)

    Nunez, Alejandro; Cruz, K.; Burgasser, A. J.; Kirkpatrick, J. D.; Reid, I. N.

    2011-01-01

    Brown dwarfs are star-like objects that, due to their very low masses (less than 75 Jupiter masses,) never reach the main sequence, and instead cool with time. This cooling leads to a breakdown of the relationship between temperature and mass that exists for stars. Therefore, brown dwarfs with similar temperatures (as indicated by spectral type) could have very different masses and ages. We are investigating the near-infrared spectra of L dwarfs with the same optically derived spectral types (implying similar effective temperatures) with the goal of distinguishing subtle differences, patterns, and/or correlations among absorption features that could reveal information about their ages and masses. Our sample consists of 43 L0-L8 dwarfs with both optical and near-infrared spectra, thus covering the 0.65 to 2.4-micron range. Our analysis included objects with either "typical” or peculiar spectra. Some of the objects with peculiar spectra are suspected low-gravity/young and blue/low-metallicity dwarfs. For each optical type, we normalized and overplotted the spectra in four bands separately: Optical, J, H, and K band. Each resulting plot was examined by eye to look for subtle differences in spectral absorption features, likely due to age and mass. We present the preliminary results from this detailed spectral analysis. In particular, our analysis reveals the major spectral differences in the near infrared of both "red” and "blue” L dwarfs. This work was funded by the RISE Grant GM R25 6066, and we acknowledge the hospitality of the American Museum of Natural History.

  1. Theoretical prediction of spectral and optical properties of bacteriochlorophylls in thermally disordered LH2 antenna complexes.

    PubMed

    Janosi, Lorant; Kosztin, Ioan; Damjanović, Ana

    2006-07-07

    A general approach for calculating spectral and optical properties of pigment-protein complexes of known atomic structure is presented. The method, that combines molecular dynamics simulations, quantum chemistry calculations, and statistical mechanical modeling, is demonstrated by calculating the absorption and circular dichroism spectra of the B800-B850 bacteriochlorophylls of the LH2 antenna complex from Rs. molischianum at room temperature. The calculated spectra are found to be in good agreement with the available experimental results. The calculations reveal that the broadening of the B800 band is mainly caused by the interactions with the polar protein environment, while the broadening of the B850 band is due to the excitonic interactions. Since it contains no fitting parameters, in principle, the proposed method can be used to predict optical spectra of arbitrary pigment-protein complexes of known structure.

  2. Structural Analysis of Polymer Composites Using Spectral Domain Optical Coherence Tomography.

    PubMed

    Shirazi, Muhammad Faizan; Jeon, Mansik; Kim, Jeehyun

    2017-05-18

    The structural analysis of nylon/graphene oxide (NY/GO) and polyetherblockamide/ trisilinolphenyl-polyhederal oligomeric silsesquioxane (PEBA/t-POSS) composites were performed using high-resolution spectral domain optical coherence tomography (SD-OCT). This optical technology revealed both cross-sectional, as well as sub-layer depth information of sample. The non-destructive real-time imaging demonstrated the nature of defects in the composites. The thickness and location of each defect point in the composites were measured using A-scan analysis on the SD-OCT images. The cross-sectional and volumetric images clearly demonstrate the effectiveness of SD-OCT for composite research, as well as the for industrial quality assurance of polymer materials.

  3. Comparative analysis of combined spectral and optical tomography methods for detection of skin and lung cancers.

    PubMed

    Zakharov, Valery P; Bratchenko, Ivan A; Artemyev, Dmitry N; Myakinin, Oleg O; Kornilin, Dmitry V; Kozlov, Sergey V; Moryatov, Alexander A

    2015-02-01

    Malignant skin tumors of different types were studied in vivo using optical coherence tomography (OCT), backscattering (BS), and Raman spectroscopy (RS). A multimodal method is proposed for early cancer detection based on complex analysis of OCT images by their relative alteration of scattered-radiation spectral intensities between malignant and healthy tissues. An increase in average accuracy of diagnosis was observed for a variety of cancer types (9% sensitivity, 8% specificity) by a multimodal RS-BS-OCT system in comparison with any of the three methods used separately. The proposed approach equalizes the processing rates for all methods and allows for simultaneous imaging and classification of tumors. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

  4. Multi-spectral optical absorption in substrate-free nanowire arrays

    SciTech Connect

    Zhang, Junpeng; Chia, Andrew; Boulanger, Jonathan; LaPierre, Ray; Dhindsa, Navneet; Khodadad, Iman; Saini, Simarjeet

    2014-09-22

    A method is presented of fabricating gallium arsenide (GaAs) nanowire arrays of controlled diameter and period by reactive ion etching of a GaAs substrate containing an indium gallium arsenide (InGaP) etch stop layer, allowing the precise nanowire length to be controlled. The substrate is subsequently removed by selective etching, using the same InGaP etch stop layer, to create a substrate-free GaAs nanowire array. The optical absorptance of the nanowire array was then directly measured without absorption from a substrate. We directly observe absorptance spectra that can be tuned by the nanowire diameter, as explained with rigorous coupled wave analysis. These results illustrate strong optical absorption suitable for nanowire-based solar cells and multi-spectral absorption for wavelength discriminating photodetectors. The solar-weighted absorptance above the bandgap of GaAs was 94% for a nanowire surface coverage of only 15%.

  5. Speckle noise reduction in high speed polarization sensitive spectral domain optical coherence tomography

    PubMed Central

    Götzinger, Erich; Pircher, Michael; Baumann, Bernhard; Schmoll, Tilman; Sattmann, Harald; Leitgeb, Rainer A.; Hitzenberger, Christoph K.

    2015-01-01

    We present a high speed polarization sensitive spectral domain optical coherence tomography system based on polarization maintaining fibers and two high speed CMOS line scan cameras capable of retinal imaging with up to 128 k A-lines/s. This high imaging speed strongly reduces motion artifacts and therefore averaging of several B-scans is possible, which strongly reduces speckle noise and improves image quality. We present several methods for averaging retardation and optic axis orientation, the best one providing a 5 fold noise reduction. Furthermore, a novel scheme of calculating images of degree of polarization uniformity is presented. We quantitatively compare the noise reduction depending on the number of averaged frames and discuss the limits of frame numbers that can usefully be averaged. PMID:21934820

  6. Optical properties and spectral emissivities at 632.8 nm in the titanium-aluminum system

    NASA Technical Reports Server (NTRS)

    Krishnan, S.; Anderson, C. D.; Weber, J. K. R.; Nordine, P. C.; Hofmeister, W. H.; Bayuzick, R. J.

    1993-01-01

    Optical properties (including spectral emissivity, refractive index, and extinction coefficient) of liquid Ti-Al alloys were measured as functions of temperature (including temperatures up to 350 K below the equilibrium liquidus temperatures), using laser ellipsometry at 632.8 nm. The experiments were conducted under containerless conditions, using electromagnetic levitation and heating supplemented by CO2 laser beam heating. It is shown that the emissivities of liquid Ti-Al alloy vary with temperature in a manner that can be understood by the same theories which are applicable to solid metals, for regions near to and above the liquidus temperature. At temperatures below the liquidus temperature, the optical properties of highly undercooled liquid Ti-Al alloys are not dependent on temperature.

  7. Spectral-domain optical coherence phase microscopy for label-free multiplexed protein microarray assay.

    PubMed

    Joo, Chulmin; Ozkumur, Emre; Unlü, M Selim; Boer, Johannes F de

    2009-10-15

    Quantitative measurement of affinities and kinetics of various biomolecular interactions such as protein-protein, protein-DNA and receptor-ligand is central to our understanding of basic molecular and cellular functions and is useful for therapeutic evaluation. Here, we describe a laser-scanning quantitative imaging method, referred to as spectral-domain optical coherence phase microscopy, as an optical platform for label-free detection of biomolecular interactions. The instrument is based on a confocal interferometric microscope that enables depth-resolved quantitative phase measurements on sensor surface with high spatial resolution and phase stability. We demonstrate picogram per square millimeter surface mass sensitivity, and show its sensing capability by presenting static and dynamic detection of multiplexed protein microarray as immobilized antigens capture their corresponding antibodies.

  8. Online monitoring of printed electronics by Spectral-Domain Optical Coherence Tomography

    PubMed Central

    Alarousu, Erkki; AlSaggaf, Ahmed; Jabbour, Ghassan E.

    2013-01-01

    Spectral-Domain Optical Coherence Tomography (SD-OCT) is an optical method capable of 3D imaging of object's internal structure with micron-scale resolution. Modern SD-OCT tools offer the speed capable of online monitoring of printed devices. This paper demonstrates the use of SD-OCT in a simulated roll-to-roll (R2R) process through monitoring some structural properties of moving screen printed interdigitated electrodes. It is shown that structural properties can be resolved for speeds up to ca. 1 m/min, which is the first step towards application of this method in real manufacturing processes, including roll-to-roll (R2R) printing. PMID:23536206

  9. Wavelength dependence of sensitivity in spectral diffuse optical imaging: effect of normalization on image reconstruction.

    PubMed

    Eames, Matthew E; Dehghani, Hamid

    2008-10-27

    Near Infrared Diffuse Optical Tomography has the potential to be used as a non-invasive imaging tool for biological tissue specifically for the diagnosis and characterization of breast cancer. Most model based reconstruction algorithms rely on calculating and inverting a large Jacobian matrix. Although this method is flexible for a wide range of complex problems, it usually results in large image artifacts from hypersensitivity around the detectors. In this work a Jacobian normalization technique is presented which takes into account the varying magnitude of different optical parameters creating a more uniform update within a spectral image reconstruction model. Using simulated data the Jacobian normalization method is used to reconstructed images of absolute chromophore and scattering parameters which are qualitatively and quantitatively as compared to conventional methods. The hypersensitivity resulting in boundary artifacts are shown to be minimized with only a small additional computational cost.

  10. Online monitoring of printed electronics by Spectral-Domain Optical Coherence Tomography.

    PubMed

    Alarousu, Erkki; AlSaggaf, Ahmed; Jabbour, Ghassan E

    2013-01-01

    Spectral-Domain Optical Coherence Tomography (SD-OCT) is an optical method capable of 3D imaging of object's internal structure with micron-scale resolution. Modern SD-OCT tools offer the speed capable of online monitoring of printed devices. This paper demonstrates the use of SD-OCT in a simulated roll-to-roll (R2R) process through monitoring some structural properties of moving screen printed interdigitated electrodes. It is shown that structural properties can be resolved for speeds up to ca. 1 m/min, which is the first step towards application of this method in real manufacturing processes, including roll-to-roll (R2R) printing.

  11. Large optical spectral range dispersion engineered silicon-based photonic crystal waveguide modulator.

    PubMed

    Hosseini, Amir; Xu, Xiaochuan; Subbaraman, Harish; Lin, Che-Yun; Rahimi, Somayeh; Chen, Ray T

    2012-05-21

    We present a dispersion engineered slow light silicon-based photonic crystal waveguide PIN modulator. Low-dispersion slow light transmission over 18 nm bandwidth under the silica light line with a group index of 26.5 is experimentally confirmed. We investigate the variations of the modulator figure of merit, V(π) × L, as a function of the optical carrier wavelength over the bandwidth of the fundamental photonic crystal waveguide defect mode. A large signal operation with a record low maximum V(π )× L of 0.0464 V · mm over the low-dispersion optical spectral range is demonstrated. We also report the device operation at 2 GHz.

  12. Optical properties and spectral emissivities at 632.8 nm in the titanium-aluminum system

    NASA Technical Reports Server (NTRS)

    Krishnan, S.; Anderson, C. D.; Weber, J. K. R.; Nordine, P. C.; Hofmeister, W. H.; Bayuzick, R. J.

    1993-01-01

    Optical properties (including spectral emissivity, refractive index, and extinction coefficient) of liquid Ti-Al alloys were measured as functions of temperature (including temperatures up to 350 K below the equilibrium liquidus temperatures), using laser ellipsometry at 632.8 nm. The experiments were conducted under containerless conditions, using electromagnetic levitation and heating supplemented by CO2 laser beam heating. It is shown that the emissivities of liquid Ti-Al alloy vary with temperature in a manner that can be understood by the same theories which are applicable to solid metals, for regions near to and above the liquidus temperature. At temperatures below the liquidus temperature, the optical properties of highly undercooled liquid Ti-Al alloys are not dependent on temperature.

  13. 30 Watts mid-infrared optical parametric oscillator based on spectral beam combination technology

    NASA Astrophysics Data System (ADS)

    Shang, Yaping; Wang, Peng; Li, Xiao; Xu, Xiaojun

    2017-01-01

    Limited by the thermal effects and the laser-induced damage characteristics of the non-linear crystals, mid-infrared (MIR) output power of single optical parametric oscillator (OPO) is hard to get further promoted with excellent beam quality. An alternative solution is the multiple-beams combination technology, which exactly provided an effective approach for decreasing the thermal effects and the damage risk of the OPO system under high power operation. In this letter, the experimental study on the spectral beam combination of three idler MIR lasers was carried out for the first time. An optical parametric system with MIR output power of 30 W at 3130nm, 3352nm, and 3670nm was finally obtained. Experimental results indicated that the beam quality M2 factors of the combined laser were measured to be 1.76 and 2.42 in the horizontal and vertical directions, respectively, which confirmed the feasibility of the schematic design.

  14. Leaf Optical Properties in Higher Plants: Linking Spectral Characteristics to Stress and Chlorophyll Concentration

    NASA Technical Reports Server (NTRS)

    Carter, Gregory A.; Knapp, Alan K.

    2000-01-01

    A number of studies have linked responses in leaf spectral reflectance, transmittance or absorptance to physiological stress. A variety of stressors including dehydration, flooding,freezing, ozone, herbicides, competition, disease, insects and deficiencies in ectomycorrhizal development and N fertilization have been imposed on species ranging from grasses to conifers and deciduous trees. In this cases, the maximum difference in reflectance within the 400 - 850 nm wavelength range between control and stressed states occurred as a reflectance increase at wavelength near 700 nm. In studies that included transmittance and absorptance as well as reflectance, maximum differences occurred as increases and decreases, respectively, near 700 nm. This common optical response to stress could be simulated closely by varying the chlorophyll concentrations in senescent leaves of five species. The optical response to stress near 700 nm, as well as corresponding changes in reflectance that occur in the green-yellow spectrum, can be explained by the general tendency of stress to reduce leaf chlorophyll concentration.

  15. Impact of amplitude jitter and signal-to-noise ratio on the nonlinear spectral compression in optical fibres

    NASA Astrophysics Data System (ADS)

    Boscolo, Sonia; Fatome, Julien; Finot, Christophe

    2017-04-01

    We numerically study the effects of amplitude fluctuations and signal-to-noise ratio degradation of the seed pulses on the spectral compression process arising from nonlinear propagation in an optical fibre. The unveiled quite good stability of the process against these pulse degradation factors is assessed in the context of optical regeneration of intensity-modulated signals, by combining nonlinear spectral compression with centered bandpass optical filtering. The results show that the proposed nonlinear processing scheme indeed achieves mitigation of the signal's amplitude noise. However, in the presence of a jitter of the temporal duration of the pulses, the performance of the device deteriorates.

  16. Optical implementation of a Hopfield-type neural network by the use of persistent spectral hole-burning media

    NASA Astrophysics Data System (ADS)

    Ollikainen, Olavi; Rebane, Aleksander

    1991-11-01

    Optical implementation of two- and four-dimensional interconnection matrices (memory matrices) in the Hopfield-type neural network is carried out by using persistent spectral hole burning (PSHB) media. The capability of the present optical scheme to correct errors in the input image is demonstrated. The technique of photoburning of persistent spectral holes provides new parallel-accessible degrees of freedom that can be used for ultrafast optical processing. A holographic `monochromator' is proposed for high-resolution parallel detection of a large number of frequency components.

  17. High spectral and spatial resolution spectroscopy of YSOs with a silicon grism and adaptive optics

    NASA Astrophysics Data System (ADS)

    Ge, J.; Lloyd, J. P.; Gavel, D.; Macintosh, B.; Max, C. E.; Ciarlo, D.; Kuzmenko, P.; Graham, J. R.

    2000-12-01

    We have obtained complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ≈ 5000 using a silicon grism at the Lick 3m telescope. These results represent our first scientific observations conducted by the high resolution silicon grisms. Coupled with the LLNL adaptive optics system, a spatial resolution of 0.2 arcsec was achieved to allow observations of the companions with separations between 0.3-1.3 arcsec. The complete wavelength coverage was achieved by placing 16 cross-dispersed echelle orders on a 256x256 HgCdTe array with the silicon grism operating on high diffraction orders and a low dispersing CaF2 grism as a cross-disperser. High spectral resolution observations allow us to characterize each of the companions. Analysis of the spectra of these YSOs will be reported. The observations also allow us to measure the optical performance of the second generation of silicon grisms made with the techniques developed in early 2000. The new silicon grism has a peak efficiency of 45% and scattered light of ~ 8% in the K band. New techniques have been developed at Penn State to further reduce scattered light in the K band (Bernecker et al. this meeting) and are being applied in fabricating the third generation of silicon grisms for scientific observations. Fabrication of the silicon grisms and work on the Lick adaptive optics system was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48. Graham and Lloyd were also supported by the Center for Adaptive Optics under the STC Program of the National Science Foundation, Agreement No. AST-9876783

  18. All-optical cryptography of M-QAM formats by using two-dimensional spectrally sliced keys.

    PubMed

    Abbade, Marcelo L F; Cvijetic, Milorad; Messani, Carlos A; Alves, Cleiton J; Tenenbaum, Stefan

    2015-05-10

    There has been an increased interest in enhancing the security of optical communications systems and networks. All-optical cryptography methods have been considered as an alternative to electronic data encryption. In this paper we propose and verify the use of a novel all-optical scheme based on cryptographic keys applied on the spectral signal for encryption of the M-QAM modulated data with bit rates of up to 200 gigabits per second.

  19. Hyperreflective dots surrounding the central retinal artery and vein in optic disc melanocytoma revealed by spectral domain optical coherence tomography.

    PubMed

    Okubo, Akiko; Unoki, Kazuhiko; Yoshikawa, Hiroshi; Ishibashi, Tatsuro; Sameshima, Munefumi; Sakamoto, Taiji

    2013-01-01

    To report findings of optic disc melanocytoma (ODM) obtained using spectral domain optical coherence tomography (SD OCT), with special reference to the central retinal artery and vein surrounded by hyperreflective dots. Retrospective review of five eyes of five patients with ODM. Demographic information, ophthalmic examination including best-corrected visual acuity, dilated funduscopic examination, and SD OCT images were evaluated. Dome-shaped, darkly pigmented tumors were seen ophthalmoscopically in the optic discs of all eyes. On OCT, the first branches of the central retinal artery and/or vein were well defined as oblique sections of tubular structures with a perivascular distribution of hyperreflective dots in the elevated retina (nerve fiber layer) over the tumor. The portions where these vessels turn toward the retina were displaced more anteriorly than those of eyes without ODM. Hyperreflective dots of various sizes were also observed in elevated retinas over the tumors, which shadowed and obscured the subjacent tissue in all eyes. SD OCT provides higher definition images of ODM relating to the branches of the central retinal artery/vein, revealing anterior displacement of vessels and perivascular distribution of hyperreflective dots that suggest melanophages and/or tumor cells or proteins and/or lipid deposits.

  20. Spectral domain optical coherence tomography with extended depth-of-focus by aperture synthesis

    NASA Astrophysics Data System (ADS)

    Bo, En; Liu, Linbo

    2016-10-01

    We developed a spectral domain optical coherence tomography (SD-OCT) with an extended depth-of-focus (DOF) by synthetizing aperture. For a designated Gaussian-shape light source, the lateral resolution was determined by the numerical aperture (NA) of the objective lens and can be approximately maintained over the confocal parameter, which was defined as twice the Rayleigh range. However, the DOF was proportional to the square of the lateral resolution. Consequently, a trade-off existed between the DOF and lateral resolution, and researchers had to weigh and judge which was more important for their research reasonably. In this study, three distinct optical apertures were obtained by imbedding a circular phase spacer in the sample arm. Due to the optical path difference between three distinct apertures caused by the phase spacer, three images were aligned with equal spacing along z-axis vertically. By correcting the optical path difference (OPD) and defocus-induced wavefront curvature, three images with distinct depths were coherently summed together. This system digitally refocused the sample tissue and obtained a brand new image with higher lateral resolution over the confocal parameter when imaging the polystyrene calibration beads.

  1. Quasi-optical analysis of a far-infrared spatio-spectral space interferometer concept

    NASA Astrophysics Data System (ADS)

    Bracken, C.; O'Sullivan, C.; Murphy, J. A.; Donohoe, A.; Savini, G.; Lightfoot, J.; Juanola-Parramon, R.

    2016-07-01

    FISICA (Far-Infrared Space Interferometer Critical Assessment) was a three year study of a far-infrared spatio-spectral double-Fourier interferometer concept. One of the aims of the FISICA study was to set-out a baseline optical design for such a system, and to use a model of the system to simulate realistic telescope beams for use with an end-to-end instrument simulator. This paper describes a two-telescope (and hub) baseline optical design that fulfils the requirements of the FISICA science case, while minimising the optical mass of the system. A number of different modelling techniques were required for the analysis: fast approximate simulation tools such as ray tracing and Gaussian beam methods were employed for initial analysis, with GRASP physical optics used for higher accuracy in the final analysis. Results are shown for the predicted far-field patterns of the telescope primary mirrors under illumination by smooth walled rectangular feed horns. Far-field patterns for both on-axis and off-axis detectors are presented and discussed.

