Science.gov

Sample records for observatory laser guide

  1. Sodium laser guide star results at the Lick Observatory

    SciTech Connect

    Friedman, H.; Erbert, G.; Kuklo, T.

    1995-10-01

    Results of return signal level and guide star spot size for a sodium laser guide star recently installed at the Lick Observatory are presented. Operational characteristics of frequency stability, amplitude stability, and pointing accuracy are discussed.

  2. Measurements of the Lick Observatory Sodium Laser Guide Star

    SciTech Connect

    Gavel, D. T., LLNL

    1998-03-01

    The Lick Observatory guide star laser has provided a beacon sufficient to close the adaptive optics loop and produce corrected images during runs in 1996 and 1997. This report summarizes measurements of the wavefront quality of the outgoing beam, photoreturn signal from the sodium beacon, and radiance distribution of the guide star on the sky, and follows with an analysis of the impact of the laser on adaptive optics system performance.

  3. Performance of laser guide star adaptive optics at Lick Observatory

    SciTech Connect

    Olivier, S.S.; An, J.; Avicola, K.

    1995-07-19

    A sodium-layer laser guide star adaptive optics system has been developed at Lawrence Livermore National Laboratory (LLNL) for use on the 3-meter Shane telescope at Lick Observatory. The system is based on a 127-actuator continuous-surface deformable mirror, a Hartmann wavefront sensor equipped with a fast-framing low-noise CCD camera, and a pulsed solid-state-pumped dye laser tuned to the atomic sodium resonance line at 589 nm. The adaptive optics system has been tested on the Shane telescope using natural reference stars yielding up to a factor of 12 increase in image peak intensity and a factor of 6.5 reduction in image full width at half maximum (FWHM). The results are consistent with theoretical expectations. The laser guide star system has been installed and operated on the Shane telescope yielding a beam with 22 W average power at 589 nm. Based on experimental data, this laser should generate an 8th magnitude guide star at this site, and the integrated laser guide star adaptive optics system should produce images with Strehl ratios of 0.4 at 2.2 {mu}m in median seeing and 0.7 at 2.2 {mu}m in good seeing.

  4. Remote Operations of Laser Guide Star Systems: Gemini Observatory.

    NASA Astrophysics Data System (ADS)

    Oram, Richard J.; Fesquet, Vincent; Wyman, Robert; D'Orgeville, Celine

    2011-03-01

    The Gemini North telescope, equipped with a 14W laser, has been providing Laser Guide Star Adaptive Optics (LGS AO) regular science queue observations for worldwide astronomers since February 2007. The new 55W laser system for MCAO was installed on the Gemini South telescope in May 2010. In this paper, we comment on how Gemini Observatory developed regular remote operation of the Laser Guide Star Facility and high-power solid-state laser as routine normal operations. Fully remote operation of the LGSF from the Hilo base facility HBF was initially trialed and then optimized and became the standard operating procedure (SOP) for LGS operation in December 2008. From an engineering perspective remote operation demands stable, well characterized and base-lined equipment sets. In the effort to produce consistent, stable and controlled laser parameters (power, wavelength and beam quality) we completed a failure mode effect analysis of the laser system and sub systems that initiated a campaign of hardware upgrades and procedural improvements to the routine maintenance operations. Finally, we provide an overview of normal operation procedures during LGS runs and present a snapshot of data accumulated over several years that describes the overall LGS AO observing efficiency at the Gemini North telescope.

  5. Adaptive optics and laser guide stars at Lick observatory

    SciTech Connect

    Brase, J.M.

    1994-11-15

    For the past several years LLNL has been developing adaptive optics systems for correction of both atmospheric turbulence effects and thermal distortions in optics for high-power lasers. Our early work focused on adaptive optics for beam control in laser isotope separation and ground-based free electron lasers. We are currently developing innovative adaptive optics and laser systems for sodium laser guide star applications at the University of California`s Lick and Keck Observeratories. This talk will describe our adaptive optics technology and some of its applications in high-resolution imaging and beam control.

  6. Laser Guide Star Based Astrophysics at Lick Observatory

    SciTech Connect

    Max, C; Gavel, D.; Friedman, H.; Olivier, S.; Macintosh, B.; Brase, J.; Avicola, K.; Gibbard, S.; An, J.

    2000-03-10

    The resolution of ground-based telescopes is typically limited to {approx}1 second of arc because of the blurring effects of atmospheric turbulence. Adaptive optics (AO) technology senses and corrects for the optical distortions due to turbulence hundreds of times per second using high-speed sensors, computers, deformable mirror, and laser technology. The goal of this project is to make AO systems widely useful astronomical tools providing resolutions up to an order of magnitude better than current, ground-based telescopes. Astronomers at the University of California Lick Observatory at Mt. Hamilton now routinely use the LLNL developed AO system for high resolution imaging of astrophysical objects. We report here on the instrument development progress and on the science observations made with this system during this 3-year ERI project.

  7. Light pollution generated by laser guide star at Canarian Observatories

    NASA Astrophysics Data System (ADS)

    Chueca, Sergio; Fuensalida, Jesus J.

    2004-11-01

    A new generation of instrument using a launching laser is been developed to correct the atmospheric image blurring and to establish optical communication with space. Then, light pollution generated by laser will be a serious operational problem in next years. This laser could affect astronomical works of adjacent telescopes when the laser lay across the field of view of the observing telescope, this is a kind of light pollution. This could be avoided with an adequate operational politic to detect possible interference between the laser and the astronomical telescopes. In this paper is analysed the mathematical probability of a cross-event happen.

  8. Near infra-red astronomy with adaptive optics and laser guide stars at the Keck Observatory

    SciTech Connect

    Max, C.E.; Gavel, D.T.; Olivier, S.S.

    1995-08-03

    A laser guide star adaptive optics system is being built for the W. M. Keck Observatory`s 10-meter Keck II telescope. Two new near infra-red instruments will be used with this system: a high-resolution camera (NIRC 2) and an echelle spectrometer (NIRSPEC). The authors describe the expected capabilities of these instruments for high-resolution astronomy, using adaptive optics with either a natural star or a sodium-layer laser guide star as a reference. They compare the expected performance of these planned Keck adaptive optics instruments with that predicted for the NICMOS near infra-red camera, which is scheduled to be installed on the Hubble Space Telescope in 1997.

  9. Initial results from the Lick Observatory Laser Guide Star Adaptive Optics System

    SciTech Connect

    Olivier, S.S.; An, J.; Avicola, K.

    1995-11-08

    A prototype adaptive optics system has been installed and tested on the 3 m Shane telescope at Lick Observatory. The adaptive optics system performance, using bright natural guide stars, is consistent with expectations based on theory. A sodium-layer laser guide star system has also been installed and tested on the Shane telescope. Operating at 15 W, the laser system produces a 9th magnitude guide star with seeing-limited size at 589 nm. Using the laser guide star, the adaptive optics system has reduced the wavefront phase variance on scales above 50 cm by a factor of 4. These results represent the first continuous wavefront phase correction using a sodium-layer laser guide star. Assuming tip-tilt is removed using a natural guide star, the measured control loop performance should produce images with a Strehl ratio of 0.4 at 2.2 {mu}m in 1 arc second seeing. Additional calibration procedures must be implemented in order to achieve these results with the prototype Lick adaptive optics system.

  10. Improved performance of the laser guide star adaptive optics system at Lick Observatory

    SciTech Connect

    An, J R; Avicola, K; Bauman, B J; Brase, J M; Campbell, E W; Carrano, C; Cooke, J B; Freeze, G J; Friedman, H W; Max, C E; Gates, E L; Gavel, D T; Kanz, V K; Kuklo, T C; Macintosh, B A; Newman, M J; Olivier, S S; Pierce, E L; Waltjen, K E; Watson, A

    1999-07-20

    Results of experiments with the laser guide star adaptive optics system on the 3-meter Shane telescope at Lick Observatory have demonstrated a factor of 4 performance improvement over previous results. Stellar images recorded at a wavelength of 2 {micro}m were corrected to over 40% of the theoretical diffraction-limited peak intensity. For the previous two years, this sodium-layer laser guide star system has corrected stellar images at this wavelength to {approx}10% of the theoretical peak intensity limit. After a campaign to improve the beam quality of the laser system, and to improve calibration accuracy and stability of the adaptive optics system using new techniques for phase retrieval and phase-shifting diffraction interferometry, the system performance has been substantially increased. The next step will be to use the Lick system for astronomical science observations, and to demonstrate this level of performance with the new system being installed on the 10-meter Keck II telescope.

