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Sample records for low-gravity optical spectral

  1. 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

  2. Low gravity phase separator

    NASA Technical Reports Server (NTRS)

    Smoot, G. F.; Pope, W. L.; Smith, L. (Inventor)

    1977-01-01

    An apparatus is described for phase separating a gas-liquid mixture as might exist in a subcritical cryogenic helium vessel for cooling a superconducting magnet at low gravity such as in planetary orbit, permitting conservation of the liquid and extended service life of the superconducting magnet.

  3. 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.

  4. 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

  5. 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

  6. Materials processing in low gravity

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.

    1990-01-01

    The final report of the Materials Processing in Low Gravity Program in which The University of Alabama in Huntsville designed, fabricated and performed various low gravity experiments in materials processing from November 7, 1989 through November 6, 1990 is presented. The facilities used in these short duration low gravity experiments include the Drop Tube and Drop Tower at Marshall Space Flight Center (MSFC), and the KC-135 aircraft at Ellington Field. During the performance of this contract, the utilization of these ground-based low gravity facilities for materials processing experiments have been instrumental in providing the opportunity to determine the feasibility of performing a number of experiments in the microgravity of Space, without the expense of a space-based experiment. Since the KC-135 was out for repairs during the latter part of the reporting period, a number of the KC-135 activities concentrated on repair and maintenance of the equipment that normally is flown on the aircraft. A number of periodic reports were given to the TCOR during the course of this contract, hence this final report is meant only to summarize the many activities performed and not redundantly cover materials already submitted.

  7. 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.

  8. 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.

  9. Optical spectral singularities as threshold resonances

    SciTech Connect

    Mostafazadeh, Ali

    2011-04-15

    Spectral singularities are among generic mathematical features of complex scattering potentials. Physically they correspond to scattering states that behave like zero-width resonances. For a simple optical system, we show that a spectral singularity appears whenever the gain coefficient coincides with its threshold value and other parameters of the system are selected properly. We explore a concrete realization of spectral singularities for a typical semiconductor gain medium and propose a method of constructing a tunable laser that operates at threshold gain.

  10. 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.

  11. Spectral efficiency of optical direct detection

    NASA Astrophysics Data System (ADS)

    Martinez, Alfonso

    2007-04-01

    The spectral efficiency (channel capacity) of the optical direct-detection channel is studied. The modeling of the optical direct-detection channel as a discrete-time Poisson channel is reviewed. Closed-form integral representations for the entropy of random variables with Poisson and negative binomial distributions are derived. The spectral efficiency achievable with an arbitrary input gamma density is expressed in closed integral form. Simple, nonasymptotic upper and lower bounds to the channel capacity are computed. Numerical results are presented and compared with previous bounds and approximations.

  12. 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.

  13. 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.

  14. Bubble behavior during solidification in low gravity

    NASA Technical Reports Server (NTRS)

    Papazian, J. M.; Wilcox, W. R.; Gutowski, R.

    1979-01-01

    The trapping and behavior of gas bubbles were studied during low-gravity solidification of carbon tetrabromide, a transparent metal-model material. The experiment was performed during a NASA-sponsored sounding rocket flight and involved gradient freeze solidification of a gas-saturated melt. Gas bubbles were evolved at the solid-liquid interface during the low-gravity interval. 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 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 cylindrical shape, in contrast to the spherical shape that had been observed in a prior low-gravity experiment. These shapes were not influenced by the gravity level (0.0001 g-0 vs g-0), but were dependent upon the initial temperature gradient. In higher purity material, however, the shape of the voids changed from cylindrical in 1g to spherical in low gravity.

  15. Inhalation risk in low-gravity spacecraft

    NASA Astrophysics Data System (ADS)

    Todd, Paul; Sklar, Michael V.; Ramirez, W. Fred; Smith, Gerald J.; Morgenthaler, George W.; McKinnon, J. T.; Oberdörster, Günter; Schulz, Jon

    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.

  16. 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.

  17. 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.

  18. 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.

  19. 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. PMID:26907410

  20. Effects of Low Gravity on Superalloy Solidification

    NASA Technical Reports Server (NTRS)

    Johnston, M. H.; Parr, R. A.; Curreri, P. A.; Alter, Wendy

    1987-01-01

    Report describes experiments on directional solidification on MAR-M246(Hf) superalloy in low gravity. Determines effects of reduction in gravity on growth of dendrites and on resultant interdendritic segregation of various constituents, particularly of additive hafnium. Interdendritic spacings and carbide contents increase.

  1. 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.

  2. 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.

  3. Solidifying Cast Iron in Low Gravity

    NASA Technical Reports Server (NTRS)

    Hendrix, J. C.; Curreri, P. A.; Stefanescu, D. M.

    1986-01-01

    Report describes study of solidification of cast iron in low and normal gravity. Because flotation, sedimentation, and convection suppressed, alloys that solidify at nearly zero gravity have unusual and potentially useful characteristics. Study conducted in airplane that repeatedly flew along parabolic trajectories. Appears iron/carbon alloys made at low gravity have greater carbon content (as high as 5 to 10 percent) than those made of Earth gravity because carbon particles do not float to top of melt.

  4. Spectral superresolution with ultrashort optical pulses.

    PubMed

    Berger, Naum K

    2012-01-10

    A superresolution technique for the measurement of transmission, reflection, and absorption spectra is proposed. An ultrashort laser pulse is propagated in a dispersive element and then periodically phase modulated. The temporal modulation is transformed into periodic spectral modulation, for which the number of harmonics, 2M+1, is determined by the modulation index. The modulated pulse is transmitted through (reflected from) the sample to be tested and measured by a spectrometer. By performing 2M+1 measurements for 2M+1 delays between the dispersed pulse and modulation signal, one can restore the spectral response of the sample with superresolution after simple processing. We numerically demonstrate the measurement of the transmission spectrum of an ultranarrow optical filter with a minimum feature of 0.43 pm by an optical spectrum analyzer with a 10 pm resolution. A twentyfold enhancement of the resolution is achieved in the presence of noise with a level of 0.1%. The advantage of the system is its full reconfigurability. PMID:22270515

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Low gravity liquid level sensor rake

    NASA Technical Reports Server (NTRS)

    Grayson, Gary D. (Inventor); Craddock, Jeffrey C. (Inventor)

    2003-01-01

    The low gravity liquid level sensor rake measures the liquid surface height of propellant in a propellant tank used in launch and spacecraft vehicles. The device reduces the tendency of the liquid propellant to adhere to the sensor elements after the bulk liquid level has dropped below a given sensor element thereby reducing the probability of a false liquid level measurement. The liquid level sensor rake has a mast attached internal to a propellant tank with an end attached adjacent the tank outlet. Multiple sensor elements that have an arm and a sensor attached at a free end thereof are attached to the mast at locations selected for sensing the presence or absence of the liquid. The sensor elements when attached to the mast have a generally horizontal arm and a generally vertical sensor.

  10. 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.

  11. 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.

  12. Low Gravity venting of Refrigerant 11

    NASA Technical Reports Server (NTRS)

    Labus, T. L.; Aydelott, J. C.; Lacovic, R. F.

    1972-01-01

    An experimental investigation was conducted in a five-second zero gravity facility to examine the effects of venting initially saturated Refrigerant 11 from a cylindrical container (15-cm diameter) under reduced gravitational conditions. The system Bond numbers studied were 0 (weightlessness), 9 and 63; the liquid exhibited a nearly zero-degree contact angle on the container surface. During the venting process, both liquid-vapor interface and liquid bulk vaporization occurred. The temperature of the liquid in the immediate vicinity of the liquid-vapor interface was found to decrease during venting, while the liquid bulk temperature remained constant. Qualitative observations of the effects of system acceleration, vent rate, and vapor volume presented. Quantitative information concerning the ullage pressure decay during low gravity venting is also included.

  13. [Spectral calibration for space-borne differential optical absorption spectrometer].

    PubMed

    Zhou, Hai-Jin; Liu, Wen-Qing; Si, Fu-Qi; Zhao, Min-Jie; Jiang, Yu; Xue, Hui

    2012-11-01

    Space-borne differential optical absorption spectrometer is used for remote sensing of atmospheric trace gas global distribution. This instrument acquires high accuracy UV/Vis radiation scattered or reflected by air or earth surface, and can monitor distribution and variation of trace gases based on differential optical absorption spectrum algorithm. Spectral calibration is the premise and base of quantification of remote sensing data of the instrument, and the precision of calibration directly decides the level of development and application of the instrument. Considering the characteristic of large field, wide wavelength range, high spatial and spectral resolution of the space-borne differential optical absorption spectrometer, a spectral calibration method is presented, a calibration device was built, the equation of spectral calibration was calculated through peak searching and regression analysis, and finally the full field spectral calibration of the instrument was realized. The precision of spectral calibration was verified with Fraunhofer lines of solar light. PMID:23387142

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. Spectral response of multilayer optical structures to dynamic mechanical loading

    NASA Astrophysics Data System (ADS)

    Scripka, David; LeCroy, Garrett; Summers, Christopher J.; Thadhani, Naresh N.

    2015-05-01

    A computational study of Distributed Bragg Reflectors (DBR) and Optical Microcavities (OMC) was conducted to ascertain their potential as time-resolved mesoscale sensors due to their unique structure-driven spectral characteristics. Shock wave propagation simulations of polymer-based DBRs and glass/ceramic-based OMCs were coupled with spectral response calculations to demonstrate the combined dynamic mechanical and spectral response of the structures. Clear spectral shifts in both structures are predicted as a function of dynamic loading magnitude. Potential applications of the structures include high spatial and temporal resolution surface maps of material states, and in-situ probing of material interfaces during dynamic loading.

  20. Low-gravity environment in Spacelab.

    PubMed

    Knabe, W; Eilers, D

    1982-04-01

    This paper presents residual and system-generated accelerations with results from g-jitter spectral measurements in the Spacelab Engineering Model. An overview (classification, brief discussion, and assessment of magnitudes) of the various constituents of the perturbative acceleration field inside the Spacelab Module is presented, both steady and fluctuating components being considered. Results of local g-jitter spectral measurements taken in the Spacelab Engineering Model (EM-1)/Long Module Configuration are presented for frequencies from less than 1 to 200 Hz. The measured results for the system-generated perturbative accelerations exhibit, in the time domain, amplitudes of the order of 10(-3) g (peak value 3.6 x 10(-3) g). Spectral values of 4 x 10(-4) g are obtained in the frequency range up to 100 Hz; up to 10 Hz, however, the spectral values remain about an order of magnitude smaller, and also between 100 and 200 Hz the perturbation level is significantly lower than below 100 Hz. Measured results from simulated crew activities show, in the time domain, a peak amplitude of 2.6 x 10(-2)g, the spectral values being 6 x 10(-3)g below 100 Hz and 1 x 10(-3)g below 10 Hz for typical perturbances. PMID:11541689

  1. OPTICAL MICROVARIABILITY IN QUASARS: SPECTRAL VARIABILITY

    SciTech Connect

    RamIrez, A.; Dultzin, D.; De Diego, J. A. E-mail: deborah@astroscu.unam.m

    2010-05-01

    We present a method that we developed to discern where the optical microvariability (OM) in quasars originates: in the accretion disk (related to thermal processes) or in the jet (related to non-thermal processes). Analyzing nearly simultaneous observations in three different optical bands of continuum emission, we are able to determine the origin of several isolated OM events. In particular, our method indicates that from nine events reported by RamIrez et al., three of them are consistent with a thermal origin, three with non-thermal, and three cannot be discerned. The implications for the emission models of OM are briefly discussed.

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

    PubMed

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

    2010-06-01

    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. PMID:20588368

  3. Volumetric (3D) compressive sensing spectral domain optical coherence tomography

    PubMed Central

    Xu, Daguang; Huang, Yong; Kang, Jin U.

    2014-01-01

    In this work, we proposed a novel three-dimensional compressive sensing (CS) approach for spectral domain optical coherence tomography (SD OCT) volumetric image acquisition and reconstruction. Instead of taking a spectral volume whose size is the same as that of the volumetric image, our method uses a sub set of the original spectral volume that is under-sampled in all three dimensions, which reduces the amount of spectral measurements to less than 20% of that required by the Shan-non/Nyquist theory. The 3D image is recovered from the under-sampled spectral data dimension-by-dimension using the proposed three-step CS reconstruction strategy. Experimental results show that our method can significantly reduce the sampling rate required for a volumetric SD OCT image while preserving the image quality. PMID:25426320

  4. 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.

  5. Elastic Optical Path Network Architecture: Framework for Spectrally-Efficient and Scalable Future Optical Networks

    NASA Astrophysics Data System (ADS)

    Jinno, Masahiko; Takara, Hidehiko; Sone, Yoshiaki; Yonenaga, Kazushige; Hirano, Akira

    This paper presents an elastic optical path network architecture as a novel networking framework to address the looming capacity crunch problem in internet protocol (IP) and optical networks. The basic idea is to introduce elasticity and adaptation into the optical domain to yield spectrally-efficient optical path accommodation, heightened network scalability through IP traffic offloading to the elastic optical layer, and enhanced survivability for serious disasters.

  6. Spectral Response of Multilayer Optical Structures to Dynamic Loading

    NASA Astrophysics Data System (ADS)

    Scripka, David; Lecroy, Garrett; Lee, Gyuhyon; Sun, Changyan; Kang, Zhitao; Summers, Christopher J.; Thadhani, Naresh N.