  2. Using the power spectral density method to characterise the surface topography of optical surfaces

    NASA Astrophysics Data System (ADS)

    Alcock, Simon G.; Ludbrook, Geoff D.; Owen, Tommy; Dockree, Richard

    2010-08-01

    Power Spectral Density (PSD) is an alternative method for specifying optical surfaces, and quantifies the contribution of each spatial regime to the total surface error. This approach naturally includes mid-range spatial frequency errors, which are often overlooked. The PSD method has recently been adopted by the Space and Astronomy industries, but has not yet received general acceptance within the synchrotron community. To assess the suitability for specifying synchrotron optics using PSD, Fast Fourier Transforms were performed on topography data from a range of optical surfaces of varying quality and manufacturing techniques. For each grade of optic, the entire regime ({100nm to {50mm) of surface errors was measured, with overlapping bandwidths, using a micro-interferometer and a Fizeau interferometer. From this heuristic information, root-mean square "roughness" can be predicted over any desired spatial range, thus allowing direct comparison of metrology data obtained by instruments with different spatial bandwidths. We present an efficient approach for calculating 1-D and 2-D PSDs using MATLAB algorithms, and discuss analysis considerations, including "field of view" effects and instrument calibration.

  3. Likelihood Ratios for Glaucoma Diagnosis Using Spectral Domain Optical Coherence Tomography

    PubMed Central

    Lisboa, Renato; Mansouri, Kaweh; Zangwill, Linda M.; Weinreb, Robert N.; Medeiros, Felipe A.

    2014-01-01

    Purpose To present a methodology for calculating likelihood ratios for glaucoma diagnosis for continuous retinal nerve fiber layer (RNFL) thickness measurements from spectral domain optical coherence tomography (spectral-domain OCT). Design Observational cohort study. Methods 262 eyes of 187 patients with glaucoma and 190 eyes of 100 control subjects were included in the study. Subjects were recruited from the Diagnostic Innovations Glaucoma Study. Eyes with preperimetric and perimetric glaucomatous damage were included in the glaucoma group. The control group was composed of healthy eyes with normal visual fields from subjects recruited from the general population. All eyes underwent RNFL imaging with Spectralis spectral-domain OCT. Likelihood ratios for glaucoma diagnosis were estimated for specific global RNFL thickness measurements using a methodology based on estimating the tangents to the Receiver Operating Characteristic (ROC) curve. Results Likelihood ratios could be determined for continuous values of average RNFL thickness. Average RNFL thickness values lower than 86μm were associated with positive LRs, i.e., LRs greater than 1; whereas RNFL thickness values higher than 86μm were associated with negative LRs, i.e., LRs smaller than 1. A modified Fagan nomogram was provided to assist calculation of post-test probability of disease from the calculated likelihood ratios and pretest probability of disease. Conclusion The methodology allowed calculation of likelihood ratios for specific RNFL thickness values. By avoiding arbitrary categorization of test results, it potentially allows for an improved integration of test results into diagnostic clinical decision-making. PMID:23972303

  4. Ultra-high resolution spectral domain optical coherence tomography using supercontinuum light source

    NASA Astrophysics Data System (ADS)

    Lim, Yiheng; Yatagai, Toyohiko; Otani, Yukitoshi

    2016-04-01

    An ultra-high resolution spectral domain optical coherence tomography (SD-OCT) was developed using a cost-effective supercontinuum laser. A spectral filter consists of a dispersive prism, a cylindrical lens and a right-angle prism was built to transmit the wavelengths in range 680-940 nm to the OCT system. The SD-OCT has achieved 1.9 μm axial resolution and the sensitivity was estimated to be 91.5 dB. A zero-crossing fringes matching method which maps the wavelengths to the pixel indices of the spectrometer was proposed for the OCT spectral calibration. A double sided foam tape as a static sample and the tip of a middle finger as a biological sample were measured by the OCT. The adhesive and the internal structure of the foam of the tape were successfully visualized in three dimensions. Sweat ducts was clearly observed in the OCT images at very high resolution. To the best of our knowledge, this is the first demonstration of ultra-high resolution visualization of sweat duct by OCT.

  5. Aortic endothelium detection using spectral estimation optical coherence tomography (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Liu, Xinyu; Chen, Si; Luo, Yuemei; Bo, En; Wang, Nanshuo; Yu, Xiaojun; Liu, Linbo

    2016-02-01

    The evaluation of the endothelium coverage on the vessel wall is most wanted by cardiologists. Arterial endothelial cells play a crucial role in keeping low-density lipoprotein and leukocytes from entering into the intima. The damage of endothelial cells is considered as the first step of atherosclerosis development and the presence of endothelial cells is an indicator of arterial healing after stent implantation. Intravascular OCT (IVOCT) is the highest-resolution coronary imaging modality, but it is still limited by an axial resolution of 10-15 µm. This limitation in axial resolution hinders our ability to visualize cellular level details associated with coronary atherosclerosis. Spectral estimation optical coherence tomography (SE-OCT) uses modern spectral estimation techniques and may help reveal the microstructures underlying the resolution limit. In this presentation, we conduct an ex vivo study using SE-OCT to image the endothelium cells on the fresh swine aorta. We find that in OCT images with an axial resolution of 10 µm, we may gain the visibility of individual endothelium cells by applying the autoregressive spectral estimation techniques to enhance the axial resolution. We believe the SE-OCT can provide a potential to evaluate the coverage of endothelium cells using current IVOCT with a 10-µm axial resolution.

  6. Optimum spectral window for imaging of art with optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Liang, Haida; Lange, Rebecca; Peric, Borislava; Spring, Marika

    2013-06-01

    Optical coherence tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists' paints. VIS-NIR (400-2,400 nm) reflectance spectra of a wide variety of paints made with historic artists' pigments have been measured. The best spectral window with which to use OCT for the imaging of subsurface structure of paintings was found to be around 2.2 μm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artists' pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 μm are highly desirable for OCT applications in art and potentially material science in general.

  7. Spectral interferometric sensors for gases and liquids using integrated optical devices

    NASA Astrophysics Data System (ADS)

    Ingenhoff, Jan; Gauglitz, Guenter; Fabricius, Norbert

    1993-04-01

    Investigations for a sensor application with an integrated optical (IO) interferometric arrangement are presented. One of the two waveguide arms of an IO-Mach-Zehnder- interferometer is covered with a thin layer of polysiloxane (superstrate), which is sensitive to hydrocarbons. The dielectric IO-devices are fabricated by IOT. Gases of organic compounds including halogenated and non-halogenated hydrocarbons cause a change of the polysiloxan's refractive index followed by an increase or decrease of the effective refractive index of the covered waveguide arm. The resulting phase shift between the guided light in the measuring and the reference arm depends on the detection wavelength and the concentration of gas. Using an LED as the light source the spectral interferogram becomes observable and so order and phase of the signal can be determined. The aim of this work is the development of a reversibly working, miniaturized sensor with a short response time. The advantages of spectral observation of the interference are discussed. A comparison between measured and calculated spectral interference signals is given.

  8. Augmenting the spectral efficiency of enhanced PAM-DMT-based optical wireless communications.

    PubMed

    Islim, Mohamed Sufyan; Haas, Harald

    2016-05-30

    The energy efficiency of pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) decreases as the modulation order of M-PAM modulation increases. Enhanced PAM-DMT (ePAM-DMT) was proposed as a solution to the reduced energy efficiency of PAM-DMT. This was achieved by allowing multiple streams of PAM-DMT to be superimposed and successively demodulated at the receiver side. In order to maintain a distortion-free unipolar ePAM-DMT system, the multiple time-domain PAM-DMT streams are required to be aligned. However, aligning the antisymmetry in ePAM-DMT is complex and results in efficiency losses. In this paper, a novel simplified method to apply the superposition modulation on M-PAM modulated discrete multitone (DMT) is introduced. Contrary to ePAM-DMT, the signal generation of the proposed system, termed augmented spectral efficiency discrete multitone (ASE-DMT), occurs in the frequency domain. This results in an improved spectral and energy efficiency. The analytical bit error rate (BER) performance bound of the proposed system is derived and compared with Monte-Carlo simulations. The system performance is shown to offer significant electrical and optical energy savings compared with ePAM-DMT and DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM).

  9. [Research on symmetrical optical waveguide based surface plasmon resonance sensing with spectral interrogation].

    PubMed

    Zhang, Yi-long; Liu, Le; Guo, Jun; Zhang, Peng-fei; Guo, Ji-hua; Ma, Hui; He, Yong-hong

    2015-02-01

    Surface plasmon resonance (SPR) sensors with spectral interrogation can adopt fiber to transmit light signals, thus leaving the sensing part separated, which is very convenient for miniaturization, remote-sensing and on-site analysis. Symmetrical optical waveguide (SOW) SPR has the same refractive index of the-two buffer media layers adjacent to the metal film, resulting in longer propagation distance, deeper penetration depth and better performance compared to conventional SPR In the present paper, we developed a symmetrical optical, waveguide (SOW) SPR sensor with wavelength interrogation. In the system, MgF2-Au-MgF2 film was used as SOW module for glucose sensing, and a fiber based light source and detection was used in the spectral interrogation. In the experiment, a refractive index resolution of 2.8 x 10(-7) RIU in fluid protocol was acquired. This technique provides advantages of high resolution and could have potential use in compact design, on-site analysis and remote sensing.

  10. Full range complex spectral domain optical coherence tomography without additional phase shifters

    PubMed Central

    Baumann, Bernhard; Pircher, Michael; Götzinger, Erich; Hitzenberger, Christoph K.

    2010-01-01

    We demonstrate a new full range complex spectral domain optical coherence tomography (FRC SD-OCT) method. Other than FRC SD-OCT systems reported in literature, which employed devices such as electro-/acousto optic modulators or piezo-driven mirrors providing the phase modulations necessary for retrieval of the complex-valued signal, the system presented works without any additional phase shifting device. The required phase shift is introduced by the galvanometer scanner used for transversally scanning the sample beam. By means of a slight displacement of the probe beam with respect to the scanning mirror’s pivot axis, the sample arm length and thus the phase is continuously modulated as the beam is scanned in lateral direction. From such modulated spectral data, the complex-valued data yielding a twofold increase of accessible depth range can be calculated using an algorithm based on the Hilbert transform. To demonstrate the performance of our method quantitative measurements of the suppression of mirror images as a function of induced phase shift were performed. In order to validate the FRC SD-OCT technique for high-speed imaging of biological tissue, we present full-range images of the human anterior chamber in vivo. PMID:19550607

  11. Optical imaging of hemoglobin oxygen saturation using a small number of spectral images for endoscopic application

    NASA Astrophysics Data System (ADS)

    Saito, Takaaki; Yamaguchi, Hiroshi

    2015-12-01

    Tissue hypoxia is associated with tumor and inflammatory diseases, and detection of hypoxia is potentially useful for their detailed diagnosis. An endoscope system that can optically observe hemoglobin oxygen saturation (StO2) would enable minimally invasive, real-time detection of lesion hypoxia in vivo. Currently, point measurement of tissue StO2 via endoscopy is possible using the commercial fiber-optic oximeter T-Stat, which is based on visible light spectroscopy at many wavelengths. For clinical use, however, imaging of StO2 is desirable to assess the distribution of tissue oxygenation around a lesion. Here, we describe our StO2 imaging technique based on a small number of wavelength ranges in the visible range. By assuming a homogeneous tissue, we demonstrated that tissue StO2 can be obtained independently from the scattering property and blood concentration of tissue using four spectral bands. We developed a prototype endoscope system and used it to observe tissue-simulating phantoms. The StO2 (%) values obtained using our technique agreed with those from the T-Stat within 10%. We also showed that tissue StO2 can be derived using three spectral band if the scattering property is fixed at preliminarily measured values.

  12. Adaptive spectral window sizes for extraction of diagnostic features from optical spectra

    PubMed Central

    Kan, Chih-wen; Lee, Andy Y.; Nieman, Linda T.; Sokolov, Konstantin; Markey, Mia K.

    2010-01-01

    We present an approach to adaptively adjust the spectral window sizes for optical spectra feature extraction. Previous studies extracted features from spectral windows of a fixed width. In our algorithm, piecewise linear regression is used to adaptively adjust the window sizes to find the maximum window size with reasonable linear fit with the spectrum. This adaptive windowing technique ensures the signal linearity in defined windows; hence, the adaptive windowing technique retains more diagnostic information while using fewer windows. This method was tested on a data set of diffuse reflectance spectra of oral mucosa lesions. Eight features were extracted from each window. We performed classifications using linear discriminant analysis with cross-validation. Using windowing techniques results in better classification performance than not using windowing. The area under the receiver-operating-characteristics curve for windowing techniques was greater than a nonwindowing technique for both normal versus mild dysplasia (MD) plus severe high-grade dysplasia or carcinama (SD) (MD+SD) and benign versus MD+SD. Although adaptive and fixed-size windowing perform similarly, adaptive windowing utilizes significantly fewer windows than fixed-size windows (number of windows per spectrum: 8 versus 16). Because adaptive windows retain most diagnostic information while reducing the number of windows needed for feature extraction, our results suggest that it isolates unique diagnostic features in optical spectra. PMID:20799843

  13. Optical fibre long period grating spectral actuators utilizing ferrofluids as outclading overlayers

    NASA Astrophysics Data System (ADS)

    Konstantaki, M.; Candiani, A.; Pissadakis, S.

    2011-03-01

    Results are presented on the spectral tuning of optical fibre long period gratings utilizing water and oil based ferrofluids as outclading overlayers, under static magnetic field stimulus. Two approaches are adopted for modifying the ambient refractive index at the position of the long period grating. In the first approach, a water based ferrofluid is controllably translated along the length of the grating via a magnetic field. Changes as high as 7.5nm and 6.5dB are monitored in the wavelength and strength, respectively, of the attenuation bands of the grating. The repeatable performance of this device for repetitive forward and backward translation verifies that no ferrofluidic residue is left on the fibre, due to silanization cladding functionalisation. In the second approach, the refractive index of an oil based ferrofluidic overlayer is modified through the magneto-optical effect. For an applied static magnetic field in the order of 400 Gauss the strength of the attenuation band of the grating is modified by more than 10% while its spectral position remains unaffected. Accordingly for the implementation of the last approach, the magnetically induced refractive index changes of ferrofluids of different solution concentrations are studied by employing diffraction efficiency measurements.

  14. Optical imaging of hemoglobin oxygen saturation using a small number of spectral images for endoscopic application.

    PubMed

    Saito, Takaaki; Yamaguchi, Hiroshi

    2015-01-01

    Tissue hypoxia is associated with tumor and inflammatory diseases, and detection of hypoxia is potentially useful for their detailed diagnosis. An endoscope system that can optically observe hemoglobin oxygen saturation (StO2) would enable minimally invasive, real-time detection of lesion hypoxia in vivo. Currently, point measurement of tissue StO2 via endoscopy is possible using the commercial fiber-optic oximeter T-Stat, which is based on visible light spectroscopy at many wavelengths. For clinical use, however, imaging of StO2 is desirable to assess the distribution of tissue oxygenation around a lesion. Here, we describe our StO2 imaging technique based on a small number of wavelength ranges in the visible range. By assuming a homogeneous tissue, we demonstrated that tissue StO2 can be obtained independently from the scattering property and blood concentration of tissue using four spectral bands. We developed a prototype endoscope system and used it to observe tissue-simulating phantoms. The StO2 (%) values obtained using our technique agreed with those from the T-Stat within 10%. We also showed that tissue StO2 can be derived using three spectral band if the scattering property is fixed at preliminarily measured values.

  15. DMD-based implementation of patterned optical filter arrays for compressive spectral imaging.

    PubMed

    Rueda, Hoover; Arguello, Henry; Arce, Gonzalo R

    2015-01-01

    Compressive spectral imaging (CSI) captures multispectral imagery using fewer measurements than those required by traditional Shannon-Nyquist theory-based sensing procedures. CSI systems acquire coded and dispersed random projections of the scene rather than direct measurements of the voxels. To date, the coding procedure in CSI has been realized through the use of block-unblock coded apertures (CAs), commonly implemented as chrome-on-quartz photomasks. These apertures block or permit us to pass the entire spectrum from the scene at given spatial locations, thus modulating the spatial characteristics of the scene. This paper extends the framework of CSI by replacing the traditional block-unblock photomasks by patterned optical filter arrays, referred to as colored coded apertures (CCAs). These, in turn, allow the source to be modulated not only spatially but spectrally as well, entailing more powerful coding strategies. The proposed CCAs are synthesized through linear combinations of low-pass, high-pass, and bandpass filters, paired with binary pattern ensembles realized by a digital micromirror device. The optical forward model of the proposed CSI architecture is presented along with a proof-of-concept implementation, which achieves noticeable improvements in the quality of the reconstruction.

  16. Geometric optimisation of an accurate cosine correcting optic fibre coupler for solar spectral measurement

    NASA Astrophysics Data System (ADS)

    Cahuantzi, Roberto; Buckley, Alastair

    2017-09-01

    Making accurate and reliable measurements of solar irradiance is important for understanding performance in the photovoltaic energy sector. In this paper, we present design details and performance of a number of fibre optic couplers for use in irradiance measurement systems employing remote light sensors applicable for either spectrally resolved or broadband measurement. The angular and spectral characteristics of different coupler designs are characterised and compared with existing state-of-the-art commercial technology. The new coupler designs are fabricated from polytetrafluorethylene (PTFE) rods and operate through forward scattering of incident sunlight on the front surfaces of the structure into an optic fibre located in a cavity to the rear of the structure. The PTFE couplers exhibit up to 4.8% variation in scattered transmission intensity between 425 nm and 700 nm and show minimal specular reflection, making the designs accurate and reliable over the visible region. Through careful geometric optimization near perfect cosine dependence on the angular response of the coupler can be achieved. The PTFE designs represent a significant improvement over the state of the art with less than 0.01% error compared with ideal cosine response for angles of incidence up to 50°.

  17. Spectral and nonlinear optical studies of Propane-1, 3-diaminium nitrate

    NASA Astrophysics Data System (ADS)

    Ayadi, R.; Lhoste, J.; Ngo, H. M.; Ledoux-Rak, I.; Mhiri, T.; Boujelbene, M.

    2016-08-01

    Propane-1, 3-diaminium nitrate [C3H12N2] (NO3)2 (PDAN), an hybrid organic-inorganic nonlinear optical material combining an acentric octupolar moiety (nitrate) with a centrosymmetric organic molecule (Propane-1, 3-diaminium) was prepared by slow evaporation technique at room temperature from its aqueous solution. Good quality and well-developed crystals of size 0.133 mm×0.092 mm×0.078 mm were harvested from the mother solution. The grown single crystals were characterized for their spectral, thermal, linear and second order nonlinear optical properties. Solid-state 13C and 1H MAS-NMR spectroscopies are in agreement with the X-ray structure. The decomposition of the title compound is confirmed by the thermogravimetric analysis (TGA). The UV-visible absorption spectrum, show that PDAN is suitable for frequency doubling applications in a wide spectral range in the visible and near IR. The NLO response of the crystal was evaluated using a SHG powder technique, indicating an effective quadratic nonlinear coefficient two times higher than that of KDP in spite of the low hyperpolarizability of the nitrate ion and of the centrosymmetric character of the diaminium derivative.

  18. Retinal nerve fiber layer evaluation in multiple sclerosis with spectral domain optical coherence tomography

    PubMed Central

    Khanifar, Aziz A; Parlitsis, George J; Ehrlich, Joshua R; Aaker, Grant D; D’Amico, Donald J; Gauthier, Susan A; Kiss, Szilárd

    2010-01-01

    Purpose: Histopathologic studies have reported retinal nerve fiber layer (RNFL) thinning in various neurodegenerative diseases. Attempts to quantify this loss in vivo have relied on time-domain optical coherence tomography (TDOCT), which has low resolution and requires substantial interpolation of data for volume measurements. We hypothesized that the significantly higher resolution of spectral-domain optical coherence tomography (SDOCT) would better detect RNFL changes in patients with multiple sclerosis, and that RNFL thickness differences between eyes with and without optic neuritis might be identified more accurately. Methods: In this retrospective case series, patients with multiple sclerosis were recruited from the Judith Jaffe Multiple Sclerosis Center at Weill Cornell Medical College in New York. Patients with a recent clinical diagnosis of optic neuritis (less than three months) were excluded. Eyes with a history of glaucoma, optic neuropathy (other than multiple sclerosis-related optic neuritis), age-related macular degeneration, or other relevant retinal and/or optic nerve disease were excluded. Both eyes of each patient were imaged with the Heidelberg Spectralis® HRA + OCT. RNFL and macular thickness were measured for each eye using the Heidelberg OCT software. These measurements were compared with validated published normal values, and were modeled as linear functions of duration of disease. The odds of an optic neuritis diagnosis as a function of RNFL and macular thickness were calculated. Results: Ninety-four eyes were prospectively evaluated using OCT. Ages of patients ranged from 26 to 69 years, with an average age of 39 years. Peripapillary RNFL thinning was demonstrated in multiple sclerosis patients; mean RNFL thickness was 88.5 μm for individuals with multiple sclerosis compared with a reported normal value of 97 μm (P < 0.001). Eyes with a history of optic neuritis had more thinning compared with those without optic neuritis (83.0

  19. Spectral Clustering for Unsupervised Segmentation of Lower Extremity Wound Beds Using Optical Images.

    PubMed

    Dhane, Dhiraj Manohar; Krishna, Vishal; Achar, Arun; Bar, Chittaranjan; Sanyal, Kunal; Chakraborty, Chandan

    2016-09-01

    Chronic lower extremity wound is a complicated disease condition of localized injury to skin and its tissues which have plagued many elders worldwide. The ulcer assessment and management is expensive and is burden on health establishment. Currently accurate wound evaluation remains a tedious task as it rely on visual inspection. This paper propose a new method for wound-area detection, using images digitally captured by a hand-held, optical camera. The strategy proposed involves spectral approach for clustering, based on the affinity matrix. The spectral clustering (SC) involves construction of similarity matrix of Laplacian based on Ng-Jorden-Weiss algorithm. Starting with a quadratic method, wound photographs were pre-processed for color homogenization. The first-order statistics filter was then applied to extract spurious regions. The filter was selected based on the performance, evaluated on four quality metrics. Then, the spectral method was used on the filtered images for effective segmentation. The segmented regions were post-processed using morphological operators. The performance of spectral segmentation was confirmed by ground-truth pictures labeled by dermatologists. The SC results were additionally compared with the results of k-means and Fuzzy C-Means (FCM) clustering algorithms. The SC approach on a set of 105 images, effectively delineated targeted wound beds yielding a segmentation accuracy of 86.73 %, positive predictive values of 91.80 %, and a sensitivity of 89.54 %. This approach shows the robustness of tool for ulcer perimeter measurement and healing progression. The article elucidates its potential to be incorporated in patient facing medical systems targeting a rapid clinical assistance.