  11. First significant image improvement from a sodium-layer laser guide star adaptive optics system at Lick Observatory

    SciTech Connect

    Olivier, S.S.; Max, C.E.; Friedman, H.W.; An, J.; Avicola, K.; Beeman, B.V.; Bissinger, H.D.; Brase, J.M.; Erbert, G.V.; Gavel, D.T.; Kanz, K.; Macintosh, B.; Neeb, K.P.; Waltjen, K.E.

    1997-07-14

    Atmospheric turbulence severely limits the resolution of ground-based telescopes. Adaptive optics can correct for the aberrations caused by the atmosphere, but requires a bright wavefront reference source in close angular proximity to the object being imaged. Since natural reference stars of the necessary brightness are relatively rare, methods of generating artificial reference beacons have been under active investigation for more than a decade. In this paper, we report the first significant image improvement achieved using a sodium-layer laser guide star as a wavefront reference for a high- order adaptive optics system. An artificial beacon was created by resonant scattering from atomic sodium in the mesosphere, at an altitude of 95 km. Using this laser guide star, an adaptive optics system on the 3 m Shane Telescope at Lick Observatory produced a factor of 2.4 increase in peak intensity and a factor of 2 decrease in full width at half maximum of a stellar image, compared with image motion compensation alone. The Strehl ratio when using the laser guide star as the reference was 65% of that obtained with a natural guide star, and the image full widths at half maximum were identical, 0.3 arc sec, using either the laser or the natural guide star. This sodium-layer laser guide star technique holds great promise for the world`s largest telescopes. 24 refs., 4 figs., 1 tab.

  12. Active beam shaping in multiple laser guide stars

    NASA Astrophysics Data System (ADS)

    Jones, Katharine J.

    2012-10-01

    Adaptive beam shaping is a critical part of multiple Laser Guide Stars (LGS) for Multiple Conjugate Adaptive Optics (MCAO) for ground-based astronomical telescopes. There are two kinds of Laser Guide Stars: Na Laser Guide Stars (at 589 nm and 92 km altitude) and Rayleigh Laser Guide Stars (at 532 nm and 20 km altitude). Multiple Conjugate Adaptive Optics (MCAO) corrects for each "layer" of atmosphere independently. Multiple Laser Guide Stars are being developed to achieve a measure of tilt and increase the isoplanatic patch. Multiple Laser Guide Stars are being combined with Multiple Conjugate Optics in the Large Binocular Telescope (LBT): more than one Laser Guide Star (4-5) and two different wavelengths: 589 nm and 532 nm. Other observatories have multiple Laser Guide Stars but only one wavelength: 589 nm or 532 nm. Because Laser Guide Stars are launched into the atmosphere, adaptive beam shaping will be carried out before the laser is launched and will be different depending on which laser is being used, presumably to effect the tightest beam which can be achieved at the power level which is required to provide the requisite return to gound-based wavefront sensors. A complete range of devices are used. Beam attenuation and divergnece will take place. Multiple Laser Guide Stars of major observatories (SOR, LBT, MMT, ESO VLT and Gemini South) will be evaluated for effective adaptive beam shaping and impact on performance

  13. Matera Laser Ranging Observatory (MLRO): An overview

    NASA Technical Reports Server (NTRS)

    Varghese, Thomas K.; Decker, Winfield M.; Crooks, Henry A.; Bianco, Giuseppe

    1993-01-01

    The Agenzia Spaziale Italiana (ASI) is currently under negotiation with the Bendix Field Engineering Corporation (BFEC) of the Allied Signal Aerospace Company (ASAC) to build a state-of-the-art laser ranging observatory for the Centro di Geodesia Spaziale, in Matera, Italy. The contract calls for the delivery of a system based on a 1.5 meter afocal Cassegrain astronomical quality telescope with multiple ports to support a variety of experiments for the future, with primary emphasis on laser ranging. Three focal planes, viz. Cassegrain, Coude, and Nasmyth will be available for these experiments. The open telescope system will be protected from dust and turbulence using a specialized dome which will be part of the building facilities to be provided by ASI. The fixed observatory facility will be partitioned into four areas for locating the following: laser, transmit/receive optics, telescope/dome enclosure, and the operations console. The optical tables and mount rest on a common concrete pad for added mechanical stability. Provisions will be in place for minimizing the effects of EMI, for obtaining maximum cleanliness for high power laser and transmit optics, and for providing an ergonomic environment fitting to a state-of-the-art multipurpose laboratory. The system is currently designed to be highly modular and adaptable for scaling or changes in technology. It is conceived to be a highly automated system with superior performance specifications to any currently operational system. Provisions are also made to adapt and accommodate changes that are of significance during the course of design and integration.

  14. Guide star targeting success for the HEAO-B observatory

    NASA Technical Reports Server (NTRS)

    Farrenkopf, R. L.; Hoffman, D. P.

    1977-01-01

    The statistics associated with the successful selection and acquisition of guide stars as attitude benchmarks for use in reorientation maneuvers of the HEAO-B observatory are considered as a function of the maneuver angle, initial attitude uncertainties, and the pertinent celestial region. Success likelihoods in excess of 0.99 are predicted assuming anticipated gyro and star tracker error sources. The maneuver technique and guide star selection constraints are described in detail. The results presented are specialized numerically to the HEAO-B observatory. However, the analytical techniques developed are considered applicable to broader classes of spacecraft requiring celestial targeting.

  15. Daytime School Guided Visits to an Astronomical Observatory in Brazil

    ERIC Educational Resources Information Center

    Colombo, Pedro Donizete, Jr.; Silva, Cibelle Celestino; Aroca, Silvia Calbo

    2010-01-01

    This article analyzes the activity "Daytime School Guided Visits" at an astronomical observatory in Brazil with pupils from primary school. The adopted research methodology relied on questionnaire applications and semistructured interviews. The objectives were to identify the influences of the visits on learning of astronomical concepts and on…

  16. Recent Science and Engineering Results with the Laser Guidestar Adaptive Optics System at Lick Observatory

    SciTech Connect

    Gavel, D T; Gates, E; Max, C; Olivier, S; Bauman, B; Pennington, D; Macintosh, B; Patience, J; Brown, C; Danforth, P; Hurd, R; Severson, S; Lloyd, J

    2002-10-17

    The Lick Observatory laser guide star adaptive optics system has undergone continual improvement and testing as it is being integrated as a facility science instrument on the Shane 3 meter telescope. Both Natural Guide Star (NGS) and Laser Guide Star (LGS) modes are now used in science observing programs. We report on system performance results as derived from data taken on both science and engineering nights and also describe the newly developed on-line techniques for seeing and system performance characterization. We also describe the future enhancements to the Lick system that will enable additional science goals such as long-exposure spectroscopy.

  17. Multi-task guiding system of the Mt. Suhora Observatory

    NASA Astrophysics Data System (ADS)

    Krzesinski, J.; Wojcik, K.

    1993-12-01

    A short description of the computer controlled guiding system using images from a sensitive TV camera is presented. The system works with a 0.6/7.5 m telescope of Mt. Suhora Observatory and can accept input from any standard video camera. The IBM 286-486 or compatible personal computer equipped with a SVGA graphic card and framegrabber card is used as a control unit. The program works under a DOS operating system. An effect of guiding on the classic photoelectric photometry and CCD image quality is discussed.

