Science.gov

Sample records for coherent laser vision

  1. Coherent laser vision system

    SciTech Connect

    Sebastion, R.L.

    1995-10-01

    The Coherent Laser Vision System (CLVS) is being developed to provide precision real-time 3D world views to support site characterization and robotic operations and during facilities Decontamination and Decommissioning. Autonomous or semiautonomous robotic operations requires an accurate, up-to-date 3D world view. Existing technologies for real-time 3D imaging, such as AM laser radar, have limited accuracy at significant ranges and have variability in range estimates caused by lighting or surface shading. Recent advances in fiber optic component technology and digital processing components have enabled the development of a new 3D vision system based upon a fiber optic FMCW coherent laser radar. The approach includes a compact scanner with no-moving parts capable of randomly addressing all pixels. The system maintains the immunity to lighting and surface shading conditions which is characteristic to coherent laser radar. The random pixel addressability allows concentration of scanning and processing on the active areas of a scene, as is done by the human eye-brain system.

  2. COHERENT LASER VISION SYSTEM (CLVS) OPTION PHASE

    SciTech Connect

    Robert Clark

    1999-11-18

    The purpose of this research project was to develop a prototype fiber-optic based Coherent Laser Vision System (CLVS) suitable for DOE's EM Robotic program. The system provides three-dimensional (3D) vision for monitoring situations in which it is necessary to update the dimensional spatial data on the order of once per second. The system has total immunity to ambient lighting conditions.

  3. Fiber optic coherent laser radar 3d vision system

    SciTech Connect

    Sebastian, R.L.; Clark, R.B.; Simonson, D.L.

    1994-12-31

    Recent advances in fiber optic component technology and digital processing components have enabled the development of a new 3D vision system based upon a fiber optic FMCW coherent laser radar. The approach includes a compact scanner with no moving parts capable of randomly addressing all pixels. The system maintains the immunity to lighting and surface shading conditions which is characteristic of coherent laser radar. The random pixel addressability allows concentration of scanning and processing on the active areas of a scene, as is done by the human eye-brain system.

  4. Fiber optic coherent laser radar 3D vision system

    SciTech Connect

    Clark, R.B.; Gallman, P.G.; Slotwinski, A.R.; Wagner, K.; Weaver, S.; Xu, Jieping

    1996-12-31

    This CLVS will provide a substantial advance in high speed computer vision performance to support robotic Environmental Management (EM) operations. This 3D system employs a compact fiber optic based scanner and operator at a 128 x 128 pixel frame at one frame per second with a range resolution of 1 mm over its 1.5 meter working range. Using acousto-optic deflectors, the scanner is completely randomly addressable. This can provide live 3D monitoring for situations where it is necessary to update once per second. This can be used for decontamination and decommissioning operations in which robotic systems are altering the scene such as in waste removal, surface scarafacing, or equipment disassembly and removal. The fiber- optic coherent laser radar based system is immune to variations in lighting, color, or surface shading, which have plagued the reliability of existing 3D vision systems, while providing substantially superior range resolution.

  5. Base program interim phase test procedure - Coherent Laser Vision System (CLVS). Final report, September 27, 1994--January 30, 1997

    SciTech Connect

    1997-05-01

    The purpose of the CLVS research project is to develop a prototype fiber-optic based Coherent Laser Vision System suitable for DOE`s EM Robotics program. The system provides three-dimensional (3D) vision for monitoring situations in which it is necessary to update geometrics on the order of once per second. The CLVS project plan required implementation in two phases of the contract, a Base Contract and a continuance option. This is the Test Procedure and test/demonstration results presenting a proof-of-concept for a system providing three-dimensional (3D) vision with the performance capability required to update geometrics on the order of once per second.

  6. Lasers and Coherent Light Sources

    NASA Astrophysics Data System (ADS)

    Svelto, Orazio; Longhi, Stefano; Della Valle, Giuseppe; Huber, Günter; Kück, Stefan; Pollnau, Markus; Hillmer, Hartmut; Kusserow, Thomas; Engelbrecht, Rainer; Rohlfing (deceased), Frank; Kaiser, Jeffrey; Malz, Ralf; Marowsky, Gerd; Mann, Klaus; Simon, Peter; Rhodes, Charles K.; Duarte, Frank J.; Borsutzky, Annette; L'Huillier, Johannes A.; Sigrist, Markus W.; Wächter, Helen; Saldin, Evgeny; Schneidmiller, Evgeny; Yurkov, Mikhail; Sauerbrey, Roland; Hein, Joachim; Gianella, Michele; Helmcke, Jürgen; Midorikawa, Katsumi; Riehle, Fritz; Steinberg, Steffen; Brand, Hans

    This chapter describes lasers and other sources of coherent light that operate in a wide wavelength range. First, the general principles for the generation of coherent continuous-wave and pulsed radiation are treated including the interaction of radiation with matter, the properties of optical resonators and their modes as well as such processes as Q-switching and mode-locking. The general introduction is followed by sections on numerous types of lasers, the emphasis being on today's most important sources of coherent light, in particular on solid-state lasers and several types of gas lasers. An important part of the chapter is devoted to the generation of coherent radiation coherent radiation by nonlinear processes with optical parametric oscillators, difference- and sum-frequency generation, and high-order harmonics. Radiation in the extended ultraviolet (EUV) and x-ray ranges can be generated by free electron lasers (FEL) and advanced x-ray sources. Ultrahigh light intensities up to 1021 W/cm2 open the door to studies of relativistic laser-matter interaction and laser particle acceleration. The chapter closes with a section on laser stabilization.

  7. Lasers and Coherent Light Sources

    NASA Astrophysics Data System (ADS)

    Svelto, Orazio; Longhi, Stefano; Valle, Giuseppe; Kück, Stefan; Huber, Günter; Pollnau, Markus; Hillmer, Hartmut; Hansmann, Stefan; Engelbrecht, Rainer; Brand, Hans; Kaiser, Jeffrey; Peterson, Alan; Malz, Ralf; Steinberg, Steffen; Marowsky, Gerd; Brinkmann, Uwe; Lo, Dennis; Borsutzky, Annette; Wächter, Helen; Sigrist, Markus; Saldin, Evgeny; Schneidmiller, Evgeny; Yurkov, Mikhail; Midorikawa, Katsumi; Hein, Joachim; Sauerbrey, Roland; Helmcke, Jürgen

    This chapter describes lasers and other sources of coherent light that operate in a wide wavelength range. First, the general principles for the generation of coherent continuous-wave and pulsed radiation are treated including the interaction of radiation with matter, the properties of optical resonators and their modes as well as such processes as Q-switching and mode-locking. The general introduction is followed by sections on numerous types of lasers, the emphasis being on today's most important sources of coherent light, in particular on solid-state lasers and several types of gas lasers. An important part of the chapter is devoted to the generation of coherent radiation by nonlinear processes with optical parametric oscillators, difference- and sum-frequency generation, and high-order harmonics. Radiation in the extended ultraviolet (EUV) and X-ray ranges can be generated by free electron lasers (FEL) and advanced X-ray sources. Ultrahigh light intensities up to 1021 W/cm2 open the door to studies of relativistic laser-matter interaction and laser particle acceleration. The chapter closes with a section on laser stabilization.

  8. Progress in coherent laser radar

    NASA Technical Reports Server (NTRS)

    Vaughan, J. M.

    1986-01-01

    Considerable progress with coherent laser radar has been made over the last few years, most notably perhaps in the available range of high performance devices and components and the confidence with which systems may now be taken into the field for prolonged periods of operation. Some of this increasing maturity was evident at the 3rd Topical Meeting on Coherent Laser Radar: Technology and Applications. Topics included in discussions were: mesoscale wind fields, nocturnal valley drainage and clear air down bursts; airborne Doppler lidar studies and comparison of ground and airborne wind measurement; wind measurement over the sea for comparison with satellite borne microwave sensors; transport of wake vortices at airfield; coherent DIAL methods; a newly assembled Nd-YAG coherent lidar system; backscatter profiles in the atmosphere and wavelength dependence over the 9 to 11 micrometer region; beam propagation; rock and soil classification with an airborne 4-laser system; technology of a global wind profiling system; target calibration; ranging and imaging with coherent pulsed and CW system; signal fluctuations and speckle. Some of these activities are briefly reviewed.

  9. Coherence properties of short cavity swept lasers

    PubMed Central

    Johnson, Bart; Atia, Walid; Kuznetsov, Mark; Goldberg, Brian D.; Whitney, Peter; Flanders, Dale C.

    2017-01-01

    It has been shown theoretically and experimentally that short cavity swept lasers are passively mode locked. We develop a mathematical model of these lasers and the light field solutions are used to predict the coherence length and coherence revival behavior. The calculations compare favorably with data from a 990–1100 nm laser swept at 100 kHz suitable for optical coherence tomography applications. PMID:28271002

  10. Coherence delay augmented laser beam homogenizer

    DOEpatents

    Rasmussen, P.; Bernhardt, A.

    1993-06-29

    The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.

  11. Coherence delay augmented laser beam homogenizer

    DOEpatents

    Rasmussen, Paul; Bernhardt, Anthony

    1993-01-01

    The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.

  12. High power coherent polarization locked laser diode.

    PubMed

    Purnawirman; Phua, P B

    2011-03-14

    We have coherently combined a broad area laser diode array to obtain high power single-lobed output by using coherent polarization locking. The single-lobed coherent beam is achieved by spatially combining four diode emitters using walk-off crystals and waveplates while their phases are passively locked via polarization discrimination. While our previous work focused on coherent polarization locking of diode in Gaussian beams, we demonstrate in this paper, the feasibility of the same polarization discrimination for locking multimode beams from broad area diode lasers. The resonator is designed to mitigate the loss from smile effect by using retro-reflection feedback in the cavity. In a 980 nm diode array, we produced 7.2 W coherent output with M2 of 1.5x11.5. The brightness of the diode is improved by more than an order of magnitude.

  13. Spatial coherence of random laser emission

    NASA Astrophysics Data System (ADS)

    Redding, B.; Choma, M. A.; Cao, H.

    2011-09-01

    Lasing action in disordered media has been studied extensively in recent years and many of its properties are well understood. However, few studies have considered the spatial coherence in these systems, despite initial observations indicating that random lasers exhibit much lower spatial coherence than conventional lasers. We performed a systematic, experimental investigation of the spatial coherence of random laser emission as a function of the scattering mean free path and the excitation volume. Lasing was achieved under optical excitation and spatial coherence was characterized by imaging the emission spot onto a Young's double slit and collecting the interference fringes in the far field. We observed dramatic differences in the spatial coherence within our parameter space. Specifically, we found that samples with a shorter mean free path relative to the excitation volume exhibited reduced spatial coherence. We provide a qualitative explanation of our experimental observations in terms of the number of excited modes and their spatial orientation. This work provides a means to realize intense, spatially incoherent laser emission for applications in which speckle or spatial cross talk limits performance.

  14. Stretchable Random Lasers with Tunable Coherent Loops.

    PubMed

    Sun, Tzu-Min; Wang, Cih-Su; Liao, Chi-Shiun; Lin, Shih-Yao; Perumal, Packiyaraj; Chiang, Chia-Wei; Chen, Yang-Fang

    2015-12-22

    Stretchability represents a key feature for the emerging world of realistic applications in areas, including wearable gadgets, health monitors, and robotic skins. Many optical and electronic technologies that can respond to large strain deformations have been developed. Laser plays a very important role in our daily life since it was discovered, which is highly desirable for the development of stretchable devices. Herein, stretchable random lasers with tunable coherent loops are designed, fabricated, and demonstrated. To illustrate our working principle, the stretchable random laser is made possible by transferring unique ZnO nanobrushes on top of polydimethylsiloxane (PDMS) elastomer substrate. Apart from the traditional gain material of ZnO nanorods, ZnO nanobrushes were used as optical gain materials so they can serve as scattering centers and provide the Fabry-Perot cavity to enhance laser action. The stretchable PDMS substrate gives the degree of freedom to mechanically tune the coherent loops of the random laser action by changing the density of ZnO nanobrushes. It is found that the number of laser modes increases with increasing external strain applied on the PDMS substrate due to the enhanced possibility for the formation of coherent loops. The device can be stretched by up to 30% strain and subjected to more than 100 cycles without loss in laser action. The result shows a major advance for the further development of man-made smart stretchable devices.

  15. Coherent Laser Radar Remote Sensing

    DTIC Science & Technology

    1983-09-30

    studies have not made a coordinated assessment of these effects. There is published workL,Z, 3 on mixing 1. Degnan, J.J., and Klein, B.J., * Optical ... Antenna Gain 2: Receiving Antennas,* Appl. Opt. 13, 2397-2401 (1974). 2. Fink, D., "Coherent Detection Signal-to-Noise.’ Appl. Opt. 14, 689-690 (1975

  16. Local vibrational coherences drive the primary photochemistry of vision.

    PubMed

    Johnson, Philip J M; Halpin, Alexei; Morizumi, Takefumi; Prokhorenko, Valentyn I; Ernst, Oliver P; Miller, R J Dwayne

    2015-12-01

    The role of vibrational coherence-concerted vibrational motion on the excited-state potential energy surface-in the isomerization of retinal in the protein rhodopsin remains elusive, despite considerable experimental and theoretical efforts. We revisited this problem with resonant ultrafast heterodyne-detected transient-grating spectroscopy. The enhanced sensitivity that this technique provides allows us to probe directly the primary photochemical reaction of vision with sufficient temporal and spectral resolution to resolve all the relevant nuclear dynamics of the retinal chromophore during isomerization. We observed coherent photoproduct formation on a sub-50 fs timescale, and recovered a host of vibrational modes of the retinal chromophore that modulate the transient-grating signal during the isomerization reaction. Through Fourier filtering and subsequent time-domain analysis of the transient vibrational dynamics, the excited-state nuclear motions that drive the isomerization reaction were identified, and comprise stretching, torsional and out-of-plane wagging motions about the local C11=C12 isomerization coordinate.

  17. Long range coherence in free electron lasers

    NASA Technical Reports Server (NTRS)

    Colson, W. B.

    1984-01-01

    The simple free electron laser (FEL) design uses a static, periodic, transverse magnetic field to undulate relativistic electrons traveling along its axis. This allows coupling to a co-propagating optical wave and results in bunching to produce coherent radiation. The advantages of the FEL are continuous tunability, operation at wavelengths ranging from centimeters to angstroms, and high efficiency resulting from the fact that the interaction region only contains light, relativistic electrons, and a magnetic field. Theoretical concepts and operational principles are discussed.

  18. Solid-state coherent laser radar wind shear measuring systems

    NASA Technical Reports Server (NTRS)

    Huffaker, R. Milton

    1992-01-01

    Coherent Technologies, Inc. (CTI) was established in 1984 to engage in the development of coherent laser radar systems and subsystems with applications in atmospheric remote sensing, and in target tracking, ranging and imaging. CTI focuses its capabilities in three major areas: (1) theoretical performance and design of coherent laser radar system; (2) development of coherent laser radar systems for government agencies such as DoD and NASA; and (3) development of coherent laser radar systems for commercial markets. The topics addressed are: (1) 1.06 micron solid-state coherent laser radar system; (2) wind measurement using 1.06 micron system; and flashlamp-pumped 2.09 micron solid-state coherent laser radar system.

  19. Coherence delay augmented laser beam homogenizer

    SciTech Connect

    Rasmussen, P.; Bernhardt, A.

    1991-12-31

    It is an object of the present invention to provide an apparatus that can reduce the apparent coherence length of a laser beam so the beam can be used with an inexpensive homogenizer to produce an output beam with a uniform spatial intensity across its entire cross section. It is a further object of the invention to provide an improved homogenizer with a variable aperture size that is simple and easily made. It is still an additional object of the invention to provide an improved liquid filled homogenizer utilizing total internal reflection for improved efficiency. These, and other objects of the invention are realized by using a ``coherence delay line,`` according to the present invention, in series between a laser and a homogenizer. The coherence delay line is an optical ``line`` that comprises two mirrors, one partially reflecting, and one totally reflecting, arranged so that light incident from the laser first strikes the partially reflecting mirror. A portion of the beam passes through, and a portion is reflected back to the totally reflecting mirror.

  20. Local vibrational coherences drive the primary photochemistry of vision

    NASA Astrophysics Data System (ADS)

    Johnson, Philip J. M.; Halpin, Alexei; Morizumi, Takefumi; Prokhorenko, Valentyn I.; Ernst, Oliver P.; Miller, R. J. Dwayne

    2015-12-01

    The role of vibrational coherence—concerted vibrational motion on the excited-state potential energy surface—in the isomerization of retinal in the protein rhodopsin remains elusive, despite considerable experimental and theoretical efforts. We revisited this problem with resonant ultrafast heterodyne-detected transient-grating spectroscopy. The enhanced sensitivity that this technique provides allows us to probe directly the primary photochemical reaction of vision with sufficient temporal and spectral resolution to resolve all the relevant nuclear dynamics of the retinal chromophore during isomerization. We observed coherent photoproduct formation on a sub-50 fs timescale, and recovered a host of vibrational modes of the retinal chromophore that modulate the transient-grating signal during the isomerization reaction. Through Fourier filtering and subsequent time-domain analysis of the transient vibrational dynamics, the excited-state nuclear motions that drive the isomerization reaction were identified, and comprise stretching, torsional and out-of-plane wagging motions about the local C11=C12 isomerization coordinate.

  1. Analysis of coherent dynamical processes through computer vision

    NASA Astrophysics Data System (ADS)

    Hack, M. J. Philipp

    2016-11-01

    Visualizations of turbulent boundary layers show an abundance of characteristic arc-shaped structures whose apparent similarity suggests a common origin in a coherent dynamical process. While the structures have been likened to the hairpin vortices observed in the late stages of transitional flow, a consistent description of the underlying mechanism has remained elusive. Detailed studies are complicated by the chaotic nature of turbulence which modulates each manifestation of the process and which renders the isolation of individual structures a challenging task. The present study applies methods from the field of computer vision to capture the time evolution of turbulent flow features and explore the associated physical mechanisms. The algorithm uses morphological operations to condense the structure of the turbulent flow field into a graph described by nodes and links. The low-dimensional geometric information is stored in a database and allows the identification and analysis of equivalent dynamical processes across multiple scales. The framework is not limited to turbulent boundary layers and can also be applied to different types of flows as well as problems from other fields of science.

  2. Coherent characteristics of solid-state lasers with corner cubes.

    PubMed

    Cheng, Yong; Liu, Xu; Liu, Yang; Tan, Chaoyong; Chen, Xia; Zhu, Mengzhen; Mi, Chaowei; Sun, Bin

    2014-05-20

    A corner cube (CC) as a peculiar coherent combination element is first, to the best of our knowledge, theoretically and experimentally proved by the authors. When a CC is used as a total-reflecting mirror in the solid-state laser resonator it can improve the laser far-field energy focalization. Furthermore, the differences between the coherent characteristics of the lasers with a corner cube resonator (CCR) and those with a Fabry-Perot resonator have been investigated, respectively. Theoretical calculation and numerical simulation have proved that the symmetric output beams of the CCR laser are coherent and the adjacent output beams are partially coherent. Based on these special coherent characteristics, a new laser coherent combining configuration, in which a CC was utilized as a total-reflecting mirror, was proposed and experimentally investigated. In our experiments, the measured far-field intensity profiles of coherent combing laser arrays are in good agreement with the numerical simulation. These novel coherent characteristics of a CC may be important for applications in solid-state lasers and laser coherent combining systems, and coherent combination may be one of the development trends and future research directions for CCR lasers.

  3. Tenth Biennial Coherent Laser Radar Technology and Applications Conference

    NASA Technical Reports Server (NTRS)

    Kavaya, Michael J. (Compiler)

    1999-01-01

    The tenth conference on coherent laser radar technology and applications is the latest in a series beginning in 1980 which provides a forum for exchange of information on recent events current status, and future directions of coherent laser radar (or lidar or lader) technology and applications. This conference emphasizes the latest advancement in the coherent laser radar field, including theory, modeling, components, systems, instrumentation, measurements, calibration, data processing techniques, operational uses, and comparisons with other remote sensing technologies.

  4. Solid-state lasers for coherent communication and remote sensing

    NASA Technical Reports Server (NTRS)

    Byer, Robert L.

    1990-01-01

    Laser development, high efficiency, high power second harmonic generation, operation of optical parametric oscillators for wavelength diversity and tunability, and studies in coherent communications are reviewed.

  5. Low Coherence Interferometry in Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Neef, A.; Seyda, V.; Herzog, D.; Emmelmann, C.; Schönleber, M.; Kogel-Hollacher, M.

    Selective Laser Melting (SLM) is an additive layer manufacturing technology that offers several advantages compared to conven- tional methods of production such as an increased freedom of design and a toolless production suited for variable lot sizes. Despite these attractive aspects today's state of the art SLM machines lack a holistic process monitoring system that detects and records typical defects during production. A novel sensor concept based on the low coherence interferometry (LCI) was integrated into an SLM production setup. The sensor is mounted coaxially to the processing laser beam and is capable of sampling distances along the optical axis. Measurements during and between the processing of powder layers can reveal crucial topology information which is closely related to the final part quality. The overall potential of the sensor in terms of quality assurance and process control is being discussed. Furthermore fundamental experiments were performed to derive the performance of the system.

  6. Nonlinear Dynamics of Arrays of Coherent Laser Beams

    DTIC Science & Technology

    2012-09-23

    AFRL-AFOSR-UK-TR-2012-0058 Nonlinear dynamics of arrays of coherent laser beams Professor Sergei K. Turitsyn Aston...Report 3. DATES COVERED (From – To) 20 June 2010 – 19 June 2012 4. TITLE AND SUBTITLE Nonlinear dynamics of arrays of coherent laser beams 5a...have been verified using numerical simulations. 15. SUBJECT TERMS EOARD, Laser Beams, Lasers 16. SECURITY CLASSIFICATION OF

  7. Tunable, Highly Stable Lasers for Coherent Lidar

    NASA Technical Reports Server (NTRS)

    Henderson, Sammy W.; Hale, Charley P.; EEpagnier, David M.

    2006-01-01

    Practical space-based coherent laser radar systems envisioned for global winds measurement must be very efficient and must contend with unique problems associated with the large platform velocities that the instruments experience in orbit. To compensate for these large platform-induced Doppler shifts in space-based applications, agile-frequency offset-locking of two single-frequency Doppler reference lasers was thoroughly investigated. Such techniques involve actively locking a frequency-agile master oscillator (MO) source to a comparatively static local oscillator (LO) laser, and effectively producing an offset between MO (the lidar slave oscillator seed source, typically) and heterodyne signal receiver LO that lowers the bandwidth of the receiver data-collection system and permits use of very high-quantum-efficiency, reasonably- low-bandwidth heterodyne photoreceiver detectors and circuits. Recent work on MO/LO offset locking has focused on increasing the offset locking range, improving the graded-InGaAs photoreceiver performance, and advancing the maturity of the offset locking electronics. A figure provides a schematic diagram of the offset-locking system.

  8. Cascaded injection resonator for coherent beam combining of laser arrays

    DOEpatents

    Kireev, Vassili [Sunnyvale, CA; Liu, Yun; Protopopescu, Vladimir [Knoxville, TN; Braiman, Yehuda [Oak Ridge, TN

    2008-10-21

    The invention provides a cascaded injection resonator for coherent beam combining of laser arrays. The resonator comprises a plurality of laser emitters arranged along at least one plane and a beam sampler for reflecting at least a portion of each laser beam that impinges on the beam sampler, the portion of each laser beam from one of the laser emitters being reflected back to another one of the laser emitters to cause a beam to be generated from the other one of the laser emitters to the beam reflector. The beam sampler also transmits a portion of each laser beam to produce a laser output beam such that a plurality of laser output beams of the same frequency are produced. An injection laser beam is directed to a first laser emitter to begin a process of generating and reflecting a laser beam from one laser emitter to another laser emitter in the plurality. A method of practicing the invention is also disclosed.

  9. Nonlinear optics with coherent free electron lasers

    NASA Astrophysics Data System (ADS)

    Bencivenga, F.; Capotondi, F.; Mincigrucci, R.; Cucini, R.; Manfredda, M.; Pedersoli, E.; Principi, E.; Simoncig, A.; Masciovecchio, C.

    2016-12-01

    We interpreted the recent construction of free electron laser (FELs) facilities worldwide as an unprecedented opportunity to bring concepts and methods from the scientific community working with optical lasers into the domain of x-ray science. This motivated our efforts towards the realization of FEL-based wave-mixing applications. In this article we present new extreme ultraviolet transient grating (X-TG) data from vitreous SiO2, collected using two crossed FEL pulses (photon frequency 38 eV) to generate the X-TG and a phase matched optical probing pulse (photon frequency 3.1 eV). This experiment extends our previous investigation, which was carried out on a nominally identical sample using a different FEL photon frequency (45 eV) to excite the X-TG. The present data are featured by a peak intensity of the X-TG signal substantially larger than that previously reported and by slower modulations of the X-TG signal at positive delays. These differences could be ascribed to the different FEL photon energy used in the two experiments or to differences in the sample properties. A systematic X-TG study on the same sample as a function of the FEL wavelength is needed to draw a consistent conclusion. We also discuss how the advances in the performance of the FELs, in terms of generation of fully coherent photon pulses and multi-color FEL emission, may push the development of original experimental strategies to study matter at the femtosecond-nanometer time-length scales, with the unique option of element and chemical state specificity. This would allow the development of advanced experimental tools based on wave-mixing processes, which may have a tremendous impact in the study of a large array of phenomena, ranging from nano-dynamics in complex materials to charge and energy transfer processes.

  10. Night vision goggles, laser eye protection, and cockpit displays

    NASA Astrophysics Data System (ADS)

    Martinsen, Gary; Havig, Paul; Dykes, James; Kuyk, Thomas; McLin, Leon

    2007-04-01

    The increasing use of lasers on the modern battlefield may necessitate the wear of laser eye protection devices (LEPDs) by warfighters. Unfortunately, LEPDs that protect against visible laser wavelengths often reduce overall light transmittance and a wearer's vision can be degraded, especially in low light conditions. Wearing night vision goggles (NVGs) provides laser eye protection behind the goggles, but NVGs do not block lasers that might enter the eye around the NVGs. Therefore, LEPDs will be worn under NVGs. People wearing NVGs look below the NVGs to read displays and for other near vision tasks. This effort involved determining the effects of wearing variable density filters on vision in low light conditions, with and without the presence of a simulated head-down display (HDD). Each subject's visual acuity was measured under moonlight illumination levels while wearing neutral density filters and LEPDs. Similar measurements of the subjects' visual detection thresholds, both on and off-axis, were made. Finally, the effects of wearing variable density filters on visual acuity on the HDD were determined. Wearing variable density filters in low-light conditions reduces visual acuity and detection. The presence of the HDD reduced acuity slightly through variable density filters but. the HDD had no effect on on-axis detection and actually improved off-axis detection. The reasons for this final finding are unclear.

  11. Laser-Driven Coherent Betatron Oscillation in a Laser-Wakefield Cavity: Formation of Sinusoid Beam Shapes and Coherent Trajectories

    SciTech Connect

    Nemeth, Karoly; Li Yuelin; Shang Hairong; Harkay, Katherine C.; Shen Baifei; Crowell, Robert; Cary, John R.

    2009-01-22

    High amplitude coherent electron-trajectories have been seen in 3D particle-in-cell simulations of the colliding pulse injection scheme of laser-wakefield accelerators in the bubble regime, and explained as a consequence of laser-driven coherent betatron oscillation in our recent paper [K. Nemeth et al., Phys. Rev. Lett. 100, 095002 (2008)]. In the present paper we provide more details on the shape of the trajectories, their relationship to the phase velocity of the laser and indicate the dependence of the phenomenon on the accuracy of the numerical representation and choice of laser/plasma parameters.

  12. The 3D laser radar vision processor system

    NASA Technical Reports Server (NTRS)

    Sebok, T. M.

    1990-01-01

    Loral Defense Systems (LDS) developed a 3D Laser Radar Vision Processor system capable of detecting, classifying, and identifying small mobile targets as well as larger fixed targets using three dimensional laser radar imagery for use with a robotic type system. This processor system is designed to interface with the NASA Johnson Space Center in-house Extra Vehicular Activity (EVA) Retriever robot program and provide to it needed information so it can fetch and grasp targets in a space-type scenario.

  13. A laser-based vision system for weld quality inspection.

    PubMed

    Huang, Wei; Kovacevic, Radovan

    2011-01-01

    Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In this paper, a laser-based vision system is developed for non-destructive weld quality inspection. The vision sensor is designed based on the principle of laser triangulation. By processing the images acquired from the vision sensor, the geometrical features of the weld can be obtained. Through the visual analysis of the acquired 3D profiles of the weld, the presences as well as the positions and sizes of the weld defects can be accurately identified and therefore, the non-destructive weld quality inspection can be achieved.

  14. Phased laser array with tailored spectral and coherence properties

    DOEpatents

    Messerly, Michael J; Dawson, Jay W; Beach, Raymond J

    2014-05-20

    Architectures for coherently combining an array of fiber-based lasers are provided. By matching their lengths to within a few integer multiples of a wavelength, the spatial and temporal properties of a single large laser are replicated, while extending the average or peak pulsed power limit.

  15. Phased laser array with tailored spectral and coherence properties

    DOEpatents

    Messerly, Michael J; Dawson, Jay W; Beach, Raymond J

    2011-03-29

    Architectures for coherently combining an array of fiber-based lasers are provided. By matching their lengths to within a few integer multiples of a wavelength, the spatial and temporal properties of a single large laser are replicated, while extending the average or peak pulsed power limit.

  16. Stereo vision based hand-held laser scanning system design

    NASA Astrophysics Data System (ADS)

    Xiong, Hanwei; Xu, Jun; Wang, Jinming

    2011-11-01

    Although 3D scanning system is used more and more broadly in many fields, such computer animate, computer aided design, digital museums, and so on, a convenient scanning device is expansive for most people to afford. In another hand, imaging devices are becoming cheaper, a stereo vision system with two video cameras cost little. In this paper, a hand held laser scanning system is design based on stereo vision principle. The two video cameras are fixed tighter, and are all calibrated in advance. The scanned object attached with some coded markers is in front of the stereo system, and can be changed its position and direction freely upon the need of scanning. When scanning, the operator swept a line laser source, and projected it on the object. At the same time, the stereo vision system captured the projected lines, and reconstructed their 3D shapes. The code markers are used to translate the coordinate system between scanned points under different view. Two methods are used to get more accurate results. One is to use NURBS curves to interpolate the sections of the laser lines to obtain accurate central points, and a thin plate spline is used to approximate the central points, and so, an exact laser central line is got, which guards an accurate correspondence between tow cameras. Another way is to incorporate the constraint of laser swept plane on the reconstructed 3D curves by a PCA (Principle Component Analysis) algorithm, and more accurate results are obtained. Some examples are given to verify the system.

  17. Optical injection enables coherence resonance in quantum-dot lasers

    NASA Astrophysics Data System (ADS)

    Ziemann, D.; Aust, R.; Lingnau, B.; Schöll, E.; Lüdge, K.

    2013-07-01

    We demonstrate that optically injected semiconductor quantum-dot lasers operated in the frequency-locked regime exhibit the counterintuitive effect of coherence resonance, i.e., the regularity of noise-induced spiking is a non-monotonic function of the spontaneous emission noise, and it is optimally correlated at a non-zero value of the noise intensity. We uncover the mechanism of coherence resonance from a microscopically based model of the quantum-dot laser structure, and show that it is related to excitability under optical injection and to a saddle-node infinite period (SNIPER) bifurcation occurring for small injection strength at the border of the frequency locking regime. By a model reduction we argue that the phenomenon of coherence resonance is generic for a wide class of optically injected lasers.

  18. Optical laser systems at the Linac Coherent Light Source

    DOE PAGES

    Minitti, Michael P.; Robinson, Joseph S.; Coffee, Ryan N.; ...

    2015-04-22

    Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump–probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump–probe experiments to be performed at LCLS.

  19. Coherent Doppler Laser Radar: Technology Development and Applications

    NASA Technical Reports Server (NTRS)

    Kavaya, Michael J.; Arnold, James E. (Technical Monitor)

    2000-01-01

    NASA's Marshall Space Flight Center has been investigating, developing, and applying coherent Doppler laser radar technology for over 30 years. These efforts have included the first wind measurement in 1967, the first airborne flights in 1972, the first airborne wind field mapping in 1981, and the first measurement of hurricane eyewall winds in 1998. A parallel effort at MSFC since 1982 has been the study, modeling and technology development for a space-based global wind measurement system. These endeavors to date have resulted in compact, robust, eyesafe lidars at 2 micron wavelength based on solid-state laser technology; in a factor of 6 volume reduction in near diffraction limited, space-qualifiable telescopes; in sophisticated airborne scanners with full platform motion subtraction; in local oscillator lasers capable of rapid tuning of 25 GHz for removal of relative laser radar to target velocities over a 25 km/s range; in performance prediction theory and simulations that have been validated experimentally; and in extensive field campaign experience. We have also begun efforts to dramatically improve the fundamental photon efficiency of the laser radar, to demonstrate advanced lower mass laser radar telescopes and scanners; to develop laser and laser radar system alignment maintenance technologies; and to greatly improve the electrical efficiency, cooling technique, and robustness of the pulsed laser. This coherent Doppler laser radar technology is suitable for high resolution, high accuracy wind mapping; for aerosol and cloud measurement; for Differential Absorption Lidar (DIAL) measurements of atmospheric and trace gases; for hard target range and velocity measurement; and for hard target vibration spectra measurement. It is also suitable for a number of aircraft operations applications such as clear air turbulence (CAT) detection; dangerous wind shear (microburst) detection; airspeed, angle of attack, and sideslip measurement; and fuel savings through

  20. 2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

    NASA Technical Reports Server (NTRS)

    Singh, Upendra N.; Bai, Yingxin; Yu, Jirong

    2009-01-01

    Carbon dioxide (CO2) has been recognized as one of the most important greenhouse gases. It is essential for the study of global warming to accurately measure the CO2 concentration in the atmosphere and continuously record its variation. A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed in NASA Langley Research Center. This laser system is capable of making a vertical profiling of CO2 from ground and column measurement of CO2 from air and space-borne platform. The transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of 50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. A Ho:YLF laser operating in the range of 2.05 micrometers can be tuned over several characteristic lines of CO2 absorption. Experimentally, a diode pumped Ho:Tm:YLF laser has been successfully used as the transmitter of coherent differential absorption lidar for the measurement of CO2 with a repetition rate of 5 Hz and pulse energy of 75 mJ. For coherent detection, high repetition rate is required for speckle averaging to obtain highly precise measurements. However, a diode pumped Ho:Tm:YLF laser can not operate in high repetition rate due to the large heat loading and up-conversion. A Tm:fiber laser pumped Ho:YLF laser with low heat loading can operate in high repetition rate. A theoretical model has been established to simulate the performance of Tm:fiber laser pumped Ho:YLF lasers. For continuous wave (CW) operation, high pump intensity with small beam

  1. Statistical properties of partially coherent cw fiber lasers.

    PubMed

    Churkin, Dmitriy V; Smirnov, Sergey V; Podivilov, Evgenii V

    2010-10-01

    We perform a detailed quantitative numerical analysis of a partially coherent quasi-cw fiber laser on the example of a high-Q normal dispersion cavity Raman fiber laser. The key role of precise spectral performances of fiber Bragg gratings forming the laser cavity is clarified. It is shown that cross-phase modulation between the pump and Stokes waves does not affect the generation. Amplitudes of different longitudinal modes strongly fluctuate, obeying the Gaussian distribution. As the intensity statistics is noticeably nonexponential, longitudinal modes should be correlated.

  2. Solid-state lasers for coherent communication and remote sensing

    NASA Technical Reports Server (NTRS)

    Byer, Robert L.

    1992-01-01

    Semiconductor-diode laser-pumped solid-state lasers have properties that are superior to other lasers for the applications of coherent communication and remote sensing. These properties include efficiency, reliability, stability, and capability to be scaled to higher powers. We have demonstrated that an optical phase-locked loop can be used to lock the frequency of two diode-pumped 1.06 micron Nd:YAG lasers to levels required for coherent communication. Monolithic nonplanar ring oscillators constructed from solid pieces of the laser material provide better than 10 kHz frequency stability over 0.1 sec intervals. We have used active feedback stabilization of the cavity length of these lasers to demonstrate 0.3 Hz frequency stabilization relative to a reference cavity. We have performed experiments and analysis to show that optical parametric oscillators (OPO's) reproduce the frequency stability of the pump laser in outputs that can be tuned to arbitrary wavelengths. Another measurement performed in this program has demonstrated the sub-shot-noise character of correlations of the fluctuations in the twin output of OPO's. Measurements of nonlinear optical coefficients by phase-matched second harmonic generation are helping to resolve inconsistency in these important parameters.

  3. Quasi mode-locking of coherent feedback random fiber laser

    NASA Astrophysics Data System (ADS)

    Ma, R.; Zhang, W. L.; Zeng, X. P.; Yang, Z. J.; Rao, Y. J.; Yao, B. C.; Yu, C. B.; Wu, Y.; Yu, S. F.

    2016-12-01

    Mode-locking is a milestone in the history of lasers that allows the generation of short light pulses and stabilization of lasers. This phenomenon is known to occur only in standard ordered lasers for long time and until recently it is found that it also occurs in disordered random lasers formed by nanoscale particles. Here, we report the realization of a so-called quasi mode-locking of coherent feedback random fiber laser which consists of a partially disordered linear cavity formed between a point reflector and a random distributed fiber Bragg grating array with an inserted graphene saturable absorber. We show that multi-groups of regular light pulses/sub-pulses with different repetition frequencies are generated within the quasi mode-locking regime through the so-called collective resonances phenomenon in such a random fiber laser. This work may provide a platform to study mode locking as well as pulse dynamic regulation of random lasing emission of coherent feedback disordered structures and pave the way to the development of novel multi-frequency pulse fiber lasers with potentially wide frequency tuning range.

  4. Quasi mode-locking of coherent feedback random fiber laser

    PubMed Central

    Ma, R.; Zhang, W. L.; Zeng, X. P.; Yang, Z. J.; Rao, Y. J.; Yao, B. C.; Yu, C. B.; Wu, Y.; Yu, S. F.

    2016-01-01

    Mode-locking is a milestone in the history of lasers that allows the generation of short light pulses and stabilization of lasers. This phenomenon is known to occur only in standard ordered lasers for long time and until recently it is found that it also occurs in disordered random lasers formed by nanoscale particles. Here, we report the realization of a so-called quasi mode-locking of coherent feedback random fiber laser which consists of a partially disordered linear cavity formed between a point reflector and a random distributed fiber Bragg grating array with an inserted graphene saturable absorber. We show that multi-groups of regular light pulses/sub-pulses with different repetition frequencies are generated within the quasi mode-locking regime through the so-called collective resonances phenomenon in such a random fiber laser. This work may provide a platform to study mode locking as well as pulse dynamic regulation of random lasing emission of coherent feedback disordered structures and pave the way to the development of novel multi-frequency pulse fiber lasers with potentially wide frequency tuning range. PMID:28004785

  5. The coherent combination of fibre lasers - Towards realistic applications

    NASA Astrophysics Data System (ADS)

    Tudor, Peter; Corner, Laura; Walczak, Roman

    2017-03-01

    To drive a laser-plasma wakefield, high peak-power laser pulses are required. For useful accelerator applications, it is also necessary to have driving lasers with high efficiency, repetition rates, and average power. The coherent combination of Ytterbium-doped fibre laser amplifiers is a promising potential solution, and previous work has demonstrated the successful combination of near-identical ultrafast fibre lasers. We report here the combination of significantly mismatched Ytterbium-doped photonic crystal fibre amplifiers with a combined efficiency of 96%, while the locked power output remained stable for 6 hours. The combined output of the system had a total gain of 12 dB, with no detrimental effect on the compressed pulse width observed.

  6. Coherence loss of partially mode-locked fibre laser

    NASA Astrophysics Data System (ADS)

    Gao, Lei; Zhu, Tao; Wabnitz, Stefan; Liu, Min; Huang, Wei

    2016-04-01

    Stochastically driven nonlinear processes limit the number of amplified modes in a natural system due to competitive mode interaction, which is accompanied by loss of coherence when increasing the complexity of the system. Specifically, we find that modulation instability, which exhibits great fluctuations when it spontaneously grows from noise in conservative systems, may possess a high degree of coherence in dissipative laser system with gain. Nonlinear mode interactions can be competitive or cooperative: adjusting the intracavity polarization state controls the process of loss of coherence. Single-shot spectra reveal that, first, the fibre laser redistributes its energy from the center wavelength mode into sidebands through parametric instabilities. Subsequently, longitudinal modes are populated via cascaded four-wave-mixing. Parametric frequency conversion populates longitudinal modes with a random distribution of position, intensity and polarization, resulting in partially (rather than highly) coherent pulses. These dynamics unveil a new route towards complex pattern formation in nonlinear laser systems, and they may be also beneficial for the understanding of supercontinuum, Kerr-combs phenomena, and optical rogue waves.

  7. Coherence loss of partially mode-locked fibre laser.

    PubMed

    Gao, Lei; Zhu, Tao; Wabnitz, Stefan; Liu, Min; Huang, Wei

    2016-04-29

    Stochastically driven nonlinear processes limit the number of amplified modes in a natural system due to competitive mode interaction, which is accompanied by loss of coherence when increasing the complexity of the system. Specifically, we find that modulation instability, which exhibits great fluctuations when it spontaneously grows from noise in conservative systems, may possess a high degree of coherence in dissipative laser system with gain. Nonlinear mode interactions can be competitive or cooperative: adjusting the intracavity polarization state controls the process of loss of coherence. Single-shot spectra reveal that, first, the fibre laser redistributes its energy from the center wavelength mode into sidebands through parametric instabilities. Subsequently, longitudinal modes are populated via cascaded four-wave-mixing. Parametric frequency conversion populates longitudinal modes with a random distribution of position, intensity and polarization, resulting in partially (rather than highly) coherent pulses. These dynamics unveil a new route towards complex pattern formation in nonlinear laser systems, and they may be also beneficial for the understanding of supercontinuum, Kerr-combs phenomena, and optical rogue waves.

  8. Coherence loss of partially mode-locked fibre laser

    PubMed Central

    Gao, Lei; Zhu, Tao; Wabnitz, Stefan; Liu, Min; Huang, Wei

    2016-01-01

    Stochastically driven nonlinear processes limit the number of amplified modes in a natural system due to competitive mode interaction, which is accompanied by loss of coherence when increasing the complexity of the system. Specifically, we find that modulation instability, which exhibits great fluctuations when it spontaneously grows from noise in conservative systems, may possess a high degree of coherence in dissipative laser system with gain. Nonlinear mode interactions can be competitive or cooperative: adjusting the intracavity polarization state controls the process of loss of coherence. Single-shot spectra reveal that, first, the fibre laser redistributes its energy from the center wavelength mode into sidebands through parametric instabilities. Subsequently, longitudinal modes are populated via cascaded four-wave-mixing. Parametric frequency conversion populates longitudinal modes with a random distribution of position, intensity and polarization, resulting in partially (rather than highly) coherent pulses. These dynamics unveil a new route towards complex pattern formation in nonlinear laser systems, and they may be also beneficial for the understanding of supercontinuum, Kerr-combs phenomena, and optical rogue waves. PMID:27126325

  9. Coherent combs in ionization by intense and short laser pulses

    NASA Astrophysics Data System (ADS)

    Krajewska, K.; Kamiński, J. Z.

    2016-03-01

    Photoionization of positive ions by a train of intense, short laser pulses is investigated within the relativistic strong field approximation, using the velocity gauge. The formation of broad peak structures in the high-energy domain of photoelectrons is observed and interpreted. The emergence of coherent photoelectron energy combs within these structures is demonstrated, and it is interpreted as the consequence of the Fraunhofer-type interference/diffraction of probability amplitudes of ionization from individual pulses comprising the train. Extensions to the coherent angular combs are also studied, and effects related to the radiation pressure are presented.

  10. Novel intra-cavity self-organization coherent erbium-doped fiber laser

    NASA Astrophysics Data System (ADS)

    Jia, Xiu-Jie; Liu, Feng-Nian; Fu, Sheng-Gui; Zhang, Jian; Liu, Yan-Ge; Guo, Zhan-Cheng; Yuan, Shu-Zhong; Kai, Gui-Yun; Dong, Xiao-Yi

    2007-03-01

    A novel all-fiber self-organization coherent Erbium-doped fiber laser is proposed and demonstrated. The laser system is composed of two independent lasers. When each of the two branch lasers operates independently, the output power is 10. 41mW and 8.69 mW respectively. By adjusting a polarization controller (PC), the two lasers achieve coherent coupling, and the output power is 24.4 mW, which is more than two times that the single laser yields. Furthermore, we bring forward and discuss the factor estimating the effect of coherent combination—coherent coupling factor. The value of growth factor to evaluate the effect of coherent combining is 1.27. The coherent fiber laser has the advantages of simple structure, high efficiency and single frequency, which conduce to coherent coupling easily.

  11. Coherent and incoherent structural dynamics in laser-excited antimony

    NASA Astrophysics Data System (ADS)

    Waldecker, Lutz; Vasileiadis, Thomas; Bertoni, Roman; Ernstorfer, Ralph; Zier, Tobias; Valencia, Felipe H.; Garcia, Martin E.; Zijlstra, Eeuwe S.

    2017-02-01

    We investigate the excitation of phonons in photoexcited antimony and demonstrate that the entire electron-lattice interactions, in particular coherent and incoherent electron-phonon coupling, can be probed simultaneously. Using femtosecond electron diffraction (FED) with high temporal resolution, we observe the coherent excitation of the fully symmetric A1 g optical phonon mode via the shift of the minimum of the atomic potential energy surface. Ab initio molecular dynamics simulations on laser excited potential energy surfaces are performed to quantify the change in lattice potential and the associated real-space amplitude of the coherent atomic oscillations. Good agreement is obtained between the parameter-free calculations and the experiment. In addition, our experimental configuration allows observing the energy transfer from electrons to phonons via incoherent electron-lattice scattering events. The electron-phonon coupling is determined as a function of electronic temperature from our DFT calculations and the data by applying different models for the energy transfer.

  12. Optimizing the Laser-Pulse Configuration for Coherent Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pestov, Dmitry; Murawski, Robert K.; Ariunbold, Gombojav O.; Wang, Xi; Zhi, Miaochan; Sokolov, Alexei V.; Sautenkov, Vladimir A.; Rostovtsev, Yuri V.; Dogariu, Arthur; Huang, Yu; Scully, Marlan O.

    2007-04-01

    We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

  13. Optimizing the laser-pulse configuration for coherent Raman spectroscopy.

    PubMed

    Pestov, Dmitry; Murawski, Robert K; Ariunbold, Gombojav O; Wang, Xi; Zhi, Miaochan; Sokolov, Alexei V; Sautenkov, Vladimir A; Rostovtsev, Yuri V; Dogariu, Arthur; Huang, Yu; Scully, Marlan O

    2007-04-13

    We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

  14. Ultrafast laser based coherent control methods for explosives detection

    SciTech Connect

    Moore, David Steven

    2010-12-06

    The detection of explosives is a notoriously difficult problem, especially at stand-off, due to their (generally) low vapor pressure, environmental and matrix interferences, and packaging. We are exploring Optimal Dynamic Detection of Explosives (ODD-Ex), which exploits the best capabilities of recent advances in laser technology and recent discoveries in optimal shaping of laser pulses for control of molecular processes to significantly enhance the standoff detection of explosives. The core of the ODD-Ex technique is the introduction of optimally shaped laser pulses to simultaneously enhance sensitivity to explosives signatures while dramatically improving specificity, particularly against matrix materials and background interferences. These goals are being addressed by operating in an optimal non-linear fashion, typically with a single shaped laser pulse inherently containing within it coherently locked control and probe subpulses. Recent results will be presented.

  15. Ultrahigh-Resolution Optical Coherence Tomography Using Femtosecond Lasers

    NASA Astrophysics Data System (ADS)

    Fujimoto, J. G.; Aguirre, A. D.; Chen, Y.; Herz, P. R.; Hsiung, P.-L.; Ko, T. H.; Nishizawa, N.; Kärtner, F. X.

    Optical coherence tomography (OCT) is an emerging optical imaging modality for biomedical research and clinical medicine. OCT can perform high resolution, cross-sectional tomographic imaging in materials and biological systems by measuring the echo time delay and magnitude of backreflected or backscattered light [1]. In medical applications, OCT has the advantage that imaging can be performed in situ and in real time, without the need to remove and process specimens as in conventional excisional biopsy and histopathology. OCT can achieve axial image resolutions of 1 to 15 μm; one to two orders of magnitude higher than standard ultrasound imaging. The image resolution in OCT is determined by the coherence length of the light source and is inversely proportional to its bandwidth. Femtosecond lasers can generate extremely broad bandwidths and have enabled major advances in ultrahigh-resolution OCT imaging. This chapter provides an overview of OCT technology and ultrahigh-resolution OCT imaging using femtosecond lasers.

  16. Coherent Laser Spectroscopy and Doppler Lidar Sensing in the Atmosphere

    NASA Astrophysics Data System (ADS)

    Vaughan, J. M.

    The principles of coherent laser spectroscopy are briefly reviewed in which a signal beam is heterodyned with an optical local oscillator beam. The frequency and single mode selectivity this provides is shown to be very advantageous. This is illustrated by recent work on the properties of different classes of light field, including the fractal character of Gaussian-Lorentzian light, and by several aspects of laser physics. In equivalent practical applications to remote sensing in the atmosphere, coherent Doppler lidar provides a powerful technique. This is illustrated by measurements of wind fields and aircraft wake vortices. Airborne equipments have been used for measurements of true airspeed, wind shear warning and atmospheric backscatter levels. Future space-borne lidars could potentially measure the global wind field - of great benefit for numerical weather forecasting and climate studies.

  17. Precision metrology of NSTX surfaces using coherent laser radar ranging

    SciTech Connect

    H.W. Kugel; D. Loesser; A. L. Roquemore; M. M. Menon; R. E. Barry

    2000-07-13

    A frequency modulated Coherent Laser Radar ranging diagnostic is being used on the National Spherical Torus Experiment (NSTX) for precision metrology. The distance (range) between the 1.5 {micro}m laser source and the target is measured by the shift in frequency of the linearly modulated beam reflected off the target. The range can be measured to a precision of < 100{micro}m at distances of up to 22 meters. A description is given of the geometry and procedure for measuring NSTX interior and exterior surfaces during open vessel conditions, and the results of measurements are elaborated.

  18. Plasmon Lasers: Coherent Light Source at Molecular Scales

    DTIC Science & Technology

    2012-01-01

    rates due to cavity damping. From [20]. where, pnth γ1β γgβΓ, with solutions of the form, γs 1 2 p pnth 1 2 p pnth 1 4p ...ers, Company Profiles, Industry Trends, Market study by http://www.freedoniagroup.com (2011), date of last visit: 18 February 2012. www.lpr...Photonics Rev., 1–21 (2012) /DOI 10.1002/lpor.201100040 LASER&PHOTONICS REVIEWS Abstract Plasmon lasers are a new class of coherent optical frequency

  19. Probing beyond the laser coherence time in optical clock comparisons

    NASA Astrophysics Data System (ADS)

    Hume, David B.; Leibrandt, David R.

    2016-03-01

    We develop differential measurement protocols that circumvent the laser noise limit in the stability of optical clock comparisons by synchronous probing of two clocks using phase-locked local oscillators. This allows for probe times longer than the laser coherence time, avoids the Dick effect, and supports Heisenberg-limited measurement precision. We present protocols for such frequency comparisons and develop numerical simulations of the protocols with realistic noise sources. These methods provide a route to reduce frequency ratio measurement durations by more than an order of magnitude.

  20. Simple laser vision sensor calibration for surface profiling applications

    NASA Astrophysics Data System (ADS)

    Abu-Nabah, Bassam A.; ElSoussi, Adnane O.; Al Alami, Abed ElRahman K.

    2016-09-01

    Due to the relatively large structures in the Oil and Gas industry, original equipment manufacturers (OEMs) have been implementing custom-designed laser vision sensor (LVS) surface profiling systems as part of quality control in their manufacturing processes. The rough manufacturing environment and the continuous movement and misalignment of these custom-designed tools adversely affect the accuracy of laser-based vision surface profiling applications. Accordingly, Oil and Gas businesses have been raising the demand from the OEMs to implement practical and robust LVS calibration techniques prior to running any visual inspections. This effort introduces an LVS calibration technique representing a simplified version of two known calibration techniques, which are commonly implemented to obtain a calibrated LVS system for surface profiling applications. Both calibration techniques are implemented virtually and experimentally to scan simulated and three-dimensional (3D) printed features of known profiles, respectively. Scanned data is transformed from the camera frame to points in the world coordinate system and compared with the input profiles to validate the introduced calibration technique capability against the more complex approach and preliminarily assess the measurement technique for weld profiling applications. Moreover, the sensitivity to stand-off distances is analyzed to illustrate the practicality of the presented technique.

  1. Laser cutting of irregular shape object based on stereo vision laser galvanometric scanning system

    NASA Astrophysics Data System (ADS)

    Qi, Li; Zhang, Yixin; Wang, Shun; Tang, Zhiqiang; Yang, Huan; Zhang, Xuping

    2015-05-01

    Irregular shape objects with different 3-dimensional (3D) appearances are difficult to be shaped into customized uniform pattern by current laser machining approaches. A laser galvanometric scanning system (LGS) could be a potential candidate since it can easily achieve path-adjustable laser shaping. However, without knowing the actual 3D topography of the object, the processing result may still suffer from 3D shape distortion. It is desirable to have a versatile auxiliary tool that is capable of generating 3D-adjusted laser processing path by measuring the 3D geometry of those irregular shape objects. This paper proposed the stereo vision laser galvanometric scanning system (SLGS), which takes the advantages of both the stereo vision solution and conventional LGS system. The 3D geometry of the object obtained by the stereo cameras is used to guide the scanning galvanometers for 3D-shape-adjusted laser processing. In order to achieve precise visual-servoed laser fabrication, these two independent components are integrated through a system calibration method using plastic thin film target. The flexibility of SLGS has been experimentally demonstrated by cutting duck feathers for badminton shuttle manufacture.

  2. Coherence in ultrafast laser-induced periodic surface structures

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Colombier, Jean-Philippe; Li, Chen; Faure, Nicolas; Cheng, Guanghua; Stoian, Razvan

    2015-11-01

    Ultrafast laser irradiation can trigger anisotropically structured nanoscaled gratinglike arrangements of matter, the laser-induced periodic surface structures (LIPSSs). We demonstrate here that the formation of LIPSS is intrinsically related to the coherence of the laser field. Employing several test materials that allow large optical excursions, we observe the effect of randomizing spatial phase in generating finite domains of ripples. Using three-dimensional finite-difference time-domain methods, we evaluate energy deposition patterns below a material's rough surface and show that modulated pattern, i.e., a spatially ordered electromagnetic solution, results from the coherent superposition of waves. By separating the field scattered from a surface rough topography from the total field, the inhomogeneous energy absorption problem is reduced to a simple interference equation. We further distinguish the contribution of the scattered near field and scattered far field on various types of inhomogeneous energy absorption features. It is found that the inhomogeneous energy absorption which could trigger the low-spatial-frequency LIPSSs (LSFLs) and high-spatial-frequency LIPSSs (HSFLs) of periodicity Λ >λ /Re(n ˜) are due to coherent superposition between the scattered far field (propagation) and the refracted field, while HSFLs of Λ <λ /Re(n ˜) are triggered by coherent superposition between the scattered near field (evanescent) and the refracted field. This is a general scenario that involves a topography-induced scattering phenomenon and stationary evanescent fields, being applied to two model case materials that exhibit large optical excursions upon excitation (W, Si) and nonplasmonic to plasmonic transitions. We indicate the occurrence of a general light interference phenomenon that does not necessarily involve wavelike surface plasmonic excitation. Finally, we discuss the role of interference field and scattered field on the enhancement of LIPSSs by

  3. Coherent communication link using diode-pumped lasers

    NASA Technical Reports Server (NTRS)

    Kane, Thomas J.; Wallace, Richard W.

    1989-01-01

    Work toward developing a diffraction limited, single frequency, modulated transmitter suitable for coherent optical communication or direct detection communication is discussed. Diode pumped, monolithic Nd:YAG nonplanar ring oscillators were used as the carrier beam. An external modulation technique which can handle high optical powers, has moderate modulation voltage, and which can reach modulation rates of 1 GHz was invented. Semiconductor laser pumped solid-state lasers which have high output power (0.5 Watt) and which oscillate at a single frequency, in a diffraction limited beam, at the wavelength of 1.06 microns were built. A technique for phase modulating the laser output by 180 degrees with a 40-volt peak to peak driving voltage is demonstrated. This technique can be adapted for amplitude modulation of 100 percent with the same voltage. This technique makes use of a resonant bulk modulator, so it does not have the power handling limitations of guided wave modulators.

  4. Coherent laser radar at 1.06 micron using Nd:YAG lasers

    NASA Technical Reports Server (NTRS)

    Kane, Thomas J.; Kozlovsky, W. J.; Byer, Robert L.; Byvik, Charles E.

    1987-01-01

    A coherent laser radar system operating at the 1.06 micron Nd:YAG laser wavelength has been built and operated. A laser-diode-pumped monolithic ring laser served as the master oscillator. A single flash-lamp-pumped zigzag slab amplified the oscillator output to a power of 2.3 kW. Single-mode optical fiber was used to collect and mix the return signal with the local-oscillator output. Signals from clouds at a range of 2.7 km and from atmospheric aerosols at a range of 600 m were detected.

  5. Influence of laser coherence on reference-matched laser Doppler velocimetry.

    PubMed

    Beuth, Thorsten; Fox, Maik; Stork, Wilhelm

    2016-03-10

    The probe length is investigated under the influence of the coherence length of Gaussian and Lorentzian spectra for the case that the focal point and the point of highest interference are matched in a strongly focused laser Doppler velocimetry setup (LDV). Isosurfaces of a -3  dB drop of the intensity maximum are estimated and suggested as an alternative, comprehensible way to define probe volumes. In the end, the equations are applied for an exemplary lidar setup to show the reduction of requirements for the coherence length of the laser source in comparison to unmatched cases.

  6. End-to-end laser radar range code for coherent cw lasers

    NASA Astrophysics Data System (ADS)

    Yoder, M. John; Seliverstov, Dima

    1996-06-01

    A user friendly modular computer code is described for CW coherent laser radar which includes all relevant physical effects needed to evaluate the probability of detection versus time after launch for ballistic missiles or other targets of interest. The beginning point of the code is the conventional laser radar range equation. Atmospheric attenuation is determined from an integral FASCODE calculation, and the laser radar range equation is solved for a curved-earth geometry including free air turbulence induced beam spreading. Several different atmospheric turbulence models are selectable. Target cross-sections can be input into the code as a function of aspect angle Coherence time and transverse coherence length limits are included in the code. Beam jitter effects are also calculated. The carrier-to-noise ratio is calculated including all of these (complicated) variables and degradations. The code then calculates the probability of detection of the target as a function of time using incoherent integration of coherent sub-pulses. The governing equations and practical results are presented for detection and tracking of long range theater ballistic missiles from airborne surveillance platforms. The use of CW lasers requires increased measurement times compared to pulsed lasers and results in an averaging of the target fading statistics.

  7. Study on welded seam recognition using circular laser vision sensor

    NASA Astrophysics Data System (ADS)

    Xu, Peiquan; Tang, Xinhua; Na, Ri; Yao, Shun

    2007-06-01

    A novel visual robotic arc welding system based on circular laser vision sensor is developed. After image de-noising, image segmentation, and image thinning, the relation of depth value of workpiece and off-axis angle 'gamma', three-dimensional (3D) calculation, and seam tracking experiments are carried out. Finally, the error for seam tracking system is analyzed. The results show that 1) 3D information can be obtained using the proposed visual robotic arc welding system and the real-time seam tracking is realized; 2) the seam tracking error is small enough for gas tungsten arc welding (GTAW) process, and this system can be used for seam location and seam tracking or seam finder.

  8. Combined Endoscopic Optical Coherence Tomography and Laser Induced Fluorescence

    NASA Astrophysics Data System (ADS)

    Barton, Jennifer K.; Tumlinson, Alexandre R.; Utzinger, Urs

    Optical coherence tomography (OCT) and laser-induced fluorescence (LIF) are promising modalities for tissue characterization in human patients and animal models. OCT detects coherently backscattered light, whereas LIF detects fluorescence emission of endogenous biochemicals, such as reduced nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FAD), collagen, and fluorescent proteins, or exogenous substances such as cyanine dyes. Given the complementary mechanisms of contrast for OCT and LIF, the combination of the two modalities could potentially provide more sensitive and specific detection of disease than either modality alone. Sample probes for both OCT and LIF can be implemented using small diameter optical fibers, suggesting a particular synergy for endoscopic applications. In this chapter, the mechanisms of contrast and diagnostic capability for both OCT and LIF are briefly examined. Evidence of complementary capability is described. Example published combined OCT-LIF systems are reviewed, one successful commercial instrument is discussed, and example applications are provided.

  9. Detecting Topological Defect Dark Matter Using Coherent Laser Ranging System.

    PubMed

    Yang, Wanpeng; Leng, Jianxiao; Zhang, Shuangyou; Zhao, Jianye

    2016-07-08

    In the last few decades, optical frequency combs with high intensity, broad optical bandwidth, and directly traceable discrete wavelengths have triggered rapid developments in distance metrology. However, optical frequency combs to date have been limited to determine the absolute distance to an object (such as satellite missions). We propose a scheme for the detection of topological defect dark matter using a coherent laser ranging system composed of dual-combs and an optical clock via nongravitational signatures. The dark matter field, which comprises a defect, may interact with standard model particles, including quarks and photons, resulting in the alteration of their masses. Thus, a topological defect may function as a dielectric material with a distinctive frequency-depend index of refraction, which would cause the time delay of a periodic extraterrestrial or terrestrial light. When a topological defect passes through the Earth, the optical path of long-distance vacuum path is altered, this change in optical path can be detected through the coherent laser ranging system. Compared to continuous wavelength(cw) laser interferometry methods, dual-comb interferometry in our scheme excludes systematic misjudgement by measuring the absolute optical path length.

  10. Detecting Topological Defect Dark Matter Using Coherent Laser Ranging System

    PubMed Central

    Yang, Wanpeng; Leng, Jianxiao; Zhang, Shuangyou; Zhao, Jianye

    2016-01-01

    In the last few decades, optical frequency combs with high intensity, broad optical bandwidth, and directly traceable discrete wavelengths have triggered rapid developments in distance metrology. However, optical frequency combs to date have been limited to determine the absolute distance to an object (such as satellite missions). We propose a scheme for the detection of topological defect dark matter using a coherent laser ranging system composed of dual-combs and an optical clock via nongravitational signatures. The dark matter field, which comprises a defect, may interact with standard model particles, including quarks and photons, resulting in the alteration of their masses. Thus, a topological defect may function as a dielectric material with a distinctive frequency-depend index of refraction, which would cause the time delay of a periodic extraterrestrial or terrestrial light. When a topological defect passes through the Earth, the optical path of long-distance vacuum path is altered, this change in optical path can be detected through the coherent laser ranging system. Compared to continuous wavelength(cw) laser interferometry methods, dual-comb interferometry in our scheme excludes systematic misjudgement by measuring the absolute optical path length. PMID:27389642

  11. Detecting Topological Defect Dark Matter Using Coherent Laser Ranging System

    NASA Astrophysics Data System (ADS)

    Yang, Wanpeng; Leng, Jianxiao; Zhang, Shuangyou; Zhao, Jianye

    2016-07-01

    In the last few decades, optical frequency combs with high intensity, broad optical bandwidth, and directly traceable discrete wavelengths have triggered rapid developments in distance metrology. However, optical frequency combs to date have been limited to determine the absolute distance to an object (such as satellite missions). We propose a scheme for the detection of topological defect dark matter using a coherent laser ranging system composed of dual-combs and an optical clock via nongravitational signatures. The dark matter field, which comprises a defect, may interact with standard model particles, including quarks and photons, resulting in the alteration of their masses. Thus, a topological defect may function as a dielectric material with a distinctive frequency-depend index of refraction, which would cause the time delay of a periodic extraterrestrial or terrestrial light. When a topological defect passes through the Earth, the optical path of long-distance vacuum path is altered, this change in optical path can be detected through the coherent laser ranging system. Compared to continuous wavelength(cw) laser interferometry methods, dual-comb interferometry in our scheme excludes systematic misjudgement by measuring the absolute optical path length.