  20. Optical Spectral Surveillance of Breast Tissue Landscapes for Detection of Residual Disease in Breast Tumor Margins

    PubMed Central

    Kennedy, Stephanie A.; Caldwell, Matthew L.; Gallagher, Jennifer E.; Junker, Marlee; Wilke, Lee G.; Barry, William T.; Geradts, Joseph; Ramanujam, Nimmi

    2013-01-01

    We demonstrate a strategy to “sense” the micro-morphology of a breast tumor margin over a wide field of view by creating quantitative hyperspectral maps of the tissue optical properties (absorption and scattering), where each voxel can be deconstructed to provide information on the underlying histology. Information about the underlying tissue histology is encoded in the quantitative spectral information (in the visible wavelength range), and residual carcinoma is detected as a shift in the histological landscape to one with less fat and higher glandular content. To demonstrate this strategy, fully intact, fresh lumpectomy specimens (n = 88) from 70 patients were imaged intra-operatively. The ability of spectral imaging to sense changes in histology over large imaging areas was determined using inter-patient mammographic breast density (MBD) variation in cancer-free tissues as a model system. We discovered that increased MBD was associated with higher baseline β-carotene concentrations (p = 0.066) and higher scattering coefficients (p = 0.007) as measured by spectral imaging, and a trend toward decreased adipocyte size and increased adipocyte density as measured by histological examination in BMI-matched patients. The ability of spectral imaging to detect cancer intra-operatively was demonstrated when MBD-specific breast characteristics were considered. Specifically, the ratio of β-carotene concentration to the light scattering coefficient can report on the relative amount of fat to glandular density at the tissue surface to determine positive margin status, when baseline differences in these parameters between patients with low and high MBD are taken into account by the appropriate selection of threshold values. When MBD was included as a variable a priori, the device was estimated to have a sensitivity of 74% and a specificity of 86% in detecting close or positive margins, regardless of tumor type. Superior performance was demonstrated in high

  1. Spectral estimation optical coherence tomography for axial super-resolution (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Liu, Xinyu; Yu, Xiaojun; Wang, Nanshuo; Bo, En; Luo, Yuemei; Chen, Si; Cui, Dongyao; Liu, Linbo

    2016-03-01

    The sample depth reflectivity profile of Fourier domain optical coherence tomography (FD-OCT) is estimated from the inverse Fourier transform of the spectral interference signals (interferograms). As a result, the axial resolution is fundamentally limited by the coherence length of the light source. We demonstrate an axial resolution improvement method by using the autoregressive spectral estimation technique to instead of the inverse Fourier transform to analyze the spectral interferograms, which is named as spectral estimation OCT (SE-OCT). SE-OCT improves the axial resolution by a factor of up to 4.7 compared with the corresponding FD-OCT. Furthermore, SE-OCT provides a complete sidelobe suppression in the point-spread function. Using phantoms such as an air wedge and micro particles, we prove the ability of resolution improvement. To test SE-OCT for real biological tissue, we image the rat cornea and demonstrate that SE-OCT enables clear identification of corneal endothelium anatomical details ex vivo. We also find that the performance of SE-OCT is depended on SNR of the feature object. To evaluate the potential usage and define the application scope of SE-OCT, we further investigate the property of SNR dependence and the artifacts that may be caused. We find SE-OCT may be uniquely suited for viewing high SNR layer structures, such as the epithelium and endothelium in cornea, retina and aorta. Given that SE-OCT can be implemented in the FD-OCT devices easily, the new capabilities provided by SE-OCT are likely to offer immediate improvements to the diagnosis and management of diseases based on OCT imaging.

  2. Development of Spectral Domain Optical Coherence Tomography for in vivo Functional Imaging of Biological Tissues

    NASA Astrophysics Data System (ADS)

    An, Lin

    Optical coherence tomography is a rapidly developing optical imaging modality capable of noninvasively providing depth resolved information of biological tissue at micrometer scale. In this thesis, we described several OCT technologies that can be used to double the imaging depth, realize functional vasculature imaging of biological tissue and increase the imaging speed of OCT system. Aim 1: Use of a scanner to introduce spatial frequency modulation to OCT spectral interferograms for in vivo full-range Fourier-domain optical coherence tomography. A novel method was developed that could easily introduce a modulation frequency onto the X-direction (i.e., B-scan) of the FDOCT scanning system, enabling full-range Fourier-domain Optical Coherence Tomography (frFDOCT). Compared to the conventional FDOCT system, the newly developed frFDOCT system can provide increased system sensitivity and deeper imaging depth. The previous technology that can achieve frFDOCT either needed multiple steps for data capturing, which is time consuming, or required additional components which increased the system's complexity. The newly developed method generates a modulation spatial frequency in the spectral interferogram by simply offsetting the probe beam at the X-scanner. Aim 2: Using optical micro-angiography to achieve in vivo volumetric imaging of vascular perfusion within human retina and choroids. Optical Micro-Angiography (OMAG) is a functional extension of FDOCT technology. It can achieve visualization of vasculature network of biological tissue. In order to apply the OMAG method to image vasculature map of human retina and choroid, a phase compensation algorithm was developed, which could minimize the motion artifacts generated by the movements of human eye and head. Aim 3: Developing ultrahigh sensitive optical micro-angiography to achieve micro vasculature imaging of biological tissue. To improve the vasculature image quality, we developed ultrahigh sensitive OMAG (UHS

  3. Ultra-wideband fiber optical parametric amplifier for spectrally-encoded microscopy (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Wei, Xiaoming; Tan, Sisi; Mussot, Arnaud; Kudlinski, Alexandre; Tsia, Kevin K.; Wong, Kenneth

    2016-03-01

    Fiber optical parametric amplifier (FOPA) has gained its popularity in the telecommunication systems at the 1.5-um window for its gain, bandwidth etc. Unfortunately, its practical application at the bio-favorable window, i.e. 1.0 um, still requires substantial efforts. Thus, here we report a versatile all-fiber optical parametric amplifier for life-science (OPALS) at 1.0 um as an add-on module for optical imaging system. The parametric gain fiber (photonic-crystal fiber (PCF), 110 m in length) is specially designed to reduce the longitudinal dispersion fluctuation, which yields a superior figure of merit, i.e. a total insertion loss of ~2.5 dB and a nonlinear coefficient of 34 /(W•km). Our OPALS delivers a superior performance in terms of gain (~158,000), bandwidth (>100 nm) and gain flatness (< 3-dB ripple). Experimentally, we show that: 1) a wavelength-varying quasi-monochrome pump achieves a 52-dB gain and 160-nm bandwidth, but at the expense of a larger gain-spectrum ripple, i.e. a bell-shaped; 2) the birefringence of the parametric gain medium, i.e. PCF in this case, can be utilized to improve the gain-spectrum flatness of OPALS by 10.5 dB, meanwhile a 100-nm bandwidth can be guaranteed; 3) the gain-spectrum flatness of OPALS can be further flattened by using a high-speed wavelength-sweeping pump, which exhibits a 110-nm flat gain spectrum with ripple less than 3 dB. Finally, we employ this versatile all-fiber OPALS as an add-on module to enhance the sensitivity of a spectrally-encoded microscope by 47 dB over an ultra-wide spectral range.

  4. Optical spectral analysis of ultra-weak photon emission from tissue culture and yeast cells

    NASA Astrophysics Data System (ADS)

    Nerudová, Michaela; Červinková, Kateřina; Hašek, Jiří; Cifra, Michal

    2015-01-01

    Optical spectral analysis of the ultra-weak photon emission (UPE) could be utilized for non-invasive diagnostic of state of biological systems and for elucidation of underlying mechanisms of UPE generation. Optical spectra of UPE from differentiated HL-60 cells and yeast cells (Saccharomyces cerevisiae) were investigated. Induced photon emission of neutrophil-like cells and spontaneous photon emission of yeast cells were measured using highly sensitive photomultiplier module Hamamatsu H7360-01 in a thermally regulated light-tight chamber. The respiratory burst of neutrophil-like HL-60 cells was induced with the PMA (phorbol 12-myristate, 13-acetate). PMA activates an assembly of NADPH oxidase, which induces a rapid formation of reactive oxygen species (ROS). Long-pass edge filters (wavelength 350, from 400 to 600 with 25 nm resolution and 650 nm) were used for optical spectral analysis. Propagation of error of indirect measurements and standard deviation were used to assess reliability of the measured spectra. Results indicate that the photon emission from both cell cultures is detectable in the six from eight examined wavelength ranges with different percentage distribution of cell suspensions, particularly 450-475, 475-500, 500-525, 525-550, 550-575 and 575-600 nm. The wavelength range of spectra from 450 to 550 nm coincides with the range of photon emission from triplet excited carbonyls (350-550 nm). The both cells cultures emitted photons in wavelength range from 550 to 600 nm but this range does not correspond with any known emitter. To summarize, we have demonstrated a clear difference in the UPE spectra between two organisms using rigorous methodology and error analysis.

  5. Comments on the Operation of Capillary Pumped Loop Devices in Low Gravity

    NASA Technical Reports Server (NTRS)

    Hallinan, K. P.; Allen, J. S.

    1999-01-01

    The operation of Capillary Pumped Loops (CPL's) in low gravity has generally been unable to match ground-based performance. The reason for this poorer performance has been elusive. In order to investigate the behavior of a CPL in low-gravity, an idealized, glass CPL experiment was constructed. This experiment, known as the Capillary-driven Heat Transfer (CHT) experiment, was flown on board the Space Shuttle Columbia in July 1997 during the Microgravity Science Laboratory mission. During the conduct of the CHT experiment an unexpected failure mode was observed. This failure mode was a result of liquid collecting and then eventually bridging the vapor return line. With the vapor return line blocked, the condensate was unable to return to the evaporator and dry-out subsequently followed. The mechanism for this collection and bridging has been associated with long wavelength instabilities of the liquid film forming in the vapor return line. Analysis has shown that vapor line blockage in present generation CPL devices is inevitable. Additionally, previous low-gravity CPL tests have reported the presence of relatively low frequency pressure oscillations during erratic system performance. Analysis reveals that these pressure oscillations are in part a result of long wavelength instabilities present in the evaporator pores, which likewise lead to liquid bridging and vapor entrapment in the porous media. Subsequent evaporation to the trapped vapor increases the vapor pressure. Eventually the vapor pressure causes ejection of the bridged liquid. Recoil stresses depress the meniscus, the vapor pressure rapidly increases, and the heated surface cools. The process then repeats with regularity.

  6. Stellar parameters of early-M dwarfs from ratios of spectral features at optical wavelengths

    NASA Astrophysics Data System (ADS)

    Maldonado, J.; Affer, L.; Micela, G.; Scandariato, G.; Damasso, M.; Stelzer, B.; Barbieri, M.; Bedin, L. R.; Biazzo, K.; Bignamini, A.; Borsa, F.; Claudi, R. U.; Covino, E.; Desidera, S.; Esposito, M.; Gratton, R.; González Hernández, J. I.; Lanza, A. F.; Maggio, A.; Molinari, E.; Pagano, I.; Perger, M.; Pillitteri, I.; Piotto, G.; Poretti, E.; Prisinzano, L.; Rebolo, R.; Ribas, I.; Shkolnik, E.; Southworth, J.; Sozzetti, A.; Suárez Mascareño, A.

    2015-05-01

    Context. Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. As a consequence, Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. However, determining the stellar parameters of M dwarfs using optical spectra has proven to be challenging. Aims: We aim to calibrate empirical relationships to determine accurate stellar parameters for early-M dwarfs (spectral types M0-M4.5) using the same spectra as those that are used for radial velocity determinations, without the necessity of acquiring IR spectra or relying on atmospheric models and/or photometric calibrations. Methods: Our methodology consists of using ratios of pseudo-equivalent widths of spectral features as a temperature diagnostic, a technique frequently used in solar-type stars. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are currently being observed in the framework of the HARPS GTO search for extrasolar planets. The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. Results: A long list of spectral features in the optical spectra of early-M dwarfs was identified. This list shows that the pseudo-equivalent width of roughly 43% of the features is strongly anticorrelated with the effective temperature. The correlation with the stellar metallicity is weaker. A total of 112 temperature sensitive ratios were identified and calibrated over the range 3100-3950 K, providing effective temperatures with typical

  7. Imposed Radiation Effects on Flame Spread over Black PMMA in Low Gravity

    NASA Technical Reports Server (NTRS)

    Olson, S. L.; Hegde, U.

    1994-01-01

    The objective of this work is to determine the effect of varying imposed radiation levels on the flame spread and burning characteristics of PMMA in low gravity. The NASA Learjet is used for these experiments; it provides an environment of 10(exp -2) g's for approximately 20 seconds. Flame spread rates are found to increase non-linearly with increased external radiant flux over the range studied. This range of imposed flux values is believed to be sufficient to compensate for the radiative loss from the flame and the surface.

  8. Draining characteristics of hemispherically bottomed cylinders in a low-gravity environment

    NASA Technical Reports Server (NTRS)

    Symons, E. P.

    1978-01-01

    An experimental investigation was conducted to study the phenomenon of vapor ingestion during the draining of a scale model, hemispherically bottomed cylindrical tank in a low-gravity environment. Where possible, experimental results are compared with previously obtained numerical predictions. It was observed that certain combinations of Weber and Bond number resulted in draining-induced axisymmetric slosh motion. The periods of the slosh waves were correlated with the square root of the draining parameter, the ratio (Weber number)/(Bond number plus one), as was the quantity of liquid remaining in the tank when vapor was ingested into the outlet line.

  9. Identification of surface defects on glass by parallel spectral domain optical coherence tomography.

    PubMed

    Chen, Zhiyan; Shen, Yi; Bao, Wen; Li, Peng; Wang, Xiaoping; Ding, Zhihua

    2015-09-07

    Defects can dramatically degrade glass quality, and automatic inspection is a trend of quality control in modern industry. One challenge in inspection in an uncontrolled environment is the misjudgment of fake defects (such as dust particles) as surface defects. Fortunately, optical changes within the periphery of a surface defect are usually introduced while those of a fake defect are not. The existence of changes within the defect peripheries can be adopted as a criterion for defect identification. However, modifications within defect peripheries can be too small to be noticeable in intensity based optical image of the glass surface, and misjudgments of modifications may occur due to the incorrectness in defect demarcation. Thus, a sensitive and reliable method for surface defect identification is demanded. To this end, a nondestructive method based on optical coherence tomography (OCT) is proposed to precisely demarcate surface defects and sensitively measure surface deformations. Suspected surface defects are demarcated using the algorithm based on complex difference from expectation. Modifications within peripheries of suspected surface defects are mapped by phase information from complex interface signal. In this way, surface defects are discriminated from fake defects using a parallel spectral domain OCT (SD-OCT) system. Both simulations and experiments are conducted, and these preliminary results demonstrate the advantage of the proposed method to identify glass surface defects.

  10. Spectral Measurements from the Optical Emission of the A.C. Plasma Anemometer

    NASA Astrophysics Data System (ADS)

    Matlis, Eric; Marshall, Curtis; Corke, Thomas; Gogineni, Sivaram

    2015-11-01

    The optical emission properties of a new class of AC-driven flow sensors based on a glow discharge (plasma) is presented. These results extend the utility of the plasma sensor that has recently been developed for measurements in high-enthalpy flows. The plasma sensor utilizes a high frequency (1MHz) AC discharge between two electrodes as the main sensing element. The voltage drop across the discharge correlates to changes in the external flow which can be calibrated for mass-flux (ρU) or pressure depending on the design of the electrodes and orientation relative to the free-stream flow direction. Recent experiments examine the potential for spectral analysis of the optical emission of the discharge to provide additional insight to the flow field. These experiments compare the optical emission of the plasma to emission from breakdown due to an ND:YAG laser. The oxygen 777.3 nm band in particular is a focus of interest as a marker for the determination of gas density.

  11. Spectral encoding method for measuring the relative arrival time between x-ray/optical pulses

    NASA Astrophysics Data System (ADS)

    Bionta, M. R.; Hartmann, N.; Weaver, M.; French, D.; Nicholson, D. J.; Cryan, J. P.; Glownia, J. M.; Baker, K.; Bostedt, C.; Chollet, M.; Ding, Y.; Fritz, D. M.; Fry, A. R.; Kane, D. J.; Krzywinski, J.; Lemke, H. T.; Messerschmidt, M.; Schorb, S.; Zhu, D.; White, W. E.; Coffee, R. N.

    2014-08-01

    The advent of few femtosecond x-ray light sources brings promise of x-ray/optical pump-probe experiments that can measure chemical and structural changes in the 10-100 fs time regime. Widely distributed timing systems used at x-ray Free-Electron Laser facilities are typically limited to above 50 fs fwhm jitter in active x-ray/optical synchronization. The approach of single-shot timing measurements is used to sort results in the event processing stage. This has seen wide use to accommodate the insufficient precision of active stabilization schemes. In this article, we review the current technique for "measure-and-sort" at the Linac Coherent Light Source at the SLAC National Accelerator Laboratory. The relative arrival time between an x-ray pulse and an optical pulse is measured near the experimental interaction region as a spectrally encoded cross-correlation signal. The cross-correlation provides a time-stamp for filter-and-sort algorithms used for real-time sorting. Sub-10 fs rms resolution is common in this technique, placing timing precision at the same scale as the duration of the shortest achievable x-ray pulses.

  12. Image slicing with a twist: spatial and spectral Nyquist sampling without anamorphic optics

    NASA Astrophysics Data System (ADS)

    Tecza, Matthias

    2014-07-01

    Integral field spectrographs have become mainstream instruments at modern telescopes because of their efficient way of collecting data-cubes. Image slicer based integral field spectrographs achieve the highest fill-factor on the detector, but due to the need to Nyquist-sample the spectra, their spatial sampling on the sky is rectangular. Using anamorphic pre-optics before the image slicer overcomes this effect further maximising the fill-factor, but introduces optical aberrations, throughput losses, and additional alignment and calibration requirements, compromising overall instrument performance. In this paper I present a concept for an image-slicer that achieves both spatial and spectral Nyquist-sampling without anamorphic pre-optics. Rotating each slitlet by 45° with respect to the dispersion direction, and arranging them into a saw-tooth pseudo-slit, leads to a lozenge shaped sampling element on the sky, however, the centres of the lozenges lie on a regular and square grid, satisfying the Nyquist sampling criterion in both spatial directions.

  13. Optimal design of an earth observation optical system with dual spectral and high resolution

    NASA Astrophysics Data System (ADS)

    Yan, Pei-pei; Jiang, Kai; Liu, Kai; Duan, Jing; Shan, Qiusha

    2017-02-01

    With the increasing demand of the high-resolution remote sensing images by military and civilians, Countries around the world are optimistic about the prospect of higher resolution remote sensing images. Moreover, design a visible/infrared integrative optic system has important value in earth observation. Because visible system can't identify camouflage and recon at night, so we should associate visible camera with infrared camera. An earth observation optical system with dual spectral and high resolution is designed. The paper mainly researches on the integrative design of visible and infrared optic system, which makes the system lighter and smaller, and achieves one satellite with two uses. The working waveband of the system covers visible, middle infrared (3-5um). Dual waveband clear imaging is achieved with dispersive RC system. The focal length of visible system is 3056mm, F/# is 10.91. And the focal length of middle infrared system is 1120mm, F/# is 4. In order to suppress the middle infrared thermal radiation and stray light, the second imaging system is achieved and the narcissus phenomenon is analyzed. The system characteristic is that the structure is simple. And the especial requirements of the Modulation Transfer Function (MTF), spot, energy concentration, and distortion etc. are all satisfied.