    2015-06-01

    Distributed Bragg Reflectors and optical microcavities are multilayer optical structures with spectral properties that are intrinsically sensitive to external perturbations. With nanometer to micrometer dimensions and near instantaneous optical response, these structures show significant potential as the basis for mesoscale time-resolved diagnostics that can be used to probe the dynamic behavior of mesoscale heterogeneous materials. In order to characterize the optical and mechanical behavior of the multilayer structures, a coupled computational-experimental study is underway. A mechanistic analysis of the spectral response of the structures to dynamic loading will be presented, along with computational simulations illustrating the observable spectral effects of 1D shock compression. Results from fabrication of specific multilayer designs and initial laser-driven shock loading experiments will be shown and compared to the simulation results. Preliminary results indicate that the magnitude of dynamic loading can be directly correlated to the altered spectral response. Potential applications of the theoretical diagnostics and challenges associated with spatially resolved data collection methodology will also be discussed. DTRA grant HDTRA-1-12-1-0052 is acknowledged. David Scripka is supported by the Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program.

  7. Perturbative analysis of spectral singularities and their optical realizations

    NASA Astrophysics Data System (ADS)

    Mostafazadeh, Ali; Rostamzadeh, Saber

    2012-08-01

    We develop a perturbative method of computing spectral singularities of a Schrödinger operator defined by a general complex potential that vanishes outside a closed interval. These can be realized as zero-width resonances in optical gain media and correspond to a lasing effect that occurs at the threshold gain. Their time-reversed copies yield coherent perfect absorption of light that is also known as antilasing. We use our general results to establish the exactness of the nth-order perturbation theory for an arbitrary complex potential consisting of n delta functions, obtain an exact expression for the transfer matrix of these potentials, and examine spectral singularities of complex barrier potentials of arbitrary shape. In the context of optical spectral singularities, these correspond to inhomogeneous gain media.

  8. 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.

  9. 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.

  10. Fusion welding experiments under low-gravity conditions using aircraft

    NASA Astrophysics Data System (ADS)

    Masubuchi, Koichi; Nayama, Michisuke

    A series of gas tungsten arc welding experiments under low-gravity conditions created using parabolic flight of aircraft were performed. The materials used were aluminum and 2219 aluminum alloy. Welding was conducted in a small chamber filled with 100 percent argon gas, and the power source was a set of storage batteries. While welding was conducted, CCD image of welding phenomena, welding current, voltage, and the gravity level of the welding table were recorded continuously. It was found that sound welds can be obtained under low-gravity conditions. The bead appearance of the weld bead made under low-gravity conditions was very smooth and flat with no ripple lines which normally exist in welds made on the earth. The observed shape of the arc plasma under low-gravity conditions was larger than that made under normal gravity condition, but the difference was not so significant. Welds made under low-gravity conditions tend to contain more porosity compared with welds made under the earth conditions.

  11. [Application of spectral optical coherent tomography (SOCT) in ophthalmology].

    PubMed

    Bieganowski, Lech; Wojtkowski, Maciej; Kowalczyk, Andrzej; Kałuzny, Jakub J

    2004-01-01

    The article describes spectral optical coherent tomography (SOCT) constructed by Medical Physics Group, Faculty of Physics, Astronomy and Informatics at Nicholas Copernicus University in Toruń (Poland). It presents the physical bases for the functioning of the constructed device and includes pictures of optical sections of various elements of the eyeball: an optic disc and the region of central fovea, a cornea and angle structures (trabecular meshwork). The article also discusses potential application of SOCT in ophthalmic diagnosis of anterior and posterior segments of the eye. PMID:15646498

  12. Hyper-spectral imaging using an optical fiber transition element

    NASA Astrophysics Data System (ADS)

    Bush, Brett C.; Otten, Leonard J., III; Schmoll, Juergen

    2007-09-01

    The Bi-static Optical Imaging Sensor (BOIS) is a 2-D imaging sensor that operates in the short-wave infra-red (SWIR) spectral regime over wavelengths from approximately 1.0 to 2.4 microns. The conceptual design of the sensor is based on integral field spectroscopy techniques. The BOIS sensor utilizes a fiber transition element consisting of multiple optical fibers to map the 2-D spatial input scene into a 1-D linear array for injection into a hyper-spectral imaging (HSI) sensor. The HSI spectrometer acquires fast time resolution snapshots (60 Hz) of the entire input target scene in numerous narrowband spectral channels covering the SWIR spectral band. The BOIS sensor is developed to spatially observe the fast time-evolving radiative signature of targets over a variety of spectral bands, thus simultaneously characterizing the overall scene in four dimensions: 2 spatial, wavelength, and time. We describe the successful design, operation, and testing of a laboratory prototype version of the BOIS sensor as well as further development of a field version of the sensor. The goal of the laboratory prototype BOIS sensor was to validate the proof-of-concept ability in the 4-D measurement concept of this unique design. We demonstrate the 2-D spatial remapping of the input scene (using SWIR laser and blackbody cavity sources) in multiple spectral channels from the spatial versus spectral pixel output of the HSI snapshot. We also describe algorithms developed in the data processing to retrieve temperatures of the observation scene from the hyper-spectral measurements.

  13. 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.

  14. 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.

  15. 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.

  16. Optical characterization in wide spectral range by a coherent spectrophotometer

    NASA Astrophysics Data System (ADS)

    Sirutkaitis, Valdas; Eckardt, Robert C.; Balachninaite, Ona; Grigonis, Rimantas; Melninkaitis, A.; Rakickas, T.

    2003-11-01

    We report on the development and use of coherent spectrophotometers specialized for the unusual requirements of characterizing nonlinear optical materials and multilayer dielectric coatings used in laser systems. A large dynamic range is required to measure the linear properties of transmission, reflection and absorption and nonlinear properties of laser-induced damage threshold and nonlinear frequency conversion. Optical parametric oscillators generate coherent radiation that is widely tunable with instantaneous powers that can range from milliwatts to megawatts and are well matched to this application. As particular example a laser spectrophotometer based on optical parametric oscillators and a diode-pumped, Q-switched Nd:YAG laser and suitable for optical characterization in the spectral range 420-4500 nm is described. Measurements include reflectance and transmittance, absorption, scattering and laser-induced damage thresholds. Possibilities of a system based on a 130-fs Ti:sapphire laser and optical parametric generators are also discussed.

  17. Radiative Structures of Lycopodium-Air Flames in Low Gravity

    NASA Technical Reports Server (NTRS)

    Berlad, A. L.; Tangirala, V.; Ross, H.; Facca, L.

    1989-01-01

    Initially uniform clouds of fuel particulates in air sustain processes which may lead to particle cloud nonuniformities. In low gravity, flame-induced Kundt's Tube phenomena are observed to form regular patterns of nonuniform particle concentrations. Irregular patterns of particle concentrations also are observed to result from selected nonuniform mixing processes. Low gravity flame propagation for each of these classes of particle cloud flames has been found to depend importantly on the flame-generated infrared radiative fields. The spatial structures of these radiative fields are described. Application is made for the observed clases of lycopodium-air flames.

  18. 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.

  19. Highly spectral efficient networks based on grouped optical path routing.

    PubMed

    Terada, Yuki; Mori, Yojiro; Hasegawa, Hiroshi; Sato, Ken-Ichi

    2016-03-21

    In order to mitigate the signal spectrum narrowing caused by optical filtering at nodes, an adequate guard band is needed between optical channels, which degrades the frequency utilization of optical fibers. In this study, we propose a grouped routing based network architecture that minimizes spectrum narrowing while greatly improving spectral efficiency. Coarse granular routing at GRE (grouped routing entity) level is employed at each ROADM node, but fine granular add/drop is adopted to retain high frequency utilization. Optical channels are packed densely in each GRE, and sufficient guard bands are inserted between GREs. As a result, signal spectrum narrowing is minimized and efficient spectrum utilization is achieved. Network design/control algorithms that support both static and dynamic traffic growth are developed. Extensive simulations demonstrate the effectiveness of the proposed architecture. To implement the scheme, current LCOS-based ROADMs are applied without any hardware changes; only the control schema are modified. PMID:27136815

  20. Control of Spectral Phase of Ultrafast Optical Pulses with Grisms

    NASA Astrophysics Data System (ADS)

    Durfee, Charles; Field, Jeff; Squier, Jeff; Kane, Steve

    2008-10-01

    High-quality dispersion management is critical for ultrafast optics. Grisms are a combination of diffraction gratings and prisms. We can use grisms for high-fidelity control of the spectral phase of ultrafast pulses, making systems much more compact and easy to adjust. While the spectral phase of a given system can be obtained with ray-tracing, analytic expressions are desirable for exploring and optimizing new designs. We show that we can analytically calculate the spectral phase of a range of grism-like structures by making a superposition of basic tilted window modules. For example, a prism pair can be described by starting with a tilted slab of glass, which defines the outer edges of the prism pair. The inner edges of the prism pair are then created by superposing a tilted slab of air, which removes glass between the prisms. We will discuss the applications of these grism designs to ultrafast amplifiers and pulse shapers.

  1. The Arcetri Spectral Code for optically thin plasmas

    NASA Astrophysics Data System (ADS)

    Landi, E.; Landini, M.

    2002-03-01

    The Arcetri Spectral Code allows one to evaluate the spectrum of the radiation emitted by hot and optically thin plasmas in the spectral range 1-2000 Å. The Arcetri Code consists of a series of files that contain the emissivity of the plasma as a function of electron temperature and density. Both line and continuum emission are considered. These quantities are calculated using a database of atomic data and transition probabilities, mostly taken from the CHIANTI database. In the present work we describe the updates to the spectrum and present the new results. A comparison with the previous version of the code allows us to assess the improvements to the spectrum; comparison with other spectral codes allows us to assess the completeness of the Arcetri Code and of the CHIANTI database.

  2. Algebraic reconstruction techniques for spectral reconstruction in diffuse optical tomography

    SciTech Connect

    Brendel, Bernhard; Ziegler, Ronny; Nielsen, Tim

    2008-12-01

    Reconstruction in diffuse optical tomography (DOT) necessitates solving the diffusion equation, which is nonlinear with respect to the parameters that have to be reconstructed. Currently applied solving methods are based on the linearization of the equation. For spectral three-dimensional reconstruction, the emerging equation system is too large for direct inversion, but the application of iterative methods is feasible. Computational effort and speed of convergence of these iterative methods are crucial since they determine the computation time of the reconstruction. In this paper, the iterative methods algebraic reconstruction technique (ART) and conjugated gradients (CGs) as well as a new modified ART method are investigated for spectral DOT reconstruction. The aim of the modified ART scheme is to speed up the convergence by considering the specific conditions of spectral reconstruction. As a result, it converges much faster to favorable results than conventional ART and CG methods.

  3. 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.

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

    PubMed Central

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

    2010-01-01

    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. PMID:20588552

  5. 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. PMID:20588552

  6. Infrared hollow optical fiber probes for reflectance spectral imaging.

    PubMed

    Huang, Chenhui; Kino, Saiko; Katagiri, Takashi; Matsuura, Yuji

    2015-05-10

    Systems for infrared reflectance imaging are built with an FT-IR spectrometer, hollow optical fibers, and a high-speed infrared camera. To obtain reflectance images of biological samples, an optical fiber probe equipped with a light source at the distal end and a hybrid fiber probe composed of fibers for beam radiation and ones for image detection have been developed. By using these systems, reflectance spectral images of lipid painted on biomedical hard tissue, which provides reflectance of around 4%, are successfully acquired. PMID:25967522

  7. Experimental Demonstration of Spectral Intensity Optical Coherence Tomography

    PubMed Central

    Ryczkowski, Piotr; Turunen, Jari; Friberg, Ari T.; Genty, Goëry

    2016-01-01

    We demonstrate experimentally spectral-domain intensity optical coherence tomography using a Mach-Zehnder interferometer with balanced detection. We show that the technique allows for a point spread function with reduced full-width at half maximum compared to conventional optical coherence tomography. The method further provides benefits similar to those of chirped-pulse interferometry in terms of dispersion cancellation but only requires a broadband incoherent source and standard detectors. The measurements are in excellent agreement with the theoretical predictions. Finally, we propose an approach that enables the elimination of potential artefacts arising from multiple interfaces. PMID:26916668

  8. 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.

  9. 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

  10. Imaging tamoxifen retinopathy using spectral-domain optical coherence tomography

    PubMed Central

    Caramoy, Albert; Scholz, Paula; Fauser, Sascha; Kirchhof, Bernd

    2011-01-01

    A case of tamoxifen retinopathy examined with spectral-domain optical coherence tomography (SD-OCT) is presented. The typical refractile deposits are located between ganglion cell layer and inner plexiform layer in SD-OCT. A defect on the outer retinal layer with disruption of the photoreceptor layer with sharp edges is seen. The still attached posterior hyaloids gives evidence of other pathomechanism involved in the outer retinal defect than that of macular hole, as suggested in the literature.

  11. 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.

  12. Optimization of narrow optical spectral filters for nonparallel monochromatic radiation.

    PubMed

    Linder, S L

    1967-07-01

    This paper delineates a method of determining the design criteria for narrow optical passband filters used in the reception of nonparallel modulated monochromatic radiation. The analysis results in straightforward mathematical expressions for calculating the filter width and design center wavelength which maximize the signal-to-noise ratio. Two cases are considered: (a) the filter is designed to have a maximum transmission (for normal incidence) at the incident wavelength, but with the spectral width optimized, and (b) both the design wavelength and the spectral width are optimized. It is shown that the voltage signal-to-noise ratio for case (b) is 2((1/2)) that of case (a). Numerical examples are calculated. PMID:20062163

  13. Suppressing Spectral Diffusion of Emitted Photons with Optical Pulses

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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. 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.