  12. Potential for coherent Doppler wind velocity lidar using neodymium lasers

    NASA Technical Reports Server (NTRS)

    Kane, T. J.; Byer, R. L.; Zhou, B.

    1984-01-01

    Existing techniques for the frequency stabilization of Nd:YAG lasers operating at 1.06 micron, and the high-gain amplification of radiation at that wavelength, make possible the construction of a coherent Doppler wind velocity lidar using Nd:YAG. Velocity accuracy and range resolution are better at 1.06 micron than at 10.6 microns at the same level of the SNR. Backscatter from the atmosphere at 1.06 micron is greater than that at 10.6 microns by about 2 orders of magnitude, but the quantum-limited noise is higher by 100 also. Near-field attenuation and turbulent effects are more severe at 1.06 micron. In some configurations and environments, the 1.06-micron wavelength may be the better choice, and there may be technological advantages favoring the use of solid-state lasers in satellite systems.

  13. Integrated scanning laser ophthalmoscopy and optical coherence tomography for quantitative multimodal imaging of retinal degeneration and autofluorescence

    NASA Astrophysics Data System (ADS)

    Issaei, Ali; Szczygiel, Lukasz; Hossein-Javaheri, Nima; Young, Mei; Molday, L. L.; Molday, R. S.; Sarunic, M. V.

    2011-03-01

    Scanning Laser Ophthalmoscopy (SLO) and Coherence Tomography (OCT) are complimentary retinal imaging modalities. Integration of SLO and OCT allows for both fluorescent detection and depth- resolved structural imaging of the retinal cell layers to be performed in-vivo. System customization is required to image rodents used in medical research by vision scientists. We are investigating multimodal SLO/OCT imaging of a rodent model of Stargardt's Macular Dystrophy which is characterized by retinal degeneration and accumulation of toxic autofluorescent lipofuscin deposits. Our new findings demonstrate the ability to track fundus autofluorescence and retinal degeneration concurrently.

  14. Speckle phase noise in coherent laser ranging: fundamental precision limitations.

    PubMed

    Baumann, Esther; Deschênes, Jean-Daniel; Giorgetta, Fabrizio R; Swann, William C; Coddington, Ian; Newbury, Nathan R

    2014-08-15

    Frequency-modulated continuous-wave laser detection and ranging (FMCW LADAR) measures the range to a surface through coherent detection of the backscattered light from a frequency-swept laser source. The ultimate limit to the range precision of FMCW LADAR, or any coherent LADAR, to a diffusely scattering surface will be determined by the unavoidable speckle phase noise. Here, we demonstrate the two main manifestations of this limit. First, frequency-dependent speckle phase noise leads to a non-Gaussian range distribution having outliers that approach the system range resolution, regardless of the signal-to-noise ratio. These outliers are reduced only through improved range resolution (i.e., higher optical bandwidths). Second, if the range is measured during a continuous lateral scan across a surface, the spatial pattern of speckle phase is converted to frequency noise, which leads to additional excess range uncertainty. We explore these two effects and show that laboratory results agree with analytical expressions and numerical simulations. We also show that at 1 THz optical bandwidth, range precisions below 10 μm are achievable regardless of these effects.

  15. Development of Coherent Laser Radar for Space Situational Awareness Applications

    NASA Astrophysics Data System (ADS)

    Prasad, N.; DiMarcantonio, A.

    2013-09-01

    NASA Langley Research Center (LaRC) is working on an innovative and high performance mobile coherent laser radar (ladar) system known as ExoSPEAR for space situational awareness applications in LEO and beyond. Based on continuously agile pulse doublet technology, the 100 W, nanosecond class, near-IR laser based coherent ladar is being developed for short dwell time measurements of resident space objects (RSOs). ExoSPEAR system is designed to provide rapid and precision tracking of RSOs over very long ranges. The goal is to demonstrate mm-class range resolution, mm/s class velocity resolution and microrad angular resolution with significantly reduced error-covariance in track accuracy. Precise orbit determination would help in advancing functionality of early warning systems for tracking uncooperative targets for planetary protection applications. Furthermore, improvements in resolution of micromotion measurements would enhance our understanding of astrodymanical properties of resident space objects. In this paper, salient features of the evolution and current experimental status of ExoSPEAR ladar architecture will be discussed. Performance simulations illustrating the dependence of range and velocity precision in LEO orbits on ladar power aperture product will be presented. Estimated limits on detectable optical cross sections of RSOs in LEO orbits will be analyzed.

  16. Coherent Laser Instrument Would Measure Range and Velocity

    NASA Technical Reports Server (NTRS)

    Chang, Daniel; Cardell, Greg; San Martin, Alejandro; Spiers, Gary

    2005-01-01

    A proposed instrument would project a narrow laser beam that would be frequency-modulated with a pseudorandom noise (PN) code for simultaneous measurement of range and velocity along the beam. The instrument performs these functions in a low mass, power, and volume package using a novel combination of established techniques. Originally intended as a low resource- footprint guidance sensor for descent and landing of small spacecraft onto Mars or small bodies (e.g., asteroids), the basic instrument concept also lends itself well to a similar application guiding aircraft (especially, small unmanned aircraft), and to such other applications as ranging of topographical features and measuring velocities of airborne light-scattering particles as wind indicators. Several key features of the instrument s design contribute to its favorable performance and resource-consumption characteristics. A laser beam is intrinsically much narrower (for the same exit aperture telescope or antenna) than a radar beam, eliminating the need to correct for the effect of sloping terrain over the beam width, as is the case with radar. Furthermore, the use of continuous-wave (CW), erbium-doped fiber lasers with excellent spectral purity (narrow line width) permits greater velocity resolution, while reducing the laser s power requirement compared to a more typical pulsed solid-state laser. The use of CW also takes proper advantage of the increased sensitivity of coherent detection, necessary in the first place for direct measurement of velocity using the Doppler effect. However, measuring range with a CW beam requires modulation to "tag" portions of it for time-of-flight determination; typically, the modulation consists of a PN code. A novel element of the instrument s design is the use of frequency modulation (FM) to accomplish both the PN-modulation and the Doppler-bias frequency shift necessary for signed velocity measurements. This permits the use of a single low-power waveguide electrooptic

  17. Compressive sensing optical coherence tomography using randomly accessible lasers

    NASA Astrophysics Data System (ADS)

    Harfouche, Mark; Satyan, Naresh; Vasilyev, Arseny; Yariv, Amnon

    2014-05-01

    We propose and demonstrate a novel a compressive sensing swept source optical coherence tomography (SSOCT) system that enables high speed images to be taken while maintaining the high resolution offered from a large bandwidth sweep. Conventional SSOCT systems sweep the optical frequency of a laser ω(t) to determine the depth of the reflectors at a given lateral location. A scatterer located at delay τ appears as a sinusoid cos (ω(t)τ ) at the photodetector. The finite optical chirp rate and the speed of analog to digital and digital to analog converters limit the acquisition rate of an axial scan. The proposed acquisition modality enables much faster image acquisition rates by interrogating the beat signal at randomly selected optical frequencies while preserving resolution and depth of field. The system utilizes a randomly accessible laser, a modulated grating Y-branch laser, to sample the interference pattern from a scene at randomly selected optical frequencies over an optical bandwidth of 5 THz , corresponding to a resolution of 30 μm in air. The depth profile is then reconstructed using an l1 minimization algorithm with a LASSO constraint. Signal-dependent noise sources, shot noise and phase noise, are analyzed and taken into consideration during the recovery. Redundant dictionaries are used to improve the reconstruction of the depth profile. A compression by a factor of 10 for sparse targets up to a depth of 15 mm in noisy environments is shown.

  18. Laser writing of coherent colour centres in diamond

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Chen; Salter, Patrick S.; Knauer, Sebastian; Weng, Laiyi; Frangeskou, Angelo C.; Stephen, Colin J.; Ishmael, Shazeaa N.; Dolan, Philip R.; Johnson, Sam; Green, Ben L.; Morley, Gavin W.; Newton, Mark E.; Rarity, John G.; Booth, Martin J.; Smith, Jason M.

    2016-12-01

    Optically active point defects in crystals have gained widespread attention as photonic systems that could be applied in quantum information technologies. However, challenges remain in the placing of individual defects at desired locations, an essential element of device fabrication. Here we report the controlled generation of single negatively charged nitrogen-vacancy (NV‑) centres in diamond using laser writing. Aberration correction in the writing optics allows precise positioning of the vacancies within the diamond crystal, and subsequent annealing produces single NV‑ centres with a probability of success of up to 45 ± 15%, located within about 200 nm of the desired position in the transverse plane. Selected NV‑ centres display stable, coherent optical transitions at cryogenic temperatures, a prerequisite for the creation of distributed quantum networks of solid-state qubits. The results illustrate the potential of laser writing as a new tool for defect engineering in quantum technologies, and extend laser processing to the single-defect domain.

  19. Coherent laser excitation of Ba-137 and Ba-138

    NASA Technical Reports Server (NTRS)

    Lam, Kai-Shue

    1992-01-01

    Computations are carried out for the 1S(6s2)-1P(6s,6p) coherent laser excitation of Ba-137 and Ba-138 in a magnetic field. Results are presented for both the steady-state and time-dependent excited-state populations of the Zeeman-split magnetic sublevels. The quantum-statistical Liouville-equation approach (for the reduced density matrix) is compared to the rate-equations approach. Significant differences are found between these, due to the interference between strongly overlapping lines (especially for Ba-137). The time-evolution profiles indicate that the Ba-137 transient time is much longer than that of Ba-138.

  20. Lasers for coherent optical satellite links with large dynamics.

    PubMed

    Chiodo, Nicola; Djerroud, Khelifa; Acef, Ouali; Clairon, André; Wolf, Peter

    2013-10-20

    We present the experimental realization of a laser system for ground-to-satellite optical Doppler ranging at the atmospheric turbulence limit. Such a system needs to display good frequency stability (a few parts in 10-14) while allowing large and well-controlled frequency sweeps of ±12  GHz at rates exceeding 100  MHz/s. Furthermore it needs to be sufficiently compact and robust for transportation to different astronomical observation sites, where it is to be interfaced with satellite ranging telescopes. We demonstrate that our system fulfills those requirements and should therefore allow operation of ground to low Earth orbit satellite coherent optical links limited only by atmospheric turbulence.

  1. Three-dimensional microscope vision system based on micro laser line scanning and adaptive genetic algorithms

    NASA Astrophysics Data System (ADS)

    Apolinar, J.; Rodríguez, Muñoz

    2017-02-01

    A microscope vision system to retrieve small metallic surface via micro laser line scanning and genetic algorithms is presented. In this technique, a 36 μm laser line is projected on the metallic surface through a laser diode head, which is placed to a small distance away from the target. The micro laser line is captured by a CCD camera, which is attached to the microscope. The surface topography is computed by triangulation by means of the line position and microscope vision parameters. The calibration of the microscope vision system is carried out by an adaptive genetic algorithm based on the line position. In this algorithm, an objective function is constructed from the microscope geometry to determine the microscope vision parameters. Also, the genetic algorithm provides the search space to calculate the microscope vision parameters with high accuracy in fast form. This procedure avoids errors produced by the missing of references and physical measurements, which are employed by the traditional microscope vision systems. The contribution of the proposed system is corroborated by an evaluation via accuracy and speed of the traditional microscope vision systems, which retrieve micro-scale surface topography.

  2. Effect of laser radiation wavelength and reepithelization process on optical quality of eye cornea after laser correction of vision

    SciTech Connect

    Kitai, M S; Semchishen, A V; Semchishen, V A

    2015-10-31

    The optical quality of the eye cornea surface after performing the laser vision correction essentially depends on the characteristic roughness scale (CRS) of the ablated surface, which is mainly determined by the absorption coefficient of the cornea at the laser wavelength. Thus, in the case of using an excimer ArF laser (λ = 193 nm) the absorption coefficient is equal to 39000 cm{sup -1}, the darkening by the dissociation products takes place, and the depth of the roughness relief can be as large as 0.23 mm. Under irradiation with the Er : YAG laser (λ = 2940 nm) the clearing is observed due to the rupture of hydrogen bonds in water, and the relief depth exceeds 1 μm. It is shown that the process of reepithelization that occurs after performing the laser vision correction leads to the improvement of the optical quality of the cornea surface. (interaction of laser radiation with matter)

  3. Mutual injection phase locking coherent combination of solid-state lasers based on corner cube.

    PubMed

    Cheng, Yong; Liu, Xu; Wan, Qiang; Zhu, Mengzhen; Mi, Chaowei; Tan, Chaoyong; Wei, Shangfang; Chen, Xia

    2013-12-01

    Coherent beam combination is an effective way to develop high-power lasers with high beam quality and high brightness. Coherent combination of six solid-state lasers based on the technique of mutual injection phase locking by using the natural coherent combination property of corner cube is first investigated. The coherent combination with 15.3 J of output energy, 1.7 mrad of divergent angle is obtained, and the combining efficiency is as high as 95.6% at 10 Hz and 85 A. The far-field profile is flattened protuberance.

  4. Study on phase-locked coherence of evanescent wave coupling in solid-state laser

    NASA Astrophysics Data System (ADS)

    Chen, Yong; Liu, Xu; Zhu, Mengzhen; Lu, Changyong; Lu, Yimin; Tan, Caoyong; Wei, Shangfang

    2016-01-01

    The mechanism and characteristics of evanescent-wave coupling in solid-state laser is analyzed theoretically and experimentally. The results shown that self-organized phase locking between laser modes can be realized by evanescentwave coupling in solid-state laser. Based on "mutual injection and evanescent wave" characteristics of corner-cube prism, the paper reveals that far-field output of corner-cube laser is the inner reason and mechanism of coherent combining distribution by theory of evanescent wave and its coherence is better than plane parallel resonator. And "mutually coupled phase locking of six lasers based cube-corner resonator" scheme is proposed on this basis.

  5. Optical coherence tomography-guided laser microsurgery for blood coagulation with continuous-wave laser diode

    NASA Astrophysics Data System (ADS)

    Chang, Feng-Yu; Tsai, Meng-Tsan; Wang, Zu-Yi; Chi, Chun-Kai; Lee, Cheng-Kuang; Yang, Chih-Hsun; Chan, Ming-Che; Lee, Ya-Ju

    2015-11-01

    Blood coagulation is the clotting and subsequent dissolution of the clot following repair to the damaged tissue. However, inducing blood coagulation is difficult for some patients with homeostasis dysfunction or during surgery. In this study, we proposed a method to develop an integrated system that combines optical coherence tomography (OCT) and laser microsurgery for blood coagulation. Also, an algorithm for positioning of the treatment location from OCT images was developed. With OCT scanning, 2D/3D OCT images and angiography of tissue can be obtained simultaneously, enabling to noninvasively reconstruct the morphological and microvascular structures for real-time monitoring of changes in biological tissues during laser microsurgery. Instead of high-cost pulsed lasers, continuous-wave laser diodes (CW-LDs) with the central wavelengths of 450 nm and 532 nm are used for blood coagulation, corresponding to higher absorption coefficients of oxyhemoglobin and deoxyhemoglobin. Experimental results showed that the location of laser exposure can be accurately controlled with the proposed approach of imaging-based feedback positioning. Moreover, blood coagulation can be efficiently induced by CW-LDs and the coagulation process can be monitored in real-time with OCT. This technology enables to potentially provide accurate positioning for laser microsurgery and control the laser exposure to avoid extra damage by real-time OCT imaging.

  6. Optical coherence tomography-guided laser microsurgery for blood coagulation with continuous-wave laser diode.

    PubMed

    Chang, Feng-Yu; Tsai, Meng-Tsan; Wang, Zu-Yi; Chi, Chun-Kai; Lee, Cheng-Kuang; Yang, Chih-Hsun; Chan, Ming-Che; Lee, Ya-Ju

    2015-11-16

    Blood coagulation is the clotting and subsequent dissolution of the clot following repair to the damaged tissue. However, inducing blood coagulation is difficult for some patients with homeostasis dysfunction or during surgery. In this study, we proposed a method to develop an integrated system that combines optical coherence tomography (OCT) and laser microsurgery for blood coagulation. Also, an algorithm for positioning of the treatment location from OCT images was developed. With OCT scanning, 2D/3D OCT images and angiography of tissue can be obtained simultaneously, enabling to noninvasively reconstruct the morphological and microvascular structures for real-time monitoring of changes in biological tissues during laser microsurgery. Instead of high-cost pulsed lasers, continuous-wave laser diodes (CW-LDs) with the central wavelengths of 450 nm and 532 nm are used for blood coagulation, corresponding to higher absorption coefficients of oxyhemoglobin and deoxyhemoglobin. Experimental results showed that the location of laser exposure can be accurately controlled with the proposed approach of imaging-based feedback positioning. Moreover, blood coagulation can be efficiently induced by CW-LDs and the coagulation process can be monitored in real-time with OCT. This technology enables to potentially provide accurate positioning for laser microsurgery and control the laser exposure to avoid extra damage by real-time OCT imaging.

  7. Optical coherence tomography-guided laser microsurgery for blood coagulation with continuous-wave laser diode

    PubMed Central

    Chang, Feng-Yu; Tsai, Meng-Tsan; Wang, Zu-Yi; Chi, Chun-Kai; Lee, Cheng-Kuang; Yang, Chih-Hsun; Chan, Ming-Che; Lee, Ya-Ju

    2015-01-01

    Blood coagulation is the clotting and subsequent dissolution of the clot following repair to the damaged tissue. However, inducing blood coagulation is difficult for some patients with homeostasis dysfunction or during surgery. In this study, we proposed a method to develop an integrated system that combines optical coherence tomography (OCT) and laser microsurgery for blood coagulation. Also, an algorithm for positioning of the treatment location from OCT images was developed. With OCT scanning, 2D/3D OCT images and angiography of tissue can be obtained simultaneously, enabling to noninvasively reconstruct the morphological and microvascular structures for real-time monitoring of changes in biological tissues during laser microsurgery. Instead of high-cost pulsed lasers, continuous-wave laser diodes (CW-LDs) with the central wavelengths of 450 nm and 532 nm are used for blood coagulation, corresponding to higher absorption coefficients of oxyhemoglobin and deoxyhemoglobin. Experimental results showed that the location of laser exposure can be accurately controlled with the proposed approach of imaging-based feedback positioning. Moreover, blood coagulation can be efficiently induced by CW-LDs and the coagulation process can be monitored in real-time with OCT. This technology enables to potentially provide accurate positioning for laser microsurgery and control the laser exposure to avoid extra damage by real-time OCT imaging. PMID:26568136

  8. Human color vision deficits induced by accidental laser exposure and potential for long-term recovery

    NASA Astrophysics Data System (ADS)

    Zwick, Harry; Lund, Brian J.; Brown, Jeremiah, Jr.; Stuck, Bruce E.; Loveday, J.

    2003-06-01

    Purpose: To evaluate long term deficits in human color discrimination induced by accidental laser macular damage and assess potential for recovery of color vision deficits. Methods: Nine laser accident cases (Q-switched Neodymium) presenting initially with confined or vitreous macular hemorrhage were evaluated with the Farnsworth-Munsell 100 Hue test within 2 days to 3 months post exposure. Both total as well as partial errors in the blue/yellow (B/Y) and red/green (R/G) regions were assessed. Independent assessment of axis orientation and complexity were obtained via a Fourier series expansion of error scores. Comparisons of both total and partial B/Y and R/G errors were made with age matched normal subjects, idiopathic and juvenile onset macular holes. Confocal Scanning Laser Ophthalmoscopy and Optical Coherence Tomography characterized the presence of retinal traction, intraretinal scar, macular thickness and macular hole formation. Results: Comparison of exposed and non-exposed age matched individuals were significant (P<.001) for both total and partial errors. In four cases where macular injury ranged from mild scar to macular hole, color discrimination errors achieved normal levels in 1 to 12 months post exposure. A mild tritan axis, dominant B/Y ("blue/yellow") errors, and retinal traction were observed in a macular hole case. At 12 months post exposure, traction about the hole disappeared, and total and partial errors were normal. Where damage involved a greater degree of scarring, retinal traction and multiple injury sites, long term recovery of total and partial error recovery was retarded with complex axis makeup. Single exposures in the paramacula produced tritan axes, while multiple exposures within and external to the macula increased total and partial R/G ("red/green") error scores. Total errors increased when paramacular hole enlargement induced macular traction. Such hole formation produced significant increases in total errors, complex axis

  9. On-chip coherent combining of angled-grating diode lasers toward bar-scale single-mode lasers.

    PubMed

    Zhao, Yunsong; Zhu, Lin

    2012-03-12

    Single mode operation of broad-area diode lasers, which is the key to obtain high power, high brightness sources, is difficult due to highly nonlinear materials and strong coupling between gain and index. Conventional broad-area lasers usually operate with multiple modes and have poor beam quality. Laser bars usually consist of incoherently combined broad-area single emitters placed side by side. In this article, we have demonstrated a novel integrated laser architecture in which Bragg diffraction is used to realize simultaneous modal control and coherent combining of broad-area diode lasers. Our experimental results show that two 100 μm wide, 1.3mm long InP broad-area lasers provide near-diffraction-limited output beam and are coherently combined at the same time without any external optical components. Furthermore, our design can be expanded to a coherently combined broad-area laser array that turns a laser bar into a coherent single mode laser with diffraction-limited beam quality.

  10. Observation of coherent effects using a mode-locked rubidium laser

    NASA Astrophysics Data System (ADS)

    Zhang, Aihua; Sautenkov, Vladimir A.; Rostovtsev, Yuri V.; Welch, George R.

    2017-02-01

    We study a diode-pumped alkaline rubidium laser operating at the D 1-line transition. The mode-locked regime of laser operation using an active technique inside the laser cavity has been demonstrated. We have also experimentally shown that the mode-locked laser radiation can be used to observe coherent effects: the electromagnetically induced transparency and the nonlinear Faraday rotation in Rb vapor.

  11. Experimental demonstration of passive coherent combining of fiber lasers by phase contrast filtering.

    PubMed

    Jeux, François; Desfarges-Berthelemot, Agnès; Kermène, Vincent; Barthelemy, Alain

    2012-12-17

    We report experiments on a new laser architecture involving phase contrast filtering to coherently combine an array of fiber lasers. We demonstrate that the new technique yields a more stable phase-locking than standard methods using only amplitude filtering. A spectral analysis of the output beams shows that the new scheme generates more resonant frequencies common to the coupled lasers. This property can enhance the combining efficiency when the number of lasers to be coupled is large.

  12. Quantum coherence in semiconductor nanostructures for improved lasers and detectors.

    SciTech Connect

    Chow, Weng Wah Dr.; Lyo, Sungkwun Kenneth; Cederberg, Jeffrey George; Modine, Normand Arthur; Biefeld, Robert Malcolm

    2006-02-01

    The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.

  13. Phase-locked laser system for use in atomic coherence experiments.

    PubMed

    Marino, Alberto M; Stroud, C R

    2008-01-01

    We describe a phase-coherent laser system designed for use in experiments involving coherently prepared atomic media. We implement a simple technique based on a sample-and-hold circuit together with a reset of the integrating electronics that makes it possible to scan continuously the relative frequency between the lasers of over tens of gigahertz while keeping them phase locked. The system consists of three external-cavity diode lasers operating around 795 nm. A low-power laser serves as a frequency reference for two high-power lasers which are phased locked with an optical phase-locked loop. We measured the residual phase noise of the system to be less than 0.04 rad(2). In order to show the application of the system towards atomic coherence experiments, we used it to implement electromagnetically induced transparency in a rubidium vapor cell and obtained a reduction in the absorption coefficient of 92%.

  14. Transverse spatial coherence of a transient nickellike silver soft-x-ray laser pumped by a single picosecond laser pulse.

    PubMed

    Lucianetti, A; Janulewicz, K A; Kroemer, R; Priebe, G; Tümmler, J; Sandner, W; Nickles, P V; Redkorechev, V I

    2004-04-15

    The degree of spatial coherence in the direction perpendicular to the target surface is reported for a transient nickellike silver x-ray laser at 13.9 nm. An x-ray laser plasma column was produced by irradiating a slab silver target with a single shaped picosecond laser pulse with energy less than 3 J. Young's double-slit method was applied to measure the fringe visibility as a function of the slit separation for different target lengths. The diameter of the equivalent incoherent source and the coherence radius of the output radiation were determined as well.

  15. Coherence and shot-to-shot spectral fluctuations in noise-like ultrafast fiber lasers.

    PubMed

    Runge, Antoine F J; Aguergaray, Claude; Broderick, Neil G R; Erkintalo, Miro

    2013-11-01

    We report on experimental studies of coherence and fluctuations in noise-like pulse trains generated by ultrafast fiber oscillators. By measuring the degree of first-order coherence using a Young's-type interference experiment, we prove the lack of phase coherence across the seemingly regular array of pulses. We further quantify the pulse-to-pulse fluctuations by recording the single-shot spectra of the megahertz pulse train, and experimentally demonstrate the existence of spectral fluctuations that remain unresolved in conventional time-averaged ensemble measurements. Phase incoherence and spectral fluctuations are contrasted with quantified coherence and spectral stability when the laser is soliton mode-locked.

  16. Effect of phase fluctuations on entanglement generation in a correlated emission laser with injected coherence

    NASA Astrophysics Data System (ADS)

    Qamar, Sajid; Qamar, Shahid; Suhail Zubairy, M.

    2010-03-01

    This proposal investigates the influence of the phase fluctuations on the time evolution of entanglement generation in a three-level correlated emission laser (CEL) with injected coherence. The atoms are injected in the cavity with an initial partial coherent superposition of the upper and lower levels. The corresponding phase φ is considered to be randomly distributed around some fixed phase φ0. The fluctuations in phase φ modifies the coherence between the two corresponding atomic levels. Therefore, we observe strong influence of phase fluctuations on the entanglement generation using the injected coherence CEL system.

  17. OCT imaging with temporal dispersion induced intense and short coherence laser source

    NASA Astrophysics Data System (ADS)

    Manna, Suman K.; le Gall, Stephen; Li, Guoqiang

    2016-10-01

    Lower coherence length and higher intensity are two indispensable requirements on the light source for high resolution and large penetration depth OCT imaging. While tremendous interest is being paid on engineering various laser sources to enlarge their bandwidth and hence lowering the coherence length, here we demonstrate another approach by employing strong temporal dispersion onto the existing laser source. Cholesteric liquid crystal (CLC) cells with suitable dispersive slope at the edge of 1-D organic photonic band gap have been designed to provide maximum reduction in coherence volume while maintaining the intensity higher than 50%. As an example, the coherence length of a multimode He-Ne laser is reduced by more than 730 times.

  18. Single laser beam of spatial coherence from an array of GaAs lasers - Free-running mode

    NASA Technical Reports Server (NTRS)

    Philipp-Rutz, E. M.

    1975-01-01

    Spatially coherent radiation from a monolithic array of three GaAs lasers in a free-running mode is reported. The lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent-beam formation makes use of the Fourier-transformation property of the internal lenses. Transverse mode control is accomplished by a spatial filter. The optical cavity is similar to that used for the phase-controlled mode of spatially coherent-beam formation; only the spatial filters are different. In the far field (when restored by an external lens), the intensities of the lasers in the array are concentrated in a single laser beam of spatial coherence, without any grating lobes. The far-field distribution of the laser array in the free-running mode differs significantly from the interference pattern of the phase-controlled mode. The modulation characteristics of the optical waveforms of the two modes are also quite different because modulation is related to the interaction of the spatial filter with the longitudinal modes of the laser array within the optical cavity. The modulation of the optical waveform of the free-running mode is nonperiodic, confirming that the fluctuations of the optical fields of the lasers are random.

  19. Development of high coherence high power 193nm laser

    NASA Astrophysics Data System (ADS)

    Tanaka, Satoshi; Arakawa, Masaki; Fuchimukai, Atsushi; Sasaki, Yoichi; Onose, Takashi; Kamba, Yasuhiro; Igarashi, Hironori; Qu, Chen; Tamiya, Mitsuru; Oizumi, Hiroaki; Ito, Shinji; Kakizaki, Koji; Xuan, Hongwen; Zhao, Zhigang; Kobayashi, Yohei; Mizoguchi, Hakaru

    2016-03-01

    We have been developing a hybrid 193 nm ArF laser system that consists of a solid state seeding laser and an ArF excimer laser amplifier for power-boosting. The solid state laser consists of an Yb-fiber-solid hybrid laser system and an Er-fiber laser system as fundamentals, and one LBO and three CLBO crystals for frequency conversion. In an ArF power amplifier, the seed laser passes through the ArF gain media three times, and an average power of 110 W is obtained. As a demonstration of the potential applications of the laser, an interference exposure test is performed.

  20. Extended coherence length Fourier domain mode locked lasers at 1310 nm.

    PubMed

    Adler, Desmond C; Wieser, Wolfgang; Trepanier, Francois; Schmitt, Joseph M; Huber, Robert A

    2011-10-10

    Fourier domain mode locked (FDML) lasers are excellent tunable laser sources for frequency domain optical coherence tomography (FD-OCT) systems due to their combination of high sweep rates, large tuning ranges, and high output powers. However, conventional FDML lasers provide coherence lengths of only 4-10 mm, limiting their use in demanding applications such as intravascular OCT where coherence lengths of >20 mm are required for optimal imaging of large blood vessels. Furthermore, like most swept lasers, conventional FDML lasers produce only one useable sweep direction per tunable filter drive cycle, halving the effective sweep rate of the laser compared to the filter drive frequency. Here, we demonstrate a new class of FDML laser incorporating broadband dispersion compensation near 1310 nm. Elimination of chromatic dispersion in the FDML cavity results in the generation of forward (short to long wavelength) and backward (long to short wavelength) sweeps with substantially identical properties and coherence lengths of >21 mm. This advance enables long-range, high-speed FD-OCT imaging without the need for optical buffering stages, significantly reducing laser cost and complexity.

  1. DEVELOPMENT OF NEW MID-INFRARED ULTRAFAST LASER SOURCES FOR COMPACT COHERENT X-RAY SOURCES

    SciTech Connect

    Sterling Backus

    2012-05-14

    In this project, we proposed to develop laser based mid-infrared lasers as a potentially robust and reliable source of ultrafast pulses in the mid-infrared region of the spectrum, and to apply this light source to generating bright, coherent, femtosecond-to-attosecond x-ray beams.

  2. Macular Cone Abnormalities in Retinitis Pigmentosa with Preserved Central Vision Using Adaptive Optics Scanning Laser Ophthalmoscopy

    PubMed Central

    Makiyama, Yukiko; Ooto, Sotaro; Hangai, Masanori; Takayama, Kohei; Uji, Akihito; Oishi, Akio; Ogino, Ken; Nakagawa, Satoko; Yoshimura, Nagahisa

    2013-01-01

    Purpose To assess macular photoreceptor abnormalities in eyes with retinitis pigmentosa (RP) with preserved central vision using adaptive optics scanning laser ophthalmoscopy (AO-SLO). Methods Fourteen eyes of 14 patients with RP (best-corrected visual acuity 20/20 or better) and 12 eyes of 12 volunteers underwent a full ophthalmologic examination, fundus autofluorescence, spectral-domain optical coherence tomography (SD-OCT), and imaging with a prototype AO-SLO system. Cone density and spatial organization of the cone mosaic were assessed using AO-SLO images. Results In 3 eyes with RP and preserved central vision, cones formed a mostly regular mosaic pattern with small patchy dark areas, and in 10 eyes, the cone mosaic patterns were less regular, and large dark regions with missing cones were apparent. Only one eye with RP demonstrated a normal, regular cone mosaic pattern. In eyes with RP, cone density was significantly lower at 0.5 mm and 1.0 mm from the center of the fovea compared to normal eyes (P<0.001 and 0.021, respectively). At 0.5 mm and 1.0 mm from the center of the fovea, a decreased number of cones had 6 neighbors in eyes with RP (P = 0.002 for both). Greater decrease in cone density was related to disruption of the photoreceptor inner segment (IS) ellipsoid band on SD-OCT images (P = 0.044); however, dark regions were seen on AO-SLO even in areas of continuous IS ellipsoid on SD-OCT. Decreased cone density correlated thinner outer nuclear layer (P = 0.029) and thinner inner segment and outer segment thickness (P = 0.011) on SD-OCT. Conclusions Cone density is decreased and the regularity of the cone mosaic spatial arrangement is disrupted in eyes with RP, even when visual acuity and foveal sensitivity are good. AO-SLO imaging is a sensitive quantitative tool for detecting photoreceptor abnormalities in eyes with RP. PMID:24260224

  3. Low spatial coherence electrically pumped semiconductor laser for speckle-free full-field imaging.

    PubMed

    Redding, Brandon; Cerjan, Alexander; Huang, Xue; Lee, Minjoo Larry; Stone, A Douglas; Choma, Michael A; Cao, Hui

    2015-02-03

    The spatial coherence of laser sources has limited their application to parallel imaging and projection due to coherent artifacts, such as speckle. In contrast, traditional incoherent light sources, such as thermal sources or light emitting diodes (LEDs), provide relatively low power per independent spatial mode. Here, we present a chip-scale, electrically pumped semiconductor laser based on a novel design, demonstrating high power per mode with much lower spatial coherence than conventional laser sources. The laser resonator was fabricated with a chaotic, D-shaped cavity optimized to achieve highly multimode lasing. Lasing occurs simultaneously and independently in ∼1,000 modes, and hence the total emission exhibits very low spatial coherence. Speckle-free full-field imaging is demonstrated using the chaotic cavity laser as the illumination source. The power per mode of the sample illumination is several orders of magnitude higher than that of a LED or thermal light source. Such a compact, low-cost source, which combines the low spatial coherence of a LED with the high spectral radiance of a laser, could enable a wide range of high-speed, full-field imaging and projection applications.

  4. Low spatial coherence electrically pumped semiconductor laser for speckle-free full-field imaging

    PubMed Central

    Redding, Brandon; Cerjan, Alexander; Huang, Xue; Lee, Minjoo Larry; Stone, A. Douglas; Choma, Michael A.; Cao, Hui

    2015-01-01

    The spatial coherence of laser sources has limited their application to parallel imaging and projection due to coherent artifacts, such as speckle. In contrast, traditional incoherent light sources, such as thermal sources or light emitting diodes (LEDs), provide relatively low power per independent spatial mode. Here, we present a chip-scale, electrically pumped semiconductor laser based on a novel design, demonstrating high power per mode with much lower spatial coherence than conventional laser sources. The laser resonator was fabricated with a chaotic, D-shaped cavity optimized to achieve highly multimode lasing. Lasing occurs simultaneously and independently in ∼1,000 modes, and hence the total emission exhibits very low spatial coherence. Speckle-free full-field imaging is demonstrated using the chaotic cavity laser as the illumination source. The power per mode of the sample illumination is several orders of magnitude higher than that of a LED or thermal light source. Such a compact, low-cost source, which combines the low spatial coherence of a LED with the high spectral radiance of a laser, could enable a wide range of high-speed, full-field imaging and projection applications. PMID:25605946

  5. Comparison of the coherence properties of superradiance and laser emission in semiconductor structures

    SciTech Connect

    Vasil'ev, Petr P; Penty, R V; White, I H

    2012-12-31

    The coherence properties of a transient electron - hole state developing during superradiance emission in semiconductor laser structures have been studied experimentally using a Michelson interferometer and Young's classic double-slit configuration. The results demonstrate that, in the lasers studied, the first-order correlation function, which quantifies spatial coherence, approaches unity for superradiant emission and is 0.2 - 0.5 for laser emission. The supercoherence is due to long-range ordering upon the superradiant phase transition. (special issue devoted to the 90th anniversary of n.g. basov)

  6. On-line estimation of laser-drilled hole depth using a machine vision method.

    PubMed

    Ho, Chao-Ching; He, Jun-Jia; Liao, Te-Ying

    2012-01-01

    The paper presents a novel method for monitoring and estimating the depth of a laser-drilled hole using machine vision. Through on-line image acquisition and analysis in laser machining processes, we could simultaneously obtain correlations between the machining processes and analyzed images. Based on the machine vision method, the depths of laser-machined holes could be estimated in real time. Therefore, a low cost on-line inspection system is developed to increase productivity. All of the processing work was performed in air under standard atmospheric conditions and gas assist was used. A correlation between the cumulative size of the laser-induced plasma region and the depth of the hole is presented. The result indicates that the estimated depths of the laser-drilled holes were a linear function of the cumulative plasma size, with a high degree of confidence. This research provides a novel machine vision-based method for estimating the depths of laser-drilled holes in real time.

  7. Strategies for eye positioning after laser-related loss of central vision

    NASA Astrophysics Data System (ADS)

    Bertera, J. H.

    1997-05-01

    Loss of foveal vision from exposure to laser light or retinal disease can seriously impair visual functions like reading and visual search. Central scotomas produce large losses in visually guided performance because central vision has the best visual resolution, compared to more peripheral retina, and is also important in the normal reflexive patten of eye movement. Relatively small central field scotomas can produce significant impairments in visual search if tasks require a high degree of foveal vision such as seeing fine detail or discriminating similar contours or letters. Subjects faced with the task of adapting to the loss of ventral vision sometimes position their eyes in ways which are either asymmetrical, not optimum, or seem to generate abnormal eye movements, even after extensive practice. Discussion includes oculomotor drift, error fixations, hyper-eccentric fixations and remedial eye positioning strategies.

  8. Development of fiber lasers and devices for coherent Raman scattering microscopy

    NASA Astrophysics Data System (ADS)

    Lamb, Erin Stranford

    As ultrafast laser technology has found expanding application in machining, spectroscopy, microscopy, surgery, and numerous other areas, the desire for inexpensive and robust laser sources has grown. Until recently, nonlinear effects in fiber systems due to the tight confinement of the light in the core have limited their performance. However, with advances in managing nonlinearity through pulse propagation physics and the use of large core fibers, the performance of fiber lasers can compete with that of their solid-state counterparts. As specific applications, such as coherent Raman scattering microscopy, emerge that stand to benefit from fiber technology, new performance challenges in areas such as laser noise are anticipated. This thesis studies nonlinear pulse propagation in fiber lasers and fiber parametric devices. Applications of dissipative solitons and self-similar pulse propagation to low-repetition rate oscillators that have the potential to simplify short-pulse amplification schemes will be examined. The rest of this thesis focuses on topics relevant to fiber laser development for coherent Raman scattering microscopy sources. Coherent pulse division and recombination inside the laser cavity will be introduced as an energy-scaling mechanism and demonstrated for a fiber soliton laser. The relative intensity noise properties of mode-locked fiber lasers, with a particular emphasis on normal dispersion lasers, will be explored in simulation and experiment. A fiber optical parametric oscillator will be studied in detail for low noise frequency conversion of picosecond pulses, and its utility for coherent Raman imaging will be demonstrated. Spectral compression of femtosecond pulses is used to generate picosecond pulses to pump this device, and this technique provides a route to future noise reduction in the system. Furthermore, this device forms a multimodal source capable of providing the picosecond pulses for coherent Raman scattering microscopy and the

  9. Long-range measurement of Rayleigh scatter signature beyond laser coherence length based on coherent optical frequency domain reflectometry.

    PubMed

    Ohno, Shingo; Iida, Daisuke; Toge, Kunihiro; Manabe, Tetsuya

    2016-08-22

    Long-range C-OFDR measurement of fiber Rayleigh scatter signature is described. The Rayleigh scatter signature, which is an interference pattern of backscatters from the random refractive indices in fibers, is known to be applicable to fiber identification and temperature or strain sensing by measuring its repeatability and its spectral shift. However, these applications have not been realized at ranges beyond the laser coherence length since laser phase noise degrades its repeatability. This paper proposes and demonstrates a method for analyzing the optical power spectrum of local Rayleigh backscatter to overcome the limitation imposed by laser phase noise. The measurable range and spatial performance are also investigated experimentally with respect to the remaining phase noise and noise reduction by signal averaging with the proposed method. The feasibility of Rayleigh scatter signature measurement for long-range applications is confirmed.

  10. Laser-Pumped Coherent X-Ray FEL

    DTIC Science & Technology

    2008-11-14

    laser field replaces the magnetic wiggler field of a conventional FEL. Depending on the intensity and quality of both the electron beam and pump laser...and Line Width 16 IV. Comparison of Theory with Simulations 17 a) Wiggler based X-Ray FEL 17 b) Laser Pumped X-Ray FEL 18 V. Conclusions 19...FEL) an intense laser field replaces the magnetic wiggler field of a conventional FEL. Depending on the intensity and quality of both the electron

  11. Laser-Camera Vision Sensing for Spacecraft Mobile Robot Navigation

    NASA Technical Reports Server (NTRS)

    Maluf, David A.; Khalil, Ahmad S.; Dorais, Gregory A.; Gawdiak, Yuri

    2002-01-01

    The advent of spacecraft mobile robots-free-flyng sensor platforms and communications devices intended to accompany astronauts or remotely operate on space missions both inside and outside of a spacecraft-has demanded the development of a simple and effective navigation schema. One such system under exploration involves the use of a laser-camera arrangement to predict relative positioning of the mobile robot. By projecting laser beams from the robot, a 3D reference frame can be introduced. Thus, as the robot shifts in position, the position reference frame produced by the laser images is correspondingly altered. Using normalization and camera registration techniques presented in this paper, the relative translation and rotation of the robot in 3D are determined from these reference frame transformations.

  12. Effect of electron heating on femtosecond laser-induced coherent acoustic phonons in noble metals

    NASA Astrophysics Data System (ADS)

    Wang, Jincheng; Guo, Chunlei

    2007-05-01

    We employ a surface plasmon technique to resolve the dynamics of femtosecond-laser-induced coherent acoustic phonons in noble metals. Clear acoustic oscillations are observed in our experiments. We further study the dependence of the initial phase of the oscillations on pump fluence, and we find that the initial phase decreases linearly with pump fluence. Our model calculations show that hot electrons instantaneously excited by femtosecond pulses contribute to the generation of coherent acoustic phonons in metals.

  13. High Power Laser Diode Arrays for 2-Micron Solid State Coherent Lidars Applications

    NASA Technical Reports Server (NTRS)

    Amzajerdian, Farzin; Meadows, Byron; Kavaya, Michael J.; Singh, Upendra; Sudesh, Vikas; Baker, Nathaniel

    2003-01-01

    Laser diode arrays are critical components of any diode-pumped solid state laser systems, constraining their performance and reliability. Laser diode arrays (LDAs) are used as the pump source for energizing the solid state lasing media to generate an intense coherent laser beam with a high spatial and spectral quality. The solid state laser design and the characteristics of its lasing materials define the operating wavelength, pulse duration, and power of the laser diodes. The pump requirements for high pulse energy 2-micron solid state lasers are substantially different from those of more widely used 1-micron lasers and in many aspects more challenging [1]. Furthermore, the reliability and lifetime demanded by many coherent lidar applications, such as global wind profiling from space and long-range clear air turbulence detection from aircraft, are beyond the capability of currently available LDAs. In addition to the need for more reliable LDAs with longer lifetime, further improvement in the operational parameters of high power quasi-cw LDAs, such as electrical efficiency, brightness, and duty cycle, are also necessary for developing cost-effective 2-micron coherent lidar systems for applications that impose stringent size, heat dissipation, and power constraints. Global wind sounding from space is one of such applications, which is the main driver for this work as part of NASA s Laser Risk Reduction Program. This paper discusses the current state of the 792 nm LDA technology and the technology areas being pursued toward improving their performance. The design and development of a unique characterization facility for addressing the specific issues associated with the LDAs for pumping 2-micron coherent lidar transmitters and identifying areas of technological improvement will be described. Finally, the results of measurements to date on various standard laser diode packages, as well as custom-designed packages with potentially longer lifetime, will be reported.

  14. Characterization of coherence-or-power selectable operation of an external-cavity semiconductor diode laser.

    PubMed

    Hyodo, Masaharu; Watanabe, Masayoshi; Kawakami, Akira; Saito, Shingo; Adachi, Masaaki

    2016-12-20

    The properties of the coherence-or-power selectable operation of an external-cavity semiconductor diode laser through the control of intracavity polarization states have been characterized in detail. In our technique, a diffraction grating and a reflector functioned as a polarization-dependent output coupler, such that the portion of light fed back to the gain medium was readily controlled by rotating the intracavity polarization axis, which resulted in the selectable operation of either a high degree of coherence or a high power for the laser output. We could continuously sweep the correlation widths over a range of approximately one order of magnitude, as well as four-fold output powers by simply rotating the intracavity half-wave plate. We also demonstrated experiments on optical phase locking, using two independent coherence-or-power selectable lasers.

  15. Stochastic method for determining the coherence length of a TEA CO2 laser

    NASA Astrophysics Data System (ADS)

    Codnia, J.; Gómez, N. D.; Azcárate, M. L.

    2013-12-01

    In this work the results of the measurement of the coherence length of a TEA CO2 laser developed in DEILAP are presented. A Michelson interferometer of about 5 m of optical path length difference was built for this purpose. A motorized translation optical mount was placed in one arm in order to enable the variation of the optical path length in many wavelengths. The length of the other arm was varied manually in steps of several tens of centimeters. Spatial filtering forced the laser to oscillate in a single transverse mode, TEM00. An innovative stochastic technique for data analysis allowed determining the amount of longitudinal modes, the amplitude and the individual average coherence length of each mode as well as the global coherence length of the laser. This technique was later compared with a method based on the analysis of the Fourier transform of the time series obtained at the interferometer input.

  16. Overlapping single photons on coherent states with two independent laser sources: a proposal

    NASA Astrophysics Data System (ADS)

    Calvo, Maria L.; Alvarez-Estrada, Ramon F.

    2016-10-01

    Some very interesting pure non-Gaussian states in quantum optics have already been produced experimentally (with one pulsed laser): the single-photon-added coherent states, among others. Important interference phenomena by superposing beams from two independent masers or lasers have been investigated earlier experimentally and theoretically. By pursuing on both subjects altogether, we propose a possible new experiment to generate single-photon-added coherent states, by employing two independent laser sources, both in continuous regime and having approximately equal frequencies and coherence times tc: we expect that such generations could occur during times of the order of tc/3 (possibly, a bit shorter). This expectation follows from a fully quantized multimode analysis of the temporal mode structure, which extends previous studies of parametric down conversion and balanced homodyne detection

  17. Solid-state lasers for coherent communication and remote sensing

    NASA Technical Reports Server (NTRS)

    Byer, Robert L.

    1991-01-01

    Work in the stabilization of monolithic Nd:YAG lasers and the application of these lasers to nonlinear optical frequency conversion is discussed. The intrinsic stability of semiconductor diode laser pumped solid state lasers has facilitated a number of demonstration in external resonant cavity harmonic generation and stable optical parametric oscillation. Relative laser frequency stabilization of 0.3 Hz was achieved, and absolute stability of a few hundred hertz is anticipated. The challenge is now to reproduce this frequency stability in the output of tunable nonlinear optical devices. Theoretical and experimental work toward this goal are continuing.

  18. Remote wind sensing with a CW diode laser lidar beyond the coherence regime.

    PubMed

    Hu, Qi; Rodrigo, Peter John; Pedersen, Christian

    2014-08-15

    We experimentally demonstrate for the first time (to our knowledge) a coherent CW lidar system capable of wind speed measurement at a probing distance beyond the coherence regime of the light source. A side-by-side wind measurement was conducted on the field using two lidar systems with identical optical designs but different laser linewidths. While one system was operating within the coherence regime, the other was measuring at least 2.4 times the coherence range. The probing distance of both lidars is 85 m and the radial wind speed correlation was measured to be r2=0.965 between the two lidars at a sampling rate of 2 Hz. Based on our experimental results, we describe a practical guideline for designing a wind lidar operating beyond the coherence regime.

  19. Differential carrier phase recovery for QPSK optical coherent systems with integrated tunable lasers.

    PubMed

    Fatadin, Irshaad; Ives, David; Savory, Seb J

    2013-04-22

    The performance of a differential carrier phase recovery algorithm is investigated for the quadrature phase shift keying (QPSK) modulation format with an integrated tunable laser. The phase noise of the widely-tunable laser measured using a digital coherent receiver is shown to exhibit significant drift compared to a standard distributed feedback (DFB) laser due to enhanced low frequency noise component. The simulated performance of the differential algorithm is compared to the Viterbi-Viterbi phase estimation at different baud rates using the measured phase noise for the integrated tunable laser.

  20. Electronic control of coherence in a two-dimensional array of photonic crystal surface emitting lasers.

    PubMed

    Taylor, R J E; Childs, D T D; Ivanov, P; Stevens, B J; Babazadeh, N; Crombie, A J; Ternent, G; Thoms, S; Zhou, H; Hogg, R A

    2015-08-20

    We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young's Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.

  1. Electronic control of coherence in a two-dimensional array of photonic crystal surface emitting lasers

    NASA Astrophysics Data System (ADS)

    Taylor, R. J. E.; Childs, D. T. D.; Ivanov, P.; Stevens, B. J.; Babazadeh, N.; Crombie, A. J.; Ternent, G.; Thoms, S.; Zhou, H.; Hogg, R. A.

    2015-08-01

    We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young’s Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.

  2. Modal study of refractive effects on x-ray laser coherence

    SciTech Connect

    Amendt, P.; London, R.A. ); Strauss, M. . Nuclear Research Center-Negev)

    1991-04-05

    The role of smoothly varying transverse gain and refraction profiles on x-ray laser intensity and coherence is analyzed by modally expanding the electric field within the paraxial approximation. Comparison with a square transverse profile reveals that smooth-edged profiles lead to: (1) a greatly reduced number of guided modes, (2) the continued cancellation of local intensity from a loosely guided mode by resonant free modes, (3) and the absence of extraneous (or anomalous) free mode resonances. These generic spectral properties should enable a considerable simplification in analyzing and optimizing the coherence properties of laboratory soft x-ray lasers. 6 refs., 3 figs.

  3. Electronic control of coherence in a two-dimensional array of photonic crystal surface emitting lasers

    PubMed Central

    Taylor, R. J. E.; Childs, D. T. D.; Ivanov, P.; Stevens, B. J.; Babazadeh, N.; Crombie, A. J.; Ternent, G.; Thoms, S.; Zhou, H.; Hogg, R. A.

    2015-01-01

    We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young’s Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering. PMID:26289621

  4. The application of cost-effective lasers in coherent UDWDM-OFDM-PON aided by effective phase noise suppression methods.

    PubMed

    Liu, Yue; Yang, Chuanchuan; Yang, Feng; Li, Hongbin

    2014-03-24

    Digital coherent passive optical network (PON), especially the coherent orthogonal frequency division multiplexing PON (OFDM-PON), is a strong candidate for the 2nd-stage-next-generation PON (NG-PON2). As is known, OFDM is very sensitive to the laser phase noise which severely limits the application of the cost-effective distributed feedback (DFB) lasers and more energy-efficient vertical cavity surface emitting lasers (VCSEL) in the coherent OFDM-PON. The current long-reach coherent OFDM-PON experiments always choose the expensive external cavity laser (ECL) as the optical source for its narrow linewidth (usually<100 KHz). To solve this problem, we introduce the orthogonal basis expansion based (OBE) phase noise suppression method to the coherent OFDM-PON and study the possibility of the application of the DFB lasers and VCSEL in coherent OFDM-PON. A typical long-reach coherent ultra dense wavelength division multiplexing (UDWDM) OFDM-PON has been set up. The numerical results prove that the OBE method can stand severe phase noise of the lasers in this architecture and the DFB lasers as well as VCSEL can be used in coherent OFDM-PON. In this paper, we have also analyzed the performance of the RF-pilot-aided (RFP) phase noise suppression method in coherent OFDM-PON.

  5. Cross modulation method of transformation of the spatial coherence of pulsed laser radiation in a nonlinear medium

    SciTech Connect

    Kitsak, M A; Kitsak, A I

    2008-04-30

    The cross modulation method of transformation of the spatial coherence of low-power pulsed laser radiation in a nonlinear medium is proposed. The method is realised experimentally in a multimode optical fibre. The estimates of the degree of spatial coherence of radiation subjected to the phase cross modulation demonstrated the high efficiency of this radiation decorrelation mechanism. (control of laser radiation parameters)

  6. Angle extended linear MEMS scanning system for 3D laser vision sensor

    NASA Astrophysics Data System (ADS)

    Pang, Yajun; Zhang, Yinxin; Yang, Huaidong; Zhu, Pan; Gai, Ye; Zhao, Jian; Huang, Zhanhua

    2016-09-01

    Scanning system is often considered as the most important part for 3D laser vision sensor. In this paper, we propose a method for the optical system design of angle extended linear MEMS scanning system, which has features of huge scanning degree, small beam divergence angle and small spot size for 3D laser vision sensor. The principle of design and theoretical formulas are derived strictly. With the help of software ZEMAX, a linear scanning optical system based on MEMS has been designed. Results show that the designed system can extend scanning angle from ±8° to ±26.5° with a divergence angle small than 3.5 mr, and the spot size is reduced for 4.545 times.

  7. Using a laser range finder mounted on a MicroVision robot to estimate environmental parameters

    NASA Astrophysics Data System (ADS)

    Fehr, Duc; Papanikolopoulos, Nikos

    2009-05-01

    In this article we will present a new robot (MicroVision) that has been designed at the University of Minnesota (UMN), Center for Distributed Robotics. Its design reminds of the designs of previous robots built at the UMN such as the COTS Scouts or the eROSIs. It is composed of a body with two wheels and a tail just like the two aforementioned robots. However, the MicroVision has more powerful processing and sensing capabilities and we utilized these to compute areas in the surrounding environment by using a convex hull approach. We are trying to estimate the projected area of an object onto the ground. This is done by the computation of convex hulls that are based on the data received from the MicroVision's laser range finder. Although localization of the robot is an important feature in being able to compute these convex hulls, localization and mapping techniques are only used as a tool and are not an end in this work. The main idea of this work is to demonstrate the ability of the laser carrying MicroVision robot to move around an object in order to get a scan from each side. From these scans, the convex hull of the shape is deduced and its projected area onto the ground is estimated.

  8. Coherent addition of high power laser diode array with a V-shape external Talbot cavity.

    PubMed

    Liu, B; Liu, Y; Braiman, Y

    2008-12-08

    We designed a V-shape external Talbot cavity for a broad-area laser diode array and demonstrated coherent laser beam combining at high power with narrow spectral linewidth. The V-shape external Talbot cavity provides good mode-discrimination and does not require a spatial filter. A multi-lobe far-field profile generated by a low filling-factor phase-locked array is confirmed by our numerical simulation.

  9. Single laser source for multimodal coherent anti-Stokes Raman scattering microscopy.

    PubMed

    Pegoraro, Adrian F; Slepkov, Aaron D; Ridsdale, Andrew; Pezacki, John Paul; Stolow, Albert

    2010-09-01

    Short laser pulse technology has significantly contributed to biomedical research, especially via nonlinear optical microscopy. Coherent anti-Stokes Raman scattering (CARS) microscopy is a label-free, chemical-selective method that is growing in importance as improved methods and light sources develop. Here we discuss different approaches to laser source development for CARS microscopy and highlight the advantages of a multimodal CARS microscope, illustrated by selected applications in biomedical research.

  10. Adaptive pulsed laser line extraction for terrain reconstruction using a dynamic vision sensor

    PubMed Central

    Brandli, Christian; Mantel, Thomas A.; Hutter, Marco; Höpflinger, Markus A.; Berner, Raphael; Siegwart, Roland; Delbruck, Tobi

    2014-01-01

    Mobile robots need to know the terrain in which they are moving for path planning and obstacle avoidance. This paper proposes the combination of a bio-inspired, redundancy-suppressing dynamic vision sensor (DVS) with a pulsed line laser to allow fast terrain reconstruction. A stable laser stripe extraction is achieved by exploiting the sensor's ability to capture the temporal dynamics in a scene. An adaptive temporal filter for the sensor output allows a reliable reconstruction of 3D terrain surfaces. Laser stripe extractions up to pulsing frequencies of 500 Hz were achieved using a line laser of 3 mW at a distance of 45 cm using an event-based algorithm that exploits the sparseness of the sensor output. As a proof of concept, unstructured rapid prototype terrain samples have been successfully reconstructed with an accuracy of 2 mm. PMID:24478619

  11. Adaptive pulsed laser line extraction for terrain reconstruction using a dynamic vision sensor.

    PubMed

    Brandli, Christian; Mantel, Thomas A; Hutter, Marco; Höpflinger, Markus A; Berner, Raphael; Siegwart, Roland; Delbruck, Tobi

    2013-01-01

    Mobile robots need to know the terrain in which they are moving for path planning and obstacle avoidance. This paper proposes the combination of a bio-inspired, redundancy-suppressing dynamic vision sensor (DVS) with a pulsed line laser to allow fast terrain reconstruction. A stable laser stripe extraction is achieved by exploiting the sensor's ability to capture the temporal dynamics in a scene. An adaptive temporal filter for the sensor output allows a reliable reconstruction of 3D terrain surfaces. Laser stripe extractions up to pulsing frequencies of 500 Hz were achieved using a line laser of 3 mW at a distance of 45 cm using an event-based algorithm that exploits the sparseness of the sensor output. As a proof of concept, unstructured rapid prototype terrain samples have been successfully reconstructed with an accuracy of 2 mm.

  12. Multi-point laser coherent detection system and its application on vibration measurement

    NASA Astrophysics Data System (ADS)

    Fu, Y.; Yang, C.; Xu, Y. J.; Liu, H.; Yan, K.; Guo, M.

    2015-05-01

    Laser Doppler vibrometry (LDV) is a well-known interferometric technique to measure the motions, vibrations and mode shapes of machine components and structures. The drawback of commercial LDV is that it can only offer a pointwise measurement. In order to build up a vibrometric image, a scanning device is normally adopted to scan the laser point in two spatial axes. These scanning laser Doppler vibrometers (SLDV) assume that the measurement conditions remain invariant while multiple and identical, sequential measurements are performed. This assumption makes SLDVs impractical to do measurement on transient events. In this paper, we introduce a new multiple-point laser coherent detection system based on spatial-encoding technology and fiber configuration. A simultaneous vibration measurement on multiple points is realized using a single photodetector. A prototype16-point laser coherent detection system is built and it is applied to measure the vibration of various objects, such as body of a car or a motorcycle when engine is on and under shock tests. The results show the prospect of multi-point laser coherent detection system in the area of nondestructive test and precise dynamic measurement.

  13. Mode-locked fiber laser with cascaded generation of coherent Raman dissipative solitons

    NASA Astrophysics Data System (ADS)

    Kharenko, Denis S.; Bednyakova, Anastasia E.; Podivilov, Evgenii V.; Fedoruk, Mikhail P.; Apolonskiy, Alexander A.; Babin, Sergey A.

    2016-03-01

    We experimentally demonstrate a cascaded generation of a conventional dissipative soliton (DS) at 1020 nm and Raman dissipative solitons (RDS) of the first (1065 nm) and second (1115 nm) orders inside a common fiber laser cavity. The generated high-energy pulses are shown to be linearly-chirped and compressible to 200-300 fs durations for all wavelengths. Moreover, the pulses are mutually coherent that has been confirmed by efficient coherent combining exhibiting ~75 fs and <40 fs interference fringes within the combined pulse envelope of a DS with the first-order RDS and the second-order RDS respectively. The numerical simulation was performed with sinusoidal (soft) and step-like (hard) spectral filters and took into account the discreetness of the laser elements. Shown that even higher degree of coherence and shorter pulses could be achieved with hard spectral filtering. This approach opens the door towards cascaded generation of multiple coherent dissipative solitons in a broad spectral range (so-called dissipative soliton comb). The demonstrated source of coherent dissipative solitons can improve numerous areas such as frequency comb generation, pulse synthesis, biomedical imaging and the generation of coherent mid-infrared supercontinuum.

  14. Coherent Computing with Injection-Locked Laser Network

    NASA Astrophysics Data System (ADS)

    Utsunomiya, S.; Wen, K.; Takata, K.; Tamate, S.; Yamamoto, Yoshihisa

    Combinatorial optimization problems are ubiquitous in our modern life. The classic examples include the protein folding in biology and medicine, the frequency assignment in wireless communications, traffic control and routing in air and on surface, microprocessor circuit design, computer vision and graph cut in machine learning, and social network control. They often belong to NP, NP-complete and NP-hard classes, for which modern digital computers and future quantum computers cannot find solutions efficiently, i.e. in polynomial time [1].

  15. Beyond the random phase approximation: Stimulated Brillouin backscatter for finite laser coherence times

    SciTech Connect

    Korotkevich, Alexander O.; Lushnikov, Pavel M.; Rose, Harvey A.

    2015-01-15

    We developed a linear theory of backward stimulated Brillouin scatter (BSBS) of a spatially and temporally random laser beam relevant for laser fusion. Our analysis reveals a new collective regime of BSBS (CBSBS). Its intensity threshold is controlled by diffraction, once cT{sub c} exceeds a laser speckle length, with T{sub c} the laser coherence time. The BSBS spatial gain rate is approximately the sum of that due to CBSBS, and a part which is independent of diffraction and varies linearly with T{sub c}. The CBSBS spatial gain rate may be reduced significantly by the temporal bandwidth of KrF-based laser systems compared to the bandwidth currently available to temporally smoothed glass-based laser systems.

  16. Automated co-alignment of coherent fiber laser arrays via active phase-locking.

    PubMed

    Goodno, Gregory D; Weiss, S Benjamin

    2012-07-02

    We demonstrate a novel closed-loop approach for high-precision co-alignment of laser beams in an actively phase-locked, coherently combined fiber laser array. The approach ensures interferometric precision by optically transducing beam-to-beam pointing errors into phase errors on a single detector, which are subsequently nulled by duplication of closed-loop phasing controls. Using this approach, beams from five coherent fiber tips were simultaneously phase-locked and position-locked with sub-micron accuracy. Spatial filtering of the sensed light is shown to extend the control range over multiple beam diameters by recovering spatial coherence despite the lack of far-field beam overlap.

  17. The influence of a light pipe on the coherence properties in laser projectors

    NASA Astrophysics Data System (ADS)

    Roelandt, Stijn; Tervo, Jani; Meuret, Youri; Verschaffelt, Guy; Thienpont, Hugo

    2014-05-01

    Light pipes are key optical components used in projection systems to transport and homogenize light from the source towards the light valve. They can provide a uniform light distribution at their output as a result of multiple internal reflections. In laser projection systems, such light pipes are useful in combination with a laser-light module consisting of one or more single-mode lasers and a rotating diffuser. The partially coherent light emanating from the rotating diffuser is transported and homogenized towards the end of the light pipe. Consequently, propagation through the light pipe will also modify the coherence properties of the laser light. In this paper, a computationally efficient simulation model is presented to propagate partially coherent light through a homogenizing rectangular light pipe. The resulting coherence function clearly differs from that of free-space propagation over the same optical path length. The implications of these results on, for example, the appearance of speckle are discussed in further detail. The simulation results are experimentally verified using a reversing wavefront Michelson interferometer. The approach described in this paper can be extended further to investigate other types of light pipes, such as tapered light pipes or even more complex ones.