  14. Double-way spectral tunability for the control of optical nanocavity resonance

    NASA Astrophysics Data System (ADS)

    Baida, Fadi I.; Grosjean, Thierry

    2015-12-01

    Scanning Near-field Optical Microscopy (SNOM) has been successful in finely tuning the optical properties of photonic crystal (PC) nanocavities. The SNOM nanoprobes proposed so far allowed for either redshifting or blueshifting the resonance peak of the PC structures. In this paper, we theoretically demonstrate the possibility of a redshifting (up to +0.65 nm) and a blueshifting (up to -5 nm) the PC cavity resonance wavelength with a single perturbation element. As an example, a fiber bowtie-aperture nano-antenna (BNA) engraved at the apex of a SNOM tip is proposed to play this role. The double-way tunability is the result of a competition between an induced electric dipole (BNA at resonance) leading to a redshift and an induced magnetic dipole (the tip metalcoating) giving rise to a blueshift of the resonance wavelength. We demonstrate that the sign of the spectral shift can be simply controlled through the tip-to-cavity distance. This study opens the way to the full postproduction control of the resonance wavelength of high quality-factor optical cavities.

  15. Spectral encoding method for measuring the relative arrival time between x-ray/optical pulses

    SciTech Connect

    Bionta, M. R.; Hartmann, N.; Weaver, M.; French, D.; Glownia, J. M.; Bostedt, C.; Chollet, M.; Ding, Y.; Fritz, D. M.; Fry, A. R.; Krzywinski, J.; Lemke, H. T.; Messerschmidt, M.; Schorb, S.; Zhu, D.; White, W. E.; Nicholson, D. J.; Cryan, J. P.; Baker, K.; Kane, D. J.; and others

    2014-08-15

    The advent of few femtosecond x-ray light sources brings promise of x-ray/optical pump-probe experiments that can measure chemical and structural changes in the 10–100 fs time regime. Widely distributed timing systems used at x-ray Free-Electron Laser facilities are typically limited to above 50 fs fwhm jitter in active x-ray/optical synchronization. The approach of single-shot timing measurements is used to sort results in the event processing stage. This has seen wide use to accommodate the insufficient precision of active stabilization schemes. In this article, we review the current technique for “measure-and-sort” at the Linac Coherent Light Source at the SLAC National Accelerator Laboratory. The relative arrival time between an x-ray pulse and an optical pulse is measured near the experimental interaction region as a spectrally encoded cross-correlation signal. The cross-correlation provides a time-stamp for filter-and-sort algorithms used for real-time sorting. Sub-10 fs rms resolution is common in this technique, placing timing precision at the same scale as the duration of the shortest achievable x-ray pulses.

  16. Optical characterization of agricultural pest insects: a methodological study in the spectral and time domains

    NASA Astrophysics Data System (ADS)

    Li, Y. Y.; Zhang, H.; Duan, Z.; Lian, M.; Zhao, G. Y.; Sun, X. H.; Hu, J. D.; Gao, L. N.; Feng, H. Q.; Svanberg, S.

    2016-08-01

    Identification of agricultural pest insects is an important aspect in insect research and agricultural monitoring. We have performed a methodological study of how spectroscopic techniques and wing-beat frequency analysis might provide relevant information. An optical system based on the combination of close-range remote sensing and reflectance spectroscopy was developed to study the optical characteristics of different flying insects, collected in Southern China. The results demonstrate that the combination of wing-beat frequency assessment and reflectance spectral analysis has the potential to successfully differentiate between insect species. Further, studies of spectroscopic characteristics of fixed specimen of insects, also from Central China, showed the possibility of refined agricultural pest identification. Here, in addition to reflectance recordings also laser-induced fluorescence spectra were investigated for all the species of insects under study and found to provide complementary information to optically distinguish insects. In order to prove the practicality of the techniques explored, clearly fieldwork aiming at elucidating the variability of parameters, even within species, must be performed.

  17. Double-way spectral tunability for the control of optical nanocavity resonance.

    PubMed

    Baida, Fadi I; Grosjean, Thierry

    2015-12-08

    Scanning Near-field Optical Microscopy (SNOM) has been successful in finely tuning the optical properties of photonic crystal (PC) nanocavities. The SNOM nanoprobes proposed so far allowed for either redshifting or blueshifting the resonance peak of the PC structures. In this paper, we theoretically demonstrate the possibility of a redshifting (up to +0.65 nm) and a blueshifting (up to -5 nm) the PC cavity resonance wavelength with a single perturbation element. As an example, a fiber bowtie-aperture nano-antenna (BNA) engraved at the apex of a SNOM tip is proposed to play this role. The double-way tunability is the result of a competition between an induced electric dipole (BNA at resonance) leading to a redshift and an induced magnetic dipole (the tip metalcoating) giving rise to a blueshift of the resonance wavelength. We demonstrate that the sign of the spectral shift can be simply controlled through the tip-to-cavity distance. This study opens the way to the full postproduction control of the resonance wavelength of high quality-factor optical cavities.

  18. Improvement of the measurement accuracy of the spectral method for evaluation parameters of the optically transparent thin films

    NASA Astrophysics Data System (ADS)

    Uhov, A. A.; Kostrin, D. K.; Gerasimov, V. A.; Selivanov, L. M.; Simon, V. A.

    2017-07-01

    In this paper the ways of increasing the measurement accuracy of the parameters of the optically transparent thin films using the spectral method are described. The proposed plotting of the envelope curves for the minima and maxima of the interference oscillations in a film and additional filtering of the spectral data, allows improving the accuracy of determining the extrema position and, consequently, increasing the accuracy of the thickness measurements of the deposited coatings.

  19. Assessment of the optic disc morphology using spectral-domain optical coherence tomography and scanning laser ophthalmoscopy.

    PubMed

    Calvo, Pilar; Ferreras, Antonio; Abadia, Beatriz; Ara, Mirian; Figus, Michele; Pablo, Luis E; Frezzotti, Paolo

    2014-01-01

    To compare the equivalent optic nerve head (OHN) parameters obtained with confocal scanning laser ophthalmoscopy (HRT3) and spectral-domain optical coherence tomography (OCT) in healthy and glaucoma patients. One hundred and eighty-two consecutive healthy subjects and 156 patients with open-angle glaucoma were divided into 2 groups according to intraocular pressure and visual field outcomes. All participants underwent imaging of the ONH with the HRT3 and the Cirrus OCT. The ONH parameters and the receiver operating characteristic (ROC) curves were compared between both groups. Mean age did not differ between the normal and glaucoma groups (59.55 ± 9.7 years and 61.05 ± 9.4 years, resp.; P = 0.15). Rim area, average cup-to-disc (C/D) ratio, vertical C/D ratio, and cup volume were different between both instruments (P < 0.001). All equivalent ONH parameters, except disc area, were different between both groups (P < 0.001). The best areas under the ROC curve were observed for vertical C/D ratio (0.980 for OCT and 0.942 for HRT3; P = 0.11). Sensitivities at 95% fixed-specificities of OCT parameters were higher than those of HRT3. Equivalent ONH parameters of Cirrus OCT and HRT3 are different and cannot be used interchangeably. ONH parameters measured with OCT yielded a slightly better diagnostic performance.

  20. Dynamic virtual optical network embedding in spectral and spatial domains over elastic optical networks with multicore fibers

    NASA Astrophysics Data System (ADS)

    Zhu, Ruijie; Zhao, Yongli; Yang, Hui; Tan, Yuanlong; Chen, Haoran; Zhang, Jie; Jue, Jason P.

    2016-08-01

    Network virtualization can eradicate the ossification of the infrastructure and stimulate innovation of new network architectures and applications. Elastic optical networks (EONs) are ideal substrate networks for provisioning flexible virtual optical network (VON) services. However, as network traffic continues to increase exponentially, the capacity of EONs will reach the physical limitation soon. To further increase network flexibility and capacity, the concept of EONs is extended into the spatial domain. How to map the VON onto substrate networks by thoroughly using the spectral and spatial resources is extremely important. This process is called VON embedding (VONE).Considering the two kinds of resources at the same time during the embedding process, we propose two VONE algorithms, the adjacent link embedding algorithm (ALEA) and the remote link embedding algorithm (RLEA). First, we introduce a model to solve the VONE problem. Then we design the embedding ability measurement of network elements. Based on the network elements' embedding ability, two VONE algorithms were proposed. Simulation results show that the proposed VONE algorithms could achieve better performance than the baseline algorithm in terms of blocking probability and revenue-to-cost ratio.

  1. Picosecond optically reconfigurable filters exploiting full free spectral range tuning of single ring and Vernier effect resonators.

    PubMed

    Bruck, Roman; Mills, Ben; Thomson, David J; Troia, Benedetto; Passaro, Vittorio M N; Mashanovich, Goran Z; Reed, Graham T; Muskens, Otto L

    2015-05-04

    We demonstrate that phase shifts larger than 2π can be induced by all-optical tuning in silicon waveguides of a few micrometers in length. By generating high concentrations of free carriers in the silicon employing absorption of ultrashort, ultraviolet laser pulses, the refractive index of silicon can be drastically reduced. As a result, the resonance wavelength of optical resonators can be freely tuned over the full free spectral range. This allows for active integrated optic devices that can be switched with GHz frequencies into any desired state by all-optical means.

  2. Growth of crystals from solutions in low gravity (A0139A)

    NASA Technical Reports Server (NTRS)

    Lind, M. D.; Nielsen, K. F.

    1984-01-01

    The objective of the low gravity crystal growth experiments is to develop a novel solute diffusion method for growing single crystals. The experiments will utilize specially designed reactors with three or more compartments separated by valves to keep the reactant solutions and solvent separated until the apparatus reaches low gravity. There will be a mechanism for opening the valves automatically to initiate the diffusion and growth processes. The reactant reservoirs will be large enough to take advantage of the time provided by the Long Duration Exposure Facility (LDEF) flight. An array of several reactors will be mounted in a 12-in.-deep end center tray located on the Earth-facing end of the LDEF. Several reactors operating simultaneously will allow experimentation with more than one crystal growth system and/or variations of conditions for each. The reactors will be enclosed in a vacuum tight container and will be surrounded by thermal insulation. The temperature (approximately 35 deg C) will be regulated and any departures from the desired temperature will be recorded. Power requirements will be provided by LiSO2 batteries.

  3. Observations of the liquid/solid interface in low-gravity melting

    NASA Technical Reports Server (NTRS)

    Otto, G. H.; Lacy, L. L.

    1974-01-01

    Time-lapsed photography of the liquid/solid interface of a melting ice cylinder was taken on Skylab 3 over a period of three hours. The same experiment was simulated on earth such that morphological and thermodynamic differences could be noted. A study of the returned color film clearly shows the dominance of surface tension effects in low-gravity melting. In the Skylab experiment, the ends of the ice cylinder melted first with the water being driven by surface tension onto the cylindrical surfaces. At any time, the principle of minimum surface area governs the overall appearance of the water-ice globule which changed from a cylindrical to a spherical shape. The latent heat of melting in low-gravity is supplied only by radiation (81%) and conduction (19%); whereas in one-g, the convective (55%) and radiative (38%) mode of heat transfer dominates over the conductive portion (7%). Information is also provided on containerless melting and heat transfer in space in the absence of convective air currents.

  4. Microgravity: Molecular Dynamics Simulations at the NCCS Probe the Behavior of Liquids in Low Gravity

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The life of the very small, whether in something as complicated as a human cell or as simple as a drop of water, is of fundamental scientific interest: By knowing how a tiny amount of material reacts to changes in its environment, scientists maybe able to answer questions about how a bulk of material would react to comparable changes. NASA is in the forefront of computational research into a broad range of basic scientific questions about fluid dynamics and the nature of liquid boundary instability. For example, one important issue for the space program is how drops of water and other materials will behave in the low-gravity environment of space and how the low gravity will affect the transport and containment of these materials. Accurate prediction of this behavior is among the aims of a set of molecular dynamics experiments carried out on the NCCSs Cray supercomputers. In conventional computational studies of materials, matter is treated as continuous - a macroscopic whole without regard to its molecular parts - and the behavior patterns of the matter in various physical environments are studied using well-established differential equations and mathematical parameters based on physical properties such as compressibility density, heat capacity, and vapor pressure of the bulk material.

  5. Effect of pressure on a burning solid in low-gravity

    NASA Technical Reports Server (NTRS)

    Goldmeer, Jeffrey S.; Urban, David; Tien, James

    1995-01-01

    Venting, or depressurization, has been discussed as a possible technique for extinguishing fires on aircraft and spacecraft. Fire suppression plans for the International Space Station Alpha (ISSA) discuss the use of depressurization as a method for extinguishing fires. In the case of an uncontrollable fire, the affected compartment would be vented from an initial pressure of 1.0 atm (14.7 psia) to a final pressure 0.33 atm (4.8 psia) within 10 minutes. However, the lack of low pressure flammability data for solid materials in a low-gravity environment presents an uncertainty for the use of the venting technique. There are also transient effects that need to be considered. It is possible that the flows induced by the venting could intensify the fire. This occurred during flammability tests conducted on board Skylab. In addition, the extinction pressure could be a function of the depressurization rate. Studies conducted with solid propellants have shown that if the pressure is reduced quickly enough, the pressure at extinction will be greater than the steady-state extinction limit. This project, which was started in 1992, is examining both the quasi steady-state and transient effects of pressure reduction on a burning solid in low-gravity. This research will provide low-g extinguishment data upon which policies and practices can be formulated for fire safety in orbiting spacecraft.

  6. Observations of the liquid/solid interface in low-gravity melting

    NASA Technical Reports Server (NTRS)

    Otto, G. H.; Lacy, L. L.

    1974-01-01

    Time-lapsed photography of the liquid/solid interface of a melting ice cylinder was taken on Skylab 3 over a period of three hours. The same experiment was simulated on earth such that morphological and thermodynamic differences could be noted. A study of the returned color film clearly shows the dominance of surface tension effects in low-gravity melting. In the Skylab experiment, the ends of the ice cylinder melted first with the water being driven by surface tension onto the cylindrical surfaces. At any time, the principle of minimum surface area governs the overall appearance of the water-ice globule which changed from a cylindrical to a spherical shape. The latent heat of melting in low-gravity is supplied only by radiation (81%) and conduction (19%); whereas in one-g, the convective (55%) and radiative (38%) mode of heat transfer dominates over the conductive portion (7%). Information is also provided on containerless melting and heat transfer in space in the absence of convective air currents.

  7. Video Analysis of Granular Gases in a Low-Gravity Environment

    NASA Astrophysics Data System (ADS)

    Lewallen, Erin

    2004-10-01

    Granular Agglomeration in Non-Gravitating Systems is a research project undertaken by the University of Tulsa Granular Dynamics Group. The project investigates the effects of weightlessness on granular systems by studying the dynamics of a "gas" of 1-mm diameter brass ball bearings driven at various amplitudes and frequencies in low-gravity. Models predict that particles in systems subjected to these conditions should exhibit clustering behavior due to energy loss through multiple inelastic collisions. Observation and study of clustering in our experiment could shed light on this phenomenon as a possible mechanism by which particles in space coalesce to form stable objects such as planetesimals and planetary ring systems. Our experiment has flown on NASA's KC-135 low gravity aircraft. Data analysis techniques for video data collected during these flights include modification of images using Adobe Photoshop and development of ball identification and tracking programs written in Interactive Data Language. By tracking individual balls, we aim to establish speed distributions for granular gases and thereby obtain values for granular temperature.

  8. Spectral splitting of optical pulses inside a dispersive medium at a temporal boundary

    DOE PAGES

    Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

    2016-11-07

    We show numerically that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which refractive index changes suddenly. At the same time, the pulse breaks into several temporally separated pulses traveling at different speeds. The number of such pulses depends on the dispersive properties of the medium. We study the effect of second- and third-order dispersion in detail but also consider briefly the impact of other higher-order terms. As a result, a temporal waveguide formed with two temporal boundaries can reflect the temporally separated pulses again and again,more » increasing the number of pulses trapped within the temporal waveguide.« less

  9. Spectral splitting of optical pulses inside a dispersive medium at a temporal boundary

    SciTech Connect

    Plansinis, Brent W.; Donaldson, William R.; Agrawal, Govind P.

    2016-11-07

    We show numerically that the spectrum of an optical pulse splits into multiple, widely separated, spectral bands when it arrives at a temporal boundary across which refractive index changes suddenly. At the same time, the pulse breaks into several temporally separated pulses traveling at different speeds. The number of such pulses depends on the dispersive properties of the medium. We study the effect of second- and third-order dispersion in detail but also consider briefly the impact of other higher-order terms. As a result, a temporal waveguide formed with two temporal boundaries can reflect the temporally separated pulses again and again, increasing the number of pulses trapped within the temporal waveguide.

  10. Monitoring small changes in blood hematocrit using phase sensitive spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Manne, Venu G. R.; Manapuram, Ravi Kiran; Sudheendran, Narendran; Larin, Kirill V.

    2010-02-01

    A new method for monitoring ultra-small changes in blood hematocrit (~0.2%) based on measurement of refractive index changes in vitro using Phase Sensitive Spectral Domain Optical Coherence Tomography modality (PhS-SDOCT) is introduced. The developed system has an axial resolution of ~8 μm, phase sensitivity of +/-0.01 radians, imaging depth of 3.4 +/- 0.01 mm in air, and image acquisition speed of 29 kHz. The experimental accuracy for monitoring refractive index changes as a function of hematocrit level in blood is found to be +/-1.5x10-4 (+/-0.2%). Obtained results indicate that the PhS-SDOCT can be used to monitor ultra-small changes in the hematocrit and in vitro and, potentially, in tissue blood vessels in vivo.

  11. TiO in the optical spectra of AGB stars: Spectral modelling

    NASA Astrophysics Data System (ADS)

    Kendall, T. R.; Couch, P. A.; Sarre, P. J.

    Absorption features due to TiO are are prominent in the optical spectra of cool, evolved, oxygen-rich stars. Recent advances in spectroscopic studies [1,2,3] of this molecule allow, for the first time, modelling of the TiO bands. We present simultaneous modelling of the α, γ and γ' bands between 5400 and 7200 Å in a number of high resolution (R=39000) spectra of M-type AGB stars. Observational data were obtained using the GIRAFFE echelle spectrograph at the 1.9m Radcliffe reflector, Sutherland, South Africa. The computational code uses three-dimensional radiative transfer and non-LTE techniques and takes into account line saturation. This spectral synthesis yields temperature information and column densities for the TiO molecule in these environments. 1. Jorgensen, U., 1994, A&A, 284, 179 2. Schwenke, D., 1998, Farad. Discuss., 109, 231 3. Plez, B., 1998, ApJ, 337, 495

  12. All optical parallel-to-serial conversion by modified spectral holography structure

    NASA Astrophysics Data System (ADS)

    Yan, X.; Cao, L.; Dai, Y.; Yang, X.; Bai, L.; Ma, G.

    2012-07-01

    In this paper, a modified spectral holography structure is demonstrated. Combining the direct space-to-time pulse shaping theory with the modified structure, we can convert a spatial domain x- y image into a y- t image, where one spatial dimension is now transformed into the time domain. Thus we realize the space-to-time or parallel-to-serial conversion. As an example, we generate the temporal equivalent of letter "A", where each pixel of the image is now represented by a short optical pulse. As a possible application of our scheme, we demonstrate the generation of trains of a femtosecond pulse sequence by our structure. The results of the paper can be applied in ultrashort pulse shaping, ultrafast communication and other relevant areas.

  13. A new generation of spectral extraction and analysis package for Fiber Optics Cassegrain Echelle Spectrograph (FOCES)

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Grupp, Frank; Kellermann, Hanna; Brucalassi, Anna; Schlichter, Jörg; Hopp, Ulrich; Bender, Ralf

    2016-08-01

    We describe a new generation of spectral extraction and analysis software package (EDRS2) for the Fibre Optics Cassegrain Echelle Spectrograph (FOCES), which will be attached to the 2m Fraunhofer Telescope on the Wendelstein Observatory. The package is developed based on Python language and relies on a variety of third party, open source packages such as Numpy and Scipy. EDRS2 contains generalized image calibration routines including overscan correction, bias subtraction, flat fielding and background correction, and can be supplemented by user customized functions to fit other echelle spectrographs. An optimal extraction method is adopted to obtain the one dimensional spectra, and the output multi order, wavelength calibrated spectra are saved in FITS files with binary table format. We introduce the algorithm and performance of major routines in EDRS2.

  14. Broadband semiconductor optical amplifiers of the spectral range 750 – 1100 nm

    SciTech Connect

    Andreeva, E V; Il'chenko, S N; Lobintsov, A A; Shramenko, M V; Ladugin, M A; Marmalyuk, A A; Yakubovich, S D

    2013-11-30

    A line of travelling-wave semiconductor optical amplifiers (SOAs) based on heterostructures used for production of broadband superluminescent diodes is developed. The pure small-signal gains of the developed SOA modules are about 25 dB, while the gain bandwidths at a level of –10 dB reach 50 – 100 nm. As a whole, the SOA modules cover the IR spectral range from 750 to 1100 nm. The SOAs demonstrate a high reliability at a single-mode fibre-coupled cw output power up to 50 mW. Examples of application of two of the developed SOA modules as active elements of broadband fast-tunable lasers are presented. (lasers)

  15. Measurement of depth-resolved thermal deformation distribution using phase-contrast spectral optical coherence tomography.