  14. 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.

  15. 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.

  16. Heterodyne detection using spectral line pairing for spectral phase encoding optical code division multiple access and dynamic dispersion compensation.

    PubMed

    Yang, Yi; Foster, Mark; Khurgin, Jacob B; Cooper, A Brinton

    2012-07-30

    A novel coherent optical code-division multiple access (OCDMA) scheme is proposed that uses spectral line pairing to generate signals suitable for heterodyne decoding. Both signal and local reference are transmitted via a single optical fiber and a simple balanced receiver performs sourceless heterodyne detection, canceling speckle noise and multiple-access interference (MAI). To validate the idea, a 16 user fully loaded phase encoded system is simulated. Effects of fiber dispersion on system performance are studied as well. Both second and third order dispersion management is achieved by using a spectral phase encoder to adjust phase shifts of spectral components at the optical network unit (ONU). PMID:23038313

  17. 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.

  18. 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.

  19. 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.

  20. Polarized spectral complexes of optical functions of monovalent mercury iodide

    NASA Astrophysics Data System (ADS)

    Sobolev, V. V.; Sobolev, V. Val.; Anisimov, D. V.

    2015-12-01

    Spectral complexes of optical functions of monovalent mercury iodide Hg2I2 were determined for E ⊥ c and E || c polarizations in the range from 2 to 5.5 eV at 4.2 K. The permittivity and characteristic electron energy loss spectra were expanded in simple components with the determination of their main parameters, including the energy of the maximum and the oscillator strength. The calculations were performed based on known reflectance spectra. Computer programs based on Kramers-Kronig relations and the improved parameter-free method of Argand diagrams were used.

  1. 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.

  2. 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.

  3. 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.

  4. Spectrally balanced detection for optical frequency domain imaging.

    PubMed

    Chen, Yueli; de Bruin, Daniel M; Kerbage, Charles; de Boer, Johannes F

    2007-12-10

    In optical frequency domain imaging (OFDI) or swept-source optical coherence tomography, balanced detection is required to suppress relative intensity noise (RIN). A regular implementation of balanced detection by combining reference and sample arm signal in a 50/50 coupler and detecting the differential output with a balanced receiver is however, not perfect. Since the splitting ratio of the 50/50 coupler is wavelength dependent, RIN is not optimally canceled at the edges of the wavelength sweep. The splitting ratio has a nearly linear shift of 0.4% per nanometer. This brings as much as +/-12% deviation at the margins of wavelength-swept range centered at 1060nm. We demonstrate a RIN suppression of 33dB by spectrally corrected balanced detection, 11dB more that regular balanced detection. PMID:19550929

  5. Spectrally efficient optical transmission based on Stokes vector direct detection.

    PubMed

    Li, An; Che, Di; Chen, Vivian; Shieh, William

    2014-06-30

    We propose a novel detection scheme called Stokes vector direct detection (SV-DD) to realize high electrical spectral efficiency and cost-effective optical communication for short and medium reach. With SV-DD, the signal is modulated in only one polarization and combined with the carrier in the orthogonal polarization for fiber transmission. At reception, the combined signal is detected in Stokes space by three or four photo-detectors. Compared with conventional DD technique, SV-DD is resilient to both chromatic dispersion and signal-to-signal beat noise. Furthermore, SV-DD does not require polarization tracking or narrow band optical filtering for carrier extraction. In this paper, we present for the first time the numerical analysis and experimental demonstration of single-carrier SV-DD. We report 62.5-Gb/s data rate single-carrier SV-DD transmission over 160-km SSMF using 12.5-Gbaud 32-QAM modulation. PMID:24977825

  6. 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. PMID:22945175

  7. Power Spectral Density Specification and Analysis of Large Optical Surfaces

    NASA Technical Reports Server (NTRS)

    Sidick, Erkin

    2009-01-01

    The 2-dimensional Power Spectral Density (PSD) can be used to characterize the mid- and the high-spatial frequency components of the surface height errors of an optical surface. We found it necessary to have a complete, easy-to-use approach for specifying and evaluating the PSD characteristics of large optical surfaces, an approach that allows one to specify the surface quality of a large optical surface based on simulated results using a PSD function and to evaluate the measured surface profile data of the same optic in comparison with those predicted by the simulations during the specification-derivation process. This paper provides a complete mathematical description of PSD error, and proposes a new approach in which a 2-dimentional (2D) PSD is converted into a 1-dimentional (1D) one by azimuthally averaging the 2D-PSD. The 1D-PSD calculated this way has the same unit and the same profile as the original PSD function, thus allows one to compare the two with each other directly.

  8. Autofocus by Bayes Spectral Entropy Applied to Optical Microscopy.

    PubMed

    Podlech, Steffen

    2016-02-01

    This study introduces a passive autofocus method based on image analysis calculating the Bayes spectral entropy (BSE). The method is applied to optical microscopy and together with the specific construction of the opto-mechanical unit, it allows the analysis of large samples with complicated surfaces without subsampling. This paper will provide a short overview of the relevant theory of calculating the normalized discrete cosine transform when analyzing obtained images, in order to find the BSE measure. Furthermore, it will be shown that the BSE measure is a strong indicator, helping to determine the focal position of the optical microscope. To demonstrate the strength and robustness of the microscope system, tests have been performed using a 1951 USAF test pattern resolution chart determining the in focus position of the microscope. Finally, this method and the optical microscope system is applied to analyze an optical grating (100 lines/mm) demonstrating the detection of the focal position. The paper concludes with an outlook of potential applications of the presented system within quality control and surface analysis. PMID:26758956

  9. Adaptive compressed sensing for spectral-domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Chen, Xiaodong; Wang, Ting; Li, Hongxiao; Yu, Daoyin

    2014-03-01

    Spectral-domain optical coherence tomography (SD-OCT) is a non-contact and non-invasive method for measuring the change of biological tissues caused by pathological changes of body. CCD with huge number of pixels is usually used in SD-OCT to increase the detecting depth, thus enhancing the hardness of data transmission and storage. The usage of compressed sensing (CS) in SD-OCT is able to reduce the trouble of large data transfer and storage, thus eliminating the complexity of processing system. The traditional CS uses the same sampling model for SD-OCT images of different tissue, leading to reconstruction images with different quality. We proposed a CS with adaptive sampling model. The new model is based on uniform sampling model, and the interference spectral of SD-OCT is considered to adjust the local sampling ratio. Compared with traditional CS, adaptive CS can modify the sampling model for images of different tissue according to different interference spectral, getting reconstruction images with high quality without changing sampling model.

  10. Optical Communications in the mid-wave IR spectral band

    NASA Astrophysics Data System (ADS)

    Prasad, Narasimha S.

    The mid-wave IR (MWIR) spectral band extending from 3 to 5 microns is considered to be a low loss atmospheric window. The MWIR wavelengths are eye safe and are attractive for several free-space applications including remote sensing of chemical and biological species, hard target imaging, range finding, target illumination, and free-space Communications. Due to the nature of light-matter interaction characteristics, MWIR wavelength based Systems can provide unique advantages over other spectral bands for these applications, The MWIR wavelengths are found to effectively penetrate natural and anthropogenic obscurants. Consequently, MWIR Systems offer increased range Performance at reduced power levels. Free-space, line-of-sight optical communication links for terrestrial as well as space based platforms using MWIR wavelengths can be designed to operate under low visibility conditions. Combined with high-bandwidth, eye-safe, covert and jam proof features, a MWIR wavelength based optical communication link could play a vital role in hostile environments.

  11. 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.

  12. Optical Polarization and Spectral Variability in the M87 Jet

    NASA Astrophysics Data System (ADS)

    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.

    2011-12-01

    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 has also been 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 ~20% at minimum to >40% at maximum, while the orientation of its electric vector stayed constant. HST-1's optical-UV spectrum is very hard (αUV-O ~ 0.5, F νvpropν-α), 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 2σ upper limits of 0.5δ pc and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet position angle (P.A.) 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 (αUV-O ~ 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.

  13. 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.

  14. Nonlinear optical signal processing for high-speed, spectrally efficient fiber optic systems and networks

    NASA Astrophysics Data System (ADS)

    Zhang, Bo

    The past decade has witnessed astounding boom in telecommunication network traffic. With the emergence of multimedia over Internet, the high-capacity optical transport systems have started to shift focus from the core network towards the end users. This trend leads to diverse optical networks with transparency and reconfigurability requirement. As single channel data rate continues to increase and channel spacing continues to shrink for high capacity, high spectral efficiency, the workload on conventional electronic signal processing elements in the router nodes continues to build up. Performing signal processing functions in the optical domain can potentially alleviate the speed bottleneck if the unique optical properties are efficiently leveraged to assist electronic processing methodologies. Ultra-high bandwidth capability along with the promise for multi-channel and format-transparent operation make optical signal processing an attractive technology which is expected to have great impact on future optical networks. For optical signal processing applications in fiber-optic network and systems, a laudable goal would be to explore the unique nonlinear optical processes in novel photonic devices. This dissertation investigates novel optical signal processing techniques through simulations and experimental demonstrations, analyzes limitations of these nonlinear processing elements and proposes techniques to enhance the system performance or designs for functional photonic modules. Two key signal-processing building blocks for future optical networks, namely slow-light-based tunable optical delay lines and SOA-based high-speed wavelength converters, are presented in the first part of the dissertation. Phase preserving and spectrally efficient slow light are experimentally demonstrated using advanced modulation formats. Functional and novel photonic modules, such as multi-channel synchronizer and variable-bit-rate optical time division multiplexer are designed and

  15. 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.

  16. 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.

  17. 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

  18. Suppressing spectral diffusion of emitted photons with optical pulses

    DOE PAGESBeta

    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 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

  19. Shift-multiplexing complex spectral-domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Huang, Haochong; Jiang, Zhuqing; Wang, Dayong; Cai, Wenyuan; Man, Tianlong; Wang, Zhe; Panezai, Spozmai

    2014-01-01

    We propose and experimentally demonstrate a shift-multiplexing complex spectral-domain optical coherence tomography (shift-multiplexing CSD-OCT) method, in which the maximum detection depth of SD-OCT can be greatly extended by incorporating the shift-multiplexing of detection positions with CSD-OCT. The tomographic imaging with twofold or threefold microscopic slides as the target sample is performed. The experimental results show that the tomographic imaging with more uniform brightness and clarity for the different depth regions in a thick sample can be achieved by the shift-multiplexing CSD-OCT system. In particular, even while the sample's depth is beyond the maximum imaging depth of CSD-OCT system, the tomographic imaging of this sample can still be realized by using the shift-multiplexing CSD-OCT method without the need for any replacement of the equipment, such as high spectral capacity grating or high resolution of CCD. The shift-multiplexing CSD-OCT system can perform the imaging with the optimization and less reduction of sensitivity for the deeper detection position in the sample.

  20. 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.

  1. 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.

  2. Ceiling Fires Studied to Simulate Low-Gravity Fires

    NASA Technical Reports Server (NTRS)

    Olson, Sandra L.

    2001-01-01

    A unique new way to study low-gravity flames in normal gravity has been developed. To study flame structure and extinction characteristics in low-stretch environments, a normal gravity low-stretch diffusion flame was generated using a cylindrical PMMA sample of varying large radii, as shown in the photograph. These experiments have demonstrated that low-gravity flame characteristics can be generated in normal gravity through the proper use of scaling. On the basis of this work, it is feasible to apply this concept toward the development of an Earth-bound method of evaluating material flammability in various gravitational environments from normal gravity to microgravity, including the effects of partial gravity low-stretch rates such as those found on the Moon (1/6g) or Mars (1/3g). During these experiments, the surface regression rates for PMMA were measured for the first time over the full range of flammability in air, from blowoff at high stretch, to quenching at low stretch, as plotted in the graph. The solid line drawn through the central portion of the data (3

  3. 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).

  4. 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

  5. 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)

  6. Optical design of multi-spectral optical system for infrared camera

    NASA Astrophysics Data System (ADS)

    Tang, Tianjin

    2015-08-01

    This paper studies about the multi-spectral imaging system and describes the design of dual-channel mirror-lens optical system with wide-field for multi-spectral sensor. Combined with the secondary imaging technology, it achieves the one hundred percent cold stop efficiency. Off-axis three-mirror reflective optics is adopted to provide an obstructive field of view and high spatial resolution over the wide-field, which is also shared by two channels. Independent relay lens are employed not only to extract the real exit-pupil matched with the cold shield, but also adjust the multiplication factors for infrared. The dichroic mirror and filters subdivide the wide spectral range into four bands, including mid-wavelength band and long-wavelength band. Each corresponds to respective field. The result shows that the Modulation Transfer Function of each band at respective fields is near the diffraction limit, which satisfies the needs of practical applications. The wavefront of the off-axis three-mirror reflective optics is also satisfactory, which is beneficial to the later alignment and measurement.

  7. 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. PMID:16712153

  8. 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.

  9. 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

  10. MTF formalism for measurement of spectral resolution of acousto-optical devices with synthesized transmission function.