  18. Coherent combining in an Yb-doped double-core fiber laser.

    PubMed

    Boullet, Johan; Sabourdy, David; Desfarges-Berthelemot, Agnès; Kermène, Vincent; Pagnoux, Dominique; Roy, Philippe; Dussardier, Bernard; Blanc, Wilfried

    2005-08-01

    Coherent combining is demonstrated in a clad-pumped Yb-doped double-core fiber laser. A slope efficiency of more than 70% is achieved with 96% of the total output power in the fundamental mode of one of the two cores. This high combining efficiency is obtained when both cores are coupled via a biconical fused taper in a Michelson interferometer configuration.

  19. 2-Micron Diode-Pumped Pulsed Laser Transmitter for SPARCLE: A Coherent Wind Lidar Shuttle Mission

    NASA Technical Reports Server (NTRS)

    Singh, Upendra N.; Yu, Jirong; Petros, Mulugeta; Barnes, Norman P.; Phillips, Mark W.

    1998-01-01

    To enable a tropospheric vector wind velocity profiling from space with a pulsed Doppler lidar, a diode-pumped, room temperature Ho:Tm:YLF coherent pulsed transmitter has been developed at NASA Langley Research Center. This pulsed laser transmitter will be a part of coherent wind lidar shuttle mission SPARCLE. The acronym stands for SPAce Readiness Coherent Lidar Experiment and is primarily a technology demonstration mission and is expected to fly in 2001 as NASA's New Millennium Program (NMP) second Earth Orbiter (EO-2) mission. The laser transmitter for SPARCLE is a Ho:Tm:YLF power oscillator operating at eye-safe wavelength of 2.05 microns. The Q-switched output energy is 125 mJ at six Hz, and it has a near-transform limited beam with a pulse width of 170 ns. The high power and high beam quality of this laser makes it well suited as a coherent wind lidar transmitter on a space platform. When the output of this power oscillator is amplified by using four diode-pumped Ho:Tm:YLF amplifiers, an output energy of 600 mJ at 10 Hz is achieved. This is the highest energy ever produced at 10 Hz, and is at least an order of magnitude greater than previously achieved for a 2-micron diode-pumped laser at room temperature.

  20. Ex-CARS: exotic configuration for coherent anti-Stokes Raman scattering microspectroscopy utilizing two laser sources

    PubMed Central

    Yakovlev, Vladislav V.; Petrov, Georgi I.; Noojin, Gary D.; Harbert, Corey; Denton, Michael; Thomas, Robert

    2011-01-01

    We propose and experimentally demonstrate a new coherent anti-Stokes Raman scattering setting, which relies on a coherent excitation of Raman vibration using a broadband ultrashort laser pulse and signal read-out using a conventional continuous wave laser radiation. Such an exotic arrangement does not require any synchronization of two laser sources and can be used for direct comparison of amplitudes of nonlinear and spontaneous Raman signals. Ex-CARS in time- (top panel) and frequency- (bottom panel) domain. PMID:20635427

  1. High-coherent-power, two-dimensional grating surface-emitting (GSE) semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Li, Shuang

    High-power semiconductor lasers, with coherent radiation, are attractive sources for many applications. However, achieving stable, coherent radiation to watt-range power from monolithic semiconductor lasers has been a challenge. This work covers the study and development of high power coherent semiconductor lasers employing novel-types of both surface-emitting and edge-emitting structures. Surface-emitting (SE) semiconductor lasers are preferred over edge-emitting lasers due to their inherent reliability, scalability, and packaging advantages. Horizontal-cavity, grating SE semiconductor lasers are promising candidates for high-power coherent sources. Here we present the design and analysis of a two-dimensional (2D) horizontal-cavity GSE laser (so called ROW-SEDFB laser), for which 2nd-order, distributed feedback/distributed Bragg reflector (DFB/DBR) gratings with central pi phaseshift are preferentially placed in the element regions of a resonant-optical-waveguide (ROW) structure. We find that beside their usual functions (feedback and outcoupling), the gratings act as an effective array-mode selector. The in-phase mode is strongly favored to lase around its resonance due both to better field overlap with the active-grating (i.e., DFB) and to lower interelement loss than the other array modes. For 20-element arrays with 700/600mum-long DFB/DBR gratings, and of 100mum-wide lateral dimension, high intermodal discrimination is obtained. The primary mechanisms behind this discrimination are found to be: absorption losses for the interelement field to the metal contact and to a semiconductor/metal grating layer, and the longitudinal guided-field overlap with the DFB region. The discrimination can be further enhanced by introducing free-carrier absorption in the interelement regions. The device has relatively uniform guided-field profiles in both lateral and longitudinal directions and a strong built-in index profile in the lateral direction. These features make the ROW

  2. Coherence Properties of Individual Femtosecond Pulses of an X-ray Free-Electron Laser

    SciTech Connect

    Vartanyants, I.A.; Singer, A.; Mancuso, A.P.; Yefanov, O.M.; Sakdinawat, A.; Liu, Y.; Bang, E.; Williams, G.J.; Cadenazzi, G.; Abbey, B.; Sinn, H.; Attwood, D.; Nugent, K.A.; Weckert, E.; Wang, T.; Zhu, D.; Wu, B.; Graves, C.; Scherz, A.; Turner, J.J.; Schlotter, W.F.; /SLAC /LERMA, Ivry /Zurich, ETH /LBL, Berkeley /ANL, APS /Argonne /SLAC /LLNL, Livermore /Latrobe U. /SLAC /SLAC /European XFEL, Hamburg /SLAC /Hamburg U.

    2012-06-06

    Measurements of the spatial and temporal coherence of single, femtosecond x-ray pulses generated by the first hard x-ray free-electron laser, the Linac Coherent Light Source, are presented. Single-shot measurements were performed at 780 eV x-ray photon energy using apertures containing double pinholes in 'diffract-and-destroy' mode. We determined a coherence length of 17 {micro}m in the vertical direction, which is approximately the size of the focused Linac Coherent Light Source beam in the same direction. The analysis of the diffraction patterns produced by the pinholes with the largest separation yields an estimate of the temporal coherence time of 0.55 fs. We find that the total degree of transverse coherence is 56% and that the x-ray pulses are adequately described by two transverse coherent modes in each direction. This leads us to the conclusion that 78% of the total power is contained in the dominant mode.

  3. Ultra-high sensitive and high resolution optical coherence tomography using a laser induced electromagnetic dipole

    NASA Astrophysics Data System (ADS)

    Kuroda, Hiroto; Baba, Motoyoshi; Suzuki, Masayuki; Yoneya, Shin

    2013-09-01

    Utilizing an optical coherence tomography measurement, we have developed a technique that actively uses a dielectric response due to an induced dipole moment caused by a mode-locked pulsed laser light source. Irradiated laser light in the material induces a photo-induced electric dipole resulting in a refractive index change for its strong electric field. Using this technique, we obtained a highly sensitive fundus retina tomogram of a human eye in vivo with a resolution of 1.3 μm by single scanning for 20 ms using 8 fs mode-locked pulse laser light with a 350 nm spread spectrum.

  4. Automatic laser welding and milling with in situ inline coherent imaging.

    PubMed

    Webster, P J L; Wright, L G; Ji, Y; Galbraith, C M; Kinross, A W; Van Vlack, C; Fraser, J M

    2014-11-01

    Although new affordable high-power laser technologies enable many processing applications in science and industry, depth control remains a serious technical challenge. In this Letter we show that inline coherent imaging (ICI), with line rates up to 312 kHz and microsecond-duration capture times, is capable of directly measuring laser penetration depth, in a process as violent as kW-class keyhole welding. We exploit ICI's high speed, high dynamic range, and robustness to interference from other optical sources to achieve automatic, adaptive control of laser welding, as well as ablation, achieving 3D micron-scale sculpting in vastly different heterogeneous biological materials.

  5. FM characteristics and compact modules for coherent semiconductor lasers coupled to an external cavity

    SciTech Connect

    Shin, C.H.; Teshima, M.; Ohtsu, M. ); Imai, T.; Yoshida, J.; Nishide, K. )

    1990-03-01

    FM responses of a semiconductor laser optically coupled off-axis to a confocal Fabry--Perot cavity were measured. It is reported that this cavity acted as a frequency discriminator and as a phase comparator for slow and fast frequency fluctuations, respectively. The crossover between them was determined by a half linewidth of the cavity. Based on these investigations, we made two kinds of coherent semiconductor laser modules. External FP cavities were made by using an optical fiber and a hemispherical micro-lens, respectively. Linewidths of these lasers were less than 25 kHz.

  6. Generation of phase - matched coherent point source in plasma media by propagated X-ray laser seeded beam

    NASA Astrophysics Data System (ADS)

    Pikuz, T.; Faenov, A.; Magnitskiy, S.; Nagorskiy, N.; Tanaka, M.; Ishino, M.; Nishikino, M.; Kando, M.; Kato, Y.; Kawachi, T.

    2016-03-01

    There is a significant interest in developing the coherent table-top X-ray lasers. Advent of plasma-based transient collisional excitation x-ray laser and particular, injection of coherent seeded beam, especially high-order harmonics, has tremendously improved the spatial coherence of such lasers, what allowed them to be the same widely used as synchrotron sources. Here we report experimental founding of unknown interference structure in a spatial profile of the output beam of the two-stage plasma X-ray laser. That allowed us experimental and theoretical discovering a new phenomenon consisted in a generation of phase-matched coherent point source in a laser plasma media by propagated X-ray laser seeded beam. This phenomenon could extend the applications of such x-ray lasers. For explanation of the observed phenomenon a new method of solving the standard system of Maxwell-Bloch equations has been developed. It was found that the interference pattern in the output laser beam was formed due to an emergence of phase-matched coherent virtual point source in the XRL amplifier and could be treated as the first observation of mirage phenomenon, analogous to the optical mirage, but in X-rays. The obtained results bring new comprehension into the physical nature of amplification of X-ray radiation in laser-induced plasma amplifiers and opening new opportunities for X-ray interferometry, holography and other applications, which requiring multiple rigidly phased sources of coherent radiation.

  7. Precise measurement of ultra-narrow laser linewidths using the strong coherent envelope

    NASA Astrophysics Data System (ADS)

    Huang, Shihong; Zhu, Tao; Liu, Min; Huang, Wei

    2017-02-01

    Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods like delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately. This is because a broadening of the Gaussian spectrum, which hides the laser’s intrinsic Lorentzian linewidth, cannot be avoided. Here, we introduce a new method using the strong coherent envelope to characterize the laser’s intrinsic linewidth through self-coherent detection. This method can eliminate the effect of the broadened Gaussian spectrum induced by the 1/f frequency noise. We analyze, in detail, the relationship between intrinsic laser linewidth, contrast difference with the second peak and the second trough (CDSPST) of the strong coherent envelope, and the length of the delaying fiber. The correct length for the delaying fiber can be chosen by combining the estimated laser linewidth (Δfest) with a specific CDSPST (ΔS) to obtain the accurate laser linewidth (Δf). Our results indicate that this method can be used as an accurate detection tool for measurements of narrow or super-narrow linewidths.

  8. Precise measurement of ultra-narrow laser linewidths using the strong coherent envelope

    PubMed Central

    Huang, Shihong; Zhu, Tao; Liu, Min; Huang, Wei

    2017-01-01

    Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods like delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately. This is because a broadening of the Gaussian spectrum, which hides the laser’s intrinsic Lorentzian linewidth, cannot be avoided. Here, we introduce a new method using the strong coherent envelope to characterize the laser’s intrinsic linewidth through self-coherent detection. This method can eliminate the effect of the broadened Gaussian spectrum induced by the 1/f frequency noise. We analyze, in detail, the relationship between intrinsic laser linewidth, contrast difference with the second peak and the second trough (CDSPST) of the strong coherent envelope, and the length of the delaying fiber. The correct length for the delaying fiber can be chosen by combining the estimated laser linewidth (Δfest) with a specific CDSPST (ΔS) to obtain the accurate laser linewidth (Δf). Our results indicate that this method can be used as an accurate detection tool for measurements of narrow or super-narrow linewidths. PMID:28181506

  9. Coherent blue emission generated by Rb two-photon excitation using diode and femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Lopez, Jesus P.; Moreno, Marco P.; de Miranda, Marcio H. G.; Vianna, Sandra S.

    2017-04-01

    The coherent blue light generated in rubidium vapor due to the combined action of an ultrashort pulse train and a continuous wave diode laser is investigated. Each step of the two-photon transition 5S–5P{}3/2–5D is excited by one of the lasers, and the induced coherence between the 5S and 6P{}3/2 states is responsible for generating the blue beam. Measurements of the excitation spectrum reveal the frequency comb structure and allow us to identify the resonant modes responsible for inducing the nonlinear process. Further, each resonant mode excites a different group of atoms, making the process selective in atomic velocity. The signal dependency on the atomic density is characterized by a sharp growth and a rapid saturation. We also show that for high intensity of the diode laser, the Stark shift at resonance causes the signal suppression observed at low atomic density.

  10. Radiation from laser accelerated electron bunches: Coherent terahertz and femtosecond X-rays

    SciTech Connect

    Leemans, W.P.; Esarey, E.; van Tilborg, J.; Michel, P.A.; Schroeder, C.B.; Toth, Cs.; Geddes, C.G.R.; Shadwick, B.A.

    2004-10-01

    Electron beam based radiation sources provide electromagnetic radiation for countless applications. The properties of the radiation are primarily determined by the properties of the electron beam. Compact laser driven accelerators are being developed that can provide ultra-short electron bunches (femtosecond duration) with relativistic energies reaching towards a GeV. The electron bunches are produced when an intense laser interacts with a dense plasma and excites a large amplitude plasma density modulation (wakefield) that can trap background electrons and accelerate them to high energies. The short pulse nature of the accelerated bunches and high particle energy offer the possibility of generating radiation from one compact source that ranges from coherent terahertz to gamma rays. The intrinsic synchronization to a laser pulse and unique character of the radiation offers a wide range of possibilities for scientific applications. Two particular radiation source regimes are discussed: Coherent terahertz emission and x-ray emission based on betatron oscillations and Thomson scattering.

  11. Active and passive sensing of collective atomic coherence in a superradiant laser

    NASA Astrophysics Data System (ADS)

    Bohnet, Justin G.; Chen, Zilong; Weiner, Joshua M.; Cox, Kevin C.; Thompson, James K.

    2013-07-01

    We study the nondemolition mapping of collective quantum coherence onto a cavity light field in a superradiant, cold-atom 87Rb Raman laser. We show theoretically that the fundamental precision of the mapping is near the standard quantum limit on phase estimation for a coherent spin state, Δϕ=1/N, where N is the number of atoms. The associated characteristic measurement time scale τW∝1/N is collectively enhanced. The nondemolition nature of the measurement is characterized by only 0.5 photon recoils deposited per atom due to optical repumping in a time τW. We experimentally realize conditional Ramsey spectroscopy in our superradiant Raman laser, compare the results to the predicted precision, and study the mapping in the presence of decoherence, far from the steady-state conditions previously considered. Finally, we demonstrate a hybrid mode of operation in which the laser is repeatedly toggled between active and passive sensing.

  12. [Laser and vision measurement research on parameters of miniature quartz plate-sensitive glass part].

    PubMed

    Wang, Xin; Zhang, Xiao-Dong

    2014-06-01

    High-precision, rapid and non-contact geometry parameter measurements of plate glass parts has become a main problem in the field of testing-related production and processing and also an important applied direction for laser spectroscopy. Accurately detect the geometric parameters of plate glass parts can not only improve the processing technology and the precision of assembly, but also bring about sub-file management according to the parameters. This paper presents a novel multi-parameter measurement method based on the laser and vision image processing technology, which can be used to measure parameters of miniature quartz plate-sensitive glass part accurately. The testing system consisting of self-adaption coaxial visual detection unit and laser vision thickness inspection unit was designed. A constant power drive control system was set up to ensure the laser diode (LD) can provide a stable light source for the testing system. A modified sub-pixel edge position algorithm of conic features was proposed to implement the sub-pixel image processing, and the parameters can be extracted. According to the data detected from curve edge points and a new-defined error function, which was minimized, the parameters of miniature quartz plate-sensitive glass part can be calculated. The experiments show that the average deviation of the measurement results is less than 2 υm, and the method has good stability and high accuracy measurement, which can meet the precision requirement of parameter measurement for miniature plate glass part.

  13. Coherent polarization locking of Q-switched Ho:YAG laser

    NASA Astrophysics Data System (ADS)

    Chua, C. F.; Tan, L. H.; Phua, P. B.

    2013-03-01

    We had demonstrated the use of Coherent Polarization Locking (CPL) to mitigate the intra-cavity optical damage in a Q-switched Ho:YAG laser. By splitting the available pump power into two individual Ho:YAG laser rods, we had passively coherent combined two orthogonal polarized lasers with output pulse energy of 9.13mJ, pulse width of 14ns, operating at 800Hz pulse repetition rate. In contrast, when all the pump power was pumped on a single Ho:YAG laser rod built with the same cavity configuration, severe optical damage was observed. It was occurred at the surface coating of the laser rod when operating at < 2kHz pulse repetition rate, thus limiting the output pulse energy to < 5mJ. We also demonstrated, first to our knowledge, that by performing Q-switching only in one of the laser arms, it resulted in pulse operation for the entire CPL laser cavity.

  14. Coherent-state description of free-electron lasers

    NASA Astrophysics Data System (ADS)

    Lee, Ching Tsung

    1990-12-01

    It is generally accepted that the overall performance of free-electron lasers (FEL) can be understood without quantum mechanics. However, there are features of FEL such as photon statistics which can only be described quantum-mechanically. Although the majority of quantum-mechanical studies of FEL are devoted to one-particle models, there are also many studies on many-body effects of FEL. Unfortunately, the mathematical derivations of these studies are so complicated that it is not easy to follow the developments with a clearer picture in mind. The origin of the problem is the quantum recoils of the electrons. So we try to gain a clearer picture of the many-body effects by making the recoilless approximation. A simple model of FEL consists of a beam of relativistic electrons propagating through a spatially periodic magnetostatic wiggler field. The resulting laser output is propagating along the same direction as that of the electron beam. Quantum-mechanical analysis of FEL are usually based on the Bambini-Renieri frame which moves in the same direction as the propagating laser beam with a relativistic speed so that: (1) the wiggler field appears almost as a plane-wave radiation, (2) the frequency of the wiggler field coincides with that of the laser, and (3) the electron motion is nonrelativistic. Although in reality the laser beam can only derive its energy at the expense of the kinetic energy of the electrons, it appears in the Bambini-Renieri frame as if the photons of the laser were scattered from the fictitious photons of the wiggler field by the electrons.

  15. Coherent summation of spatially distorted laser Doppler signals by using a two-dimensional heterodyne detector array

    NASA Technical Reports Server (NTRS)

    Chan, Kin P.; Killinger, Dennis K.

    1992-01-01

    Phase-sensitive coherent summation of individual heterodyne detector array signals was demonstrated for the enhanced detection of spatially distorted laser Doppler returns. With the use of a 2 x 2 heterodyne detector array, the phase and amplitude of a time-varying speckle pattern was detected, and the signal-to-noise ratio of the Doppler shift estimate was shown to be improved by a factor of 2, depending on the extent of spatial coherence loss. These results are shown to agree with a first-order analysis and indicate the advantage of coherent summation for both short-range laser Doppler velocimetry and long-range atmospheric coherent lidar.

  16. Phasing surface emitting diode laser outputs into a coherent laser beam

    DOEpatents

    Holzrichter, John F.

    2006-10-10

    A system for generating a powerful laser beam includes a first laser element and at least one additional laser element having a rear laser mirror, an output mirror that is 100% reflective at normal incidence and <5% reflective at an input beam angle, and laser material between the rear laser mirror and the output mirror. The system includes an injector, a reference laser beam source, an amplifier and phase conjugater, and a combiner.

  17. Fast and intuitive programming of adaptive laser cutting of lace enabled by machine vision

    NASA Astrophysics Data System (ADS)

    Vaamonde, Iago; Souto-López, Álvaro; García-Díaz, Antón

    2015-07-01

    A machine vision system has been developed, validated, and integrated in a commercial laser robot cell. It permits an offline graphical programming of laser cutting of lace. The user interface allows loading CAD designs and aligning them with images of lace pieces. Different thread widths are discriminated to generate proper cutting program templates. During online operation, the system aligns CAD models of pieces and lace images, pre-checks quality of lace cuts and adapts laser parameters to thread widths. For pieces detected with the required quality, the program template is adjusted by transforming the coordinates of every trajectory point. A low-cost lace feeding system was also developed for demonstration of full process automation.

  18. Coherence effects in the ultra-intense laser-induced ultrafast response of complex atoms

    NASA Astrophysics Data System (ADS)

    Li, Yongqiang; Yuan, Jianmin

    2016-05-01

    Both coherent pumping and energy relaxation play important roles in understanding physical processes of ultra-intense coherent light-matter interactions. Here, using a large-scale quantum master equation approach, we describe dynamical processes of practical open quantum systems driven by both coherent and stochastic interactions. As examples, two typical cases of light-matter interactions are studied. First, we investigate coherent dynamics of inner-shell electrons of a neon gas irradiated by a high intensity X-ray laser along with vast number of decaying channels. In these single-photon dominated processes, we find that, due to coherence-induced Rabi oscillations and power broadening effects, the photon absorptions of a neon gas can be suppressed resulting in differences in ionization processes and final ion-stage distributions. Second, we take helium as an example of multi-photon and multichannel interference dominated electron dynamics, by investigating the transient absorption of an isolated atto-second pulse in the presence of a femto-second infrared laser pulse.

  19. Evidence for beta corticomuscular coherence during human standing balance: Effects of stance width, vision, and support surface.

    PubMed

    Jacobs, J V; Wu, G; Kelly, K M

    2015-07-09

    The role of the cerebral cortex in maintaining human standing balance remains unclear. Beta corticomuscular coherence (CMC) provides a measure of communication between the sensory-motor cortex and muscle, but past literature has not demonstrated significant beta CMC during human stance. This study evaluated the effects of stance width, vision, and surface compliance on beta CMC during human stance using methods to enhance sensitivity to CMC. Ten healthy, young adults stood for three 60-s trials in each of a wide or narrow stance width while on a firm surface and in narrow stance on a foam surface, each with eyes open or closed. Beta CMC was calculated between contralateral electroencephalographic and electromyographic recordings. Electromyography was recorded from bilateral tibialis anterior and gastrocnemius lateralis muscles. CMC magnitude was defined as the average integrated area of coherence spectrum above a significance threshold. Measures of center-of-pressure (COP) sway were derived from force plates under the subjects' feet. Results of CMC from four muscles across six stance conditions (a total of 24 combinations) demonstrated significant average CMC magnitude from every subject in 20 combinations and significant average CMC magnitude in nine of 10 subjects in the remaining four combinations. The CMC magnitude was significantly larger in the wide-stance condition than in the narrow-stance condition with eyes open. No significant differences were detected when comparing eyes-open to eyes-closed conditions or when comparing firm- to foam-surface conditions. Correlations between CMC magnitude and COP sway elicited some significant relationships, but there was no consistent direction or pattern of correlation based on muscle or stance condition. Results demonstrate that significant beta CMC is evident during human standing balance, and that beta CMC is responsive to changes in mechanical, but not visual or surface, conditions.

  20. Optical modeling of the Q-switch lasers with a coherent gain model

    NASA Astrophysics Data System (ADS)

    Lawrence, George N.; Yu, Anthony; Schwarz, Jens

    2011-10-01

    Q-switch lasers are traditionally modeled using the rate equation approximation[1]. This model is effective in relating the energy of the population inversion to the energy in the optical pulse. It is especially effective when augmented by the Frantz-Nodvik theory that effectively builds in conservation of energy. However, the rate equation approximation theory cannot independently describe the formation of longitudinal modes and, because it does not correctly consider the finite response time of the medium, its accuracy in predicting the very fast rise time of Q-switch pulses is suspect. A more powerful based on the laser gain in terms of radiating, resonant dipoles-the coherent gain model-is needed. This paper reports progress to incorporate the more advanced coherent gain into a 3D, time resolved numerical model that can predict both sub-nanosecond effects, the growth of longitudinal modes in the Q-switched laser, and other coherent effects. Work remains to be done to explore the capabilities of this model to its full range of possibilities. Sandia National Laboratories has been interested in short pulse modeling and provided support for the development of the coherent gain model which is now being applied to the NASA Q-switch program to address fast rise times and the formation of longitudinal modes[2]-[6].

  1. LISP: a laser imaging simulation package for developing and testing laser vision systems

    NASA Astrophysics Data System (ADS)

    Wu, Kung C.

    1993-01-01

    The difficulties commonly encountered in developing laser imaging technologies are: (1) high cost of the laser system, and (2) time and cost involved in modeling and maneuvering a physical environment for the desired scenes. In contrast to the real imaging systems, computer generated laser images provide researchers with fast, accurate, cost-effective data for testing and developing algorithms. The laser imaging simulation package (LISP) described in this paper provides an interactive solid modeler that allows users to construct the artificial environment by various solid modelling techniques. Two fast ray tracing algorithms were developed and discussed in this paper for generating the near realistic laser data of any desired scene. These computer generated laser data facilitates the researchers in developing laser imaging algorithms. Thus, LISP not only provides an ideal testbed for developing and testing algorithms, but also an opportunity to explore the limitation of laser imaging applications.

  2. Improved semi-conductor laser device, operating, at room temperature, with an array of three lasers in the spatially coherent, free running mode

    NASA Technical Reports Server (NTRS)

    Rutz, E. M.

    1975-01-01

    The peak pulse power was increased by operating an array of three homostructure Ga As lasers in the laser device. A spatial filter in the laser device selects the spatially coherent, free running, mode. The optical peak power is 5 watts, which is three times the peak power of a single laser in the array. The far-field distribution of the three laser array is a single Gaussian beam of spatial coherence without sidelobes or grating lobes. The length of the optical pulses of spatial coherence was increased to 200 ns by improved heat transfer from the p-n junctions of the lasers to the metal housing of the pulse transformer, and by doubling the core area and increasing the turns of the primary windings of the pulse transformer. The mechanical stability of the laser device was improved and the transition from mechanical alignment to electro-mechanical alignment control, was facilitated.

  3. Coherent frequency combs produced by self frequency modulation in quantum cascade lasers

    SciTech Connect

    Khurgin, J. B.; Dikmelik, Y.; Hugi, A.; Faist, J.

    2014-02-24

    One salient characteristic of Quantum Cascade Laser (QCL) is its very short τ ∼ 1 ps gain recovery time that so far thwarted the attempts to achieve self-mode locking of the device into a train of single pulses. We show theoretically that four wave mixing, combined with the short gain recovery time causes QCL to operate in the self-frequency-modulated regime characterized by a constant power in time domain and stable coherent comb in the frequency domain. Coherent frequency comb may enable many potential applications of QCL's in sensing and measurement.

  4. Swept source optical coherence microscopy using a Fourier domain mode-locked laser

    NASA Astrophysics Data System (ADS)

    Huang, Shu-Wei; Aguirre, Aaron D.; Huber, Robert A.; Adler, Desmond C.; Fujimoto, James G.

    2007-05-01

    Swept source optical coherence microscopy (OCM) enables cellular resolution en face imaging as well as integration with optical coherence tomography (OCT) cross sectional imaging. A buffered Fourier domain mode-locked (FDML) laser light source provides high speed, three dimensional imaging. Image resolutions of 1.6 µm × 8 µm (transverse × axial) with a 220 µm × 220 µm field of view and sensitivity higher than 98 dB are achieved. Three dimensional cellular imaging is demonstrated in vivo in the Xenopus laevis tadpole and ex vivo in the rat kidney and human colon.

  5. Competition between coherent emission and broadband spontaneous emission in the quantum free electron laser

    SciTech Connect

    Robb, G. R. M.; Bonifacio, R.

    2013-03-15

    We extend previous analyses of spontaneous emission in a quantum free electron laser (QFEL) and competition between spontaneous and coherent QFEL emission to include a broad distribution of photon frequencies and momenta appropriate for spontaneous undulator radiation. We show that although the predictions of monochromatic and broadband models predict different electron momentum distributions for the quantum regime due to spontaneous emission alone after many photon emissions, the inclusion of broadband spontaneous emission has a negligible effect on the competition between spontaneous and coherent emission in the QFEL. Numerical results from both models are well described by the same condition for the threshold/critical value of spontaneous emission rate.

  6. Coherent and spectral beam combining of fiber lasers using volume Bragg gratings

    NASA Astrophysics Data System (ADS)

    Jain, Apurva; Drachenberg, Derrek; Andrusyak, Oleksiy; Venus, George; Smirnov, Vadim; Glebov, Leonid

    2010-04-01

    Five-channel spectral beam combining (SBC) using volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass with 0.5 nm spectral separation between channels and combined power >750 W has been recently reported. We report on improvements in this technique with the use of thermal control of VBGs that allows precise high-power alignment required for dense SBC with 0.25 nm spectral separation of channels. Experimental results of passive coherent beam combining (CBC) of fiber lasers using multiplexed VBGs are presented and analyzed. Methods for achieving 100 kW class systems using novel hybrid architectures that combine both coherent and spectral beam combining are discussed.

  7. Spatio-temporal coherence of free-electron laser radiation in the extreme ultraviolet determined by a Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Hilbert, V.; Rödel, C.; Brenner, G.; Döppner, T.; Düsterer, S.; Dziarzhytski, S.; Fletcher, L.; Förster, E.; Glenzer, S. H.; Harmand, M.; Hartley, N. J.; Kazak, L.; Komar, D.; Laarmann, T.; Lee, H. J.; Ma, T.; Nakatsutsumi, M.; Przystawik, A.; Redlin, H.; Skruszewicz, S.; Sperling, P.; Tiggesbäumker, J.; Toleikis, S.; Zastrau, U.

    2014-09-01

    A key feature of extreme ultraviolet (XUV) radiation from free-electron lasers (FELs) is its spatial and temporal coherence. We measured the spatio-temporal coherence properties of monochromatized FEL pulses at 13.5 nm using a Michelson interferometer. A temporal coherence time of (59±8) fs has been determined, which is in good agreement with the spectral bandwidth given by the monochromator. Moreover, the spatial coherence in vertical direction amounts to about 15% of the beam diameter and about 12% in horizontal direction. The feasibility of measuring spatio-temporal coherence properties of XUV FEL radiation using interferometric techniques advances machine operation and experimental studies significantly.

  8. Spatio-temporal coherence of free-electron laser radiation in the extreme ultraviolet determined by a Michelson interferometer

    SciTech Connect

    Hilbert, V.; Rödel, C.; Zastrau, U.; Brenner, G.; Düsterer, S.; Dziarzhytski, S.; Harmand, M.; Przystawik, A.; Redlin, H.; Toleikis, S.; Döppner, T.; Ma, T.; Fletcher, L.; Förster, E.; Glenzer, S. H.; Lee, H. J.; Hartley, N. J.; Kazak, L.; Komar, D.; Skruszewicz, S.; and others

    2014-09-08

    A key feature of extreme ultraviolet (XUV) radiation from free-electron lasers (FELs) is its spatial and temporal coherence. We measured the spatio-temporal coherence properties of monochromatized FEL pulses at 13.5 nm using a Michelson interferometer. A temporal coherence time of (59±8) fs has been determined, which is in good agreement with the spectral bandwidth given by the monochromator. Moreover, the spatial coherence in vertical direction amounts to about 15% of the beam diameter and about 12% in horizontal direction. The feasibility of measuring spatio-temporal coherence properties of XUV FEL radiation using interferometric techniques advances machine operation and experimental studies significantly.

  9. High-speed modelocked semiconductor lasers and applications in coherent photonic systems

    NASA Astrophysics Data System (ADS)

    Lee, Wangkuen

    1.55-mum high-speed modelocked semiconductor lasers are theoretically and experimentally studied for various coherent photonic system applications. The modelocked semiconductor lasers (MSLs) are designed with high-speed (>5 GHz) external cavity configurations utilizing monolithic two-section curved semiconductor optical amplifiers. By exploiting the saturable absorber section of the monolithic device, passive or hybrid mode-locking techniques are used to generate short optical pulses with broadband optical frequency combs. Laser frequency stability is improved by applying the Pound-Drever-Hall (PDH) frequency stabilization technique to the MSLs. The improved laser performance after the frequency stabilization (a frequency drifting of less than 350 MHz), is extensively studied with respect to the laser linewidth (˜ 3 MHz), the relative intensity noise (RIN) (< -150 dB/Hz), as well as the modal RIN (˜ 3 dB reduction). MSL to MSL, and tunable laser to MSL synchronization is demonstrated by using a dual-mode injection technique and a modulation sideband injection technique, respectively. Dynamic locking behavior and locking bandwidth are experimentally and theoretically studied. Stable laser synchronization between two MSLs is demonstrated with an injection seed power on the order of a few microwatt. Several coherent heterodyne detections based on the synchronized MSL systems are demonstrated for applications in microwave photonic links and ultra-dense wavelength division multiplexing (UD-WDM) system. In addition, efficient coherent homodyne balanced receivers based on synchronized MSLs are developed and demonstrated for a spectrally phase-encoded optical CDMA (SPE-OCDMA) system.

  10. Human detection from a mobile robot using fusion of laser and vision information.

    PubMed

    Fotiadis, Efstathios P; Garzón, Mario; Barrientos, Antonio

    2013-09-04

    This paper presents a human detection system that can be employed on board a mobile platform for use in autonomous surveillance of large outdoor infrastructures. The prediction is based on the fusion of two detection modules, one for the laser and another for the vision data. In the laser module, a novel feature set that better encapsulates variations due to noise, distance and human pose is proposed. This enhances the generalization of the system, while at the same time, increasing the outdoor performance in comparison with current methods. The vision module uses the combination of the histogram of oriented gradients descriptor and the linear support vector machine classifier. Current approaches use a fixed-size projection to define regions of interest on the image data using the range information from the laser range finder. When applied to small size unmanned ground vehicles, these techniques suffer from misalignment, due to platform vibrations and terrain irregularities. This is effectively addressed in this work by using a novel adaptive projection technique, which is based on a probabilistic formulation of the classifier performance. Finally, a probability calibration step is introduced in order to optimally fuse the information from both modules. Experiments in real world environments demonstrate the robustness of the proposed method.

  11. Simultaneous intrinsic and extrinsic parameter identification of a hand-mounted laser-vision sensor.

    PubMed

    Lee, Jong Kwang; Kim, Kiho; Lee, Yongseok; Jeong, Taikyeong

    2011-01-01

    In this paper, we propose a simultaneous intrinsic and extrinsic parameter identification of a hand-mounted laser-vision sensor (HMLVS). A laser-vision sensor (LVS), consisting of a camera and a laser stripe projector, is used as a sensor component of the robotic measurement system, and it measures the range data with respect to the robot base frame using the robot forward kinematics and the optical triangulation principle. For the optimal estimation of the model parameters, we applied two optimization techniques: a nonlinear least square optimizer and a particle swarm optimizer. Best-fit parameters, including both the intrinsic and extrinsic parameters of the HMLVS, are simultaneously obtained based on the least-squares criterion. From the simulation and experimental results, it is shown that the parameter identification problem considered was characterized by a highly multimodal landscape; thus, the global optimization technique such as a particle swarm optimization can be a promising tool to identify the model parameters for a HMLVS, while the nonlinear least square optimizer often failed to find an optimal solution even when the initial candidate solutions were selected close to the true optimum. The proposed optimization method does not require good initial guesses of the system parameters to converge at a very stable solution and it could be applied to a kinematically dissimilar robot system without loss of generality.

  12. Human Detection from a Mobile Robot Using Fusion of Laser and Vision Information

    PubMed Central

    Fotiadis, Efstathios P.; Garzón, Mario; Barrientos, Antonio

    2013-01-01

    This paper presents a human detection system that can be employed on board a mobile platform for use in autonomous surveillance of large outdoor infrastructures. The prediction is based on the fusion of two detection modules, one for the laser and another for the vision data. In the laser module, a novel feature set that better encapsulates variations due to noise, distance and human pose is proposed. This enhances the generalization of the system, while at the same time, increasing the outdoor performance in comparison with current methods. The vision module uses the combination of the histogram of oriented gradients descriptor and the linear support vector machine classifier. Current approaches use a fixed-size projection to define regions of interest on the image data using the range information from the laser range finder. When applied to small size unmanned ground vehicles, these techniques suffer from misalignment, due to platform vibrations and terrain irregularities. This is effectively addressed in this work by using a novel adaptive projection technique, which is based on a probabilistic formulation of the classifier performance. Finally, a probability calibration step is introduced in order to optimally fuse the information from both modules. Experiments in real world environments demonstrate the robustness of the proposed method. PMID:24008280

  13. Simultaneous Intrinsic and Extrinsic Parameter Identification of a Hand-Mounted Laser-Vision Sensor

    PubMed Central

    Lee, Jong Kwang; Kim, Kiho; Lee, Yongseok; Jeong, Taikyeong

    2011-01-01

    In this paper, we propose a simultaneous intrinsic and extrinsic parameter identification of a hand-mounted laser-vision sensor (HMLVS). A laser-vision sensor (LVS), consisting of a camera and a laser stripe projector, is used as a sensor component of the robotic measurement system, and it measures the range data with respect to the robot base frame using the robot forward kinematics and the optical triangulation principle. For the optimal estimation of the model parameters, we applied two optimization techniques: a nonlinear least square optimizer and a particle swarm optimizer. Best-fit parameters, including both the intrinsic and extrinsic parameters of the HMLVS, are simultaneously obtained based on the least-squares criterion. From the simulation and experimental results, it is shown that the parameter identification problem considered was characterized by a highly multimodal landscape; thus, the global optimization technique such as a particle swarm optimization can be a promising tool to identify the model parameters for a HMLVS, while the nonlinear least square optimizer often failed to find an optimal solution even when the initial candidate solutions were selected close to the true optimum. The proposed optimization method does not require good initial guesses of the system parameters to converge at a very stable solution and it could be applied to a kinematically dissimilar robot system without loss of generality. PMID:22164104

  14. Semiconductor laser's on-line coherence calibration and testing of frequency stability

    NASA Astrophysics Data System (ADS)

    Zakharov, Yu. N.; Popov, A. Yu.; Tyurin, A. V.

    2008-05-01

    One of the main constituent parts of optical coherent measuring apparatus is laser as source with stable performance of frequency, radiation intensity, and light beam uniformity. At present time semiconductor lasers are rather attractive devices in view of there low prices, small size, serviceability. Progress in its quality leads to including them not only in lightheads, but as lighting unit in measuring apparatus. In order to guarantee accuracy of measuring instruments, all parts of them must have stable performance, and in this respect semiconductor laser demand stabilization more that one characteristic quantity at once. And frequency stability on the one hand is overwhelmingly important for constancy of optical measuring instruments, on the other hand our investigations show that its regulatory control is very arduous task. Both holographic methods and phase modulated speckle interferometry clearly recognize smooth frequency shift and frequency jumping depending on pumping current and temperature. And for repeatability it's required to return both of them. So it is necessary laser frequency testing during working. For interferometric comparison circuit it is frequency variation that exerts influence on fringes pattern generation, so just this parameter should be traced in the course of measuring. Specially prepared test object, introduced in holographic scheme, allows to uncover frequency variation, if they had have place, and to reproduce coherence function of laser source. Complicated coherence function of semiconductor lasers can destroy interference pattern or foul the interpretation of it. So this coherence calibration is also very useful for results validity. Phase modulated speckle interferometry method allows to build phase correlation portraits, analogical to interferograms, hence multiwavelength contour generation masks the picture of intrinsic object information too. Both real wavelength change and nonresolution area, when coherence length is less

  15. MAPM: A coherent dual CO2 laser DIAL system

    NASA Technical Reports Server (NTRS)

    Grant, W. B.; Bogan, J. R.

    1986-01-01

    The Mobile Atmospheric Pollutant Mapping System (MAPM) is a dual CO2 laser DIAL system with heterodyne detection that is being developed for large distance range resolved measurement of organic solvent vapors and aerosol clouds. The components have been chosen to allow measurements to be made to distances of 6 to 7 km in a period of 20 to 30 s. The major components of the system are listed. MAPM is being integrated into a system and will be tested with several organic solvent gases and vapors in a remotely positioned sample chamber and with a free release of ethylene. Experimental results and system performance are discussed.

  16. Manipulating coherence resonance in a quantum dot semiconductor laser via electrical pumping.

    PubMed

    Otto, Christian; Lingnau, Benjamin; Schöll, Eckehard; Lüdge, Kathy

    2014-06-02

    Excitability and coherence resonance are studied in a semiconductor quantum dot laser under short optical self-feedback. For low pump levels, these are observed close to a homoclinic bifurcation, which is in correspondence with earlier observations in quantum well lasers. However, for high pump levels, we find excitability close to a boundary crisis of a chaotic attractor. We demonstrate that in contrast to the homoclinic bifurcation the crisis and thus the excitable regime is highly sensitive to the pump current. The excitability threshold increases with the pump current, which permits to adjust the sensitivity of the excitable unit to noise as well as to shift the optimal noise strength, at which maximum coherence is observed. The shift adds up to more than one order of magnitude, which strongly facilitates experimental realizations.

  17. Decoupling gain and feedback in coherent random lasers: experiments and simulations.

    PubMed

    Consoli, Antonio; López, Cefe

    2015-11-18

    We propose and demonstrate a coherent random laser in which the randomly distributed scattering centres are placed outside the active region. This architecture is implemented by enclosing a dye solution between two agglomerations of randomly positioned titanium dioxide nanoparticles. The same spectral signature, consisting of sharp spikes with random spectral positions, is detected emerging from both ensembles of titanium dioxide nanoparticles. We interpret this newly observed behaviour as due to the optical feedback given by back-scattered light from the scattering agglomerations, which also act as output couplers. A simple model is presented to simulate the observed behaviour, considering the amplitude and phase round trip conditions that must be satisfied to sustain lasing action. Numerical simulations reproduce the experimental reports, validating our simple model. The presented results suggest a new theoretical and experimental approach for studying the complex behavior of coherent random lasers and stimulate the realization of new devices based on the proposed architecture, with different active and scattering materials.

  18. Decoupling gain and feedback in coherent random lasers: experiments and simulations

    NASA Astrophysics Data System (ADS)

    Consoli, Antonio; López, Cefe

    2015-11-01

    We propose and demonstrate a coherent random laser in which the randomly distributed scattering centres are placed outside the active region. This architecture is implemented by enclosing a dye solution between two agglomerations of randomly positioned titanium dioxide nanoparticles. The same spectral signature, consisting of sharp spikes with random spectral positions, is detected emerging from both ensembles of titanium dioxide nanoparticles. We interpret this newly observed behaviour as due to the optical feedback given by back-scattered light from the scattering agglomerations, which also act as output couplers. A simple model is presented to simulate the observed behaviour, considering the amplitude and phase round trip conditions that must be satisfied to sustain lasing action. Numerical simulations reproduce the experimental reports, validating our simple model. The presented results suggest a new theoretical and experimental approach for studying the complex behavior of coherent random lasers and stimulate the realization of new devices based on the proposed architecture, with different active and scattering materials.

  19. High Repetition Rate Pulsed 2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

    NASA Technical Reports Server (NTRS)

    Singh, Uprendra N.; Bai, Yingxin; Yu, Jirong; Petros, Mulugeta; Petzar, Paul J.; Trieu, Bo C.; Lee, Hyung

    2009-01-01

    A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed at NASA Langley Research Center. Such a laser transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of approximately 50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. The measured standard deviation of the laser frequency jitter is about 3 MHz.

  20. Laser Heated High Density Fluids Probed by Coherent Anti-Stokes Raman Spectroscopy

    SciTech Connect

    Baer, B J; Yoo, C

    2004-05-19

    We describe an integrated experimental method of Coherent Antistoke Raman Spectroscopy (CARS), laser-heating and diamond-anvil cell (DAC) technologies probing molecular vibrations of transparent molecular fluids at the pressure-temperature conditions of energetic detonation and Giant planetary interiors. In this method, we use a microfabricated metal toroid to conductively heat a surrounding transparent sample in a DAC, using a CW Nd:YLF laser. The laser is operated at a TEM{sub 01*} mode to match the shape of the toroid and thus produces a uniform heating area. The CARS probe utilizes two pulsed lasers with similar cavity lengths: a commercial narrow-band mode-locked Q-switched Nd:YAG laser and a home-built broadband dye laser. A strong CARS signal is then produced from the sample in the central region of laser-heated metal toroid where the two laser pulses spatially and temporally coincide. In this paper, we will demonstrate that this technique is capable of producing high quality vibrational spectra from nitrogen fluid above 2000 K and 13 GPa, where the application of spontaneous Raman spectroscopy is limited because of intense thermal radiation.

  1. Laser metrology for coherent multi-telescope arrays

    DOEpatents

    Shao, M.; Massie, N.A.

    1993-05-04

    In multi-telescope arrays that comprise multiple telescopes, a beam-combining module, and flat mirrors for directing light beams from the multiple telescopes to the beam combining module, a laser metrology system is used for monitoring various pathlengths along a beam path where deviations are likely. Some pathlengths are defined simply by a pair of retroreflectors or reflectors at both ends. Lengths between pairs of retroreflectors are measured and monitored by laser interferometers. One critical pathlength deviation is related to the displacement of the flat mirror. A reference frame is set up relative to the beam-combining module to form and define the coordinate system within which the positions of the flat mirrors are measured and monitored. In the preferred embodiment, a pair of retroreflectors along the optical axis of the beam-combining module defines a reference frame. A triangle is formed by the reference frame as the base and another retroreflector at the flat mirror as the vertex. The triangle is used to monitor the position of the flat mirror. A beam's pathlength is dynamically corrected in response to the monitored deviations.

  2. Laser metrology for coherent multi-telescope arrays

    DOEpatents

    Shao, Michael; Massie, Norbert A.

    1993-01-01

    In multi-telescope arrays that comprise multiple telescopes, a beam-combining module, and flat mirrors for directing light beams from the multiple telescopes to the beam combining module, a laser metrology system is used for monitoring various pathlengths along a beam path where deviations are likely. Some pathlengths are defined simply by a pair of retroreflectors or reflectors at both ends. Lengths between pairs of retroreflectors are measured and monitored by laser interferometers. One critical pathlength deviation is related to the displacement of the flat mirror. A reference frame is set up relative to the beam-combining module to form and define the coordinate system within which the positions of the flat mirrors are measured and monitored. In the preferred embodiment, a pair of retroreflectors along the optical axis of the beam-combining module defines a reference frame. A triangle is formed by the reference frame as the base and another retroreflector at the flat mirror as the vertex. The triangle is used to monitor the position of the flat mirror. A beam's pathlength is dynamically corrected in response to the monitored deviations.

  3. Laser metrology for coherent multi-telescope arrays

    SciTech Connect

    Shao, M.; Massie, N.A.

    1990-01-01

    In multi-telescope arrays that comprise multiple telescopes, a beam-combining module, and flat mirrors for directing light beams from the multiple telescopes to the beam combining module, a laser metrology system is used for monitoring various pathlengths along a beam path where deviations are likely. Some pathlengths are defined simply by a pair of retroreflectors or reflectors at both ends. Lengths between pairs of retroreflectors are measured and monitored by laser interferometers. One critical pathlength deviation is related to the displacement of the flat mirror. A reference frame is set up relative to the beam-combining module to form and define the coordinate system within which the positions of the flat mirrors are measured and monitored. In the preferred embodiment, a pair of retroreflectors along the optical axis of the beam-combining module defines a reference frame. A triangle is formed by the reference frame as the base and another retroreflector at the flat mirror as the vertex. The triangle is used to monitor the position of the flat mirror. A beam's pathlength is dynamically corrected in response to the monitored deviations.

  4. Coherent sources for mid-infrared laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Honzátko, Pavel; Baravets, Yauhen; Mondal, Shyamal; Peterka, Pavel; Todorov, Filip

    2016-12-01

    Mid-infrared laser absorption spectroscopy (LAS) is useful for molecular trace gas concentration measurements in gas mixtures. While the gas chromatography-mass spectrometry is still the gold standard in gas analysis, LAS offers several advantages. It takes tens of minutes for a gas mixture to be separated in the capillary column precluding gas chromatography from real-time control of industrial processes, while LAS can measure the concentration of gas species in seconds. LAS can be used in a wide range of applications such as gas quality screening for regulation, metering and custody transfer,1 purging gas pipes to avoid explosions,1 monitoring combustion processes,2 detection and quantification of gas leaks,3 by-products monitoring to provide feedback for the real-time control of processes in petrochemical industry,4 real-time control of inductively coupled plasma etch reactors,5, 6 and medical diagnostics by means of time-resolved volatile organic compound (VOC) analysis in exhaled breath.7 Apart from the concentration, it also permits us to determine the temperature, pressure, velocity and mass flux of the gas under observation. The selectivity and sensitivity of LAS is linked to a very high spectral resolution given by the linewidth of single-frequency lasers. Measurements are performed at reduced pressure where the collisional and Doppler broadenings are balanced. The sensitivity can be increased to ppb and sometimes to ppt ranges by increasing the interaction length in multi-pass gas cells or resonators and also by adopting modulation techniques.8

  5. Dual-comb coherent Raman spectroscopy with lasers of 1-GHz pulse repetition frequency.

    PubMed

    Mohler, Kathrin J; Bohn, Bernhard J; Yan, Ming; Mélen, Gwénaëlle; Hänsch, Theodor W; Picqué, Nathalie

    2017-01-15

    We extend the technique of multiplex coherent Raman spectroscopy with two femtosecond mode-locked lasers to oscillators of a pulse repetition frequency of 1 GHz. We demonstrate a spectra of liquids, which span 1100  cm-1 of Raman shifts. At a resolution of 6  cm-1, their measurement time may be as short as 5 μs for a refresh rate of 2 kHz. The waiting period between acquisitions is improved 10-fold compared to previous experiments with two lasers of 100-MHz repetition frequencies.

  6. Optical coherent tomography with electrically tunable semiconductor laser using FMCW techniques

    NASA Astrophysics Data System (ADS)

    Haberland, Udo; Blazek, Vladimir; Schmitt, Hans J.

    1996-12-01

    Imaging of highly scattering objects in scattering media can play an important part in assessing melanoma in human skin. The technique to be presented is based on frequency modulated continuous waves using a coherent tunable semiconductor laser irradiating a Michelson interferometer. The electrically tunable laser is characterized and the procedure to linearize the instantaneous frequency with time is described. The temporal point spread function of dilute milk is measured. Finally the performance of our imaging system is demonstrated on 2D-images of solid scattering phantoms and of an eye of a pig.

  7. Electric field detection of coherent synchrotron radiation in a storage ring generated using laser bunch slicing

    SciTech Connect

    Katayama, I.; Shimosato, H.; Bito, M.; Furusawa, K.; Adachi, M.; Zen, H.; Kimura, S.; Katoh, M.; Shimada, M.; Yamamoto, N.; Hosaka, M.; Ashida, M.

    2012-03-12

    The electric field of coherent synchrotron radiation (CSR) generated by laser bunch slicing in a storage ring has been detected by an electro-optic sampling method. The gate pulses for sampling are sent through a large-mode-area photonic-crystal fiber. The observed electric field profile of the CSR is in good agreement with the spectrum of the CSR observed using Fourier transform far-infrared spectrometry, indicating good phase stability in the CSR. The longitudinal density profiles of electrons modulated by laser pulses were evaluated from the electric field profile.

  8. Invited Article: Progress in coherent lithography using table-top extreme ultraviolet lasers.

    PubMed

    Li, W; Urbanski, L; Marconi, M C

    2015-12-01

    Compact (table top) lasers emitting at wavelengths below 50 nm had expanded the spectrum of applications in the extreme ultraviolet (EUV). Among them, the high-flux, highly coherent laser sources enabled lithographic approaches with distinctive characteristics. In this review, we will describe the implementation of a compact EUV lithography system capable of printing features with sub-50 nm resolution using Talbot imaging. This compact system is capable of producing consistent defect-free samples in a reliable and effective manner. Examples of different patterns and structures fabricated with this method will be presented.

  9. Coherent chirped pulse laser network with Mickelson phase conjugator.

    PubMed

    Okulov, A Yu

    2014-04-10

    The mechanisms of nonlinear phase-locking of a large fiber amplifier array are analyzed. The preference is given to the most suitable configuration for a coherent coupling of thousands of fundamental spatial mode fiber beams into a single smooth beam ready for chirped pulse compression. It is shown that a Michelson phase-conjugating configuration with double passage through an array of fiber amplifiers has the definite advantage compared to a one-way fiber array coupled in a Mach-Zehnder configuration. Regardless of the amount of synchronized fiber amplifiers, the Michelson phase-conjugating interferometer is expected to do a perfect compensation of the phase-piston errors and collimation of backwardly amplified fiber beams on an entrance/output beam splitter. In both configurations, the nonlinear transformation of the stretched pulse envelope, due to gain saturation, is capable of randomizing the position of chirp inside an envelope; thus it may reduce the visibility of the interference pattern at an output beam splitter. Certain advantages are inherent to the sech-form temporal envelope because of the exponential precursor and self-similar propagation in gain medium. The Gaussian envelope is significantly compressed in a deep gain saturation regime, and the frequency chirp position inside pulse envelope is more deformed.

  10. Characterization of the coherence properties of a multilongitudinal-mode erbium-doped fiber ring laser using a Michelson interferometer

    NASA Astrophysics Data System (ADS)

    Roy, Vincent; Piche, Michel; Babin, Francois; Schinn, Gregory W.

    2000-12-01

    The coherence properties of a widely tunable, multilongitudinal-mode erbium-doped fiber ring laser are investigated by means of an extremely long-arm scanning Michelson interferometer. A return of the coherence is observed at each integer multiple ofthe cavity length with a slowly decaying envelope over several kilometres.

  11. Long Coherence Length 193 nm Laser for High-Resolution Nano-Fabrication

    DTIC Science & Technology

    2008-06-27

    ns pulses, considering Kerr self phase modulation and perhaps Kramers- Kronig self phase modulation as well? What conversion efficiency to 193.4 nm is...Kramers- Kronig phase related to Actinix 31 6/27/2008 Long Coherence Length 193-nm Laser for High-Resolution Nano-Fabrication DARPA Phase I STTR Final...by. Usually the n 2 contribution is the larger of the two, and better characterized. I do not include a Kramers- Kronig contribution in the

  12. Phase-cycling coherent anti-Stokes Raman scattering using shaped femtosecond laser pulses.

    PubMed

    Li, Baolei; Warren, Warren S; Fischer, Martin C

    2010-12-06

    We demonstrate a homodyne coherent anti-Stokes Raman scattering (CARS) technique based on femtosecond laser pulse shaping. This technique utilizes fast phase cycling to extract nonlinear Raman signatures with a self-generated reference signal acting as a local oscillator. The local oscillator is generated at the focus and is intrinsically stable relative to the Raman signal even in highly scattering samples. We can therefore retrieve phase information from the Raman signal and can suppress the ubiquitous non-resonant background.

  13. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Control of laser machining of polycrystalline diamond plates by the method of low-coherence optical interferometry

    NASA Astrophysics Data System (ADS)

    Kononenko, Vitalii V.; Konov, Vitalii I.; Pimenov, S. M.; Volkov, P. V.; Goryunov, A. V.; Ivanov, V. V.; Novikov, M. A.; Markelov, V. A.; Tertyshnik, A. D.; Ustavshchikov, S. S.

    2005-07-01

    The possibility of applying low-coherence fibre optics interferometry for local contactless measurement of the optical thickness of polycrystalline diamond plates during high-power laser-pulse processing of their rough surface is demonstrated. A unique automated experimental system is developed to control the thickness of samples during ablation of their surface by a scanning 248-nm KrF excimer laser beam. It is shown that this technique is suitable for on-line control of laser polishing and for preparing plane-parallel plates.

  14. Propagation of coherently combined truncated laser beam arrays with beam distortions in non-Kolmogorov turbulence.

    PubMed

    Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin

    2012-08-10

    The propagation properties of coherently combined truncated laser beam arrays with beam distortions through non-Kolmogorov turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity and the beam width of coherently combined truncated laser beam arrays with beam distortions propagating through turbulence are derived based on the combination of statistical optics methods and the extended Huygens-Fresnel principle. The effect of beam distortions, such as amplitude modulation and phase fluctuation, is studied by numerical examples. The numerical results reveal that phase fluctuations have significant influence on the spreading of coherently combined truncated laser beam arrays in non-Kolmogorov turbulence, and the effects of the phase fluctuations can be negligible as long as the phase fluctuations are controlled under a certain level, i.e., a>0.05 for the situation considered in the paper. Furthermore, large phase fluctuations can convert the beam distribution rapidly to a Gaussian form, vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the parameters of the non-Kolmogorov turbulence.

  15. The Use of Computer Vision Algorithms for Automatic Orientation of Terrestrial Laser Scanning Data

    NASA Astrophysics Data System (ADS)

    Markiewicz, Jakub Stefan

    2016-06-01

    The paper presents analysis of the orientation of terrestrial laser scanning (TLS) data. In the proposed data processing methodology, point clouds are considered as panoramic images enriched by the depth map. Computer vision (CV) algorithms are used for orientation, which are applied for testing the correctness of the detection of tie points and time of computations, and for assessing difficulties in their implementation. The BRISK, FASRT, MSER, SIFT, SURF, ASIFT and CenSurE algorithms are used to search for key-points. The source data are point clouds acquired using a Z+F 5006h terrestrial laser scanner on the ruins of Iłża Castle, Poland. Algorithms allowing combination of the photogrammetric and CV approaches are also presented.

  16. CONTROL OF LASER RADIATION PARAMETERS: Cross modulation method of transformation of the spatial coherence of pulsed laser radiation in a nonlinear medium

    NASA Astrophysics Data System (ADS)

    Kitsak, M. A.; Kitsak, A. I.

    2008-04-01

    The cross modulation method of transformation of the spatial coherence of low-power pulsed laser radiation in a nonlinear medium is proposed. The method is realised experimentally in a multimode optical fibre. The estimates of the degree of spatial coherence of radiation subjected to the phase cross modulation demonstrated the high efficiency of this radiation decorrelation mechanism.

  17. Extrinsic parameter calibration of stereo vision sensors using spot laser projector.

    PubMed

    Liu, Zhen; Yin, Yang; Liu, Shaopeng; Chen, Xu

    2016-09-01

    The on-site calibration of stereo vision sensors plays an important role in the measurement field. Image coordinate extraction of feature points of existing targets is difficult under complex light conditions in outdoor environments, such as strong light and backlight. This paper proposes an on-site calibration method for stereo vision sensors based on a spot laser projector for solving the above-mentioned problem. The proposed method is used to mediate the laser spots on the parallel planes for the purpose of calibrating the coordinate transformation matrix between two cameras. The optimal solution of a coordinate transformation matrix is then solved by nonlinear optimization. Simulation experiments and physical experiments are conducted to validate the performance of the proposed method. Under the condition that the field of view is approximately 400  mm×300  mm, the proposed method can reach a calibration accuracy of 0.02 mm. This accuracy value is comparable to that of the method using a planar target.

  18. Strong reduction of the degree of spatial coherence of a laser beam propagating through a preformed plasma.

    PubMed

    Michel, P; Labaune, C; Bandulet, H C; Lewis, K; Depierreux, S; Hulin, S; Bonnaud, G; Tikhonchuk, V T; Weber, S; Riazuelo, G; Baldis, H A; Michard, A

    2004-04-30

    A strong reduction of the spatial coherence of a laser beam after its propagation through a plasma has been measured using a Fresnel biprism interferometer. The laser beam was diffraction limited; the coherence width was reduced from 40 mm in vacuum down to a few mm with the plasma. Numerical results based on a paraxial model exhibit a coherence degree close to the experimental one; they also prove the importance of taking into account the nonlocal transport effects in numerical simulations for such plasma conditions.

  19. Spatial coherence properties of a compact and ultrafast laser-produced plasma keV x-ray source

    SciTech Connect

    Boschetto, D.; Mourou, G.; Rousse, A.; Mordovanakis, A.; Hou, Bixue; Nees, J.; Kumah, D.; Clarke, R.

    2007-01-01

    The authors use Fresnel diffraction from knife-edges to demonstrate the spatial coherence of a tabletop ultrafast x-ray source produced by laser-plasma interaction. Spatial coherence is achieved in the far field by producing micrometer-scale x-ray spot dimensions. The results show an x-ray source size of 6 {mu}m that leads to a transversal coherence length of 20 {mu}m at a distance of 60 cm from the source. Moreover, they show that the source size is limited by the spatial spread of the absorbed laser energy.

  20. Vision of nuclear physics with photo-nuclear reactions by laser-driven γ beams

    NASA Astrophysics Data System (ADS)

    Habs, D.; Tajima, T.; Schreiber, J.; Barty, C. P. J.; Fujiwara, M.; Thirolf, P. G.

    2009-11-01

    A laser-accelerated dense electron sheet with an energy E=tilde{γ} mc^2 can be used as a relativistic mirror to coherently reflect a second laser with photon energy ħω, thus generating by the Doppler boost [A. Einstein, Annalen der Physik 17, 891 (1905); D. Habs et al., Appl. Phys. B 93, 349 (2008)] brilliant high-energy photon beams with hbarω^'=4tilde{γ}^2hbarω and short duration for many new nuclear physics experiments. While the shortest-lived atomic levels are in the atto-second range, nuclear levels can have lifetimes down to zeptoseconds. We discuss how the modulation of electron energies in phase-locked laser fields used for as-measurements [E. Goulielmakis et al., Science 317, 769 (2007)] can be carried over to the new direct measurement of fs-zs nuclear lifetimes by modulating the energies of accompanying conversion electrons or emitted protons. In the field of nuclear spectroscopy we discuss the new perspective as a function of increasing photon energy. In nuclear systems a much higher sensitivity is predicted to the time variation of fundamental constants compared to atomic systems [V. Flambaum, arXiv:nucl-th/0801.1994v1 (2008)]. For energies up to 50 keV Mössbauer-like recoilless absorption allows to produce nuclear bosonic ensembles with many delocalized coherent polaritons [G.V. Smirnov et al., Phys. Rev. A 71, 023804 (2005)] for the first time. Using the ( γ, n) reaction to produce cold, polarized neutrons with a focusing ellipsoidal device [P. Böni, Nucl. Instrum. Meth. A 586, 1 (2008); Ch. Schanzer et al., Nucl. Instrum. Meth. 529, 63 (2004)], brilliant cold polarized micro-neutron beams become available. The compact and relatively cheap laser-generated γ beams may serve for extended studies at university-based facilities.

  1. Quantitative monitoring of laser-treated engineered skin using optical coherence tomography.

    PubMed

    Ahn, Yujin; Lee, Chan-Young; Baek, Songyee; Kim, Taeho; Kim, Pilun; Lee, Sunghoon; Min, Daejin; Lee, Haekwang; Kim, Jeehyun; Jung, Woonggyu

    2016-03-01

    Nowadays, laser therapy is a common method for treating various dermatological troubles such as acne and wrinkles because of its efficient and immediate skin enhancement. Although laser treatment has become a routine procedure in medical and cosmetic fields, the prevention of side-effects, such as hyperpigmentation, redness and burning, still remains a critical issue that needs to be addressed. In order to reduce the side-effects while attaining efficient therapeutic outcomes, it is essential to understand the light-skin interaction through evaluation of physiological changes before and after laser therapy. In this study, we introduce a quantitative tissue monitoring method based on optical coherence tomography (OCT) for the evaluation of tissue regeneration after laser irradiation. To create a skin injury model, we applied a fractional CO2 laser on a customized engineered skin model, which is analogous to human skin in terms of its basic biological function and morphology. The irradiated region in the skin was then imaged by a high-speed OCT system, and its morphologic changes were analyzed by automatic segmentation software. Volumetric OCT images in the laser treated area clearly visualized the wound healing progress at different time points and provided comprehensive information which cannot be acquired through conventional monitoring methods. The results showed that the laser wound in engineered skins was mostly recovered from within 1~2 days with a fast recovery time in the vertical direction. However, the entire recovery period varied widely depending on laser doses and skin type. Our results also indicated that OCT-guided laser therapy would be a very promising protocol for optimizing laser treatment for skin therapy.