  18. Laser guide star measurements at Lawrence Livermore National Laboratory

    SciTech Connect

    Friedman, H.; Avicola, K.; Bissinger, H.; Brase, J.; Duff, J.; Gavel, D.; Horton, J.; Max, C.; Olivier, S.; Rapp, D.; Salmon, T.; Smauley, D.; Waltjen, K.

    1993-02-01

    Recent studies from the Laser Guide Star Project at Lawrence Livermore National Laboratory are presented. Photometry of the return signal has shown that the photon return is approximately 10 photons/cm{sup 2}ms at the pupil of the receiving telescope in agreement with a detailed model of the sodium interaction. Wavefronts of the laser guide star have also been measured with a Shack-Hartmann technique and power spectra have been shown to agree with those of nearby natural stars. Plans for closed loop demonstrations using the laser guide star at LLNL and nearby Lick Observatory are discussed.

  19. Compliance guide for laser products

    SciTech Connect

    Not Available

    1985-09-01

    Manufacturers of products subject to performance standards under the Radiation Control for Health and Safety Act of 1968 are required to furnish various reports to the Center for Devices and Radiological Health (FDA). The guide is for use by manufacturers of lasers and laser products in preparing Initial Reports and Model Change Reports on Lasers and Products Containing Lasers. The publication incorporates changes from the 1985 amendments to the standard and supersedes previous editions.

  20. Diffractively Coupled, Refractively Guided Lasers

    NASA Technical Reports Server (NTRS)

    Katz, Joseph; Cser, Jim; Marshall, William K.

    1987-01-01

    Semiconductor-laser arrays more reliable, more powerful, and easier to make. Improved design intended to eliminate undesired electromagnetic modes and mode shifts sometimes occuring in gain-guided variety. Reflected from mirror/window at end of common resonator section of laser, energy refracted from each laser enters adjacent laser. Mutual coupling establishes phase relationships among lasers. Monolithic laser array made by standard epitaxial techniques. Made in part with polymeric materials to mitigate some deleterious effects of all-expitaxial processing. Potential applications include optical communications, ranging, printing, and recording.

  1. Design and performance of a laser guide star system for the Keck II telescope

    SciTech Connect

    Friedman, H. W., LLNL

    1998-05-18

    A laser system to generate sodium-layer guide stars has been designed, built and delivered to the Keck Observatory in Hawaii. The system uses frequency doubled YAG lasers to pump liquid dye lasers and produces 20 W of average power. The design and performance results of this laser system are presented.

  2. The Central laser facility at the Pierre Auger Observatory

    SciTech Connect

    Arqueros, F.; Bellido, J.; Covault, C.; D'Urso, D.; Di Giulio, C.; Facal, P.; Fick, B.; Guarino, F.; Malek, M.; Matthews, J.A.J.; Matthews, J.; Meyhandan, R.; Monasor, M.; Mostafa, M.; Petrinca, P.; Roberts, M.; Sommers, P.; Travnicek, P.; Valore, L.; Verzi, V.; Wiencke, Lawrence; /Utah U.

    2005-07-01

    The Central Laser Facility is located near the middle of the Pierre Auger Observatory in Argentina. It features a UV laser and optics that direct a beam of calibrated pulsed light into the sky. Light scattered from this beam produces tracks in the Auger optical detectors which normally record nitrogen fluorescence tracks from cosmic ray air showers. The Central Laser Facility provides a ''test beam'' to investigate properties of the atmosphere and the fluorescence detectors. The laser can send light via optical fiber simultaneously to the nearest surface detector tank for hybrid timing analyses. We describe the facility and show some examples of its many uses.

  3. Smithsonian Astrophysical Observatory laser tracking systems

    NASA Technical Reports Server (NTRS)

    Pearlman, M. R.; Lanham, N. W.; Lehr, C. G.; Wohn, J.

    1977-01-01

    The four SAO laser satellite-ranging systems, located in Brazil, Peru, Australia, and Arizona, have been in operation for more than five years and have provided ranging data at accuracy levels of a meter or better. The paper examines system hardware (laser transmitter, the electronics, mount, photoreceiver, minicomputer, and station timing) and software (prediction program, calibration programs, and data handling and quick-look programs) and also considers calibration, station operation, and system performance.

  4. OCDR guided laser ablation device

    DOEpatents

    Dasilva, Luiz B.; Colston, Jr., Bill W.; James, Dale L.

    2002-01-01

    A guided laser ablation device. The device includes a mulitmode laser ablation fiber that is surrounded by one or more single mode optical fibers that are used to image in the vicinity of the laser ablation area to prevent tissue damage. The laser ablation device is combined with an optical coherence domain reflectometry (OCDR) unit and with a control unit which initializes the OCDR unit and a high power laser of the ablation device. Data from the OCDR unit is analyzed by the control unit and used to control the high power laser. The OCDR images up to about 3 mm ahead of the ablation surface to enable a user to see sensitive tissue such as a nerve or artery before damaging it by the laser.

  5. Design of a fieldable laser system for a sodium guide star

    SciTech Connect

    Friedman, H.; Erbert, G.; Kuklo, T.; Salmon, T.; Smauley, D.; Thompson, G.; Wong, Nan

    1994-03-17

    The design and background data for a sodium layer laser guide star system to be installed on the 3 meter telescope at Lick Observatory is presented. A 30 W dye laser at 589 nm and 10 kHz will be mounted on the telescope and will be pumped by fiber coupled frequency doubled YAG laser located in a separate room.

  6. Wavefront Measurement for Laser-Guiding Diagnostic

    SciTech Connect

    Shiraishi, S.; Gonsalves, A. J.; Lin, C.; Nakamura, K.; Osterhoff, J.; Sokollik, T.; van Tilborg, J.; Geddes, C. G. R.; Schroeder, C. B.; Toth, Cs.; Esarey, E.; Leemans, W. P.

    2010-11-04

    The wavefront of a short laser pulse after interaction in a laser-plasma accelerator (LPA) was measured to diagnose laser-guiding quality. Experiments were performed on a 100 TW class laser at the LOASIS facility of LBNL using a hydrogen-filled capillary discharge waveguide. Laser-guiding with a pre-formed plasma channel allows the laser pulse to propagate over many Rayleigh lengths at high intensity and is crucial to accelerate electrons to the highest possible energy. Efficient coupling of laser energy into the plasma is realized when the laser and the channel satisfy a matched guiding condition, in which the wavefront remains flat within the channel. Using a wavefront sensor, the laser-guiding quality was diagnosed based on the wavefront of the laser pulse exiting the plasma channel. This wavefront diagnostic will contribute to achieving controlled, matched guiding in future experiments.

  7. Wavefront Measurement for Laser-Guiding Diagnostic

    SciTech Connect

    University of Chicago; Lawrence Berkeley National Laboratory; Shiraishi, S.; Gonsalves, A. J.; Lin, C.; Nakamura, K.; Osterhoff, J.; Sokollik, T.; Tilborg, J. van; Geddes, C. G. R.; Schroeder, C. B.; Toth, Cs.; Esarey, E.; Leemans, W. P.

    2010-06-01

    The wavefront of a short laser pulse after interaction in a laser-plasma accelerator (LPA) was measured to diagnose laser-guiding quality. Experiments were performed on a 100 TW class laser at the LOASIS facility of LBNL using a hydrogenfilled capillary discharge waveguide. Laser-guiding with a pre-formed plasma channel allows the laser pulse to propagate over many Rayleigh lengths at high intensity and is crucial to accelerate electrons to the highest possible energy. Efficient coupling of laser energy into the plasma is realized when the laser and the channel satisfy a matched guiding condition, in which the wavefront remains flat within the channel. Using a wavefront sensor, the laser-guiding quality was diagnosed based on the wavefront of the laser pulse exiting the plasma channel. This wavefront diagnostic will contribute to achieving controlled, matched guiding in future experiments.