    PubMed

    Zhang, Yun; Dong, Bo; Bai, Yulei; Ye, Shuangli; Lei, Zhenkun; Zhou, Yanzhou

    2015-10-19

    An updated B-scan method is proposed for measuring the evolution of thermal deformation fields in polymers. In order to measure the distributions of out-of-plane deformation and normal strain field, phase-contrast spectral optical coherence tomography (PC-SOCT) was performed with the depth range and resolution of 4.3 mm and 10.7 μm, respectively, as thermal loads were applied to three different multilayer samples. The relation between temperature and material refractive index was predetermined before the measurement. After accounting for the refractive index, the thermal deformation fields in the polymer were obtained. The measured thermal expansion coefficient of silicone sealant was approximately equal to its reference value. This method allows correctly assessing the mechanical properties in semitransparent polymers.

  16. 3D optical phase reconstruction within PMMA samples using a spectral OCT system

    NASA Astrophysics Data System (ADS)

    Briones-R., Manuel d. J.; De La Torre-Ibarra, Manuel H.; Mendoza Santoyo, Fernando

    2015-08-01

    The optical coherence tomography (OCT) technique has proved to be a useful method in biomedical areas such as ophthalmology, dentistry, dermatology, among many others. In all these applications the main target is to reconstruct the internal structure of the samples from which the physician's expertise may recognize and diagnose the existence of a disease. Nowadays OCT has been applied one step further and is used to study the mechanics of some particular type of materials, where the resulting information involves more than just their internal structure and the measurement of parameters such as displacements, stress and strain. Here we report on a spectral OCT system used to image the internal 3D microstructure and displacement maps from a PMMA (Poly-methyl-methacrylate) sample, subjected to a deformation by a controlled three point bending and tilting. The internal mechanical response of the polymer is shown as consecutive 2D images.

  17. Spectral Dependence of the Refractive Index of Magneto-Optical Metamaterials

    NASA Astrophysics Data System (ADS)

    Kozik, S. E.; Smirnov, A. G.

    2017-01-01

    A new approach is proposed for determining the optical properties of metamaterials with a complex unit cell geometry. It is based on the concept of an effective dielectric constant ɛeff (ω) and magnetic permeability μeff (ω) as a sum of Lorentzian functions, each of which is responsible for a certain dipole or multipole resonance of the structure. It is found that for "fishnet" metamaterials the spectral dependences ɛeff (ω) and magnetic permeability μeff (ω) are determined by a small number of resonances. This approach is used to calculate the effective dielectric constant and magnetic permeability of metamaterials with ordered and disordered unit cells. The spectra obtained by this analytical model are in good agreement with numerical simulations.

  18. Extending the effective imaging depth in spectral domain optical coherence tomography by dual spatial frequency encoding

    NASA Astrophysics Data System (ADS)

    Wu, Tong; Wang, Qingqing; Liu, Youwen; Wang, Jiming

    2016-03-01

    We present a spatial frequency domain multiplexing method for extending the imaging depth range of a SDOCT system without any expensive device. This method uses two reference arms with different round-trip optical delay to probe different depth regions within the sample. Two galvo scanners with different pivot-offset distances in the reference arms are used for spatial frequency modulation and multiplexing. While simultaneously driving the galvo scanners in the reference arms and the sample arm, the spatial spectrum of the acquired two-dimensional OCT spectral interferogram corresponding to the shallow and deep depth of the sample will be shifted to the different frequency bands in the spatial frequency domain. After data filtering, image reconstruction and fusion the spatial frequency multiplexing SDOCT system can provide an approximately 1.9 fold increase in the effective ranging depth compared with that of a conventional single-reference-arm full-range SDOCT system.

  19. 80GHz waveform generator by optical Fourier synthesis of four spectral sidebands (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Fatome, Julien; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe

    2016-04-01

    Versatile and easy to implement methods to generate arbitrary optical waveforms at high repetition rates are of considerable interest with applications in optical communications, all-optical signal processing, instrumentation systems and microwave signal manipulation. While shaping sinusoidal, Gaussian or hyperbolic secant intensity profiles is commonly achieved by means of modulators or mode-locked lasers, other pulse profiles such as parabolic, triangular or flat-top shapes still remain challenging to synthesize. In this context, several strategies were already explored. First, the linear pulse shaping is a common method to carve an initial ultrashort pulse train into the desired shape. The line-by-line shaping of a coherent frequency comb made of tens of spectral components was also investigated to generate more complex structures whereas Fourier synthesis of a few discrete frequencies spectrum was exploited to efficiently generate high-fidelity ultrafast periodic intensity profiles. Besides linear shaping techniques, several nonlinear methods were implemented to benefit from the adiabatic evolution of the intensity pulse profile upon propagation in optical fibers. Other examples of efficient methods are based on the photonic generation involving specific Mach-Zehnder modulators, microwave photonic filters as well as frequency-to-time conversion. In this contribution, we theoretically and experimentally demonstrate a new approach enabling the synthesis of periodic high-repetition rate pulses with various intensity profiles ranging from parabola to triangular and flat-top pulses. More precisely by linear phase and amplitude shaping of only four spectral lines is it possible to reach the targeted temporal profile. Indeed, tailoring the input symmetric spectrum only requires the determination of two physical parameters: the phase difference between the inner and outer spectral sidebands and the ratio between the amplitude of these sidebands. Therefore, a systematic

  20. Spectral-domain optical coherence tomography features of mild and severe acute solar retinopathy.

    PubMed

    Hossein, Mohammad; Jabbarpoor Bonyadi, Mohammad Hossein; Bonyadi, Jabbarpour; Soheilian, Rasam; Soheilian, Masoud; Peyman, Gholam A

    2011-09-08

    Photochemical/thermal retinal damage that results from unprotected solar eclipse viewing has vague presentations and sometimes misleading diagnosis, especially in cases with unclear history. Spectral-domain optical coherence tomography (SD-OCT) is a non-invasive imaging technique useful in differential diagnosis that can reveal characteristic foveal alterations in solar retinopathy to an unprecedented quasi histologic level. The authors present high-resolution SD-OCT findings correlated with clinical findings in three eyes of two cases with acute solar retinopathy. SD-OCT can precisely define the site and extent of damage in acute solar retinopathy. In mild forms, damage may be limited to the outer retina with inner segment/outer segment disruption. In severe forms, full thickness macular damage may be seen. Advances in retinal imaging have improved our ability to provide precise correlation with clinical presentation and prognosis.

  1. Achromatopsia: case presentation and literature review emphasising the value of spectral domain optical coherence tomography.

    PubMed

    Yu, Xiao Xi; Rego, Robert E; Shechtman, Diana

    2014-11-01

    A literature review and case presentation are used to discuss the diagnostic value of spectral domain optical coherence tomography (SD-OCT) in the assessment and management of congenital achromatopsia. A 24-year-old Hispanic man presented to the clinic with a longstanding history of decreased vision and associated possible recent progression. A comprehensive eye examination and a battery of tests including SD-OCT, fundus photography, electroretinogram (ERG) and Farnsworth D-15 were completed. SD-OCT and photopic ERG confirmed the clinical diagnosis of congenital achromatopsia. There was the classic subfoveal flattened hyporeflective 'punched out' zone, resulting from an absence of inner segment/outer segment junction. SD-OCT findings associated with congenital achromatopsia have been documented recently, helping in the diagnosis of the condition. The SD-OCT findings have further expanded our knowledge of congenital achromatopsia, while also aiding in the management of the disease.

  2. Efficient rational Chebyshev pseudo-spectral method with domain decomposition for optical waveguides modal analysis.

    PubMed

    Abdrabou, Amgad; Heikal, A M; Obayya, S S A

    2016-05-16

    We propose an accurate and computationally efficient rational Chebyshev multi-domain pseudo-spectral method (RC-MDPSM) for modal analysis of optical waveguides. For the first time, we introduce rational Chebyshev basis functions to efficiently handle semi-infinite computational subdomains. In addition, the efficiency of these basis functions is enhanced by employing an optimized algebraic map; thus, eliminating the use of PML-like absorbing boundary conditions. For leaky modes, we derived a leaky modes boundary condition at the guide-substrate interface providing an efficient technique to accurately model leaky modes with very small refractive index imaginary part. The efficiency and numerical precision of our technique are demonstrated through the analysis of high-index contrast dielectric and plasmonic waveguides, and the highly-leaky ARROW structure; where finding ARROW leaky modes using our technique clearly reflects its robustness.

  3. Birefringence imaging of biological tissue by spectral domain polarization sensitive optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Jing, Zhijun; Fan, Chuanmao; Jiang, Jingying; Gong, Qiang; Ma, Zhenhe; Zhang, Fan; Yao, Jianquan; Wang, R. K.

    2007-02-01

    A spectral domain Polarization sensitive optical coherence tomography (SDPS-OCT) system has been developed to acquire depth images of biological tissues such as porcine tendon, rabbit eye. The Stocks vectors (I, Q, U, and V) of the backscattered light from the biological tissues have been reconstructed. Further, the phase retardation and polarization degree between the two orthogonal polarizing states have been computed. Reconstructed images, i.e. birefringence images, from Stokes parameters, retardation and polarization degree of biological tissues show significant local variations in the polarization state. And the birefringence contrast of biological tissue possibly changes by some outside force. In addition, the local thickness of the birefringence layer determined with our system is significant. The results presented show SDPS-OCT is a potentially powerful technique to investigate tissue structural properties on the basis of the fact that any fibrous structure with biological tissues can influence the polarization state of light.

  4. Spectral and angular characteristics of dielectric resonator metasurface at optical frequencies

    SciTech Connect

    Zou, Longfang; López-García, Martin; Oulton, Ruth; Klemm, Maciej; Withayachumnankul, Withawat; Fumeaux, Christophe; Shah, Charan M.; Mitchell, Arnan; Bhaskaran, Madhu; Sriram, Sharath

    2014-11-10

    The capability of manipulating light at subwavelength scale has fostered the applications of flat metasurfaces in various fields. Compared to metallic structure, metasurfaces made of high permittivity low-loss dielectric resonators hold the promise of high efficiency by avoiding high conductive losses of metals at optical frequencies. This letter investigates the spectral and angular characteristics of a dielectric resonator metasurface composed of periodic sub-arrays of resonators with a linearly varying phase response. The far-field response of the metasurface can be decomposed into the response of a single grating element (sub-array) and the grating arrangement response. The analysis also reveals that coupling between resonators has a non-negligible impact on the angular response. Over a wide wavelength range, the simulated and measured angular characteristics of the metasurface provide a definite illustration of how different grating diffraction orders can be selectively suppressed or enhanced through antenna sub-array design.

  5. Growth, spectral, optical and thermal characterisation of semiorganic NLO material: L-histidinium hexaflurosilicate single crystal

    NASA Astrophysics Data System (ADS)

    Ilayaraja, P.; Srividya, J.; Anbalagan, G.

    2017-06-01

    Semiorganic L-histidinium hexaflurosilicate single crystal was grown by solvent evaporation solution growth technique. From PXRD, the crystallographic data were found as a=8.3496 Å, b=8.3376 Å, c=29.2973 Å and α= β=γ=90˚ with tetragonal crystal system (S. G. P41212). The crystalline perfection was studied by HRXRD. The molecular structure was identified using FT-IR and FTRaman spectral analysis. The crystal has 60% transparent in the visible region with a lower cutoff wavelength of 224 nm and optical band gap 4.15 eV. Laser damage threshold and frequency conversion efficiency were calculated as 3.89 GW/cm2 and 52 mV, respectively. Thermal studies indicate that the crystal was stable up to 260°C.

  6. Advanced spectral fiber optic sensor systems and their application in energy facility monitoring

    NASA Astrophysics Data System (ADS)

    Willsch, Reinhardt; Ecke, Wolfgang; Bosselmann, Thomas; Willsch, Michael; Lindner, Eric; Bartelt, Hartmut

    2011-06-01

    Various spectral-encoded fiber optic sensor concepts and advanced system solutions for application in energy facility monitoring have been investigated. The technological maturity, high performance and reliability of multiplexed fiber Bragg grating (FBG) sensor arrays and networks for the measurement of temperature, dynamic strain, air flow, and magnetic field distributions in electric power generators increasing their efficiency will be demonstrated by selected examples of field testing under harsh environmental conditions. For high-temperature combustion monitoring in gas turbines, beside silica FBGs with enhanced temperature stability also sapphire FBGs and Fabry-Perot sensors have been tested and evaluated as well as fiber-based black-body thermal radiation sensors. Finally, the potential of FBG sensors for application in cryo-energetic facilities such as super-conductive high-power motors and experimental nuclear fusion reactors will be discussed.

  7. Three-dimensional spectral domain optical coherence tomography in chronic exposure to welding arc

    PubMed Central

    Saxena, Sandeep; Mishra, Nibha; Meyer, Carsten H

    2014-01-01

    Three-dimensional spectral domain optical coherence tomography was performed in a 26-year-old man with chronic exposure to welding arc. Advanced macular visualisation provided significant findings of inner segment-ellipsoid zone disruption with the presence of cystoid changes and hyper-reflective material in the area of disruption. The external limiting membrane was intact in both the eyes. C-scan retinal pigment epithelium fit map of the left eye revealed a well-delineated defect whereas the right eye showed a poorly delineated smaller defect. The hyper-reflective material can be hypothesised to originate from the disrupted photoreceptor layer. The hyper-reflective material was more evident in the left eye which could be correlated with more marked diminution of vision and a prominent yellow lesion at the fovea. PMID:24832707

  8. Fast retinal layer segmentation of spectral domain optical coherence tomography images

    NASA Astrophysics Data System (ADS)

    Zhang, Tianqiao; Song, Zhangjun; Wang, Xiaogang; Zheng, Huimin; Jia, Fucang; Wu, Jianhuang; Li, Guanglin; Hu, Qingmao

    2015-09-01

    An approach to segment macular layer thicknesses from spectral domain optical coherence tomography has been proposed. The main contribution is to decrease computational costs while maintaining high accuracy via exploring Kalman filtering, customized active contour, and curve smoothing. Validation on 21 normal volumes shows that 8 layer boundaries could be segmented within 5.8 s with an average layer boundary error <2.35 μm. It has been compared with state-of-the-art methods for both normal and age-related macular degeneration cases to yield similar or significantly better accuracy and is 37 times faster. The proposed method could be a potential tool to clinically quantify the retinal layer boundaries.

  9. Synthesis, growth, spectral, optical and thermal studies of thiourea family crystal: TTPB

    NASA Astrophysics Data System (ADS)

    Subashini, A.; Rajarajan, K.; Sagadevan, Suresh

    2017-02-01

    In the present work, bulk size single crystal of tetrakis thiourea potassium bromide [K(N2H4CS)4Br]; (TTPB) has been grown from an aqueous solution using slow evaporation solution growth method. The XRD result proved that the compound crystallize in tetragonal crystal system with space group P41. The FT-IR spectrum of TTPB has clearly identified the functional groups of thiourea in the resulting compound. The TG-DTA and DSC studies have been carried out on the grown sample of TTPB and the results are reported. The etching and scanning electron microscope studies were also carried out to understand the growth pattern and surface morphology of TTPB. The spectral, optical and thermal studies of TTPB are compared with the similar thiourea complex crystal [K(N2H4CS)4I]; (TTPI) and reported.

  10. Apparatus and method using a holographic optical element for converting a spectral distribution to image points

    NASA Technical Reports Server (NTRS)

    McGill, Matthew J. (Inventor); Scott, Vibart S. (Inventor); Marzouk, Marzouk (Inventor)

    2001-01-01

    A holographic optical element transforms a spectral distribution of light to image points. The element comprises areas, each of which acts as a separate lens to image the light incident in its area to an image point. Each area contains the recorded hologram of a point source object. The image points can be made to lie in a line in the same focal plane so as to align with a linear array detector. A version of the element has been developed that has concentric equal areas to match the circular fringe pattern of a Fabry-Perot interferometer. The element has high transmission efficiency, and when coupled with high quantum efficiency solid state detectors, provides an efficient photon-collecting detection system. The element may be used as part of the detection system in a direct detection Doppler lidar system or multiple field of view lidar system.

  11. OPTICAL SPECTRAL OBSERVATIONS OF A FLICKERING WHITE-LIGHT KERNEL IN A C1 SOLAR FLARE

    SciTech Connect

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-10

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, ≤0.''5 (10{sup 15} cm{sup 2}) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a ''blue continuum bump'' in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  12. Optical Spectral Observations of a Flickering White-light Kernel in a C1 Solar Flare

    NASA Astrophysics Data System (ADS)

    Kowalski, Adam F.; Cauzzi, Gianna; Fletcher, Lyndsay

    2015-01-01

    We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, <=0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.

  13. Spectral Optical Properties of the Polluted Atmosphere of Mexico City (Spring-Summer 1992)

    NASA Technical Reports Server (NTRS)

    Vasilyev, O. B.; Contreras, A. Leyva; Valazquez, A. Muhlia; Peralta-Fabi, R.; Ivlev, L. S.; Kovalenko, A. P.; Vasilyev, A. V.; Jukov, V. M.; Welch, Ronald M.

    1995-01-01

    A joint Mexican, Russian, and American research effort has been initiated to develop new methods to remotely sense atmospheric parameters using ground-based, aircraft, and satellite observations. As a first step in this program, ground-based spectrophotometric measurements of the direct solar radiation have been obtained for the extremely polluted Mexico City atmosphere for the period of April-June 1992. These observations were made at more than 1300 channels in the spectral range of 0.35-0.95 microns. In the UltraViolet (UV) portions of the spectrum (e.g., 0.35 microns), aerosol optical thicknesses were found to range between 0.6 and 1.2; in the visible portion of the spectrum (e. g., 0.5 microns) they ranged from 0.5 to 0.8; and in the Near-Infrared (NIR) spectra (e.g., 0.85 micron), values of 0.3 - 0.5 were found. Applying a Spectral Optical Depth (SOD) model of tau(lambda) = C + A(lambda(sup -varies as), values of 1.55 less than varies as less than 1.85 were obtained for polluted, cloudless days, with values of 1.25 less than varies as less than 1.60 on days with haze. The aerosol particles in the polluted Mexico City atmosphere were found to be strongly absorbing, with a single-scattering albedo of 0.7 - 0.9 in the UV, 0.6 - 0.8 in the visible portion of the spectrum, and 0.4 - 0.7 in the NIR. These values are possibly consistent with a high soot concentration, contributed both by vehicular traffic and heavy industry. Analysis of the measured aerosol SOD using the optical parameters of an urban aerosol model pemiits the concentration of aerosol particles to be estimated in the vertical column; a maximum value of 3 x 10(exp 9) 1/sq cm was found. This concentration of aerosol particles exceeds that found in most other regions of the globe by at least an order of magnitude. Near the ground the aerosol size distributions measured using an optical particle counter were found to be strongly multimodal.

  14. Detection limits of multi-spectral optical imaging under the skin surface

    NASA Astrophysics Data System (ADS)

    Binzoni, T.; Vogel, A.; Gandjbakhche, A. H.; Marchesini, R.

    2008-02-01

    The present work shows that the optical/biological information contained in a typical spectral image mainly reflects the properties of a small (conic like) volume of tissue situated vertically under each individual pixel. The objects appearing on a spectral image reasonably reproduce the correct geometrical shape and size (like a non-deformed shadow) of underlying inclusions of pathological tissue. The information contained in a spectral image comes from a depth that does not exceed ~2-3 mm. The number of photons that visit a given tissue voxel situated at a depth larger than ~2 mm represents less than the 1% of the total number of photons reaching the corresponding detection pixel (forming the image). A pathological inclusion (e.g. a pool of blood or vascular tumor) situated at a depth of ~0.5 mm with a thickness of 0.5 mm produces an image intensity contrast of ~5% (for images taken at wavelengths in the 600-1000 nm range) when compared to the normal skin background. The same inclusion at a depth of 20 µm provides a contrast decreasing from 55 to 20% with respect to an increase in wavelength. The dermis/hypodermis interface behaves as a partial barrier for the photons, limiting their access to deeper skin regions. The image contrast depends on the depth and the type of chromophore contained in the inclusion. An increase in the concentration of a given molecule may produce different contrast, independently of the depth, depending on the characteristics of the skin layer where this change occurs.

  15. Spectral phase-based automatic calibration scheme for swept source-based optical coherence tomography systems

    NASA Astrophysics Data System (ADS)

    Ratheesh, K. M.; Seah, L. K.; Murukeshan, V. M.

    2016-11-01

    The automatic calibration in Fourier-domain optical coherence tomography (FD-OCT) systems allows for high resolution imaging with precise depth ranging functionality in many complex imaging scenarios, such as microsurgery. However, the accuracy and speed of the existing automatic schemes are limited due to the functional approximations and iterative operations used in their procedures. In this paper, we present a new real-time automatic calibration scheme for swept source-based optical coherence tomography (SS-OCT) systems. The proposed automatic calibration can be performed during scanning operation and does not require an auxiliary interferometer for calibration signal generation and an additional channel for its acquisition. The proposed method makes use of the spectral component corresponding to the sample surface reflection as the calibration signal. The spectral phase function representing the non-linear sweeping characteristic of the frequency-swept laser source is determined from the calibration signal. The phase linearization with improved accuracy is achieved by normalization and rescaling of the obtained phase function. The fractional-time indices corresponding to the equidistantly spaced phase intervals are estimated directly from the resampling function and are used to resample the OCT signals. The proposed approach allows for precise calibration irrespective of the path length variation induced by the non-planar topography of the sample or galvo scanning. The conceived idea was illustrated using an in-house-developed SS-OCT system by considering the specular reflection from a mirror and other test samples. It was shown that the proposed method provides high-performance calibration in terms of axial resolution and sensitivity without increasing computational and hardware complexity.