  2. 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.

  3. Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum

    NASA Astrophysics Data System (ADS)

    de A. Camargo, Franco V.; Grimmelsmann, Lena; Anderson, Harry L.; Meech, Stephen R.; Heisler, Ismael A.

    2017-01-01

    The observation of coherent quantum effects in photosynthetic light-harvesting complexes prompted the question whether quantum coherence could be exploited to improve the efficiency in new energy materials. The detailed characterization of coherent effects relies on sensitive methods such as two-dimensional electronic spectroscopy (2D-ES). However, the interpretation of the results produced by 2D-ES is challenging due to the many possible couplings present in complex molecular structures. In this work, we demonstrate how the laser spectral profile can induce electronic coherencelike signals in monomeric chromophores, potentially leading to data misinterpretation. We argue that the laser spectrum acts as a filter for certain coherence pathways and thus propose a general method to differentiate vibrational from electronic coherences.

  4. Coherent beam combination of fiber lasers with a strongly confined waveguide: numerical model.

    PubMed

    Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin

    2012-08-20

    Self-imaging properties of fiber lasers in a strongly confined waveguide (SCW) and their application in coherent beam combination (CBC) are studied theoretically. Analytical formulas are derived for the positions, amplitudes, and phases of the N images at the end of an SCW, which is important for quantitative analysis of waveguide CBC. The formulas are verified with experimental results and numerical simulation of a finite difference beam propagation method (BPM). The error of our analytical formulas is less than 6%, which can be reduced to less than 1.5% with Goos-Hahnchen penetration depth considered. Based on the theoretical model and BPM, we studied the combination of two laser beams based on an SCW. The effects of the waveguide refractive index and Gaussian beam waist are studied. We also simulated the CBC of nine and 16 fiber lasers, and a single beam without side lobes was achieved.

  5. Second user workshop on high-power lasers at the Linac Coherent Light Source

    DOE PAGES

    Heimann, Phil; Glenzer, Siegfried

    2015-05-28

    The second international workshop on the physics enabled by the unique combination of high-power lasers with the world-class Linac Coherent Light Source (LCLS) free-electron X-ray laser beam was held in Stanford, CA, on October 7–8, 2014. The workshop was co-organized by UC Berkeley, Lawrence Berkeley, Lawrence Livermore, and SLAC National Accelerator Laboratories. More than 120 scientists, including 40 students and postdoctoral scientists who are working in high-intensity laser-matter interactions, fusion research, and dynamic high-pressure science came together from North America, Europe, and Asia. The focus of the second workshop was on scientific highlights and the lessons learned from 16 newmore » experiments that were performed on the Matter in Extreme Conditions (MEC) instrument since the first workshop was held one year ago.« less

  6. Finger joint imaging by laser transillumination computed tomography based on coherent detection imaging method

    NASA Astrophysics Data System (ADS)

    Tanosaki, Shinji; Sasaki, Yoshiaki; Takagi, Michiaki; Ishikawa, Akira; Suzuki, Jota; Emori, Ryota; Inage, Hiroki; Yuasa, Tetsuya; Taniguchi, Hiroshi; Devaraj, Balasigamani; Akatsuka, Takao

    2003-07-01

    In this research, we investigate the imaging properties of tansillumination laser CT system based on the coherent detection imaging (CDI) method, for early diagnosis of rheumatoid arthritis, from the viewpoints of morphological and quantitative imaging. First, to investigate the morphological imaging ability, the index finger PIP joint of a healthy volunteer was imaged with the laser CT, X-ray CT, and MRI. By comparison of these images, we present that the laser CT delineates the bone region with high spatial resolution of sub-millimeters. Next, to investigate the quantitative imaging, three kinds of the physical phantoms simulating bone, made from polyurethane including different concentrations of CaCO3, were imaged. We present that quantitative measurement is possible by demonstrating a satisfactory linear relationship between the averaged pixel value of the reconstructed images and the actual concentrations. These results demonstrate the feasibility of early diagnosis for rheumatoid arthritis.

  7. Compact MEMS external cavity tunable laser with ultra-narrow linewidth for coherent detection.

    PubMed

    Zhang, Di; Zhao, Jianyi; Yang, Qi; Liu, Wen; Fu, Yanfeng; Li, Chao; Luo, Ming; Hu, Shenglei; Hu, Qianggao; Wang, Lei

    2012-08-27

    A compact and ultra-narrow linewidth tunable laser with an external cavity based on a simple single-axis-MEMS mirror is presented in this paper. We discuss the simulation of this tunable laser using a two-step hybrid analysis method to obtain an optimal design of the device. A wide wavelength tuning range about 40 nm in C-band with a narrow linewidth of less than 50 kHz and wavelength accuracy of ± 1 GHz over the entire tuning range can be achieved experimentally. We also conduct several experiments under different conditions to test the tunable laser. This device shows an excellent performance in both single-carrier polarization-multiplexed quadrature phase-shift keying (PM-QPSK) and multi-carrier orthogonal frequency division multiplexing (OFDM) coherent systems.

  8. Middle infrared active coherent laser spectrometer for standoff detection of chemicals.

    PubMed

    Macleod, Neil A; Rose, Rebecca; Weidmann, Damien

    2013-10-01

    Using a quantum cascade laser emitting at 7.85 μm, a middle infrared active coherent laser spectrometer has been developed for the standoff detection of vapor phase chemicals. The first prototype has been tested using diffuse target backscattering at ranges up to ~30 m. Exploiting the continuous frequency tuning of the laser source, spectra of water vapor, methane, nitrous oxide, and hydrogen peroxide were recorded. A forward model of the instrument was used to perform spectral unmixing and retrieve line-of-sight integrated concentrations and their one-sigma uncertainties. Performance was found to be limited by speckle noise originating from topographic targets. For absorbers with large absorption cross sections such as nitrous oxide (>10(-19) cm(2)·molecule(-1)), normalized detection sensitivities range between 14 and 0.3 ppm·m·Hz(-1/2), depending on the efficiency of the speckle reduction scheme implemented.

  9. Temporal Evolution of Self-Modulated Laser Wakefields Measured by Coherent Thomson Scattering

    SciTech Connect

    Ting, A.; Krushelnick, K.; Moore, C.I.; Burris, H.R.; Esarey, E.; Krall, J.; Sprangle, P. |

    1996-12-01

    Coherent Thomson scattering of a picosecond probe laser was used to measure the time evolution of plasma wakefields produced by a high intensity laser pulse (7{times}10{sup 18} W/cm{sup 2}) in an underdense plasma ({ital n}{sub {ital e}}{approx_equal}10{sup 19} cm{sup {minus}3}) in the self-modulated laser wakefield accelerator configuration. Large amplitude plasma wakefields which lasted less than 5ps were observed to decay into ion acoustic waves. The time scales associated with these measurements were consistent with the effects of the modulational instability and the enhancement of scattered signal from plasma channel formation. {copyright} {ital 1996 The American Physical Society.}

  10. Second user workshop on high-power lasers at the Linac Coherent Light Source

    SciTech Connect

    Heimann, Phil; Glenzer, Siegfried

    2015-05-28

    The second international workshop on the physics enabled by the unique combination of high-power lasers with the world-class Linac Coherent Light Source (LCLS) free-electron X-ray laser beam was held in Stanford, CA, on October 7–8, 2014. The workshop was co-organized by UC Berkeley, Lawrence Berkeley, Lawrence Livermore, and SLAC National Accelerator Laboratories. More than 120 scientists, including 40 students and postdoctoral scientists who are working in high-intensity laser-matter interactions, fusion research, and dynamic high-pressure science came together from North America, Europe, and Asia. The focus of the second workshop was on scientific highlights and the lessons learned from 16 new experiments that were performed on the Matter in Extreme Conditions (MEC) instrument since the first workshop was held one year ago.

  11. Optical coherence tomography (OCT) in laser tissue bonding of incisions in the cornea

    NASA Astrophysics Data System (ADS)

    Porat, Yishai; Gabay, Ilan; Varssano, David; Barequet, Irina; Neudorfer, Meira; Rosner, Mordechai; Katzir, Abraham

    2015-03-01

    Temperature controlled laser bonding of the cornea is analyzed in this paper using optical coherence tomography imaging, histological section evaluations and tensile strength measurements. The heat generated to obtain the bonding causes changes to the tissue structure, which appear as a bowl shaped lesion around the heated spot. Optical coherence tomography is established as an appropriate modality for the assessment of these lesions, using the other methods for validation. A quantitative analysis of the lesions attributes is produced, using a dedicated image processing algorithm. By means of this method we observed that the depth of the lesion is the most effective measure in estimating the extent of the tissue reaction to heat. A comparison of the measured lesion depth, produced by different heating profiles, is presented. This comparison shows a linear dependence on both the temperature and the exposure time, within the boundaries of the experiment. The bond strength was evaluated for several set temperatures (with 20 seconds heating time in each case) displaying an optimal value at 70°C. Yet if an incision was successfully bonded, it held a higher burst pressure for a higher temperature value. These findings demonstrate the plausibility of an integrated laser tissue bonding apparatus with an optical coherence tomography probe, which will provide, for the first time, a real time feedback of the tissue structural change, and indicate the bonding progress and end point.

  12. High-coherence electron and ion bunches from laser-cooled atoms.

    PubMed

    Sparkes, Ben M; Thompson, Daniel J; McCulloch, Andrew J; Murphy, Dene; Speirs, Rory W; Torrance, Joshua S J; Scholten, Robert E

    2014-08-01

    Cold atom electron and ion sources produce electron bunches and ion beams by photoionization of laser-cooled atoms. They offer high coherence and the potential for high brightness, with applications including ultra-fast electron-diffractive imaging of dynamic processes at the nanoscale. The effective brightness of electron sources has been limited by nonlinear divergence caused by repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that electron bunches with ellipsoidal shape and uniform density distribution have linear internal Coulomb fields, such that the Coulomb explosion can be reversed using conventional optics. Our source can create bunches shaped in three dimensions and hence in principle achieve the transverse spatial coherence and brightness needed for picosecond-diffractive imaging with nanometer resolution. Here we present results showing how the shaping capability can be used to measure the spatial coherence properties of the cold electron source. We also investigate space-charge effects with ions and generate electron bunches with durations of a few hundred picoseconds. Future development of the cold atom electron and ion source will increase the bunch charge and charge density, demonstrate reversal of Coulomb explosion, and ultimately, ultra-fast coherent electron-diffractive imaging.

  13. Self-calibration of vision parameters via genetic algorithms with simulated binary crossover and laser line projection

    NASA Astrophysics Data System (ADS)

    Alanís, Francisco Carlos Mejía; Rodríguez, J. Apolinar Muñoz

    2015-05-01

    A self-calibration technique based on genetic algorithms (GAs) with simulated binary crossover (SBX) and laser line imaging is presented. In this technique, the GA determines the vision parameters based on perspective projection geometry. The GA is constructed by means of an objective function, which is deduced from the equations of the laser line projection. To minimize the objective function, the GA performs a recombination of chromosomes through the SBX. This procedure provides the vision parameters, which are represented as chromosomes. The approach of the proposed GA is to achieve calibration and recalibration without external references and physical measurements. Thus, limitations caused by the missing of references are overcome to make self-calibration and three-dimensional (3-D) vision. Therefore, the proposed technique improves the self-calibration obtained by GAs with references. Additionally, 3-D vision is carried out via laser line position and vision parameters. The contribution of the proposed method is elucidated based on the accuracy of the self-calibration, which is performed with GAs.

  14. Monitoring coherent electron wave packet excitation dynamics by two-color attosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Yuan, Kai-Jun; Bandrauk, André D.

    2016-11-01

    We propose a method to monitor coherent electron wave packet (CEWP) excitation dynamics with two-color attosecond laser pulses. Simulations are performed on aligned H2+ by numerically solving the three-dimensional time-dependent Schrödinger equation with combinations of a resonant linearly polarized λl= 100/70 nm pump pulse and a circularly polarized λc=5 nm attosecond probe pulse. It is found that time dependent diffraction patterns in molecular frame photoelectron angular distributions (MFPADs) produced by the circular probe pulse exhibit sensitivity to the molecular alignments and time-dependent geometry of the CEWPs during and after the coherent excitation between the ground and excited states induced by the linear pump pulse. The time dependent MFPADs are described by an ultrafast diffraction model for the ionization of the bound CEWPs.

  15. Dual-frequency laser Doppler velocimeter for speckle noise reduction and coherence enhancement.

    PubMed

    Cheng, Chih-Hao; Lee, Chia-Wei; Lin, Tzu-Wei; Lin, Fan-Yi

    2012-08-27

    We study the characteristics of a dual-frequency laser Doppler velocimeter (DF-LDV) based on an optically injected semiconductor laser. The laser operated in a period-one (P1) dynamical state with two optical frequencies separated by 11.25 GHz is used as the dual-frequency light source. With a microwave beat signal carried by the light, the DF-LDV possesses both the advantages of good directionality, high intensity, and high spatial resolution from the light and low speckle noise and good coherence from the microwave, respectively. By phase-locking the two frequency components with a microwave signal, the coherence of the dual-frequency light source can be further improved and the detection range can be much extended. In this paper, velocity resolutions of the DF-LDV with different amounts of speckle noise and at different detection ranges are experimentally measured and analyzed. Compared with the conventional single-frequency LDV (SF-LDV), the velocity resolution of the DF-LDV is improved by 8 × 10(3) times from 2.5 m/s to 0.31 mm/s for a target with a longitudinal velocity vz = 4 cm/s, a transverse velocity vt = 5 m/s, and at a detection range of 108 m.

  16. Infrared-laser-assisted photoionization of helium by coherent extreme ultraviolet light

    SciTech Connect

    Tong Xiaomin; Toshima, Nobuyuki

    2010-04-15

    We investigate the infrared (IR)-laser-assisted photoionization of He by a coherent extreme ultraviolet (euv) light solving the time-dependent Schroedinger equation. A combined field of the 13th and 15th harmonics created from the same IR laser source is used to ionize He atoms coherently. We show that the ionization probabilities oscillate as a function of the time delay between the IR and the euv pulses. On the other hand, the oscillation amplitude increases as the IR intensity increases, reaches a maximum when the IR intensity is around 6x10{sup 12} W/cm{sup 2}, and then decreases as the IR intensity increases further. Decomposing the ionization probabilities by the 13th and 15th harmonics, we illustrate that the oscillation amplitude is small for a lower IR laser intensity due to the fact that the transition strength by the 13th harmonic is much smaller than the one by the 15th harmonic. When the IR intensity increases further above 6x10{sup 12} W/cm{sup 2}, the transition strength by the 13th harmonic becomes larger than the one by the 15th harmonic and the oscillation amplitude is reduced again. By tuning the relative field strengths of the 13th and 15th harmonics or the IR intensity, we can control the oscillation amplitude.

  17. Measuring the coherence properties of light emission from laser-plasma interactions. Final report

    SciTech Connect

    Batha, S.H.

    1998-03-06

    Several detrimental instabilities can be excited when a high-intensity laser interacts with plasma. The temporal evolution and spectra of the scattered light emitted by many of these instabilities are used to characterize the instabilities and to benchmark theories. It has been difficult to image the emission region with sufficient resolution to make quantitative comparisons with theory. Direct measurement of the emission region would yield information on ponderomotive steepening phenomena, the true emission zone of convective instabilities, and on the saturation of absolute instabilities. The increase in laser intensity caused by the filamentation instability is conjectured to elevate the levels of parametric instabilities found in high-energy laser-plasma interactions. Because the diameter of the filaments is very small (on the order of 10 {micro}m), it is impossible to image the emission sites directly and either to prove or to disprove this conjecture. The research reported here examines an alternate method of measuring the emission region of scattered light from parametric instabilities. This report provides a brief background of coherence theory by defining the relevant parameters in Section 2. A concrete example of the effect that multiple scattering sites would have on the proposed measurement is provided in Section 3. The following section briefly describes experiments that might be able to demonstrate the proposed technique. The conclusion raises the issue of coherence and its effect on the expected angular distribution of scattering light from parametric instabilities.

  18. An efficient quantum jump method for coherent energy transfer dynamics in photosynthetic systems under the influence of laser fields

    NASA Astrophysics Data System (ADS)

    Ai, Qing; Fan, Yuan-Jia; Jin, Bih-Yaw; Cheng, Yuan-Chung

    2014-05-01

    We present a non-Markovian quantum jump (NMQJ) approach for simulating coherent energy transfer dynamics in molecular systems in the presence of laser fields. By combining a coherent modified Redfield theory (CMRT) and a NMQJ method, this new approach inherits the broad-range validity from the CMRT and highly efficient propagation from the NMQJ. To implement NMQJ propagation of CMRT, we show that the CMRT master equation can be cast into a generalized Lindblad form. Moreover, we extend the NMQJ approach to treat time-dependent Hamiltonian, enabling the description of excitonic systems under coherent laser fields. As a benchmark of the validity of this new method, we show that the CMRT-NMQJ method accurately describes the energy transfer dynamics in a prototypical photosynthetic complex. Finally, we apply this new approach to simulate the quantum dynamics of a dimer system coherently excited to coupled single-excitation states under the influence of laser fields, which allows us to investigate the interplay between the photoexcitation process and ultrafast energy transfer dynamics in the system. We demonstrate that laser-field parameters significantly affect coherence dynamics of photoexcitations in excitonic systems, which indicates that the photoexcitation process must be explicitly considered in order to properly describe photon-induced dynamics in photosynthetic systems. This work should provide a valuable tool for efficient simulations of coherent control of energy flow in photosynthetic systems and artificial optoelectronic materials.

  19. Multimode dynamics in quantum cascade lasers: From coherent instability to mode locking

    NASA Astrophysics Data System (ADS)

    Wang, Christine Yi-Ting

    Quantum Cascade Lasers (QCLs) are unipolar semiconductor lasers based on intersubband transitions in quantum wells. Since their invention in 1994, these lasers have undergone tremendous improvement, and have become the most prominent coherent light source in the mid-infrared and terahertz spectral ranges. However, the understanding of multimode regimes in QCLs is still in its infancy, and there has not been much effort toward generating ultrafast pulses from QCLs. The recent development of low loss, high power QCLs enables the study of those previously under-investigated aspects. This thesis can be divided into two main parts. In the first part, we study the multimode regimes in QCLs. We find that QCLs, because of their extremely fast gain recovery time, differ from diode lasers in multimode operation. While a saturable absorber can often lead to self mode-locking in lasers with long gain recovery compared to the cavity round-trip time, in QCLs it lowers the threshold of a coherent multimode instability, which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago. The main experimental signature of RNGH instability is a splitting corresponding to twice the Rabi frequency in optical spectrum. In QCLs this coherent instability is enhanced due to the large Rabi frequency compared to the relaxation rates. We have also shown that spatial hole burning, which is not so readily observable in diode lasers, also plays an important role in QCLs. Both experimental data and simulations based on Maxwell-Bloch equations are presented. In the second part of this thesis, we demonstrate active mode-locking in QCLs. The stable mode-locked pulse train was generated by actively modulating the pumping current of a small section on a QCL. Stable mode locking was confirmed by second-order interferometric autocorrelation measurements, and a FWHM of 3 ps and about 0.5 pJ per pulse were deduced

  20. Dual use of image based tracking techniques: Laser eye surgery and low vision prosthesis

    NASA Technical Reports Server (NTRS)

    Juday, Richard D.

    1994-01-01

    With a concentration on Fourier optics pattern recognition, we have developed several methods of tracking objects in dynamic imagery to automate certain space applications such as orbital rendezvous and spacecraft capture, or planetary landing. We are developing two of these techniques for Earth applications in real-time medical image processing. The first is warping of a video image, developed to evoke shift invariance to scale and rotation in correlation pattern recognition. The technology is being applied to compensation for certain field defects in low vision humans. The second is using the optical joint Fourier transform to track the translation of unmodeled scenes. Developed as an image fixation tool to assist in calculating shape from motion, it is being applied to tracking motions of the eyeball quickly enough to keep a laser photocoagulation spot fixed on the retina, thus avoiding collateral damage.

  1. Dual Use of Image Based Tracking Techniques: Laser Eye Surgery and Low Vision Prosthesis

    NASA Technical Reports Server (NTRS)

    Juday, Richard D.; Barton, R. Shane

    1994-01-01

    With a concentration on Fourier optics pattern recognition, we have developed several methods of tracking objects in dynamic imagery to automate certain space applications such as orbital rendezvous and spacecraft capture, or planetary landing. We are developing two of these techniques for Earth applications in real-time medical image processing. The first is warping of a video image, developed to evoke shift invariance to scale and rotation in correlation pattern recognition. The technology is being applied to compensation for certain field defects in low vision humans. The second is using the optical joint Fourier transform to track the translation of unmodeled scenes. Developed as an image fixation tool to assist in calculating shape from motion, it is being applied to tracking motions of the eyeball quickly enough to keep a laser photocoagulation spot fixed on the retina, thus avoiding collateral damage.

  2. Reliable optical pump architecture for highly coherent lasers used in space metrology applications

    NASA Astrophysics Data System (ADS)

    Erlig, Hernan; Qiu, Yueming; Poberezhskiy, Ilya; Meras, Patrick; Wu, James

    2010-07-01

    Laser-based metrology has been identified as an enabling technology in the deployment of large, spaceborne observatories, where nanometer-level knowledge of fiducial displacement drives overall system performance. In particular, Nd:YAG NPRO (non-planar ring oscillator) based lasers have received considerable attention in this application because of their inherent high coherence at wavelengths of interest (1064 and 1319nm). However, the use of NPRO based lasers in decade long space missions is limited by typical 800nm-band pump laser diode wearout and random failure rates. Therefore, reliably achieving multi-hundred milliwatt NPRO power over prolonged mission lifetimes requires innovative pump architectures. In this paper we present a pump architecture capable of supporting continuous NPRO operation over 5.5yrs at 300mW with reliability exceeding 99.7%. The proposed architecture relies on a low-loss, high port count, all-fiber optical coupler to combine the outputs of multiple single-mode pump laser diodes. This coupler is capable of meeting the exacting environmental requirements placed by a space mission, such as SIM Lite.

  3. Application of optical coherence tomography and high-frequency ultrasound imaging during noninvasive laser vasectomy

    NASA Astrophysics Data System (ADS)

    Cilip, Christopher M.; Allaf, Mohamad E.; Fried, Nathaniel M.

    2012-04-01

    A noninvasive approach to vasectomy may eliminate male fear of complications related to surgery and increase its acceptance. Noninvasive laser thermal occlusion of the canine vas deferens has recently been reported. Optical coherence tomography (OCT) and high-frequency ultrasound (HFUS) are compared for monitoring laser thermal coagulation of the vas in an acute canine model. Bilateral noninvasive laser coagulation of the vas was performed in six dogs (n=12 vasa) using a Ytterbium fiber laser wavelength of 1075 nm, incident power of 9.0 W, pulse duration of 500 ms, pulse rate of 1 Hz, and 3-mm-diameter spot. Cryogen spray cooling was used to prevent skin burns during the procedure. An OCT system with endoscopic probe and a HFUS system with 20-MHz transducer were used to image the vas immediately before and after the procedure. Vasa were then excised and processed for gross and histologic analysis for comparison with OCT and HFUS images. OCT provided high-resolution, superficial imaging of the compressed vas within the vas ring clamp, while HFUS provided deeper imaging of the vas held manually in the scrotal fold. Both OCT and high HFUS are promising imaging modalities for real-time confirmation of vas occlusion during noninvasive laser vasectomy.

  4. Laser tissue coagulation and concurrent optical coherence tomography through a double-clad fiber coupler.

    PubMed

    Beaudette, Kathy; Baac, Hyoung Won; Madore, Wendy-Julie; Villiger, Martin; Godbout, Nicolas; Bouma, Brett E; Boudoux, Caroline

    2015-04-01

    Double-clad fiber (DCF) is herein used in conjunction with a double-clad fiber coupler (DCFC) to enable simultaneous and co-registered optical coherence tomography (OCT) and laser tissue coagulation. The DCF allows a single channel fiber-optic probe to be shared: i.e. the core propagating the OCT signal while the inner cladding delivers the coagulation laser light. We herein present a novel DCFC designed and built to combine both signals within a DCF (>90% of single-mode transmission; >65% multimode coupling). Potential OCT imaging degradation mechanisms are also investigated and solutions to mitigate them are presented. The combined DCFC-based system was used to induce coagulation of an ex vivo swine esophagus allowing a real-time assessment of thermal dynamic processes. We therefore demonstrate a DCFC-based system combining OCT imaging with laser coagulation through a single fiber, thus enabling both modalities to be performed simultaneously and in a co-registered manner. Such a system enables endoscopic image-guided laser marking of superficial epithelial tissues or laser thermal therapy of epithelial lesions in pathologies such as Barrett's esophagus.

  5. Criterion of transverse coherence of self-amplified spontaneous emission in high gain free electron laser amplifiers

    SciTech Connect

    Xie, M.; Kim, K.J.

    1995-12-31

    In a high gain free electron laser amplifier based on Self-Amplified Spontaneous Emission (SASE) the spontaneous radiation generated by an electron beam near the undulator entrance is amplified many orders of magnitude along the undulator. The transverse coherence properties of the amplified radiation depends on both the amplification process and the coherence of the seed radiation (the undulator radiation generated in the first gain length or so). The evolution of the transverse coherence in the amplification process is studied based on the solution of the coupled Maxwell-Vlasov equations including higher order transverse modes. The coherence of the seed radiation is determined by the number of coherent modes in the phase space area of the undulator radiation. We discuss the criterion of transverse coherence and identify governing parameters over a broad range of parameters. In particular we re-examine the well known emittance criterion for the undulator radiation, which states that full transverse coherence is guaranteed if the rms emittance is smaller than the wavelength divided by 4{pi}. It is found that this criterion is modified for SASE because of the different optimization conditions required for the electron beam. Our analysis is a generalization of the previous study by Yu and Krinsky for the case of vanishing emittance with parallel electron beam. Understanding the transverse coherence of SASE is important for the X-ray free electron laser projects now under consideration at SLAC and DESY.

  6. Enabling coherent control of trapped ions with economical multi-laser frequency stabilization technology

    NASA Astrophysics Data System (ADS)

    Lybarger, Warren Emanuel, Jr.

    A phase-locked scanning stability transfer cavity (SSTC) for transferring the absolute frequency stability of an iodine referenced He-Ne (master) laser to three otherwise uncalibrated (slave) lasers (at 844, 1033, & 1092 nm) of a trapped-Sr+ quantum information processing (QIP) apparatus is described. When locked, the 422 nm frequency-doubled Doppler-cooling laser exhibits an error of <1 MHz RMS for several hours, and similar stability is achieved with the other slave lasers. When unlocked, each slave laser drifts by a large fraction (or more) of the corresponding transition linewidth in minutes, thus making reliable laser cooling, ion state readout, and execution of QIP algorithms practically infeasible. The SSTC makes coherent control of Sr+ possible by addressing this problem, and the QIP apparatus is now sufficiently stable for single user operation. New single-ion experimental capabilities include ground state cooling, high-fidelity Rabi flopping, Ramsey interferometry, and sympathetic cooling of 88Sr+( 86Sr+) with 86Sr+( 88Sr+). A 2.5 msec coherence time has been achieved with the optical quoit encoded in a |5 2S 1/2> ↔ |4 2D5/2> quadrupole transition, a precision measurement of the isotope shift of the qubit transition in 86Sr+ relative to 88Sr+ is reported, and a single-ion heating rate consistent with results throughout the trapped-ion community is reported. The SSTC is simple to implement, uses no custom optics, and it has a higher scanning rate than previously demonstrated SSTC's. Phase-locked SSTC's are shown to have an advantage over the more common displacement-locked SSTC in the low finesse regime, and they are an attractive alternative to passively stable but complex optical references and diode lasers designed to address the same problem. The SSTC is useful in spectroscopic applications with other ion species, atoms, and molecules, in general. An appendix is dedicated to describing in detail an advanced trapped-ion quantum processor concept

  7. In situ 24 kHz coherent imaging of morphology change in laser percussion drilling.

    PubMed

    Webster, Paul J L; Yu, Joe X Z; Leung, Ben Y C; Anderson, Mitchell D; Yang, Victor X D; Fraser, James M

    2010-03-01

    We observe sample morphology changes in real time (24 kHz) during and between percussion drilling pulses by integrating a low-coherence microscope into a laser micromachining platform. Nonuniform cut speed and sidewall evolution in stainless steel are observed to strongly depend on assist gas. Interpulse morphology relaxation such as hole refill is directly imaged, showing dramatic differences in the material removal process dependent on pulse duration/peak power (micros/0.1 kW, ps/20 MW) and material (steel, lead zirconate titanate PZT). Blind hole depth precision is improved by over 1 order of magnitude using in situ feedback from the imaging system.

  8. Polarized multiplex coherent anti-Stokes Raman scattering using a picosecond laser and a fiber supercontinuum.

    PubMed

    Michel, Sébastien; Courjaud, Antoine; Mottay, Eric; Finot, Christophe; Dudley, John; Rigneault, Hervé

    2011-02-01

    We perform multiplex coherent anti-Stokes Raman scattering (CARS) micro-spectroscopy with a picosecond pulsed laser and a broadband supercontinuum (SC) generated in photonic crystal fiber. CARS signal stability is achieved using an active fiber coupler that avoids thermal and mechanical drifts. We obtain multiplex CARS spectra for test liquids in the 600-2000 cm(-1) spectral range. In addition we investigate the polarization dependence of the CARS spectra when rotating the pump beam linear polarization state relative to the linearly polarized broad stokes SC. From these polarization measurements we deduce the Raman depolarization ratio, the resonant versus nonresonant contribution, the Raman resonance frequency, and the linewidth.

  9. Beam shaping to improve the free-electron laser performance at the Linac Coherent Light Source

    NASA Astrophysics Data System (ADS)

    Ding, Y.; Bane, K. L. F.; Colocho, W.; Decker, F.-J.; Emma, P.; Frisch, J.; Guetg, M. W.; Huang, Z.; Iverson, R.; Krzywinski, J.; Loos, H.; Lutman, A.; Maxwell, T. J.; Nuhn, H.-D.; Ratner, D.; Turner, J.; Welch, J.; Zhou, F.

    2016-10-01

    A new operating mode has been developed for the Linac Coherent Light Source (LCLS) in which we shape the longitudinal phase space of the electron beam. This mode of operation is realized using a horizontal collimator located in the middle of the first bunch compressor to truncate the head and tail of the beam. With this method, the electron beam longitudinal phase space and current profile are reshaped, and improvement in lasing performance can be realized. We present experimental studies at the LCLS of the beam shaping effects on the free-electron laser performance.

  10. Polarized multiplex coherent anti-Stokes Raman scattering using a picosecond laser and a fiber supercontinuum

    NASA Astrophysics Data System (ADS)

    Michel, Sébastien; Courjaud, Antoine; Mottay, Eric; Finot, Christophe; Dudley, John; Rigneault, Hervé

    2011-02-01

    We perform multiplex coherent anti-Stokes Raman scattering (CARS) micro-spectroscopy with a picosecond pulsed laser and a broadband supercontinuum (SC) generated in photonic crystal fiber. CARS signal stability is achieved using an active fiber coupler that avoids thermal and mechanical drifts. We obtain multiplex CARS spectra for test liquids in the 600-2000 cm-1 spectral range. In addition we investigate the polarization dependence of the CARS spectra when rotating the pump beam linear polarization state relative to the linearly polarized broad stokes SC. From these polarization measurements we deduce the Raman depolarization ratio, the resonant versus nonresonant contribution, the Raman resonance frequency, and the linewidth.

  11. Mutual Coherence of Two Coupled Multiline Continuous-Wave HF Lasers

    DTIC Science & Technology

    1988-12-07

    trace of P2(6) single-line fringe pattern. 8 REFERENCES 1. G. E. Palma and W. J . Fader, Proc. Soc. Photo-Opt. Instrum . Eng. 440, 153 (1983). 2. M. B...REPORT SD-TR-88-105 Mutual Coherence of Two Coupled 00 Multiline Continuous-Wave HF Lasers cvD J . M. BERNARD, R. A. CHODZKO, and H. MIRELS...Spencer and W. E. Lamb, Jr., Phys. Rev. A 5, 893 (1972). 3. W. W. Chow, Opt. Lett. 10, 442 (1984). 4. H. Mirels, Appl. Opt. 25, 2130 (1986). 5. D. J

  12. High coherent bi-chromatic laser with gigahertz splitting produced by the high diffraction orders of acousto-optic modulator used for coherent population trapping experiments.

    PubMed

    Yun, Peter; Tan, Bozhong; Deng, Wei; Gu, Sihong

    2011-12-01

    To prepare the coherent population trapping (CPT) states with rubidium and cesium, the commonly used atoms in CPT studies, a coherent bi-chromatic light field with frequency difference of several GHz is a basic requirement. With a 200 MHz center frequency acousto-optic modulator (AOM), we have realized bi-chromatic laser fields with several GHz frequency splits through high diffraction orders. We have experimentally studied the coherence between two frequency components of a bi-chromatic laser beam, which is composed of ±6 orders with frequency split of 3 GHz diffracted from the same laser beam, and the measured residual phase noise is Δφ(2)<0.019 rad(2). The bi-chromatic laser fields were used to prepare CPT states with (85)Rb and (87)Rb atoms, and high contrast CPT signals were obtained. For CPT states preparation, our study result shows that it is a feasible approach to generate the bi-chromatic light field with larger frequency splits through high diffraction orders of AOM.

  13. Visible-Light Optical Coherence Tomography Angiography for Monitoring Laser-Induced Choroidal Neovascularization in Mice

    PubMed Central

    Shah, Ronil S.; Soetikno, Brian T.; Yi, Ji; Liu, Wenzhong; Skondra, Dimitra; Zhang, Hao F.; Fawzi, Amani A.

    2016-01-01

    Purpose This study sought to determine the earliest time-point at which evidence of choroidal neovascularization (CNV) could be detected with visible-light optical coherence tomography angiography (vis-OCTA) in a mouse model of laser-induced CNV. Methods Visible light-OCTA was used to study laser-induced CNV at different time-points after laser injury to monitor CNV development and measure CNV lesion size. Measurements obtained from vis-OCTA angiograms were compared with histopathologic measurements from isolectin-stained choroidal flatmounts. Results Choroidal neovascularization area measurements between the vis-OCTA system and isolectin-stained choroidal flatmounts were significantly different in area for days 2 to 4 postlaser injury, and were not significantly different in area for days 5, 7, and 14. Choroidal neovascularization area measurements taken from the stained flatmounts were larger than their vis-OCTA counterparts for all time-points. Both modalities showed a similar trend of CNV size increasing from the day of laser injury until a peak of day 7 postlaser injury and subsequently decreasing by day 14. Conclusions The earliest vis-OCTA can detect the presence of aberrant vessels in a mouse laser-induced CNV model is 5 days after laser injury. Visible light-OCTA was able to visualize the maximum of the CNV network 7 days postlaser injury, in accordance with choroidal flatmount immunostaining. Visible light-OCTA is a reliable tool in both detecting the presence of CNV development, as well as accurately determining the size of the lesion in a mouse laser-induced CNV model. PMID:27409510

  14. Wave optics simulation of spatially partially coherent beams: Applications to free space laser communications

    NASA Astrophysics Data System (ADS)

    Xiao, Xifeng

    One of the main drawbacks that prevent the extensive application of free space laser communications is the atmospheric turbulence through which the beam must propagate. For the past four decades, much attention has been devoted to finding different methods to overcome this difficulty. A partially coherent beam (PCB) has been recognized as an effective approach to improve the performance of an atmospheric link. It has been examined carefully with most analyses considering the Gaussian Schell-model (GSM) beam. However, practical PCBs may not follow GSM theory and are better examined through some numerical simulation approach such as a wave optics simulation. Consequently, an approach for modeling the spatially PCB in wave optics simulation is presented here. The approach involves the application of a sequence of random phase screens to an initial beam field and the summation of the intensity results after propagation. The relationship between the screen parameters and the spatial coherence function for the beam is developed and the approach is verified by comparing results with analytic formulations for a Gaussian Schell-model (GSM) beam. A variety of simulation studies were performed for this dissertation. The propagation through turbulence of a coherent beam and a particular version of a PCB, a pseudo-partially coherent beam (PPCB), is analyzed. The beam is created with a sequence of several Gaussian random phase screens for each atmospheric realization. The average intensity profiles, the scintillation index and aperture averaging factor for a horizontal propagation scenario are examined. Comparisons between these results and their corresponding analytic results for the well-known GSM beam are also made. Cumulative probability density functions for the received irradiance are initially investigated. Following the general simulation investigations, a performance metric is proposed as a general measure for optimizing the transverse coherence length of a partial

  15. Full-Field Optical Coherence Tomography Using Galvo Filter-Based Wavelength Swept Laser

    PubMed Central

    Shirazi, Muhammad Faizan; Kim, Pilun; Jeon, Mansik; Kim, Jeehyun

    2016-01-01

    We report a wavelength swept laser-based full-field optical coherence tomography for measuring the surfaces and thicknesses of refractive and reflective samples. The system consists of a galvo filter–based wavelength swept laser and a simple Michelson interferometer. Combinations of the reflective and refractive samples are used to demonstrate the performance of the system. By synchronizing the camera with the source, the cross-sectional information of the samples can be seen after each sweep of the swept source. This system can be effective for the thickness measurement of optical thin films as well as for the depth investigation of samples in industrial applications. A resolution target with a glass cover slip and a step height standard target are imaged, showing the cross-sectional and topographical information of the samples. PMID:27869659

  16. Delivery of picosecond lasers in multimode fibers for coherent anti-Stokes Raman scattering imaging.

    PubMed

    Wang, Zhiyong; Yang, Yaliang; Luo, Pengfei; Gao, Liang; Wong, Kelvin K; Wong, Stephen T C

    2010-06-07

    We investigated the possibility of using standard commercial multimode fibers (MMF), Corning SMF28 fibers, to deliver picosecond excitation lasers for coherent anti-Stokes Raman scattering (CARS) imaging. We theoretically and/or experimentally analyzed issues associated with the fiber delivery, such as dispersion length, walk-off length, nonlinear length, average threshold power for self-phase modulations, and four-wave mixing (FWM). These analyses can also be applied to other types of fibers. We found that FWM signals are generated in MMF, but they can be filtered out using a long-pass filter for CARS imaging. Finally, we demonstrated that MMF can be used for delivery of picosecond excitation lasers in the CARS imaging system without any degradation of image quality.

  17. Third user workshop on high-power lasers at the Linac Coherent Light Source

    SciTech Connect

    Bolme, Cynthia Anne; Glenzer, Sigfried; Fry, Alan

    2016-03-24

    On October 5–6, 2015, the third international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA [1 R. Falcone, S. Glenzer, and S. Hau-Riege, Synchrotron Radiation News 27(2), 56–58 (2014)., 2 P. Heimann and S. Glenzer, Synchrotron Radiation News 28(3), 54–56 (2015).]. Here, the workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory. More than 110 scientists attended from North America, Europe, and Asia to discuss high-energy-density (HED) science that is enabled by the unique combination of high-power lasers with the LCLS X-rays at the LCLS-Matter in Extreme Conditions (MEC) endstation.

  18. Third user workshop on high-power lasers at the Linac Coherent Light Source

    DOE PAGES

    Bolme, Cynthia Anne; Glenzer, Sigfried; Fry, Alan

    2016-03-24

    On October 5–6, 2015, the third international user workshop focusing on high-power lasers at the Linac Coherent Light Source (LCLS) was held in Menlo Park, CA, USA [1 R. Falcone, S. Glenzer, and S. Hau-Riege, Synchrotron Radiation News 27(2), 56–58 (2014)., 2 P. Heimann and S. Glenzer, Synchrotron Radiation News 28(3), 54–56 (2015).]. Here, the workshop was co-organized by Los Alamos National Laboratory and SLAC National Accelerator Laboratory. More than 110 scientists attended from North America, Europe, and Asia to discuss high-energy-density (HED) science that is enabled by the unique combination of high-power lasers with the LCLS X-rays at themore » LCLS-Matter in Extreme Conditions (MEC) endstation.« less

  19. Monitoring changes of optical attenuation coefficients of acupuncture points during laser acupuncture by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Huang, Yimei; Yang, Hongqin; Wang, Yuhua; Zheng, Liqin; Xie, Shusen

    2010-11-01

    The physical properties of acupuncture point were important to discover the mechanism of acupuncture meridian. In this paper, we used an optical coherence tomography to monitor in vivo the changes of optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point during laser irradiation on Yangxi acupuncture point. The optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point were obtained by fitting the raw data according to the Beer-Lambert's law. The experimental results showed that the optical attenuation coefficient of Hegu acupuncture point decreased during the laser acupuncture, in contrast to a barely changed result in that of non-acupuncture point. The significant change of optical attenuation coefficient of Hegu acupuncture point indicated that there was a correlation between Hegu and Yangxi acupuncture points to some extent.

  20. Laser-based space debris removal: design guidelines for coherent coupling power transmission

    NASA Astrophysics Data System (ADS)

    Kästel, Jürgen; Speiser, Jochen

    2016-10-01

    Space debris presents an increasing threat to the lifetime of commercial and military space assets. Laser-based space debris removal systems could potentially mitigate this threat by targeting debris objects in the cm-range. In order to reach this goal a minimum fluence of a few J/cm² on the debris object and a pulse repetition rate of several 10 Hz are necessary. These requirements can be met by coupling 1000-2000 independent 10 J laser sources coherently and employing a sending telescope with a diameter of 5 m. We analyze which parameters are critical to the effectiveness of the transmission system and deduce design guidelines. In particular the effects of non-optimum filling factors, secondary mirror size, emitter intensity distribution and phase jitter of the individual emitters are discussed and compared.

  1. Observation of fine structures in laser-driven electron beams using coherent transition radiation.

    PubMed

    Glinec, Y; Faure, J; Norlin, A; Pukhov, A; Malka, V

    2007-05-11

    We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam.

  2. Measurement and modeling of the effects of atmospheric turbulence on coherent laser propagation characteristics and FSO system performance

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Lu, Wei; Sun, Jianfeng; Liu, Liren

    2013-09-01

    We investigate the random phase fluctuations of coherent laser propagate through the turbulent atmosphere, and introduce a model of its impact on optical heterodyne reception free space coherent laser optical communication (FSO) system. A polarization based shearing interferometer is used to detect the distorted laser wave-front and reconstruct the wave-front after propagate through a 1Km near-ground atmospheric channel. Further, the heterodyne efficiency of the heterodyne reception system would be given under special consideration of the mismatch between the signal field and the local oscillator. By analyzing the heterodyne efficiency data and the real-time atmospheric coherence length data, a mathematical model of the effects of atmospheric turbulence on FSO system performance is given.

  3. Enhancement of spin coherence using Q-factor engineering in semiconductor microdisc lasers.

    PubMed

    Ghosh, S; Wang, W H; Mendoza, F M; Myers, R C; Li, X; Samarth, N; Gossard, A C; Awschalom, D D

    2006-04-01

    Semiconductor microcavities offer unique means of controlling light-matter interactions in confined geometries, resulting in a wide range of applications in optical communications and inspiring proposals for quantum information processing and computational schemes. Studies of spin dynamics in microcavities, a new and promising research field, have revealed effects such as polarization beats, stimulated spin scattering and giant Faraday rotation. Here, we study the electron spin dynamics in optically pumped GaAs microdisc lasers with quantum wells and interface-fluctuation quantum dots in the active region. In particular, we examine how the electron spin dynamics are modified by the stimulated emission in the discs, and observe an enhancement of the spin-coherence time when the optical excitation is in resonance with a high-quality (Q approximately 5,000) lasing mode. This resonant enhancement, contrary to expectations from the observed trend in the carrier-recombination time, is then manipulated by altering the cavity design and dimensions. In analogy with devices based on excitonic coherence, this ability to engineer coherent interactions between electron spins and photons may provide new pathways towards spin-dependent quantum optoelectronics.

  4. Adaptive engineering of coherent soft-x-rays by temporal and spatial laser-pulse shaping

    NASA Astrophysics Data System (ADS)

    Pfeifer, Thomas

    2005-03-01

    We demonstrate qualitative amplitude shaping of the coherent soft x-ray spectrum produced in the process of high-harmonic generation. This is accomplished by applying adaptive femtosecond pulse shaping methods. We performed the basic operations of complete spectral control by 1) selective generation of extended parts of the high-harmonic spectra, 2) tunable single harmonic generation and 3) creation of spectral holes (suppression of harmonics) in the plateau region of the spectrum. Our ability to qualitatively ``engineer'' the coherent spectral properties by application of temporal and spatial laser-pulse-shaping methods has immediate consequences for the developing field of attosecond x-ray science. Control over the spectrum is directly related to the control over the attosecond pulse shape as we will show by comparing experiment with simulation. In addition, even more important is the prospect to extend the field of coherent control into the soft x-ray range. In the future, the proposed technique will allow us to directly manipulate electronic motion on its natural attosecond time scale.

  5. Evaluation of Laser-Assisted Trans-Nail Drug Delivery with Optical Coherence Tomography

    PubMed Central

    Tsai, Meng-Tsan; Tsai, Ting-Yen; Shen, Su-Chin; Ng, Chau Yee; Lee, Ya-Ju; Lee, Jiann-Der; Yang, Chih-Hsun

    2016-01-01

    The nail provides a functional protection to the fingertips and surrounding tissue from external injuries. The nail plate consists of three layers including dorsal, intermediate, and ventral layers. The dorsal layer consists of compact, hard keratins, limiting topical drug delivery through the nail. In this study, we investigate the application of fractional CO2 laser that produces arrays of microthermal ablation zones (MAZs) to facilitate drug delivery in the nails. We utilized optical coherence tomography (OCT) for real-time monitoring of the laser–skin tissue interaction, sparing the patient from an invasive surgical sampling procedure. The time-dependent OCT intensity variance was used to observe drug diffusion through an induced MAZ array. Subsequently, nails were treated with cream and liquid topical drugs to investigate the feasibility and diffusion efficacy of laser-assisted drug delivery. Our results show that fractional CO2 laser improves the effectiveness of topical drug delivery in the nail plate and that OCT could potentially be used for in vivo monitoring of the depth of laser penetration as well as real-time observations of drug delivery. PMID:27973451

  6. Analytical estimation of laser phase noise induced BER floor in coherent receiver with digital signal processing.

    PubMed

    Vanin, Evgeny; Jacobsen, Gunnar

    2010-03-01

    The Bit-Error-Ratio (BER) floor caused by the laser phase noise in the optical fiber communication system with differential quadrature phase shift keying (DQPSK) and coherent detection followed by digital signal processing (DSP) is analytically evaluated. An in-phase and quadrature (I&Q) receiver with a carrier phase recovery using DSP is considered. The carrier phase recovery is based on a phase estimation of a finite sum (block) of the signal samples raised to the power of four and the phase unwrapping at transitions between blocks. It is demonstrated that errors generated at block transitions cause the dominating contribution to the system BER floor when the impact of the additive noise is negligibly small in comparison with the effect of the laser phase noise. Even the BER floor in the case when the phase unwrapping is omitted is analytically derived and applied to emphasize the crucial importance of this signal processing operation. The analytical results are verified by full Monte Carlo simulations. The BER for another type of DQPSK receiver operation, which is based on differential phase detection, is also obtained in the analytical form using the principle of conditional probability. The principle of conditional probability is justified in the case of differential phase detection due to statistical independency of the laser phase noise induced signal phase error and the additive noise contributions. Based on the achieved analytical results the laser linewidth tolerance is calculated for different system cases.

  7. Feasibility of ablative fractional laser-assisted drug delivery with optical coherence tomography

    PubMed Central

    Yang, Chih-Hsun; Tsai, Meng-Tsan; Shen, Su-Chin; Ng, Chau Yee; Jung, Shih-Ming

    2014-01-01

    Fractional resurfacing creates hundreds of microscopic wounds in the skin without injuring surrounding tissue. This technique allows rapid wound healing owing to small injury regions, and has been proven as an effective method for repairing photodamaged skin. Recently, ablative fractional laser (AFL) treatment has been demonstrated to facilitate topical drug delivery into skin. However, induced fractional photothermolysis depends on several parameters, such as incident angle, exposure energy, and spot size of the fractional laser. In this study, we used fractional CO2 laser to induce microscopic ablation array on the nail for facilitating drug delivery through the nail. To ensure proper energy delivery without damaging tissue structures beneath the nail plate, optical coherence tomography (OCT) was implemented for quantitative evaluation of induced microscopic ablation zone (MAZ). Moreover, to further study the feasibility of drug delivery, normal saline was dripped on the exposure area of fingernail and the speckle variance in OCT signal was used to observe water diffusion through the ablative channels into the nail plate. In conclusion, this study establishes OCT as an effective tool for the investigation of fractional photothermolysis and water/drug delivery through microscopic ablation channels after nail fractional laser treatment. PMID:25426321

  8. Coherent infrared radiation from the ALS generated via femtosecond laser modulation of the electron beam

    SciTech Connect

    Byrd, J.M.; Hao, Z.; Martin, M.C.; Robin, D.S.; Sannibale, F.; Schoenlein, R.W.; Venturini, M.; Zholents, A.A.; Zolotorev, M.S.

    2004-07-01

    Interaction of an electron beam with a femtosecond laser pulse co-propagating through a wiggler at the ALS produces large modulation of the electron energies within a short {approx}100 fs slice of the electron bunch. Propagating around the storage ring, this bunch develops a longitudinal density perturbation due to the dispersion of electron trajectories. The length of the perturbation evolves with a distance from the wiggler but is much shorter than the electron bunch length. This perturbation causes the electron bunch to emit short pulses of temporally and spatially coherent infrared light which are automatically synchronized to the modulating laser. The intensity and spectra of the infrared light were measured in two storage ring locations for a nominal ALS lattice and for an experimental lattice with the higher momentum compaction factor. The onset of instability stimulated by laser e-beam interaction had been discovered. The infrared signal is now routinely used as a sensitive monitor for a fine tuning of the laser beam alignment during data accumulation in the experiments with femtosecond x-ray pulses.

  9. Field performance of an all-semiconductor laser coherent Doppler lidar.

    PubMed

    Rodrigo, Peter John; Pedersen, Christian

    2012-06-15

    We implement and test what, to our knowledge, is the first deployable coherent Doppler lidar (CDL) system based on a compact, inexpensive all-semiconductor laser (SL). To demonstrate the field performance of our SL-CDL remote sensor, we compare a 36 h time series of averaged radial wind speeds measured by our instrument at an 80 m distance to those simultaneously obtained from an industry-standard sonic anemometer (SA). An excellent degree of correlation (R2=0.994 and slope=0.996) is achieved from a linear regression analysis of the CDL versus SA wind speed data. The lidar system is capable of providing high data availability, ranging from 85% to 100% even under varying outdoor (temperature and humidity) conditions during the test period. We also show the use of our SL-CDL for monitoring the dependence of aerosol backscatter on relative humidity. This work points to the feasibility of a more general class of low-cost, portable remote sensors based on all-SL emitters for applications that require demanding laser stability and coherence.

  10. High-speed Optical Coherence Tomography for Management after Laser in Situ Keratomileusis

    PubMed Central

    Avila, Mariana; Li, Yan; Song, Jonathan C.; Huang, David

    2007-01-01

    PURPOSE: To report applications of optical coherence tomography (OCT) in the management of laser in situ keratomileusis (LASIK) related problems. SETTING: Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. METHODS: Five patients referred for LASIK-related problems were enrolled in a prospective observational study. Clinical examination, ultrasound (US) pachymetry, Placido ring slit-scanning corneal topography (Orbscan II, Bausch & Lomb), and high-speed corneal OCT were performed. RESULTS: In cases of regression and keratectasia, OCT provided thickness measurements of the cornea, flap, and posterior stromal bed. Locations of tissue loss and flap interface planes were identified in a case with a recut enhancement complication. The information was used to determine whether further laser ablation was safe, confirm keratectasia, and manage complications. Optical coherence tomography measurements of central corneal thickness agreed well with US pachymetry measurements (difference 6.4 mm G 11.7 [SD]) (P Z .026), while Orbscan significantly underestimated corneal thickness (-67.5 ± 72.5 μm) (P = .17). CONCLUSIONS: High-speed OCT provided noncontact imaging and measurement of LASIK anatomy. It was useful in monitoring LASIK results and evaluating complications. PMID:17081866

  11. Decoupling gain and feedback in coherent random lasers: experiments and simulations

    PubMed Central

    Consoli, Antonio; López, Cefe

    2015-01-01

    We propose and demonstrate a coherent random laser in which the randomly distributed scattering centres are placed outside the active region. This architecture is implemented by enclosing a dye solution between two agglomerations of randomly positioned titanium dioxide nanoparticles. The same spectral signature, consisting of sharp spikes with random spectral positions, is detected emerging from both ensembles of titanium dioxide nanoparticles. We interpret this newly observed behaviour as due to the optical feedback given by back-scattered light from the scattering agglomerations, which also act as output couplers. A simple model is presented to simulate the observed behaviour, considering the amplitude and phase round trip conditions that must be satisfied to sustain lasing action. Numerical simulations reproduce the experimental reports, validating our simple model. The presented results suggest a new theoretical and experimental approach for studying the complex behavior of coherent random lasers and stimulate the realization of new devices based on the proposed architecture, with different active and scattering materials. PMID:26577668

  12. Multi-photon excited coherent random laser emission in ZnO powders.

    PubMed

    Tolentino Dominguez, Christian; Gomes, Maria de A; Macedo, Zélia S; de Araújo, Cid B; Gomes, Anderson S L

    2015-01-07

    We report the observation and analysis of anti-Stokes coherent random laser (RL) emission from zinc oxide (ZnO) powders excited by one-, two- or three-photon femtosecond laser radiation. The ZnO powders were produced via a novel proteic sol-gel, low-cost and environmentally friendly route using coconut water in the polymerization step of the metal precursor. One- and two-photon excitation at 354 nm and 710 nm, respectively, generated single-band emissions centred at about 387 nm. For three-photon excitation, the emission spectra showed a strong ultraviolet (UV) band (380-396 nm) attributed to direct three-photon absorption from the valence band to the conduction band. The presence of an intensity threshold and a bandwidth narrowing of the UV band from about 20 to 4 nm are clear evidence of RL action. The observation of multiple sub-nanometre narrow peaks in the emission spectra for excitation above the RL threshold is consistent with random lasing by coherent feedback.

  13. Multi-photon excited coherent random laser emission in ZnO powders

    NASA Astrophysics Data System (ADS)

    Tolentino Dominguez, Christian; Gomes, Maria De A.; Macedo, Zélia S.; de Araújo, Cid B.; Gomes, Anderson S. L.

    2014-11-01

    We report the observation and analysis of anti-Stokes coherent random laser (RL) emission from zinc oxide (ZnO) powders excited by one-, two- or three-photon femtosecond laser radiation. The ZnO powders were produced via a novel proteic sol-gel, low-cost and environmentally friendly route using coconut water in the polymerization step of the metal precursor. One- and two-photon excitation at 354 nm and 710 nm, respectively, generated single-band emissions centred at about 387 nm. For three-photon excitation, the emission spectra showed a strong ultraviolet (UV) band (380-396 nm) attributed to direct three-photon absorption from the valence band to the conduction band. The presence of an intensity threshold and a bandwidth narrowing of the UV band from about 20 to 4 nm are clear evidence of RL action. The observation of multiple sub-nanometre narrow peaks in the emission spectra for excitation above the RL threshold is consistent with random lasing by coherent feedback.

  14. Coherent imaging of biological samples with femtosecond pulses at the free-electron laser FLASH

    NASA Astrophysics Data System (ADS)

    Mancuso, A. P.; Gorniak, Th; Staier, F.; Yefanov, O. M.; Barth, R.; Christophis, C.; Reime, B.; Gulden, J.; Singer, A.; Pettit, M. E.; Nisius, Th; Wilhein, Th; Gutt, C.; Grübel, G.; Guerassimova, N.; Treusch, R.; Feldhaus, J.; Eisebitt, S.; Weckert, E.; Grunze, M.; Rosenhahn, A.; Vartanyants, I. A.

    2010-03-01

    Coherent x-ray imaging represents a new window to imaging non-crystalline, biological specimens at unprecedented resolutions. The advent of free-electron lasers (FEL) allows extremely high flux densities to be delivered to a specimen resulting in stronger scattered signal from these samples to be measured. In the best case scenario, the diffraction pattern is measured before the sample is destroyed by these intense pulses, as the processes involved in radiation damage may be substantially slower than the pulse duration. In this case, the scattered signal can be interpreted and reconstructed to yield a faithful image of the sample at a resolution beyond the conventional radiation damage limit. We employ coherent x-ray diffraction imaging (CXDI) using the free-electron LASer in Hamburg (FLASH) in a non-destructive regime to compare images of a biological sample reconstructed using different, single, femtosecond pulses of FEL radiation. Furthermore, for the first time, we demonstrate CXDI, in-line holography and Fourier transform holography (FTH) of the same unicellular marine organism using an FEL and present diffraction data collected using the third harmonic of FLASH, reaching into the water window. We provide quantitative results for the resolution of the CXDI images as a function of pulse intensity, and compare this with the resolutions achieved with in-line holography and FTH.

  15. Safety and Hazard Analysis for the Coherent/Acculite Laser Based Sandia Remote Sensing System (Trailer B70).

    SciTech Connect

    Augustoni, Arnold L.

    2005-09-01

    A laser safety and hazard analysis is presented, for the Coherent(r) driven Acculite(r) laser central to the Sandia Remote Sensing System (SRSS). The analysis is based on the 2000 version of the American National Standards Institute's (ANSI) Standard Z136.1, for Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for Safe Use of Lasers Outdoors. The trailer (B70) based SRSS laser system is a mobile platform which is used to perform laser interaction experiments and tests at various national test sites. The trailer based SRSS laser system is generally operated on the United State Air Force Starfire Optical Range (SOR) at Kirtland Air Force Base (KAFB), New Mexico. The laser is used to perform laser interaction testing inside the laser trailer as well as outside the trailer at target sites located at various distances. In order to protect personnel who work inside the Nominal Hazard Zone (NHZ) from hazardous laser exposures, it was necessary to determine the Maximum Permissible Exposure (MPE) for each laser wavelength (wavelength bands) and calculate the appropriate minimum Optical Density (ODmin) necessary for the laser safety eyewear used by authorized personnel. Also, the Nominal Ocular Hazard Distance (NOHD) and The Extended Ocular Hazard Distance (EOHD) are calculated in order to protect unauthorized personnel who may have violated the boundaries of the control area and might enter into the laser's NHZ for testing outside the trailer. 4Page intentionally left blank

  16. On the performance of joint iterative detection and decoding in coherent optical channels with laser frequency fluctuations

    NASA Astrophysics Data System (ADS)

    Castrillón, Mario A.; Morero, Damián A.; Agazzi, Oscar E.; Hueda, Mario R.

    2015-08-01

    The joint iterative detection and decoding (JIDD) technique has been proposed by Barbieri et al. (2007) with the objective of compensating the time-varying phase noise and constant frequency offset experienced in satellite communication systems. The application of JIDD to optical coherent receivers in the presence of laser frequency fluctuations has not been reported in prior literature. Laser frequency fluctuations are caused by mechanical vibrations, power supply noise, and other mechanisms. They significantly degrade the performance of the carrier phase estimator in high-speed intradyne coherent optical receivers. This work investigates the performance of the JIDD algorithm in multi-gigabit optical coherent receivers. We present simulation results of bit error rate (BER) for non-differential polarization division multiplexing (PDM)-16QAM modulation in a 200 Gb/s coherent optical system that includes an LDPC code with 20% overhead and net coding gain of 11.3 dB at BER = 10-15. Our study shows that JIDD with a pilot rate ⩽ 5 % compensates for both laser phase noise and laser frequency fluctuation. Furthermore, since JIDD is used with non-differential modulation formats, we find that gains in excess of 1 dB can be achieved over existing solutions based on an explicit carrier phase estimator with differential modulation. The impact of the fiber nonlinearities in dense wavelength division multiplexing (DWDM) systems is also investigated. Our results demonstrate that JIDD is an excellent candidate for application in next generation high-speed optical coherent receivers.

  17. En face optical coherence tomography investigation of apical microleakage after laser-assisted endodontic treatment.

    PubMed

    Todea, Carmen; Balabuc, Cosmin; Sinescu, Cosmin; Filip, Laura; Kerezsi, Cristina; Calniceanu, Mircea; Negrutiu, Meda; Bradu, Adrian; Hughes, Michael; Podoleanu, Adrian Gh

    2010-09-01

    The aim of our study was to evaluate the potential of en face optical coherence tomography (OCT) for the detection of apical microleakage after 980 nm and 1,064 nm laser-assisted endodontic treatment. Ninety, human, single-rooted teeth with one straight root canal and closed apices were used. All roots were prepared biomechanically to the working length at an apical size 30 and 0.06 taper. The teeth were divided into three equal groups of 30 samples each, according to the treatment to be applied to the root canal. Group I received 980 nm diode laser (3 W, 0.01 s on time, 0.01 s off time, 5 s per procedure, four procedures); group II received neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1.5 W, 15 Hz, 5 s per procedure, four procedures). In group III the root canals were approached conventionally only. In all groups the root canal filling was performed with AH Plus endodontic sealer and gutta-percha points. An en face OCT prototype was used for the investigation of apical microleakage. According to one-way analysis of variance (ANOVA) and en face OCT, the number of defects in the laser groups was significantly lower (P < 0.005) than in the control group. No statistical differences were noted between the laser groups (P = 0.049). En face OCT imaging proved that laser-assisted endodontic treatment improved the prognosis of root canal filling and led to a reduction in apical microleakage.

  18. Qualification Testing of Laser Diode Pump Arrays for a Space-Based 2-micron Coherent Doppler Lidar

    NASA Technical Reports Server (NTRS)

    Amzajerdian, Farzin; Meadows, Byron L.; Baker, Nathaniel R.; Barnes, Bruce W.; Singh, Upendra N.; Kavaya, Michael J.

    2007-01-01

    The 2-micron thulium and holmium-based lasers being considered as the transmitter source for space-based coherent Doppler lidar require high power laser diode pump arrays operating in a long pulse regime of about 1 msec. Operating laser diode arrays over such long pulses drastically impact their useful lifetime due to the excessive localized heating and substantial pulse-to-pulse thermal cycling of their active regions. This paper describes the long pulse performance of laser diode arrays and their critical thermal characteristics. A viable approach is then offered that allows for determining the optimum operational parameters leading to the maximum attainable lifetime.

  19. Observation of mode instability and coherence collapse in a single-frequency polarization-maintaining fiber ring laser

    NASA Astrophysics Data System (ADS)

    Ma, Mingxiang; Hu, Zhengliang; Xu, Pan; Hu, Yongming

    2014-06-01

    Mode instability acts as a common feature in single-frequency fiber ring lasers. The mechanism of coherence collapse by mode instability is theoretically analyzed and demonstrated with an unbalanced fiber Michelson interferometer utilizing phase modulation, which is illuminated by a single-frequency erbium-doped fiber ring laser. Multiform mode instability phenomena accompanied with coherence collapse are observed and discussed in detail by tracing the dynamics of the interference fringe visibility. The results show that mode instability would introduce extra phase noises like a false alarm to interferometric fiber optic sensing systems.