  8. Image improvement from a sodium-layer laser guide star adaptive optics system

    SciTech Connect

    Max, C. E., LLNL

    1997-06-01

    A sodium-layer laser guide star beacon with high-order adaptive optics at Lick Observatory produced a factor of 2.4 intensity increase and a factor of 2 decrease in full width at half maximum for an astronomical point source, compared with image motion compensation alone. Image full widths at half maximum were identical for laser and natural guide stars (0.3 arc seconds). The Strehl ratio with the laser guide star was 65% of that with a natural guide star. This technique should allow ground-based telescopes to attain the diffraction limit, by correcting for atmospheric distortions.

  9. The Central Raman Laser Facility at the Pierre Auger Observatory

    NASA Astrophysics Data System (ADS)

    medina, C.; Mayotte, E.; Wiencke, L. R.; Rizi, V.; Grillo, A.

    2013-12-01

    We describe the newly upgraded Central Raman Laser Facility (CRLF) located close to the center of the Piere Auger observatory (PAO) in Argentina. The CRLF features a Raman Lidar receiver, a 335 nm wavelength solid state laser, a robotic beam energy calibration system, and a weather station, all powered by solar energy and operated autonomously using a single board computer. The system optics are arranged to direct the laser beam into the atmosphere in steered and vertical modes with adjustable polarization settings,and it is measured in a bi-static configuration by the 4 fluorescence stations of the Pierre Auger observatory. Additionally the system optics can be easily switched to provide a fixed vertical beam that is measured by a Raman Lidar receiver in mono-static configuration,allowing an independent measurement of the aerosol optical depth τ(z,t) and other properties of the atmosphere. A description of the CLRF's installation, hardware and software integration, initial operations and examples of data collected, will also be presented.

  10. LIGO - The Laser Interferometer Gravitational-Wave Observatory

    NASA Technical Reports Server (NTRS)

    Abramovici, Alex; Althouse, William E.; Drever, Ronald W. P.; Gursel, Yekta; Kawamura, Seiji; Raab, Frederick J.; Shoemaker, David; Sievers, Lisa; Spero, Robert E.; Thorne, Kip S.

    1992-01-01

    The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics for gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.

  11. Direct observation of laser guided corona discharges.

    PubMed

    Wang, Tie-Jun; Wei, Yingxia; Liu, Yaoxiang; Chen, Na; Liu, Yonghong; Ju, Jingjing; Sun, Haiyi; Wang, Cheng; Lu, Haihe; Liu, Jiansheng; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2015-01-01

    Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere. PMID:26679271

  12. Direct observation of laser guided corona discharges

    NASA Astrophysics Data System (ADS)

    Wang, Tie-Jun; Wei, Yingxia; Liu, Yaoxiang; Chen, Na; Liu, Yonghong; Ju, Jingjing; Sun, Haiyi; Wang, Cheng; Lu, Haihe; Liu, Jiansheng; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2015-12-01

    Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere.

  13. Direct observation of laser guided corona discharges

    PubMed Central

    Wang, Tie-Jun; Wei, Yingxia; Liu, Yaoxiang; Chen, Na; Liu, Yonghong; Ju, Jingjing; Sun, Haiyi; Wang, Cheng; Lu, Haihe; Liu, Jiansheng; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2015-01-01

    Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere. PMID:26679271

  14. Consistency analysis on laser signal in laser guided weapon simulation

    NASA Astrophysics Data System (ADS)

    Yin, Ruiguang; Zhang, Wenpan; Guo, Hao; Gan, Lin

    2015-10-01

    The hardware-in-the-loop simulation is widely used in laser semi-active guidance weapon experiments, the authenticity of the laser guidance signal is the key problem of reliability. In order to evaluate the consistency of the laser guidance signal, this paper analyzes the angle of sight, laser energy density, laser spot size, atmospheric back scattering, sun radiation and SNR by comparing the different working state between actual condition and hardware-in-the-loop simulation. Based on measured data, mathematical simulation and optical simulation result, laser guidance signal effects on laser seeker are determined. By using Monte Carlo method, the laser guided weapon trajectory and impact point distribution are obtained, the influence of the systematic error are analyzed. In conclusion it is pointed out that the difference between simulation system and actual system has little influence in normal guidance, has great effect on laser jamming. The research is helpful to design and evaluation of laser guided weapon simulation.

  15. Implementation of the Chicago sum frequency laser at Palomar laser guide star test bed

    NASA Astrophysics Data System (ADS)

    Velur, Viswa; Kibblewhite, Edward J.; Dekany, Richard G.; Troy, Mitchell; Petrie, Hal L.; Thicksten, Robert P.; Brack, Gary; Trin, Thang; Cheselka, Matthew

    2004-10-01

    Work is underway at the University of Chicago and Caltech Optical Observatories to implement a sodium laser guide star adaptive optics system for the 200 inch Hale telescope at Palomar Observatory. The Chicago sum frequency laser (CSFL) consists of two pulsed, diode-pumped, mode-locked Nd:YAG lasers working at 1.064 micron and 1.32 micron wavelengths. Light from the two laser beams is mixed in a non-linear crystal to produce radiation centered at 589 nm with a spectral width of 1.0 GHz (FWHM) to match that of the Sodium-D2 line. Currently the 1.064 micron and 1.32 micron lasers produce 14 watts and 8 watts of TEM-00 power respectively. The laser runs at 500 Hz rep. rate with 10% duty cycle. This pulse format is similar to that of the MIT-Lincoln labs and allows range gating of unwanted Rayleigh scatter down an angle of 60 degrees to zenith angle. The laser system will be kept in the Coude lab and will be projected up to a laser launch telescope (LLT) bore-sited to the Hale telescope. The beam-transfer optics, which conveys the laser beam from the Coude lab to the LLT, consists of motorized mirrors that are controlled in real time using quad-cell positioning systems. This needs to be done to prevent laser beam wander due to deflections of the telescope while tracking. There is a central computer that monitors the laser beam propagation up to the LLT, the interlocks and safety system status, laser status and actively controls the motorized mirrors. We plan to install a wide-field visible camera (for high flying aircraft) and a narrow field of view (FoV) IR camera (for low-flying aircraft) as part of our aircraft avoidance system.

  16. Laser-guide-stars used for cophasing broad capture ranges

    NASA Astrophysics Data System (ADS)

    Martinez, P.; Janin-Potiron, P.

    2016-08-01

    Context. Segmented primary mirrors are indispensable to master the steady increase in spatial resolution. Phasing optics systems must reduce segment misalignments to guarantee the high optical quality required for astronomical science programs. Aims: Modern telescopes routinely use adaptive optics systems to compensate for the atmosphere and use laser-guide-stars to create artificial stars as bright references in the field of observation. Because multiple laser-guide-star adaptive optics are being implemented in all major observatories, we propose to use man-made stars not only for adaptive optics, but for phasing optics. Methods: We propose a method called the doublet-wavelength coherence technique (DWCT), exploiting the D lines of sodium in the mesosphere using laser guide-stars. The signal coherence properties are then used. Results: The DWCT capture range exceeds current abilities by a factor of 100. It represents a change in paradigm by improving the phasing optics capture range from micrometric to millimetric. It thereby potentially eliminates the need of a man-made mechanical pre-phasing step. Conclusions: Extremely large telescopes require hundreds of segments, several of which need to be substituted on a daily basis to be recoated. The DWCT relaxes mechanical integration requirements and speeds up integration and re-integration process.

  17. Multiple laser guide stars (LGS) for multiple conjugate adaptive optics (MCAO)

    NASA Astrophysics Data System (ADS)

    Jones, Katharine J.