  16. Optical coherence tomography spectral analysis for detecting apoptosis in vitro and in vivo

    NASA Astrophysics Data System (ADS)

    Farhat, Golnaz; Giles, Anoja; Kolios, Michael C.; Czarnota, Gregory J.

    2015-12-01

    Apoptosis is a form of programmed cell death characterized by a series of predictable morphological changes at the subcellular level, which modify the light-scattering properties of cells. We present a spectroscopic optical coherence tomography (OCT) technique to detect changes in subcellular morphology related to apoptosis in vitro and in vivo. OCT data were acquired from acute myeloid leukemia (AML) cells treated with cisplatin over a 48-h period. The backscatter spectrum of the OCT signal acquired from the cell samples was characterized by calculating its in vitro integrated backscatter (IB) and spectral slope (SS). The IB increased with treatment duration, while the SS decreased, with the most significant changes occurring after 24 to 48 h of treatment. These changes coincided with striking morphological transformations in the cells and their nuclei. Similar trends in the spectral parameter values were observed in vivo in solid tumors grown from AML cells in mice, which were treated with chemotherapy and radiation. Our results provide a strong foundation from which future experiments may be designed to further understand the effect of cellular morphology and kinetics of apoptosis on the OCT signal and demonstrate the feasibility of using this technique in vivo.

  17. Anterior segment spectral domain optical coherence tomography imaging of patients with anterior scleritis.

    PubMed

    Levison, Ashleigh L; Lowder, Careen Y; Baynes, Kimberly M; Kaiser, Peter K; Srivastava, Sunil K

    2016-08-01

    The purpose of the study was to describe the findings seen on anterior segment spectral domain optical coherence tomography (SD-OCT) in patients with anterior scleritis and determine the feasibility of using SD-OCT to image and grade the degree of scleral inflammation and monitor response to treatment. All patients underwent slit lamp examination by a uveitis specialist, and the degree of scleral inflammation was recorded. Spectral domain OCT imaging was then performed of the conjunctiva and scleral tissue using a standardized acquisition protocol. The scans were graded and compared to clinical findings. Twenty-eight patients with anterior scleritis and ten patients without ocular disease were included in the study. Seventeen of the scleritis patients were followed longitudinally. Common findings on SD-OCT in patients with active scleritis included changes in hyporeflectivity within the sclera, nodules, and visible vessels within the sclera. There was significant variation in findings on SD-OCT within each clinical grade of active scleritis. These changes on SD-OCT improved with treatment and clinical improvement. SD-OCT imaging provided various objective measures that could be used in the future to grade inflammatory activity in patients with anterior scleritis. Longitudinal imaging of patients with active scleritis demonstrated that SD-OCT may have great utility in monitoring response to treatment.

  18. Visible light spectral domain optical coherence microscopy system for ex vivo imaging

    NASA Astrophysics Data System (ADS)

    Lichtenegger, Antonia; Harper, Danielle J.; Augustin, Marco; Eugui, Pablo; Fialová, Stanislava; Woehrer, Adelheid; Hitzenberger, Christoph K.; Baumann, Bernhard

    2017-02-01

    A visible light spectral domain optical coherence microscopy system operating in the wavelength range of 450-680 nm was developed. The resulting large wavelength range of 230 nm enabled an ultrahigh axial resolution of 0.88μm in tissue. The setup consisted of a Michelson interferometer combined with a homemade spectrometer with a spectral resolution of 0.03 nm. Scanning of 1 x 1 mm2 and 0.5 x 0.5 mm2 areas was performed by an integrated microelectromechanical mirror. After scanning the light beam is focused onto the tissue by a commercial objective with a 10 x magnification, resulting in a transverse resolution of 2 μm . Specification measurements showed that a -89 dB sensitivity with a 24 dB/mm roll-off could be achieved with the system. First of all the capabilities of the system were tested by investigating millimeter paper, tape and the USAF (US Air Force) 1951 resolution test target. Finally cerebral tissues from non-pathological and Alzheimer's disease affected brains were investigated. The results showed that structures, such as white and gray matter, could be distinguished. Furthermore a first effort was made to differentiate Alzheimer's disease from healthy brain tissue.

  19. Optical CDMA with Embedded Spectral-Polarization Coding over Double Balanced Differential-Detector

    NASA Astrophysics Data System (ADS)

    Huang, Jen-Fa; Yen, Chih-Ta; Chen, Bo-Hau

    A spectral-polarization coding (SPC) optical code-division multiple-access (OCDMA) configuration structured over arrayed-waveguide grating (AWG) router is proposed. The polarization-division double balanced detector is adopted to execute difference detection and enhances system performance. The signal-to-noise ratio (SNR) is derived by taking the effect of PIIN into account. The result indicates that there would be up to 9-dB SNR improvement than the conventional spectral-amplitude coding (SAC) structures with Walsh-Hadamard codes. Mathematical deriving results of the SNR demonstrate the system embedded with the orthogonal state of polarization (SOP) will suppress effectively phase-induced intensity noise (PIIN). In addition, we will analyze the relations about bit error rate (BER) vs. the number of active users under the different encoding schemes and compare them with our proposed scheme. The BER vs. the effective power under the different encoding scheme with the same number of simultaneous active user conditions are also revealed. Finally, the polarization-matched factor and the difference between simulated and experimental values are discussed.

  20. Imaging of the intact mouse cochlea by spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Gao, Simon S.; Yuan, Tao; Xia, Anping; Raphael, Patrick; Shelton, Ryan L.; Applegate, Brian E.; Oghalai, John S.

    2011-03-01

    Current medical imaging modalities, such as MRI and CT, do not provide high enough resolution to detect many changes within the cochlea that cause hearing loss. We sought to develop the technique of optical coherence tomography (OCT) to image the cochlea noninvasively and within its native environment. We used spectral domain OCT with 950 nm as the center wavelength and a bandwidth of ~100 nm to image freshly excised normal mouse cochlea at different developmental ages. The OCT system has an axial resolution of ~4 μm (in air) and a lateral resolution of ~10 μm. When we imaged normal adult mouse cochleae through the round window membrane, Reissner's membrane, the basilar membrane, the tectorial membrane, the spiral ligament, the spiral limbus, and the modiolus could be clearly identified. When we imaged intact adult cochleae, we were able to image through ~130 μm of bone and tissue to see up to a depth of ~600 μm, and all of the previously identified structures were still visible. Imaging of early postnatal mice during the timeline of cochlear development permitted visualization of the expected structural differences from adult cochleae. Therefore, we conclude that spectral domain OCT is an effective technique for noninvasive imaging of the murine cochlea.

  1. Structure-function relationships using spectral-domain optical coherence tomography: comparison with scanning laser polarimetry.

    PubMed

    Aptel, Florent; Sayous, Romain; Fortoul, Vincent; Beccat, Sylvain; Denis, Philippe

    2010-12-01

    To evaluate and compare the regional relationships between visual field sensitivity and retinal nerve fiber layer (RNFL) thickness as measured by spectral-domain optical coherence tomography (OCT) and scanning laser polarimetry. Prospective cross-sectional study. One hundred and twenty eyes of 120 patients (40 with healthy eyes, 40 with suspected glaucoma, and 40 with glaucoma) were tested on Cirrus-OCT, GDx VCC, and standard automated perimetry. Raw data on RNFL thickness were extracted for 256 peripapillary sectors of 1.40625 degrees each for the OCT measurement ellipse and 64 peripapillary sectors of 5.625 degrees each for the GDx VCC measurement ellipse. Correlations between peripapillary RNFL thickness in 6 sectors and visual field sensitivity in the 6 corresponding areas were evaluated using linear and logarithmic regression analysis. Receiver operating curve areas were calculated for each instrument. With spectral-domain OCT, the correlations (r(2)) between RNFL thickness and visual field sensitivity ranged from 0.082 (nasal RNFL and corresponding visual field area, linear regression) to 0.726 (supratemporal RNFL and corresponding visual field area, logarithmic regression). By comparison, with GDx-VCC, the correlations ranged from 0.062 (temporal RNFL and corresponding visual field area, linear regression) to 0.362 (supratemporal RNFL and corresponding visual field area, logarithmic regression). In pairwise comparisons, these structure-function correlations were generally stronger with spectral-domain OCT than with GDx VCC and with logarithmic regression than with linear regression. The largest areas under the receiver operating curve were seen for OCT superior thickness (0.963 ± 0.022; P < .001) in eyes with glaucoma and for OCT average thickness (0.888 ± 0.072; P < .001) in eyes with suspected glaucoma. The structure-function relationship was significantly stronger with spectral-domain OCT than with scanning laser polarimetry, and was better expressed

  2. Spectral areas and ratios classifier algorithm for pancreatic tissue classification using optical spectroscopy.

    PubMed

    Chandra, Malavika; Scheiman, James; Simeone, Diane; McKenna, Barbara; Purdy, Julianne; Mycek, Mary-Ann

    2010-01-01

    Pancreatic adenocarcinoma is one of the leading causes of cancer death, in part because of the inability of current diagnostic methods to reliably detect early-stage disease. We present the first assessment of the diagnostic accuracy of algorithms developed for pancreatic tissue classification using data from fiber optic probe-based bimodal optical spectroscopy, a real-time approach that would be compatible with minimally invasive diagnostic procedures for early cancer detection in the pancreas. A total of 96 fluorescence and 96 reflectance spectra are considered from 50 freshly excised tissue sites-including human pancreatic adenocarcinoma, chronic pancreatitis (inflammation), and normal tissues-on nine patients. Classification algorithms using linear discriminant analysis are developed to distinguish among tissues, and leave-one-out cross-validation is employed to assess the classifiers' performance. The spectral areas and ratios classifier (SpARC) algorithm employs a combination of reflectance and fluorescence data and has the best performance, with sensitivity, specificity, negative predictive value, and positive predictive value for correctly identifying adenocarcinoma being 85, 89, 92, and 80%, respectively.

  3. New bright optical spectrophotometric standards: A-type stars from the STIS Next Generation Spectral Library

    NASA Astrophysics Data System (ADS)

    Allende Prieto, C.; del Burgo, C.

    2016-02-01

    Exoplanets have sparked interest in extremely high signal-to-noise ratio spectroscopic observations of very bright stars, in a regime where flux calibrators, in particular DA white dwarfs, are not available. We argue that A-type stars offer a useful alternative and reliable space-based spectrophotometry is now available for a number of bright ones in the range 3 < V < 8 mag. By means of comparing observed spectrophotometry and model fluxes, we identify 18 new very bright trustworthy A-type flux standards for the optical range (400-800 nm), and provide scaled model fluxes for them. Our tests suggest that the absolute fluxes for these stars in the optical are reliable to within 3 per cent. We limit the spectral range to 400-800 nm, since our models have difficulties to reproduce the observed fluxes in the near-infrared and, especially, in the near-UV, where the discrepancies rise up to ˜10 per cent. Based on our model fits, we derive angular diameters with an estimated accuracy of about 1 per cent.

  4. Parabolic BM-scan technique for full range Doppler spectral domain optical coherence tomography.

    PubMed

    Jaillon, Franck; Makita, Shuichi; Yabusaki, Masaki; Yasuno, Yoshiaki

    2010-01-18

    A full range spectral domain optical coherence tomography (SD-OCT) technique that relies on the linear phase modulation of one of the interferometer arms has been widely utilized. Although this method is useful, the mirror image elimination is not perfect for samples in which regions with high axial motion exist. In this paper, we introduce a new modulation pattern to overcome this mirror image elimination failure. This new modulation is a parabolic phase modulation in the transverse scanning direction, and is applied to the SD-OCT reference beam by an electro-optic modulator. Flow phantom and in vivo experiments demonstrate that for moving structures with large velocities, this parabolic phase modulation technique presents better mirror image elimination than a standard linear phase modulation method. A direct consequence of this enhanced mirror image removal is an improved velocity range obtained with phase-resolved Doppler imaging. Consequently, applying the proposed technique in retinal blood flow measurements may be useful for ophthalmologic diagnosis.

  5. Auto- and cross-power spectral analysis of dual trap optical tweezer experiments using Bayesian inference.

    PubMed

    von Hansen, Yann; Mehlich, Alexander; Pelz, Benjamin; Rief, Matthias; Netz, Roland R

    2012-09-01

    The thermal fluctuations of micron-sized beads in dual trap optical tweezer experiments contain complete dynamic information about the viscoelastic properties of the embedding medium and-if present-macromolecular constructs connecting the two beads. To quantitatively interpret the spectral properties of the measured signals, a detailed understanding of the instrumental characteristics is required. To this end, we present a theoretical description of the signal processing in a typical dual trap optical tweezer experiment accounting for polarization crosstalk and instrumental noise and discuss the effect of finite statistics. To infer the unknown parameters from experimental data, a maximum likelihood method based on the statistical properties of the stochastic signals is derived. In a first step, the method can be used for calibration purposes: We propose a scheme involving three consecutive measurements (both traps empty, first one occupied and second empty, and vice versa), by which all instrumental and physical parameters of the setup are determined. We test our approach for a simple model system, namely a pair of unconnected, but hydrodynamically interacting spheres. The comparison to theoretical predictions based on instantaneous as well as retarded hydrodynamics emphasizes the importance of hydrodynamic retardation effects due to vorticity diffusion in the fluid. For more complex experimental scenarios, where macromolecular constructs are tethered between the two beads, the same maximum likelihood method in conjunction with dynamic deconvolution theory will in a second step allow one to determine the viscoelastic properties of the tethered element connecting the two beads.

  6. New optical mountings of the spectral devices with concave diffraction gratings and high entrance slit

    NASA Astrophysics Data System (ADS)

    Sokolova, Elena A.; Reyes Cortes, Santiago D.

    1996-11-01

    The concave diffraction grating is both the dispersive and the focusing element at the same time. It can be the only optical unit of monochromator or polychromator. Using the concave diffraction gratings with nonequidistant and curved grooves gives the possibility for correction of the aberrations in the useful region of spectrum and provides the devices with determined focal surfaces. To increase the height of the entrance slit of the spectroscopic device we have to eliminate the first and the second-order astigmatism aberrations. Consideration of this type of aberration is very important now in view of the new types of spectral devices using fiber optics and multielement detectors being developed. These new elements allow us to register the spectrum of extended objects or a number of spectrums simultaneously. For the case of the double monochromator we noticed, that the second-order astigmatism can be completely eliminated if the second part of the double monochromator is equivalent to its first part, but the ray tracing is inverse. The experiment on the mathematical model of the double monochromator confirms this idea. For the case of polychromator or CCD spectrometer we can compensate that aberrations using the illumination system, consists of the spherical mirror. The angle of incidence of the light to the mirror is calculated such a way, that the astigmatism of the grating is compensated by the astigmatism of the mirror.

  7. Spectral areas and ratios classifier algorithm for pancreatic tissue classification using optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Chandra, Malavika; Scheiman, James; Simeone, Diane; McKenna, Barbara; Purdy, Julianne; Mycek, Mary-Ann

    2010-01-01

    Pancreatic adenocarcinoma is one of the leading causes of cancer death, in part because of the inability of current diagnostic methods to reliably detect early-stage disease. We present the first assessment of the diagnostic accuracy of algorithms developed for pancreatic tissue classification using data from fiber optic probe-based bimodal optical spectroscopy, a real-time approach that would be compatible with minimally invasive diagnostic procedures for early cancer detection in the pancreas. A total of 96 fluorescence and 96 reflectance spectra are considered from 50 freshly excised tissue sites-including human pancreatic adenocarcinoma, chronic pancreatitis (inflammation), and normal tissues-on nine patients. Classification algorithms using linear discriminant analysis are developed to distinguish among tissues, and leave-one-out cross-validation is employed to assess the classifiers' performance. The spectral areas and ratios classifier (SpARC) algorithm employs a combination of reflectance and fluorescence data and has the best performance, with sensitivity, specificity, negative predictive value, and positive predictive value for correctly identifying adenocarcinoma being 85, 89, 92, and 80%, respectively.

  8. Combined spectrally encoded confocal microscopy and optical frequency domain imaging system

    NASA Astrophysics Data System (ADS)

    Kang, DongKyun; Suter, Melissa J.; Boudoux, Caroline; Yachimski, Patrick S.; Bouma, Brett E.; Nishioka, Norman S.; Tearney, Guillermo J.

    2009-02-01

    Spectrally encoded confocal microscopy (SECM) and optical frequency domain imaging (OFDI) are two reflectancebased imaging technologies that may be utilized for high-resolution microscopic screening of internal organs. SECM provides en face images of tissues with a high lateral resolution of 1-2 μm, and a penetration depth of up to 300 μm. OFDI generates cross-sectional images of tissue architecture with a resolution of 10-20 μm and a penetration depth of 1- 2 mm. Since the two technologies yield complementary microscopic information on two different size scales (SECM-cellular and OFDI-architectural) that are commonly used for histopathologic evaluation, their combination may allow for more accurate optical diagnosis. Here, we report the integration of these two imaging modalities in a single bench top system. SECM images of swine small intestine showed the presence of goblet cells, and OFDI images revealed the finger-shaped villous architecture. In clinical study of 9 gastroesophageal biopsies from 8 patients, a diverse set of architectural and cellular features was observed, including squamous mucosa with mild hyperplasia and gastric antral mucosa with gastric pits and crypts. The capability of this multimodality device to enable the visualization of microscopic features on these two size scales supports our hypothesis that improved diagnostic accuracy may be obtained by merging these two technologies into a single instrument.

  9. Evaluating Optical Classification for Fermi Blazar Candidates with a Statistical Method Using Broadband Spectral Indices

    NASA Astrophysics Data System (ADS)

    Yi, Ting-Feng; Zhang, Jin; Lu, Rui-Jing; Huang, Rui; Liang, En-Wei

    2017-03-01

    We aim to test whether a blazar candidate of uncertain type (BCU) in the third Fermi catalog of active galactic nuclei (3LAC) can be potentially classified as a BL Lac object or a flat-spectrum radio quasar (FSRQ) by performing a statistical analysis of its broadband spectral properties. We find that 34% of the radio-selected BCUs (583 BCUs) are BL Lac-like and 20% are FSRQ-like, at a 90% level of confidence. Similarly, 77.3% of the X-ray-selected BCUs (176 BCUs) are evaluated as BL Lac-like and 6.8% may be FSRQ-like sources. And 88.7% of the BL Lac-like BCUs that have synchrotron peak frequencies available are high synchrotron peaked BL Lacs in the X-ray-selected BCUs. The percentages are accordingly 62% and 7.3% in the sample of 124 optically selected BCUs. The high ratio of the number of BL Lac-like sources to the number of FSRQ-like BCUs in the X-ray-selected and optically selected BCU samples is due to selection effects. Examining the consistency between our evaluation and spectroscopic identification case by case with a sample of 78 radio-selected BCUs, it is found that the statistical analysis and its resulting classifications agree with the results of the optical follow-up spectroscopic observations. Our observation campaign for high-| {ρ }{{s}}| BCUs selected with our method, i.e., | {ρ }{{s}}| > 0.8, is ongoing.

  10. A Large Catalog of Homogeneous Ultra-Violet/Optical GRB Afterglows: Temporal and Spectral Evolution

    NASA Astrophysics Data System (ADS)

    Roming, Peter W. A.; Koch, T. Scott; Oates, Samantha R.; Porterfield, Blair L.; Bayless, Amanda J.; Breeveld, Alice A.; Gronwall, Caryl; Kuin, N. P. M.; Page, Mat J.; de Pasquale, Massimiliano; Siegel, Michael H.; Swenson, Craig A.; Tobler, Jennifer M.

    2017-02-01

    We present the second Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray burst (GRB) afterglow catalog, greatly expanding on the first Swift UVOT GRB afterglow catalog. The second catalog is constructed from a database containing over 120,000 independent UVOT observations of 538 GRBs first detected by Swift, the High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL), the Interplanetary Network (IPN), Fermi, and Astro-rivelatore Gamma a Immagini Leggero (AGILE). The catalog covers GRBs discovered from 2005 January 17 to 2010 December 25. Using photometric information in three UV bands, three optical bands, and a “white” or open filter, the data are optimally coadded to maximize the number of detections and normalized to one band to provide a detailed light curve. The catalog provides positional, temporal, and photometric information for each burst, as well as Swift Burst Alert Telescope and X-ray Telescope (XRT) GRB parameters. Temporal slopes are provided for each UVOT filter. The temporal slope per filter of almost half the GRBs are fit with a single power law, but one to three breaks are required in the remaining bursts. Morphological comparisons with the X-ray reveal that ∼ 75 % of the UVOT light curves are similar to one of the four morphologies identified by Evans et al. (2009). The remaining ∼ 25 % have a newly identified morphology. For many bursts, redshift- and extinction-corrected UV/optical spectral slopes are also provided at 2 × 103, 2 × 104, and 2 × 105 s.