  20. Mode coherence measurements across a 1.5 THz spectral bandwidth of a passively mode-locked quantum dash laser.

    PubMed

    Watts, Regan; Rosales, Ricardo; Lelarge, Francois; Ramdane, Abderrahim; Barry, Liam

    2012-05-01

    The mode coherence of adjacent and non-adjacent spectral modes of a passively mode locked quantum dash (QDash) semiconductor laser are deduced through radio frequency beat-tone linewidth measurements. A wavelength conversion scheme that uses degenerate four wave mixing in a semiconductor optical amplifier is proposed which considerably extends the mode spacing beyond the limit imposed by conventional fast-photodetection and electrical spectrum analysis of around 100 GHz. Using this scheme, the mode coherence of the QDash laser was measured out to the thirty-first harmonic, or a mode separation of 1.5 THz.

  1. Effect of polarization controlling on coherent beam combining of two-fiber laser arrays of interferometric configuration.

    PubMed

    Cao, Jianqiu; Lu, Qisheng; Chen, Sheng-Ping; Hou, Jing; Xu, Xiaojun

    2009-01-15

    The effect of polarization controlling on coherent beam combining of two-fiber laser arrays of interferometric configuration is researched. Three kinds of arrays, built on the basis of Michelson and Mach-Zehnder interferometers, are investigated experimentally. It is found that polarization controlling is not necessary for coherent beam combining of the Michelson interferometric array but necessary for that of Mach-Zehnder interferometric arrays. These results reveal the important role of polarization in the self-organization process of interferometric laser arrays.

  2. Analyzing the propagation behavior of coherence and polarization degrees of a phase-locked partially coherent radial flat-topped array laser beam in underwater turbulence.

    PubMed

    Kashani, Fatemeh Dabbagh; Yousefi, Masoud

    2016-08-10

    In this research, based on an analytical expression for cross-spectral density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of the array setup's circle, effective width of the spectral degree of coherence, and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that any change in the amount of turbulence factors that increase the turbulence power reduces the EWSDC significantly and causes the reduction in the degree of polarization, and occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.

  3. Modification of the Coherence Properties of a Laser Beam Propagating through a Plasma and its Consequences for Stimulated Scattering Instabilities

    SciTech Connect

    Labaune, C; Baldis, H A; Bandulet, H; Depierreux, S; Fuchs, J; Michel, P; Pesme, D

    2002-11-19

    The control of coherence is a critical issue for the high-power lasers used in inertial confinement fusion (ICF). The level of coherence is an important parameter for the control of the light intensity distribution as well as the growth rate of parametric instabilities. Over the past few years, experimental and theoretical studies have evidenced the ability of an underdense plasma to reduce the spatial and temporal coherence of an intense laser beam propagating through it. As any process affecting laser propagation, plasma-induced incoherence appears fundamental for ICF for it can impact on wave-coupling conditions. We present results obtained with the six-beam LULI laser facility, in the nanosecond regime, showing direct evidences of the reduction of spatial and temporal coherence of an initially RPP-smoothed laser beam after propagation through a preformed plasma. Plasma induced incoherence (PII) proceeds from several mechanisms which include self-focusing and filament instabilities and non-linear coupling between self-focusing and forward stimulated Brillouin scattering (FSBS). Part of these experiments was dedicated to the understanding of the physical mechanisms involved in PII, as the break up of a single hot spot and the existence of ion acoustic waves having small wave vectors transverse to the interaction beam which are produced in the PII processes. The spatial and temporal characteristics of these waves give a unique access to the influence of PII on stimulated Brillouin and Raman scattering.

  4. Resonance laser-plasma excitation of coherent terahertz phonons in the bulk of fluorine-bearing crystals under high-intensity femtosecond laser irradiation

    SciTech Connect

    Potemkin, F V; Mareev, E I; Khodakovskii, N G; Mikheev, P M

    2013-08-31

    The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)

  5. Laser vision: lidar as a transformative tool to advance critical zone science

    NASA Astrophysics Data System (ADS)

    Harpold, A. A.; Marshall, J. A.; Lyon, S. W.; Barnhart, T. B.; Fisher, B.; Donovan, M.; Brubaker, K. M.; Crosby, C. J.; Glenn, N. F.; Glennie, C. L.; Kirchner, P. B.; Lam, N.; Mankoff, K. D.; McCreight, J. L.; Molotch, N. P.; Musselman, K. N.; Pelletier, J.; Russo, T.; Sangireddy, H.; Sjöberg, Y.; Swetnam, T.; West, N.

    2015-01-01

    Laser vision: lidar as a transformative tool to advance critical zone science. Observation and quantification of the Earth surface is undergoing a revolutionary change due to the increased spatial resolution and extent afforded by light detection and ranging (lidar) technology. As a consequence, lidar-derived information has led to fundamental discoveries within the individual disciplines of geomorphology, hydrology, and ecology. These disciplines form the cornerstones of Critical Zone (CZ) science, where researchers study how interactions among the geosphere, hydrosphere, and ecosphere shape and maintain the "zone of life", extending from the groundwater to the vegetation canopy. Lidar holds promise as a transdisciplinary CZ research tool by simultaneously allowing for quantification of topographic, vegetative, and hydrological data. Researchers are just beginning to utilize lidar datasets to answer synergistic questions in CZ science, such as how landforms and soils develop in space and time as a function of the local climate, biota, hydrologic properties, and lithology. This review's objective is to demonstrate the transformative potential of lidar by critically assessing both challenges and opportunities for transdisciplinary lidar applications. A review of 147 peer-reviewed studies utilizing lidar showed that 38 % of the studies were focused in geomorphology, 18 % in hydrology, 32 % in ecology, and the remaining 12 % have an interdisciplinary focus. We find that using lidar to its full potential will require numerous advances across CZ applications, including new and more powerful open-source processing tools, exploiting new lidar acquisition technologies, and improved integration with physically-based models and complementary in situ and remote-sensing observations. We provide a five-year vision to utilize and advocate for the expanded use of lidar datasets to benefit CZ science applications.

  6. Numerical analysis of 50 Gbaud homodyne coherent receivers relying on line-coding and injection locking in lasers

    NASA Astrophysics Data System (ADS)

    Xydas, Yannis; Ressopoulos, Constantinos; Bogris, Adonis

    2015-12-01

    We present a numerical analysis of 50 Gbaud coherent detection enabled by injection locked lasers and line coding. The coherent receiver was tested with respect to an ideal receiver for two higher order modulation formats (16-QAM, QPSK) and under diverse operating regimes relating to the slave laser linewidth properties, the injection level and the frequency detuning between the incoming signal and the slave laser. The impact of the slave laser properties and line coding techniques on the receiver performance is highlighted showing that the technique could be used as a practical solution in order to enable low-cost and short reach n × 100 Gb/s Ethernet communication systems with the potential of flexibility in terms of the data rate.

  7. A C IIH II frequency-stabilized erbium-doped fiber laser and its application to coherent communication

    NASA Astrophysics Data System (ADS)

    Yoshida, Masato; Kasai, Keisuke; Hongo, Jumpei; Nakazawa, Masataka

    2007-02-01

    We have described a frequency-stabilized, polarization-maintained erbium fiber ring laser. This laser has no frequency modulation at the output beam. A tunable single-mode laser has also been newly developed by simultaneously controlling a tunable FBG with a 1.5 GHz bandwidth and a PZT in the cavity. The frequency stability reached as high as 1.3 x 10 -11 for an integration time of 1 s and the linewidth was as narrow as 4 kHz. Using this coherent laser as a light source, we successfully transmitted a 20 Msymbol/s coherent quadrature amplitude modulation (QAM) signal over 525 km and achieved error free transmission.

  8. Measurement of optical path length change following pulsed laser irradiation using differential phase optical coherence tomography.

    PubMed

    Kim, Jihoon; Oh, Junghwan; Milner, Thomas E

    2006-01-01

    Differential phase optical coherence tomography (DPOCT) is introduced to measure optical path length changes in response to pulsed laser irradiation (585 nm). An analytical equation that includes thermoelastic surface displacement and thermorefractive index change is derived to predict optical path length change in response to pulsed laser irradiation for both "confined surface" and "free surface" model systems. The derived equation is tested by comparing predicted values with data recorded from experiments using two model systems. Thermorefractive index change and the thermal expansion coefficient are deduced from differential phase change (dDeltaphi) and temperature increase (DeltaT0) measurements. The measured n(T0)beta(T0)+dndT[=1.7410(-4)+/-1.710(-6) (1K)] in the free surface experiment matches with the National Institute of Standards and Technology (NIST) data value [=1.7710(-4) (1K)]. Exclusion of lateral thermal expansion in the analytical model for the confined surface experiment causes difference between the measured dndT[=-2.310(-4)+/-7.310(-6)(1K)] and the NIST value [=-9.4510(-5) (1K)]. In spite of the difference in the confined surface experiment, results of our studies indicate DPOCT can detect dynamic optical path length change in response to pulsed laser irradiation with high sensitivity, and applications to tissue diagnostics may be possible.

  9. Towards in vivo laser coagulation and concurrent optical coherence tomography through double-clad fiber devices

    NASA Astrophysics Data System (ADS)

    Beaudette, Kathy; Lo, William; Villiger, Martin; Shishkov, Milen; Godbout, Nicolas; Bouma, Brett E.; Boudoux, Caroline

    2016-03-01

    There is a strong clinical need for an optical coherence tomography (OCT) system capable of delivering concurrent coagulation light enabling image-guided dynamic laser marking for targeted collection of biopsies, as opposed to a random sampling, to reduce false-negative findings. Here, we present a system based on double-clad fiber (DCF) capable of delivering pulsed laser light through the inner cladding while performing OCT through the core. A previously clinically validated commercial OCT system (NVisionVLE, Ninepoint Medical) was adapted to enable in vivo esophageal image-guided dynamic laser marking. An optimized DCF coupler was implemented into the system to couple both modalities into the DCF. A DCF-based rotary joint was used to couple light to the spinning DCF-based catheter for helical scanning. DCF-based OCT catheters, providing a beam waist diameter of 62μm at a working distance of 9.3mm, for use with a 17-mm diameter balloon sheath, were used for ex vivo imaging of a swine esophagus. Imaging results using the DCF-based clinical system show an image quality comparable with a conventional system with minimal crosstalk-induced artifacts. To further optimize DCF catheter optical design in order to achieve single-pulse marking, a Zemax model of the DCF output and its validation are presented.

  10. Active coherent laser spectrometer for remote detection and identification of chemicals

    NASA Astrophysics Data System (ADS)

    MacLeod, Neil A.; Weidmann, Damien

    2012-10-01

    Currently, there exists a capability gap for the remote detection and identification of threat chemicals. We report here on the development of an Active Coherent Laser Spectrometer (ACLaS) operating in the thermal infrared and capable of multi-species stand-off detection of chemicals at sub ppm.m levels. A bench top prototype of the instrument has been developed using distributed feedback mid-infrared quantum cascade lasers as spectroscopic sources. The instrument provides active eye-safe illumination of a topographic target and subsequent spectroscopic analysis through optical heterodyne detection of the diffuse backscattered field. Chemical selectivity is provided by the combination of the narrow laser spectral bandwidth (typically < 2 MHz) and frequency tunability that allows the recording of the full absorption spectrum of any species within the instrument line of sight. Stand-off detection at distances up to 12 m has been demonstrated on light molecules such as H2O, CH4 and N2O. A physical model of the stand-off detection scenario including ro-vibrational molecular absorption parameters was used in conjunction with a fitting algorithm to retrieve quantitative mixing ratio information on multiple absorbers.

  11. Fast spectral coherent anti-Stokes Raman scattering microscopy with high-speed tunable picosecond laser.

    PubMed

    Cahyadi, Harsono; Iwatsuka, Junichi; Minamikawa, Takeo; Niioka, Hirohiko; Araki, Tsutomu; Hashimoto, Mamoru

    2013-09-01

    We develop a coherent anti-Stokes Raman scattering (CARS) microscopy system equipped with a tunable picosecond laser for high-speed wavelength scanning. An acousto-optic tunable filter (AOTF) is integrated in the laser cavity to enable wavelength scanning by varying the radio frequency waves applied to the AOTF crystal. An end mirror attached on a piezoelectric actuator and a pair of parallel plates driven by galvanometer motors are also introduced into the cavity to compensate for changes in the cavity length during wavelength scanning to allow synchronization with another picosecond laser. We demonstrate fast spectral imaging of 3T3-L1 adipocytes every 5  cm-1 in the Raman spectral region around 2850  cm-1 with an image acquisition time of 120 ms. We also demonstrate fast switching of Raman shifts between 2100 and 2850  cm-1, corresponding to CD2 symmetric stretching and CH2 symmetric stretching vibrations, respectively. The fast-switching CARS images reveal different locations of recrystallized deuterated and nondeuterated stearic acid.

  12. Broadband Fourier domain mode-locked laser for optical coherence tomography at 1060 nm

    NASA Astrophysics Data System (ADS)

    Marschall, Sebastian; Klein, Thomas; Wieser, Wolfgang; Torzicky, Teresa; Pircher, Michael; Biedermann, Benjamin R.; Pedersen, Christian; Hitzenberger, Christoph K.; Huber, Robert; Andersen, Peter E.

    2012-01-01

    Optical coherence tomography (OCT) in the 1060nm range is interesting for in vivo imaging of the human posterior eye segment (retina, choroid, sclera) due to low absorption in water and deep penetration into the tissue. Rapidly tunable light sources, such as Fourier domain mode-locked (FDML) lasers, enable acquisition of densely sampled three-dimensional datasets covering a wide field of view. However, semiconductor optical amplifiers (SOAs)-the typical laser gain media for swept sources-for the 1060nm band could until recently only provide relatively low output power and bandwidth. We have implemented an FDML laser using a new SOA featuring broad gain bandwidth and high output power. The output spectrum coincides with the wavelength range of minimal water absorption, making the light source ideal for OCT imaging of the posterior eye segment. With a moderate SOA current (270 mA) we achieve up to 100nm total sweep range and 12 μm depth resolution in air. By modulating the current, we can optimize the output spectrum and thereby improve the resolution to 9 μm in air (~6.5 μm in tissue). The average output power is higher than 20mW. Both sweep directions show similar performance; hence, both can be used for OCT imaging. This enables an A-scan rate of 350 kHz without buffering the light source output.

  13. High-coherence semiconductor lasers based on integral high-Q resonators in hybrid Si/III-V platforms.

    PubMed

    Santis, Christos Theodoros; Steger, Scott T; Vilenchik, Yaakov; Vasilyev, Arseny; Yariv, Amnon

    2014-02-25

    The semiconductor laser (SCL) is the principal light source powering the worldwide optical fiber network. The ever-increasing demand for data is causing the network to migrate to phase-coherent modulation formats, which place strict requirements on the temporal coherence of the light source that no longer can be met by current SCLs. This failure can be traced directly to the canonical laser design, in which photons are both generated and stored in the same, optically lossy, III-V material. This leads to an excessive and large amount of noisy spontaneous emission commingling with the laser mode, thereby degrading its coherence. High losses also decrease the amount of stored optical energy in the laser cavity, magnifying the effect of each individual spontaneous emission event on the phase of the laser field. Here, we propose a new design paradigm for the SCL. The keys to this paradigm are the deliberate removal of stored optical energy from the lossy III-V material by concentrating it in a passive, low-loss material and the incorporation of a very high-Q resonator as an integral (i.e., not externally coupled) part of the laser cavity. We demonstrate an SCL with a spectral linewidth of 18 kHz in the telecom band around 1.55 μm, achieved using a single-mode silicon resonator with Q of 10(6).

  14. INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Coherent phase control of excitation of atoms by bichromatic laser radiation in an electric field

    NASA Astrophysics Data System (ADS)

    Astapenko, Valerii A.

    2005-06-01

    A new method for coherent phase control of excitation of atoms in a discrete spectrum under the action of bichromatic laser radiation with the frequency ratio 1:2 is analysed. An important feature of this control method is the presence of a electrostatic field, which removes the parity selection rule for one of the control channels. It is shown that for the phase difference between the monochromatic radiation components, corresponding to the destructive interference between channels, there exists the electrostatic field strength at which the excited atomic transition is 'bleached'. It is proposed to use luminescence at the adjacent atomic transition for detecting the phase dependence of optical excitation.

  15. Mitigation of Laser Beam Scintillation in Free-Space Optical Communication Systems Through Coherence-Reducing Optical Materials

    NASA Technical Reports Server (NTRS)

    Renner, Christoffer J.

    2005-01-01

    Free-space optical communication systems (also known as lasercom systems) offer several performance advantages over traditional radio frequency communication systems. These advantages include increased data rates and reduced operating power and system weight. One serious limiting factor in a lasercom system is Optical turbulence in Earth's atmosphere. This turbulence breaks up the laser beam used to transmit the information into multiple segments that interfere with each other when the beam is focused onto the receiver. This interference pattern at the receiver changes with time causing fluctuations in the received optical intensity (scintillation). Scintillation leads to intermittent losses of the signal and an overall reduction in the lasercom system's performance. Since scintillation is a coherent effect, reducing the spatial and temporal coherence of the laser beam will reduce the scintillation. Transmitting a laser beam through certain materials is thought to reduce its coherence. Materials that were tested included: sapphire, BK7 glass, fused silica and others. The spatial and temporal coherence of the laser beam was determined by examining the interference patterns (fringes) it formed when interacting with various interferometers and etalons.

  16. System simulation method for fiber-based homodyne multiple target interferometers using short coherence length laser sources

    NASA Astrophysics Data System (ADS)

    Fox, Maik; Beuth, Thorsten; Streck, Andreas; Stork, Wilhelm

    2015-09-01

    Homodyne laser interferometers for velocimetry are well-known optical systems used in many applications. While the detector power output signal of such a system, using a long coherence length laser and a single target, is easily modelled using the Doppler shift, scenarios with a short coherence length source, e.g. an unstabilized semiconductor laser, and multiple weak targets demand a more elaborated approach for simulation. Especially when using fiber components, the actual setup is an important factor for system performance as effects like return losses and multiple way propagation have to be taken into account. If the power received from the targets is in the same region as stray light created in the fiber setup, a complete system simulation becomes a necessity. In previous work, a phasor based signal simulation approach for interferometers based on short coherence length laser sources has been evaluated. To facilitate the use of the signal simulation, a fiber component ray tracer has since been developed that allows the creation of input files for the signal simulation environment. The software uses object oriented MATLAB code, simplifying the entry of different fiber setups and the extension of the ray tracer. Thus, a seamless way from a system description based on arbitrarily interconnected fiber components to a signal simulation for different target scenarios has been established. The ray tracer and signal simulation are being used for the evaluation of interferometer concepts incorporating delay lines to compensate for short coherence length.

  17. Degradation of picosecond temporal contrast of Ti:sapphire lasers with coherent pedestals.

    PubMed

    Khodakovskiy, Nikita; Kalashnikov, Mikhail; Gontier, Emilien; Falcoz, Franck; Paul, Pierre-Mary

    2016-10-01

    Recompressed pulses from Ti:sapphire chirped-pulse lasers are accompanied by a slowly decaying post-pulse pedestal that is coherent with the main pulse. The pedestal typically consists of numerous pulses with temporal separation in the picosecond range. The source of this artifact lies in the Ti:sapphire active medium itself, both in the Kerr-lens mode-locked oscillator and in subsequent amplifiers. In the presence of substantial self-phase modulation, after recompression the post-pedestal generates a mirror-symmetric pre-pulse pedestal. This pedestal severely degrades the leading edge of the output pulse. This degradation is far more limiting than the original post-pedestal and severely lowers the achievable temporal contrast.

  18. Picosecond x-ray strain rosette reveals direct laser excitation of coherent transverse acoustic phonons

    PubMed Central

    Lee, Sooheyong; Williams, G. Jackson; Campana, Maria I.; Walko, Donald A.; Landahl, Eric C.

    2016-01-01

    Using a strain-rosette, we demonstrate the existence of transverse strain using time-resolved x-ray diffraction from multiple Bragg reflections in laser-excited bulk gallium arsenide. We find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times before thermal equilibrium is achieved. Our measurements are described by a new model where the Poisson ratio drives transverse motion, resulting in the creation of shear waves without the need for an indirect process such as mode conversion at an interface. Using the same excitation geometry with the narrow-gap semiconductor indium antimonide, we detected coherent transverse acoustic oscillations at frequencies of several GHz. PMID:26751616

  19. Determining helicity and topological structure of coherent vortex beam from laser speckle

    NASA Astrophysics Data System (ADS)

    R. V, Vinu; Singh, Rakesh Kumar

    2016-09-01

    We propose and experimentally demonstrate a technique to quantitatively determine the topological structure of the vortex beam coaxially launched into the random scattering media with another non-vortex beam of the orthogonal polarization component. The proposed technique applies the coherent superposition of the random electromagnetic fields and a priori knowledge of correlation of one of the random fields to determine the polarization correlation of the other. The polarization correlation of the random field is used to determine the topological charge and phase structure of the vortex beam from the laser speckle. The application of the proposed technique is demonstrated by determining the helicity and topological charge of the vortex beam for three different cases.

  20. Coherent destruction of tunneling in graphene irradiated by elliptically polarized lasers

    NASA Astrophysics Data System (ADS)

    Gagnon, Denis; Fillion-Gourdeau, François; Dumont, Joey; Lefebvre, Catherine; MacLean, Steve

    2017-01-01

    Photo-induced transition probabilities in graphene are studied theoretically from the viewpoint of Floquet theory. Conduction band populations are computed for a strongly, periodically driven graphene sheet under linear, circular, and elliptic polarization. Features of the momentum spectrum of excited quasi-particles can be directly related to the avoided crossing of the Floquet quasi-energy levels. In particular, the impact of the ellipticity and the strength of the laser excitation on the avoided crossing structure—and on the resulting transition probabilities—is studied. It is shown that the ellipticity provides an additional control parameter over the phenomenon of coherent destruction of tunneling in graphene, allowing one to selectively suppress multiphoton resonances.

  1. A comparison study of optical coherence elastography and laser Michelson vibrometry

    NASA Astrophysics Data System (ADS)

    Li, Jiasong; Liu, Chih-Hao; Schill, Alexander; Singh, Manmohan; Kistenev, Yury V.; Larin, Kirill V.

    2016-03-01

    Quantitative elastography is a power technique to detect and analyze the changes in biomedical properties of tissues in normal and pathological states. In this study, two noncontact elastography techniques, laser Michelson vibrometry (LMV) and optical coherence elastography (OCE), were utilized to quantify the Young's modulus of tissue-mimicking agar phantoms of various concentrations. Low-amplitude (micrometer scale) elastic waves were induced by a focused air-pulse delivery system and imaged by the respective systems. The Young's modulus as assessed by both elastographic techniques was similar and was compared to the stiffness as measured by uniaxial mechanical testing. The results show that both techniques accurately quantified the elasticity. OCE can provide absolute elastic wave temporal profile, depth-resolved measurement and superior displacement sensitivity compared to LMV, but LMV is significantly cheaper (10X) and easier to implement than OCE.

  2. Picosecond x-ray strain rosette reveals direct laser excitation of coherent transverse acoustic phonons

    SciTech Connect

    Lee, Sooheyong; Williams, G. Jackson; Campana, Maria I.; Walko, Donald A.; Landahl, Eric C.

    2016-01-11

    Using a strain-rosette, we demonstrate the existence of transverse strain using time-resolved x-ray diffraction from multiple Bragg reflections in laser-excited bulk gallium arsenide. We find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times before thermal equilibrium is achieved. Our measurements are described by a new model where the Poisson ratio drives transverse motion, resulting in the creation of shear waves without the need for an indirect process such as mode conversion at an interface. Finally, using the same excitation geometry with the narrow-gap semiconductor indium antimonide, we detected coherent transverse acoustic oscillations at frequencies of several GHz.

  3. Prospects of coherent control in turbid media: Bounds on focusing broadband laser pulses

    SciTech Connect

    Shapiro, Evgeny A.; Drane, Thomas M.; Milner, Valery

    2011-11-15

    We study the prospects of controlling transmission of broadband and bichromatic laser pulses through turbid samples. The ability to focus transmitted broadband light is limited via both the scattering properties of the medium and the technical characteristics of the experimental setup. There are two time scales given by pulse stretching in the near- and far-field regions which define the maximum bandwidth of a pulse amenable to focusing. In the geometric-optics regime of wave propagation in the medium, a single setup can be optimal for focusing light at frequencies {omega} and n{omega} simultaneously, providing the basis for the 1+n coherent quantum control. Beyond the regime of geometric optics, we discuss a simple solution for the shaping, which provides the figure of merit for one's ability to simultaneously focus several transmission modes.

  4. Picosecond x-ray strain rosette reveals direct laser excitation of coherent transverse acoustic phonons

    DOE PAGES

    Lee, Sooheyong; Williams, G. Jackson; Campana, Maria I.; ...

    2016-01-11

    Using a strain-rosette, we demonstrate the existence of transverse strain using time-resolved x-ray diffraction from multiple Bragg reflections in laser-excited bulk gallium arsenide. We find that anisotropic strain is responsible for a considerable fraction of the total lattice motion at early times before thermal equilibrium is achieved. Our measurements are described by a new model where the Poisson ratio drives transverse motion, resulting in the creation of shear waves without the need for an indirect process such as mode conversion at an interface. Finally, using the same excitation geometry with the narrow-gap semiconductor indium antimonide, we detected coherent transverse acousticmore » oscillations at frequencies of several GHz.« less

  5. Doppler cooling with coherent trains of laser pulses and a tunable velocity comb

    SciTech Connect

    Ilinova, Ekaterina; Ahmad, Mahmoud; Derevianko, Andrei

    2011-09-15

    We explore the possibility of decelerating and Doppler cooling an ensemble of two-level atoms by a coherent train of short, nonoverlapping laser pulses. We derive analytical expressions for mechanical force exerted by the train. In frequency space the force pattern reflects the underlying frequency comb structure. The pattern depends strongly on the ratio of the atomic lifetime to the repetition time between the pulses and pulse area. For example, in the limit of short lifetimes, the frequency-space peaks of the optical force wash out. We propose to tune the carrier-envelope offset frequency to follow the Doppler-shifted detuning as atoms decelerate; this leads to compression of atomic velocity distribution about comb teeth and results in a ''velocity comb''--a series of narrow equidistant peaks in the velocity space.

  6. Doublet Pulse Coherent Laser Radar for Tracking of Resident Space Objects

    NASA Technical Reports Server (NTRS)

    Prasad, Narasimha S.; Rudd, Van; Shald, Scott; Sandford, Stephen; Dimarcantonio, Albert

    2014-01-01

    In this paper, the development of a long range ladar system known as ExoSPEAR at NASA Langley Research Center for tracking rapidly moving resident space objects is discussed. Based on 100 W, nanosecond class, near-IR laser, this ladar system with coherent detection technique is currently being investigated for short dwell time measurements of resident space objects (RSOs) in LEO and beyond for space surveillance applications. This unique ladar architecture is configured using a continuously agile doublet-pulse waveform scheme coupled to a closed-loop tracking and control loop approach to simultaneously achieve mm class range precision and mm/s velocity precision and hence obtain unprecedented track accuracies. Salient features of the design architecture followed by performance modeling and engagement simulations illustrating the dependence of range and velocity precision in LEO orbits on ladar parameters are presented. Estimated limits on detectable optical cross sections of RSOs in LEO orbits are discussed.

  7. Single Shot Coherence Properties of the Free-Electron Laser SACLA in the Hard X-ray Regime

    PubMed Central

    Lehmkühler, Felix; Gutt, Christian; Fischer, Birgit; Schroer, Martin A.; Sikorski, Marcin; Song, Sanghoon; Roseker, Wojciech; Glownia, James; Chollet, Mathieu; Nelson, Silke; Tono, Kensuke; Katayama, Tetsuo; Yabashi, Makina; Ishikawa, Tetsuya; Robert, Aymeric; Grübel, Gerhard

    2014-01-01

    We measured the coherence properties of the free-electron laser SACLA on a single shot basis at an X-ray energy of 8 keV. By analysing small-angle X-ray scattering speckle patterns from colloidal dispersions we found a degree of transverse coherence of βt = 0.79 ± 0.09. Taking detector properties into account, we developed a simulation model in oder to determine the degree of coherence from intensity histograms. Finally we calculated a coherence time of τc = 0.1 fs and a pulse duration of 5.2 fs which corresponds with previous predictions. PMID:24913261

  8. Coherent diffraction imaging analysis of shape-controlled nanoparticles with focused hard X-ray free-electron laser pulses.

    PubMed

    Takahashi, Yukio; Suzuki, Akihiro; Zettsu, Nobuyuki; Oroguchi, Tomotaka; Takayama, Yuki; Sekiguchi, Yuki; Kobayashi, Amane; Yamamoto, Masaki; Nakasako, Masayoshi

    2013-01-01

    We report the first demonstration of the coherent diffraction imaging analysis of nanoparticles using focused hard X-ray free-electron laser pulses, allowing us to analyze the size distribution of particles as well as the electron density projection of individual particles. We measured 1000 single-shot coherent X-ray diffraction patterns of shape-controlled Ag nanocubes and Au/Ag nanoboxes and estimated the edge length from the speckle size of the coherent diffraction patterns. We then reconstructed the two-dimensional electron density projection with sub-10 nm resolution from selected coherent diffraction patterns. This method enables the simultaneous analysis of the size distribution of synthesized nanoparticles and the structures of particles at nanoscale resolution to address correlations between individual structures of components and the statistical properties in heterogeneous systems such as nanoparticles and cells.

  9. Development of high coherence, 200mW, 193nm solid-state laser at 6 kHz

    NASA Astrophysics Data System (ADS)

    Nakazato, T.; Tsuboi, M.; Onose, T.; Tanaka, Y.; Sarukura, N.; Ito, S.; Kakizaki, K.; Watanabe, S.

    2015-02-01

    The high coherent, high power 193-nm ArF lasers are useful for interference lithography and microprosessing applications. In order to achieve high coherence ArF lasers, we have been developing a high coherence 193 nm solid state laser for the seeding to a high power ArF laser. We used the sum frequency mixing of the fourth harmonic (FH) of a 904-nm Ti:sapphire laser with a Nd:YVO4 laser (1342 nm) to generate 193-nm light. The laser system consists of a single-mode Ti:sapphire oscillator seeded by a 904-nm external cavity laser diode, a Pockels cell, a 6-pass amplifier, a 4-pass amplifier, a 2-pass amplifier and a wavelength conversion stage. The required repetition rate of 6 kHz corresponding to the ArF laser, along with a low gain at 904 nm induces serious thermal lens effects; extremely short focal lengths of the order of cm and bi-foci in the vertical and horizontal directions. From the analysis of thermal lens depending on pump intensity, we successfully compensated the thermal lens by dividing a 527-nm pump power with 15, 25 and 28 W to 3-stage amplifiers with even passes, resulting in the output power above 10W with a nearly diffraction limited beam. This 904-nm output was converted to 3.8 W in the second harmonic by LBO, 0.5 W in FH by BBO sequentially. Finally the output power of 230 mW was obtained at 193 nm by mixing the FH with a 1342-nm light in CLBO.

  10. LADAR vision technology for automated rendezvous and capture

    NASA Technical Reports Server (NTRS)

    Frey, Randy W.

    1991-01-01

    LADAR Vision Technology at Autonomous Technologies Corporation consists of two sensor/processing technology elements: high performance long range multifunction coherent Doppler laser radar (LADAR) technology; and short range integrated CCD camera with direct detection laser ranging sensors. Algorithms and specific signal processing implementations have been simulated for both sensor/processing approaches to position and attitude tracking applicable to AR&C. Experimental data supporting certain sensor measurement accuracies have been generated.

  11. BCH Codes for Coherent Star DQAM Systems with Laser Phase Noise

    NASA Astrophysics Data System (ADS)

    Leong, Miu Yoong; Larsen, Knud J.; Jacobsen, Gunnar; Zibar, Darko; Sergeyev, Sergey; Popov, Sergei

    2017-03-01

    Coherent optical systems have relatively high laser phase noise, which affects the performance of forward error correction (FEC) codes. In this paper, we propose a method for selecting Bose-Chaudhuri-Hocquenghem (BCH) codes for coherent systems with star-shaped constellations and M-ary differential quadrature amplitude modulation (DQAM). Our method supports constellations of any order M which is a power of 2, and includes differential M-ary phase shift keying as a special case. Our approach is straightforward, requiring only short pre-FEC simulations to parameterize a statistical model, based on which we select codes analytically. It is applicable to pre-FEC bit error rates (BERs) of around 10-3. We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of 10-5, codes selected with our method yield BERs within 2× target. Lastly, we extend our method to systems with interleaving, which enables us to use codes with lower overhead.

  12. Spatial structure and coherence properties of Brillouin scatter from CO2 laser-target interaction

    NASA Astrophysics Data System (ADS)

    Mitchel, G. R.; Grek, B.; Johnston, T. W.; Pépin, H.; Church, P.; Martin, F.

    1982-05-01

    The spatial structure and coherence properties of 10.6-μm light scattered from CO2 laser-target interactions in oblique incidence show many unexpected features. It is found that the Brillouin backscatter is neither a phase conjugate nor a ray retrace of the incident beam. Rather, it shows a preference for scattering directions other than those exactly antiparallel to the incident beam, apparently related to the angular distribution of the scattering source and also of the plasma corona that serves as the Brillouin amplifying medium. As well, the backscatter phasefront is strongly perturbed with respect to the incident phasefront. This is an indication of turbulence in the corona and/or memory of the structure in the source that is then amplified. Small-scale structures seen in the reimaged backscatter are due to phase perturbation and cannot be simply interpreted as geometric images of a (filamented) source. The phasefront of light that is scattered obliquely from the plasma is much more coherent.

  13. Vision sensing techniques in aeronautics and astronautics

    NASA Technical Reports Server (NTRS)

    Hall, E. L.

    1988-01-01

    The close relationship between sensing and other tasks in orbital space, and the integral role of vision sensing in practical aerospace applications, are illustrated. Typical space mission-vision tasks encompass the docking of space vehicles, the detection of unexpected objects, the diagnosis of spacecraft damage, and the inspection of critical spacecraft components. Attention is presently given to image functions, the 'windowing' of a view, the number of cameras required for inspection tasks, the choice of incoherent or coherent (laser) illumination, three-dimensional-to-two-dimensional model-matching, edge- and region-segmentation techniques, and motion analysis for tracking.

  14. Influence of truncation factor on coherent beam combining based on a triangular fiber laser array

    NASA Astrophysics Data System (ADS)

    Zhi, Dong; Ma, Yan-xing; Wang, Xiao-lin; Zhou, Pu; Si, Lei

    2016-10-01

    In this paper, we present an experimental comparison of coherent beam combining (CBC) effect with different truncation factors based on a triangle fiber laser array for the first time to our best knowledge. First, we fabricate a triangle fiber laser array based on adaptive fiber optics collimators with the fixed focusing length of 0.18m and clear aperture of 50mm. Two output fiber arrays (6/125 fiber array and 20/400 fiber array) with different numerical apertures (0.12 and 0.065, respectively) are used to generate different truncation factors. The direct measurement method is used to measure the intensity distribution of the two collimated beams with different sizes. Results show that the beam diameters are 14.5mm and 27.6mm for 20/400 output fiber and 6/125 output fiber, separately. This means that two fiber laser arrays with truncation factors of 0.29 and 0.55 are achieved. Then we numerically calculate the CBC efficiencies of two situations with different truncation factors. The analytical results show that the CBC efficiency improves from 0.144 with truncation factor of 0.29 to 0.413 with truncation factor of 0.55. At last, a CBC experiment platform is set up. Throughout the whole experiment, single frequency dithering algorithm and SPGD algorithm are separately used to perform the phase-locking control and the tilt control. Two CBC experiments of triangle fiber laser arrays are achieved successfully both with residual phase errors about λ/15. By analysis the experimental results, we get the CBC efficiencies are 0.099 (69% of 0.144) and 0.264 (64% of 0.413) for the two fiber arrays. The experimental results identify the importance of truncation factor on CBC efficiency and provide an important reference on the selection of fiber array parameters in order to achieve the largest energy proportion in the central lobe.

  15. Coherent pulse and environmental characteristics of the intramolecular proton-transfer lasers based on 3-hydroxyflavone and fisetin

    NASA Astrophysics Data System (ADS)

    Parthenopoulos, Dimitri A.; Kasha, Michael

    1988-04-01

    Coherent stimulated emission and laser beams of good quality are reported for 3-hydroxyfiavone (3-HF) and a polyhydroxyfiavone, risetin, acting as intramolecular proton-transfer lasers. The laser beam quality of these materials is comparable to that observed for rhodamine-6G. Studies of amplified spontaneous emission of 3-hydroxyflavone in highly polar solvents are also reported. The very large changes in dipole moment upon electronic excitation of 3-HF expected according to ZINDO semiempirical molecular orbital calculations fail to give rise to spectral shifts in the high dielectric constant solvents. The results are interpreted as a masking spectral effect caused by specific hydrogen bonding by the solvent.

  16. Optical emission of a plasma from low-density targets irradiated with coherence-controllable laser radiation

    NASA Astrophysics Data System (ADS)

    Fronya, A. A.; Borisenko, N. G.; Puzyrev, V. N.; Sahakyan, A. T.; Starodub, A. N.; Yakushev, O. F.

    2017-03-01

    The results of experiments on the interaction of nanosecond laser radiation with low-density volume-structured targets of different density and thickness are reported. The targets were irradiated by laser radiation with controllable coherence. The primary objective was to investigate the effect of target parameters on the characteristics of radiation scattered by the plasma. The spectral characteristics of the radiation scattered by the plasma in the backward direction and in the direction of laser beam propagation were obtained. Also the radiation scattering patterns were recorded.

  17. Three-dimensional non-destructive optical evaluation of laser-processing performance using optical coherence tomography

    PubMed Central

    Kim, Youngseop; Choi, Eun Seo; Kwak, Wooseop; Shin, Yongjin; Jung, Woonggyu; Ahn, Yeh-Chan; Chen, Zhongping

    2014-01-01

    We demonstrate the use of optical coherence tomography (OCT) as a non-destructive diagnostic tool for evaluating laser-processing performance by imaging the features of a pit and a rim. A pit formed on a material at different laser-processing conditions is imaged using both a conventional scanning electron microscope (SEM) and OCT. Then using corresponding images, the geometrical characteristics of the pit are analyzed and compared. From the results, we could verify the feasibility and the potential of the application of OCT to the monitoring of the laser-processing performance. PMID:24932051

  18. Coherent anti-Stokes Raman scattering imaging with a laser source delivered by a photonic crystal fiber.

    PubMed

    Wang, Haifeng; Huff, Terry B; Cheng, Ji-Xin

    2006-05-15

    We demonstrate laser-scanning coherent anti-Stokes Raman scattering (CARS) imaging with two excitation laser beams delivered by a large-mode-area photonic crystal fiber. The group-velocity dispersion and self-phase modulation effects are largely suppressed due to the large mode area of the fiber and the use of picosecond pulses. The fiber delivery preserves the signal level and image spatial resolution well. High-quality images of live spinal cord tissues are acquired using the fiber-delivered laser source. Our method provides a basic platform for developing a flexible and compact CARS imaging system.

  19. Coherent Electronic Wave Packet Motion in C60 Controlled by the Waveform and Polarization of Few-Cycle Laser Fields

    NASA Astrophysics Data System (ADS)

    Li, H.; Mignolet, B.; Wachter, G.; Skruszewicz, S.; Zherebtsov, S.; Süßmann, F.; Kessel, A.; Trushin, S. A.; Kling, Nora G.; Kübel, M.; Ahn, B.; Kim, D.; Ben-Itzhak, I.; Cocke, C. L.; Fennel, T.; Tiggesbäumker, J.; Meiwes-Broer, K.-H.; Lemell, C.; Burgdörfer, J.; Levine, R. D.; Remacle, F.; Kling, M. F.

    2015-03-01

    Strong laser fields can be used to trigger an ultrafast molecular response that involves electronic excitation and ionization dynamics. Here, we report on the experimental control of the spatial localization of the electronic excitation in the C60 fullerene exerted by an intense few-cycle (4 fs) pulse at 720 nm. The control is achieved by tailoring the carrier-envelope phase and the polarization of the laser pulse. We find that the maxima and minima of the photoemission-asymmetry parameter along the laser-polarization axis are synchronized with the localization of the coherent electronic wave packet at around the time of ionization.

  20. Laser linewidth and fiber nonlinearity tolerance study of C-16QAM compared to square 16QAM in coherent OFDM system

    NASA Astrophysics Data System (ADS)

    Xu, Fei; Qiao, Yaojun; Zhou, Ji; Guo, Mengqi; Tian, Huiping

    2017-03-01

    We introduced an effective modulation format circle 16 quadrature amplitude modulation (C-16QAM) to improve the laser linewidth induced phase noise and fiber nonlinear effects tolerance in coherent orthogonal frequency division multiplexing (OFDM) system without other losses compared to square 16QAM. Although C-16QAM has improved the performance of single channel system with Viterbi-Viterbi carrier phase estimation, C-16QAM using in coherent OFDM system has not been performed and such configuration of system may solve many problems in the next generation access networks. Here we numerically studied two separate manifestations of phase noise generated by laser linewidth and fiber nonlinear effects. We take these two kinds of phase noise into consideration separately by investigating the influence of laser linewidth with fixed launch power into transmission fiber and the influence of fiber nonlinear effects with fixed laser linewidth. We find that the C-16QAM improves the laser linewidth induced phase noise significantly and improves fiber nonlinear effects tolerance to a certain degree compared to square 16QAM. This coherent C-16QAM OFDM system may have great prospects for the next generation access networks for these significantly improvements.

  1. Exploring Ramsey-coherent population trapping atomic clock realized with pulsed microwave modulated laser

    SciTech Connect

    Yang, Jing; Yun, Peter; Tian, Yuan; Tan, Bozhong; Gu, Sihong

    2014-03-07

    A scheme for a Ramsey-coherent population trapping (CPT) atomic clock that eliminates the acousto-optic modulator (AOM) is proposed and experimentally studied. Driven by a periodically microwave modulated current, the vertical-cavity surface-emitting laser emits a continuous beam that switches between monochromatic and multichromatic modes. Ramsey-CPT interference has been studied with this mode-switching beam. In eliminating the AOM, which is used to generate pulsed laser in conventional Ramsey-CPT atomic clock, the physics package of the proposed scheme is virtually the same as that of a conventional compact CPT atomic clock, although the resource budget for the electronics will slightly increase as a microwave switch should be added. By evaluating and comparing experimentally recorded signals from the two Ramsey-CPT schemes, the short-term frequency stability of the proposed scheme was found to be 46% better than the scheme with AOM. The experimental results suggest that the implementation of a compact Ramsey-CPT atomic clock promises better frequency stability.

  2. Human retinal imaging using visible-light optical coherence tomography guided by scanning laser ophthalmoscopy

    PubMed Central

    Yi, Ji; Chen, Siyu; Shu, Xiao; Fawzi, Amani A.; Zhang, Hao F.

    2015-01-01

    We achieved human retinal imaging using visible-light optical coherence tomography (vis-OCT) guided by an integrated scanning laser ophthalmoscopy (SLO). We adapted a spectral domain OCT configuration and used a supercontinuum laser as the illumating source. The center wavelength was 564 nm and the bandwidth was 115 nm, which provided a 0.97 µm axial resolution measured in air. We characterized the sensitivity to be 86 dB with 226 µW incidence power on the pupil. We also integrated an SLO that shared the same optical path of the vis-OCT sample arm for alignment purposes. We demonstrated the retinal imaging from both systems centered at the fovea and optic nerve head with 20° × 20° and 10° × 10° field of view. We observed similar anatomical structures in vis-OCT and NIR-OCT. The contrast appeared different from vis-OCT to NIR-OCT, including slightly weaker signal from intra-retinal layers, and increased visibility and contrast of anatomical layers in the outer retina. PMID:26504622

  3. Laser-ablated silicon nanoparticles: optical properties and perspectives in optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Kirillin, M. Yu; Sergeeva, E. A.; Agrba, P. D.; Krainov, A. D.; Ezhov, A. A.; Shuleiko, D. V.; Kashkarov, P. K.; Zabotnov, S. V.

    2015-07-01

    Due to their biocompatibility silicon nanoparticles have high potential in biomedical applications, especially in optical diagnostics. In this paper we analyze properties of the silicon nanoparticles formed via laser ablation in water and study the possibility of their application as contrasting agents in optical coherence tomography (OCT). The nanoparticles suspension was produced by picosecond laser irradiation of monocrystalline silicon wafers in water. According to transmission electron microcopy analysis the silicon nanoparticles in the obtained suspension vary in size from 2 to 200 nm while concentration of the particles is estimated as 1013cm-3. The optical properties of the suspension in the range from 400 to 1000 nm were studied by spectrophotometry measurements revealing a scattering coefficient of about 0.1 mm-1 and a scattering anisotropy factor in the range of 0.2-0.4. In OCT study a system with a central wavelength of 910 nm was employed. Potential of the silicon nanoparticles as a contrasting agent for OCT is studied in experiments with agarose gel phantoms. Topical application of the nanoparticles suspension allowed the obtaining of the contrast of structural features of phantom up to 14 dB in the OCT image.

  4. Coherence and resonance effects in the ultra-intense laser-induced ultrafast response of complex atoms

    PubMed Central

    Li, Yongqiang; Gao, Cheng; Dong, Wenpu; Zeng, Jiaolong; Zhao, Zengxiu; Yuan, Jianmin

    2016-01-01

    Both coherent pumping and energy relaxation play important roles in understanding physical processes of ultra-intense coherent light-matter interactions. Here, using a large-scale quantum master equation approach, we describe dynamical processes of practical open quantum systems driven by both coherent and stochastic interactions. As examples, two typical cases of light-matter interactions are studied. First, we investigate coherent dynamics of inner-shell electrons of a neon gas irradiated by a high-intensity X-ray laser along with vast number of decaying channels. In these single-photon dominated processes, we find that, due to coherence-induced Rabi oscillations and power broadening effects, the photon absorptions of a neon gas can be suppressed resulting in differences in ionization processes and final ion-stage distributions. Second, we take helium as an example of multiphoton and multichannel interference dominated electron dynamics, by investigating the transient absorption of an isolated attosecond pulse in the presence of a femtosecond infrared laser pulse. PMID:26732822

  5. Raman-pumped Fourier-domain mode-locked laser: analysis of operation and application for optical coherence tomography.

    PubMed

    Klein, Thomas; Wieser, Wolfgang; Biedermann, Benjamin R; Eigenwillig, Christoph M; Palte, Gesa; Huber, Robert

    2008-12-01

    We demonstrate a Raman-pumped Fourier-domain mode-locked (FDML) fiber laser and optical coherence tomography imaging with this source. The wavelength sweep range of only 30 nm centered around 1550 nm results in limited axial resolution, hence a nonbiological sample is imaged. An output power of 1.9 mW was achieved at a sweep rate of 66 kHz and a maximum ranging depth of ~2.5 cm. Roll-off characteristics are found to be similar to FDML lasers with semiconductor optical amplifiers as gain media. The application of Raman gain also enables unperturbed cavity ring-down experiments in FDML lasers for the first time, providing direct access to the photon lifetime in the laser cavity. Good agreement with nonswept cw operation is proof of the stationary operation of FDML lasers.

  6. Discretely swept optical coherence tomography system using super-structure grating distributed Bragg reflector lasers at 1561-1639nm

    NASA Astrophysics Data System (ADS)

    Choi, D.; Yoshimura, R.; Hiro-Oka, H.; Furukawa, H.; Goto, A.; Satoh, N.; Igarashi, A.; Nakanishi, M.; Shimizu, K.; Ohbayashi, K.

    2012-01-01

    We have developed swept source optical coherence tomography (OCT) system with an optical comb swept source system. The swept source system comprised of two super-structured grating distributed Bragg reflector lasers covering a wavelength range from 1561-1693 nm. A method to scan these lasers to obtain an interference signal without stitching noises, which are inherent in these lasers, and to connect two lasers without concatenation noise is explained. Method to reduce optical aliasing noises in this optical comb swept laser OCT is explained and demonstrated based on the characteristic of the optical aliasing noises in this particular OCT system. By reduction of those noises, a sensitivity of 124 dB was realized. The A-scan rate, resolution and depth range were 3.1 kHz, 16 μm (in air) and 12 mm, respectively. Deep imaging penetration into tissue is demonstrated for two selected samples.

  7. Nonlinear theory of a two-photon correlated-spontaneous-emission laser: A coherently pumped two-level--two-photon laser

    SciTech Connect

    Lu, N.; Zhao, F.; Bergou, J.

    1989-05-15

    We develop a nonlinear theory of a two-photon correlated-spontaneous-emission laser (CEL) by using an effective interaction Hamiltonian for a two-level system coupled by a two-photon transition. Assuming that the active atoms are prepared initially in a coherent superposition of two atomic levels involved in the two-photon transition, we derive a master equation for the field-density operator by using our quantum theory for coherently pumped lasers. The steady-state properties of the two-photon CEL are studied by converting the field master equation into a Fokker-Planck equation for the antinormal-ordering Q representation of the field-density operator. Because of the injected atomic coherence, the drift and diffusion coefficients become phase sensitive. This leads to laser phase locking and an extra two-photon CEL gain. The laser field can build up from a vacuum in the no-population-inversion region, in contrast to an ordinary two-photon laser for which triggering is needed. We find an approximate steady-state solution of the Q representation for the laser field, which consists of two identical peaks of elliptical type. We calculate the phase variance and, for any given mean photon number, obtain the minimum variance in the phase quadrature as a function of the initial atomic variables. Squeezing of the quantum noise in the phase quadrature is found and it exhibits the following features: (1) it is possible only when the laser intensity is smaller than a certain value; (2) it becomes most significant for small mean photon number, which is achievable in the no-population-inversion region; and (3) a maximum of 50% squeezing can be asymptotically approached in the small laser intensity limit.

  8. 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.

  9. High Flux Spatially Coherent X-ray Generation from Laser Wakefield Accelerators

    NASA Astrophysics Data System (ADS)

    McGuffey, Chris

    2011-10-01

    Nonlinear plasma waves driven by existing ultra-intense short-pulse lasers can trap large numbers of electrons from the plasma (as many as 5 ×109) and accelerate them to ~ GeV energy over ~ 1 cm . The details of the trapping process and plasma wave structure dictate that the trapped electrons undergo transverse oscillatory motion on the microscopic scale of the plasma structure, resulting in short wavelength betatron radiation. These x-ray beams are presumed to retain the short-pulse characteristic of the laser, resulting in high peak flux, making the source a candidate for ultrafast temporally resolved imaging applications. Presented here are experimental studies of the scalings of fluence upon laser power, gas jet length, and electron beam parameters. The spectrum was directly measured by single hit spectroscopy to be broad and smooth with peak photon energy exceeding 10 keV . Additional measurements indicate that the beam source size can be as small as 1 μm and that the radiation exhibits spatial coherence. These two key characteristics allow advanced imaging capabilities including phase contrast imaging and tomography, as demonstrated by radiography studies of biological specimens. Collaborators: S. Kneip (Imperial College London), T. Matsuoka (Present affiliation: Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science), W. Schumaker, V. Chvykov, F. Dollar, M. Vargas, G. Kalintchenko, V. Yanovsky, A. Maksimchuk, A. G. R. Thomas, and K. Krushelnick (University of Michigan). This work was supported by the NSF (award PHY-0114336), the NSF/DNDO (award F021166), and the NRC (award 38-09-953).

  10. Progress in coherent lithography using table-top extreme ultraviolet lasers

    NASA Astrophysics Data System (ADS)

    Li, Wei

    Nanotechnology has drawn a wide variety of attention as interesting phenomena occurs when the dimension of the structures is in the nanometer scale. The particular characteristics of nanoscale structures had enabled new applications in different fields in science and technology. Our capability to fabricate these nanostructures routinely for sure will impact the advancement of nanoscience. Apart from the high volume manufacturing in semiconductor industry, a small-scale but reliable nanofabrication tool can dramatically help the research in the field of nanotechnology. This dissertation describes alternative extreme ultraviolet (EUV) lithography techniques which combine table-top EUV laser and various cost-effective imaging strategies. For each technique, numerical simulations, system design, experiment result and its analysis will be presented. In chapter II, a brief review of the main characteristics of table-top EUV lasers will be addressed concentrating on its high power and large coherence radius that enable the lithography application described herein. The development of a Talbot EUV lithography system which is capable of printing 50nm half pitch nanopatterns will be illustrated in chapter III. A detailed discussion of its resolution limit will be presented followed by the development of X-Y-Z positioning stage, the fabrication protocol for diffractive EUV mask, and the pattern transfer using self- developed ion beam etching, and the dose control unit. In addition, this dissertation demonstrated the capability to fabricate functional periodic nanostructures using Talbot EUV lithography. After that, resolution enhancement techniques like multiple exposure, displacement Talbot EUV lithography, fractional Talbot EUV lithography, and Talbot lithography using 18.9nm amplified spontaneous emission laser will be demonstrated. Chapter IV will describe a hybrid EUV lithography which combines the Talbot imaging and interference lithography rendering a high resolution

  11. Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis

    DOE PAGES

    Sikorski, Marcin; Song, Sanghoon; Schropp, Andreas; ...

    2015-04-14

    X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus' location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging.

  12. Focus characterization at an X-ray free-electron laser by coherent scattering and speckle analysis

    PubMed Central

    Sikorski, Marcin; Song, Sanghoon; Schropp, Andreas; Seiboth, Frank; Feng, Yiping; Alonso-Mori, Roberto; Chollet, Matthieu; Lemke, Henrik T.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Zhang, Wenkai; Robert, Aymeric; Zhu, Diling

    2015-01-01

    X-ray focus optimization and characterization based on coherent scattering and quantitative speckle size measurements was demonstrated at the Linac Coherent Light Source. Its performance as a single-pulse free-electron laser beam diagnostic was tested for two typical focusing configurations. The results derived from the speckle size/shape analysis show the effectiveness of this technique in finding the focus’ location, size and shape. In addition, its single-pulse compatibility enables users to capture pulse-to-pulse fluctuations in focus properties compared with other techniques that require scanning and averaging. PMID:25931074

  13. Solid state active/passive night vision imager using continuous-wave laser diodes and silicon focal plane arrays

    NASA Astrophysics Data System (ADS)

    Vollmerhausen, Richard H.

    2013-04-01

    Passive imaging offers covertness and low power, while active imaging provides longer range target acquisition without the need for natural or external illumination. This paper describes a focal plane array (FPA) concept that has the low noise needed for state-of-the-art passive imaging and the high-speed gating needed for active imaging. The FPA is used with highly efficient but low-peak-power laser diodes to create a night vision imager that has the size, weight, and power attributes suitable for man-portable applications. Video output is provided in both the active and passive modes. In addition, the active mode is Class 1 eye safe and is not visible to the naked eye or to night vision goggles.

  14. A compact and efficient hyper coherent light source of visible violet laser diode based on Pound-Drever-Hall technique

    NASA Astrophysics Data System (ADS)

    Sasaki, Wakao; Yashiro, Hideyuki; Miura, Yukio; Mizutani, Kouki; Nakajima, Jun

    2007-09-01

    In the present work, we have developed an efficient and well stablized hyper coherent diode laser light source as compact as even portable using commercially available visible 400 nm band laser diodes. The attained coherence of the present system can always be controlled at the best condition indifferent to changes in its settled environmental conditions by applying Pound-Drever-Hall technique in which the frequency of a 160mW type 405nm GaN violet laser diode is locked to a reference Fabry-Perot cavity by negative electrical feedback for the injection current of the laser diode based on FM sideband technique. In addition to this frequency stabilization system, we have also realized a stability evaluation system that can measure the Allan variance of the frequency fluctuations of our frequency stabilized laser source in real-time basis by using simple devices of a portable computer and a digital signal processing unit. As a result, we have accomplished a compact and efficient hyper coherent laser system which can always perform its optimum conditions even if the environmental conditions around the laser are to be dynamically changed when used in a field basis. The attained values of power spectral density (PSD) of FM noise calculated from the error signals of our system under controlled condition were better by about 1~2 orders than typical values of free-running conditions in the fourier frequency domain from 100Hz to 300kHz. The best achieved value of PSD was about 2.56×10 7 [Hz2/Hz] in the fourier frequency domain from 100Hz to 1kHz, while as for the Allan variance as another measure of frequency stability, the achieved value of the minimum square root of Allan variance was 3.46×10 -11 in a 400nm type violet laser diode at integration time of 10 ms, which has been well comparable to the hyper coherent condition for the laser diode light sources.

  15. Multiple defocused coherent diffraction imaging: method for simultaneously reconstructing objects and probe using X-ray free-electron lasers.

    PubMed

    Hirose, Makoto; Shimomura, Kei; Suzuki, Akihiro; Burdet, Nicolas; Takahashi, Yukio

    2016-05-30

    The sample size must be less than the diffraction-limited focal spot size of the incident beam in single-shot coherent X-ray diffraction imaging (CXDI) based on a diffract-before-destruction scheme using X-ray free electron lasers (XFELs). This is currently a major limitation preventing its wider applications. We here propose multiple defocused CXDI, in which isolated objects are sequentially illuminated with a divergent beam larger than the objects and the coherent diffraction pattern of each object is recorded. This method can simultaneously reconstruct both objects and a probe from the coherent X-ray diffraction patterns without any a priori knowledge. We performed a computer simulation of the prposed method and then successfully demonstrated it in a proof-of-principle experiment at SPring-8. The prposed method allows us to not only observe broad samples but also characterize focused XFEL beams.

  16. Nuclear-Pumped Lasers. [efficient conversion of energy liberated in nuclear reactions to coherent radiation

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The state of the art in nuclear pumped lasers is reviewed. Nuclear pumped laser modeling, nuclear volume and foil excitation of laser plasmas, proton beam simulations, nuclear flashlamp excitation, and reactor laser systems studies are covered.

  17. Vehicle type affects filling of fractional laser-ablated channels imaged by optical coherence tomography.

    PubMed

    Olesen, Uffe Høgh; Mogensen, Mette; Haedersdal, Merete

    2017-04-01

    Ablative fractional laser (AFXL) is an emerging method that enhances topical drug delivery. Penetrating the skin in microscopic, vertical channels, termed microscopic treatment zones (MTZs), the fractional technique circumvents the skin barrier and allows increased uptake of topically applied drugs. This study aims to elucidate the impact of vehicle type on the filling of MTZs from application of liquid, gel, and cream vehicles. Ex vivo pig skin was exposed to 10,600 nm fractional CO2 laser at 5% density, 120 μm beam diameter, and fluences of 40 and 80 mJ/microbeam (mJ/mb). Six repetitions were performed for each of six interventions (2 fluences and 3 vehicle types, n = 36). MTZ dimensions and filling by vehicle type were evaluated by optical coherence tomography, using blue tissue dye as a contrast-enhancing agent. Outcome measure was degree of MTZ filling assessed as percentages of empty, partially filled, and completely filled MTZs (108-127 MTZs/intervention analyzed) and evaluated statistically using Kruskal-Wallis and Dunn's tests. MTZs reached mid-dermal levels of 225 μm (40 mJ/mb) and 375 μm (80 mJ/mb) penetration depths (p < 0.0001). Filling of MTZs depended on type of applied vehicle. At 80 mJ/mb, liquid (67% completely filled, p < 0.01) and gel (60%, p < 0.05) formulations filled MTZs significantly better than cream formulation (31%). At 40 mJ/mb, liquid and gel formulations filled 90% (p < 0.05) and 77% (p > 0.05) of MTZs completely versus 55% for cream formulation. Thus, filling was overall greater for more superficial MTZs. In conclusion, vehicle type affects filling of MTZs, which may be of importance for AFXL-assisted drug delivery.

  18. Observation of Laser Induced Magnetization Dynamics in Co/Pd Multilayers with Coherent X-ray Scattering

    SciTech Connect

    Wu, Benny

    2012-04-05

    We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.

  19. Optimisation of wide-band parametric amplification stages of a femtosecond laser system with coherent combining of fields

    SciTech Connect

    Bagayev, S N; Trunov, V I; Pestryakov, E V; Leshchenko, V E; Frolov, S A; Vasiliev, V A

    2014-05-30

    For the first time the pulses with the energy of ∼150 mJ and the spectrum corresponding to the transform-limited duration of ∼20 fs amplified in three-stage parametric amplifiers have been coherently combined in a dual-channel femtosecond laser system. The efficiency of coherent combining of above 90% has been obtained at the residual relative time jitter of amplified pulses of 110 as. For the first time the modulation of spectrum was experimentally observed under the parametric amplification of a wideband femtosecond radiation in crystals placed in series. The model of parametric luminescence evolution was developed which allows one to calculate the whole range of the frequency-angular spectrum that, in addition to simulations of the contrast of amplified pulses, gives the possibility of optimising the amplifier efficiency. The results of experiments on measuring the contrast are presented and compared with the calculated data. Methods for enhancing the contrast in the created laser system are analysed. Possible schemes of multibeam pumping of the output cascade are considered for obtaining a petawatt power in the laser system based on cascades of a parametric amplifier in LBO crystals which is being developed at the Institute of Laser Physics of SB RAS. (lasers)

  20. Elastic properties of soft tissue-mimicking phantoms assessed by combined use of laser ultrasonics and low coherence interferometry.

    PubMed

    Li, Chunhui; Huang, Zhihong; Wang, Ruikang K

    2011-05-23

    Advances in the field of laser ultrasonics have opened up new possibilities in medical applications. This paper evaluates this technique as a method that would allow for rapid characterization of the elastic properties of soft biological tissue. In doing so, we propose a novel approach that utilizes a low coherence interferometer to detect the laser-induced surface acoustic waves (SAW) from the tissue-mimicking phantoms. A Nd:YAG focused laser line-source is applied to one- and two-layer tissue-mimicking agar-agar phantoms, and the generated SAW signals are detected by a time domain low coherence interferometry system. SAW phase velocity dispersion curves are calculated, from which the elasticity of the specimens is evaluated. We show that the experimental results agree well with those of the theoretical expectations. This study is the first report that a laser-generated SAW phase velocity dispersion technique is applied to soft materials. This technique may open a way for laser ultrasonics to detect the mechanical properties of soft tissues, such as skin.

  1. Loose powder detection and surface characterization in selective laser sintering via optical coherence tomography

    PubMed Central

    Guan, Guangying; Hirsch, Matthias; Syam, Wahyudin P.; Leach, Richard K.; Huang, Zhihong

    2016-01-01

    Defects produced during selective laser sintering (SLS) are difficult to non-destructively detect after build completion without the use of X-ray-based methods. Overcoming this issue by assessing integrity on a layer-by-layer basis has become an area of significant interest for users of SLS apparatus. Optical coherence tomography (OCT) is used in this study to detect surface texture and sub-surface powder, which is un-melted/insufficiently sintered, is known to be a common cause of poor part integrity and would prevent the use of SLS where applications dictate assurance of defect-free parts. To demonstrate the capability of the instrument and associated data-processing algorithms, samples were built with graduated porosities which were embedded in fully dense regions in order to simulate defective regions. Simulated in situ measurements were then correlated with the process parameters used to generate variable density regions. Using this method, it is possible to detect loose powder and differentiate between densities of ±5% at a sub-surface depth of approximately 300 μm. In order to demonstrate the value of OCT as a surface-profiling technique, surface texture datasets are compared with focus variation microscopy. Comparable results are achieved after a spatial bandwidth- matching procedure. PMID:27493569

  2. Loose powder detection and surface characterization in selective laser sintering via optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Guan, Guangying; Hirsch, Matthias; Syam, Wahyudin P.; Leach, Richard K.; Huang, Zhihong; Clare, Adam T.