    PubMed

    Yushkov, Konstantin B; Molchanov, Vladimir Ya

    2013-09-15

    We demonstrate use of the modulation transfer function method in the spectral domain for dynamic measurement of the spectral resolution and modulation contrast of acousto-optic light dispersive delay lines and programmable filters with synthesized transmission. The method is useful for performance characterization of acousto-optic devices for ultrafast pulse shaping and adaptive spectroscopy. PMID:24104818

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

    NASA Technical Reports Server (NTRS)

    Cintala, Mark J.

    1987-01-01

    Innumerable efforts were made to understand the cratering process and its ramifications in terms of planetary observations, during which the 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-g centrifuge experiments. Considerable insight into the effects of gravity, among other factors, was gained. Even so, other avenues of investigation were out of reach to workers confined to the terrestrial laboratory. 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; their names and affiliations are listed.

  13. Low gravity thermal stratification of liquid helium on SHOOT

    NASA Astrophysics Data System (ADS)

    Shirron, P. J.; Dipirro, M. J.

    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.

  14. 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.

  15. 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.

  16. 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.

  17. Further studies of propellant sloshing under low-gravity conditions

    NASA Technical Reports Server (NTRS)

    Dodge, F. T.

    1971-01-01

    A variational integral is formulated from Hamilton's Principle and is proved to be equivalent to the usual differential equations of low-gravity sloshing in ellipsoidal tanks. It is shown that for a zero-degree contact angle the contact line boundary condition corresponds to the stuck condition, a result that is due to the linearization of the equations and the ambiguity in the definition of the wave height at the wall. The variational integral is solved by a Rayleigh-Ritz technique. Results for slosh frequency when the free surface is not bent-over compare well with previous numerical solutions. When the free surface is bent over, however, the results for slosh frequency are considerably larger than those predicted by previous finite-difference, numerical approaches: the difference may be caused by the use of a zero degree contact angle in the present theory in contrast to the nonzero contact angle used in the numerical approaches.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Modeling aggregation of dust monomers in low gravity environments

    NASA Astrophysics Data System (ADS)

    Doyon, Julien; Rioux, Claude

    The modeling of aggregation phenomena in microgravity is of paramount relevance to the understanding of the formation of planets. Relevant experiments have been carried out at a ground based laboratory and on aircraft providing low gravity during parabolic flight.1 Other possible environments are rockets, shuttles and the international space station. Numerical simulation of aggregation can provide us a tool to understand the formal and the-oretical background of the phenomena. The comparison between low gravity experiment and modeling prediction may confirm a theory. Also, experiments that are hard to perform can be simulated on computers allowing a vast choice of physical properties. Simulations to date have been constrained to ensembles of 100 to 1000 monomers.2 We have been able to extend such numbers to 10 000 monomers and the final goal is about 100 000 monomers, where gravitational effects become relevant yielding spheroidal systems of particles (planetesimals and planetoids). Simulations made are assumed to be diffusion processes where colliding particles will stick together with a certain probability. Future work shall include other interactions like electrostatic or magnetic forces. Recent results are to be shown at the meeting. I acknowledge the support from the ELIPS program (jointly between Canadian and European space agencies). The guidance of Prof. Slobodrian is warmly thanked. References. 1. R.J. Slobodrian, C. Rioux and J.-C. Leclerc, Microgravity Research and Aplications in Phys-ical Sciences and Biotechnology, Proceedings of the First International Symposium, Sorrento, Italy (2000) ESA SP-454, p.779-786. and Refs. therein. 2. P. Deladurantaye, C Rioux and R.J Slobodrian, Chaos, Solitons Fractals , (1997), pp. 1693-1708. Carl Robert and Eric Litvak, Software " Fractal", private communication.

  3. 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.

  4. Hybrid optical spectral and time division multiplexing for passive interferometric fibre optic sensor networks

    NASA Astrophysics Data System (ADS)

    Al-Raweshidy, H. S.; Edwards, D. J.

    1993-01-01

    A new technique called hybrid optical spectral and time division multiplexing for passive interferometric fibre optic sensor networks has been developed. The idea of this technique is initially to modulate the optical spectrum with different sub-carrier frequencies at different time interval lasting for a period T. A proper selection for the sub-carrier values could minimise the crosstalk between sensors. The use of a synchronised gating signal at the detector output enables the simultaneous interrogation of signals from different sensors. A two-interferometric sensor network has been demonstrated and a 42 dB crosstalk has been achieved. The salient features of this technique are the simplicity, low crosstalk and high number of permissible sensors.

  5. 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.

  6. 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.

  7. Quality assessment for spectral domain optical coherence tomography (OCT) images

    NASA Astrophysics Data System (ADS)

    Liu, Shuang; Paranjape, Amit S.; Elmaanaoui, Badr; Dewelle, Jordan; Rylander, H. Grady, III; Markey, Mia K.; Milner, Thomas E.

    2009-02-01

    Retinal nerve fiber layer (RNFL) thickness, a measure of glaucoma progression, can be measured in images acquired by spectral domain optical coherence tomography (OCT). The accuracy of RNFL thickness estimation, however, is affected by the quality of the OCT images. In this paper, a new parameter, signal deviation (SD), which is based on the standard deviation of the intensities in OCT images, is introduced for objective assessment of OCT image quality. Two other objective assessment parameters, signal to noise ratio (SNR) and signal strength (SS), are also calculated for each OCT image. The results of the objective assessment are compared with subjective assessment. In the subjective assessment, one OCT expert graded the image quality according to a three-level scale (good, fair, and poor). The OCT B-scan images of the retina from six subjects are evaluated by both objective and subjective assessment. From the comparison, we demonstrate that the objective assessment successfully differentiates between the acceptable quality images (good and fair images) and poor quality OCT images as graded by OCT experts. We evaluate the performance of the objective assessment under different quality assessment parameters and demonstrate that SD is the best at distinguishing between fair and good quality images. The accuracy of RNFL thickness estimation is improved significantly after poor quality OCT images are rejected by automated objective assessment using the SD, SNR, and SS.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. Spectral-Domain Optical Coherence Tomography Findings in Lipemia Retinalis.

    PubMed

    Özturk, Banu Turgut; Bozkurt, Banu; Meşen, Ali; Gonul, Saban; İpekci, Süleyman Hilmi

    2016-06-01

    Severe hypertriglyceridemia can give rise to a fundus appearance with whitish-colored retinal vessels called lipemia retinalis. A 52-year-old man with hypertriglyceridemia presented with a best-corrected visual acuity of 20/20 in both eyes and creamy-white retinal vessels on fundus. Spectral-domain optical coherence tomography (SD-OCT) revealed hyperreflective and engorged retinal vessels and white dots mainly accumulated in the inner nuclear and ganglion cell layer. Follow-up fundus examination after plasmapheresis sessions revealed normal retinal vessels. The hyperreflective appearance of the retinal vessels in OCT reversed rapidly 5 days after the treatment, whereas hyperreflective dots in retina disappeared slowly in 3 months. OCT is useful in demonstrating inner retinal changes associated with lipemia retinalis at histopathological level. The hyperreflective dots in inner retina associated with leakage from superficial retinal capillaries attested the correlation of their location with their origin. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:589-592.]. PMID:27327291

  13. 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.

  14. 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. PMID:21164657

  15. Impact of High-Frequency Spectral Phase Modulation on the Temporal Profile of Short Optical Pulses

    SciTech Connect

    Dorrer, C.; Bromage, J.

    2008-03-18

    The impact of high-frequency spectral phase modulation on the temporal intensity of optical pulses is derived analytically and simulated in two different regimes. The temporal contrast of an optical pulse close to the Fourier-transform limit is degraded by a pedestal related to the power spectral density of the spectral phase modulation. When the optical pulse is highly chirped, its intensity modulation is directly related to the spectral phase variations with a transfer function depending on the second-order dispersion of the chirped pulse. The metrology of the spectral phase of an optical pulse using temporal-intensity measurements performed after chirping the pulse is studied. The effect of spatial averaging is also discussed.

  16. Experimental measurements of the spectral absorption coefficient of pure fused silica optical fibers.

    PubMed

    Moore, Travis J; Jones, Matthew R

    2015-02-20

    Knowledge of the spectral absorption coefficient of fused silica optical fibers is important in modeling heat transfer in the processes and applications in which these fibers are used. An experimental method used to measure the spectral absorption coefficient of optical fibers is presented. Radiative energy from a blackbody radiator set at different temperatures is directed through the optical fibers and into an FTIR spectrometer. Spectral instrument response functions are calculated for different fiber lengths. The ratios of the slopes of the instrument response functions for the different lengths of fibers are used to solve for the spectral absorption coefficient of the fibers. The spectral absorption coefficient of low OH pure fused silica optical fibers is measured between the wavelengths 1.5 and 2.5 μm. PMID:25968202

  17. Spectral-domain optical coherence tomography of macula in myopia.

    PubMed

    Choovuthayakorn, Janejit; Laowong, Taksaorn; Watanachai, Nawat; Patikulsila, Direk; Chaikitmongkol, Voraporn

    2016-06-01

    The aim of this study is to determine the associations between regional macular thickness and gender, age, axial length, and degree of myopia in young and middle-aged healthy myopic eyes. One hundred and seventy-one subjects with -0.5 diopters of myopia or worse underwent prospective macular thickness measurement by Spectralis spectral-domain optical coherence tomography. Subjects' mean age was 32.40 ± 8.25 years (range 18 to 49 years), with 45 % being male. The mean degree of myopia was -4.57 ± 3.52 diopters, with a mean axial length of 25.09 ± 1.67 mm. Multivariate regression analysis demonstrated significantly thicker central (mean 9.13 µm thicker) and inner subfields (mean 8.55 µm thicker) in males (P values were <0.001 and 0.002, respectively). In addition, in both genders, for each millimeter of increased axial length, the central subfield thickness increased by 2.11 µm, the inner subfield decreased by 2.25 µm, and the outer subfield decreased by 3.62 µm (P values were 0.010, <0.001, and <0.001, respectively). Factors including gender and axial length affect baseline regional macular thickness in young and middle-age myopic subjects. The central subfield and inner subfield were affected by both gender and axial length, while the outer subfield was affected only by axial length. The macular thickness of myopic subjects with macular disease should be interpreted in light of these factors. PMID:26290135

  18. 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.

  19. 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

  20. Three-dimensional tracker for spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Iftimia, Nicusor V.; Bigelow, Chad E.; Ustun, Teoman E.; Bloom, Benjamin; Ferguson, R. Daniel; Milner, Thomas E.

    2007-02-01

    Spectral domain optical coherence tomography (SDOCT) is a relatively new imaging technique that allows high-speed cross-sectional scanning of retinal structures with little motion artifact. However, instrumentation for these systems is not yet fast enough to collect high-density three-dimensional retinal maps free of the adverse effects of lateral eye movements. Low coherence interferometry instruments must also contend with axial motion primarily from head movements that shift the target tissue out of the coherence detection range. Traditional SDOCT instruments suffer from inherent deficiencies that exacerbate the effect of depth motion, including limited range, depth-dependent signal attenuation, and complex conjugate overlap. We present initial results on extension of our transverse retinal tracking system to three-dimensions especially for SDOCT imagers. The design and principle of operation of two depth tracking techniques, adaptive ranging (AR) and Doppler velocity (DV) tracking, are presented. We have integrated the threedimensional tracking hardware into a hybrid line scanning laser ophthalmoscope (LSLO)/SDOCT imaging system. Imaging and tracking performance was characterized by tests involving a limited number of human subjects. The hybrid imager could switch between wide-field en-face confocal LSLO images, high-resolution cross-sectional OCT images, and an interleaved mode of sequential LSLO and OCT images. With 3-D tracking, the RMS error for axial motion decreased to <50 µm and for lateral motion decreased to <10 µm. The development of real-time tracking and SDOCT image processing hardware is also discussed. Future implementation of 3-D tracking should increase the yield of usable images and decrease the patient measurement time for clinical SDOCT systems.

  1. 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

  2. Use of Multiband Acousto-optic Filters for Spectrally Encoded Signals Generation in Incoherent Optical Communication Systems

    NASA Astrophysics Data System (ADS)

    Byshevski-Konopko, O. A.; Proklov, V. V.; Filatov, A. L.; Lugovskoi, A. V.; Korablev, E. M.

    New acousto-optical (AO) coder of spectrally optical signals for optical code division multiple access systems (O-CDMA) was proposed and investigated. The coder was developed on a base of multi-frequency acousto-optical filter (MAOF). Control RF signals for MAOF were synthesized taking into account intermodulation distortions and interferences between different carrier frequencies incoming to MAOF. An industrial LED was used under system investigation.