  11. THE PHOTOMETRIC AND SPECTRAL EVOLUTION OF THE 2008 LUMINOUS OPTICAL TRANSIENT IN NGC 300

    SciTech Connect

    Humphreys, Roberta M.; Davidson, Kris; Bond, Howard E.; Bedin, Luigi R.; Bonanos, Alceste Z.; Berto Monard, L. A. G.; Prieto, Jose L.; Walter, Frederick M. E-mail: kd@astro.umn.edu E-mail: luigi.bedin@oapd.inaf.it

    2011-12-20

    The 2008 optical transient in NGC 300 is one of a growing class of intermediate-luminosity transients that brighten several orders of magnitude from a previously optically obscured state. The origin of their eruptions is not understood. Our multi-wavelength photometry and spectroscopy from maximum light to more than a year later provide a record of its post-eruption behavior. We describe its changing spectral energy distribution, the evolution of its absorption- and emission-line spectrum, the development of a bipolar outflow, and the rapid transition from a dense wind to an optically thin ionized wind. In addition to strong, narrow hydrogen lines, the F-type absorption-line spectrum of the transient is characterized by strong Ca II and [Ca II] emission. The very broad wings of the Ca II triplet and the asymmetric [Ca II] emission lines are due to strong Thomson scattering in the expanding ejecta. Post-maximum, the hydrogen and Ca II lines developed double-peaked emission profiles that we attribute to a bipolar outflow. Between approximately 60 and 100 days after maximum, the F-type absorption spectrum, formed in its dense wind, weakened and the wind became transparent to ionizing radiation. We discuss the probable evolutionary state of the transient and similar objects such as SN 2008S and conclude that they were most likely post-red supergiants or post-asymptotic giant branch stars on a blue loop to warmer temperatures when the eruption occurred. These objects are not luminous blue variables.

  12. Growth, spectral, optical, and dielectric studies on novel semiorganic NLO single crystal: d-phenylglycine hydrochloride

    NASA Astrophysics Data System (ADS)

    Uma, B.; Sakthi Murugesan, K.; Jayavel, R.; Krishnan, S.; Boaz, B. Milton

    2014-05-01

    Good quality novel semiorganic nonlinear optical single crystal of d-phenylglycine hydrochloride has been grown from the aqueous solution by low temperature solution growth method. X-ray diffraction reveals that the crystal crystallises into orthorhombic system with noncentrosymmetric space group P212121. Experimental parameters are evaluated based on single-crystal XRD and the calculated values of the polarisability were compared with the values of polarisability using Clausius-Mossotti equation. The functional groups present in the grown crystal were confirmed by Fourier transform infrared spectral analysis. The 1H and 13C FT-NMR has been recorded to elucidate the molecular structure. Ultraviolet-visible-near infra-red absorption studies on this crystal reveal that the minimum absorption region is around 228 nm. The optical band gap of the crystal was found to be 2.9 eV. The scanning electron microscope study has been carried out to determine the surface morphology of the grown crystal. Photoluminescence studies show that the material emits violet fluorescence. Thermal studies bring forth that the crystal is thermally stable up to 255 °C. Dielectric studies reveal that both the dielectric constant and dielectric loss decrease with the increase in frequency as like the typical semiorganic nonlinear optical crystals such as bisthiourea zinc chloride, bisthiourea cadmium chloride and l-arginine dihydrogen phosphate. Electrical conductivity measurements were carried out and the Arrhenius plot is used to determine the value of activation energy. The Kurtz powder analysis on the crystal confirms the existence of second harmonic generation properties. The SHG efficiency was found to be 1.15 times that of KDP crystal.

  13. Three-dimensional choroidal segmentation in spectral OCT volumes using optic disc prior information

    NASA Astrophysics Data System (ADS)

    Hu, Zhihong; Girkin, Christopher A.; Hariri, Amirhossein; Sadda, SriniVas R.

    2016-03-01

    Recently, much attention has been focused on determining the role of the peripapillary choroid - the layer between the outer retinal pigment epithelium (RPE)/Bruchs membrane (BM) and choroid-sclera (C-S) junction, whether primary or secondary in the pathogenesis of glaucoma. However, the automated choroidal segmentation in spectral-domain optical coherence tomography (SD-OCT) images of optic nerve head (ONH) has not been reported probably due to the fact that the presence of the BM opening (BMO, corresponding to the optic disc) can deflect the choroidal segmentation from its correct position. The purpose of this study is to develop a 3D graph-based approach to identify the 3D choroidal layer in ONH-centered SD-OCT images using the BMO prior information. More specifically, an initial 3D choroidal segmentation was first performed using the 3D graph search algorithm. Note that varying surface interaction constraints based on the choroidal morphological model were applied. To assist the choroidal segmentation, two other surfaces of internal limiting membrane and innerouter segment junction were also segmented. Based on the segmented layer between the RPE/BM and C-S junction, a 2D projection map was created. The BMO in the projection map was detected by a 2D graph search. The pre-defined BMO information was then incorporated into the surface interaction constraints of the 3D graph search to obtain more accurate choroidal segmentation. Twenty SD-OCT images from 20 healthy subjects were used. The mean differences of the choroidal borders between the algorithm and manual segmentation were at a sub-voxel level, indicating a high level segmentation accuracy.

  14. Analysis of Normal Peripapillary Choroidal Thickness via Spectral Domain Optical Coherence Tomography

    PubMed Central

    Ho, Joseph; Branchini, Lauren; Regatieri, Caio; Krishnan, Chandrasekharan; Fujimoto, James G.; Duker, Jay S.

    2011-01-01

    PURPOSE To analyze the normal peripapillary choroidal thickness utilizing a commercial spectral domain optical coherence tomography (OCT) device and determine the inter-grader reproducibility of this method. DESIGN Retrospective, non-comparative, non-interventional case series. PARTICIPANTS Thirty-six eyes of 36 normal patients seen at the New England Eye Center between April and September 2010. METHODS All patients underwent high-definition scanning with the Cirrus HD-OCT. Two raster scans were obtained per eye, a horizontal and a vertical scan, both of which were centered at the optic nerve. Two independent graders individually measured the choroidal thickness. Choroidal thickness was measured from the posterior edge of the retinal pigment epithelium to the choroid-scleral junction at 500 μm intervals away from the optic nerve in the superior, inferior, nasal and temporal quadrants. Statistical analysis was conducted to compare mean choroidal thicknesses. Inter-grader reproducibility was assessed by intraclass correlation coefficient and Pearson’s correlation coefficient. Average choroidal thickness in each quadrant was compared to retinal nerve fiber layer (RNFL) thickness in their respective quadrants. MAIN OUTCOME MEASURES Peripapillary choroidal thickness, intraclass coefficient, Pearson’s correlation coefficient. RESULTS The peripapillary choroid in the inferior quadrant was significantly thinner compared to all other quadrants (p< 0.001). None of the other quadrants were significantly different from each other in terms of thickness. The inferior peripapillary choroid was significantly thinner compared to all other quadrants at all distances measured away from the optic nerve (p< 0.001). Generally, the peripapillary choroid increases in thickness the farther it was away from the optic nerve and eventually approaching a plateau. Intraclass correlation coefficient ranged from 0.62 to 0.93 and Pearson’s correlation coefficient ranged from 0.74 to 0.95 (p

  15. Polypoidal choroidal vasculopathy: simultaneous indocyanine green angiography and eye-tracked spectral domain optical coherence tomography findings.

    PubMed

    Khan, Samira; Engelbert, Michael; Imamura, Yutaka; Freund, K Bailey

    2012-06-01

    To describe simultaneous scanning laser ophthalmoscope indocyanine green angiographic and eye-tracked spectral-domain optical coherence tomography findings in eyes with polypoidal choroidal vasculopathy (PCV). Eighteen eyes of 18 patients with PCV because of a variety of different diagnoses were imaged with simultaneous scanning laser ophthalmoscope indocyanine green angiography and eye-tracked spectral-domain optical coherence tomography to localize the polyps and their associated vascular structures with respect to the retinal layers. Regardless of the underlying diagnosis, simultaneous scanning laser ophthalmoscope indocyanine green angiography and eye-tracked spectral-domain optical coherence tomography imaging localized the polypoidal structures of PCV to within larger Type 1 neovascular complexes occurring within or above Bruch membrane. In 8 eyes, PCV appeared to adhere to the undersurface of an elevated retinal pigment epithelial detachment. In 1 eye, a PCV lesion was detected within the neurosensory retina having apparently eroded through the overlying retinal pigment epithelium. Simultaneous scanning laser ophthalmoscope indocyanine green angiography and eye-tracked spectral-domain optical coherence tomography demonstrate that a majority of PCV represents a variant of the Type 1 neovascular growth pattern, which can occur in a variety of different neovascularized maculopathies. Polypoidal choroidal vasculopathy lesions appear to originate from long-standing choroidal neovascularization, rather than from the choroidal vasculature itself. Given these observations, PCV would be more accurately described as a neovasculopathy rather than as a choroidal vasculopathy.

  16. Optic Disc and Macular Imaging in Blind Eyes from Non-glaucomatous Optic Neuropathy: A Study with Spectral-domain Optical Coherence Tomography.

    PubMed

    Hansapinyo, Linda; Cheng, Andy C O; Chan, Noel C Y; Chan, Carmen K M

    2017-02-01

    The purpose of this study was to determine and compare the optic disc and macular thickness measurements using two spectral-domain optical coherence tomography (SD-OCT) instruments in long-standing blind eyes diagnosed with non-glaucomatous optic neuropathies (NGON). A prospective observational case-series design was used. Twelve eyes from 12 NGON patients with no light perception for at least 6 months underwent optic disc and macular imaging with Cirrus HD-OCT and Spectralis OCT. The correlation between the peripapillary retinal nerve fibre layer (PRNFL) and macular ganglion cell layer and inner plexiform layer (GCL+IPL) thicknesses, and between the duration of no light perception (NLP) and PRNFL/GCL+IPL thicknesses were determined using Spearman's correlation analysis. The mean average PRNFL thickness was 55.9 ± 4.8 µm for Cirrus HD-OCT, which was significantly thicker than that measured by Spectralis OCT (31.9 ± 7.4 µm; p < 0.001). The mean central macular thickness on Cirrus HD-OCT was normal, but there was global thinning at the other macular areas. The mean average GCL+IPL thickness on Cirrus HD-OCT was 51.8 ± 5.8 µm. There was a good correlation between average PRNFL thickness and GCL+IPL thickness (r = 0.830, p = 0.002); however, there was no significant correlation between the duration of NLP to the average PRNFL thickness (on either instruments) or GCL+IPL thickness on Cirrus HD-OCT (p > 0.7). These results show that there was residual PRNFL thickness in NGON eyes with NLP, which varied significantly between SD-OCT instruments. The values of the residual PRNFL and GCL+IPL thicknesses in blind eyes (the "floor" effect) may be useful for prognostic purposes for patients with partial optic atrophy.

  17. Free Vibration Sloshing Analysis in Axisymmetric Baffled Containers under Low-Gravity Condition

    NASA Astrophysics Data System (ADS)

    Ebrahimian, M.; Noorian, M. A.; Haddadpour, H.

    2015-03-01

    The free vibrations analysis of liquid sloshing is carried out for arbitrary axisymmetric containers under low-gravity condition using boundary element method. A potential flow theory is used to model the flow field and the free-surface Laplace-Young equation is used to model the surface tension effect. The obtained governing equations are solved using eigenanalysis techniques to determine the natural frequencies and mode shapes of the sloshing liquid. The results for a circular cylindrical container are compared to the analytical values and very good agreement is achieved for the slipping and anchored contact line assumptions. Furthermore, some baffled containers are also analysed and the effects of baffles on the sloshing frequencies under low and zero gravity conditions are investigated and some conclusions are outlined.

  18. Low gravity thermal stratification of liquid helium on SHOOT. [Superfluid Helium On-Orbit Transfer

    NASA Technical Reports Server (NTRS)

    Shirron, P. J.; Dipirro, M. J.

    1992-01-01

    Estimates of the extent and impact of thermal stratification are presented as well as predictions of the behavior of the HeI/HeII boundary. Although thermal stratification of cryogens can be problematic and lead to their inefficient use in low gravity, for SHOOT the occurrence is beneficial both during ground hold and in orbit and presents no hazards. On the ground the parasitic heat load is both reduced and more efficiently removed. In orbit the pumpdown proceeds at a much more rapid rate, allowing orbital operations to begin earlier. The thermal conductivity of the aluminum tank and the normal liquid plus cooling at the liquid/vapor interface as the vapor bubble grows are sufficient to prevent undesirably high vapor pressures in the tank.

  19. On the facet-skeletal transition of snow crystals - Experiments in high and low gravity

    NASA Technical Reports Server (NTRS)

    Alena, T.; Hallett, J.; Saunders, C. P. R.

    1990-01-01

    A laboratory investigation of the influence of air velocity on the growth of columnar ice crystals from the vapor over the range -3 to -5 C shows that the linear growth velocity increases and that columns transform to sheath crystals or needles as air velocity increases from a few cm/s to 40 cm/s. Comparison with a similar transition of plates to dendrites shows that, macroscopically, in both cases the facets sprout rounded tips at a critical velocity which is lower for higher ambient supersaturation. Studies in low gravity show that chamber scale convection under normal gravity may have significant influence on growth even in the absence of an imposed air velocity. Falling snow crystals become more skeletal in shape as they grow and fall with increasing velocity. This development depends critically on temperature (+ or - 0.5 C) and demonstrates that the snow crystal shape is even more dependent on environmental growth conditions that previously thought.

  20. On the facet-skeletal transition of snow crystals - Experiments in high and low gravity

    NASA Astrophysics Data System (ADS)

    Alena, T.; Hallett, J.; Saunders, C. P. R.

    1990-07-01

    A laboratory investigation of the influence of air velocity on the growth of columnar ice crystals from the vapor over the range -3 to -5 C shows that the linear growth velocity increases and that columns transform to sheath crystals or needles as air velocity increases from a few cm/s to 40 cm/s. Comparison with a similar transition of plates to dendrites shows that, macroscopically, in both cases the facets sprout rounded tips at a critical velocity which is lower for higher ambient supersaturation. Studies in low gravity show that chamber scale convection under normal gravity may have significant influence on growth even in the absence of an imposed air velocity. Falling snow crystals become more skeletal in shape as they grow and fall with increasing velocity. This development depends critically on temperature (+ or - 0.5 C) and demonstrates that the snow crystal shape is even more dependent on environmental growth conditions that previously thought.

  1. LDEF (Postflight), AO139A : Growth of Crystals From Solutions in Low Gravity, Tray G06

    NASA Technical Reports Server (NTRS)

    1990-01-01

    LDEF (Postflight), AO139A : Growth of Crystals From Solutions in Low Gravity, Tray G06 The postflight photograph was taken in the SAEF II at KSC after the experiment tray was removed from the LDEF. The experiment tray flanges have become discolored with a light tan stain except where the tray clamp blocks were located. A darker stain appears to exist at the intersection of the white cover plate and the upper left flange of the experiment tray. The Crystal Growth experiment appears to have survived the extended mission with no visible damage. The experiment cover plate, originally white, appears to be discolored by a very light brown stain but is intact and securely in place.

  2. Developments in low-gravity cryogenic propellant acquisition and thermal control systems

    NASA Technical Reports Server (NTRS)

    Cady, E. C.; Blackmon, J. B.

    1974-01-01

    Development programs are described for two low-gravity cryogenic propellant acquisition systems: a full-screen liner system, and a refillable start-tank. First, based on experimental LH2 screen flow data, the fluid-dynamic characteristics of an integrated screen/thermodynamic vent system were analyzed for a design compared to 17.5 cu fg supercritical life-support systems, and for a Tug orbital LH2/LQ2 resupply system. Second, the analysis, design, fabrication, and test of a 10 cu ft, annular-screen start-tank with a wall-mounted thermodynamic vent was performed. The test program demonstrated that the system expelled LH2 against 1-g and performed properly over a range of conditions.

  3. Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

    NASA Technical Reports Server (NTRS)

    Tian, Huameng; Stefanescu, Doru M.; Curreri, Peter A.

    1990-01-01

    The effect of gravity on the processes of nucleation and growth of Fe-C alloys during directional solidification was investigated in experiments in which inoculated and uninoculated samples of an alloy of the gray iron type were solidified on ground (1 g) and under the low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It was found that a higher number of grains was obtained during solidification in high-g condition, due to higher convection in high-g. It was demonstrated that grain multiplication due to convection can contribute up to 23 percent of the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was found that the contribution of the convection-induced nucleation can be as high as 30 percent, but can be zero at very low or very high grain numbers.

  4. Influence of low-gravity solidification on heterogeneous nucleation in stable iron-carbon alloys

    NASA Technical Reports Server (NTRS)

    Tian, Huameng; Stefanescu, Doru M.; Curreri, Peter A.

    1990-01-01

    The effect of gravity on the processes of nucleation and growth of Fe-C alloys during directional solidification was investigated in experiments in which inoculated and uninoculated samples of an alloy of the gray iron type were solidified on ground (1 g) and under the low-gravity (low-g) and high-gravity (high-g) conditions obtained by aircraft parabolic flights. It was found that a higher number of grains was obtained during solidification in high-g condition, due to higher convection in high-g. It was demonstrated that grain multiplication due to convection can contribute up to 23 percent of the total number of grains resulting from heterogeneous nucleation of uninoculated samples. For the case of inoculated samples, it was found that the contribution of the convection-induced nucleation can be as high as 30 percent, but can be zero at very low or very high grain numbers.

  5. On the facet-skeletal transition of snow crystals - Experiments in high and low gravity

    NASA Technical Reports Server (NTRS)

    Alena, T.; Hallett, J.; Saunders, C. P. R.

    1990-01-01

    A laboratory investigation of the influence of air velocity on the growth of columnar ice crystals from the vapor over the range -3 to -5 C shows that the linear growth velocity increases and that columns transform to sheath crystals or needles as air velocity increases from a few cm/s to 40 cm/s. Comparison with a similar transition of plates to dendrites shows that, macroscopically, in both cases the facets sprout rounded tips at a critical velocity which is lower for higher ambient supersaturation. Studies in low gravity show that chamber scale convection under normal gravity may have significant influence on growth even in the absence of an imposed air velocity. Falling snow crystals become more skeletal in shape as they grow and fall with increasing velocity. This development depends critically on temperature (+ or - 0.5 C) and demonstrates that the snow crystal shape is even more dependent on environmental growth conditions that previously thought.

  6. Retinal fluorescein and indocyanine green angiography and spectral-domain optical coherence tomography findings in acute retinal pigment epitheliitis.

    PubMed

    Baillif, Stéphanie; Wolff, Benjamin; Paoli, Vincent; Gastaud, Pierre; Mauget-Faÿsse, Martine

    2011-06-01

    To determine the specific location of the initial lesion in acute retinal pigment epitheliitis. Four patients diagnosed with acute retinal pigment epitheliitis were studied. Fundus photographs, fluorescein angiography and indocyanine green angiography, and spectral-domain optical coherence tomography findings were reviewed. Four healthy young patients presented with acute onset of unilateral decreased vision. Ophthalmoscopy showed macular pigment mottling with surrounding yellow hypopigmented areas at the level of the retinal pigment epithelium (RPE). Fluorescein angiography revealed transmission hyperfluorescence. Early-phase and midphase indocyanine green angiography images showed a patchy macular hyperfluorescence. At late phase of indocyanine green angiography, a hyperfluorescent halo with a cockadelike appearance of the macular area was observed. Spectral-domain optical coherence tomography showed a disruption of the photoreceptors' inner segment and outer segment interface associated with a wider disruption of the RPE inner band. These disrupted lines were replaced by a dome-shaped highly reflective lesion involving the RPE inner layer, the photoreceptors' inner segment and outer segment layers, and, in two cases, the outer nuclear layer. With time, indocyanine green angiography showed resolution of the observed lesions. Spectral-domain optical coherence tomography showed restored and continuous inner segment and outer segment layers and RPE inner band. Spectral-domain optical coherence tomography findings suggest that the initial lesion in acute retinal pigment epitheliitis is located at the junction between the photoreceptor outer segments and the apical side of the RPE cells. Indocyanine green angiography and spectral-domain optical coherence tomography show that the RPE appears to be more widely involved than the neurosensory retina.

  7. Transport phenomena in the crystallization of lysozyme by osmotic dewatering and liquid-liquid diffusion in low gravity

    NASA Technical Reports Server (NTRS)

    Todd, Paul; Sportiello, Michael G.; Gregory, Derek; Cassanto, John M.; Alvarado, Ulises A.; Ostroff, Robert; Korszun, Z. R.

    1993-01-01

    Two methods of protein crystallization, osmotic dewatering and liquid-liquid diffusion, like the vapor diffusion (hanging-drop and sessile-drop) methods allow a gradual approach to supersaturation conditions. The crystallization of hen egg-white lysozyme, an extensively characterized protein crystal, in the presence of sodium chloride was used as an experimental model with which to compare these two methods in low gravity and in the laboratory. Comparisons of crystal growth rates by the two methods under the two conditions have, to date, indicated that the rate of crystal growth by osmotic dewatering is nearly the same in low gravity and on the ground, while much faster crystal growth rates can be achieved by the liquid-liquid diffusion method in low gravity.

  8. Transport phenomena in the crystallization of lysozyme by osmotic dewatering and liquid-liquid diffusion in low gravity

    NASA Technical Reports Server (NTRS)

    Todd, Paul; Sportiello, Michael G.; Gregory, Derek; Cassanto, John M.; Alvarado, Ulises A.; Ostroff, Robert; Korszun, Z. R.