    2012-10-01

    For wavefront sensing and control, the most extensive use of Mult-Conjugate Adaptive Optics (MCAO) systems for extended-path aberration compensation lies with the use of multiple Laser Guide Stars (LGS) for Multi-Conjugate Adaptive Optics (MCAO). Ground-based adaptive optics systems were initially developed by the Starfire Optical Range (SOR) in 1983. Both Rayleigh guide stars and Na guide stars have been developed. More recently, both laser systems, Na LGS at 93 km and Rayleigh guide stars at 20 km, are being combined in the Large Binocular Telescope (LBT) for multiple LGS for Multiple Conjugate Adaptive Optics (MCAO) (M. Hart et al, 2011). Each side of the LBT has 3 Rayleigh LGS which are projected into two triangular constellations. A sodium LGS will be added to each aperture using the same launch optics as the Rayleigh beacons. This will combine low altitude Rayleigh LGS and high altitude Na laser guide stars into a uniquely powerful tomographic wavefront sensing system for Multi-Conjugate Adaptive Optics. Other observatories have used either Rayleigh guide stars or Na guide stars. ESO VLT has 4 Na LGS. MMT has 5 Rayleigh guide stars. Gemini Multi-Conjugate Adaptive Optics System (GEMS) has 5 Na LGS. The many multiple LGS MCAO observatories will be compared for effective design and projected performance.

  18. Laser guiding for GeV laser-plasma accelerators.

    PubMed

    Leemans, Wim; Esarey, Eric; Geddes, Cameron; Schroeder, Carl; Tóth, Csaba

    2006-03-15

    Guiding of relativistically intense laser beams in preformed plasma channels is discussed for development of GeV-class laser accelerators. Experiments using a channel guided laser wakefield accelerator at Lawrence Berkeley National Laboratory (LBNL) have demonstrated that near mono-energetic 100 MeV-class electron beams can be produced with a 10 TW laser system. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator, together with loading of the accelerating structure with beam, is the key to production of mono-energetic electron beams. Increasing the energy towards a GeV and beyond will require reducing the plasma density and design criteria are discussed for an optimized accelerator module. The current progress and future directions are summarized through comparison with conventional accelerators, highlighting the unique short-term prospects for intense radiation sources based on laser-driven plasma accelerators. PMID:16483950

  19. AFIRE: fiber Raman laser for laser guide star adaptive optics

    NASA Astrophysics Data System (ADS)

    Bonaccini Calia, D.; Hackenberg, W.; Chernikov, S.; Feng, Y.; Taylor, L.

    2006-06-01

    Future adaptive optics systems will benefit from multiple sodium laser guide stars in achieving satisfactory sky coverage in combination with uniform and high-Strehl correction over a large field of view. For this purpose ESO is developing with industry AFIRE, a turn-key, rack-mounted 589-nm laser source based on a fiber Raman laser. The fiber laser will deliver the beam directly at the projector telescope. The required output power is in the order of 10 W in air per sodium laser guide star, in a diffraction-limited beam and with a bandwidth of < 2 GHz. This paper presents the design and first demonstration results obtained with the AFIRE breadboard. 4.2W CW at 589nm have so far been achieved with a ~20% SHG conversion efficiency.

  20. Laser Guiding for GeV Laser-Plasma Accelerators

    SciTech Connect

    Leemans, Wim; Esarey, Eric; Geddes, Cameron; Schroeder, C.B.; Toth, Csaba

    2005-06-06

    Guiding of relativistically intense laser beams in preformed plasma channels is discussed for development of GeV-class laser accelerators. Experiments using a channel guided laser wakefield accelerator (LWFA) at LBNL have demonstrated that near mono-energetic 100 MeV-class electron beams can be produced with a 10 TW laser system. Analysis, aided by particle-in-cell simulations, as well as experiments with various plasma lengths and densities, indicate that tailoring the length of the accelerator, together with loading of the accelerating structure with beam, is the key to production of mono-energetic electron beams. Increasing the energy towards a GeV and beyond will require reducing the plasma density and design criteria are discussed for an optimized accelerator module. The current progress and future directions are summarized through comparison with conventional accelerators, highlighting the unique short term prospects for intense radiation sources based on laser-driven plasma accelerators.

  1. Image improvement from a sodium-layer laser guide star adaptive optics system

    SciTech Connect

    Max, C.E.; Olivier, S.S.; Friedman, H.W.

    1997-09-12

    A sodium-layer laser guide star beacon with high-order adaptive optics at Lick Observatory (Mount Hamilton, California) produced a factor of 2.4 intensity increase and a factor of 2 decrease in full width at half maximum for an astronomical point source, compared with image motion compensation alone. The image full widths at half maximum were identical for laser and natural guide stars (0.3 arc second). The Strehl ratio with the laser guide star was 65 percent of that with a natural guide star. This technique should allow ground-based telescopes to attain the diffraction limit, by correcting for atmospheric distortions. 21 refs., 4 figs., 1 tab.

  2. Coupling coefficient of gain-guided lasers

    NASA Technical Reports Server (NTRS)

    Katz, J.; Kapon, E.; Lindsey, C.; Margalit, S.; Yariv, A.

    1984-01-01

    An analytical model is presented for the coupling coefficient for two gain-guided coupled waveguides, e.g., semiconductor laser arrays. A common parabolic gain distribution is assumed for the lasers, and the effective dielectric constant distribution is approximated in terms of the bulk refraction index, wavelength, power filling factor, and the antiguiding factor. The fundamental mode is then formulated and used in an integral for the coupling coefficient. The dependence of the coefficient of various waveguide parameters is described.

  3. Guided transmission for 10 micron tunable lasers

    NASA Technical Reports Server (NTRS)

    Yu, C.; Sabzali, A.; Yekrangian, A.

    1986-01-01

    Performance characteristics are reported for two types of IR tunable laser guided transmission, one of which incorporates a CO2 laser, metallic piping or fiber-optics, and a detector system, while the other employs a tunable diode laser, fiber-optics, and a detector system. While existing technology furnishes low loss, rugged, near-single mode piping, fiber-optics exhibits appreciably higher loss, and its multimode fibers are fragile and chemically unstable. Studies have accordingly concentrated on such relevant fiber parameters as loss, toxicity, hygroscopicity, refractive index, flexibility, and thermal behavior at low temperature.

  4. Water jet guided laser versus saw dicing

    NASA Astrophysics Data System (ADS)

    Dushkina, Natalia M.; Wagner, Frank R.; Boillat, Christophe; Buchilly, Jean-Marie; Richerzhagen, Bernold

    2003-07-01

    The incessantly growing demands for higher speed of the wireless telecommunications and more compact devices require using of thin compound semiconductor wafers. The dicing is the very last process of the wafer manufacturing. At this stage the IC pattern is completely built up and the wafer has the highest value. Therefore, the goal of the singulation process is to provide the highest possible throughput. The conventional saw techniques "struggle" at their speed limits, while the conventional laser is not an appropriate dicing tool due to the strong thermal effect and big heat affected zones. The water-jet guided laser technology provides cool laser dicing since the laser is coupled in a fine stable water-jet and conducted to the work piece by means of total internal reflection like through an optical fiber, as the relatively low water pressure (10 - 30 MPa) of the tiny jet with diameter 40 - 100 μm results in a negligible force on the sample. This technology provides higher cutting speeds and burr-free kerf quality. By means of the Laser MicroJet, wafers as thin as 25 μm could be diced in streets of 50 μm width, with almost 100% wafer throughput. Here we compare the water-jet guided laser cutting with conventional techniques for dicing of thin semiconductor wafers. The results for Silicon and GaAs/Ge wafers are discussed in terms of speed, kerf quality and die fracture strength.