    2016-07-01

    Defects produced during selective laser sintering (SLS) are difficult to non-destructively detect after build completion without the use of X-ray-based methods. Overcoming this issue by assessing integrity on a layer-by-layer basis has become an area of significant interest for users of SLS apparatus. Optical coherence tomography (OCT) is used in this study to detect surface texture and sub-surface powder, which is un-melted/insufficiently sintered, is known to be a common cause of poor part integrity and would prevent the use of SLS where applications dictate assurance of defect-free parts. To demonstrate the capability of the instrument and associated data-processing algorithms, samples were built with graduated porosities which were embedded in fully dense regions in order to simulate defective regions. Simulated in situ measurements were then correlated with the process parameters used to generate variable density regions. Using this method, it is possible to detect loose powder and differentiate between densities of ±5% at a sub-surface depth of approximately 300 μm. In order to demonstrate the value of OCT as a surface-profiling technique, surface texture datasets are compared with focus variation microscopy. Comparable results are achieved after a spatial bandwidth- matching procedure.

  3. Quantum dynamics with fermion coupled coherent states: Theory and application to electron dynamics in laser fields

    SciTech Connect

    Kirrander, Adam; Shalashilin, Dmitrii V.

    2011-09-15

    We present an alternate version of the coupled-coherent-state method, specifically adapted for solving the time-dependent Schroedinger equation for multielectron dynamics in atoms and molecules. This theory takes explicit account of the exchange symmetry of fermion particles, and it uses fermion molecular dynamics to propagate trajectories. As a demonstration, calculations in the He atom are performed using the full Hamiltonian and accurate experimental parameters. Single- and double-ionization yields by 160-fs and 780-nm laser pulses are calculated as a function of field intensity in the range 10{sup 14}-10{sup 16} W/cm{sup 2}, and good agreement with experiments by Walker et al. is obtained. Since this method is trajectory based, mechanistic analysis of the dynamics is straightforward. We also calculate semiclassical momentum distributions for double ionization following 25-fs and 795-nm pulses at 1.5x10{sup 15} W/cm{sup 2}, in order to compare them with the detailed experiments by Rudenko et al. For this more challenging task, full convergence is not achieved. However, major effects such as the fingerlike structures in the momentum distribution are reproduced.

  4. Multispectral scanning laser ophthalmoscopy combined with optical coherence tomography for simultaneous in vivo mouse retinal imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Pengfei; Zam, Azhar; Jian, Yifan; Wang, Xinlei; Burns, Marie E.; Sarunic, Marinko V.; Pugh, Edward N.; Zawadzki, Robert J.

    2015-03-01

    A compact, non-invasive multi-modal system has been developed for in vivo mouse retina imaging. It is configured for simultaneously detecting green and red fluorescent protein signals with scanning laser ophthalmoscopy (SLO) back-scattered light from the SLO illumination beam, and depth information about different retinal layers by means of Optical Coherence Tomography (OCT). Simultaneous assessment of retinal characteristics with different modalities can provide a wealth of information about the structural and functional changes in the retinal neural tissue and chorio-retinal vasculature in vivo. Additionally, simultaneous acquisition of multiple channels facilitates analysis of the data of different modalities by automatic temporal and structural co-registration. As an example of the instrument's performance we imaged the retina of a mouse with constitutive expression of GFP in microglia cells (Cx3cr1GFP/+), and which also expressed the red fluorescent protein mCherry in Müller glial cells by means of adeno-associated virus delivery (AAV2) of an mCherry cDNA driven by the GFAP (glial fibrillary acid protein) promoter.

  5. Doublet Pulse Coherent Laser Radar for Orbital Debris Tracking of Resident Space Objects

    NASA Astrophysics Data System (ADS)

    Prasad, N.; Rudd, V.,; DiMarcantonio, A.; Sandford, S.

    2014-09-01

    In this paper, the development of a long range ladar system known as ExoSPEAR at NASA Langley Research Center for tracking rapidly moving resident space objects is discussed. Based on 100 W, nanosecond class, near-IR laser, this ladar system with coherent detection technique is currently being investigated for short dwell time measurements of resident space objects (RSOs) in LEO and beyond for space surveillance applications. This unique ladar architecture is configured using a continuously agile doublet-pulse waveform scheme coupled to a closed-loop tracking and control loop approach to simultaneously achieve mm class range precision and mm/s velocity precision and hence obtain unprecedented track accuracies. Salient features of the design architecture followed by performance simulations illustrating the dependence of range and velocity precision in LEO orbits on ladar power aperture product will be presented. Estimated limits on detectable optical cross sections of RSOs in LEO orbits will be analyzed. The suitability of this ladar for precision orbit determination will be discussed.

  6. Dual-band optical coherence tomography using a single supercontinuum laser source

    NASA Astrophysics Data System (ADS)

    Chen, Siyu; Shu, Xiao; Yi, Ji; Fawzi, Amani; Zhang, Hao F.

    2016-06-01

    We developed a simultaneous visible-light (Vis) and near-infrared (NIR) dual-band optical coherence tomography (OCT) system using a single supercontinuum laser source. The goal was to benchmark our newly developed Vis-OCT against the well-developed NIR-OCT. The Vis-OCT subsystem operated at 91 nm full-width-at-half-maximum (FWHM) bandwidth centered at 566 nm the NIR-OCT subsystem operated at 93 nm FWHM bandwidth centered at 841 nm. The axial resolutions were 1.8 and 4.4 μm in air for the Vis- and NIR-OCT subsystems, respectively. We compared the respective performances, including anatomical imaging, angiography, absolute retinal blood flow measurements, and spectroscopic analysis for retinal blood oxygen saturation (sO2), between the two subsystems in rodents in vivo. While demonstrating minor discrepancies related to operation wavelengths, both subsystems showed comparable performances in the first three tests. However, we were only able to retrieve sO2 using the Vis-OCT subsystem.

  7. Design optimization and transverse coherence analysis for an x-ray free electron laser driven by SLAC LINAC

    SciTech Connect

    Xie, M.

    1995-12-31

    I present a design study for an X-ray Free Electron Laser driven by the SLAC linac, the Linac Coherent Light Source (LCLS). The study assumes the LCLS is based on Self-Amplified Spontaneous Emission (SASE). Following a brief review of the fundamentals of SASE, I will provide without derivation a collection of formulas relating SASE performance to the system parameters. These formulas allow quick evaluation of FEL designs and provide powerful tools for optimization in multi-dimensional parameter space. Optimization is carried out for the LCLS over all independent system parameters modeled, subjected to a number of practical constraints. In addition to the optimizations concerning gain and power, another important consideration for a single pass FEL starting from noise is the transverse coherence property of the amplified radiation, especially at short wavelength. A widely used emittance criteria for FELs requires that the emittance is smaller than the radiation wavelength divided by 4{pi}. For the LCLS the criteria is violated by a factor of 5, at a normalized emittance of 1.5 mm-mrad, wavelength of 1.5 {angstrom}, and beam energy of 15 GeV. Thus it is important to check quantitatively the emittance effect on the transverse coherence. I will examine the emittance effect on transverse coherence by analyzing different transverse modes and show that full transverse coherence can be obtained even at the LCLS parameter regime.

  8. a Comparison of Different Coherent Deep Ultraviolet Generations Using Second Harmonic Generation with Blue Laser Diode Excitation

    NASA Astrophysics Data System (ADS)

    Tangtrongbenchasil, C.; Nonaka, K.

    2008-11-01

    Nano-focus beam applications of short wavelength approximately 220 nm now play important roles in engineering and industrial sections. At present, light sources at approximately 220 nm are commercially available but large size, difficult to maintain, and expensive. Compact wavelength tunable and cost effective light sources at approximately 220 nm are required. Laser diode with sum-frequency generation methods are employed to generated the shorter wavelength approximately 220 nm. This paper presents comparison of second harmonic generation schemes using a nonlinear optic crystal and two types of laser diode, which are a 440 nm single mode blue laser diode and a 450 nm multimode Fabry-Perot blue laser diode, has potential to generate wide tunable coherent deep ultraviolet-c at approximately 220 nm. Using the blue laser diode with the sum-frequency technique, a high second harmonic power is hardly observed due to low conversion efficiency. The best performance of second harmonic generation using blue laser diode, nonlinear optic crystal, and an high-Q external cavity laser diode was observed as 1.1 μW second harmonic ultraviolet-c power at 224.45 nm ultraviolet-c wavelength and 5.75 nm ultraviolet wavelength tunability. In addition, the improvement of increasing second harmonic power approximately 220 nm and the limitation of wavelength tuning of short wavelength are also theoretically discussed in this paper.

  9. Tunnel vision for US X-ray free-electron laser

    NASA Astrophysics Data System (ADS)

    Banks, Michael

    2017-03-01

    Construction can begin on a major upgrade to the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory in the US after the tunnel that will house the facility was cleared of equipment.

  10. Coherent X-ray and laser spectroscopy measurements of diffusion in concentrated alpha-crystallin solutions

    NASA Astrophysics Data System (ADS)

    Karunaratne, V. N. C.

    The mammalian eye lens is composed of a concentrated solution of water soluble proteins called crystallins. Alpha-crystallin, the most abundant protein found in the lens, plays a crucial role in maintaining lens transparency and lens accommodation. However, alpha-crystallins along with other ocular proteins suffer from irreversible processes such as oxidation. One cause of oxidation is radiation-induced radical formation which alters the inter-molecular interactions, thereby degrading the normal function of ocular proteins. The main goal of this thesis is to quantify molecular scale dynamics of concentrated solutions of alpha-crystallins using coherent X-rays and visible laser light. I believe a detailed analysis of the dynamics pertaining to alpha-crystallin will provide the foundation to understand molecular scale mechanisms that lead to conditions like cataract and presbyopia. I explore the dynamics of concentrated alpha-crystallin solutions by measuring diffusive motion over a range of length scales using Dynamic light scattering (DLS) and X-ray photon correlation spectroscopy (XPCS). To a certain extent, the dynamical properties of crystallins obtained in this manner are consistent with established theories in colloidal physics. However, there are some deviations, which I will address in this thesis. In terms of X-ray data, I employed a new, efficient photon correlation technique to obtain the best possible signal, furthermore this technique is embedded in a stand-alone software program that has the ability to provide real time results, quickly and efficiently with the help of high performance computing resources available at Northern Illinois University (NIU). The technique has potential to be used by the coherent X-ray spectroscopy community in the future. In addition, by using X-ray scattering data, I probe potential modifications and or damage effects on alpha-crystallins due to radiation exposure. The damage analysis methodology described in this thesis

  11. Dependence of the phase-coherence time in CdS1-xSex on the laser pulse width

    NASA Astrophysics Data System (ADS)

    Schwab, H.; Klingshirn, C.

    1992-03-01

    We performed degenerate-four-wave-mixing (DFWM) experiments in CdS1-xSex mixed crystals with laser pulses of different duration. It was found that the measured phase-coherence times (T2) are critically dependent on the spectral width and by that on the temporal half-width (τlaser) of the exciting laser. In an experiment with 10-ps pulses we find values for T2 of up to 3 ns. Under the same conditions in the same sample, the maximum observed value for T2 is 100 ps for τlaser=1 ps. With even shorter pulses, the phase-coherence time drops below 80 fs, which is the temporal resolution of our experiment. In addition, the line shape of the dephasing curves as well as the density dependence of T2 are substantially changed. The reason for these findings is based on the structure of these crystals. The compositional disorder leads to the formation of localized states. Within the same spectral region, one also finds extended excitons. The interaction of carriers of both kinds is then responsible for the observed effects.

  12. Concept for image-guided vitreo-retinal fs-laser surgery: adaptive optics and optical coherence tomography for laser beam shaping and positioning

    NASA Astrophysics Data System (ADS)

    Matthias, Ben; Brockmann, Dorothee; Hansen, Anja; Horke, Konstanze; Knoop, Gesche; Gewohn, Timo; Zabic, Miroslav; Krüger, Alexander; Ripken, Tammo

    2015-03-01

    Fs-lasers are well established in ophthalmic surgery as high precision tools for corneal flap cutting during laser in situ keratomileusis (LASIK) and increasingly utilized for cutting the crystalline lens, e.g. in assisting cataract surgery. For addressing eye structures beyond the cornea, an intraoperative depth resolved imaging is crucial to the safety and success of the surgical procedure due to interindividual anatomical disparities. Extending the field of application even deeper to the posterior eye segment, individual eye aberrations cannot be neglected anymore and surgery with fs-laser is impaired by focus degradation. Our demonstrated concept for image-guided vitreo-retinal fs-laser surgery combines adaptive optics (AO) for spatial beam shaping and optical coherence tomography (OCT) for focus positioning guidance. The laboratory setup comprises an adaptive optics assisted 800 nm fs-laser system and is extended by a Fourier domain optical coherence tomography system. Phantom structures are targeted, which mimic tractional epiretinal membranes in front of excised porcine retina within an eye model. AO and OCT are set up to share the same scanning and focusing optics. A Hartmann-Shack sensor is employed for aberration measurement and a deformable mirror for aberration correction. By means of adaptive optics the threshold energy for laser induced optical breakdown is lowered and cutting precision is increased. 3D OCT imaging of typical ocular tissue structures is achieved with sufficient resolution and the images can be used for orientation of the fs-laser beam. We present targeted dissection of the phantom structures and its evaluation regarding retinal damage.

  13. Lidar-radar velocimetry using a pulse-to-pulse coherent rf-modulated Q-switched laser.

    PubMed

    Vallet, M; Barreaux, J; Romanelli, M; Pillet, G; Thévenin, J; Wang, L; Brunel, M

    2013-08-01

    An rf-modulated pulse train from a passively Q-switched Nd:YAG laser has been generated using an extra-cavity acousto-optic modulator. The rf modulation reproduces the spectral quality of the local oscillator. It leads to a high pulse-to-pulse phase coherence, i.e., phase memory, over thousands of pulses. The potentialities of this transmitter for lidar-radar are demonstrated by performing Doppler velocimetry on indoor moving targets. The experimental results are in good agreement with a model based on elementary signal processing theory. In particular, we show experimentally and theoretically that lidar-radar is a promising technique that allows discrimination between translation and rotation movements. Being independent of the laser internal dynamics, this scheme can be applied to any Q-switched laser.

  14. Coherent control of the electron quantum paths for the generation of single ultrashort atto second laser pulse

    SciTech Connect

    Liu, I-Lin; Li, Peng-Cheng; Chu, Shih-I

    2011-09-15

    We report a mechanism and a realizable approach for the coherent control of the generation of an isolated and ultrashort atto second (as) laser pulse from atoms by optimizing the two-color laser fields with a proper time delay. Optimizing the laser pulse shape allows the control of the electron quantum paths and enables high-harmonic generation from the long- and short-trajectory electrons to be enhanced and split near the cutoff region. In addition, it delays the long-trajectory electron emission time and allows the production of extremely short atto second pulses in a relatively narrow time duration. As a case study, we show that an isolated 30 as pulse with a bandwidth of 127 eV can be generated directly from the contribution of long-trajectory electrons alone.

  15. Indication of Te segregation in laser-irradiated ZnTe observed by in situ coherent-phonon spectroscopy

    SciTech Connect

    Shimada, Toru; Kamaraju, N.; Frischkorn, Christian; Wolf, Martin; Kampfrath, Tobias

    2014-09-15

    We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80 MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6 THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material.

  16. Eyesafe coherent detection wind lidar based on a beam-combined pulsed laser source.

    PubMed

    Lombard, L; Valla, M; Planchat, C; Goular, D; Augère, B; Bourdon, P; Canat, G

    2015-03-15

    We report on a coherent wind lidar built with two coherently-beam-combined fiber amplifiers. The lidar performances of the combined-amplifier and the single-amplifier are compared using two criterions: carrier-to-noise ratio and wind speed noise floor. In both cases, lidar performances are not degraded with a combined source and are close to the theoretical optimum. Combined sources are well suited to improve coherent wind lidar accuracy, range, and integration time.

  17. Ex vivo optical coherence tomography and laser induced fluorescence spectroscopy imaging of murine gastrointestinal tract

    NASA Astrophysics Data System (ADS)

    Hariri, Lida; Tumlinson, Alexandre R.; Wade, Norman; Besselsen, David; Utzinger, Urs; Gerner, Eugene; Barton, Jennifer

    2005-04-01

    Optical Coherence Tomography (OCT) and Laser Induced Fluorescence Spectroscopy (LIF) have separately been found to have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models of human disease is unknown. We combine the two modalities to survey the GI tract of a variety of mouse strains and sample dysplasias and inflammatory bowel disease (IBD) of the small and large intestine. Segments of duodenum and lower colon 2.5 cm in length and the entire esophagus from 10 mice each of two colon cancer models (ApcMin and AOM treated A/J) and two IBD models (Il-2 and Il-10) and 5 mice each of their respective controls were excised. OCT images and LIF spectra were obtained simultaneously from each tissue sample within 1 hour of extraction. Histology was used to classify tissue regions as normal, Peyer"s patch, dysplasia, adenoma, or IBD. Features in corresponding regions of OCT images were analyzed. Spectra from each of these categories were averaged and compared via the student's t-test. Features in OCT images correlated to histology in both normal and diseased tissue samples. In the diseased samples, OCT was able to identify early stages of mild colitis and dysplasia. In the sample of IBD, the LIF spectra displayed unique peaks at 635nm and 670nm, which were attributed to increased porphyrin production in the proliferating bacteria of the disease. These peaks have the potential to act as a diagnostic for IBD. OCT and LIF appear to be useful and complementary modalities for imaging mouse models.

  18. Investigation of acid-etched CO2 laser ablated enamel surfaces using polarization sensitive optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Nahm, Byung J.; Kang, Hobin; Chan, Kenneth; Fried, Daniel

    2012-01-01

    A carbon dioxide laser operating at the highly absorbed wavelength of 9.3μm with a pulse duration of 10-15μs is ideally suited for caries removal and caries prevention. The enamel thermally modified by the laser has enhanced resistance to acid dissolution. This is an obvious advantage for caries prevention; however, it is often necessary to etch the enamel surface to increase adhesion to composite restorative materials and such surfaces may be more resistant to etching. The purpose of the study was to non-destructively measure the susceptibility of laser-ablated enamel surfaces to acid dissolution before and after acid-etching using Polarization Sensitive Optical Coherence Tomography (PS-OCT). PS-OCT was used to acquire images of bovine enamel surfaces after exposure to laser irradiation at ablative fluence, acid-etching, and a surface softened dissolution model. The integrated reflectivity from lesion and the lesion depth were measured using PS-OCT. Samples were also sectioned for examination by Polarized Light Microscopy (PLM). PS-OCT images showed that acid-etching greatly accelerated the formation of subsurface lesions on both laser-irradiated and non-irradiated surfaces (P<0.05). A 37.5% phosphoric acid etch removed the laser modified enamel layer after 5-10 seconds.

  19. Generation of coherent 19- and 38-nm radiation at a free-electron laser directly seeded at 38 nm.

    PubMed

    Ackermann, S; Azima, A; Bajt, S; Bödewadt, J; Curbis, F; Dachraoui, H; Delsim-Hashemi, H; Drescher, M; Düsterer, S; Faatz, B; Felber, M; Feldhaus, J; Hass, E; Hipp, U; Honkavaara, K; Ischebeck, R; Khan, S; Laarmann, T; Lechner, C; Maltezopoulos, Th; Miltchev, V; Mittenzwey, M; Rehders, M; Rönsch-Schulenburg, J; Rossbach, J; Schlarb, H; Schreiber, S; Schroedter, L; Schulz, M; Schulz, S; Tarkeshian, R; Tischer, M; Wacker, V; Wieland, M

    2013-09-13

    Initiating the gain process in a free-electron laser (FEL) from an external highly coherent source of radiation is a promising way to improve the pulse properties such as temporal coherence and synchronization performance in time-resolved pump-probe experiments at FEL facilities, but this so-called "seeding" suffers from the lack of adequate sources at short wavelengths. We report on the first successful seeding at a wavelength as short as 38.2 nm, resulting in GW-level, coherent FEL radiation pulses at this wavelength as well as significant second harmonic emission at 19.1 nm. The external seed pulses are about 1 order of magnitude shorter compared to previous experiments allowing an ultimate time resolution for the investigation of dynamic processes enabling breakthroughs in ultrafast science with FELs. The seeding pulse is the 21st harmonic of an 800-nm, 15-fs (rms) laser pulse generated in an argon medium. Methods for finding the overlap of seed pulses with electron bunches in spatial, longitudinal, and spectral dimensions are discussed and results are presented. The experiment was conducted at FLASH, the FEL user facility at DESY in Hamburg, Germany.

  20. TECHNICAL DESIGN NOTE: High-precision, low-coherence Fizeau interferometer using a pulsed laser diode for measurement of transparent plates

    NASA Astrophysics Data System (ADS)

    Bitou, Youichi; Ueki, Nobuaki

    2010-07-01

    A high-precision, low-coherence Fizeau interferometer system using a pulsed laser diode has been developed for the measurement of the flatness of transparent plates. A pulsed laser diode with a wavelength of around 633 nm was used as the low-coherence light source. A Twyman-Green interferometer with the pulsed laser diode was connected to the Fizeau interferometer. By adjusting the optical path differences in both interferometers, the interference fringe pattern due only to the reference and measurement surfaces could be observed. The accuracy of the measurements was found to be similar to that of a conventional Fizeau interferometer.

  1. Coherent Beam Combining of High Power Broad-Area Laser Diode Array with a Closed-V-shape External Talbot Cavity

    SciTech Connect

    Liu, Bo; Liu, Yun; Braiman, Yehuda

    2010-01-01

    We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one grating's tilted angle.

  2. Coherent beam combining of high power broad-area laser diode array with a closed-V-shape external Talbot cavity.

    PubMed

    Liu, B; Liu, Y; Braiman, Y

    2010-03-29

    We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one grating's tilted angle.

  3. Ultra-short longitudinal spatial coherence length of laser light with the combined effect of spatial, angular, and temporal diversity

    SciTech Connect

    Ahmad, Azeem E-mail: mehtads@physics.iitd.ac.in; Dubey, Vishesh; Mehta, D. S. E-mail: mehtads@physics.iitd.ac.in; Srivastava, Vishal

    2015-03-02

    We demonstrate ultra-high axial-resolution topography and tomography of multilayered objects using pseudo thermal light source, i.e., laser. The longitudinal spatial coherence (LSC) length of light was significantly reduced by synthesizing a pseudo thermal source with the combined effect of spatial, angular, and temporal diversity. Thus, generating a low spatially coherent (i.e., broad angular frequency spectrum) light source having narrow temporal frequency spectrum. The LSC length was reduced less than 10 μm using a very low magnification lens. Experimental results of optical sectioning of multilayer objects with high axial-resolution of the order of 4 μm was achieved which is comparable to broadband light source. The present system does not require any dispersion compensation optical system for biological samples as a highly monochromatic light source is used.

  4. Toward optimizing partial spatially coherent beams for free space laser communications

    NASA Astrophysics Data System (ADS)

    Xiao, Xifeng; Voelz, David

    2007-09-01

    A performance metric is proposed as a general measure for optimizing the transverse coherence length l c of a partial spatially coherent beam for a given communication scenario. The expression is essentially the mean intensity minus the standard deviation of the intensity and we seek to maximize this quantity. It is preliminarily verified by the probability of fade with log-normal distribution model under the weak turbulence condition. We also examine it as a function of l c using wave optics simulations and compared these results with the relationships predicted by analytic theory under weak to medium-strong turbulence conditions. Our results verify there exists a unique coherence length that can optimize the receiver beam quality. After calculating the probability of fades of the optimal partially coherent beam and the fully coherent beam and comparing them with the wave optics simulation results, good agreement was observed.

  5. Quality inspection guided laser processing of irregular shape objects by stereo vision measurement: application in badminton shuttle manufacturing

    NASA Astrophysics Data System (ADS)

    Qi, Li; Wang, Shun; Zhang, Yixin; Sun, Yingying; Zhang, Xuping

    2015-11-01

    The quality inspection process is usually carried out after first processing of the raw materials such as cutting and milling. This is because the parts of the materials to be used are unidentified until they have been trimmed. If the quality of the material is assessed before the laser process, then the energy and efforts wasted on defected materials can be saved. We proposed a new production scheme that can achieve quantitative quality inspection prior to primitive laser cutting by means of three-dimensional (3-D) vision measurement. First, the 3-D model of the object is reconstructed by the stereo cameras, from which the spatial cutting path is derived. Second, collaborating with another rear camera, the 3-D cutting path is reprojected to both the frontal and rear views of the object and thus generates the regions-of-interest (ROIs) for surface defect analysis. An accurate visual guided laser process and reprojection-based ROI segmentation are enabled by a global-optimization-based trinocular calibration method. The prototype system was built and tested with the processing of raw duck feathers for high-quality badminton shuttle manufacture. Incorporating with a two-dimensional wavelet-decomposition-based defect analysis algorithm, both the geometrical and appearance features of the raw feathers are quantified before they are cut into small patches, which result in fully automatic feather cutting and sorting.

  6. CONTROL OF LASER RADIATION PARAMETERS: Transformation of the spatial coherence of pulsed laser radiation transmitted in the nonlinear regime through a multimode graded-index fibre

    NASA Astrophysics Data System (ADS)

    Kitsak, A. I.; Kitsak, M. A.

    2006-01-01

    A method is proposed for transformation of the spatial coherence of pulsed laser radiation upon nonlinear interaction in a multimode fibre. The specific features of the transmission of correlation properties of radiation in a graded-index fibre with regular and irregular profiles of the refractive index of the fibre core are analysed. A comparative analysis of the parameter of global degree of radiation coherence at the output of inhomogeneous waveguide and non-waveguide media is performed. It is shown that the most efficient mechanism of decorrelation of pulsed radiation in an optical fibre is fluctuations of the phase of radiation scattered by inhomogeneities of the refractive index of the fibre core induced due to nonlinear interaction with radiation with the spatially inhomogeneous intensity distribution.

  7. Generation and Amplification of Coherent Radiation with Optical Orbital Angular Momentum in a Free-Electron Laser

    NASA Astrophysics Data System (ADS)

    Hemsing, Erik Willard

    The object of this work is to examine how coherent light that carries orbital angular momentum (OAM) can be generated and amplified in a single pass, high-gain free-electron laser (FEL) at the fundamental operating frequency. This concept unites two rapidly expanding, but at present largely non-overlapping fields of study: high-order OAM light modes, which interact in new ways with matter, and FELs, in which a relativistically energetic electron beam emits coherent, ultra high-brightness, highly frequency-tunable light. The ability to generate OAM light in an FEL enables new regimes of laser interaction physics to be explored at wavelengths down to hard x-rays. The theoretical portion of this dissertation attempts to provide a new predictive mathematical framework. It builds on existing work, and describes the three-dimensional electromagnetic field of the high-gain FEL as a sum of OAM modes such that the amplification properties of individual modes can be characterized. The effects of uncorrelated energy spread, longitudinal space charge, energy detuning, and transverse emittance in the electron beam are included, as is the diffraction of the laser light. Theoretical predictions are corroborated by detailed numerical Genesis 1.3 simulations. When the theory is extended to frequency harmonics, a novel interaction is uncovered that generates a helical electron beam density distribution. These predictions are also supported by numerical Tredi simulations. This type of highly correlated structure is shown to naturally emit OAM light, and forms the basis of a new high-gain, high-mode generation (HGHMG) scheme proposed in its entirety here. The experimental section examines the helical microbunching concept in a proof-of-principle experiment dubbed HELIX, performed at the UCLA Neptune laboratory. We present detailed measurement of the coherent transition radiation emitted by the 12.5 MeV electron beam that is microbunched in a second harmonic interaction with an input

  8. Optical coherence tomography vs. high-frequency ultrasound during noninvasive laser coagulation of the canine vas deferens

    NASA Astrophysics Data System (ADS)

    Cilip, Christopher M.; Allaf, Mohamad E.; Fried, Nathaniel M.

    2012-02-01

    A noninvasive approach to vasectomy may eliminate male fear of complications related to surgery and increase its acceptance. Noninvasive laser thermal occlusion of the canine vas deferens has recently been reported. In this study, optical coherence tomography (OCT) and high-frequency ultrasound (HFUS) are compared for monitoring laser thermal coagulation of the vas in an acute canine model. Bilateral noninvasive laser coagulation of the vas was performed in 6 dogs (n=12 vasa) using a Ytterbium fiber laser wavelength of 1075 nm, incident power of 9.0 W, pulse duration of 500 ms, pulse rate of 1 Hz, and 3-mm-diameter spot. Cryogen spray cooling was used to prevent skin burns during the procedure. An OCT system with endoscopic probe and a HFUS system with 20-MHz transducer were used to image the vas immediately before and after the procedure. Vasa were then excised and processed for gross and histologic analysis for comparison with OCT and HFUS images. OCT provided high-resolution, superficial imaging of the compressed vas within the vas ring clamp, while HFUS provided deeper imaging of the vas held manually in the scrotal fold. Both OCT and high HFUS are promising imaging modalities for real-time confirmation of vas occlusion during noninvasive laser vasectomy.

  9. Single-beam coherent anti-Stokes Raman scattering spectroscopy of N 2 using a shaped 7 fs laser pulse

    NASA Astrophysics Data System (ADS)

    Roy, Sukesh; Wrzesinski, Paul; Pestov, Dmitry; Gunaratne, Tissa; Dantus, Marcos; Gord, James R.

    2009-08-01

    The feasibility is explored by single-beam coherent anti-Stokes Raman scattering (CARS) spectroscopy of gas-phase diatomic molecules related to combusting flows, with implications for gas-phase thermometry. We demonstrate CARS of gas-phase N 2 using a shaped ˜ 7 fs laser pulse, investigate the dependence of the CARS signal on the total pressure of the probed environment, both in pure N 2 and in mixtures with Ar, discuss the observed signal-to-noise ratio, and suggest improvements to be considered for reliable single-shot measurements at flame temperatures.

  10. A final report to the Laboratory Directed Research and Development committee on Project 93-ERP-075: ``X-ray laser propagation and coherence: Diagnosing fast-evolving, high-density laser plasmas using X-ray lasers``

    SciTech Connect

    Wan, A.S.; Cauble, R.; Da Silva, L.B.; Libby, S.B.; Moreno, J.C.

    1996-02-01

    This report summarizes the major accomplishments of this three-year Laboratory Directed Research and Development (LDRD) Exploratory Research Project (ERP) entitled ``X-ray Laser Propagation and Coherence: Diagnosing Fast-evolving, High-density Laser Plasmas Using X-ray Lasers,`` tracking code 93-ERP-075. The most significant accomplishment of this project is the demonstration of a new laser plasma diagnostic: a soft x-ray Mach-Zehnder interferometer using a neonlike yttrium x-ray laser at 155 {angstrom} as the probe source. Detailed comparisons of absolute two-dimensional electron density profiles obtained from soft x-ray laser interferograms and profiles obtained from radiation hydrodynamics codes, such as LASNEX, will allow us to validate and benchmark complex numerical models used to study the physics of laser-plasma interactions. Thus the development of soft x-ray interferometry technique provides a mechanism to probe the deficiencies of the numerical models and is an important tool for, the high-energy density physics and science-based stockpile stewardship programs. The authors have used the soft x-ray interferometer to study a number of high-density, fast evolving, laser-produced plasmas, such as the dynamics of exploding foils and colliding plasmas. They are pursuing the application of the soft x-ray interferometer to study ICF-relevant plasmas, such as capsules and hohlraums, on the Nova 10-beam facility. They have also studied the development of enhanced-coherence, shorter-pulse-duration, and high-brightness x-ray lasers. The utilization of improved x-ray laser sources can ultimately enable them to obtain three-dimensional holographic images of laser-produced plasmas.

  11. High-power coherent GaAs-based monolithic semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Botez, Dan

    2001-11-01

    Stable-beam operation to high coherent powers from large aperture devices can only be obtained from active-photonic- lattice (APL) structures of large built-in index step. Resonant phase-locked arrays of antiguides, so called ROW array, have provided 1.6W CW coherent power from 200micrometers - wide apertures. Two-dimensional surface-emitting APLs combining ROW arrays and DFB-DBR structures with central (pi) phase-shift are capable of providing coherent powers in the multi-watt range. ARROW-type devices, simpler APL structures, hold the potential for emitting 1W single-mode CW power reliability in stable beam patterns.

  12. Experimental analysis of adaptive optics compensation in free-space coherent laser communications

    NASA Astrophysics Data System (ADS)

    Anzuola, Esdras; Belmonte, Aniceto

    2016-09-01

    In this work we present a practical, experimental analysis of the effects of adaptive optics compensation on the performance of free-space coherent optical receivers. In order to fulfill this objective, we have developed a laboratory test bed for simulating atmospheric turbulence using Kolmogorov statistics; we have implemented a digital-signal-processing-based phase shift keying heterodyne coherent receiver; and we have integrated a compact module operating a low-cost adaptive optics system that applies modal and zonal wavefront correction. We have checked our experimental results against previously reported analytical models describing the performance of coherent receivers using atmospheric compensation techniques.

  13. Successful Restoration of Visual Acuity with an Extended Range of Vision Intraocular Lens after Multifocal Laser Ablation.

    PubMed

    Black, Sondra

    2016-01-01

    As our baby boomer population is aging and developing cataracts, so are our post-LASIK patients. These patients underwent LASIK surgery as they wished to be spectacle-free and are hoping to remain so after intraocular lens (IOL) surgery. Unfortunately, very little information is available regarding the suitability of presbyopia correcting IOLs for post-LASIK patients. This case represents successful implantation of an extended range of vision IOL in a 59-year-old patient who underwent multifocal ablation excimer laser surgery 12 years before. Emmetropia was targeted for the dominant eye and -0.5 D for the fellow eye. The 13 month follow-up after bilateral implantation of the TECNIS Symfony IOL revealed an uncorrected visual acuity of 20/25 for distance, 20/20 for intermediate and 20/16 for near. The patient is very happy and did not report any visual symptoms when asked. This successful case should encourage surgeons to consider implanting an extended range of vision IOLs in post-LASIK patients.

  14. Successful Restoration of Visual Acuity with an Extended Range of Vision Intraocular Lens after Multifocal Laser Ablation

    PubMed Central

    Black, Sondra

    2016-01-01

    As our baby boomer population is aging and developing cataracts, so are our post-LASIK patients. These patients underwent LASIK surgery as they wished to be spectacle-free and are hoping to remain so after intraocular lens (IOL) surgery. Unfortunately, very little information is available regarding the suitability of presbyopia correcting IOLs for post-LASIK patients. This case represents successful implantation of an extended range of vision IOL in a 59-year-old patient who underwent multifocal ablation excimer laser surgery 12 years before. Emmetropia was targeted for the dominant eye and −0.5 D for the fellow eye. The 13 month follow-up after bilateral implantation of the TECNIS Symfony IOL revealed an uncorrected visual acuity of 20/25 for distance, 20/20 for intermediate and 20/16 for near. The patient is very happy and did not report any visual symptoms when asked. This successful case should encourage surgeons to consider implanting an extended range of vision IOLs in post-LASIK patients. PMID:28101037

  15. A Five-Axis Robotic Laser And Vision Integrated "On-Line" Welding System

    NASA Astrophysics Data System (ADS)

    Uddin, M. N.; Berardi, Elvio; DuCharme, R. C.; Salada, D. A.; Speranza, J. J.

    1986-11-01

    A five axis robotic laser welding system has been designed and built for an "on-line" automotive joining application. A high power CO2 laser beam is manipulated through the use of a robotic beam delivery system and is focused onto the work piece. An optical probe communicates the coordinates or geometry of the parts to the clamping and welding robots. The essential features of the robots, laser, optical probes and clamping system have been discussed. The system versatilities also have been outlined.

  16. Phase-sensitive optical coherence tomography-based vibrometry using a highly phase-stable akinetic swept laser source

    SciTech Connect

    Applegate, Brian E.; Park, Jesung; Carbajal, Esteban; Oghalai, John S.

    2015-12-31

    Phase-sensitive Optical Coherence Tomography (PhOCT) is an emerging tool for in vivo investigation of the vibratory function of the intact middle and inner ear. PhOCT is able to resolve micron scale tissue morphology in three dimensions as well as measure picometer scale motion at each spatial position. Most PhOCT systems to date have relied upon the phase stability offered by spectrometer detection. On the other hand swept laser source based PhOCT offers a number of advantages including balanced detection, long imaging depths, and high imaging speeds. Unfortunately the inherent phase instability of traditional swept laser sources has necessitated complex user developed hardware/software solutions to restore phase sensitivity. Here we present recent results using a prototype swept laser that overcomes these issues. The akinetic swept laser is electronically tuned and precisely controls sweeps without any mechanical movement, which results in high phase stability. We have developed an optical fiber based PhOCT system around the akinetic laser source that had a 1550 nm center wavelength and a sweep rate of 140 kHz. The stability of the system was measured to be 4.4 pm with a calibrated reflector, thus demonstrating near shot noise limited performance. Using this PhOCT system, we have acquired structural and vibratory measurements of the middle ear in a mouse model, post mortem. The quality of the results suggest that the akinetic laser source is a superior laser source for PhOCT with many advantages that greatly reduces the required complexity of the imaging system.

  17. Joint mitigation of laser phase noise and fiber nonlinearity for polarization-multiplexed QPSK and 16-QAM coherent transmission systems.

    PubMed

    Morsy-Osman, Mohamed; Zhuge, Qunbi; Chen, Lawrence R; Plant, David V

    2011-12-12

    We propose the use of pilot-aided (PA) transmission, enabled by single-sideband-subcarrier modulation of both quadratures in the DSP-domain, in single-carrier systems to mitigate jointly laser phase noise and fiber nonlinearity. In addition to tolerance against laser phase noise, we show that the proposed scheme also improves the nonlinear tolerance of both polarization-division-multiplexed (PDM) QPSK and 16-QAM coherent transmission systems by increasing the maximum allowable launch power by 1 dB and 1.5 dB, respectively. The improved nonlinear performance of both systems also manifests itself as an increase in the maximum reach by 720 km and 480 km, respectively. Finally, when digital-to-analog converters (DACs) with lower bit resolutions are used at the transmitter, PA transmission is shown to preserve the same performance improvement over the non-PA case.

  18. Simultaneous Confocal Scanning Laser Ophthalmoscopy Combined with High-Resolution Spectral-Domain Optical Coherence Tomography: A Review

    PubMed Central

    Castro Lima, Verônica; Rodrigues, Eduardo B.; Nunes, Renata P.; Sallum, Juliana F.; Farah, Michel E.; Meyer, Carsten H.

    2011-01-01

    We aimed to evaluate technical aspects and the clinical relevance of a simultaneous confocal scanning laser ophthalmoscope and a high-speed, high-resolution, spectral-domain optical coherence tomography (SDOCT) device for retinal imaging. The principle of confocal scanning laser imaging provides a high resolution of retinal and choroidal vasculature with low light exposure. Enhanced contrast, details, and image sharpness are generated using confocality. The real-time SDOCT provides a new level of accuracy for assessment of the angiographic and morphological correlation. The combined system allows for simultaneous recordings of topographic and tomographic images with accurate correlation between them. Also it can provide simultaneous multimodal imaging of retinal pathologies, such as fluorescein and indocyanine green angiographies, infrared and blue reflectance (red-free) images, fundus autofluorescence images, and OCT scans (Spectralis HRA + OCT; Heidelberg Engineering, Heidelberg, Germany). The combination of various macular diagnostic tools can lead to a better understanding and improved knowledge of macular diseases. PMID:22132313

  19. Implementation of a Coherent Anti-Stokes Raman Scattering (CARS) System on a Ti:Sapphire and OPO Laser Based Standard Laser Scanning Microscope.

    PubMed

    Mytskaniuk, Vasyl; Bardin, Fabrice; Boukhaddaoui, Hassan; Rigneault, Herve; Tricaud, Nicolas

    2016-07-17

    Laser scanning microscopes combining a femtosecond Ti:sapphire laser and an optical parametric oscillator (OPO) to duplicate the laser line have become available for biologists. These systems are primarily designed for multi-channel two-photon fluorescence microscopy. However, without any modification, complementary non-linear optical microscopy such as second-harmonic generation (SHG) or third harmonic generation (THG) can also be performed with this set-up, allowing label-free imaging of structured molecules or aqueous medium-lipid interfaces. These techniques are well suited for in-vivo observation, but are limited in chemical specificity. Chemically selective imaging can be obtained from inherent vibration signals based on Raman scattering. Confocal Raman microscopy provides 3D spatial resolution, but it requires high average power and long acquisition time. To overcome these difficulties, recent advances in laser technology have permitted the development of nonlinear optical vibrational microscopy, in particular coherent anti-Stokes Raman scattering (CARS). CARS microscopy has therefore emerged as a powerful tool for biological and live cell imaging, by chemically mapping lipids (via C-H stretch vibration), water (via O-H stretch vibrations), proteins or DNA. In this work, we describe the implementation of the CARS technique on a standard OPO-coupled multiphoton laser scanning microscope. It is based on the in-time synchronization of the two laser lines by adjusting the length of one of the laser beam path. We present a step-by-step implementation of this technique on an existing multiphoton system. A basic background in experimental optics is helpful and the presented system does not require expensive supplementary equipment. We also illustrate CARS imaging obtained on myelin sheaths of sciatic nerve of rodent, and we show that this imaging can be performed simultaneously with other nonlinear optical imaging, such as standard two-photon fluorescence technique

  20. Coherent supercontinuum generation from 1.4 to 4 μm in a tapered fluorotellurite microstructured fiber pumped by a 1980 nm femtosecond fiber laser

    NASA Astrophysics Data System (ADS)

    Li, Nan; Wang, Fang; Yao, Chuanfei; Jia, Zhixu; Zhang, Lei; Feng, Yan; Hu, Minglie; Qin, Guanshi; Ohishi, Yasutake; Qin, Weiping

    2017-02-01

    Coherent supercontinuum light expanding from 1.4 to 4 μm is generated in a 4 cm long tapered fluorotellurite microstructured fiber (MF) pumped by a 1980 nm femtosecond fiber laser. The spectral broadening in the tapered fluorotellurite MF is caused by self-phase modulation, the Raman soliton, and red-shifted dispersive wave generation. Our results show that tapered fluorotellurite MFs are promising nonlinear medium for generating coherent broadband mid-infrared supercontinuum light.

  1. The FERMI@Elettra free-electron-laser source for coherent X-ray physics: photon properties, beam transport system, and applications

    SciTech Connect

    Allaria, Enrico; Callegari, Carlo; Cocco, Daniele; Fawley, William M.; Kiskinova, Maya; Masciovecchio, Claudio; Parmigiani, Fulvio

    2010-04-05

    FERMI@Elettra is comprised of two free electron lasers (FELs) that will generate short pulses (tau ~;; 25 to 200 fs) of highly coherent radiation in the XUV and soft X-ray region. The use of external laser seeding together with a harmonic upshift scheme to obtain short wavelengths will give FERMI@Elettra the capability to produce high quality, longitudinal coherent photon pulses. This capability together with the possibilities of temporal synchronization to external lasers and control of the output photon polarization will open new experimental opportunities not possible with currently available FELs. Here we report on the predicted radiation coherence properties and important configuration details of the photon beam transport system. We discuss the several experimental stations that will be available during initial operations in 2011, and we give a scientific perspective on possible experiments that can exploit the critical parameters of this new light source.

  2. Generating high-brightness and coherent soft x-ray pulses in the water window with a seeded free-electron laser

    NASA Astrophysics Data System (ADS)

    Zhou, Kaishang; Feng, Chao; Deng, Haixiao; Wang, Dong

    2017-01-01

    We propose a new scheme to generate high-brightness and temporal coherent soft x-ray radiation in a seeded free-electron laser. The proposed scheme is based on the coherent harmonic generation (CHG) and superradiant principles. A CHG scheme is first used to generate a coherent signal at ultrahigh harmonics of the seed. This coherent signal is then amplified by a series of chicane-undulator modules via the fresh bunch and superradiant processes in the following radiator. Using a representative of a realistic set of parameters, three-dimensional simulations have been carried out and the simulations results demonstrated that 10 GW-level ultrashort (˜20 fs ) coherent radiation pulses in the water window can be achieved by using a 1.6 GeV electron beam based on the proposed technique.

  3. Visualization of hair follicles using high-speed optical coherence tomography based on a Fourier domain mode locking laser

    NASA Astrophysics Data System (ADS)

    Tsai, M.-T.; Chang, F.-Y.

    2012-04-01

    In this study, a swept-source optical coherence tomography (SS-OCT) system with a Fourier domain mode locking (FDML) laser is proposed for a dermatology study. The homemade FDML laser is one kind of frequency-sweeping light source, which can provide output power of >20 mW and an output spectrum of 65 nm in bandwidth centered at 1300 nm, enabling imaging with an axial resolution of 12 μm in the OCT system. To eliminate the forward scans from the laser output and insert the delayed backward scans, a Mach-Zehnder configuration is implemented. Compared with conventional frequency-sweeping light sources, the FDML laser can achieve much higher scan rates, as high as ˜240 kHz, which can provide a three-dimensional imaging rate of 4 volumes/s. Furthermore, the proposed high-speed SS-OCT system can provide three-dimensional (3D) images with reduced motion artifacts. Finally, a high-speed SS-OCT system is used to visualize hair follicles, demonstrating the potential of this technology as a tool for noninvasive diagnosis of alopecia.

  4. Linearly polarized, dual wavelength frequency-modulated continuous-wave fiber laser for simultaneous coherent distance and speed measurements

    NASA Astrophysics Data System (ADS)

    Chen, Tao; Wu, Jun; Xu, Weiming; He, Zhiping; Qian, Liqun; Shu, Rong

    2016-07-01

    We have experimentally demonstrated a high power linearly polarized, dual wavelength frequency-modulated continuous-wave (FMCW) fiber laser with master-oscillator power-amplifier (MOPA) configuration, which is specially designed for simultaneous coherent distance and speed measurements. Two single longitudinal mode laser diodes working at 1550.12 and 1554.13 nm are employed as the seeds of the fiber MOPA. The wavelengths of the seeds are externally modulated by two acousto-optic frequency shifters (AOFSes) with a symmetrical sawtooth wave from 330-460 MHz in the frequency domain. The modulation periodicities for the two seeds are 26 and 26.3 μs, respectively, by which the distance ambiguity can be eliminated and therefore the detection range can be extended to a great extent. The seeds are then amplified independently to reduce their power differences during frequency modulation. After being coupled and boosted with three successive fiber amplifiers, an output power of 12.1 W is recorded from the FMCW laser with a power instability   <0.14% over 1.5 h. The measured PER and full divergence angle of the laser are  >18 dB and  <25 μrad, respectively, indicating its excellent performance for field measurements.

  5. Simultaneous multimodal ophthalmic imaging using swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography

    PubMed Central

    Malone, Joseph D.; El-Haddad, Mohamed T.; Bozic, Ivan; Tye, Logan A.; Majeau, Lucas; Godbout, Nicolas; Rollins, Andrew M.; Boudoux, Caroline; Joos, Karen M.; Patel, Shriji N.; Tao, Yuankai K.

    2016-01-01

    Scanning laser ophthalmoscopy (SLO) benefits diagnostic imaging and therapeutic guidance by allowing for high-speed en face imaging of retinal structures. When combined with optical coherence tomography (OCT), SLO enables real-time aiming and retinal tracking and provides complementary information for post-acquisition volumetric co-registration, bulk motion compensation, and averaging. However, multimodality SLO-OCT systems generally require dedicated light sources, scanners, relay optics, detectors, and additional digitization and synchronization electronics, which increase system complexity. Here, we present a multimodal ophthalmic imaging system using swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography (SS-SESLO-OCT) for in vivo human retinal imaging. SESLO reduces the complexity of en face imaging systems by multiplexing spatial positions as a function of wavelength. SESLO image quality benefited from single-mode illumination and multimode collection through a prototype double-clad fiber coupler, which optimized scattered light throughput and reduce speckle contrast while maintaining lateral resolution. Using a shared 1060 nm swept-source, shared scanner and imaging optics, and a shared dual-channel high-speed digitizer, we acquired inherently co-registered en face retinal images and OCT cross-sections simultaneously at 200 frames-per-second. PMID:28101411

  6. Simultaneous multimodal ophthalmic imaging using swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography.

    PubMed

    Malone, Joseph D; El-Haddad, Mohamed T; Bozic, Ivan; Tye, Logan A; Majeau, Lucas; Godbout, Nicolas; Rollins, Andrew M; Boudoux, Caroline; Joos, Karen M; Patel, Shriji N; Tao, Yuankai K

    2017-01-01

    Scanning laser ophthalmoscopy (SLO) benefits diagnostic imaging and therapeutic guidance by allowing for high-speed en face imaging of retinal structures. When combined with optical coherence tomography (OCT), SLO enables real-time aiming and retinal tracking and provides complementary information for post-acquisition volumetric co-registration, bulk motion compensation, and averaging. However, multimodality SLO-OCT systems generally require dedicated light sources, scanners, relay optics, detectors, and additional digitization and synchronization electronics, which increase system complexity. Here, we present a multimodal ophthalmic imaging system using swept-source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography (SS-SESLO-OCT) for in vivo human retinal imaging. SESLO reduces the complexity of en face imaging systems by multiplexing spatial positions as a function of wavelength. SESLO image quality benefited from single-mode illumination and multimode collection through a prototype double-clad fiber coupler, which optimized scattered light throughput and reduce speckle contrast while maintaining lateral resolution. Using a shared 1060 nm swept-source, shared scanner and imaging optics, and a shared dual-channel high-speed digitizer, we acquired inherently co-registered en face retinal images and OCT cross-sections simultaneously at 200 frames-per-second.

  7. Attosecond Light and Science at the Time-scale of the Electron - Coherent X-Rays from Tabletop Ultrafast Lasers

    SciTech Connect

    Margaret, Murnane

    2010-03-31

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  8. Attosecond Light and Science at the Time-scale of the Electron - Coherent X-Rays from Tabletop Ultrafast Lasers

    ScienceCinema

    Margaret, Murnane [University of Colorado, Boulder and NIST

    2016-07-12

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  9. Final Scientific/Technical Report for DE-FG03-02NA00063 Coherent imaging of laser-plasma interactions using XUV high harmonic radiation

    SciTech Connect

    Henry Kapteyn

    2006-06-06

    The objective of this project was to develop experimental techniques for using coherent extreme-ultraviolet (EUV) radiation generated using the high-order harmonic generation technique, as an illumination source for studies of high-density plasmas relevant to the stockpile stewardship mission. In this project, we made considerable progress, including the first demonstration of imaging of dynamic processes using this coherent ultrashort pulse light. This work also stimulated considerable progress in the development of the required ultrashort EUV pulses, and in the development of new laser technologies that have been commercialized. We also demonstrated the first EUV sources that exhibit full intrinsic optical coherence. This work resulted in 12 publications.

  10. Laser Safety for the Experimental Halls at SLAC_s Linac Coherent Light Source (LCLS)

    SciTech Connect

    Woods, Michael; Anthony, Perry; Barat, Ken; Gilevich, Sasha; Hays, Greg; White, William E.; /SLAC

    2009-01-15

    The LCLS at the SLAC National Accelerator Laboratory will be the world's first source of an intense hard x-ray laser beam, generating x-rays with wavelengths of 1nm and pulse durations less than 100fs. The ultrafast x-ray pulses will be used in pump-probe experiments to take stop-motion pictures of atoms and molecules in motion, with pulses powerful enough to take diffraction images of single molecules, enabling scientists to elucidate fundamental processes of chemistry and biology. Ultrafast conventional lasers will be used as the pump. In 2009, LCLS will deliver beam to the Atomic Molecular and Optical (AMO) Experiment, located in one of 3 x-ray Hutches in the Near Experimental Hall (NEH). The NEH includes a centralized Laser Hall, containing up to three Class 4 laser systems, three x-ray Hutches for experiments and vacuum transport tubes for delivering laser beams to the Hutches. The main components of the NEH laser systems are a Ti:sapphire oscillator, a regen amplifier, green pump lasers for the oscillator and regen, a pulse compressor and a harmonics conversion unit. Laser safety considerations and controls for the ultrafast laser beams, multiple laser controlled areas, and user facility issues are discussed.

  11. Resonant cavity based time-domain multiplexing techniques for coherently combined fiber laser systems

    NASA Astrophysics Data System (ADS)

    Zhou, T.; Ruppe, J.; Stanfield, P.; Nees, J.; Wilcox, R.; Galvanauskas, A.

    2015-10-01

    This paper describes novel time-domain multiplexing techniques that use various resonant cavity configurations for increasing pulse energy extraction per each parallel amplification channel of a coherently combined array. Two different techniques are presented: a so-called N2 coherent array combining technique, applicable to a periodic pulse train, and a coherent pulse stacking amplification (CPSA) technique, applicable to a pulse burst. The first technique is a coherent combining technique, which achieves simultaneous beam combining and time-domain pulse multiplexing/down-counting using traveling-wave Fabry-Perot type resonators. The second technique is purely a time-domain pulse multiplexing technique, used with either a single amplifier or an amplifier array, which uses traveling-wave Gires-Tourmois type resonators. The importance of these techniques is that they can enable stacking of very large number of pulses, thus increasing effective amplified-pulse duration potentially by 102 to 103 times, and reducing fiber array size by the corresponding factor. This could lead to very compact coherently combined arrays even for generating very high pulse energies in the range of 1 to 100 J.

  12. Low Vision

    MedlinePlus

    ... USAJobs Home > Statistics and Data > Low Vision Low Vision Low Vision Defined: Low Vision is defined as the best- ... 2010 U.S. Age-Specific Prevalence Rates for Low Vision by Age, and Race/Ethnicity Table for 2010 ...

  13. Proof of the Feasibility of Coherent and Incoherent Schemes for Pumping a Gamma-ray Laser

    DTIC Science & Technology

    1992-12-31

    been adequate to identify 29 first -class candidates, but further evaluation cannot proceed without remeasurements of nuclear properties with higher... under this contract. Resolution of the question of the feasibility of a gamma-ray laser now rests upon the determination of: 1) the identity of the best...the critical keys in the development of the first laser. There was a broad absorption band linked through efficient cascading to the narrow laser lavel

  14. Electronically-Steerable, Coherent Laser Arrays: REALLY Small, Lightweight, High Power Lasers for DoD Applications (BRIEFING CHARTS)

    DTIC Science & Technology

    2007-03-07

    Optics Element LiNO3 Electric Field Controller • Intensity • Phase • Polarization APPLET SPGD Algorithm implemented on FPGA Fiber Laser Amplifier...Need High Power Fiber Laser Amplifiers – 2 kW – Single Transverse Mode – Single Polarization – < λ/20 Phase Noise – No SBS/SRS - Narrowline These 2...limiting factor Fiber Laser Technology – 100 kW • Explore Ultimate Fiber Amplifier Array Scaling Limits – Single-Mode (M2 < 1.5) – Single-

  15. High sensitivity stand-off detection and quantification of chemical mixtures using an active coherent laser spectrometer (ACLaS)

    NASA Astrophysics Data System (ADS)

    MacLeod, Neil A.; Weidmann, Damien

    2016-05-01

    High sensitivity detection, identification and quantification of chemicals in a stand-off configuration is a highly sought after capability across the security and defense sector. Specific applications include assessing the presence of explosive related materials, poisonous or toxic chemical agents, and narcotics. Real world field deployment of an operational stand-off system is challenging due to stringent requirements: high detection sensitivity, stand-off ranges from centimeters to hundreds of meters, eye-safe invisible light, near real-time response and a wide chemical versatility encompassing both vapor and condensed phase chemicals. Additionally, field deployment requires a compact, rugged, power efficient, and cost-effective design. To address these demanding requirements, we have developed the concept of Active Coherent Laser Spectrometer (ACLaS), which can be also described as a middle infrared hyperspectral coherent lidar. Combined with robust spectral unmixing algorithms, inherited from retrievals of information from high-resolution spectral data generated by satellitebased spectrometers, ACLaS has been demonstrated to fulfil the above-mentioned needs. ACLaS prototypes have been so far developed using quantum cascade lasers (QCL) and interband cascade lasers (ICL) to exploit the fast frequency tuning capability of these solid state sources. Using distributed feedback (DFB) QCL, demonstration and performance analysis were carried out on narrow-band absorbing chemicals (N2O, H2O, H2O2, CH4, C2H2 and C2H6) at stand-off distances up to 50 m using realistic non cooperative targets such as wood, painted metal, and bricks. Using more widely tunable external cavity QCL, ACLaS has also been demonstrated on broadband absorbing chemicals (dichloroethane, HFC134a, ethylene glycol dinitrate and 4-nitroacetanilide solid) and on complex samples mixing narrow-band and broadband absorbers together in a realistic atmospheric background.

  16. Application of Optical Coherence Tomography to Identify Pulp Exposure During Access Cavity Preparation Using an Er:YAG Laser

    PubMed Central

    Ding, Jiangfeng; Watanabe, Satoshi; Iino, Yoshiko; Kokuzawa, Chizuko; Anjo, Tomoo; Suda, Hideaki; Sumi, Yasunori

    2014-01-01

    Abstract Objective: The study aimed to evaluate the ability of optical coherence tomography (OCT) to guide and identify pulp exposure using an erbium: yttrium–aluminum–garnet (Er:YAG) laser. Background data: The Er:YAG laser has been proven to be effective in ablating dental hard tissue and offers advantages, as there is none of the vibration and noise you get with conventional methods, but it has limitations in relation to the tactile feedback that would aid in identification of entry into the pulp chamber. Based on depth-resolved optical reflectivity, OCT technology has been developed to provide high-resolution, cross-sectional images of the internal structure of biological tissues. Materials and methods: The pulp chambers of 20 human mandibular incisors were examined, and the average thickness of hard tissue covering the pulp chamber was assessed using micro-computed tomography (micro-CT) images. An Er:YAG laser was used to gradually penetrate the hard tissue over the pulp chamber under microscopic guidance. The preparation was constantly imaged using a swept-source OCT at 10 sec intervals until a pulp chamber exposure was identified using the technology. The pulp exposure was re-examined under the microscope and compared with micro-CT images for verification. Results: The pulp exposures of 20 incisors were all verified microscopically and with micro-CT images. The thickness of hard tissue penetrated by the laser ranged from 0.44 to 1.69 mm. Conclusions: Swept-source OCT is a useful tool for identifying pulp exposure during access opening with the Er: YAG laser. PMID:24905930

  17. Effect of the degree of phase-correlation of laser sources on the transmission and optical coherent detection in radio-over-fibre systems

    NASA Astrophysics Data System (ADS)

    Maldonado-Basilio, Ramón; Li, Ran; Abdul-Majid, Sawsan; Nikkhah, Hamdam; Leong, Kin-Wai; Hall, Trevor J.

    2013-01-01

    The deployment of high capacity Radio-over-Fiber (RoF) systems rely, among many aspects, on the capability to efficiently generate, transport, and detect millimeter-wave carriers modulated at high data rates. Photonic approaches based on the heterodyne beating of two free-running laser sources have been proposed as an alternative to generate multi-Gbps quadrature phase modulated signals imposed on millimeter wave carriers. Implementing photonic approaches in the down-link avoids the need for electronic generation of high frequency carriers and decreases the requirements at the base band electronics. In addition, implementing complex modulation formats overcomes some of the typical issues found in intensity modulation direct detection approaches such as non­ linearity, receiver sensitivity and dynamic range. In this work, the performance improvement of a coherent RoF system carrying 10 Gbps QPSK signals is numerically analyzed in terms of both the frequency linewidth and the degree of phase correlation between the lasers utilised at the down-link (for the optical heterodyne beating) and at the up-link (for the optical coherent detection). Relative to phase correlated lasers featuring linewidths of 5 MHz, the peak power of the 60 G Hz carrier generated at the down-link is reduced by 8 dB for un-correlated lasers. In addition, the error vector magnitude of the received signal at the up-link is improved from over 20% (for un-correlated lasers and linewidths of 5 MHz) to around 15% (for correlated lasers) at an optical received power of -30 dBm. The results obtained reinforce the idea of using coherent comb laser sources with phase correlated modes located at the Central Office. It also motivates the eventual deployment of techniques to control the degree of phase correlation between the lasers used as signal and local oscillator at the optical coherent receivers.

  18. Coherent Rayleigh-Brillouin Scattering in High Intensity Laser Fields: Optical Lattice gas Heating (Briefing Charts)

    DTIC Science & Technology

    2012-07-01

    ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NO. Air Force Research Laboratory (AFMC) AFRL/RQRC 10 E. Saturn Blvd. Edwards AFB CA 93524-7680...unlimited CRBS Results Low Intensity • Experiment and DSMC show good agreement with six-moment model (s6) for low intensity (X. Pan , “Coherent

  19. Asymmetric lateral coherence of betatron radiation emitted in laser-driven light sources

    NASA Astrophysics Data System (ADS)

    Paroli, B.; Chiadroni, E.; Ferrario, M.; Petrillo, V.; Potenza, M. A. C.; Rossi, A. R.; Serafini, L.; Shpakov, V.

    2015-08-01

    We show that the radiation emitted by betatron oscillations of a high-energy electron beam undergoing wake-field acceleration is endowed with peculiar coherence properties which deliver quantitative information about the electron trajectories. Such results are achieved by means of accurate numerical simulations and a simple geometrical model gives a clear physical interpretation.

  20. Monolithic narrow-linewidth InGaAsP semiconductor laser for coherent optical communications

    NASA Technical Reports Server (NTRS)

    Palfrey, S. L.; Enstrom, R. E.; Longeway, P. A.

    1989-01-01

    A design for a monolithic narrow-linewidth InGaAsP diode laser has been developed using a multiple-quantum-well (MQW) extended-passive-cavity distributed-Bragg-reflector (DBR) laser design. Theoretical results indicate that this structure has the potential for a linewidth of 100 kHz or less. To realize this device, a number of the fabrication techniques required to integrate low-loss passive waveguides with active regions have been developed using a DBR laser structure. In addition, the MOCVD growth of InGaAs MQW laser structures has been developed, and threshold current densities as low as 1.6 kA/sq cm have been obtained from broad-stripe InGaAs/InGaAsP separate-confinement-heterostructure MQW lasers.

  1. Stereo vision and laser odometry for autonomous helicopters in GPS-denied indoor environments

    NASA Astrophysics Data System (ADS)

    Achtelik, Markus; Bachrach, Abraham; He, Ruijie; Prentice, Samuel; Roy, Nicholas

    2009-05-01

    This paper presents our solution for enabling a quadrotor helicopter to autonomously navigate unstructured and unknown indoor environments. We compare two sensor suites, specifically a laser rangefinder and a stereo camera. Laser and camera sensors are both well-suited for recovering the helicopter's relative motion and velocity. Because they use different cues from the environment, each sensor has its own set of advantages and limitations that are complimentary to the other sensor. Our eventual goal is to integrate both sensors on-board a single helicopter platform, leading to the development of an autonomous helicopter system that is robust to generic indoor environmental conditions. In this paper, we present results in this direction, describing the key components for autonomous navigation using either of the two sensors separately.

  2. Characterization of Fourier domain mode-locked wavelength swept laser for optical coherence tomography imaging.

    PubMed

    Jeon, Min Yong; Zhang, Jun; Chen, Zhongping

    2008-03-17

    We present characteristics of a wavelength swept laser with a scanning fiber Fabry-Perot filter at 1300 nm. We investigate the dependence of the scanning frequencies in the swept laser. In conventional wavelength swept lasers, the relative intensity of the laser output decreases significantly as the scanning frequency increases. The peak wavelength of the output spectrum is red-shifted due to the nonlinear frequency downshifting in the semiconductor optical amplifier (SOA). In the Fourier domain mode-locked (FDML) wavelength swept laser, we investigate transient intensity profiles and the full width at half maximum in response to the injection currents and detuning of the scanning frequency. The degradation of the scanning range of the swept laser is caused by the deviation from the scanning frequency at 45.6 kHz. In addition, transient intensity profiles show significant asymmetric behavior in response to the detuned frequencies. Finally, the axial resolution and sensitivity as a function of imaging depth are analyzed for both forward and backward scans. With the FDML laser, the detection sensitivity up to 102 dB is achieved for the backward scans. The backward scans exhibit higher axial resolution and sensitivity than the forward scan.