    1993-01-01

    Two methods of protein crystallization, osmotic dewatering and liquid-liquid diffusion, like the vapor diffusion (hanging-drop and sessile-drop) methods allow a gradual approach to supersaturation conditions. The crystallization of hen egg-white lysozyme, an extensively characterized protein crystal, in the presence of sodium chloride was used as an experimental model with which to compare these two methods in low gravity and in the laboratory. Comparisons of crystal growth rates by the two methods under the two conditions have, to date, indicated that the rate of crystal growth by osmotic dewatering is nearly the same in low gravity and on the ground, while much faster crystal growth rates can be achieved by the liquid-liquid diffusion method in low gravity.

  9. A comparison of low-gravity measurements on-board Columbia during STS-40

    NASA Technical Reports Server (NTRS)

    Rogers, Melissa J. B.; Baugher, C. R.; Blanchard, R. C.; Delombard, R.; Durgin, W. W.; Matthiesen, D. H.; Neupert, W.; Roussel, P.

    1993-01-01

    The first NASA Spacelab Life Sciences mission (SLS-1) flew 5 Jun. to 14 Jun. 1991 on the orbiter Columbia (STS-40). The purpose of the mission was to investigate the human body's adaptation to the low-gravity conditions of space flight and the body's readjustment after the mission to the 1 g environment of earth. In addition to the life sciences experiments manifested for the Spacelab module, a variety of experiments in other scientific disciplines flew in the Spacelab and in Get Away Special (GAS) Canisters on the GAS Bridge Assembly. Several principal investigators designed and flew specialized accelerometer systems to better assess the results of their experiments by means of a low-gravity environment characterization. This was also the first flight of the NASA Microgravity Science and Applications Division (MSAD) sponsored Space Acceleration Measurement System (SAMS) and the first flight of the NASA Orbiter Experiments Office (OEX) sponsored Orbital Acceleration Research Experiment accelerometer (OARE). A brief introduction to seven STS-40 accelerometer systems are presented and the resulting data are discussed and compared. During crew sleep periods, acceleration magnitudes in the 10(exp -6) to 10(exp -5) g range were recorded in the Spacelab module and on the GAS Bridge Assembly. Magnitudes increased to the 10(exp -4) g level during periods of nominal crew activity. Vernier thruster firings caused acceleration shifts on the order of 10(exp -4) g and primary thruster firings caused accelerations as great as 10(exp -2) g. Frequency domain analysis revealed typical excitation of Orbiter and Spacelab structural modes at 3.5, 4.7, 5.2, 6.2, 7, and 17 Hz.

  10. Viscosity Measurement of Highly Viscous Liquids Using Drop Coalescence in Low Gravity

    NASA Technical Reports Server (NTRS)

    Antar, Basil N.; Ethridge, Edwin; Maxwell, Daniel

    1999-01-01

    The method of drop coalescence is being investigated for use as a method for determining the viscosity of highly viscous undercooled liquids. Low gravity environment is necessary in this case to minimize the undesirable effects of body forces and liquid motion in levitated drops. Also, the low gravity environment will allow for investigating large liquid volumes which can lead to much higher accuracy for the viscosity calculations than possible under 1 - g conditions. The drop coalescence method is preferred over the drop oscillation technique since the latter method can only be applied for liquids with vanishingly small viscosities. The technique developed relies on both the highly accurate solution of the Navier-Stokes equations as well as on data from experiments conducted in near zero gravity environment. In the analytical aspect of the method two liquid volumes are brought into contact which will coalesce under the action of surface tension alone. The free surface geometry development as well as its velocity during coalescence which are obtained from numerical computations are compared with an analogous experimental model. The viscosity in the numerical computations is then adjusted to bring into agreement of the experimental results with the calculations. The true liquid viscosity is the one which brings the experiment closest to the calculations. Results are presented for method validation experiments performed recently on board the NASA/KC-135 aircraft. The numerical solution for this validation case was produced using the Boundary Element Method. In these tests the viscosity of a highly viscous liquid, in this case glycerine at room temperature, was determined to high degree of accuracy using the liquid coalescence method. These experiments gave very encouraging results which will be discussed together with plans for implementing the method in a shuttle flight experiment.

  11. Sliding-cavity fluid contactors in low-gravity fluids, materials, and biotechnology research.

    PubMed

    Todd, Paul; Vellinger, John C; Sengupta, Shramik; Sportiello, Michael G; Greenberg, Alan R; Krantz, William B

    2002-10-01

    The well-known method of sliding-cavity fluid contactors used by Gosting for diffusion measurements and by Tiselius in electrophoresis has found considerable use in low-gravity research. To date, sliding-cavity contactors have been used in liquid diffusion experiments, interfacial transport experiments, biomolecular crystal growth, biphasic extraction, multistage extraction, microencapsulation, seed germination, invertebrate development, and thin-film casting. Sliding-cavity technology has several advantages for spaceflight: it is simple, it accommodates small samples, samples can be fully enclosed, phases can be combined, multiple samples can be processed at high sample density, real-time observations can be made, and mixed and diffused samples can be compared. An analysis of the transport phenomena that govern the sliding-cavity method is offered. During sliding of one liquid over another flow rates between 0.001 and 0.1m/sec are developed, giving Reynolds numbers in the range 0.1-100. Assuming no slip at liquid-solid boundaries shear rates are of the order 1sec(-1). The measured consequence is the transfer of 2-5% of the content of a cavity to the opposite cavity. In the absence of gravity, buoyancy-driven transport is assumed absent. Transport processes are limited to (1) molecular diffusion, in which reactants diffuse toward one another at rates that depend on their diffusion coefficient and concentration gradient (Fick's second law), (2) solutocapillary (Marangoni) flow driven by surface-tension gradients, (3) capillary flow (drop spreading) at liquid-solid three-phase lines leading to immiscible phase demixing, and (4) vapor-phase diffusive mass transfer in evaporative processes. Quantitative treatment of these phenomena has been accomplished over the past few years in low-gravity research in space and on aircraft.

  12. Parameters of Selected Central Stars of Planetary Nebulae from Consistent Optical and UV Spectral Analysis

    NASA Astrophysics Data System (ADS)

    Kaschinski, Cornelius Bernhard

    optical emission lines, from which the mass loss rate is determined in case of a purely optical based analysis, depends on the square of the density. A possible clumpiness in the winds would thus lead to an uncertainty in the determination of atmospheric mass loss rates from the strength of such optical recombination lines. Since the mass loss rate is not a free parameter, but is rather a function of the other stellar parameters, this may lead to an uncertainty in the determination of the stellar parameters. We used the improved code to re-evaluate, with respect to the influence of clumping on the appearance of the UV spectra, the optical parameter set determined in an earlier study that employed clumping in its models to achieve fits to the observed optical lines. We found that, with and without clumping, wind strengths and terminal velocities in accordance to their stellar parameters from the optical analysis yield spectra which are incompatible with the optical and UV observations, whereas our self-consistent models achieve good fits to both observations. Moreover, moderate clumping factors are found to have the same order of influence on the optical recombination lines as the density (velocity field) has. During the same study we also derived shock temperatures and ratios of X-ray to bolometric luminosities so as to reproduce the highly ionized O VI line in the Far Ultraviolet Spectroscopic Explorer spectral range. These values agree with those derived for O stars, again confirming the similarity of massive O type CSPN and massive O star atmospheres. Based on the derived shock structures of our sample of CSPNs we investigated the possible influence of shocks on emission line studies from HII regions. Here, tools for the inversion of line ratios into desired physical properties are required and come in the form of diagnostic ratios or diagrams which are based on grids of photoionization models. We calculated such a grid of shock influenced ionizing fluxes from a

  13. From Planetesimals to Dust: Low-gravity Experiments on Recycling Solids at the Inner Edges of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    de Beule, Caroline; Kelling, Thorben; Wurm, Gerhard; Teiser, Jens; Jankowski, Tim

    2013-01-01

    Transporting solids of different sizes is an essential process in the evolution of protoplanetary disks and planet formation. Large solids are supposed to drift inward; high-temperature minerals found in comets are assumed to have been transported outward. From low-gravity experiments on parabolic flights, we studied the light-induced erosion of dusty bodies caused by a solid-state greenhouse effect and photophoresis within a dust bed's upper layers. The gravity levels studied were 0.16g, 0.38g, 1g, and 1.7g. The light flux during the experiments was 12 ± 2 kW m-2 and the ambient pressure was 6 ± 0.9 mbar. Light-induced erosion is strongly gravity dependent, which is in agreement with a developed model. In particular for small dusty bodies ((sub)-planetesimals), efficient erosion is possible at the optically thin inner edges of protoplanetary disks. Light-induced erosion prevents significant parts of a larger body from moving too close to the host star and being subsequently accreted. The small dust produced continues to be subject to photophoresis and is partially transported upward and outward over the surface of the disk; the resulting small dust particles are observed over the disk's lifetime. The fraction of eroded dust participates in subsequent cycles of growth during planetesimal formation. Another fraction of dust might be collected by a body of planetary size if this body is already present close to the disk edge. Either way, light-induced erosion is an efficient recycling process in protoplanetary disks.

  14. FROM PLANETESIMALS TO DUST: LOW-GRAVITY EXPERIMENTS ON RECYCLING SOLIDS AT THE INNER EDGES OF PROTOPLANETARY DISKS

    SciTech Connect

    De Beule, Caroline; Kelling, Thorben; Wurm, Gerhard; Teiser, Jens; Jankowski, Tim

    2013-01-20

    Transporting solids of different sizes is an essential process in the evolution of protoplanetary disks and planet formation. Large solids are supposed to drift inward; high-temperature minerals found in comets are assumed to have been transported outward. From low-gravity experiments on parabolic flights, we studied the light-induced erosion of dusty bodies caused by a solid-state greenhouse effect and photophoresis within a dust bed's upper layers. The gravity levels studied were 0.16g, 0.38g, 1g, and 1.7g. The light flux during the experiments was 12 {+-} 2 kW m{sup -2} and the ambient pressure was 6 {+-} 0.9 mbar. Light-induced erosion is strongly gravity dependent, which is in agreement with a developed model. In particular for small dusty bodies ((sub)-planetesimals), efficient erosion is possible at the optically thin inner edges of protoplanetary disks. Light-induced erosion prevents significant parts of a larger body from moving too close to the host star and being subsequently accreted. The small dust produced continues to be subject to photophoresis and is partially transported upward and outward over the surface of the disk; the resulting small dust particles are observed over the disk's lifetime. The fraction of eroded dust participates in subsequent cycles of growth during planetesimal formation. Another fraction of dust might be collected by a body of planetary size if this body is already present close to the disk edge. Either way, light-induced erosion is an efficient recycling process in protoplanetary disks.

  15. High-speed spectral calibration by complex FIR filter in phase-sensitive optical coherence tomography

    PubMed Central

    Kim, Sangmin; Raphael, Patrick D.; Oghalai, John S.; Applegate, Brian E.

    2016-01-01

    Swept-laser sources offer a number of advantages for Phase-sensitive Optical Coherence Tomography (PhOCT). However, inter- and intra-sweep variability leads to calibration errors that adversely affect phase sensitivity. While there are several approaches to overcoming this problem, our preferred method is to simply calibrate every sweep of the laser. This approach offers high accuracy and phase stability at the expense of a substantial processing burden. In this approach, the Hilbert phase of the interferogram from a reference interferometer provides the instantaneous wavenumber of the laser, but is computationally expensive. Fortunately, the Hilbert transform may be approximated by a Finite Impulse-Response (FIR) filter. Here we explore the use of several FIR filter based Hilbert transforms for calibration, explicitly considering the impact of filter choice on phase sensitivity and OCT image quality. Our results indicate that the complex FIR filter approach is the most robust and accurate among those considered. It provides similar image quality and slightly better phase sensitivity than the traditional FFT-IFFT based Hilbert transform while consuming fewer resources in an FPGA implementation. We also explored utilizing the Hilbert magnitude of the reference interferogram to calculate an ideal window function for spectral amplitude calibration. The ideal window function is designed to carefully control sidelobes on the axial point spread function. We found that after a simple chromatic correction, calculating the window function using the complex FIR filter and the reference interferometer gave similar results to window functions calculated using a mirror sample and the FFT-IFFT Hilbert transform. Hence, the complex FIR filter can enable accurate and high-speed calibration of the magnitude and phase of spectral interferograms. PMID:27446666

  16. Characterizing Aerosol Distributions and Optical Properties Using the NASA Langley High Spectral Resolution Lidar

    SciTech Connect

    Hostetler, Chris; Ferrare, Richard

    2013-02-14

    The objective of this project was to provide vertically and horizontally resolved data on aerosol optical properties to assess and ultimately improve how models represent these aerosol properties and their impacts on atmospheric radiation. The approach was to deploy the NASA Langley Airborne High Spectral Resolution Lidar (HSRL) and other synergistic remote sensors on DOE Atmospheric Science Research (ASR) sponsored airborne field campaigns and synergistic field campaigns sponsored by other agencies to remotely measure aerosol backscattering, extinction, and optical thickness profiles. Synergistic sensors included a nadir-viewing digital camera for context imagery, and, later in the project, the NASA Goddard Institute for Space Studies (GISS) Research Scanning Polarimeter (RSP). The information from the remote sensing instruments was used to map the horizontal and vertical distribution of aerosol properties and type. The retrieved lidar parameters include profiles of aerosol extinction, backscatter, depolarization, and optical depth. Products produced in subsequent analyses included aerosol mixed layer height, aerosol type, and the partition of aerosol optical depth by type. The lidar products provided vertical context for in situ and remote sensing measurements from other airborne and ground-based platforms employed in the field campaigns and was used to assess the predictions of transport models. Also, the measurements provide a data base for future evaluation of techniques to combine active (lidar) and passive (polarimeter) measurements in advanced retrieval schemes to remotely characterize aerosol microphysical properties. The project was initiated as a 3-year project starting 1 January 2005. It was later awarded continuation funding for another 3 years (i.e., through 31 December 2010) followed by a 1-year no-cost extension (through 31 December 2011). This project supported logistical and flight costs of the NASA sensors on a dedicated aircraft, the subsequent

  17. SHELS: OPTICAL SPECTRAL PROPERTIES OF WISE 22 {mu}m SELECTED GALAXIES

    SciTech Connect

    Hwang, Ho Seong; Geller, Margaret J.; Kurtz, Michael J.; Fabricant, Daniel G.; Dell'Antonio, Ian P. E-mail: mgeller@cfa.harvard.edu E-mail: dfabricant@cfa.harvard.edu

    2012-10-10

    We use a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), covering a 4 deg{sup 2} region of a deep imaging survey, the Deep Lens Survey (DLS), to study the optical spectral properties of Wide-field Infrared Survey Explorer (WISE) 22 {mu}m selected galaxies. Among 507 WISE 22 {mu}m selected sources with (S/N){sub 22{mu}m} {>=} 3 ( Almost-Equal-To S{sub 22{mu}m} {approx}> 2.5 mJy), we identify the optical counterparts of 481 sources ({approx}98%) at R < 25.2 in the very deep, DLS R-band source catalog. Among them, 337 galaxies at R < 21 have SHELS spectroscopic data. Most of these objects are at z < 0.8. The infrared (IR) luminosities are in the range 4.5 Multiplication-Sign 10{sup 8}(L{sub Sun }) {approx}< L{sub IR} {approx}< 5.4 Multiplication-Sign 10{sup 12}(L{sub Sun }). Most 22 {mu}m selected galaxies are dusty star-forming galaxies with a small (<1.5) 4000 A break. The stacked spectra of the 22 {mu}m selected galaxies binned in IR luminosity show that the strength of the [O III] line relative to H{beta} grows with increasing IR luminosity. The optical spectra of the 22 {mu}m selected galaxies also show that there are some ({approx}2.8%) unusual galaxies with very strong [Ne III] {lambda}3869, 3968 emission lines that require hard ionizing radiation such as active galactic nuclei (AGNs) or extremely young massive stars. The specific star formation rates (sSFRs) derived from the 3.6 and 22 {mu}m flux densities are enhanced if the 22 {mu}m selected galaxies have close late-type neighbors. The sSFR distribution of the 22 {mu}m selected galaxies containing AGNs is similar to the distribution for star-forming galaxies without AGNs. We identify 48 dust-obscured galaxy candidates with large ({approx}> 1000) mid-IR to optical flux density ratio. The combination of deep photometric and spectroscopic data with WISE data suggests that WISE can probe the universe to z {approx} 2.

  18. Spectral-Domain Optical Coherence Tomography as a Potential Biomarker in Huntington's Disease.

    PubMed

    Andrade, Carlos; Beato, João; Monteiro, Ana; Costa, Andreia; Penas, Susana; Guimarães, Joana; Reis, Fernando Falcão; Garrett, Carolina

    2016-03-01

    Spectral-domain optical coherence tomography has been used in several neurological conditions, and peripapillary and macular measurements have been proposed as potential biomarkers in these disorders. The aim of this study was to investigate retinal and choroidal changes in Huntington's disease and to evaluate any potential correlation with the stage of the disease. A cross-sectional observational study compared patients with Huntington's disease and controls. Patients were evaluated using the Unified Huntington's Disease Rating Scale. Spectral-domain optical coherence tomography with enhanced depth imaging was used, and peripapillary choroidal and retinal nerve fiber layer thickness and macular retinal and choroidal thickness were evaluated. Fifteen eyes of 8 patients and 16 eyes of 8 sex-, age-, and mean refractive error-matched healthy controls were included. Average (231.3 ± 52.8 vs 296.2 ± 57.1, P = 0.033), central (341.8 ± 70.5 vs 252.0 ± 57.9, P = 0.015), and inferior (225.3 ± 57.9 vs 313.8 ± 55.2, P = 0.007) macular choroidal thickness were significantly reduced in patients, in comparison with controls. No differences were observed in macular retina or peripapillary retinal and choroidal measurements. However, there was a negative correlation between Total Motor Score of the Unified Huntington's Disease Rating Scale and average (r(2)  = 0.585, P = 0.027), superior (r(2)  = 0.653, P = 0.015), nasal (r(2)  = 0.642, P = 0.017), and inferior (r(2)  = 0.574, P = 0.029) macular retinal thickness. Our results suggest that both the choroidal and retinal macula are altered in Huntington's disease and may become useful biomarkers for monitoring neurodegeneration in this disease. The involvement of the choroid may also support the recent findings of vascular involvement in Huntington's disease. © 2016 International Parkinson and Movement Disorder Society.

  19. Spectral reflectance studies and optical surface alteration in the search for links between meteorites and asteroids

    NASA Astrophysics Data System (ADS)

    Clark, Beth Ellen

    1993-01-01

    The ordinary chondrites (OC's) are the most numerous and most ancient of meteorites, but as yet their Solar System source region has not been identified. Meteoriticists have scrutinized these meteorites for clues as to the origin and evolution of the Solar System. They are among the most chemically primitive meteorites known, having been relatively unprocessed since their formation 4.6 billion years ago. The textures they preserve are records of prevailing conditions during the formation of the planets. There is a long history to the search for the ordinary chondrite parent bodies. Dynamical modelling indicates that they are most likely to be from the main asteroid belt at 2.5 AU. This happens to be where the S-type asteroids are located, and hence the 'OC meteorite-S Type asteroid controversy' arises. S-type asteroid reflectance spectra indicate surface compositions of olivine, pyroxene, and Fe,Ni metal. These are also the minerals that compose the ordinary chondrites, and so a genetic link is indicated. The subject of this dissertation is the connection, or lack thereof, between the ordinary chondrites and the S-type asteroids. To begin the investigations, Chapter two is a report on laboratory experiments which were performed in an attempt to simulate the optical surfaces or ordinary chondrite patent bodies to see if the optical properties of the S-type asteroids could be manufactured. The next chapter is a three-parameter analysis of the main spectral features which were found to be most altered by the experiments in Chapter two. Chapter four is an examination of the first spacecraft images of an S-type asteroid, 951 Gaspra, with possible mineralogic implications. Chapter five is a presentation of a new infrared telescopic survey of the S-type asteroids. Specifically, we investigate the suggestion that the OC parent-bodies may be found among the smaller main-belt asteroids. Finally, in Chapter six, an analysis of the compositions of S-type asteroids is performed

  20. Detection and calculation of reflected spectral shifts in fiber-Bragg gratings (FBG) in polarization maintaining optical fiber

    NASA Astrophysics Data System (ADS)

    Quintana, Joel; Gonzalez, Virgilio

    2014-04-01

    Fiber-Bragg Gratings (FBG) for Structural Health Monitoring (SHM) have been studied extensively as they offer electrically passive operation, EMI immunity, high sensitivity, and multiple multiplexing schemes, as compared to conventional electricity based strain sensors. FBG sensors written in Polarization Maintaining (PM) optical fiber offer an additional dimension of strain measurement simplifying sensor implementation within a structure. This simplification however, adds complexity to the detection of the sensor's optical response to its corresponding applied strain. We propose a method that calculates spectral shifts caused by axial and traversal strains for PM FBG sensors. The system isolates the orthogonal propagating optical waves incident to the optical interrogators. The post-processing algorithm determines the wavelength shifts, and compares to a predetermined baseline then correlates the shift magnitudes to a respective strain. This exercise validates the method of optical detection and shift calculation of multi-axis sensors as an automated, integrated system.