  3. Precision spectral manipulation of optical pulses using a coherent photon echo memory.

    PubMed

    Buchler, B C; Hosseini, M; Hétet, G; Sparkes, B M; Lam, P K

    2010-04-01

    Photon echo schemes are excellent candidates for high efficiency coherent optical memory. They are capable of high-bandwidth multipulse storage, pulse resequencing and have been shown theoretically to be compatible with quantum information applications. One particular photon echo scheme is the gradient echo memory (GEM). In this system, an atomic frequency gradient is induced in the direction of light propagation leading to a Fourier decomposition of the optical spectrum along the length of the storage medium. This Fourier encoding allows precision spectral manipulation of the stored light. In this Letter, we show frequency shifting, spectral compression, spectral splitting, and fine dispersion control of optical pulses using GEM. PMID:20364227

  4. Profile and Determinants of Retinal Optical Intensity in Normal Eyes with Spectral Domain Optical Coherence Tomography

    PubMed Central

    Chen, Haoyu; Yang, Jianling; Shi, Fei; Zheng, Ce; Zhu, Weifang; Xiang, Dehui; Chen, Xinjian; Zhang, Mingzhi

    2016-01-01

    Purpose To investigate the profile and determinants of retinal optical intensity in normal subjects using 3D spectral domain optical coherence tomography (SD OCT). Methods A total of 231 eyes from 231 healthy subjects ranging in age from 18 to 80 years were included and underwent a 3D OCT scan. Forty-four eyes were randomly chosen to be scanned by two operators for reproducibility analysis. Distribution of optical intensity of each layer and regions specified by the Early Treatment of Diabetic Retinopathy Study (ETDRS) were investigated by analyzing the OCT raw data with our automatic graph-based algorithm. Univariate and multivariate analyses were performed between retinal optical intensity and sex, age, height, weight, spherical equivalent (SE), axial length, image quality, disc area and rim/disc area ratio (R/D area ratio). Results For optical intensity measurements, the intraclass correlation coefficient of each layer ranged from 0.815 to 0.941, indicating good reproducibility. Optical intensity was lowest in the central area of retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer and photoreceptor layer, except for the retinal pigment epithelium (RPE). Optical intensity was positively correlated with image quality in all retinal layers (0.553<β<0.851, p<0.01), and negatively correlated with age in most retinal layers (-0.362<β<-0.179, p<0.01), except for the RPE (β = 0.456, p<0.01), outer nuclear layer and photoreceptor layer (p>0.05). There was no relationship between retinal optical intensity and sex, height, weight, SE, axial length, disc area and R/D area ratio. Conclusions There was a specific pattern of distribution of retinal optical intensity in different regions. The optical intensity was affected by image quality and age. Image quality can be used as a reference for normalization. The effect of age needs to be taken into consideration when using OCT for diagnosis. PMID:26863010

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. High spectral resolution lidar to measure optical scattering properties of atmospheric aerosols. I - Theory and instrumentation

    NASA Technical Reports Server (NTRS)

    Shipley, S. T.; Tracy, D. H.; Eloranta, E. W.; Roesler, F. L.; Weinman, J. A.; Trauger, J. T.; Sroga, J. T.

    1983-01-01

    A high spectral resolution lidar technique to measure optical scattering properties of atmospheric aerosols is described. Light backscattered by the atmosphere from a narrowband optically pumped oscillator-amplifier dye laser is separated into its Doppler broadened molecular and elastically scattered aerosol components by a two-channel Fabry-Perot polyetalon interferometer. Aerosol optical properties, such as the backscatter ratio, optical depth, extinction cross section, scattering cross section, and the backscatter phase function, are derived from the two-channel measurements.

  15. Spectrally narrow mid-infrared optically pumped lasers with partial surface DBR.

    PubMed

    Yang, Chi; Kaspi, Ron; Tilton, Michael L; Chavez, Joseph R; Ongstad, Andrew P; Dente, Gregory C

    2012-05-01

    An optically pumped mid-infrared edge-emitting laser is described, in which a Distributed Bragg Reflector grating partially occupies the surface, and provides spectral narrowing in a high power device. A quasi-continuous-wave power of 3 Watts is obtained at 3.6 µm that is contained within a spectral width of 7 nm. PMID:22565707

  16. Spectral separation of Cr3+ optical centers in stoichiometric magnesium-doped lithium niobate crystals

    NASA Astrophysics Data System (ADS)

    Galutskii, V. V.; Stroganova, E. V.; Yakovenko, N. A.

    2011-03-01

    The broadband luminescence of chromium optical centers with strongly overlapping spectral lines and similar emission probabilities from excited 4 T 2 states of red and green Cr3+ centers in stoichiometric magnesium-doped lithium niobate crystals has been separated for the first time. The spectral-luminescence characteristics and parameters of intracenter interaction between red and green optical Cr3+ centers in stoichiometric lithium niobate have been calculated. The luminescence quantum efficiencies of red and green chromium centers are determined.

  17. Tunable all-optical single-bandpass photonic microwave filter based on spectrally sliced broad optical source and phase modulation.

    PubMed

    Chen, Ming; Pan, Wei; Zou, Xihua; Luo, Bin; Yan, Lianshan; Liu, Xinkai

    2013-01-10

    A tunable all-optical single-bandpass photonic microwave filter (PMF) based on spectrally sliced broadband optical source and phase modulation is proposed and experimentally demonstrated. A broadband optical source and a Mach-Zehnder interferometer (MZI) are used to generate continuous optical spectral samples, which are employed to form a finite impulse response filter with a single-bandpass response with the help of a single-mode fiber. A phase modulator is then adopted to eliminate the baseband components in the filtering response. The center frequency of the PMF can be tuned by changing the free spectral range of the MZI. An experiment is performed, and the results demonstrate that the proposed PMF has a single-bandpass without baseband components and a tuning range of 5-15 GHz. PMID:23314649

  18. Generation of spectral-encoded signals in noncoherent optical communication systems based on acousto-optic multiwavelength filters

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    New acousto-optical (AO) methods and devices necessary for the creation of noncoherent optical code division multiple access (O-CDMA) systems are considered. Based on an AO multiwavelength filter, an original device generating spectral-encoded signals for O-CDMA systems with optimum WDM has been created and studied. It is shown that modern AO technology is capable of surmounting difficulties that previously hindered the transition of optical communication systems to CDMA data transmission.

  19. 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.

  20. Optic Disc Vascularization in Glaucoma: Value of Spectral-Domain Optical Coherence Tomography Angiography

    PubMed Central

    Lévêque, Pierre-Maxime; Zéboulon, Pierre; Brasnu, Emmanuelle; Baudouin, Christophe; Labbé, Antoine

    2016-01-01

    Purpose. To detect changes in optic nerve head (ONH) vascularization in glaucoma patients using spectral-domain OCT angiography (OCT-A). Material and Method. Fifty glaucoma patients and 30 normal subjects were evaluated with OCT-A (AngioVue®, Optovue). The total ONH vessel density and temporal disc vessel density were measured. Clinical data, visual field (VF) parameters, and spectral-domain OCT evaluation (RNFL: retinal nerve fiber layer thickness, GCC: ganglion cell complex thickness, and rim area) were recorded for glaucoma patients. Correlations among total and temporal ONH vessel density and structural and VF parameters were analyzed. Results. In the glaucoma group, total and temporal ONH vessel density were reduced by 24.7% (0.412 versus 0.547; p < 0.0001) and 22.88% (0.364 versus 0.472; p = 0.001), respectively, as compared with the control group. Univariate analysis showed significant correlation between rim area (mm2) and temporal ONH vessel density (r = 0.623; p < 0.0001) and total ONH vessel density (r = 0.609; p < 0.0001). Significant correlations were found between temporal and total ONH vessel density and RNFL, GCC, VF mean deviation, and visual field index. Conclusion. In glaucoma patients OCT-A might detect reduced ONH blood vessel density that is associated with structural and functional glaucomatous damage. OCT-A might become a useful tool for the evaluation of ONH microcirculation changes in glaucoma. PMID:26998352

  1. Spectral properties of strongly correlated bosons in two-dimensional optical lattices

    SciTech Connect

    Knap, Michael; Arrigoni, Enrico; Linden, Wolfgang von der

    2010-01-01

    Spectral properties of the two-dimensional Bose-Hubbard model, which emulates ultracold gases of atoms confined in optical lattices, are investigated by means of the variational cluster approach. The phase boundary of the quantum phase transition from Mott phase to superfluid phase is calculated and compared to recent work. Moreover the single-particle spectral functions in both the first and the second Mott lobe are presented and the corresponding densities of states and momentum distributions are evaluated. A qualitatively similar intensity distribution of the spectral weight can be observed for spectral functions in the first and the second Mott lobe.

  2. Experimental realization of spectral shaping using nonlinear optical holograms.

    PubMed

    Leshem, Anat; Shiloh, Roy; Arie, Ady

    2014-09-15

    We experimentally demonstrate the spectral shaping of a signal generated by a three-wave mixing process using a nonlinear spectral hologram. These holograms are based on binary spatial modulation of the second-order nonlinear coefficient. Here we present the first experimental realization, to the best of our knowledge, of this concept, encoding a nonlinear hologram in a KTiOPO(4) crystal by electric field poling. Two different spectra in the form of the second-order Hermite-Gauss function and the Airy function are shown using the sum-frequency generation process. PMID:26466274

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

    NASA Astrophysics Data System (ADS)

    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.

  4. 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

  5. F-104 low-gravity calibration tests for materials processing in space precursory experiments

    NASA Technical Reports Server (NTRS)

    Poorman, R. M.

    1980-01-01

    A precursory low-gravity flight experiment in an F-104 aircraft was conducted to check out the vehicle as a suitable flight test carrier for microgravity experiments. Calibration experiment verification tests in the F-104 were completed. Three flight parabolas were flown. The test data shows all the test parameters recorded by telemetry to have reasonable values. Photographic records are clear and distinct.Solidification modes were the same as those observed in other low gravity environments. The F-104 has been proven to be a useful test bed for low gravity experiments which require less than 60 seconds of low g time.

  6. Spectrally resolved detection in transient-reflectivity measurements of coherent optical phonons in diamond

    NASA Astrophysics Data System (ADS)

    Nakamura, Kazutaka G.; Ohya, Kazuma; Takahashi, Hiroshi; Tsuruta, Tetsuya; Sasaki, Hiroya; Uozumi, Shin-ichi; Norimatsu, Katsura; Kitajima, Masahiro; Shikano, Yutaka; Kayanuma, Yosuke

    2016-07-01

    Coherent optical phonons in bulk solid systems play a crucial role in understanding and designing light-matter interactions and can be detected by the transient-reflectivity measurement. In this paper, we demonstrate spectrally resolved detection of coherent optical phonons in diamond from ultrashort infrared pump-probe measurements using optical bandpass filters. We show that this enhances the sensitivity approximately 35 times in measuring the coherent oscillations in the transient reflectivity compared with the commonly used spectrally integrated measurement. To explain this observation, we discuss its mechanism.

  7. Spectral Domain Optical Coherence Tomography and Adaptive Optics: Imaging Photoreceptor Layer Morphology to Interpret Preclinical Phenotypes

    PubMed Central

    Rha, Jungtae; Dubis, Adam M.; Wagner-Schuman, Melissa; Tait, Diane M.; Godara, Pooja; Schroeder, Brett; Stepien, Kimberly

    2012-01-01

    Recent years have seen the emergence of advances in imaging technology that enable in vivo evaluation of the living retina. Two of the more promising techniques, spectral domain optical coherence tomography (SD-OCT) and adaptive optics (AO) fundus imaging provide complementary views of the retinal tissue. SD-OCT devices have high axial resolution, allowing assessment of retinal lamination, while the high lateral resolution of AO allows visualization of individual cells. The potential exists to use one modality to interpret results from the other. As a proof of concept, we examined the retina of a 32 year-old male, previously diagnosed with a red-green color vision defect. Previous AO imaging revealed numerous gaps throughout his cone mosaic, indicating that the structure of a subset of cones had been compromised. Whether the affected cells had completely degenerated or were simply morphologically deviant was not clear. Here an AO fundus camera was used to re-examine the retina (~6 years after initial exam) and SD-OCT to examine retinal lamination. The static nature of the cone mosaic disruption combined with the normal lamination on SD-OCT suggests that the affected cones are likely still present. PMID:20238030

  8. Crystal growth, spectral, optical and thermal properties of semiorganic nonlinear optical material: Picolinic acid hydrochloride

    NASA Astrophysics Data System (ADS)

    Gowri, S.; Uma Devi, T.; Sajan, D.; Surendra Dilip, C.; Chandramohan, A.; Lawrence, N.

    2013-06-01

    The bulk single crystal of 2-picolinic acid hydrochloride (PHCL) (a semi-organic nonlinear optical material of dimensions 25 × 15 × 10 mm3) was successfully grown by slow solvent evaporation technique. The XRD results revealed the cell parameters and the centrosymmetric nature of the crystal structure. FT-IR spectral study identified the functional groups, nature of bonding and their bond strength. The UV-Vis-NIR studies recognized the optical transmittance window and the lower cut off wavelength of the PHCL crystal and thus it could be performed as a NLO material. 1H NMR and 13CNMR spectra were correlated with the XRD standard for the molecular structure reveals harmony of the materials. Thermal properties of the crystal were studied by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA); the derived kinetic parameter values support the intuitive association of picolinicacid and HCl leads to the spontaneous formation of PHCL with a first order reaction. The presence of a proton and a proton acceptor groups provide the necessary stability to induce charge asymmetry in the PHCL structure. The load dependent hardness values of the crystal were measured by microhardness testing.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Thiessen, David B.; Wei, Wei; Marston, Philip L.