  3. Narrow linewidth single-mode semiconductor laser development for coherent detection lidar

    NASA Technical Reports Server (NTRS)

    Mansour, Kamjou; Ksendzov, Alexander; Menzies, Robert T.; Maker, Paul D.; Muller, Richard E.; Manfra, M. J.; Turner, George W.

    2003-01-01

    High power, tunable, single mode, narrow linewidth semiconductor lasers in the 2.05-(micro)m wavelength region are needed to develop semiconductor laser reference oscillators for optical remote sensing from Earth orbit. 2.05-I1/4m narrow linewidth monolithic distributed feedback (DFB) and distributed Bragg reflector (DBR) with the external grating ridge waveguide lasers fabricated from epitaxially grown InGaAs/InGaAsP/InP and in InGaAsSb/AlGaAsSb/GaSb heterostructures are reported.

  4. High Average Power Diode Pumped Solid State Lasers: Power Scaling With High Spectral and Spatial Coherence

    DTIC Science & Technology

    2009-03-30

    thulium upper laser level through cross-relaxation [5, 6]. Phosphate glass is also an attractive host for high-power single-frequency 2-µm Tm3+- doped...12, (8), p. 512 (1976) [4] D. G. Lancaster, A. Sabella, A. Hemming, S. Bennetts, S.D. Jackson, “Power-scalable thulium and holmium fibre lasers...efficient high-power thulium -doped germanate glass fiber laser,” Optics Letters, 32, (6), p. 638 (2007) [6] S. Jackson, “Power scaling method for 2-μm

  5. Spatial coherence measurement of a scanning laser system and applicability of the Zernike's approximation to the exit pupil on the scan mirror

    NASA Astrophysics Data System (ADS)

    Kubota, Shigeo

    2012-11-01

    Spatial coherence of the scanning laser beam was observed on the Young's experimental set up using 50-μm-wide, 200-μm-separation double slits, which measured the less than unity fringe visibility in the Fraunhofer diffraction pattern of the double slits illuminated by the scanning laser beam at horizontal scan frequency 21 kHz, while approximately unity in case of the illumination by the laser beam at rest. This fact allow us to use the Zernike's approximation when applying the van Cittert Zernike theorem to the scanning laser system such as the laser pico-projectors in order to estimate its speckle contrast in the projected image on the screen diffuser. The predicted and measured speckle contrasts showed excellent agreement on the screen illuminated by the laser projector.

  6. Annual Scientific Report for DE-FG03-02NA00063 Coherent imaging of laser-plasma interactions using XUV high harmonic radiation

    SciTech Connect

    Prof. Henry C. Kapteyn

    2005-05-03

    In this project, we use coherent short-wavelength light generated using high-order harmonic generation as a probe of laser-plasma dynamics and phase transitions on femtosecond time-scales. The interaction of ultrashort laser pulses with materials and plasmas is relevant to stockpile stewardship, to understanding the equation of state of matter at high pressures and temperatures, and to plasma concepts such as the fast-ignitor ICF fusion concept and laser-based particle acceleration. Femtosecond laser technology makes it possible to use a small-scale setup to generate 20fs pulses with average power >10W at multiple kHz repetition rates, that can be focused to intensities in excess of 1017W/cm2. These lasers can be used either to rapidly heat materials to initiate phase transitions, or to create laser plasmas over a wide parameter space. These lasers can also be used to generate fully spatially coherent XUV beams with which to probe these materials and plasma systems. We are in process of implementing imaging studies of plasma hydrodynamics and warm, dense matter. The data will be compared with simulation codes of laser-plasma interactions, making it possible to refine and validate these codes.

  7. Real-time optical coherence tomography observation of retinal tissue damage during laser photocoagulation therapy on ex-vivo porcine samples

    NASA Astrophysics Data System (ADS)

    Steiner, P.; Považay, B.; Stoller, M.; Morgenthaler, P.; Inniger, D.; Arnold, P.; Sznitman, R.; Meier, Ch.

    2015-07-01

    Retinal laser photocoagulation represents a widely used treatment for retinal pathologies such as diabetic chorioretinopathy or diabetic edema. For effective treatment, an appropriate choice of the treatment energy dose is crucial to prevent excessive tissue damage caused by over-irradiation of the retina. In this manuscript we investigate simultaneous and time-resolved optical coherence tomography for its applicability to provide feedback to the ophthalmologist about the introduced retinal damage during laser photocoagulation. Time-resolved and volumetric optical coherence tomography data of 96 lesions on ex-vivo porcine samples, set with a 577 nm laser prototype and irradiance of between 300 and 8800 W=cm2 were analyzed. Time-resolved scans were compared to volumetric scans of the lesion and correlated with ophthalmoscopic visibility. Lastly, image parameters extracted from optical coherence tomography Mscans, suitable for lesion classification were identified. Results presented in this work support the hypothesis that simultaneous optical coherence tomography provides valuable information about the extent of retinal tissue damage and may be used to guide retinal laser photocoagulation in the future.

  8. Assessment of ultra-high resolution optical coherence tomography for monitoring tissue effects caused by laser photocoagulation of ex-vivo porcine retina

    NASA Astrophysics Data System (ADS)

    Steiner, Patrick; Enzmann, Volker; Wolf, Sebastian; Bossen, Anke; Meier, Christoph; Sznitman, Raphael

    2015-03-01

    Retinal laser photocoagulation is an established and successful treatment for a variety of retinal diseases. While being a valuable treatment modality, laser photocoagulation shows the drawback of employing high energy lasers which are capable of physically destroying the neural retina. For reliable therapy, it is therefore crucial to closely monitor the therapy effects caused in the retinal tissue. A depth resolved representation of optical tissue properties as provided by optical coherence tomography may provide valuable information about the treatment effects in the retinal layers if recorded simultaneously to laser coagulation. Therefore, in this work, the use of ultra-high resolution optical coherence tomography to represent tissue changes caused by conventional and selective retinal photocoagulation is investigated. Laser lesions were placed on porcine retina ex-vivo using a 577 nm laser as well as a pulsed laser at 527 nm built for selective treatment of the retinal pigment epithelium. Applied energies were varied to generate lesions best representing the span from under- to overtreatment. The lesions were examined using a custom-designed optical coherence tomography system with an axial resolution of 1.78 μm and 70 kHz Ascan rate. Optical coherence tomography scans included volume scans before and after irradiation, as well as time lapse scans (Mscan) of the lesions. Results show OCT lesion visibility thresholds to be below the thresholds of ophthalmoscopic inspection. With the ultra-high resolution OCT, 42% - 44% of ophthalmoscopically invisible lesions could be detected and lesions that were under- or overexposed could be distinguished using the OCT data.

  9. A 1000 Hz Pulsed Solid-State Raman Laser for Coherent Lidar Measurement of Wake Vortices

    NASA Technical Reports Server (NTRS)

    Koch, Grady J.; Murray, James; Lytle, Carroll; Nguyen, Chi

    1997-01-01

    Included in the overview is a discussion of the 1.5 micron laser specifications, eye safety and cost, scan rates, pulselength, range capability issues, Raman beam cleanup, receiver layout, and the real-time processor and display.

  10. Coherent THz Repetitive Pulse Generation in a GaSe Crystal by Dual-wavelength Nd:YLF Laser

    NASA Astrophysics Data System (ADS)

    Bezotosnyi, V. V.; Cheshev, E. A.; Gorbunkov, M. V.; Koromyslov, A. L.; Krokhin, O. N.; Mityagin, Yu. A.; Popov, Yu. M.; Savinov, S. A.; Tunkin, V. G.

    We present modification of difference frequency generator of coherent THz radiation in a nonlinear GaSe crystal using dual-wavelength diode-pumped solid-state Nd:YLF laser. Generation at the two wavelengths (1.047 and 1.053 μm) was carried out by equalization of the gains at these wavelengths near the frequency degeneracy of the transverse modes in resonator cavity, Q-switched by acousto-optical modulator. The main parameters of the device were measured: angular synchronism (width 0.6 degrees), polarization ratio (1:100), conversion efficiency (10-7), pulse power (0.8 mW), frequency and width (53,8 сm-1, 0,6 сm-1), pulse width and repetition rate (10 ns,7 kHz). The method is promising for practical purposes.

  11. Physical design of a wavelength tunable fully coherent VUV source using a self-seeding free electron laser

    NASA Astrophysics Data System (ADS)

    Li, He-Ting; Jia, Qi-Ka

    2014-05-01

    In order to meet the requirements of the synchrotron radiation users, a fully coherent VUV free electron laser (FEL) has been preliminarily designed. One important goal of this design is that the radiation wavelength can be easily tuned in a broad range (70-170 nm). In the light of the users' demand and our actual conditions, the self-seeding scheme is adopted for this proposal. Firstly, we attempted to fix the electron energy and only changed the undulator gap to vary the radiation wavelength; however, our analysis implies that this is difficult because of the great difference of the power gain length and FEL efficiency at different wavelengths. Therefore, we have considered dividing the wavelength range into three subareas. In each subarea, a constant electron energy is used and the wavelength tuning is realized only by adjusting the undulator gap. The simulation results show that this scheme has an acceptable performance.

  12. The performance of coherent receiver controlled by the phase lock loop in dual rate free-space laser communication

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoping; Sun, Jianfeng; Hou, Peipei; Lu, Wei; Xu, Qian; Liu, Liren

    2015-09-01

    The technique of differential phase shift keying(DPSK) modulation is applied into demodulating phase information in the coherent optical receiver. The dual rate free-space receiving structure on the base of Mach-Zehnder delay interferometer with the lens is used suitably for differential delay which is equal to the one bit corresponding to a certain data rate. Delay distance at the interference receiver is varied with transmission rata from satellite to ground. Differential information is obtained by the subtraction of the two successive wave-front phases when made to interfere. The phase demodulation is extremely sensitive to phase fluctuation. Because of the incident light through atmospheric turbulence, the wave-front of optical signal became jittered in the temporal and spatial domain rapidly. In the paper, the dual rate free-space laser communication receiver for phase lock to stable signal light phase is proposed, increasing the homodyne efficiency and decreasing the bit error rate.

  13. Integrating photoacoustic ophthalmoscopy with scanning laser ophthalmoscopy, optical coherence tomography, and fluorescein angiography for a multimodal retinal imaging platform

    NASA Astrophysics Data System (ADS)

    Song, Wei; Wei, Qing; Liu, Tan; Kuai, David; Burke, Janice M.; Jiao, Shuliang; Zhang, Hao F.

    2012-06-01

    Photoacoustic ophthalmoscopy (PAOM) is a newly developed retinal imaging technology that holds promise for both fundamental investigation and clinical diagnosis of several blinding diseases. Hence, integrating PAOM with other existing ophthalmic imaging modalities is important to identify and verify the strengths of PAOM compared with the established technologies and to provide the foundation for more comprehensive multimodal imaging. To this end, we developed a retinal imaging platform integrating PAOM with scanning laser ophthalmoscopy (SLO), spectral-domain optical coherence tomography (SD-OCT), and fluorescein angiography (FA). In the system, all the imaging modalities shared the same optical scanning and delivery mechanisms, which enabled registered retinal imaging from all the modalities. High-resolution PAOM, SD-OCT, SLO, and FA images were acquired in both albino and pigmented rat eyes. The reported in vivo results demonstrate the capability of the integrated system to provide comprehensive anatomic imaging based on multiple optical contrasts.

  14. Single-pulse enhanced coherent diffraction imaging of bacteria with an X-ray free-electron laser

    NASA Astrophysics Data System (ADS)

    Fan, Jiadong; Sun, Zhibin; Wang, Yaling; Park, Jaehyun; Kim, Sunam; Gallagher-Jones, Marcus; Kim, Yoonhee; Song, Changyong; Yao, Shengkun; Zhang, Jian; Zhang, Jianhua; Duan, Xiulan; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya; Fan, Chunhai; Zhao, Yuliang; Chai, Zhifang; Gao, Xueyun; Earnest, Thomas; Jiang, Huaidong

    2016-09-01

    High-resolution imaging offers one of the most promising approaches for exploring and understanding the structure and function of biomaterials and biological systems. X-ray free-electron lasers (XFELs) combined with coherent diffraction imaging can theoretically provide high-resolution spatial information regarding biological materials using a single XFEL pulse. Currently, the application of this method suffers from the low scattering cross-section of biomaterials and X-ray damage to the sample. However, XFELs can provide pulses of such short duration that the data can be collected using the “diffract and destroy” approach before the effects of radiation damage on the data become significant. These experiments combine the use of enhanced coherent diffraction imaging with single-shot XFEL radiation to investigate the cellular architecture of Staphylococcus aureus with and without labeling by gold (Au) nanoclusters. The resolution of the images reconstructed from these diffraction patterns were twice as high or more for gold-labeled samples, demonstrating that this enhancement method provides a promising approach for the high-resolution imaging of biomaterials and biological systems.

  15. Velocity gradients in spatially resolved laser Doppler flowmetry and dynamic light scattering with confocal and coherence gating

    NASA Astrophysics Data System (ADS)

    Uribe-Patarroyo, Néstor; Bouma, Brett E.

    2016-08-01

    Dynamic light scattering (DLS) is widely used to characterize diffusive motion to obtain precise information on colloidal suspensions by calculating the autocorrelation function of the signal from a heterodyne optical system. DLS can also be used to determine the flow velocity field in systems that exhibit mass transport by incorporating the effects of the deterministic motion of scatterers on the autocorrelation function, a technique commonly known as laser Doppler flowmetry. DLS measurements can be localized with confocal and coherence gating techniques such as confocal microscopy and optical coherence tomography, thereby enabling the determination of the spatially resolved velocity field in three dimensions. It has been thought that spatially resolved DLS can determine the axial velocity as well as the lateral speed in a single measurement. We demonstrate, however, that gradients in the axial velocity of scatterers exert a fundamental influence on the autocorrelation function even in well-behaved, nonturbulent flow. By obtaining the explicit functional relation between axial-velocity gradients and the autocorrelation function, we show that the velocity field and its derivatives are intimately related and their contributions cannot be separated. Therefore, a single DLS measurement cannot univocally determine the velocity field. Our extended theoretical model was found to be in good agreement with experimental measurements.

  16. Velocity gradients in spatially-resolved laser Doppler flowmetry and dynamic light scattering with confocal and coherence gating

    PubMed Central

    Uribe-Patarroyo, Néstor; Bouma, Brett E.

    2016-01-01

    Dynamic light scattering (DLS) is widely used to characterize diffusive motion to obtain precise information on colloidal suspensions by calculating the autocorrelation function of the signal from a heterodyne optical system. DLS can also be used to determine the flow velocity field in systems that exhibit mass transport by incorporating the effects of the deterministic motion of scatterers on the autocorrelation function, a technique commonly known as laser Doppler flowmetry. DLS measurements can be localized with confocal and coherence gating techniques such as confocal microscopy and optical coherence tomography, thereby enabling the determination of the spatially-resolved velocity field in three dimensions. It has been thought that spatially-resolved DLS can determine the axial velocity as well as the lateral speed in a single measurement. We demonstrate, however, that gradients in the axial velocity of scatterers exert a fundamental influence on the autocorrelation function even in well-behaved, non-turbulent flow. By obtaining the explicit functional relation between axial-velocity gradients and the autocorrelation function, we show that the velocity field and its derivatives are intimately related and their contributions cannot be separated. Therefore, a single DLS measurement cannot univocally determine the velocity field. Our extended theoretical model was found to be in good agreement with experimental measurements. PMID:27627357

  17. Single-pulse enhanced coherent diffraction imaging of bacteria with an X-ray free-electron laser

    PubMed Central

    Fan, Jiadong; Sun, Zhibin; Wang, Yaling; Park, Jaehyun; Kim, Sunam; Gallagher-Jones, Marcus; Kim, Yoonhee; Song, Changyong; Yao, Shengkun; Zhang, Jian; Zhang, Jianhua; Duan, Xiulan; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya; Fan, Chunhai; Zhao, Yuliang; Chai, Zhifang; Gao, Xueyun; Earnest, Thomas; Jiang, Huaidong

    2016-01-01

    High-resolution imaging offers one of the most promising approaches for exploring and understanding the structure and function of biomaterials and biological systems. X-ray free-electron lasers (XFELs) combined with coherent diffraction imaging can theoretically provide high-resolution spatial information regarding biological materials using a single XFEL pulse. Currently, the application of this method suffers from the low scattering cross-section of biomaterials and X-ray damage to the sample. However, XFELs can provide pulses of such short duration that the data can be collected using the “diffract and destroy” approach before the effects of radiation damage on the data become significant. These experiments combine the use of enhanced coherent diffraction imaging with single-shot XFEL radiation to investigate the cellular architecture of Staphylococcus aureus with and without labeling by gold (Au) nanoclusters. The resolution of the images reconstructed from these diffraction patterns were twice as high or more for gold-labeled samples, demonstrating that this enhancement method provides a promising approach for the high-resolution imaging of biomaterials and biological systems. PMID:27659203

  18. High-intensity coherent vacuum ultraviolet source using unfocussed commercial dye lasers.

    PubMed

    Albert, Daniel R; Proctor, David L; Davis, H Floyd

    2013-06-01

    Using two or three commercial pulsed nanosecond dye lasers pumped by a single 30 Hz Nd:YAG laser, generation of 0.10 mJ pulses at 125 nm (6 × 10(13) photons∕pulse) has been demonstrated by resonance enhanced four-wave mixing of collimated (unfocussed) laser beams in mercury (Hg) vapor. Phase matching at various vacuum ultraviolet (VUV) wavelengths is achieved by tuning one laser in the vicinity of the 6 (1)S0 → 6 (3)P1 resonance near 253.1 nm. A number of different mixing schemes are characterized. Our observations using broadband lasers (~0.15 cm(-1) bandwidths) are compared to previous calculations pertaining to four-wave mixing of low intensity narrowband laser beams. Prospects for further increases in pulse energies are discussed. We find that VUV tuning curves and intensities are in good agreement with theoretical predictions. The utility of the VUV light source is demonstrated by "soft universal" single-photon VUV ionization in crossed molecular beam studies and for generation of light at 130.2 nm for oxygen atom Rydberg time-of-flight experiments.

  19. Nondestructive assessment of dentin demineralization using polarization-sensitive optical coherence tomography after exposure to fluoride and laser irradiation.

    PubMed

    Manesh, Saman K; Darling, Cynthia L; Fried, Daniel

    2009-08-01

    Previous studies have demonstrated that polarization-sensitive optical coherence tomography (PS-OCT) can be used to image natural and artificial caries in dentin. The purpose of this study was to measure nondestructively the severity of artificial caries lesions in dentin and determine the efficacy of intervention with anticaries agents including fluoride and lasers. Although several studies have assessed the utility of PS-OCT to image caries lesions in enamel and to quantify the lesion severity, only a few studies have focused on lesions in dentin. In this study, images of artificial dentin lesions on extracted human teeth were acquired with PS-OCT. Before exposure to an artificial demineralizing solution, three incisions were made on the sample surfaces using either Er:YAG, Nd:YAG (lambda = 355 nm), or TEA CO(2) lasers and selected areas were treated with topical fluoride to create six unique treatment areas for each of the three laser conditions investigated. The integrated reflectivity and depth of demineralization were calculated for each of the six areas on each sample using the PS-OCT images. Polarized light microscopy (PLM) and transverse microradiography (TMR) were used to measure lesion severity on histological thin sections for comparison. PS-OCT successfully measured the inhibition of demineralization by topical fluoride. Laser irradiation was not particularly effective in increasing or decreasing the rate of dentin demineralization. PLM and TMR corroborated those results. This study demonstrates that PS-OCT can be used to measure demineralization on dentin surfaces and determine the degree of inhibition of demineralization by anticaries agents.

  20. Computer aided techniques to support speckle laser experimental setup and online vision

    NASA Astrophysics Data System (ADS)

    Braga, Roberto A.; Godinho, Robson P.; Nozela, José Roberto A.; Silva, Michel M.

    2012-10-01

    The use of dynamic speckle laser, also called biospeckle laser (BSL), presents a series of challenges to its adoption, as it is the case for its use in real time, and when ones desires to adjust the experimental setup. The technical analysis of the BSL adopted in real time has reduced spatial resolution of the captured image, while the adjustment of preparing an experiment still demands the trial of a specialist. In this work two approaches have been proposed to improve the efficiency of BSL real-time adjustments to support the experimental setup. The use of the method known as Motion History Image (MHI) was carry out over a series of BSL images. The MHI was the basis for the implementation of a graphical interface for real-time identification of areas of activity, and then delimiting the regions of interest. The results showed that the MHI was effective in the reproduction of the activities of speckle patterns in real time without reducing image resolution, and as an instrument for delimit of regions of activity, supporting the analyst in the choice of lighting adjustments and image assembling.

  1. Characterizing transverse coherence of an ultra-intense focused X-ray free-electron laser by an extended Young's experiment.

    PubMed

    Inoue, Ichiro; Tono, Kensuke; Joti, Yasumasa; Kameshima, Takashi; Ogawa, Kanade; Shinohara, Yuya; Amemiya, Yoshiyuki; Yabashi, Makina

    2015-11-01

    Characterization of transverse coherence is one of the most critical themes for advanced X-ray sources and their applications in many fields of science. However, for hard X-ray free-electron laser (XFEL) sources there is very little knowledge available on their transverse coherence characteristics, despite their extreme importance. This is because the unique characteristics of the sources, such as the ultra-intense nature of XFEL radiation and the shot-by-shot fluctuations in the intensity distribution, make it difficult to apply conventional techniques. Here, an extended Young's interference experiment using a stream of bimodal gold particles is shown to achieve a direct measurement of the modulus of the complex degree of coherence of XFEL pulses. The use of interference patterns from two differently sized particles enables analysis of the transverse coherence on a single-shot basis without a priori knowledge of the instantaneous intensity ratio at the particles. For a focused X-ray spot as small as 1.8 µm (horizontal) × 1.3 µm (vertical) with an ultrahigh intensity that exceeds 10(18) W cm(-2) from the SPring-8 Ångstrom Compact free-electron LAser (SACLA), the coherence lengths were estimated to be 1.7 ± 0.2 µm (horizontal) and 1.3 ± 0.1 µm (vertical). The ratios between the coherence lengths and the focused beam sizes are almost the same in the horizontal and vertical directions, indicating that the transverse coherence properties of unfocused XFEL pulses are isotropic. The experiment presented here enables measurements free from radiation damage and will be readily applicable to the analysis of the transverse coherence of ultra-intense nanometre-sized focused XFEL beams.

  2. Characterization of semiconductor-laser phase noise and estimation of bit-error rate performance with low-speed offline digital coherent receivers.

    PubMed

    Kikuchi, Kazuro

    2012-02-27

    We develop a systematic method for characterizing semiconductor-laser phase noise, using a low-speed offline digital coherent receiver. The field spectrum, the FM-noise spectrum, and the phase-error variance measured with such a receiver can completely describe phase-noise characteristics of lasers under test. The sampling rate of the digital coherent receiver should be much higher than the phase-fluctuation speed. However, 1 GS/s is large enough for most of the single-mode semiconductor lasers. In addition to such phase-noise characterization, interpolating the taken data at 1.25 GS/s to form a data stream at 10 GS/s, we can predict the bit-error rate (BER) performance of multi-level modulated optical signals at 10 Gsymbol/s. The BER degradation due to the phase noise is well explained by the result of the phase-noise measurements.

  3. Temporally-coherent terawatt attosecond XFEL synchronized with a few cycle laser

    PubMed Central

    Kumar, Sandeep; Parc, Yong Woon; Landsman, Alexandra S.; Kim, Dong Eon

    2016-01-01

    Attosecond metrology using laser-based high-order harmonics has been significantly advanced and applied to various studies of electron dynamics in atoms, molecules and solids. Laser-based high-order harmonics have a limitation of low power and photon energies. There is, however, a great demand for even higher power and photon energy. Here, we propose a scheme for a terawatt attosecond (TW-as) X-ray pulse in X-ray free-electron laser controlled by a few cycle IR pulse, where one dominant current spike in an electron bunch is used repeatedly to amplify a seeded radiation to a terawatt level. This scheme is relatively simple, compact, straightforward, and also produces a temporally and spectrally clean pulse. The viability of this scheme is demonstrated in simulations using Pohang accelerator laboratory (PAL)-XFEL beam parameters. PMID:27892964

  4. Temporally-coherent terawatt attosecond XFEL synchronized with a few cycle laser.

    PubMed

    Kumar, Sandeep; Parc, Yong Woon; Landsman, Alexandra S; Kim, Dong Eon

    2016-11-28

    Attosecond metrology using laser-based high-order harmonics has been significantly advanced and applied to various studies of electron dynamics in atoms, molecules and solids. Laser-based high-order harmonics have a limitation of low power and photon energies. There is, however, a great demand for even higher power and photon energy. Here, we propose a scheme for a terawatt attosecond (TW-as) X-ray pulse in X-ray free-electron laser controlled by a few cycle IR pulse, where one dominant current spike in an electron bunch is used repeatedly to amplify a seeded radiation to a terawatt level. This scheme is relatively simple, compact, straightforward, and also produces a temporally and spectrally clean pulse. The viability of this scheme is demonstrated in simulations using Pohang accelerator laboratory (PAL)-XFEL beam parameters.

  5. Temporally-coherent terawatt attosecond XFEL synchronized with a few cycle laser

    NASA Astrophysics Data System (ADS)

    Kumar, Sandeep; Parc, Yong Woon; Landsman, Alexandra S.; Kim, Dong Eon

    2016-11-01

    Attosecond metrology using laser-based high-order harmonics has been significantly advanced and applied to various studies of electron dynamics in atoms, molecules and solids. Laser-based high-order harmonics have a limitation of low power and photon energies. There is, however, a great demand for even higher power and photon energy. Here, we propose a scheme for a terawatt attosecond (TW-as) X-ray pulse in X-ray free-electron laser controlled by a few cycle IR pulse, where one dominant current spike in an electron bunch is used repeatedly to amplify a seeded radiation to a terawatt level. This scheme is relatively simple, compact, straightforward, and also produces a temporally and spectrally clean pulse. The viability of this scheme is demonstrated in simulations using Pohang accelerator laboratory (PAL)-XFEL beam parameters.

  6. Coherence in laser-driven electrons at the surface and in the volume of solid matter

    NASA Astrophysics Data System (ADS)

    Hommelhoff, Peter

    2017-01-01

    The femtosecond frequency comb allows controlling the carrier field of ultrashort laser pulses. We show two examples on how this control over fields oscillating with a few hundred terahertz can be utilized to control electrons at the surface and in the volume of solids. After a brief discussion of strong-field physics at metal needle tips, we show how ultrafast two-color laser pulses allow quantum path interference to dramatically alter the emission current from sharp tips, with an interference visibility of 94%. With carrier-envelope phase-controlled laser pulses, we show furthermore how light-field sensitive currents can be excited in monolayer graphene via an interplay of interband and intraband electron dynamics including multiple Landau-Zener transitions.

  7. Laser vision: lidar as a transformative tool to advance critical zone science

    NASA Astrophysics Data System (ADS)

    Harpold, A. A.; Marshall, J. A.; Lyon, S. W.; Barnhart, T. B.; Fisher, B. A.; Donovan, M.; Brubaker, K. M.; Crosby, C. J.; Glenn, N. F.; Glennie, C. L.; Kirchner, P. B.; Lam, N.; Mankoff, K. D.; McCreight, J. L.; Molotch, N. P.; Musselman, K. N.; Pelletier, J.; Russo, T.; Sangireddy, H.; Sjöberg, Y.; Swetnam, T.; West, N.

    2015-06-01

    . We propose that using lidar to its full potential will require numerous advances, including new and more powerful open-source processing tools, exploiting new lidar acquisition technologies, and improved integration with physically based models and complementary in situ and remote-sensing observations. We provide a 5-year vision that advocates for the expanded use of lidar data sets and highlights subsequent potential to advance the state of CZ science.

  8. Phase-matched generation of coherent soft and hard X-rays using IR lasers

    DOEpatents

    Popmintchev, Tenio V.; Chen, Ming-Chang; Bahabad, Alon; Murnane, Margaret M.; Kapteyn, Henry C.

    2013-06-11

    Phase-matched high-order harmonic generation of soft and hard X-rays is accomplished using infrared driving lasers in a high-pressure non-linear medium. The pressure of the non-linear medium is increased to multi-atmospheres and a mid-IR (or higher) laser device provides the driving pulse. Based on this scaling, also a general method for global optimization of the flux of phase-matched high-order harmonic generation at a desired wavelength is designed.

  9. TEMPORAL COHERENCE AND FREQUENCY VS TIME CHARACTERISTICS OF A Q-SPOILED RUBY LASER,

    DTIC Science & Technology

    of change of the laser frequency during the Q-spoiled emission pulse is approximately twenty times the rate of change during a single spike of an...linear in the change in the number of excited states in the laser. Since the rate of change of population inversion during Q-spoiled emission is much...larger than for normal lasing it was expected, prior to this work, that a greater rate of change of frequency should be observed. This has now been confirmed. (Author)

  10. Optical coherence tomography for visualizing transient strains and measuring large deformations in laser-induced tissue reshaping

    NASA Astrophysics Data System (ADS)

    Zaitsev, Vladimir Y.; Matveyev, Alexander L.; Matveev, Lev A.; Gelikonov, Grigory V.; Omelchenko, Alexander I.; Shabanov, Dmitry V.; Baum, Olga I.; Svistushkin, Valery M.; Sobol, Emil N.

    2016-11-01

    In the context of the development of emerging laser-assisted thermo-mechanical technologies for non-destructive reshaping of avascular collagenous tissues (cartilages and cornea), we report the first application of phase-sensitive optical coherence tomography (OCT) for visualizing transient strains involving supra-wavelength inter-frame displacements of scatterers. Usually phase-sensitive OCT assumes the visualization of sub-pixel and even sub-wavelength displacements of scatterers and fairly small strains (say, <10-3), which conventionally implies the necessity of averaging for enhancing the effective signal-to-noise ratio and, correspondingly, the application of small-amplitude actuators producing periodic deformations. The original approach used here allows for direct estimation of elevated strains ~10-2 (close to onset of intense speckle blinking) obviating the necessity of averaging and phase unwrapping for supra-wavelength inter-frame displacements. We demonstrate the possibility of mapping aperiodic thermally-induced transient strains with resultant large deformations on order of tens per cent. Such strains are typical in laser tissue reshaping, but are far beyond the range of conventionally discussed OCT-based strain mapping.

  11. Coherence transfer of subhertz-linewidth laser light via an optical fiber noise compensated by remote users.

    PubMed

    Wu, Lifei; Jiang, Yanyi; Ma, Chaoqun; Yu, Hongfu; Bi, Zhiyi; Ma, Longsheng

    2016-09-15

    We present a technique for the coherence transfer of laser light through a fiber link, where the optical phase noise induced by environmental perturbation via the fiber link is compensated by remote users. When compensating the fiber noise by remote users, the time base at the remote site independent from that at the local site does not destroy the performance of the fiber output light. Using this technique, we demonstrate the transfer of subhertz-linewidth laser light through a 25-km-long, lab-based spooled fiber. After being compensated, the relative linewidth between the fiber input and output light is 1 mHz, and the relative frequency instability is 4×10-17 at 1 s averaging time and scales down to 2×10-19 at 800 s averaging time. The frequency uncertainty of the light after transferring through the fiber relative to that of the input light is 3.0×10-19. This system is suitable for the simultaneous transfer of an optical signal to a number of end users within a city.

  12. A camera for coherent diffractive imaging and holography with a soft-X-ray free electron laser

    SciTech Connect

    Bajt, S; Chapman, H N; Spiller, E; Alameda, J; Woods, B; Frank, M; Bogan, M J; Barty, A; Boutet, S; Marchesini, S; Hau-Riege, S P; Hajdu, J; Shapiro, D

    2007-09-24

    We describe a camera to record coherent scattering patterns with a soft-X-ray free-electron laser. The camera consists of a laterally-graded multilayer mirror which reflects the diffraction pattern onto a CCD detector. The mirror acts as a bandpass filter both for wavelength and angle, which isolates the desired scattering pattern from non-sample scattering or incoherent emission from the sample. The mirror also solves the particular problem of the extreme intensity of the FEL pulses, which are focused to greater than 10{sup 14} W/cm{sup 2}. The strong undiffracted pulse passes through a hole in the mirror and propagates on to a beam dump at a distance behind the instrument rather than interacting with a beamstop placed near the CCD. The camera concept is extendable for the full range of the fundamental wavelength of the FLASH FEL (i.e. between 6 nm and 60 nm) and into the water window. We have fabricated and tested various multilayer mirrors for wavelengths of 32 nm, 16 nm, 13.5 nm, and 4.5 nm. At the shorter wavelengths mirror roughness must be minimized to reduce scattering from the mirror. We have recorded over 30,000 diffraction patterns at the FLASH free-electron laser with no observable mirror damage or degradation of performance.

  13. Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals

    NASA Astrophysics Data System (ADS)

    Tang, Jau

    2008-04-01

    In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (<70nm for aluminum and <200nm for gold), but becomes less dependent if further thickness increases. Coherent phonon excitation and propagation from the stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

  14. Fractal frequency spectrum in laser resonators and three-dimensional geometric topology of optical coherent waves

    NASA Astrophysics Data System (ADS)

    Tung, J. C.; Tuan, P. H.; Liang, H. C.; Huang, K. F.; Chen, Y. F.

    2016-08-01

    We theoretically verify that the symmetry breaking in spherical resonators can result in a fractal frequency spectrum that is full of numerous new accidental degeneracies to cluster around the unperturbed degenerate cavity. We further experimentally discover that the fractal frequency spectrum excellently reflects the intimate connection between the emission power and the degenerate mode numbers. It is observed that the wave distributions of lasing modes at the accidental degeneracies are strongly concentrated on three-dimensional (3D) geometric topology. Considering the overlapping effect, the wave representation of the coherent states is analytically derived to manifest the observed 3D geometric surfaces.

  15. Enhanced Tissue Ablation Efficiency with a Mid-Infrared Nonlinear Frequency Conversion Laser System and Tissue Interaction Monitoring Using Optical Coherence Tomography

    PubMed Central

    Kim, Bongkyun; Kim, Dae Yu

    2016-01-01

    We report development of optical parametric oscillator (OPO)-based mid-infrared laser system that utilizes a periodically poled nonlinear crystal pumped by a near-infrared (NIR) laser. We obtained a mid-infrared average output of 8 W at an injection current of 20 A from a quasi-phase-matched OPO using an external cavity configuration. Laser tissue ablation efficiency is substantially affected by several parameters, including an optical fluence rate, wavelength of the laser source, and the optical properties of target tissue. Dimensions of wavelength and radiant exposure dependent tissue ablation are quantified using Fourier domain optical coherence tomography and the ablation efficiency was compared to a non-converted NIR laser system. PMID:27128916

  16. Application of corneal tomography before keratorefractive procedure for laser vision correction.

    PubMed

    Luz, Allan; Lopes, Bernardo; Salomão, Marcela; Ambrósio, Renato

    2016-05-01

    Ectasia after refractive surgery represents a major concern among refractive surgeons. Corneal abnormalities and preexisting corneal ectasia are the most important risk factors. Corneal topography and central corneal thickness are the factors traditionally screening for in refractive surgery candidates. Study of the anterior surface by Placido topography allows for identification of keratoconus before biomicroscopy. However, this is insufficient for the evaluation of pre-operative refractive surgery. There are cases of ectasia after laser in situ keratomilusis (LASIK) without identifiable risk factors such that there is a need to go beyond the corneal surface. A key requirement is quantifying susceptibility to corneal biomechanical instability and progression to ectasia. Tomographic indices derived from elevation maps and pachymetry spatial variation produce a Belin Ambrosio display final D index (BAD-D index), which has shown better results compared to surface curvature indices for detecting very mild forms of ectasia. A logistic regression formula, integrating age, residual stromal bed, and BAD-D (Ectasia Susceptibility Score, ESS) resulted in a significant improvement in accuracy, leading to 100% sensitivity and 94% specificity for detecting susceptible cases. A comprehensive corneal structural analysis based on corneal segmental tomography can detect susceptible corneas, which increases safety for refractive surgery patients.

  17. Reliable Optical Pump Architecture for Highly Coherent Lasers Used in Space Metrology Applications

    NASA Technical Reports Server (NTRS)

    Erlig, Herman; Qiu, Yueming; Poberezhskiy, Ilya Y.; Meras, Patrick L.; Chang, Daniel H.; Wu, Yen-Hung

    2012-01-01

    The design and initial demonstration of a laser pump module (LPM) incorporating single-mode, grating-stabilized 808-nm diode lasers and a low-loss, high-port-count optical combiner are completed. The purpose of the developed LPM is to reliably pump an Nd:YAG crystal in the laser head (LH), which serves as the optical metrology source for SIMLite mission. Using the narrow-linewidth, single-mode laser diodes enables placement of the pump power near Nd adsorption peak, which enhances pumping efficiency. Grating stabilization allows for stable pump spectra as diode operating temperature and bias current change. The low-loss, high-port-count optical combiner enables efficient combining of tens of pumps. Overall, the module supports 5+ years of continuous operation at 2 W of pump power with reliability approaching 100 percent. The LPM consists of a laser diode farm (LDF) and a pump beam combiner (PBC). An array of 807- to 808-nm fiber-pigtailed laser diodes makes up the LDF. A Bragg grating in each 5- m core single-mode (SM) fiber pigtail acts to stabilize the lasing spectra over a range of diode operating conditions. These commercially available single-mode laser diodes can deliver up to 150 mW of optical power. The outputs from the multiple pumps in the LDF are routed to the PBC, which is a 37-input by 1-output all-fiber device. The input ports consist of 5- m core SM fiber, while the output port consists of 105- m core, 0.15 NA (numerical aperture) multi-mode (MM) fiber. The combiner is fabricated by fusing the 37 input fibers while simultaneously tapering the fused region. At the completion of this process, the MM fiber is spliced to the end of the adiabatic taper, and, for protection, the combiner is sheathed by a capillary tube. A compact and robust metal housing was designed and fabricated to protect the PBC during space deployment.

  18. Passive coherent discriminator using phase diversity for the simultaneous measurement of frequency noise and intensity noise of a continuous-wave laser

    NASA Astrophysics Data System (ADS)

    Michaud-Belleau, V.; Bergeron, H.; Light, P. S.; Hébert, N. B.; Deschênes, J. D.; Luiten, A. N.; Genest, J.

    2016-10-01

    The frequency noise and intensity noise of a laser set the performance limits in many modern photonics applications and, consequently, must often be characterized. As lasers continue to improve, the measurement of these noises however becomes increasingly challenging. Current approaches for the characterization of very high-performance lasers often call for a second laser with equal or higher performance to the one that is to be measured, an incoherent interferometer having an extremely long delay-arm, or an interferometer that relies on an active device. These instrumental features can be impractical or problematic under certain experimental conditions. As an alternative, this paper presents an entirely passive coherent interferometer that employs an optical 90° hybrid coupler to perform in-phase and quadrature detection. We demonstrate the technique by measuring the frequency noise power spectral density of a highly-stable 192 THz (1560 nm) fiber laser over five frequency decades. Simultaneously, we are able to measure its relative intensity noise power spectral density and characterize the correlation between its amplitude noise and phase noise. We correct some common misconceptions through a detailed theoretical analysis and demonstrate the necessity to account for normal imperfections of the optical 90° hybrid coupler. We finally conclude that this passive coherent discriminator is suitable for reliable and simple noise characterization of highly-stable lasers, with bandwidth and dynamic range benefits but susceptibility to additive noise contamination.

  19. Tuning of successively scanned two monolithic Vernier-tuned lasers and selective data sampling in optical comb swept source optical coherence tomography.

    PubMed

    Choi, Dong-Hak; Yoshimura, Reiko; Ohbayashi, Kohji

    2013-01-01

    Monolithic Vernier tuned super-structure grating distributed Bragg reflector (SSG-DBR) lasers are expected to become one of the most promising sources for swept source optical coherence tomography (SS-OCT) with a long coherence length, reduced sensitivity roll-off, and potential capability for a very fast A-scan rate. However, previous implementations of the lasers suffer from four main problems: 1) frequencies deviate from the targeted values when scanned, 2) large amounts of noise appear associated with abrupt changes in injection currents, 3) optically aliased noise appears due to a long coherence length, and 4) the narrow wavelength coverage of a single chip limits resolution. We have developed a method of dynamical frequency tuning, a method of selective data sampling to eliminate current switching noise, an interferometer to reduce aliased noise, and an excess-noise-free connection of two serially scanned lasers to enhance resolution to solve these problems. An optical frequency comb SS-OCT system was achieved with a sensitivity of 124 dB and a dynamic range of 55-72 dB that depended on the depth at an A-scan rate of 3.1 kHz with a resolution of 15 μm by discretely scanning two SSG-DBR lasers, i.e., L-band (1.560-1.599 μm) and UL-band (1.598-1.640 μm). A few OCT images with excellent image penetration depth were obtained.

  20. Proof of the Feasibility of Coherent and Incoherent Schemes for Pumping a Gamma-Ray Laser

    DTIC Science & Technology

    1991-12-31

    utilized under this contract. Resolution of the question of the feasibility of a gamma-ray laser now rests upon the determination of: I) the identity of...even for an idealized nuclear material, computations of threshold levels of pumping are not without difficulty. However. under idealized conditions...125Te’" at 35.5 keV are clearly visible. ments. In particular, the charge passed to the converter Because of the shorter isomeric lifetimes the SrF2

  1. Ultrahigh resolution optical coherence tomography using high power fiber laser supercontinuum at 1.7 μm wavelength region

    NASA Astrophysics Data System (ADS)

    Ishida, S.; Kawagoe, H.; Aramaki, M.; Sakakibara, Y.; Omoda, E.; Kataura, H.; Nishizawa, N.

    2013-03-01

    Optical coherence tomography (OCT) is a non-invasive optical imaging technology for micron-scale cross-sectional imaging of biological tissue and materials. We have been investigating ultrahigh resolution optical coherence tomography (UHR-OCT) using fiber based supercontinuum (SC) source. Although UHR-OCT has many advantages in medical equipments, low penetration depth is a serious limitation for wider applications. Recently, we have demonstrated high penetration depth UHR-OCT by use of fiber based Gaussian shaped SC source at 1.7 μm center wavelength. However, the penetration depth has been limited by the low power of SC source. In this paper, to realize deeper penetration imaging, we have developed the high power Gaussian shaped SC source at 1.7 μm wavelength region based on the custom-made Er-doped ultrashort pulse fiber laser with single-wall carbon nanotube and nonlinear phenomena in fibers. This SC source has 43.3 mW output power, 242 nm full-width at half maximum bandwidth, and 109 MHz repetition rate. The repetition rate and average power were almost twice as large as those of previous SC source. Using this light source, 105 dB sensitivity and ultrahigh resolution of 4.3 μm in tissue were achieved simultaneously. We have demonstrated the UHR-OCT imaging of pig thyroid gland and hamster's cheek pouch with this developed SC source and compared the images with those measured by the previous SC source. We have observed the fine structures such as round or oval follicles, epithelium, connective tissue band, and muscular layer. From the comparison of the UHR-OCT images and signals, we confirmed the improvement of imaging contrast and penetration depth with the developed SC source.

  2. Quantification of volumetric cerebral blood flow using hybrid laser speckle contract and optical coherence tomography (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Valim, Niksa; Dunn, Andrew K.

    2016-03-01

    Studying neurovascular blood flow function in cerebrovascular activities requires accurate visualization and characterization of blood flow volume as well as the dynamics of blood cells in microcirculation. In this study, we present a novel integration of laser speckle contrast imaging (LSCI) and spectral domain optical coherence tomography (SD-OCT) for rapid volumetric imaging of blood flow in cortical capillaries. LSCI uses the illumination of wide-field near infrared light (NIR) and monitors back scattered light to characterize the relative dynamics of blood flow in microcirculation. Absolute measurement of blood cells and blood volume requires high-resolution volumetric structural information. SD-OCT system uses coherence gating to measure scattered light from a small volume within high structural resolution. The structural imaging system rapidly assesses large number of capillaries for spatio-temporal tracking of red blood cells (RBC). A very fast-ultra resolution SD-OCT system was developed for imaging high-resolution volumetric samples. The system employed an ultra wideband light source (1310 ± 200 nm in wavelength) corresponding to an axial resolution of 3 micrometers in tissue. The spectrometer of the SD-OCT was customized for a maximum scanning rate of 147,000 line/s. We demonstrated a fast volumetric OCT angiography algorithm to visualize large numbers of vessels in a 2-mm deep sample volume. A LSCI system that has been developed previously in our group was integrated to the imaging system for the characterization of dynamic blood cells. The conjunction data from LSCI and SD-OCT systems imply the feasibility of accurate quantification of absolute cortical blood flow.

  3. Coherent X-Ray Diffraction Imaging of Chloroplasts from Cyanidioschyzon merolae by Using X-Ray Free Electron Laser.

    PubMed

    Takayama, Yuki; Inui, Yayoi; Sekiguchi, Yuki; Kobayashi, Amane; Oroguchi, Tomotaka; Yamamoto, Masaki; Matsunaga, Sachihiro; Nakasako, Masayoshi

    2015-07-01

    Coherent X-ray diffraction imaging (CXDI) is a lens-less technique for visualizing the structures of non-crystalline particles with the dimensions of submicrometer to micrometer at a resolution of several tens of nanometers. We conducted cryogenic CXDI experiments at 66 K to visualize the internal structures of frozen-hydrated chloroplasts of Cyanidioschyzon merolae using X-ray free electron laser (XFEL) as a coherent X-ray source. Chloroplast dispersed specimen disks at a number density of 7/(10×10 µm(2)) were flash-cooled with liquid ethane without staining, sectioning or chemical labeling. Chloroplasts are destroyed at atomic level immediately after the diffraction by XFEL pulses. Thus, diffraction patterns with a good signal-to-noise ratio from single chloroplasts were selected from many diffraction patterns collected through scanning specimen disks to provide fresh specimens into the irradiation area. The electron density maps of single chloroplasts projected along the direction of the incident X-ray beam were reconstructed by using the iterative phase-retrieval method and multivariate analyses. The electron density map at a resolution of 70 nm appeared as a C-shape. In addition, the fluorescence image of proteins stained with Flamingo™ dye also appeared as a C-shape as did the autofluorescence from Chl. The similar images suggest that the thylakoid membranes with an abundance of proteins distribute along the outer membranes of chloroplasts. To confirm the present results statistically, a number of projection structures must be accumulated through high-throughput data collection in the near future. Based on the results, we discuss the feasibility of XFEL-CXDI experiments in the structural analyses of cellular organelles.

  4. Comparison of self-reported quality of vision outcomes after myopic LASIK with two femtosecond lasers: a prospective, eye-to-eye study

    PubMed Central

    Sáles, Christopher S; Manche, Edward E

    2016-01-01

    Purpose To compare self-reported quality of vision (QoV) outcomes after myopic LASIK (laser-assisted in situ keratomileusis) with two femtosecond lasers. Design Prospective, randomized, eye-to-eye study. Methods Consecutive myopic patients were treated with wavefront-guided LASIK bilaterally. Eyes were randomized according to ocular dominance. The flap of one eye was made with the IntraLase FS 60 kHz femtosecond laser with a conventional 70° side-cut, and the flap of the fellow eye was made with the IntraLase iFS 150 kHz femtosecond laser with an inverted 130° side-cut. Patients completed the validated, Rasch-tested, linear-scaled 30-item QoV questionnaire preoperatively and at Months 1, 3, 6, and 12. Results The study enrolled 120 fellow eyes in 60 patients. None of the measured QoV parameters exhibited statistically significant differences between the groups preoperatively or at any postoperative time point. Conclusion Creating LASIK flaps with an inverted side-cut using a 150 kHz femtosecond laser and with a conventional 70° side-cut using a 60 kHz femtosecond laser resulted in no significant differences in self-reported QoV assessed by the QoV questionnaire. PMID:27621589

  5. Ultrafast Coherent Diffraction Imaging with X-ray Free-Electron Lasers

    SciTech Connect

    Chapman, H N; Bajt, S; Barty, A; Benner, W; Bogan, M; Frank, M; Hau-Riege, S; London, R; Marchesini, S; Spiller, E; Szoke, A; Woods, B; Boutet, S; Hodgson, K; Hajdu, J; Bergh, M; Burmeister, F; Caleman, C; Huldt, G; Maia, F; Seibert, M M; der Spoel, D v

    2006-08-22

    The ultrafast pulses from X-ray free-electron lasers will enable imaging of non-periodic objects at near-atomic resolution [1, Neutze]. These objects could include single molecules, protein complexes, or virus particles. The specimen would be completely destroyed by the pulse in a Coulomb explosion, but that destruction will only happen after the pulse. The scattering from the sample will give structural information about the undamaged object. There are many technical challenges that must be addressed before carrying out such experiments at an XFEL, which we are doing so with experiments at FLASH, the soft-X-ray FEL at DESY.

  6. On-chip nanostructuring and impedance trimming of transparent and flexible ITO electrodes by laser induced coherent sub-20 nm cuts

    NASA Astrophysics Data System (ADS)

    Afshar, Maziar; Leber, Moritz; Poppendieck, Wigand; König, Karsten; Seidel, Helmut; Feili, Dara

    2016-01-01

    In this work, the effect of laser-induced nanostructuring of transparent indium tin oxide (ITO) electrodes on flexible glass is investigated. Multi-electrode arrays (MEA) for electrical and optical characterization of biological cells were fabricated using standard MEMS technologies. Optimal sputter parameters concerning oxygen flow, sputter power and ambient pressure for ITO layers with both good optical and electrical properties were determined. Afterwards, coherent sub-20 nm wide and 150 nm deep nanocuts of many micrometers in length were generated within the ITO electrodes by a sub-15 femtosecond (fs) pulsed laser. The influence of laser processing on the electrical and optical properties of electrodes was investigated. The electrochemical impedance of the manufactured electrodes was measured before and after laser modification using electrochemical impedance spectroscopy. A small reduction in electrode impedance was observed. These nanostructured electrodes show also polarizing effects by the visible spectrum.

  7. Monitoring collagen remodeling on opto-thermal response of photoaged skin irradiated by Er:YAG laser with optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoman; Wu, Shulian; Li, Hui

    2010-11-01

    The Optical Coherence Tomography technology was used to perform noninvasive cross-sectional imaging of internal structures in photoaged mouse skin irradiated by Er:YAG laser. The mice were irradiated chronically with a steady dose of ultraviolet irradiation. Various laser light doses were irradiated on the back skins of the photoaged mouse. An OCT was used to observe the process of the collagen remodeling in dermis. The relationship between optical characteristic parameter such as attenuation coefficient and light dose was discovered. The total attenuation coefficient increased when the light dose increased. Our findings showed that Er:YAG laser could be used for the symptoms of the photoaged skin with some degree of thermal damage in the dermis, and the OCT could image the progress of collagen remodeling in photoaged mouse dermis. The OCT may be a useful tool for the determination of optimal parameters for laser skin treatment.

  8. Capturing a reflective cross-sectional image of an optical fiber with partially coherent laser light to measure the refractive index profile of a multimode optical fiber.

    PubMed

    Sheu, Fang-Wen; Jhang, Heng-Jian

    2013-01-28

    We focused partially coherent laser light onto an optical fiber end-face and captured a high-quality reflective cross-sectional image of the fiber. By analyzing the reflected light intensity distribution of the captured fiber image, we can achieve refractive-index profiling of a step-index multimode optical fiber. The measurement error caused by the reflected light from the other fiber end-face positioned in air can be greatly improved by inserting that end of the fiber into water. This simple and easy technique for fiber index profiling by employing reduced-coherence laser light is very useful in determining the refractive index profiles of various multimode optical fibers.

  9. CONTROL OF LASER RADIATION PARAMETER: Temporal evolution of a coherent stimulated radiation pulse in the three-level system in a Pr3+ : LaF3 crystal

    NASA Astrophysics Data System (ADS)

    Agafonov, Aleksandr I.; Grigoryan, Grigorii G.; Znamenskiy, Nikolay V.; Manykin, Eduard A.; Orlov, Yurii V.; Petrenko, Evgenii A.; Shashkov, Andrei Yu

    2004-09-01

    The temporal characteristics of coherent stimulated radiation at the 3P0— 3H6 transition in the Pr3+ ion in a LaF3 matrix are studied by tuning the pump frequency in the vicinity of the 3H4— 3P0 transition. It is found that in the case of the exact tuning to the resonance, a laser pulse, consisting of a train of picosecond spikes of total duration about 10 ns, was delayed by 3-4 ns with respect to the pump pulse onset. As the pump pulse detuning was increased, the shape of the coherent laser pulse changes and its delay increased up to 10 ns. The experimental results are interpreted theoretically.

  10. Generation of Bright, Spatially Coherent Soft X-Ray High Harmonics in a Hollow Waveguide Using Two-Color Synthesized Laser Pulses

    NASA Astrophysics Data System (ADS)

    Jin, Cheng; Stein, Gregory J.; Hong, Kyung-Han; Lin, C. D.

    2015-07-01

    We investigate the efficient generation of low-divergence high-order harmonics driven by waveform-optimized laser pulses in a gas-filled hollow waveguide. The drive waveform is obtained by synthesizing two-color laser pulses, optimized such that highest harmonic yields are emitted from each atom. Optimization of the gas pressure and waveguide configuration has enabled us to produce bright and spatially coherent harmonics extending from the extreme ultraviolet to soft x rays. Our study on the interplay among waveguide mode, atomic dispersion, and plasma effect uncovers how dynamic phase matching is accomplished and how an optimized waveform is maintained when optimal waveguide parameters (radius and length) and gas pressure are identified. Our analysis should help laboratory development in the generation of high-flux bright coherent soft x rays as tabletop light sources for applications.

  11. Record Stability via Improved Laser Coherence in Strontium-87 Optical Clocks

    NASA Astrophysics Data System (ADS)

    Campbell, Sara; Nicholson, Travis; Martin, Michael; Bloom, Benjamin; Williams, Jason; Bishof, Michael; Zhang, Xibo; Swallows, Matthew; Ye, Jun

    2013-05-01

    Many-particle clocks are promising candidates for next-generation frequency standards because quantum projection noise scales down with the square root of atom number. Previously, these clocks had been unable to demonstrate stability better than that of single-particle clocks, due to laser noise-induced instability via the Dick effect. We show that a better optical local oscillator with a 10-16 thermal noise floor directly results in a tenfold improvement in clock stability, now reaching 1 ×10-17 in 1000 s. Leveraging the superior precision of a many-particle clock, we are working toward a full systematic evaluation of our clock accuracy with a goal of 1 ×10-17 fractional uncertainty. One of the important systematics inherent in many-particle clocks is the density-dependent frequency shift. In a new system that traps thousands of atoms at low density, we now measure the density shift with a fractional uncertainty of 8 . 2 ×10-19. Additionally, to further improve our clock stability, we have developed a novel technique to evaluate the noise spectrum of our ultra-stable laser using 87Sr atoms as a quantum reference.

  12. Investigation of optical attenuation imaging using optical coherence tomography for monitoring of scars undergoing fractional laser treatment.

    PubMed

    Es'haghian, Shaghayegh; Gong, Peijun; Chin, Lixin; Harms, Karl-Anton; Murray, Alexandra; Rea, Suzanne; Kennedy, Brendan F; Wood, Fiona M; Sampson, David D; McLaughlin, Robert A

    2017-04-01

    We demonstrate the use of the near-infrared attenuation coefficient, measured using optical coherence tomography (OCT), in longitudinal assessment of hypertrophic burn scars undergoing fractional laser treatment. The measurement method incorporates blood vessel detection by speckle decorrelation and masking, and a robust regression estimator to produce 2D en face parametric images of the attenuation coefficient of the dermis. Through reliable co-location of the field of view across pre- and post-treatment imaging sessions, the study was able to quantify changes in the attenuation coefficient of the dermis over a period of ∼20 weeks in seven patients. Minimal variation was observed in the mean attenuation coefficient of normal skin and control (untreated) mature scars, as expected. However, a significant decrease (13 ± 5%, mean ± standard deviation) was observed in the treated mature scars, resulting in a greater distinction from normal skin in response to localized damage from the laser treatment. By contrast, we observed an increase in the mean attenuation coefficient of treated (31 ± 27%) and control (27 ± 20%) immature scars, with numerical values incrementally approaching normal skin as the healing progressed. This pilot study supports conducting a more extensive investigation of OCT attenuation imaging for quantitative longitudinal monitoring of scars. En face 2D OCT attenuation coefficient map of a treated immature scar derived from the pre-treatment (top) and the post-treatment (bottom) scans. (Vasculature (black) is masked out.) The scale bars are 0.5 mm.

  13. Single-particle coherent diffractive imaging with a soft x-ray free electron laser: towards soot aerosol morphology

    NASA Astrophysics Data System (ADS)

    Bogan, Michael J.; Starodub, Dmitri; Hampton, Christina Y.; Sierra, Raymond G.

    2010-10-01

    The first of its kind, the Free electron LASer facility in Hamburg, FLASH, produces soft x-ray pulses with unprecedented properties (10 fs, 6.8-47 nm, 1012 photons per pulse, 20 µm diameter). One of the seminal FLASH experiments is single-pulse coherent x-ray diffractive imaging (CXDI). CXDI utilizes the ultrafast and ultrabright pulses to overcome resolution limitations in x-ray microscopy imposed by x-ray-induced damage to the sample by 'diffracting before destroying' the sample on sub-picosecond timescales. For many lensless imaging algorithms used for CXDI it is convenient when the data satisfy an oversampling constraint that requires the sample to be an isolated object, i.e. an individual 'free-standing' portion of disordered matter delivered to the centre of the x-ray focus. By definition, this type of matter is an aerosol. This paper will describe the role of aerosol science methodologies used for the validation of the 'diffract before destroy' hypothesis and the execution of the first single-particle CXDI experiments being developed for biological imaging. FLASH CXDI now enables the highest resolution imaging of single micron-sized or smaller airborne particulate matter to date while preserving the native substrate-free state of the aerosol. Electron microscopy offers higher resolution for single-particle analysis but the aerosol must be captured on a substrate, potentially modifying the particle morphology. Thus, FLASH is poised to contribute significant advancements in our knowledge of aerosol morphology and dynamics. As an example, we simulate CXDI of combustion particle (soot) morphology and introduce the concept of extracting radius of gyration of fractal aggregates from single-pulse x-ray diffraction data. Future upgrades to FLASH will enable higher spatially and temporally resolved single-particle aerosol dynamics studies, filling a critical technological need in aerosol science and nanotechnology. Many of the methodologies described for FLASH will

  14. The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser

    SciTech Connect

    Schlotter, W. F.; Turner, J. J.; Rowen, M.; Holmes, M.; Messerschmidt, M.; Moeller, S.; Krzywinski, J.; Lee, S.; Coffee, R.; Hays, G.; Heimann, P.; Krupin, O.; Soufli, R.; Fernandez-Perea, M.; Hau-Riege, S.; Kelez, N.; Beye, M.; Gerken, N.; Sorgenfrei, F.; Wurth, W.; and others

    2012-04-15

    The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480-2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics. Preliminary commissioning results are presented including the first soft x-ray single-shot energy spectrum from a free electron laser.

  15. Characterization of Wavelength-Tunable Quantum Dot External Cavity Laser for 1.3-µm-Waveband Coherent Light Sources

    NASA Astrophysics Data System (ADS)

    Yamamoto, Naokatsu; Akahane, Kouichi; Kawanishi, Tetsuya; Sotobayashi, Hideyuki; Yoshioka, Yuki; Takai, Hiroshi

    2012-02-01

    A sandwiched sub-nano separator (SSNS) growth technique of producing high-density, high-quality InAs/InGaAs quantum dot (QD) structures on GaAs substrates is proposed. The SSNS technique achieved a density of 8.2 ×1010/cm2 by suppressing giant dot formation. The QD structures fabricated by the SSNS technique were used to form a ridge-type waveguide QD optical gain chip for O-band optical gain. With this chip, we successfully demonstrated the generation of a wavelength-tunable fine-tooth optical frequency comb in the O-band from a QD optical frequency comb laser (QD-CML), and synchronized short-optical-pulse generation (˜14 ps) with gigahertz-order repetition from a hybrid mode-locked QD-CML. We also successfully demonstrated a wavelength tunable QD-ECL with a wide wavelength tuning range (1265-1320 nm) and a narrow linewidth (210 kHz) in the O-band. It is expected that these QD coherent light sources will become attractive photonic devices for many scientific applications in the 1.0-1.3 µm waveband.

  16. High-speed polarization sensitive optical coherence tomography scan engine based on Fourier domain mode locked laser.

    PubMed

    Bonesi, Marco; Sattmann, Harald; Torzicky, Teresa; Zotter, Stefan; Baumann, Bernhard; Pircher, Michael; Götzinger, Erich; Eigenwillig, Christoph; Wieser, Wolfgang; Huber, Robert; Hitzenberger, Christoph K

    2012-11-01

    We report on a new swept source polarization sensitive optical coherence tomography scan engine that is based on polarization maintaining (PM) fiber technology. The light source is a Fourier domain mode locked laser with a PM cavity that operates in the 1300 nm wavelength regime. It is equipped with a PM buffer stage that doubles the fundamental sweep frequency of 54.5 kHz. The fiberization allows coupling of the scan engine to different delivery probes. In a first demonstration, we use the system for imaging human skin at an A-scan rate of 109 kHz. The system illuminates the sample with circularly polarized light and measures reflectivity, retardation, optic axis orientation, and Stokes vectors simultaneously. Furthermore, depolarization can be quantified by calculating the degree of polarization uniformity (DOPU). The high scanning speed of the system enables dense sampling in both, the x- and y-direction, which provides the opportunity to use 3D evaluation windows for DOPU calculation. This improves the spatial resolution of DOPU images considerably.

  17. Imaging of nanoparticle-labeled stem cells using magnetomotive optical coherence tomography, laser speckle reflectometry, and light microscopy

    NASA Astrophysics Data System (ADS)

    Cimalla, Peter; Werner, Theresa; Winkler, Kai; Mueller, Claudia; Wicht, Sebastian; Gaertner, Maria; Mehner, Mirko; Walther, Julia; Rellinghaus, Bernd; Wittig, Dierk; Karl, Mike O.; Ader, Marius; Funk, Richard H. W.; Koch, Edmund

    2015-03-01

    Cell transplantation and stem cell therapy are promising approaches for regenerative medicine and are of interest to researchers and clinicians worldwide. However, currently, no imaging technique that allows three-dimensional in vivo inspection of therapeutically administered cells in host tissues is available. Therefore, we investigate magnetomotive optical coherence tomography (MM-OCT) of cells labeled with magnetic particles as a potential noninvasive cell tracking method. We develop magnetomotive imaging of mesenchymal stem cells for future cell therapy monitoring. Cells were labeled with fluorescent iron oxide nanoparticles, embedded in tissue-mimicking agar scaffolds, and imaged using a microscope setup with an integrated MM-OCT probe. Magnetic particle-induced motion in response to a pulsed magnetic field of 0.2 T was successfully detected by OCT speckle variance analysis, and cross-sectional and volumetric OCT scans with highlighted labeled cells were obtained. In parallel, fluorescence microscopy and laser speckle reflectometry were applied as two-dimensional reference modalities to image particle distribution and magnetically induced motion inside the sample, respectively. All three optical imaging modalities were in good agreement with each other. Thus, magnetomotive imaging using iron oxide nanoparticles as cellular contrast agents is a potential technique for enhanced visualization of selected cells in OCT.