  5. Plasma channel guided laser wakefield accelerator

    NASA Astrophysics Data System (ADS)

    Geddes, Cameron Guy Robinson

    2005-11-01

    High quality electron beams (several 109 electrons above 80 MeV energy with percent energy spread and low divergence) have been produced for the first time in a compact, high gradient, all-optical laser accelerator by extending the interaction distance using a pre-formed plasma density channel to guide the drive laser pulse. Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (wake) driven by the radiation pressure of an intense laser, have over the past decade demonstrated accelerating fields thousands of times greater than those achievable in conventional radio-frequency accelerators. This has spurred interest in them as compact next-generation sources of energetic electrons and radiation. To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance resulted in low-energy beams with 100 percent electron energy spread, which has limited potential applications. Optical guiding of relativistically intense (>1018 W/cm 2) laser pulses over distances greater than 10 diffraction lengths is demonstrated herein using plasma channels, which have a density minimum on the axis of propagation, formed by hydrodynamic shock. Laser modes with peak powers of up to 4 TW---twice the self-guiding threshold---were guided without aberration by tuning the plasma density profile. The transmitted optical spectrum showed that the pulse remained in the channel over the entire length, and no accelerated electrons were observed at these powers. Simulations indicated that a large plasma wave was driven by the 4 TW pulse, indicating a possible dark current free structure for a laser wakefield accelerator using controlled injection. The presence of a large plasma wave was verified by increasing laser power and observing electron acceleration. At a guided drive pulse power of 9 TW (500 mJ in 50 fs

  6. Synchronization of Geodetic Observatories thanks to Time Transfer by Laser Link

    NASA Astrophysics Data System (ADS)

    Belli, Alexandre; Exertier, Pierre; Samain, Etienne; Vernotte, François

    2015-08-01

    Since 2008, the Time Transfer by Laser Link experiment (T2L2) onboard Jason-2 at 1336 km allows the clock synchronization by an optical link between ground clocks (generally H-maser) and the space instrument. The space segment includes roughly a detector, a timer, a frequency reference (Ultra Stable Oscillator, USO, provided by the DORIS system) and a Laser Reflector Array. Taking into account the current precision and accuracy of the laser ranging technology and the specifications of the space instrument, the stability of the ground to space time transfer is established at a few picoseconds (ps) over 100 seconds. The combination of any two ground stations (from the International Laser Ranging network) referred to their H-maser clock provides, in common view, a very stable ground to ground time transfer of 10 ps over the common pass (around 10 minutes). The accuracy, of around 100 ps between two time calibrated observatories, is demonstrated thanks to several experiments and a rigourous error budget. However, several geodetic observatories reveal to have a time shift of hundreds of nanoseconds, between their local time reference system and UTC. In order to provide geodetic observatories with a unique time reference frame we used the T2L2 instrument to transfer time in the non-common view mode, all around the international laser network.We show that T2L2 is able to provide accurate frequencies, which are deduced from the ground to space time transfers over each laser station at a few 10-13. Thanks to this monitoring of the frequency variations of the onboard oscillator, we established a physical model to be integrated over 10,000 seconds (around one orbital revolution). This model is built by considering all observatories, weighted by the accuracy of their ground clock. The Grasse geodetic observatory is used to calibrate the model because it is bring back to UTC thanks to a permanent GPS link calibrated tothe Paris Observatory (UTC(OP)). By applying this model, we

  7. Compact Fiber Laser for 589nm Laser Guide Star Generation

    NASA Astrophysics Data System (ADS)

    Pennington, D.; Drobshoff, D.; Mitchell, S.; Brown, A.

    Laser guide stars are crucial to the broad use of astronomical adaptive optics, because they facilitate access to a large fraction of possible locations on the sky. Lasers tuned to the 589 nm atomic sodium resonance can create an artificial beacon at altitudes of 95-105 km, thus coming close to reproducing the light path of starlight. The deployment of multiconjugate adaptive optics on large aperture telescopes world-wide will require the use of three to nine sodium laser guide stars in order to achieve uniform correction over the aperture with a high Strehl value. Current estimates place the minimum required laser power at > 10 W per laser for a continuous wave source, though a pulsed format, nominally 6?s in length at ~ 16.7 kHz, is currently preferred as it would enable tracking the laser through the Na layer to mitigate spot elongation. The lasers also need to be compact, efficient, robust and turnkey. We are developing an all-fiber laser system for generating a 589 nm source for laser-guided adaptive optics. Fiber lasers are more compact and insensitive to alignment than their bulk laser counterparts, and the heat-dissipation characteristics of fibers, coupled with the high efficiencies demonstrated and excellent spatial mode characteristics, make them a preferred candidate for many high power applications. Our design is based on sum-frequency mixing an Er/Yb:doped fiber laser operating at 1583 nm with a 938 nm Nd:silica fiber laser in a periodically poled crystal to generate 589 nm. We have demonstrated 14 W at 1583 nm with an Er/Yb:doped fiber laser, based on a Koheras single frequency fiber oscillator amplified in an IPG Photonics fiber amplifier. The Nd:silica fiber laser is a somewhat more novel device, since the Nd3+ ions must operate on the resonance transition (i.e. 4F3/2-4I9/2), while suppressing ASE losses at the more conventional 1088 nm transition. Optimization of the ratio of the fiber core and cladding permits operation of the laser at room

  8. Guide star lasers for adaptive optics

    NASA Astrophysics Data System (ADS)

    Roberts, William Thomas, Jr.

    Exploitation of the imaging capabilities of the new generation of ground-based astronomical telescopes relies heavily on Adaptive Optics (AO). Current AO system designs call for sodium guide star lasers capable of producing at least eight Watts of power tuned to the peak of the sodium D2 line, with a high duty cycle to avoid saturation, and with 0.5-1.0 GHz spectral broadening. This work comprises development and testing of six candidate laser systems and materials which may afford a path to achieving these goals. An end-pumped CW dye laser producing 4.0 Watts of tuned output power was developed and used to obtain the first accurate measurement of sodium layer scattering efficiency. Methods of optimizing the laser output through improving pump overlap efficiency and reducing the number of intracavity scattering surfaces are covered. The 1181 nm fluorescence peak of Mn5+ ion in Ba5 (PO4)3Cl could be tuned and doubled to reach 589 nm. While efforts to grow this crystal were under way, the Mn5+ ion in natural apatite (Ca5(PO4)3F) was studied as a potential laser material. Fluorescence saturation measurements and transmission saturation are presented, as well as efforts to obtain CW lasing in natural apatite. A Q-switched laser color-center laser in LiF : F-2 was developed and successfully tuned and doubled to the sodium D 2 line. Broad-band lasing of 80 mW and tuned narrow-band lasing of 35 mW at 1178 nm were obtained with 275 mW of input pump power at 1064 nm. The measured thermal properties of this material indicate its potential for scaling to much higher power. A Q-switched intracavity Raman laser was developed in which CaWO 4 was used to shift a Nd:YAG laser, the frequency-doubled output of which was centered at 589.3 nm. To obtain light at 589.0 nm, a compositionally tuned pump laser of Nd : Y3Ga1.1Al3.9O 12 was produced which generated the desired shift, but was inhomogeneous broadened, limiting the tunable power of the material. Finally, temperature tuning of

  9. MLRS - A lunar/artificial satellite laser ranging facility at the McDonald Observatory

    NASA Technical Reports Server (NTRS)

    Shelus, P. J.

    1985-01-01

    Experience from lunar and satellite laser ranging experiments carried out at McDonald Observatory has been used to design the McDonald Laser Ranging Station (MLRS). The MLRS is a dual-purpose installation designed to obtain observations from the LAGEOS satellite and lunar targets. The instruments used at the station include a telescope assembly 0.76 meters in diameter; a Q-switched doubled neodymium YAG laser with a pulse rate of three nanoseconds; and a GaAs photodetector with Fabry-Perot interferometric filter. A functional diagram of the system is provided. The operating parameters of the instruments are summarized in a table.

  10. The Laser Interferometer Gravitational-Wave Observatory: Lasers at the Frontiers of Astrophysics

    NASA Astrophysics Data System (ADS)

    Reitze, David

    2005-04-01

    The Laser Interferometric Gravitational-Wave Observatory (LIGO) is poised to open a new window on the universe - the detection of gravitational waves from distant large-scale astrophysical sources. Gravitational waves were predicted by Einstein almost 90 years ago but never been observed directly despite a number of experiments over the last 40 years. While there exists strong indirect evidence for gravitational waves, it is only with the construction of large-scale high precision interferometers that direct detection of gravitational waves is possible. Gravitational waves are miniscule dynamic strains applied to space-time by motion of massive astrophysical objects. A passing gravitational wave will expand and contract the distance between two mirrors (`test masses') in the arms of an interferometer. Direct observation of gravitational waves presents a formidable challenge, because the magnitude of the dynamic strain is expected to be infinitesimal, less than one part in 10-22. The astrophysical motivation for detecting gravitational waves is compelling. Unlike the visible sky, the gravitational wave `sky' is completely unexplored. The LIGO detectors and its partner GEO600 in Europe have the sensitivity to observe gravitational waves not only in our own galaxy, but in neighboring galaxies, thus opening an absolutely unique window into these phenomena. In the first part of the presentation, we will give an overview of gravitational waves - what they are and where they come from -- and describe in general terms the techniques that gravitational wave astrophysicists use to hunt for them. In the second part of the presentation, we describe the LIGO interferometers emphasizing the critical role that lasers and optics play in its operation.