    2002-11-01

    The cylindrical liquid bridge of arbitrary size surrounded by air or vacuum is a fluid configuration that is essentially unique to the zero-gravity environment. An associated technology, which is enhanced in zero gravity, is the float-zone process of crystal growth, which involves a molten liquid bridge between a feed rod and the growing cylindrical crystal. There are several advantages to the crystal growth process in using long molten zones. Unfortunately, long liquid bridges are more susceptible to g-jitter. Also, a cylindrical liquid bridge in zero gravity is unstable if its length exceeds its circumference, or stated in another way, when the slenderness, defined as the length to diameter ratio, exceeds pi. This is the well-known Rayleigh-Plateau (RP) instability involving the growth of a varicose mode leading to breaking of the bridge. Stabilization of liquid bridges in air in the low-gravity environment of NASA's KC-135 aircraft has been demonstrated for slenderness values in excess of 4.0 using two techniques, passive acoustic stabilization (PAS) and active electrostatic stabilization (AES). The PAS method is theoretically capable of stabilizing a bridge of any length, provided a sound field of appropriate dimension is available. The AES method in its current form controls only the (2,0) mode of the bridge, which is the varicose mode that becomes unstable when the slenderness (S) exceeds pi. By controlling only the (2,0) mode, the current form of the AES method cannot stabilize cylindrical bridges beyond S=4.493 at which point the (3,0) mode becomes unstable. At present, the longest bridge stabilized on the KC-135 by the AES method had a slenderness of 4.4 3. The AES method has the advantage that it can be used to control both the frequency and damping of the (2,0) mode of the bridge. This would be useful in reducing the susceptibility of a long molten zone to g-jitter in that the (2,0) mode frequency could be shifted away from a particularly noisy vibration

  11. Effects of spectral discrimination in high-spectral-resolution lidar on the retrieval errors for atmospheric aerosol optical properties.

    PubMed

    Cheng, Zhongtao; Liu, Dong; Luo, Jing; Yang, Yongying; Su, Lin; Yang, Liming; Huang, Hanlu; Shen, Yibing

    2014-07-10

    This paper presents detailed analysis about the effects of spectral discrimination on the retrieval errors for atmospheric aerosol optical properties in high-spectral-resolution lidar (HSRL). To the best of our knowledge, this is the first study that focuses on this topic comprehensively, and our goal is to provide some heuristic guidelines for the design of the spectral discrimination filter in HSRL. We first introduce a theoretical model for retrieval error evaluation of an HSRL instrument with a general three-channel configuration. The model only takes the error sources related to the spectral discrimination parameters into account, while other error sources not associated with these focused parameters are excluded on purpose. 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 to promote the retrieval accuracy. More specifically, we find that a large SDR can reduce retrieval errors conspicuously for atmosphere at low altitudes, while its effect on the retrieval for high altitudes is very limited. A large molecular transmittance contributes to good retrieval accuracy everywhere, particularly at high altitudes, where the signal-to-noise ratio is small. Since the molecular transmittance and SDR are often trade-offs, we suggest considering a suitable SDR for higher molecular transmittance instead of using unnecessarily high SDR when designing the spectral discrimination filter. These conclusions are expected to be applicable to most of the HSRL instruments, which have similar configurations as the one discussed here. PMID:25090057

  12. 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. PMID:26907048

  13. Compressive sensing spectral domain optical coherence tomography with dispersion compensation

    NASA Astrophysics Data System (ADS)

    Xu, Daguang; Huang, Yong; Kang, Jin U.

    2014-03-01

    In this paper, we describe a novel CS method that incorporates dispersion compensation into the CS reconstruction of spectral domain OCT (SD OCT) signal. We show that A-scans with dispersion compensation can be obtained by multiplying the dispersion correcting term to the undersampled linear-in-wavenumber spectral data before the CS reconstruction. We also implemented fast CS reconstruction by taking the advantage of fast Fourier transform (FFT). The matrix-vector multiplication commonly used in the CS reconstruction is implemented by a two-step procedure. Compared to the CS reconstruction with matrix multiplication, our method can obtain dispersion compensated A-scan at least 5 times faster. Experimental results show that the proposed method can achieve high quality image with dispersion compensation.

  14. Observation of the optical and spectral characteristics of ball lightning.

    PubMed

    Cen, Jianyong; Yuan, Ping; Xue, Simin

    2014-01-24

    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. PMID:24484145

  15. 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.

  16. 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.

  17. A method to correct for spectral artifacts in optical-CT dosimetry

    PubMed Central

    Pierquet, Michael; Jordan, Kevin; Oldham, Mark

    2011-01-01

    The recent emergence of radiochromic dosimeters with low inherent light-scattering presents the possibility of fast 3D dosimetry using broad-beam optical computed tomography (optical-CT). Current broad beam scanners typically employ either a single or a planar array of light-emitting diodes (LED) for the light source. The spectrum of light from LED sources is polychromatic and this, in combination with the non-uniform spectral absorption of the dosimeter, can introduce spectral artifacts arising from preferential absorption of photons at the peak absorption wavelengths in the dosimeter. Spectral artifacts can lead to large errors in the reconstructed attenuation coefficients, and hence dose measurement. This work presents an analytic method for correcting for spectral artifacts which can be applied if the spectral characteristics of the light source, absorbing dosimeter, and imaging detector are known or can be measured. The method is implemented here for a PRESAGE® dosimeter scanned with the DLOS telecentric scanner (Duke Large field-of-view Optical-CT Scanner). Emission and absorption profiles were measured with a commercial spectrometer and spectrophotometer, respectively. Simulations are presented that show spectral changes can introduce errors of 8% for moderately attenuating samples where spectral artifacts are less pronounced. The correction is evaluated by application to a 16 cm diameter PRESAGE® cylindrical dosimeter irradiated along the axis with two partially overlapping 6 × 6 cm fields of different doses. The resulting stepped dose distribution facilitates evaluation of the correction as each step had different spectral contributions. The spectral artifact correction was found to accurately correct the reconstructed coefficients to within ~1.5%, improved from ~7.5%, for normalized dose distributions. In conclusion, for situations where spectral artifacts cannot be removed by physical filters, the method shown here is an effective correction. Physical

  18. 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.

  19. 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.

  20. Small-scale impacts as a trigger for an avalanche in a low-gravity environment

    NASA Astrophysics Data System (ADS)

    Hofmann, M.; Sierks, H.; Blum, J.

    2014-07-01

    The European Space Agency's Rosetta spacecraft was launched in 2004 and will rendezvous with comet 67P/Churyumov-Gerasimenko in 2014. On its route towards the comet, it flew by asteroid (21) Lutetia on 10 July 2010, with a closest approach distance of 3170 km. OSIRIS --- the Optical, Spectroscopic, and Infrared Remote Imaging System onboard Rosetta [1] --- took 462 images of Lutetia, using 21 broad- and narrow-band filters covering a wavelength range from 240 to 1000 nm [2]. The surface of Lutetia is covered with a thick layer of regolith. On the slopes of several craters, this regolith layer collapsed in landslide-like events. A possible trigger mechanism for these low-gravity avalanches is the impact of a small mm to cm-sized body. We conducted an experiment, where samples of different granular materials were tilted at different angles with respect to the vector of gravity. We accelerated a small mm-sized metal sphere to velocities up to 1.5 m/s and shot it into the sloped granular material. The impacts and any events triggered by the impact were recorded using a high-speed high-resolution camera. The experiment was implemented at the center of applied space technology and microgravity (ZARM) vacuum drop tower in Bremen in August 2012. The experiment was placed in an evacuated cylinder and mounted on a centrifuge that was spun with varying rotation rates to accommodate the vacuum and low gravity present on the surfaces of asteroids. A total of 20 experiments, as described above, were realized during 10 drops. The tilt angle and the magnitude of artificial gravity were varied for two different materials, a ground HED meteorite and the JSC MARS-1 Martian soil simulant. Additional ground-based experiments in 1g environment were conducted at a later time. We analyzed the images using an image subtraction algorithm to track movement from one frame to the next. In subsequent steps, we observed the behavior of the material on the surface as well as in deeper layers to

  1. Small scale impacts as trigger for an avalanche in a low gravity environment

    NASA Astrophysics Data System (ADS)

    Hofmann, M.; Sierks, H.; Blum, J.

    2013-09-01

    The European Space Agency's Rosetta spacecraft was launched in 2004 and will rendezvous with comet 67P/Churyumov-Gerasimenko in 2014. On its route towards the comet, it flew by asteroid (21) Lutetia on 10 July 2010, with a closest approach distance of 3170 km. OSIRIS - the Optical, Spectroscopic, and Infrared Remote Imaging System on board Rosetta [1] - took 462 images of Lutetia, using 21 broad- and narrowband filters covering a wavelength range from 240 to 1000 nm [2]. The surface of Lutetia is covered with a thick layer of regolith. On slopes of several craters this regolith layer collapsed in landslide like events. A possible trigger mechanism for these low-gravity avalanches is the impact of a small mm to cm-sized body. We conducted an experiment where samples of different granular materials were tilted at different angles with respect to the vector of gravity. We accelerated a small mm-sized metal sphere to velocities up to 1.5 m/s and shot it into the sloped granular material. The impacts and any events triggered by the impact were recorded using a high-speed high-resolution camera. The experiment was implemented at the center of applied space technology and microgravity (ZARM) vacuum drop tower in Bremen in August 2012. The experiment was placed in an evacuated cylinder and mounted on a centrifuge that was spun with varying rotation rates to accommodate the vacuum and low gravity present on the surfaces of asteroids. A total of 20 experiments as described above were realized during 10 drops. The tilt angle and the magnitude of artificial gravity were varied for two different materials, a ground HED meteorite and the JSC MARS-1 Martian soil simulant. Additional groundbased experiments in 1g environment were conducted at a later time. We analyzed the images using an image subtraction algorithm to track movement from one frame to the next. In subsequent steps we observed the behavior of the material on the surface as well as in deeper layers to characterize

  2. Measurement of the Soret coefficients for a ternary hydrocarbon mixture in low gravity environment

    NASA Astrophysics Data System (ADS)

    Ahadi, Amirhossein; Van Varenbergh, S.; Saghir, M. Ziad

    2013-05-01

    While the Soret coefficients of binary mixtures have been widely measured in the past, here we report the first measurement of the Soret coefficient of a ternary mixture in a low gravity environment on board the International Space Station. The sample was contained in a 10 mm × 10 mm × 5 mm (w, l, h) cell and was monitored by means of a Mach-Zehnder interferometer at two wavelengths. The analyzed sample was a mixture of tetrahydronaphthalene, isobutylbenzene, and dodecane at the weight fraction of 0.1/0.8/0.1. While the lateral walls of the cell did not possess complete thermal isolation, the separation of the components in the central region of the cavity was comparable to purely diffusive behavior. The same experimental parameters have been monitored in Run7 and Run12 of the Selectable Optical Diagnostics Instrument-Diffusion and Soret Coefficient experiment in order to verify the accuracy of the setup. The similarity of the results demonstrates the repeatability of thermodiffusion experiments in a microgravity environment. There was nearly equal separation of the tetrahydronaphthalene and isobutylbenzene components in opposite directions, while dodecane experienced a weak separation in the same direction as isobutylbenzene. Finally, Fourier image processing and calculations of the transient separation of the components were used to analyze the heat transfer in the system and to measure the Soret coefficients for this ternary mixture. The successful measurements shown in this work can serve as the standard for ground experiments and for numerical modeling of hydrocarbon mixtures.

  3. 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.

  4. 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.

  5. 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.

  6. A study of the fundamental operations of a capillary driven heat transfer device in both normal and low gravity Part 1. Liquid slug formation in low gravity

    NASA Astrophysics Data System (ADS)

    Allen, Jeffrey S.; Hallinan, Kevin; Lekan, Jack

    1998-01-01

    Research has been conducted to observe the operation of a capillary pumped loop (CPL) in both normal and low gravity environments in order to ascertain the causes of device failure. The failures of capillary pumped heat transport devices in low gravity; specifically; evaporator dryout, are not understood and the available data for analyzing the failures is incomplete. To observe failure in these devices an idealized experimental CPL was configured for testing in both a normal-gravity and a low-gravity environment. The experimental test loop was constructed completely of Pyrex tubing to allow for visualization of system operations. Heat was added to the liquid on the evaporator side of the loop using resistance heaters and removed on the condenser side via forced convection of ambient air. A video camera was used to record the behavior of both the condenser and the evaporator menisci simultaneously. Low-gravity experiments were performed during the Microgravity Science Laboratory (MSL-1) mission performed onboard the Space Shuttle Columbia in July of 1997. During the MSL-1 mission, a failure mechanism, heretofore unreported, was observed. In every experiment performed a slug of liquid would form at the transition from a bend to a straight run in the vapor line. Ultimately, this liquid slug prevents the flow of vapor to the condenser causing the condenser to eventually dryout. After condenser dryout, liquid is no longer fed into the evaporator and it, too, will dry out resulting in device failure. An analysis is presented to illustrate the inevitable formation of such liquid slugs in CPL devices in low gravity.

  7. Sparse OCT: optimizing compressed sensing in spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Liu, Xuan; Kang, Jin U.

    2011-03-01

    We applied compressed sensing (CS) to spectral domain optical coherence tomography (SD-OCT). Namely, CS was applied to the spectral data in reconstructing A-mode images. This would eliminate the need for a large amount of spectral data for image reconstruction and processing. We tested the CS method by randomly undersampling k-space SD-OCT signal. OCT images are reconstructed by solving an optimization problem that minimizes the l1 norm to enforce sparsity, subject to data consistency constraints. Variable density random sampling and uniform density random sampling were studied and compared, which shows the former undersampling scheme can achieve accurate signal recovery using less data.