  18. Comparing Laser Peripheral Iridotomy to Cataract Extraction in Narrow Angle Eyes Using Anterior Segment Optical Coherence Tomography

    PubMed Central

    Melese, Ephrem; Peterson, Jeffrey R.; Feldman, Robert M.; Baker, Laura A.; Bell, Nicholas P.; Chuang, Alice Z.

    2016-01-01

    Purpose To evaluate the changes in anterior chamber angle (ACA) parameters in primary angle closure (PAC) spectrum eyes before and after cataract extraction (CE) and compare to the changes after laser peripheral iridotomy (LPI) using anterior segment optical coherence tomography (ASOCT). Methods Twenty-eight PAC spectrum eyes of 18 participants who underwent CE and 34 PAC spectrum eyes of 21 participants who underwent LPI were included. ASOCT images with 3-dimensional mode angle analysis scans were taken with the CASIA SS-1000 (Tomey Corp., Nagoya, Japan) before and after CE or LPI. Mixed-effect model analysis was used to 1) compare best-corrected visual acuity, intraocular pressure, and ACA parameters before and after CE; 2) identify and estimate the effects of potential contributing factors affecting changes in ACA parameters; and 3) compare CE and LPI treatment groups. Results The increase in average angle parameters (TISA750 and TICV750) was significantly greater after CE than LPI. TICV750 increased by 102% (2.114 [±1.203] μL) after LPI and by 174% (4.546 [± 1.582] μL) after CE (P < 0.001). Change of TICV750 in the CE group was significantly affected by age (P = 0.002), race (P = 0.006), and intraocular lens power (P = 0.037). Conclusions CE results in greater anatomic changes in the ACA than LPI in PAC spectrum eyes. ASOCT may be used to follow anatomic changes in the angle after intervention. PMID:27606482

  19. Assessment of the Optic Disc Morphology Using Spectral-Domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy

    PubMed Central

    Calvo, Pilar; Ferreras, Antonio; Abadia, Beatriz; Ara, Mirian; Figus, Michele; Pablo, Luis E.; Frezzotti, Paolo

    2014-01-01

    Objective. To compare the equivalent optic nerve head (OHN) parameters obtained with confocal scanning laser ophthalmoscopy (HRT3) and spectral-domain optical coherence tomography (OCT) in healthy and glaucoma patients. Methods. One hundred and eighty-two consecutive healthy subjects and 156 patients with open-angle glaucoma were divided into 2 groups according to intraocular pressure and visual field outcomes. All participants underwent imaging of the ONH with the HRT3 and the Cirrus OCT. The ONH parameters and the receiver operating characteristic (ROC) curves were compared between both groups. Results. Mean age did not differ between the normal and glaucoma groups (59.55 ± 9.7 years and 61.05 ± 9.4 years, resp.; P = 0.15). Rim area, average cup-to-disc (C/D) ratio, vertical C/D ratio, and cup volume were different between both instruments (P < 0.001). All equivalent ONH parameters, except disc area, were different between both groups (P < 0.001). The best areas under the ROC curve were observed for vertical C/D ratio (0.980 for OCT and 0.942 for HRT3; P = 0.11). Sensitivities at 95% fixed-specificities of OCT parameters were higher than those of HRT3. Conclusions. Equivalent ONH parameters of Cirrus OCT and HRT3 are different and cannot be used interchangeably. ONH parameters measured with OCT yielded a slightly better diagnostic performance. PMID:25110668

  20. Direct Coulomb explosion imaging of coherent rotational dynamics induced by few-cycle laser pulses in light and heavy hydrogen

    NASA Astrophysics Data System (ADS)

    Bocharova, Irina; Magrakvelidze, Maia; Ranitovic, Predrag; Ray, Dipanwita; Cocke, Lewis; Litvinyuk, Igor

    2008-05-01

    We followed fast evolution of angular distributions for H2 and D2 molecules after their interaction with 8 fs 800 nm laser pulses. The rotating molecules were exploded by another few-cycle probe pulse time-delayed for up to 10 ps in respect to the pump. For neutral molecules we observed coherent rotational dynamics characterized by periodic revivals without noticeable decoherence within the 10 ps time-scale. For D2 up to 4 rotational states were involved in the wavepackets for each of the two spin isomers. In light hydrogen the resulting dynamics was dominated by beating of just two rotational states. The experimental data are in excellent agreement with our numerical simulations obtained by solving time-dependent Schr"odinger equation. For molecules that were ionized by the pump pulse we observed both vibrational and rotational dynamics. Time-dependent angular distributions for the molecular ions exhibit transient alignment only soon after the pulse (20 fs for H2^+ and 40 fs for D2^+) with no consequent revivals within the next 10 ps.

  1. Vessel Labeling in Combined Confocal Scanning Laser Ophthalmoscopy and Optical Coherence Tomography Images: Criteria for Blood Vessel Discrimination

    PubMed Central

    Motte, Jeremias; Alten, Florian; Ewering, Carina; Osada, Nani; Kadas, Ella M.; Brandt, Alexander U.; Oberwahrenbrock, Timm; Clemens, Christoph R.; Eter, Nicole; Paul, Friedemann; Marziniak, Martin

    2014-01-01

    Introduction The diagnostic potential of optical coherence tomography (OCT) in neurological diseases is intensively discussed. Besides the sectional view of the retina, modern OCT scanners produce a simultaneous top-view confocal scanning laser ophthalmoscopy (cSLO) image including the option to evaluate retinal vessels. A correct discrimination between arteries and veins (labeling) is vital for detecting vascular differences between healthy subjects and patients. Up to now, criteria for labeling (cSLO) images generated by OCT scanners do not exist. Objective This study reviewed labeling criteria originally developed for color fundus photography (CFP) images. Methods The criteria were modified to reflect the cSLO technique, followed by development of a protocol for labeling blood vessels. These criteria were based on main aspects such as central light reflex, brightness, and vessel thickness, as well as on some additional criteria such as vascular crossing patterns and the context of the vessel tree. Results and Conclusion They demonstrated excellent inter-rater agreement and validity, which seems to indicate that labeling of images might no longer require more than one rater. This algorithm extends the diagnostic possibilities offered by OCT investigations. PMID:25203135

  2. Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum

    PubMed Central

    Seghilani, Mohamed S.; Myara, Mikhael; Sellahi, Mohamed; Legratiet, Luc; Sagnes, Isabelle; Beaudoin, Grégoire; Lalanne, Philippe; Garnache, Arnaud

    2016-01-01

    The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here “orbital birefringence”, based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create “orbital gain dichroism” allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 μm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications. PMID:27917885

  3. Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum

    NASA Astrophysics Data System (ADS)

    Seghilani, Mohamed S.; Myara, Mikhael; Sellahi, Mohamed; Legratiet, Luc; Sagnes, Isabelle; Beaudoin, Grégoire; Lalanne, Philippe; Garnache, Arnaud

    2016-12-01

    The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here “orbital birefringence”, based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create “orbital gain dichroism” allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 μm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications.

  4. Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum.

    PubMed

    Seghilani, Mohamed S; Myara, Mikhael; Sellahi, Mohamed; Legratiet, Luc; Sagnes, Isabelle; Beaudoin, Grégoire; Lalanne, Philippe; Garnache, Arnaud

    2016-12-05

    The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here "orbital birefringence", based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create "orbital gain dichroism" allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 μm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications.

  5. Narrowband solid state vuv coherent source for laser cooling of antihydrogen

    NASA Astrophysics Data System (ADS)

    Michan, J. Mario; Polovy, Gene; Madison, Kirk W.; Fujiwara, Makoto C.; Momose, Takamasa

    2015-11-01

    We describe the design and performance of a solid-state pulsed source of narrowband (< 100 MHz) Lyman- α radiation designed for the purpose of laser cooling magnetically trapped antihydrogen. Our source utilizes an injection seeded Ti:Sapphire amplifier cavity to generate intense radiation at 729.4 nm, which is then sent through a frequency doubling stage and a frequency tripling stage to generate 121.56 nm light. Although the pulse energy at 121.56 nm is currently limited to 12 nJ with a repetition rate of 10 Hz, we expect to obtain greater than 0.1 μJ per pulse at 10 Hz by further optimizing the alignment of the pulse amplifier and the efficiency of the frequency tripling stage. Such a power will be sufficient for cooling a trapped antihydrogen atom from 500 mK to 20mK.

  6. Ab Initio Theory of Coherent Laser-Induced Magnetization in Metals

    NASA Astrophysics Data System (ADS)

    Berritta, Marco; Mondal, Ritwik; Carva, Karel; Oppeneer, Peter M.

    2016-09-01

    We present the first materials specific ab initio theory of the magnetization induced by circularly polarized laser light in metals. Our calculations are based on nonlinear density matrix theory and include the effect of absorption. We show that the induced magnetization, commonly referred to as inverse Faraday effect, is strongly materials and frequency dependent, and demonstrate the existence of both spin and orbital induced magnetizations which exhibit a surprisingly different behavior. We show that for nonmagnetic metals (such as Cu, Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe, Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We compute effective optomagnetic fields that correspond to the induced magnetizations and provide guidelines for achieving all-optical helicity-dependent switching.

  7. Changes in the statistical and quantum features of the cavity radiation of a two-photon coherent beat laser due to phase fluctuation

    NASA Astrophysics Data System (ADS)

    Tesfa, Sintayehu

    2010-11-01

    A detailed derivation of the master equation and the corresponding time evolution of the cavity radiation of a coherent beat laser when the atoms are initially prepared in a partial coherent superposition is presented. It turns out that the quantum features and intensity of the cavity radiation are considerably modified by the phase fluctuation arising due to the practical incapability of preparing atoms in the intended perfect coherent superposition. New terms having opposite signs than the contribution of the driving radiation emerged in the master equation. This can be taken as an indication of a competing effect between the two in the manifestation of the nonclassical features. This, on the other hand, means that there is a chance to regain the quantum properties that might have been lost due to faulty preparation in engineering the driving mechanism and vice versa. In light of this, quite remarkably, the cavity radiation is shown to exhibit nonclassical features including two-mode squeezing and entanglement when there is no driving and when the atoms are initially prepared in a partial maximum atomic coherence superposition, contrary to earlier predictions for the case of perfect coherence.

  8. Optical Coherence Tomography Angiography in Mice: Comparison with Confocal Scanning Laser Microscopy and Fluorescein Angiography

    PubMed Central

    Giannakaki-Zimmermann, Helena; Kokona, Despina; Wolf, Sebastian; Ebneter, Andreas; Zinkernagel, Martin S.

    2016-01-01

    Purpose Optical coherence tomography angiography (OCT-A) allows noninvasive visualization of retinal vessels in vivo. OCT-A was used to characterize the vascular network of the mouse retina and was compared with fluorescein angiography (FA) and histology. Methods In the present study, OCT-A based on a Heidelberg Engineering Spectralis system was used to investigate the vascular network in mice. Data was compared with FA and confocal microscopy of flat-mount histology stained with isolectin IB4. For quantitative analysis the National Cancer Institute's AngioTool software was used. Vessel density, the number of vessel junctions, and endpoints were measured and compared between the imaging modalities. Results The configuration of the superficial capillary network was comparable with OCT-A and flat-mount histology in BALBc mice. However, vessel density and the number of vessel junctions per region of interest (P = 0.0161 and P = 0.0015, respectively) in the deep vascular network of BALBc mice measured by OCT-A was significantly higher than with flat-mount histology. In C3A.Cg-Pde6b+Prph2Rd2/J mice, where the deep capillary plexus is absent, analysis of the superficial network provided similar results for all three imaging modalities. Conclusion OCT-A is a helpful imaging tool for noninvasive, in vivo imaging of the vascular plexus in mice. It may offer advantages over FA and confocal microscopy especially for imaging the deep vascular plexus. Translational Relevance The present study shows that OCT-A can be employed for small animal imaging to assess the vascular network and offers advantages over flat-mount histology and FA. PMID:27570710

  9. Laser thermal therapy monitoring using complex differential variance in optical coherence tomography

    PubMed Central

    Lo, William C. Y.; Uribe-Patarroyo, Néstor; Nam, Ahhyun S.; Villiger, Martin; Vakoc, Benjamin J.; Bouma, Brett E.

    2016-01-01

    Conventional thermal therapy monitoring techniques based on temperature are often invasive, limited by point sampling, and are indirect measures of tissue injury, while techniques such as magnetic resonance and ultrasound thermometry are limited by their spatial resolution. The visualization of the thermal coagulation zone at high spatial resolution is particularly critical to the precise delivery of thermal energy to epithelial lesions. In this work, an integrated thulium laser thermal therapy monitoring system was developed based on complex differential variance (CDV), which enables the 2D visualization of the dynamics of the thermal coagulation process at high spatial and temporal resolution with an optical frequency domain imaging system. With proper calibration to correct for noise, the CDV-based technique was shown to accurately delineate the thermal coagulation zone, which is marked by the transition from high CDV upon heating to a significantly reduced CDV once the tissue is coagulated, in 3 different tissue types ex vivo: skin, retina, and esophagus. The ability to delineate thermal lesions in multiple tissue types at high resolution opens up the possibility of performing microscopic image-guided procedures in a vast array of epithelial applications ranging from dermatology, ophthalmology, to gastroenterology and beyond. PMID:27623742

  10. Tuning of successively scanned two monolithic Vernier-tuned lasers and selective data sampling in optical comb swept source optical coherence tomography

    PubMed Central

    Choi, Dong-hak; Yoshimura, Reiko; Ohbayashi, Kohji

    2013-01-01

    Monolithic Vernier tuned super-structure grating distributed Bragg reflector (SSG-DBR) lasers are expected to become one of the most promising sources for swept source optical coherence tomography (SS-OCT) with a long coherence length, reduced sensitivity roll-off, and potential capability for a very fast A-scan rate. However, previous implementations of the lasers suffer from four main problems: 1) frequencies deviate from the targeted values when scanned, 2) large amounts of noise appear associated with abrupt changes in injection currents, 3) optically aliased noise appears due to a long coherence length, and 4) the narrow wavelength coverage of a single chip limits resolution. We have developed a method of dynamical frequency tuning, a method of selective data sampling to eliminate current switching noise, an interferometer to reduce aliased noise, and an excess-noise-free connection of two serially scanned lasers to enhance resolution to solve these problems. An optical frequency comb SS-OCT system was achieved with a sensitivity of 124 dB and a dynamic range of 55-72 dB that depended on the depth at an A-scan rate of 3.1 kHz with a resolution of 15 μm by discretely scanning two SSG-DBR lasers, i.e., L-band (1.560-1.599 μm) and UL-band (1.598-1.640 μm). A few OCT images with excellent image penetration depth were obtained. PMID:24409394

  11. SOLID-STATE AND LIQUID LASERS: Generation of tunable radiation in a BeAl2O4:Ti3+ laser subjected to pulsed coherent pumping at a high repetition frequency

    NASA Astrophysics Data System (ADS)

    Pestryakov, Efim V.; Trunov, V. I.; Alimpiev, A. I.

    1987-05-01

    Coherent pumping of a titanium-activated chrysoberyl laser, by the second harmonic of a continuously pumped YAG:Nd laser operating in the Q-switched regime at a pulse repetition frequency 3-15 kHz, made it possible to achieve a conversion efficiency of ~5% and tuning of the emission wavelength in the range 0.73-0.95 µ. It was found experimentally that the lifetime of an excited state of the Ti3+ ions decreased on increase in temperature from 4.9 µsec at 300 K to 0.2 µsec at 500 K.

  12. Picosecond pulses of coherent MM-wave radiation in a photoinjector-driven waveguide free-selected laser

    SciTech Connect

    Fochs, S.N.; Le Sage, G.P.; Feng, L.

    1995-12-31

    A 5 MeV, high repetition rate (2.142 GHz in burst mode), high brightness, tabletop photoinjector is currently under construction at the UC Davis Department of Applied Science, on the LLNL site. Ultrashort pulses of coherent synchrotron radiation can be generated by transversally accelerating the electron beam with a wiggler in either metallic or dielectric-loaded waveguide FEL structures. This interaction is investigated theoretically and experimentally. Subpicosecond photoelectron bunches will be produced in the photoinjector by irradiating a high quantum efficiency Cs{sub 2}Te (Cesium Telluride) photocathode with a train of 100 UV (210 nm), ultra-short (250 fs) laser pulses. These bunches will be accelerated in a 1-1/2 cell {pi}-mode X-band RF gun e energized by a 20 MW, 8,568 GHz SLAC klystron. The peak current is 0.25 kA (0.25 nC, 1 ps), with a normalized beam emittance {epsilon}{sub n}<2.5 {pi} mm-mrad. This prebunched electron beam is then transversally accelerated in a cylindrical waveguide by a 30-mm period, 10 period long helical wiggler. The peak wiggler field is adjusted to 8.5 kG, so that the group velocity of the radiated electromagnetic waves matches the axial velocity of the electron bunch (grazing condition, zero slippage). Chirped output pulses in excess of 2 MW power are predicted, with an instantaneous bandwidth extending from 125 GHz to 225 GHz and a pulse duration of 15 ps (HWHM). To produce even shorter pulses, a dielectric-loaded waveguide can be used. The dispersion relation of this waveguide structure has an inflection point (zero group velocity dispersion). If the grazing condition is satisfied at this point, the final output pulse duration is no longer determined by slippage, or by group velocity dispersion and bandwidth, but by higher-order dispersive effects yielding transform-limited pulses.

  13. Imaging retinal degeneration in mice by combining Fourier domain optical coherence tomography and fluorescent scanning laser ophthalmoscopy

    NASA Astrophysics Data System (ADS)

    Hossein-Javaheri, Nima; Molday, Laurie L.; Xu, Jing; Molday, Robert S.; Sarunic, Marinko V.

    2009-02-01

    Visualization of the internal structures of the retina is critical for clinical diagnosis and monitoring of pathology as well as for medical research investigating the root causes of retinal degeneration. Optical Coherence Tomography (OCT) is emerging as the preferred technique for non-contact sub-surface depth-resolved imaging of the retina. The high resolution cross sectional images acquired in vivo by OCT can be compared to histology to visually delineate the retinal layers. The recent demonstration of the significant sensitivity increase obtained through use of Fourier domain (FD) detection with OCT has been used to facilitate high speed scanning for volumetric reconstruction of the retina in software. The images acquired by OCT are purely structural, relying on refractive index differences in the tissue for contrast, and do not provide information on the molecular content of the sample. We have constructed a FDOCT prototype and combined it with a fluorescent Scanning Laser Ophthalmoscope (fSLO) to permit real time alignment of the field of view on the retina. The alignment of the FDOCT system to the specimen is crucial for the registration of measurements taken throughout longitudinal studies. In addition, fluorescence detection has been integrated with the SLO to enable the en face localization of a molecular contrast signal, which is important for retinal angiography, and also for detection of autofluorescence associated with some forms of retinal degeneration, for example autofluorescence lipofuscin accumulations are associated with Stargardt's Macular Dystrophy. The integrated FD OCT/fSLO system was investigated for imaging the retina of the mice in vivo.

  14. Development of a kilowatt-class, joule-level ultrafast laser for driving compact high average power coherent EUV/soft x-ray sources

    NASA Astrophysics Data System (ADS)

    Reagan, Brendan A.; Baumgarten, Cory M.; Pedicone, Michael A.; Bravo, Herman; Yin, Liang; Woolston, Mark; Wang, Hanchen; Menoni, Carmen S.; Rocca, Jorge J.

    2016-03-01

    Our recent progress in the development of high energy / high average power, chirped pulse amplification laser systems based on diode-pumped, cryogenically-cooled Yb:YAG amplifiers is discussed, including the demonstration of a laser that produces 1 Joule, sub-10 picosecond duration, λ = 1.03μm pulses at 500 Hz repetition rate. This compact, all-diodepumped laser combines a mode-locked Yb:KYW oscillator and a water-cooled Yb:YAG preamplifer with two cryogenic power amplification stages to produce 1.5 Joule pulses with high beam quality which are subsequently compressed. This laser system occupies an optical table area of less than 1.5x3m2. This laser was employed to pump plasma-based soft x-ray lasers at λ = 10-20nm at repetition rates >=100 Hz. To accomplish this, temporally-shaped pulses were focused at grazing incidence into a high aspect ratio line focus using cylindrical optics on a high shot capacity rotating metal target. This results in an elongated plasma amplifier that produces microjoule pulses at several narrow-linewidth EUV wavelengths between λ = 109Å and 189Å. The resulting fraction of a milliwatt average powers are the highest reported to date for a compact, coherent source operating at these wavelengths, to the best of our knowledge.

  15. Influence of the finite linewidth of the laser radiation spectrum on the shape of the coherent population trapping resonance line in an optically dense medium with a buffer gas

    SciTech Connect

    Barantsev, K. A. Popov, E. N.; Litvinov, A. N.

    2015-11-15

    The theory of coherent population trapping resonance is developed for the finite linewidth of the laser radiation spectrum in an optically dense medium of Λ atoms in a cell with a buffer gas. Equations are derived for the atomic density matrix and laser emission spectrum transfer in a cell with working and buffer gases at a finite temperature. The dependence of the quality factor of coherent population trapping resonance on the linewidth of the laser radiation spectrum is studied by measuring transmitted radiation and fluorescence signals.

  16. Quantum coherent control of blue, green and red emissions from codoped lanthanide ions of Er3+/Tm3+/Yb3+ by two shaped infrared ultrashort laser beams

    NASA Astrophysics Data System (ADS)

    Cheng, Wenjing; Zhang, Shian; Jia, Tianqing; Ma, Jing; Sun, Zhenrong

    2014-01-01

    The enhancement and tunable color emissions from codoped lanthanide ions of Er3+/Tm3+/Yb3+ have been studied extensively in recent decades. In this paper, we present a new scheme for quantum coherent control of two-photon absorption (TPA) and color emission in codoped lanthanide ions of Er3+/Tm3+/Yb3+ by properly phase shaping two infrared ultrashort laser beams at central frequencies of 10 650 cm-1 and 7650 cm-1, respectively. Compared with the results irradiated by transform-limited pulses, the TPA probabilities of the blue, green and red emissions are independently controlled in the ranges 0-13.3, 0-14.5 and 0-1.0, respectively. The effects of the energy states of lanthanide ions and the laser spectral bandwidths on the coherent features are also discussed. The TPA probabilities for the blue and green emissions increase with the laser spectral bandwidths and decrease with the energy bandwidths of the final level states. As the intermediate energy level shifts in the range 10 100-10 500 cm-1, the TPA probabilities for the blue and green emissions change in the ranges 7-15 and 8-17, respectively.

  17. A Correlation Study between Two Adjacent Same-Meridian Acupoints after Laser-Needle Acupuncture with Optical Coherence Tomography and Diffuse Reflectance Spectra

    PubMed Central

    Wu, Xiuli; Wei, Huajiang; Ni, Yirong; Liu, Zhiming; Yang, Hongqin; Xie, Shusen; Zhou, Lianpeng

    2016-01-01

    This study is to investigate the correlations among Sanjian (LI3), Hegu (LI4), and Yangxi (LI5) acupoints and their corresponding nonacupoints on the Yangming Large Intestine Meridian of Hand before and after laser irradiation using optical coherence tomography (OCT) and diffuse reflectance spectra. The experiment was conducted on 10 healthy people. A 658 nm laser with 50 mW output power was used for irradiating LI4, LI5 acupoints and their corresponding nonacupoints. As to LI4 acupoint with laser irradiation for duration of 15 or 45 minutes, the OCT backscattered light intensities of LI4 and LI5 acupoints increased significantly, and the reflectance intensities (RIs) of the LI3, LI4, and LI5 acupoints decreased significantly. As to LI5 acupoint with laser irradiation for duration of 15 or 45 minutes, the changes of OCT backscattered light intensities of the corresponding irradiated acupoint and LI4 acupoint increased significantly, and the RIs decreased significantly. However, the OCT backscattered light intensities and RIs for their nonacupoints were almost not changed. The results show that an association exists between two adjacent same-meridian acupoints on the same meridian after laser-needle acupuncture to some extent. PMID:27990169

  18. A high speed three-dimensional spectral domain optical coherence tomography with <2 μm axial resolution using wide bandwidth femtosecond mode-locked laser

    NASA Astrophysics Data System (ADS)

    Kuroda, Hiroto; Baba, Motoyoshi; Suzuki, Masayuki; Yoneya, Shin

    2013-06-01

    We have developed an ultra-high-resolution optical coherence tomography (OCT) equipment, using a 200 nm bandwidth spectrometer and a mode-locked femtosecond laser. We have characterized this OCT, obtaining high spatial resolution in the axial direction of less than 2 μm in air via single scanning, within only 20 ms. This corresponds to an ultra-high resolution of less than 1.3 μm for measurements at the fundus retina. High resolution and high speed imaging enables us to selectively obtain a clear three dimensional (3D) lamina cribrosa itself from a 3D optic disc (OD) image in vivo.

  19. Comment on ``Competition between coherent emission and broadband spontaneous emission in the quantum free electron laser'' [Phys. Plasmas 20, 033106 (2013)

    NASA Astrophysics Data System (ADS)

    Petrillo, V.; Rossi, A. R.; Serafini, L.

    2013-12-01

    We point out that in the equation for the electron distribution evolution during Thomson/Compton or undulator radiation used in the paper: "Competition between coherent emission and broadband spontaneous emission in the quantum free electron laser" by G. R. M. Robb and R. Bonifacio [Phys. Plasmas 20, 033106 (2013)], the weight function should be the distribution of the number of emitted photons and not the photon energy distribution. Nevertheless, the considerations expressed in this comment do not alter the conclusions drawn in the paper in object.

  20. Vision problems

    MedlinePlus

    ... shade or curtain hanging across part of your visual field. Optic neuritis : inflammation of the optic nerve ... Impaired vision; Blurred vision Images Crossed eyes Eye Visual acuity test Slit-lamp exam Visual field test ...

  1. X-ray-optical cross-correlator for gas-phase experiments at the Linac Coherent Light Source free-electron laser

    SciTech Connect

    Schorb, S.; Cryan, J. P.; Glownia, J. M.; Bionta, M. R.; Coffee, R. N.; Swiggers, M.; Carron, S.; Castagna, J.-C.; Bozek, J. D.; Messerschmidt, M.; Schlotter, W. F.; Bostedt, C.; Gorkhover, T.; Erk, B.; Boll, R.; Schmidt, C.; Rudenko, A.; Rolles, D.; Rouzee, A.

    2012-03-19

    X-ray-optical pump-probe experiments at the Linac Coherent Light Source (LCLS) have so far been limited to a time resolution of 280 fs fwhm due to timing jitter between the accelerator-based free-electron laser (FEL) and optical lasers. We have implemented a single-shot cross-correlator for femtosecond x-ray and infrared pulses. A reference experiment relying only on the pulse arrival time information from the cross-correlator shows a time resolution better than 50 fs fwhm (22 fs rms) and also yields a direct measurement of the maximal x-ray pulse length. The improved time resolution enables ultrafast pump-probe experiments with x-ray pulses from LCLS and other FEL sources.

  2. Theoretical calculation on ICI reduction using digital coherent superposition of optical OFDM subcarrier pairs in the presence of laser phase noise.

    PubMed

    Yi, Xingwen; Xu, Bo; Zhang, Jing; Lin, Yun; Qiu, Kun

    2014-12-15

    Digital coherent superposition (DCS) of optical OFDM subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-OFDM that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to OFDM subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-OFDM is expected to be beneficial to certain optical fiber transmissions.

  3. Efficient generation of coherent blue light at 440 nm by intracavity-frequency-tripling 1319-nm emission from a Nd:YAG laser.

    PubMed

    Mu, Xiaodong; Ding, Yujie J

    2005-06-01

    A new route for efficiently generating coherent blue light has been explored based on intracavity effective third-harmonic generation in one partly periodically poled KTiOPO4 crystal placed inside the cavity of a diode-pumped Nd:YAG laser. To achieve efficient conversion, we use a dual-temperature oven to separately control the phase-matching conditions for the two second-order nonlinear processes. In addition, a Fabry-Perot cavity at 660 nm is incorporated into the crystal to increase the blue power significantly. When the laser is Q switched to produce long pulses, an average power of 118 mW is generated at 440 nm at a pump power of 10 W.

  4. A Virtual Blind Cane Using a Line Laser-Based Vision System and an Inertial Measurement Unit.

    PubMed

    Dang, Quoc Khanh; Chee, Youngjoon; Pham, Duy Duong; Suh, Young Soo

    2016-01-13

    A virtual blind cane system for indoor application, including a camera, a line laser and an inertial measurement unit (IMU), is proposed in this paper. Working as a blind cane, the proposed system helps a blind person find the type of obstacle and the distance to it. The distance from the user to the obstacle is estimated by extracting the laser coordinate points on the obstacle, as well as tracking the system pointing angle. The paper provides a simple method to classify the obstacle's type by analyzing the laser intersection histogram. Real experimental results are presented to show the validity and accuracy of the proposed system.

  5. A Virtual Blind Cane Using a Line Laser-Based Vision System and an Inertial Measurement Unit

    PubMed Central

    Dang, Quoc Khanh; Chee, Youngjoon; Pham, Duy Duong; Suh, Young Soo

    2016-01-01

    A virtual blind cane system for indoor application, including a camera, a line laser and an inertial measurement unit (IMU), is proposed in this paper. Working as a blind cane, the proposed system helps a blind person find the type of obstacle and the distance to it. The distance from the user to the obstacle is estimated by extracting the laser coordinate points on the obstacle, as well as tracking the system pointing angle. The paper provides a simple method to classify the obstacle’s type by analyzing the laser intersection histogram. Real experimental results are presented to show the validity and accuracy of the proposed system. PMID:26771618

  6. Proposed Studies Of Radiation Damping In Laser Interaction With An Ultra-thin, Coherently Reflecting Electron Sheet, Regarded As A Macro-particle

    NASA Astrophysics Data System (ADS)

    Habs, D.; Kiefer, D.; Henig, A.; Hörlein, R.; Schreiber, J.; Allinger, K.; Bin, J.; Thirolf, P.; Lang, C.; Yamazaki, T.; Homma, K.

    2010-04-01

    We introduce the concept of an ultra-thin, dense electron sheet as a macro-particle—similar to an electron microbunch of an FEL—where N electrons coherently reflect in the inner rest frame of the bunch. This ultra-thin electron sheet is pushed out off an ultra-thin Diamond-Like Carbon (DLC) target by a driver laser and acts as a relativistic flying mirror [1, 2] for a production laser. The space charge forces of the electron sheet are balanced by the trapping fields of the driver laser, of the remaining ion sheet and of the counter propagating production laser, resulting in longitudinally bound electrons. Like in the Mössbauer effect of nuclei the photon recoil is taken up by the N electrons of the macro-particle. The Landau-Lifshitz equation [3] for the classical radiation damping reaction of an external laser force Fext, here especially the Lorentz force, has been deduced as the first and second term in a Taylor series expansion ∑n = o∞(1/n!)(τ0)ndnFext/dtn, where τ0 = 2e2/(3mec3) = r0/c is the critical time and r0 is the classical electron radius. For the macro-particle the mass me is replaced by M = Nṡme, the charge e by q = Nṡe and the critical time τ0 by τmac = Nṡτ0. Thus the reflected fields and the radiation damping fields can be strongly enhanced and studied experimentally. Here we can test experimentally how higher order terms of the Taylor expansion contribute. For higher orders n the number N is reduced due the reduced coherence volume of the electron sheet, resulting in a convergence of the power series. Possible higher order terms increase the reflectivity of the relativistic mirror further and lead to much higher fields, which may even reach the Schwinger limit for the vacuum. They also would result in Doppler boosted higher order Landau-Lifshitz harmonics. In quantum mechanics new acceleration radiation effects like the Unruh effect [4, 5] are predicted, where now the single detector-like electron may be replaced by the N

  7. Laser-driven plasma wakefield electron acceleration and coherent femtosecond pulse generation in X-ray and gamma ranges

    NASA Astrophysics Data System (ADS)

    Trunov, V. I.; Lotov, K. V.; Gubin, K. V.; Pestryakov, E. V.; Bagayev, S. N.; Logachev, P. V.

    2017-01-01

    The laser wakefield acceleration (LWFA) of electrons in capillaries and gas jets followed by inverse Compton scattering of high intensity femtosecond laser pulses is discussed. The drive and scattered pulses will be produced by the two-channel multi-terawatt laser system developed in ILP SB RAS.

  8. Compact, High-Power, Fiber-Laser-Based Coherent Sources Tunable in the Mid-Infrared and THz Spectrum

    DTIC Science & Technology

    2015-02-20

    Ti:sapphire laser as pump source. In cw operation, we have achieved world-record output powers, while in the ultrafast femtosecond time-scale we have...continuous-wave (cw) and ultrafast femtosecond time-scales using compact fiber lasers and Kerr-lensmode- locked Ti:sapphire laser as pump source. In cw...compact fiber lasers and Kerr-lens- mode-locked Ti:sapphire laser as pump source. In cw operation, we have achieved world-record output powers, while in

  9. Analyzing the average intensity distribution and beam width evolution of phase-locked partially coherent radial flat-topped array laser beams in oceanic turbulence

    NASA Astrophysics Data System (ADS)

    Yousefi, M.; Kashani, F. D.; Mashal, A.

    2017-02-01

    In this research, an analytical expression for cross-spectral density matrix elements (and consequently, average intensity) of partially coherent flat-topped (PCFT) radial array laser beams in weak oceanic turbulence are derived based on the extended Huygens-Fresnel principle and the previously developed knowledge of the propagation of a partially coherent beam in atmosphere. Mean-squared beam width is calculated analytically using average intensity formula. The simulation is done by considering the effects of source parameters (such as the radius of the array setup’s circle and effective width of spectral degree of coherence) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature-salinity fluctuations, Kolmogorov micro-scale, and the rate of dissipation of the mean squared temperature) in detail. It is found that when salinity fluctuations in the ocean dominate temperature fluctuations, the average intensity of the PCFT array beam becomes more broad and the array beam profile conversion process to a single wider Gaussian beam profile will occur at a faster rate. For the same turbulent conditions and the same initial beam width, the divergence of a flat-topped array beam is less than the Gaussian array beam. The simulation and calculation results are shown by graphs.

  10. Femtosecond laser-induced crystallization of amorphous Sb{sub 2}Te{sub 3} film and coherent phonon spectroscopy characterization and optical injection of electron spins

    SciTech Connect

    Li Simian; Huang Huan; Wang Yang; Wu Yiqun; Gan Fuxi; Zhu Weiling; Wang Wenfang; Chen Ke; Yao Daoxin; Lai Tianshu

    2011-09-01

    A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb{sub 2}Te{sub 3} film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb{sub 2}Te{sub 3} film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A{sub 1g}{sup 1} and E{sub g}) of crystalline Sb{sub 2}Te{sub 3} enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb{sub 2}Te{sub 3} film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb{sub 2}Te{sub 3}-like topological insulators.

  11. Phase-sensitive optical coherence tomography using an Vernier-tuned distributed Bragg reflector swept laser in the mouse middle ear.

    PubMed

    Park, Jesung; Carbajal, Esteban F; Chen, Xi; Oghalai, John S; Applegate, Brian E

    2014-11-01

    Phase-sensitive optical coherence tomography (PhOCT) offers exquisite sensitivity to mechanical vibration in biological tissues. There is growing interest in using PhOCT for imaging the nanometer scale vibrations of the ear in animal models of hearing disorders. Swept-source-based systems offer fast acquisition speeds, suppression of common mode noise via balanced detection, and good signal roll-off. However, achieving high phase stability is difficult due to nonlinear laser sweeps and trigger jitter in a typical swept laser source. Here, we report on the initial application of a Vernier-tuned distributed Bragg reflector (VT-DBR) swept laser as the source for a fiber-based PhOCT system. The VT-DBR swept laser is electronically tuned and precisely controls sweeps without mechanical movement, resulting in highly linear sweeps with high wavelength stability and repeatability. We experimentally measured a phase sensitivity of 0.4 pm standard deviation, within a factor of less than 2 of the computed shot-noise limit. We further demonstrated the system by making ex vivo measurements of the vibrations of the mouse middle ear structures.

  12. The optical pumping of alkali atoms using coherent radiation from semi-conductor injection lasers and incoherent radiation from resonance lamps

    NASA Technical Reports Server (NTRS)

    Singh, G.

    1973-01-01

    An experimental study for creating population differences in the ground states of alkali atoms (Cesium 133) is presented. Studies made on GaAs-junction lasers and the achievement of population inversions among the hyperfine levels in the ground state of Cs 133 by optically pumping it with radiation from a GaAs diode laser. Laser output was used to monitor the populations in the ground state hyperfine levels as well as to perform the hyperfine pumping. A GaAs laser operated at about 77 K was used to scan the 8521 A line of Cs 133. Experiments were performed both with neon-filled and with paraflint-coated cells containing the cesium vapor. Investigations were also made for the development of the triple resonance coherent pulse technique and for the detection of microwave induced hyperfine trasistions by destroying the phase relationships produced by a radio frequency pulse. A pulsed cesium resonance lamp developed, and the lamp showed clean and reproducible switching characteristics.

  13. Attosecond Light and Science at the Time-scale of the Electron-Coherent X-Rays from Tabletop Ultrafast Lasers

    SciTech Connect

    Murnane, Margaret

    2010-03-31

    Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources at very short wavelengths, even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. This advance is possible by taking nonlinear optics techniques to an extreme - physics that is the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. Several applications have already been demonstrated, including making a movie of how electrons rearrange in a chemical bond changes shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. Nature 460, 1088 (2009); Science 317, 775 (2007); Physical Review Letters 103, 257402 (2009); Nature Materials 9, 26 (2010); Nature 463, 214 (2010); Science 322, 1207 (2008).

  14. Lasers.

    ERIC Educational Resources Information Center

    Schewe, Phillip F.

    1981-01-01

    Examines the nature of laser light. Topics include: (1) production and characteristics of laser light; (2) nine types of lasers; (3) five laser techniques including holography; (4) laser spectroscopy; and (5) laser fusion and other applications. (SK)

  15. Low Vision Aids and Low Vision Rehabilitation

    MedlinePlus

    ... Vision Resources Low Vision Rehabilitation and Low Vision Aids Written by: David Turbert Edited by: Robert H ... covers most services, but not devices.) Low vision aids There are many low vision aids and devices ...

  16. Optical 16-QAM-52-OFDM transmission at 4 Gbit/s by directly modulating a coherently injection-locked colorless laser diode.

    PubMed

    Chi, Yu-Chieh; Li, Yi-Cheng; Wang, Huai-Yung; Peng, Peng-Chun; Lu, Hai-Han; Lin, Gong-Ru

    2012-08-27

    Coherently injection-locked and directly modulated weak-resonant-cavity laser diode (WRC-FPLD) for back-to-back optical 16-quadrature-amplitude-modulation (QAM) and 52-subcarrier orthogonal frequency division multiplexing (OFDM) transmission with maximum bit rate up to 4 Gbit/s at carrier frequency of 2.5 GHz is demonstrated. The WRC-FPLD transmitter source is a specific design with very weak-resonant longitudinal modes to preserve its broadband gain spectral characteristics for serving as a colorless WDM-PON transmitter. Under coherent injection-locking, the relative-intensity noise (RIN) of the injection-locked WRC-FPLD can be suppressed to ?105 dBc/Hz and the error vector magnitude of the received optical OFDM data is greatly reduced with the amplitude error suppressed down 5.5%. Such a coherently injection-locked single-mode WRC-FPLD can perform both the back-to-back and the 25-km-SMF 16-QAM-52-OFDM transmissions with a symbol rate of 20-MSa/s in each OFDM subcarrier. After coherent injection locking, the BER of the back-to-back transmitted 16-QAM-52-OFDM data is reduced to 2.5 × 10(-5) at receiving power of ?10 dBm. After propagating along a 25-km-long SMF, a receiving power sensitivity of ?7.5 dBm is required to obtain a lowest BER of 2.5 × 10(-5), and a power penalty of 2.7 dB is observed when comparing with the back-to-back transmission.

  17. Partially coherent ultrafast spectrography

    PubMed Central

    Bourassin-Bouchet, C.; Couprie, M.-E.

    2015-01-01

    Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, that is, that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. Here we demonstrate how frequency-resolved optical gating (FROG), the first and one of the most widespread techniques for pulse characterization, can be adapted to measure partially coherent pulses even down to the attosecond timescale. No modification of experimental apparatuses is required; only the processing of the measurement changes. To do so, we take our inspiration from other branches of physics where partial coherence is routinely dealt with, such as quantum optics and coherent diffractive imaging. This will have important and immediate applications, such as enabling the measurement of X-ray free-electron laser pulses despite timing jitter. PMID:25744080

  18. Partially coherent ultrafast spectrography

    NASA Astrophysics Data System (ADS)

    Bourassin-Bouchet, C.; Couprie, M.-E.

    2015-03-01

    Modern ultrafast metrology relies on the postulate that the pulse to be measured is fully coherent, that is, that it can be completely described by its spectrum and spectral phase. However, synthesizing fully coherent pulses is not always possible in practice, especially in the domain of emerging ultrashort X-ray sources where temporal metrology is strongly needed. Here we demonstrate how frequency-resolved optical gating (FROG), the first and one of the most widespread techniques for pulse characterization, can be adapted to measure partially coherent pulses even down to the attosecond timescale. No modification of experimental apparatuses is required; only the processing of the measurement changes. To do so, we take our inspiration from other branches of physics where partial coherence is routinely dealt with, such as quantum optics and coherent diffractive imaging. This will have important and immediate applications, such as enabling the measurement of X-ray free-electron laser pulses despite timing jitter.

  19. Coherence, Complexity and Creativity

    NASA Astrophysics Data System (ADS)

    Arecchi, Fortunato Tito

    We review the ideas and experiments that established the onset of laser coherence beyond a suitable threshold. That threshold is the first of a chain of bifurcations in a non linear dynamics, leading eventually to deterministic chaos in lasers. In particular, the so called HC behavior has striking analogies with the electrical activity of neurons. Based on these considerations, we develop a dynamical model of neuron synchronization leading to coherent global perceptions. Synchronization implies a transitory control of neuron chaos. Depending on the time duration of this control, a cognitive agent has different amounts of awareness. Combining this with a stream of external inputs, one can point at an optimal use of internal resources, that is called cognitive creativity. While coherence is associated with long range correlations, complexity arises whenever an array of coupled dynamical systems displays multiple paths of coherence. What is the relation among the three concepts in the title? While coherence is associated with long range correlations, complexity arises whenever an array of coupled dynamical systems displays multiple paths of coherence. Creativity corresponds to a free selection of a coherence path within a complex nest. As sketched above, it seems dynamically related to chaos control.

  20. Low Vision FAQs

    MedlinePlus

    ... USAJobs Home > Low Vision > Low Vision FAQs Healthy Vision Diabetes Diabetes Home How Much Do You Know? ... los Ojos Cómo hablarle a su oculista Low Vision FAQs What is low vision? Low vision is ...

  1. Development of all-solid-state coherent 589 nm light source: toward the realization of sodium lidar and laser guide star adaptive optics

    NASA Astrophysics Data System (ADS)

    Saito, Norihito; Akagawa, Kazuyuki; Kato, Mayumi; Takazawa, Akira; Hayano, Yutaka; Saito, Yoshihiko; Ito, Meguru; Takami, Hideki; Iye, Masanori; Wada, Satoshi

    2006-12-01

    We report an all-solid-state coherent 589 nm light source in single-pass sum-frequency generation (SFG) with actively mode-locked Nd:YAG lasers for the realization of sodium lidar and laser guide star adaptive optics. The Nd:YAG lasers are constructed as a LD-side-pumped configuration and are operated at 1064 and 1319 nm for 589 nm light generation in SFG. Output powers of 16.5 and 5.3 W at 1064 and 1319 nm are obtained with two pumping chambers. Each chamber consisted of three 80-W-LD arrays. Single transverse mode TEM 00; M2 ~1.1 is achieved with adjustment of cavity length considering thermal lens effect with increase of input LD power. The cavity length is set to approximately 1 m. Accordingly the mode-locked lasers are operated at a repetition rate of approximately 150 MHz. Synchronization of two pulse trains at 1064 and 1319 nm is accomplished by control of phase difference between two radio frequencies input in acousto-optic mode-lockers. Then temporal delay is controlled with a resolution of 37 ps/degree. Pump beams are mixed in periodically poled stoichiometric lithium tantalate (PPSLT) without an antireflection coating. The effective aperture and length of the crystal are 0.5 × 2 mm2 and 15 mm. When input intensity is set at 5.6 MW/cm , an average output power of 4.6 W is obtained at 589.159 nm. Precise tuning to the sodium D II line is accomplished by thermal control of etalons set in the Nd:YAG lasers. The output power at 589.159 nm is stably maintained within +/-1.2% for 8 hours.

  2. Accidental Laser Injury to the Eye.

    PubMed

    Kandari, Jamal Al; Raizada, Seemant; Razzak, Ahmed Abdul

    2010-03-09

    The unprotected human eye is extremely sensitive to laser radiation and can be permanently damaged from direct or reflected beams. Two cases of retinal injury by laser exposure outside hospital setting are reported. Two patients presented in retina clinic in Al-Bahar eye center in Kuwait with complaints of decrease in vision following exposure to unknown light. Case 1 was exposed to a laser used in military warfare and Case 2 exposed to laser pointer. Routine slit lamp examination and fundus examination of the patient was done along with fundus fluorescien angiography (FFA) and Optical coherence tomography (OCT). Patients were followed up in out patient department for 6 months. Patient with military laser exposure had severe permanent vision loss and persisted even after 6 months. Patient exposed to laser pointer beam had transient visual loss, which improved to 20/25 at 7 months follow-up. Laser retinal damage should be suspected in any patient with visual complaints after obvious exposure to unknown strong light. The treatment for laser retinal injuries is extremely limited and hence prevention is essential.

  3. Test results for 320 nm and 390 nm remote sensing sources using a 150 mJ, 100 Hz repetition rate, injection-seeded diode-pumped Nd:YAG slab-laser developed by Coherent Technologies, Inc.

    SciTech Connect

    Armstrong, Darrell Jewell

    2005-07-01

    This report describes results of tests using a laser system designed by Coherent Technologies, Inc., in conjunction with Sandia developed nonlinear optics technology. Test results are described for three different optical parametric oscillators built at Sandia. The report concludes with recommendations for future work.

  4. Laser Frequency Stabilization for Coherent Lidar Applications using Novel All-Fiber Gas Reference Cell Fabrication Technique

    NASA Technical Reports Server (NTRS)

    Meras, Patrick, Jr.; Poberezhskiy, Ilya Y.; Chang, Daniel H.; Levin, Jason; Spiers, Gary D.

    2008-01-01

    Compact hollow-core photonic crystal fiber (HC-PCF)gas frequency reference cell was constructed using a novel packaging technique that relies on torch-sealing a quartz filling tube connected to a mechanical splice between regular and hollow-core fibers. The use of this gas cell for laser frequency stabilization was demonstrated by locking a tunable diode laser to the center of the P9 line from the (nu)1+(nu)3 band of acetylene with RMS frequency error of 2.06 MHz over 2 hours. This effort was performed in support of a task to miniaturize the laser frequency stabilization subsystem of JPL/LMCT Laser Absorption Spectrometer (LAS) instrument.

  5. Coherent control of plasma dynamics.

    PubMed

    He, Z-H; Hou, B; Lebailly, V; Nees, J A; Krushelnick, K; Thomas, A G R

    2015-05-15

    Coherent control of a system involves steering an interaction to a final coherent state by controlling the phase of an applied field. Plasmas support coherent wave structures that can be generated by intense laser fields. Here, we demonstrate the coherent control of plasma dynamics in a laser wakefield electron acceleration experiment. A genetic algorithm is implemented using a deformable mirror with the electron beam signal as feedback, which allows a heuristic search for the optimal wavefront under laser-plasma conditions that is not known a priori. We are able to improve both the electron beam charge and angular distribution by an order of magnitude. These improvements do not simply correlate with having the 'best' focal spot, as the highest quality vacuum focal spot produces a greatly inferior electron beam, but instead correspond to the particular laser phase front that steers the plasma wave to a final state with optimal accelerating fields.

  6. Analysis of Coherent Lidar Data

    DTIC Science & Technology

    2007-11-02

    for understanding and predicting atmospheric processes. Recent advances in solid-state lasers have produced coherent Doppler lidar with improved...for the spatial statistics. The performance of coherent Doppler lidar in the weak signal regime was deter- mined by computer simulations and from data...reliable comparison of coherent Doppler lidar wind measurements. A new theoretical prediction of the effects of the pulse averaging of the wind field

  7. High-power supercontinuum generation using high-repetition-rate ultrashort-pulse fiber laser for ultrahigh-resolution optical coherence tomography in 1600 nm spectral band

    NASA Astrophysics Data System (ADS)

    Yamanaka, Masahito; Kawagoe, Hiroyuki; Nishizawa, Norihiko

    2016-02-01

    We describe the generation of a high-power, spectrally smooth supercontinuum (SC) in the 1600 nm spectral band for ultrahigh-resolution optical coherence tomography (UHR-OCT). A clean SC was achieved by using a highly nonlinear fiber with normal dispersion properties and a high-quality pedestal-free pulse obtained from a passively mode-locked erbium-doped fiber laser operating at 182 MHz. The center wavelength and spectral width were 1578 and 172 nm, respectively. The output power of the SC was 51 mW. Using the developed SC source, we demonstrated UHR-OCT imaging of biological samples with a sensitivity of 109 dB and an axial resolution of 4.9 µm in tissue.

  8. Nonlinear polarization dynamics in a weakly birefringent all-normal dispersion photonic crystal fiber: toward a practical coherent fiber supercontinuum laser

    PubMed Central

    Tu, Haohua; Liu, Yuan; Liu, Xiaomin; Turchinovich, Dmitry; Lægsgaard, Jesper; Boppart, Stephen A.

    2012-01-01

    Dispersion-flattened dispersion-decreased all-normal dispersion (DFDD-ANDi) photonic crystal fibers have been identified as promising candidates for high-spectral-power coherent supercontinuum (SC) generation. However, the effects of the unintentional birefringence of the fibers on the SC generation have been ignored. This birefringence is widely present in nonlinear non-polarization maintaining fibers with a typical core size of 2 µm, presumably due to the structural symmetry breaks introduced in the fiber drawing process. We find that an intrinsic form-birefringence on the order of 10−5 profoundly affects the SC generation in a DFDD-ANDi photonic crystal fiber. Conventional simulations based on the scalar generalized nonlinear Schrödinger equation (GNLSE) fail to reproduce the prominent observed features of the SC generation in a short piece (9-cm) of this fiber. However, these features can be qualitatively or semi-quantitatively understood by the coupled GNLSE that takes into account the form-birefringence. The nonlinear polarization effects induced by the birefringence significantly distort the otherwise simple spectrotemporal field of the SC pulses. We therefore propose the fabrication of polarization-maintaining DFDD-ANDi fibers to avoid these adverse effects in pursuing a practical coherent fiber SC laser. PMID:22274457

  9. Simultaneous 1310/1550 dual-band swept laser source and fiber-based dual-band common-path swept source optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Mao, Youxin; Chang, Shoude; Murdock, Erroll; Flueraru, Costel

    2011-08-01

    A simultaneous two wavelength band swept laser source and a fiber-based dual-band common-path swept source optical coherence tomography is reported. Simultaneous 1310/1550 dual-wavelength tuning is performed by using two fiber-ring cavities with corresponding optical semiconductor amplifier as their gain mediums and two narrowband optical filters with a single dual-window polygonal scanner. Measured average output powers of 60 mW and 27 mW have been achieved for 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 nm to 1387 nm for 1310 nm band and from 1519 nm to 1581 nm for 1550 nm band at an A-scan rate of 65 kHz. A broadband 1310/1550 wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form a dual-band common-path swept-source optical coherence tomography. Simultaneous OCT imaging at 1310 and 1550 nm is achieved by using a depth ratio correction method. This technique allows potentially for in vivo endoscopic high-speed functional OCT imaging with high quality spectroscopic contrast with low computational costs. On the other hand, the common path configuration is able to reject common mode noise and potentially implement high stability quantitative phase measurements.

  10. Communication: two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS): simultaneous planar imaging and multiplex spectroscopy in a single laser shot.

    PubMed

    Bohlin, Alexis; Kliewer, Christopher J

    2013-06-14

    Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15,000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm(2).

  11. Communication: Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS): Simultaneous planar imaging and multiplex spectroscopy in a single laser shot

    NASA Astrophysics Data System (ADS)

    Bohlin, Alexis; Kliewer, Christopher J.

    2013-06-01

    Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15 000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm2.

  12. Development and calibration of mirrors and gratings for the soft x-ray materials science beamline at the Linac Coherent Light Source free-electron laser.

    PubMed

    Soufli, Regina; Fernández-Perea, Mónica; Baker, Sherry L; Robinson, Jeff C; Gullikson, Eric M; Heimann, Philip; Yashchuk, Valeriy V; McKinney, Wayne R; Schlotter, William F; Rowen, Michael

    2012-04-20

    This work discusses the development and calibration of the x-ray reflective and diffractive elements for the Soft X-ray Materials Science (SXR) beamline of the Linac Coherent Light Source (LCLS) free-electron laser (FEL), designed for operation in the 500 to 2000 eV region. The surface topography of three Si mirror substrates and two Si diffraction grating substrates was examined by atomic force microscopy (AFM) and optical profilometry. The figure of the mirror substrates was also verified via surface slope measurements with a long trace profiler. A boron carbide (B4C) coating especially optimized for the LCLS FEL conditions was deposited on all SXR mirrors and gratings. Coating thickness uniformity of 0.14 nm root mean square (rms) across clear apertures extending to 205 mm length was demonstrated for all elements, as required to preserve the coherent wavefront of the LCLS source. The reflective performance of the mirrors and the diffraction efficiency of the gratings were calibrated at beamline 6.3.2 at the Advanced Light Source synchrotron. To verify the integrity of the nanometer-scale grating structure, the grating topography was examined by AFM before and after coating. This is to our knowledge the first time B4C-coated diffraction gratings are demonstrated for operation in the soft x-ray region.

  13. Development and calibration of mirrors and gratings for the Soft X-ray materials science beamline at the Linac Coherent Light Source free-electron laser

    SciTech Connect

    Soufli, Regina; Fernandez-Perea, Monica; Baker, Sherry L.; Robinson, Jeff C.; Gullikson, Eric M.; Heimann, Philip; Yashchuk, Valerie V.; McKinney, Wayne R.; Schlotter, William F.; Rowen, Michael

    2012-04-18

    This article discusses the development and calibration of the x-ray reflective and diffractive elements for the Soft X-ray Materials Science (SXR) beamline of the Linac Coherent Light Source (LCLS) free-electron laser (FEL), designed for operation in the 500 – 2000 eV region. The surface topography of three Si mirror substrates and two Si diffraction grating substrates was examined by atomic force microscopy (AFM) and optical profilometry. The figure of the mirror substrates was also verified via surface slope measurements with a long trace profiler. A boron carbide (B4C) coating especially optimized for the LCLS FEL conditions was deposited on all SXR mirrors and gratings. Coating thickness uniformity of 0.14 nm root mean square (rms) across clear apertures extending to 205 mm length was demonstrated for all elements, as required to preserve the coherent wavefront of the LCLS source. The reflective performance of the mirrors and the diffraction efficiency of the gratings were calibrated at beamline 6.3.2 at the Advanced Light Source synchrotron. To verify the integrity of the nanometer-scale grating structure, the grating topography was examined by AFM before and after coating. This is to our knowledge the first time B4C-coated diffraction gratings are demonstrated for operation in the soft x-ray region.

  14. Development and calibration of mirrors and gratings for the Soft X-ray materials science beamline at the Linac Coherent Light Source free-electron laser

    DOE PAGES

    Soufli, Regina; Fernandez-Perea, Monica; Baker, Sherry L.; ...

    2012-04-18

    This article discusses the development and calibration of the x-ray reflective and diffractive elements for the Soft X-ray Materials Science (SXR) beamline of the Linac Coherent Light Source (LCLS) free-electron laser (FEL), designed for operation in the 500 – 2000 eV region. The surface topography of three Si mirror substrates and two Si diffraction grating substrates was examined by atomic force microscopy (AFM) and optical profilometry. The figure of the mirror substrates was also verified via surface slope measurements with a long trace profiler. A boron carbide (B4C) coating especially optimized for the LCLS FEL conditions was deposited on allmore » SXR mirrors and gratings. Coating thickness uniformity of 0.14 nm root mean square (rms) across clear apertures extending to 205 mm length was demonstrated for all elements, as required to preserve the coherent wavefront of the LCLS source. The reflective performance of the mirrors and the diffraction efficiency of the gratings were calibrated at beamline 6.3.2 at the Advanced Light Source synchrotron. To verify the integrity of the nanometer-scale grating structure, the grating topography was examined by AFM before and after coating. This is to our knowledge the first time B4C-coated diffraction gratings are demonstrated for operation in the soft x-ray region.« less

  15. Communication: Two-dimensional gas-phase coherent anti-Stokes Raman spectroscopy (2D-CARS): Simultaneous planar imaging and multiplex spectroscopy in a single laser shot

    SciTech Connect

    Bohlin, Alexis; Kliewer, Christopher J.

    2013-01-01

    Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a powerful tool for chemical sensing, molecular dynamics measurements, and rovibrational spectroscopy since its development over 30 years ago, finding use in fields of study as diverse as combustion diagnostics, cell biology, plasma physics, and the standoff detection of explosives. The capability for acquiring resolved CARS spectra in multiple spatial dimensions within a single laser shot has been a long-standing goal for the study of dynamical processes, but has proven elusive because of both phase-matching and detection considerations. Here, by combining new phase matching and detection schemes with the high efficiency of femtosecond excitation of Raman coherences, we introduce a technique for single-shot two-dimensional (2D) spatial measurements of gas phase CARS spectra. We demonstrate a spectrometer enabling both 2D plane imaging and spectroscopy simultaneously, and present the instantaneous measurement of 15, 000 spatially correlated rotational CARS spectra in N2 and air over a 2D field of 40 mm2.

  16. Computer vision

    NASA Technical Reports Server (NTRS)

    Gennery, D.; Cunningham, R.; Saund, E.; High, J.; Ruoff, C.

    1981-01-01

    The field of computer vision is surveyed and assessed, key research issues are identified, and possibilities for a future vision system are discussed. The problems of descriptions of two and three dimensional worlds are discussed. The representation of such features as texture, edges, curves, and corners are detailed. Recognition methods are described in which cross correlation coefficients are maximized or numerical values for a set of features are measured. Object tracking is discussed in terms of the robust matching algorithms that must be devised. Stereo vision, camera control and calibration, and the hardware and systems architecture are discussed.

  17. Analyzing the propagation behavior of scintillation index and bit error rate of a partially coherent flat-topped laser beam in oceanic turbulence.

    PubMed

    Yousefi, Masoud; Golmohammady, Shole; Mashal, Ahmad; Kashani, Fatemeh Dabbagh

    2015-11-01

    In this paper, on the basis of the extended Huygens-Fresnel principle, a semianalytical expression for describing on-axis scintillation index of a partially coherent flat-topped (PCFT) laser beam of weak to moderate oceanic turbulence is derived; consequently, by using the log-normal intensity probability density function, the bit error rate (BER) is evaluated. The effects of source factors (such as wavelength, order of flatness, and beam width) and turbulent ocean parameters (such as Kolmogorov microscale, relative strengths of temperature and salinity fluctuations, rate of dissipation of the mean squared temperature, and rate of dissipation of the turbulent kinetic energy per unit mass of fluid) on propagation behavior of scintillation index, and, hence, on BER, are studied in detail. Results indicate that, in comparison with a Gaussian beam, a PCFT laser beam with a higher order of flatness is found to have lower scintillations. In addition, the scintillation index and BER are most affected when salinity fluctuations in the ocean dominate temperature fluctuations.

  18. Data processing software suite SITENNO for coherent X-ray diffraction imaging using the X-ray free-electron laser SACLA

    PubMed Central

    Sekiguchi, Yuki; Oroguchi, Tomotaka; Takayama, Yuki; Nakasako, Masayoshi

    2014-01-01

    Coherent X-ray diffraction imaging is a promising technique for visualizing the structures of non-crystalline particles with dimensions of micrometers to sub-micrometers. Recently, X-ray free-electron laser sources have enabled efficient experiments in the ‘diffraction before destruction’ scheme. Diffraction experiments have been conducted at SPring-8 Angstrom Compact free-electron LAser (SACLA) using the custom-made diffraction apparatus KOTOBUKI-1 and two multiport CCD detectors. In the experiments, ten thousands of single-shot diffraction patterns can be collected within several hours. Then, diffraction patterns with significant levels of intensity suitable for structural analysis must be found, direct-beam positions in diffraction patterns determined, diffraction patterns from the two CCD detectors merged, and phase-retrieval calculations for structural analyses performed. A software suite named SITENNO has been developed to semi-automatically apply the four-step processing to a huge number of diffraction data. Here, details of the algorithm used in the suite are described and the performance for approximately 9000 diffraction patterns collected from cuboid-shaped copper oxide particles reported. Using the SITENNO suite, it is possible to conduct experiments with data processing immediately after the data collection, and to characterize the size distribution and internal structures of the non-crystalline particles. PMID:24763651

  19. Optimal generation of spatially coherent soft X-ray isolated attosecond pulses in a gas-filled waveguide using two-color synthesized laser pulses

    PubMed Central

    Jin, Cheng; Hong, Kyung-Han; Lin, C. D.

    2016-01-01

    We numerically demonstrate the generation of intense, low-divergence soft X-ray isolated attosecond pulses in a gas-filled hollow waveguide using synthesized few-cycle two-color laser waveforms. The waveform is a superposition of a fundamental and its second harmonic optimized such that highest harmonic yields are emitted from each atom. We then optimize the gas pressure and the length and radius of the waveguide such that bright coherent high-order harmonics with angular divergence smaller than 1 mrad are generated, for photon energy from the extreme ultraviolet to soft X-rays. By selecting a proper spectral range enhanced isolated attosecond pulses are generated. We study how dynamic phase matching caused by the interplay among waveguide mode, neutral atomic dispersion, and plasma effect is achieved at the optimal macroscopic conditions, by performing time-frequency analysis and by analyzing the evolution of the driving laser’s electric field during the propagation. Our results, when combined with the on-going push of high-repetition-rate lasers (sub- to few MHz’s) may eventually lead to the generation of high-flux, low-divergence soft X-ray tabletop isolated attosecond pulses for applications. PMID:27929036

  20. Scanning near-field optical coherent anti-Stokes Raman microscopy (SNOM-CARS) with femtosecond laser pulses in vibrational and electronic resonance.

    PubMed

    Namboodiri, Mahesh; Khan, Tahir Zeb; Bom, Sidhant; Flachenecker, Günter; Materny, Arnulf

    2013-01-14

    Accessing ultrafast photoinduced molecular dynamics on a femtosecond time-scale with vibrational selectivity and at the same time sub-diffraction limited spatial resolution would help to gain important information about ultrafast processes in nanostructures. While nonlinear Raman techniques have been used to obtain highly resolved images in combination with near-field microscopy, the use of femtosecond laser pulses in electronic resonance still constitutes a big challenge. Here, we present our first results on coherent anti-Stokes Raman scattering (fs-CARS) with femtosecond laser pulses detected in the near-field using scanning near-field optical microscopy (SNOM). We demonstrate that highly spatially resolved images can be obtained from poly(3-hexylthiophene) (P3HT) nano-structures where the fs-CARS process was in resonance with the P3HT absorption and with characteristic P3HT vibrational modes without destruction of the samples. Sub-diffraction limited lateral resolution is achieved. Especially the height resolution clearly surpasses that obtained with standard microCARS. These results will be the basis for future investigations of mode-selective dynamics in the near field.