  11. Electromagnetically Induced Guiding of Counter-propagating Lasers in Plasmas

    SciTech Connect

    First Author = G. Shvets; A. Pukhov

    1998-05-01

    The interaction of counter-propagating laser pulses in a plasma is considered. When the frequencies of the two lasers are close, nonlinear modification of the refraction index results in the mutual focusing of the two beams. A short (of order the plasma period) laser pulse can also be nonlinearly focused by a long counter-propagating beam which extends over the entire guiding length. This phenomenon of electromagnetically induced guiding can be utilized in laser-driven plasma accelerators.

  12. Laser guide star adaptive optics: Present and future

    SciTech Connect

    Olivier, S.S.; Max, C.E.

    1993-03-01

    Feasibility demonstrations using one to two meter telescopes have confirmed the utility of laser beacons as wavefront references for adaptive optics systems. Laser beacon architectures suitable for the new generation of eight and ten meter telescopes are presently under study. This paper reviews the concept of laser guide star adaptive optics and the progress that has been made by groups around the world implementing such systems. A description of the laser guide star program at LLNL and some experimental results is also presented.

  13. Analytical model for ring heater thermal compensation in the Advanced Laser Interferometer Gravitational-wave Observatory.

    PubMed

    Ramette, Joshua; Kasprzack, Marie; Brooks, Aidan; Blair, Carl; Wang, Haoyu; Heintze, Matthew

    2016-04-01

    Advanced laser interferometer gravitational-wave detectors use high laser power to achieve design sensitivity. A small part of this power is absorbed in the interferometer cavity mirrors where it creates thermal lenses, causing aberrations in the main laser beam that must be minimized by the actuation of "ring heaters," which are additional heater elements that are aimed to reduce the temperature gradients in the mirrors. In this article we derive the first, to the best of our knowledge, analytical model of the temperature field generated by an ideal ring heater. We express the resulting optical aberration contribution to the main laser beam in this axisymmetric case. Used in conjunction with wavefront measurements, our model provides a more complete understanding of the thermal state of the cavity mirrors and will allow a more efficient use of the ring heaters in the Advanced Laser Interferometer Gravitational-wave Observatory. PMID:27139664

  14. Laser beam riding guided system principle and design research

    NASA Astrophysics Data System (ADS)

    Qu, Zhou; Jin, Yi; Xu, Zhou; Xing, Hao

    2016-01-01

    With the development of science and technology, precision-strike weapons has been considered to be important for winning victory in military field. Laser guidance is a major method to execute precision-strike in modern warfare. At present, the problems of primary stage of Laser guidance has been solved with endeavors of countries. Several technical aspects of laser-beam riding guided system have been mature, such as atmosphere penetration of laser beam, clutter inhibition on ground, laser irradiator, encoding and decoding of laser beam. Further, laser beam quality, equal output power and atmospheric transmission properties are qualified for warfare situation. Riding guidance instrument is a crucial element of Laser-beam riding guided system, and is also a vital element of airborne, vehicle-mounted and individual weapon. The optical system mainly consist of sighting module and laser-beam guided module. Photoelectric detector is the most important sensing device of seeker, and also the key to acquire the coordinate information of target space. Currently, in consideration of the 1.06 u m of wavelength applied in all the semi-active laser guided weapons systems, lithium drifting silicon photodiode which is sensitive to 1.06 u m of wavelength is used in photoelectric detector. Compared to Solid and gas laser, diode laser has many merits such as small volume, simple construction, light weight, long life, low lost and easy modulation. This article introduced the composition and operating principle of Laser-beam riding guided system based on 980 nm diode laser, and made a analysis of key technology; for instance, laser irradiator, modulating disk of component, laser zooming system. Through the use of laser diode, Laser-beam riding guided system is likely to have smaller shape and very light.

  15. Laser guide stars and adaptive optics for astronomy

    SciTech Connect

    Max, C.E.

    1992-07-15

    Five papers are included: feasibility experiment for sodium-alyer laser guide stars at LLNL; system design for a high power sodium beacon laser; sodium guide star adaptive optics system for astronomical imaging in the visible and near-infrared; high frame-rate, large field wavefront sensor; and resolution limits for ground-based astronomical imaging. Figs, tabs, refs.

  16. Adaptive Optics with Sodium Laser Guide Stars

    NASA Astrophysics Data System (ADS)

    Lloyd-Hart, M.; Angel, J. R. P.; Jacobsen, B.; Wittman, D.; McCarthy, D.; Martinez, T.

    1994-12-01

    Adaptive optics requires a reference source of light in the sky to measure wavefront aberration introduced by atmospheric turbulence. Natural stars are ideal for this purpose, but the density of bright stars is not sufficient to provide complete sky coverage. The problem can be overcome with an artificial beacon generated from resonant backscattering off mesospheric sodium atoms exited by a low-power laser tuned to the D2 resonance. Recent experiments at the Multiple Mirror Telescope (MMT) have demonstrated for the first time that an adaptive optics system using a sodium laser guide beacon can be used to improve the imaging quality of the telescope. A beacon of mv = 10.4 was used to control the relative image motion between two of the six apertures of the MMT, while a natural star was used to measure the absolute tilt. A factor of two improvement in the K-band Strehl ratio was measured, and the resolution improved from 0(\\?.58) to 0(\\?.41) . The experiment demonstrated all the features needed for correction of telescopes of 6.5 to 8-m diameter to the diffraction limit in the near infrared with a single sodium laser beacon.

  17. Dynamics of laser-guided alternating current high voltage discharges

    NASA Astrophysics Data System (ADS)

    Daigle, J.-F.; Théberge, F.; Lassonde, P.; Kieffer, J.-C.; Fujii, T.; Fortin, J.; Châteauneuf, M.; Dubois, J.

    2013-10-01

    The dynamics of laser-guided alternating current high voltage discharges are characterized using a streak camera. Laser filaments were used to trigger and guide the discharges produced by a commercial Tesla coil. The streaking images revealed that the dynamics of the guided alternating current high voltage corona are different from that of a direct current source. The measured effective corona velocity and the absence of leader streamers confirmed that it evolves in a pure leader regime.

  18. Laser system design for the generation of a sodium-layer laser guide star

    SciTech Connect

    Friedman, H.W.

    1993-01-01

    The design considerations for a laser system used to generate a sodium-layer guide star are presented. Laser technology developed for the Atomic Vapor Laser Isotope Separation (AVLIS) Program is shown to be directly relevant to this problem and results of a demonstration using the AVLIS laser to generate such a guide star are shown. The design of a compact laser suitable for use at a large telescope such as the Keck is also presented.

  19. Arm locking for space-based laser interferometry gravitational wave observatories

    NASA Astrophysics Data System (ADS)

    Yu, Yinan; Mitryk, Shawn; Mueller, Guido

    2014-09-01

    Laser frequency stabilization is a critical part of the interferometry measurement system of space-based gravitational wave observatories such as the Laser Interferometer Space Antenna (LISA). Arm locking as a proposed frequency stabilization technique transfers the stability of the long arm lengths to the laser frequency. The arm locking sensor synthesizes an adequately filtered linear combination of the interspacecraft phase measurements to estimate the laser frequency noise, which can be used to control the laser frequency. At the University of Florida we developed the hardware-based University of Florida LISA Interferometer Simulator to study and verify laser frequency noise reduction and suppression techniques under realistic LISA-like conditions. These conditions include the variable Doppler shifts among the spacecraft, LISA-like signal travel times, optical transponders, realistic laser frequency, and timing noise. We review the different types of arm locking sensors and discuss their expected performance in LISA. The presented results are supported by results obtained during experimental studies of arm locking under relevant LISA-like conditions. We measured the noise suppression as well as initial transients and frequency pulling in the presence of Doppler frequency errors. This work has demonstrated the validity and feasibility of arm locking in LISA.