  8. 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. PMID:26625084

  9. Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

    PubMed

    Cao, Z; Lu, R; Wang, Q; Tessema, N; Jiao, Y; van den Boom, H P A; Tangdiongga, E; Koonen, A M J

    2014-06-15

    Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis. PMID:24978496

  10. Absolute velocity measurement using three-beam spectral-domain Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Sharma, P.; Verma, Y.; Kumar, S.; Gupta, P. K.

    2015-09-01

    We report the development of a three-beam spectral-domain Doppler optical coherence tomography setup that allows single interferometer-based measurement of absolute flow velocity. The setup makes use of galvo-based phase shifting to remove complex conjugate mirror artifact and a beam displacer in the sample arm to avoid cross talk image. The results show that the developed approach allows efficient utilization of the imaging range of the spectral-domain optical coherence tomography setup for three-beam-based velocity measurement.

  11. 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.

  12. 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.

  13. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

    NASA Astrophysics Data System (ADS)

    Reddy, S. Lakshmi; Fayazuddin, Md.; Frost, Ray L.; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.

  14. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite.

    PubMed

    Reddy, S Lakshmi; Fayazuddin, Md; Frost, Ray L; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals. PMID:17324611

  15. 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.

  16. Optical turbulence and spectral condensate in long fibre lasers

    PubMed Central

    Turitsyna, E. G.; Falkovich, Gregory; El-Taher, Atalla; Shu, Xuewen; Harper, Paul; Turitsyn, Sergei K.

    2012-01-01

    We study numerically optical turbulence using the particular example of a recently created, ultra-long fibre laser. For normal fibre dispersion, we observed an intermediate state with an extremely narrow spectrum (condensate), which experiences instability and a sharp transition to a fluctuating regime with a wider spectrum. We demonstrate that the number of modes has an impact on the condensate's lifetime. The smaller the number of modes, the more resistant is the condensate to perturbations. Experimental results show a good agreement with numerical simulations. PMID:22870062

  17. Research on the principle and experimentation of optical compressive spectral imaging

    NASA Astrophysics Data System (ADS)

    Chen, Yuheng; Chen, Xinhua; Zhou, Jiankang; Ji, Yiqun; Shen, Weimin

    2013-12-01

    The optical compressive spectral imaging method is a novel spectral imaging technique that draws in the inspiration of compressed sensing, which takes on the advantages such as reducing acquisition data amount, realizing snapshot imaging, increasing signal to noise ratio and so on. Considering the influence of the sampling quality on the ultimate imaging quality, researchers match the sampling interval with the modulation interval in former reported imaging system, while the depressed sampling rate leads to the loss on the original spectral resolution. To overcome that technical defect, the demand for the matching between the sampling interval and the modulation interval is disposed of and the spectral channel number of the designed experimental device increases more than threefold comparing to that of the previous method. Imaging experiment is carried out by use of the experiment installation and the spectral data cube of the shooting target is reconstructed with the acquired compressed image by use of the two-step iterative shrinkage/thresholding algorithms. The experimental result indicates that the spectral channel number increases effectively and the reconstructed data stays high-fidelity. The images and spectral curves are able to accurately reflect the spatial and spectral character of the target.

  18. Etalon of optical frequency for the telecommunication spectral region

    NASA Astrophysics Data System (ADS)

    Lazar, Josef; Ruzicka, Bohdan; Cip, Ondrej

    2004-09-01

    We present a design of a stabilized laser system, an etalon of the optical frequency at the 1.5 μm band following the demands of the telecommunication industry in the Czech Republic. Our laser system employs a DFB laser diode in a two stage fully digital stabilizing scheme. The linear absorption arrangement with an acetylene filled absorption cell of a pressure about 1 kPa is used to lock the laser to the Doppler-broadened lines. To achieve a reliable and robust stabilization of the laser frequency we arranged a two-loop digital servo-system overcoming the problem of a narrow locking range of the detected transition. The wavelength of the laser is modulated by current and the servo-control and tuning is performed by a fast and precise thermal control. To achieve the resolution of the weak sub-Doppler transitions we assembled a locking scheme via frequency-modulation spectroscopy to the high finesse cavity. The system is assembled using predominantly fibre-optic components. A technology of acetylene absorption cells with AR coated windows is presented as well.

  19. 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.

  20. Bone Remodeling in Choroidal Osteoma Monitored by Fundus Photography and Spectral-Domain Optical Coherence Tomography

    PubMed Central

    Kamalden, Tengku Ain; Lingam, Gopal; Sundar, Gangadhara

    2014-01-01

    Choroidal osteoma is a benign ossifying tumor of the choroid, consisting of mature bone tissue. It has been described to enlarge and evolve at varying rates over time. Here, we report and quantify the progression of a unilateral choroidal osteoma in a 7-year-old boy by fundus photography, and document tumor remodeling by spectral domain optical coherence tomography images. PMID:27175357

  1. Real-time in vivo imaging by high-speed spectral optical coherence tomography.

    PubMed

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

    2003-10-01

    An improved spectral optical coherence tomography technique is used to obtain cross-sectional ophthalmic images at an exposure time of 64 micros per A-scan. This method allows real-time images as well as static tomograms to be recorded in vivo. PMID:14514087

  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. Optical properties of mucous membrane in the spectral range 350-2000 nm

    NASA Astrophysics Data System (ADS)

    Bashkatov, A. N.; Genina, É. A.; Kochubey, V. I.; Tuchin, V. V.; Chikina, E. É.; Knyazev, A. B.; Mareev, O. V.

    2004-12-01

    The optical characteristics of the mucous membrane from the human maxillary sinus are studied experimentally. The experiments were carried out in vitro in the spectral range 350-2000 nm. On the basis of the measured total transmittance and diffuse reflectance spectra, the absorption and transport scattering coefficients are calculated in the entire range in terms of the inverse adding-doubling method.

  5. Optical properties of human colon tissues in the 350 - 2500 nm spectral range

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  6. Interferometry and holography in a low-gravity environment

    NASA Technical Reports Server (NTRS)

    Owen, R. B.

    1982-01-01

    The groundwork for the use of advanced optical measurement techniques in Space Shuttle materials processing in space (MPS) experiments is being laid in tests, conducted aboard a NASA KC-135 aircraft flying a parabolic trajectory, involving a Mach-Zehnder interferometer and a sideband holographic unit. The two experiments described are (1) the observation of flow during solidification, in which fluid concentration and temperature profiles were measured during unidirectional solidification of a saturated NH4Cl-H2O solution, and (2) the observation of electrodeposition flow, in which interferometry is used to provide quantitative data required in the understanding of electrochemical process transport properties. The free-floating holographic unit was operated in the microgravity environment to both test the practicality of optical systems in such conditions and test the shock and vibration characteristics of the package.

  7. Full-field swept-source optical coherence tomography with Gaussian spectral shaping

    NASA Astrophysics Data System (ADS)

    Dubey, Satish Kumar; Sheoran, Gyanendra; Anna, Tulsi; Anand, Arun; Mehta, Dalip Singh; Shakher, Chandra

    2008-09-01

    A swept source system was realized in the wavelength range of 810-875 nm with the combination of a broad-band superluminescent diode (SLD) and an acousto-optic tunable filter (AOTF) as a frequency-tuning device. SLD has two spectral centers at 820 nm and 845 nm with spectral bandwidth (FWHM) of around 40 nm. Gaussian spectral shaping was performed onto the original SLD spectrum while reconstructing OCT images for various test samples such as onion slice and fingerprint impression taken on a glass substrate. As a pulse can be considered a Gaussian distribution of frequencies, spectral shaping yields sharper Fourier peaks. Application of Gaussian spectrum facilitates in precisely locating the reflective boundaries within the sample that results in improved OCT images.

  8. Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings.

    PubMed

    Eom, Tae Joong; Ahn, Yeh-Chan; Kim, Chang-Seok; Chen, Zhongping

    2011-03-01

    We present a calibration protocol to obtain the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply to the spectral-domain optical coherence tomography (SD-OCT) using fiber Bragg gratings. We have used five gratings with different center wavelengths covering the broadband source spectral range. All have a narrow spectral bandwidth (0.05 nm) and the same reflectivity (92%) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37 deg incident angle, 53.11 deg diffraction angle, and 70.0-mm focal length. The spectral resolution of 0.187 nm was recalculated from the alignment factors. PMID:21456856

  9. 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.

  10. Spectral Domain Optical Coherence Tomography in Diffuse Unilateral Subacute Neuroretinitis

    PubMed Central

    Garcia Filho, Carlos Alexandre de A.; Soares, Ana Claudia Medeiros de A. G.; Penha, Fernando Marcondes; Garcia, Carlos Alexandre de Amorim

    2011-01-01

    Purpose. To describe the SD-OCT findings in patients with diffuse unilateral subacute neuroretinitis (DUSN) and evaluate CRT and RNFL thickness. Methods. Patients with clinical diagnosis of DUSN who were submitted to SD-OCT were included in the study. Complete ophthalmologic examination and SD-OCT were performed. Cirrus scan strategy protocols used were 200 × 200 macular cube, optic nerve head cube, and HD-5 line raster. Results. Eight patients with DUSN were included. Mean RNFL thickness was 80.25 μm and 104.75 μm for affected and normal eyes, respectively. Late stage had mean RNFL thickness of 74.83 μm compared to 96.5 μm in early stage. Mean CMT was 205.5 μm for affected eyes and 255.13 μm for normal fellow eyes. Conclusion. RNFL and CMT were thinner in DUSN eyes compared to normal eyes. Late-stage disease had more pronounced thinning compared to early-stage patients. This thinning in RNFL and CMT may reflect the low visual acuity in patients with DUSN. PMID:21860780

  11. 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.

  12. 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

  13. 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.

  14. Near-infrared optical mammography with broadband spectral imaging for spatially resolved oximetry

    NASA Astrophysics Data System (ADS)

    Yu, Yang; Sassaroli, Angelo; Homer, Marc J.; Graham, Roger A.; Fantini, Sergio

    2011-02-01

    We report the development of an instrument for diffuse spectral imaging of the human breast operating over the wavelength range 650-900 nm. This instrument images the slightly compressed human breast in a planar geometry by performing a tandem scan, over the x-y plane, of a 3 mm illumination optical fiber and a 5 mm collection optical fiber that are collinear and located on opposite sides of the breast. An edge-correction algorithm accounts for breast thickness variability over the x-y plane, a second-derivative imaging algorithm enhances the display of optical inhomogeneities, and a paired-wavelength spectral method yields oxygenation maps. We report our results of oxygenation mapping in eighteen human subjects, two of which are breast cancer patients, one with a ductal carcinoma in situ, the other with an invasive ductal carcinoma.

  15. Design and optimization of a spectrometer for spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Hosseiny, Hamid; Carmelo Rosa, Carla

    2014-08-01

    There are several factors such as the chosen optical source, central wavelength, spectral bandwidth, spectrometer optical components and the detector specifications that affect the overall performance of a spectral domain optical coherence tomography (SD-OCT) imaging system. Among these factors a good design and implementation of the spectrometer is of paramount importance as it directly affects the system resolution, sensitivity fall-off, maximum imaging depth, SNR and in general the system performance. This study demonstrates the design steps and some considerations during the design of a spectrometer. The imaging performance of this design is assessed. The obtained experimental results prove an improvement of the overall performance of the common path SD-OCT imaging system and agree with the expected outcome from the design stage.

  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. Measurement of the Soret coefficients for a ternary hydrocarbon mixture in low gravity environment.

    PubMed

    Ahadi, Amirhossein; Varenbergh, S Van; Saghir, M Ziad

    2013-05-28

    While the Soret coefficients of binary mixtures have been widely measured in the past, here we report the first measurement of the Soret coefficient of a ternary mixture in a low gravity environment on board the International Space Station. The sample was contained in a 10 mm × 10 mm × 5 mm (w, l, h) cell and was monitored by means of a Mach-Zehnder interferometer at two wavelengths. The analyzed sample was a mixture of tetrahydronaphthalene, isobutylbenzene, and dodecane at the weight fraction of 0.1∕0.8∕0.1. While the lateral walls of the cell did not possess complete thermal isolation, the separation of the components in the central region of the cavity was comparable to purely diffusive behavior. The same experimental parameters have been monitored in Run7 and Run12 of the Selectable Optical Diagnostics Instrument-Diffusion and Soret Coefficient experiment in order to verify the accuracy of the setup. The similarity of the results demonstrates the repeatability of thermodiffusion experiments in a microgravity environment. There was nearly equal separation of the tetrahydronaphthalene and isobutylbenzene components in opposite directions, while dodecane experienced a weak separation in the same direction as isobutylbenzene. Finally, Fourier image processing and calculations of the transient separation of the components were used to analyze the heat transfer in the system and to measure the Soret coefficients for this ternary mixture. The successful measurements shown in this work can serve as the standard for ground experiments and for numerical modeling of hydrocarbon mixtures. PMID:23742467

  18. Spectral and temporal properties of optical signals with multiple sinusoidal phase modulations.

    PubMed

    Dorrer, C

    2014-02-10

    Optical signals generated by multiple sinusoidal temporal phase modulations (multi-FMs) applied to a monochromatic field are studied from the viewpoint of their optical spectrum and temporal modulations arising from spectral impairments. Statistical analysis based on the central limit theorem shows that the signals' optical spectrum converges to a normal distribution as the number of modulations increases, allowing one to predict the frequency range containing a given fraction of the total energy with the associated cumulative density function. The conversion of frequency modulation to amplitude modulation is analyzed and simulated for arbitrary multi-FM signals. These developments are of theoretical and practical importance for high-energy laser systems, where optical pulses are phase modulated in the front end to smooth out the on-target beam profile and prevent potentially catastrophic damage to optical components. PMID:24663283

  19. 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.

  20. 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.

  1. Spectral-Reflectance Linear Models for Optical Color-Pattern Recognition

    NASA Astrophysics Data System (ADS)

    Nieves, Juan L.; Hernández-Andrés, Javier; Valero, Eva; Romero, Javier

    2004-03-01

    We propose a new method of color-pattern recognition by optical correlation that uses a linear description of spectral reflectance functions and the spectral power distribution of illuminants that contains few parameters. We report on a method of preprocessing color input scenes in which the spectral functions are derived from linear models based on principal-component analysis. This multichannel algorithm transforms the red-green-blue (RGB) components into a new set of components that permit a generalization of the matched filter operations that are usually applied in optical pattern recognition with more-stable results under changes in illumination in the source images. The correlation is made in the subspace spanned by the coefficients that describe all reflectances according to a suitable basis for linear representation. First we illustrate the method in a control experiment in which the scenes are captured under known conditions of illumination. The discrimination capability of the algorithm improves upon the conventional RGB multichannel decomposition used in optical correlators when scenes are captured under different illuminant conditions and is slightly better than color recognition based on uniform color spaces (e.g., the CIELab system). Then we test the coefficient method in situations in which the target is captured under a reference illuminant and the scene that contains the target under an unknown spectrally different illuminant. We show that the method prevents false alarms caused by changes in the illuminant and that only two coefficients suffice to discriminate polychromatic objects.

  2. 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. PMID:27142874

  3. 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.

  4. 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.

  5. Remote Fourier transform-infrared spectral imaging system with hollow-optical fiber bundle.

    PubMed

    Huang, Chenhui; Kino, Saiko; Katagiri, Takashi; Matsuura, Yuji

    2012-10-10

    A spectral imaging system consisting of a Fourier transform-infrared spectrometer, a high-speed infrared camera, and a bundle of hollow-optical fibers transmitting infrared radiation images was constructed. Infrared transmission spectra were obtained by carefully processing multiple interferograms taken by high-speed photography. Infrared spectral images of a variety of samples captured by the system were measured. We successfully detected existence maps of the oil and fat of biological samples by mapping the transmission of specific wavelengths in the spectrum. PMID:23052066

  6. 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. PMID:16114535

  7. Study on spectrally agile staring sensor using acousto-optic tunable filter

    NASA Astrophysics Data System (ADS)

    Cui, Yan; Zhang, Minghui

    1992-08-01

    The spectrally agile staring sensor (SASS) is an instrument system that is able to get image and spectrum information. This paper analyzes the expression of signal-to-noise ratio and overall performance of the SASS system that uses an acousto-optic tunable filter as its spectral filter, and points out improving methods and limiting factors of the system performance. The complete SASS system experimental set-up is constructed. Using this set-up, the theory is verified, and the image and spectrum information of the simulated target is acquired.

  8. 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. PMID:27101274

  9. Spectral and temporal phase measurement by optical frequency-domain reflectometry

    NASA Astrophysics Data System (ADS)

    Robillart, Bruno; Calò, Cosimo; Fall, Abdoulaye; Lamare, François; Gottesman, Yaneck; Benkelfat, Badr-Eddine

    2014-03-01

    The capability of measuring the spectral and temporal phase of an optical signal is of fundamental importance for the advanced characterization of photonic and optoelectronic components, biochemical sensors, structural monitoring sensors and distributed sensor networks. To address this problem, several techniques have been developed (frequency-resolved optical gating (FROG), spectral phase interferometry for direct electric-field reconstruction (SPIDER), stepped-heterodyne technique, laser Doppler vibrometry (LDV) and Doppler optical coherence tomography (OCT)). However, such techniques often lack of versatility for the mentioned applications. Swept-wavelength interferometric techniques and, among these, optical frequency-domain reflectometry (OFDR) are flexible and highly sensitive tools for complete characterization of amplitude and phase of target devices. In this work, we investigate the spectral and temporal phase measurement capabilities of OFDR. Precise characterization of spectral phase information is demonstrated by retrieving the phase response of a commercial optical filter, the Finisar Waveshaper 1000 S/X, programmable in attenuation and phase over C+L band (1530- 1625 nm). The presented results show accurate retrieval of group delay dispersion (GDD) and discrete phase shift as well as filter attenuation profile. Although some intrinsic accuracy limitations of OFDR phase measurements may be encountered (and herein specified), we show that information encoded in OFDR reflectogram data is very rich when adequately exploited. In addition to previously published results, we demonstrate the high sensitivity of the technique to Doppler effects. From practical point of view, such sensitivity can be beneficially exploited for the characterisation of dynamical aspects of samples under test. Unlike LDV, OFDR allows the simultaneous retrieval of the temporal position of several localised reflecting target along the beam path. All these aspects make OFDR a highly

  10. Retrieval and analysis of a polarized high-spectral-resolution lidar for profiling aerosol optical properties.

    PubMed

    Liu, Dong; Yang, Yongying; Cheng, Zhongtao; Huang, Hanlu; Zhang, Bo; Ling, Tong; Shen, Yibing

    2013-06-01

    Taking advantage of the broad spectrum of the Cabannes-Brillouin scatter from atmospheric molecules, the high spectral resolution lidar (HSRL) technique employs a narrow spectral filter to separate the aerosol and molecular scattering components in the lidar return signals and therefore can obtain the aerosol optical properties as well as the lidar ratio (i.e., the extinction-to-backscatter ratio) which is normally selected or modeled in traditional backscatter lidars. A polarized HSRL instrument, which employs an interferometric spectral filter, is under development at the Zhejiang University (ZJU), China. In this paper, the theoretical basis to retrieve the aerosol lidar ratio, depolarization ratio and extinction and backscatter coefficients, is presented. Error analyses and sensitivity studies have been carried out on the spectral transmittance characteristics of the spectral filter. The result shows that a filter that has as small aerosol transmittance (i.e., large aerosol rejection rate) and large molecular transmittance as possible is desirable. To achieve accurate retrieval, the transmittance of the spectral filter for molecular and aerosol scattering signals should be well characterized. PMID:23736562

  11. Small Scale Impacts as trigger for an avalanche in a low gravity environment

    NASA Astrophysics Data System (ADS)

    Hofmann, Marc; Sierks, Holger; Blum, Jürgen

    2014-05-01

    The European Space Agency's Rosetta spacecraft was launched in 2004 and will rendezvous with comet 67P/Churyumov-Gerasimenko in 2014. On its route towards the comet, it flew by asteroid (21) Lutetia on 10 July 2010, with a closest approach distance of 3170 km. OSIRIS - the Optical, Spectroscopic, and Infrared Remote Imaging System on board Rosetta [1] - took 462 images of Lutetia, using 21 broad- and narrowband filters covering a wavelength range from 240 to 1000 nm [2]. The surface of Lutetia is covered with a thick layer of regolith. On slopes of several craters this regolith layer collapsed in landslide like events. A possible trigger mechanism for these low-gravity avalanches is the impact of a small mm to cm-sized body. We conducted an experiment where samples of different granular materials were tilted at different angles with respect to the vector of gravity. We accelerated a small mm-sized metal sphere to velocities up to 1.5 m/s and shot it into the sloped granular material. The impacts and any events triggered by the impact were recorded using a high-speed high-resolution camera. The experiment was implemented at the center of applied space technology and microgravity (ZARM) vacuum drop tower in Bremen in August 2012. The experiment was placed in an evacuated cylinder and mounted on a centrifuge that was spun with varying rotation rates to accommodate the vacuum and low gravity present on the surfaces of asteroids. A total of 20 experiments as described above were realized during 10 drops. The tilt angle and the magnitude of artificial gravity were varied for two different materials, a ground HED meteorite and the JSC MARS-1 Martian soil simulant. Additional ground-based experiments in 1g environment were conducted at a later time. We analyzed the images using an image subtraction algorithm to track movement from one frame to the next. In subsequent steps we observed the behavior of the material on the surface as well as in deeper layers to characterize

  12. 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

  13. 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.

  14. 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.

  15. Spectroscopic OCT by Grating-Based Temporal Correlation Coupled to Optical Spectral Analysis

    PubMed Central

    Froehly, L.; Ouadour, M.; Furfaro, L.; Sandoz, P.; Leproux, P.; Huss, G.; Couderc, V.

    2008-01-01

    Spectroscopic optical coherence tomography (spectroscopic OCT) is an echographic-like optical method for biomedical functional imaging. Current spectroscopic optical coherence tomography (OCT) methods rely on a posteriori numerical calculation. We present an alternative for optically accessing the spectroscopic information in OCT, that is, without postprocessing, by using a grating-based correlation and a wavelength demultiplexing system. Spectrally resolved A-scan is directly recorded on the image sensor. Due to the grating-based system, no correlation scan is necessary. The signal is registered in the wavelength-depth plane on a 2D camera that provides a large number of resolved points. In the frame of this paper, we present the principle of the system as well as demonstration results. Advantages and drawback of this system compared to others are discussed. PMID:18385813

  16. 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.

  17. In-vivo full depth of eye imaging spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Dai, Cuixia; Zhou, Chuanqing; Jiao, Shuliang; Xi, Peng; Ren, Qiushi

    2011-09-01

    It is necessary to apply the spectral-domain optical coherence tomography (SD-OCT) to image the whole eye segment for practically iatrical application, but the imaging depth of SD-OCT is limited by the spectral resolution of the spectrometer. By now, no result about this research has been reported. In our study, a new dual channel dual focus OCT system is adopted to image the whole eye segment. The cornea and the crystalline lens are simultaneously imaged by using full range complex spectral-domain OCT in one channel, the retina is detected by the other. The new system was successfully tested in imaging of the volunteer' eye in vivo. The preliminary results presented in this paper demonstrated the feasibility of this approach.

  18. (sup 4)He Experiments Near T(sub lambda) in a Low-Gravity Simulator

    NASA Technical Reports Server (NTRS)

    Liu, Y.; Larson, M.; Israelsson, U.

    1998-01-01

    We report on our latest measurements of gravity reduction in the low-gravity simulator. We made these measurements using a new thermal conductivity cell design that is 0.5cm in diameter and 0.5cm in height.

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

    PubMed Central

    Ackermann, Marko; van den Bogert, Antonie J.

    2012-01-01

    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. PMID:22365845

  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. PMID:22365845

  1. 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.

  2. 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.

  3. 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.

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

    PubMed

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

    2015-05-01

    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. PMID:25969193

  5. 80 GHz waveform generated by the optical Fourier synthesis of four spectral sidebands

    NASA Astrophysics Data System (ADS)

    Fatome, Julien; Hammani, Kamal; Kibler, Bertrand; Finot, Christophe

    2016-01-01

    Using the linear phase shaping of a simple four-line optical frequency comb, we experimentally demonstrate the generation of various optical waveforms such as parabolic, triangular or flat-top pulse trains at a repetition rate of 80 GHz. The initial 80 GHz comb is obtained through the nonlinear spectral broadening of a 40 GHz carrier-suppressed sinusoidal beating in a highly nonlinear fiber. Proof-of-principle experiments are reported for two distinct configurations of the waveform generated: continuous trains and bunches of shaped pulses.

  6. 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. PMID:23101475

  7. Optical coherence tomography contrast enhancement using spectroscopic analysis with spectral autocorrelation

    NASA Astrophysics Data System (ADS)

    Adler, Desmond C.; Ko, Tony H.; Herz, Paul R.; Fujimoto, James G.

    2004-11-01

    Enhanced tissue contrast in developmental biology specimens is demonstrated in vivo using a new type of spectroscopic optical coherence tomography analysis that is insensitive to spectroscopic noise sources. The technique is based on a statistical analysis of spectral modulation at each image pixel, and provides contrast based on both the intensity of the backscattered light and the distribution of scattering particle sizes. Since the technique does not analyze optical power at absolute wavelengths, it is insensitive to all spectroscopic noise that appears as local Doppler shifts. No exogenous contrast agents or dyes are required, and no additional components are needed to correct for reference arm motion.

  8. Coulomb field strength measurement by electro-optic spectral decoding system at the CALIFES beam line

    NASA Astrophysics Data System (ADS)

    Pan, R.; Jamison, S. P.; Lefevre, T.; Gillespie, W. A.

    2016-06-01

    Electro-optic (EO) techniques are increasingly used for longitudinal bunch profile measurements. A bunch profile monitor, based on electro-optic spectral decoding (EOSD), has been developed and demonstrated on the CALIFES beam line at CERN. The EO response is analysed using a frequency domain description, and two methods for extraction of absolute Coulomb field strengths from the electron bunch are demonstrated. Measurements at field strengths up to 1.3 MV/m agree with the expectation based on independent charge measurements.

  9. 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.

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

    PubMed Central

    Hwang, Jungseek

    2016-01-01

    We investigate temperature smearing effects on the electron-boson spectral density function (I2χ(ω)) obtained from optical data using a maximum entropy inversion method. We start with two simple model input I2χ(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 I2χ(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 I2χ(ω) with the input ones. From this approach we find that the inversion process can recover the input I2χ(ω) almost perfectly when the quality of fits is good enough and also temperature smearing (or thermal broadening) effects appear in the I2χ(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 I2χ(ω) extracted from the optical data contain intrinsic temperature-dependent evolutions. PMID:27029840