  20. Sodium Laser Guide Star Adaptive Optics Imaging Polarimetry of Herbig Ae/Be Stars

    SciTech Connect

    Perrin, M D; Graham, J R; Lloyd, J P; Kalas, P; Gates, E L; Gavel, D T; Pennington, D M; Max, C E

    2004-01-08

    The future of high-resolution ground-based optical and infrared astronomy requires the successful implementation of laser guide star adaptive optics systems. We present the first science results from the Lick Observatory sodium beacon laser guide star system. By coupling this system to a near-infrared (J;H;Ks bands) dual-channel imaging polarimeter, we achieve very high sensitivity to light scattered in the circumstellar enviroment of Herbig Ae/Be stars on scales of 100-300 AU. Observations of LkH{alpha} 198 reveal a highly polarized, biconical nebula 10 arcseconds in diameter (6000 AU) . We also observe a polarized jet-like feature associated with the deeply embedded source LkH{alpha} 198-IR. The star LkH{alpha} 233 presents a narrow, unpolarized dark lane dividing its characteristic butterfly-shaped polarized reflection nebulosity. This linear structure is oriented perpendicular to an optical jet and bipolar cavity and is consistent with the presence of an optically thick circumstellar disk blocking our direct view of the star. These data suggest that the evolutionary picture developed for the lower-mass T Tauri stars is also relevant to the Herbig Ae/Be stars and demonstrate the ability of laser guide star adaptive optics systems to obtain scientific results competitive with natural guide star adaptive optics or space-based telescopes.

  1. Coupling mechanism of gain-guided integrated semiconductor laser arrays

    NASA Technical Reports Server (NTRS)

    Kapon, E.; Lindsey, C.; Margalit, S.; Yariv, A.; Katz, J.

    1984-01-01

    It is shown that a gain-guided laser array couples via propagating fields rather than the evanescent mode coupling typically responsible for directional coupling in passive (directional couplers) and active (laser array) devices. It is shown that these phase-locked modes exhibit an interference pattern, in the junction plane, which arises from the curvature of the phase fronts of optical fields of the interacting lasers. The experimental results are interpreted with the aid of a simple theoretical model, and the effect of the observed mode pattern on the coupling of gain-guided lasers is discussed.

  2. Electromagnetically induced guiding of counterpropagating lasers in plasmas

    SciTech Connect

    Shvets, G.; Pukhov, A.

    1999-01-01

    The interaction of counterpropagating laser pulses in a plasma is considered. When the frequencies of the two lasers are close, nonlinear modification of the refraction index results in the mutual focusing of the two beams. A short (of order of the plasma period) laser pulse can also be nonlinearly focused by a long counterpropagating beam which extends over the entire guiding length. This phenomenon of electromagnetically induced guiding can be utilized in laser-driven plasma accelerators. {copyright} {ital 1999} {ital The American Physical Society}

  3. Cryogenic far-infrared laser absorptivity measurements of the Herschel Space Observatory telescope mirror coatings.

    PubMed

    Fischer, Jacqueline; Klaassen, Tjeerd; Hovenier, Niels; Jakob, Gerd; Poglitsch, Albrecht; Sternberg, Oren

    2004-07-01

    Far-infrared laser calorimetry was used to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 K to simulate the operating temperature of the telescope in its planned orbit about the second Lagrangian point, L2, of the Earth-Sun system. Together, the telescope's equilibrium temperature in space and the emissivity of the mirror surfaces will determine the far-infrared-submillimeter background and thus the sensitivity of two of the three astronomical instruments aboard the observatory if stray-light levels can be kept low relative to the mirror emission. Absorptivities of both clean and dust-contaminated samples were measured at 70, 118, 184, and 496 microm. Theoretical fits to the data predict absorptivities of 0.2-0.4% for the clean sample and 0.2-0.8% for the dusty sample, over the spectral range of the Herschel Space Observatory instruments. PMID:15250543

  4. The study of laser beam riding guided system based on 980nm diode laser

    NASA Astrophysics Data System (ADS)

    Qu, Zhou; Xu, Haifeng; Sui, Xin; Yang, Kun

    2015-10-01

    With the development of science and technology, precision-strike weapons has been considered to be important for winning victory in military field. Laser guidance is a major method to execute precision-strike in modern warfare. At present, the problems of primary stage of Laser guidance has been solved with endeavors of countries. Several technical aspects of laser-beam riding guided system have been mature, such as atmosphere penetration of laser beam, clutter inhibition on ground, laser irradiator, encoding and decoding of laser beam. Further, laser beam quality, equal output power and atmospheric transmission properties are qualified for warfare situation. Riding guidance instrument is a crucial element of Laser-beam riding guided system, and is also a vital element of airborne, vehicle-mounted and individual weapon. The optical system mainly consist of sighting module and laser-beam guided module. Photoelectric detector is the most important sensing device of seeker, and also the key to acquire the coordinate information of target space. Currently, in consideration of the 1.06 u m of wavelength applied in all the semi-active laser guided weapons systems, lithium drifting silicon photodiode which is sensitive to 1.06 u m of wavelength is used in photoelectric detector. Compared to Solid and gas laser, diode laser has many merits such as small volume, simple construction, light weight, long life, low lost and easy modulation. This article introduced the composition and operating principle of Laser-beam riding guided system based on 980 nm diode laser, and made a analysis of key technology; for instance, laser irradiator, modulating disk of component, laser zooming system. Through the use of laser diode, Laser-beam riding guided system is likely to have smaller shape and very light.

  5. Laser guiding at>1018 W/cm2 in plasma channels formed by theignitor heater method

    SciTech Connect

    Geddes, C.G.R.; Toth, C.; vanTilborg, J.; Leemans, W.P.

    2004-05-01

    Experiments explore guiding of intense laser pulses, optimization using channel formation beams and gas jet targets, and the interplay of channel guiding and relativistic self guiding. Impact on laser wakefield particle acceleration is being assessed.

  6. Guiding of relativistic laser pulses by preformed plasmachannels

    SciTech Connect

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

    2004-12-10

    Guiding of relativistically intense (>1018 W/cm2) laser pulses over more than 10 diffraction lengths has been demonstrated using plasma channels formed by hydrodynamic shock. Pulses up to twice the self guiding threshold power were guided without aberration by tuning the guide profile. Transmitted spectra and mode images showed the pulse remained in the channel over the entire length. Experiments varying guided mode power and simulations show a large plasma wave was driven.Operating just below the trapping threshold produces a dark current free structure suitable for controlled injection.

  7. The Laser Guide Star System for Adaptive Optics at Subaru Telescope

    NASA Astrophysics Data System (ADS)

    Hayano, Y.; Saito, Y.; Ito, M.; Saito, N.; Akagawa, K.; Takazawa, A.; Ito, M.; Wada, S.; Takami, H.; Iye, M.

    -power laser beam with no suffer from the non-linear scatter effect, i.e. stimulated Brillouin scatter, in the PCF. The laser launching telescope (LLT) has an output clear aperture as 50 cm. It is classical Cassegrain type optical configuration with tertiary mirror to insert the laser beam from the side. The wavefront error is designed to be 60 to 70nm. The LLT is a copy product what European Southern Observatory has been designed for the laser guide star system at Very Large Telescope. We succeeded to launch the laser beam to the sky on October 12, 2006. After several tests on the sky, we succeeded to get an image of the laser guide star with the size of more than 10 arc second. The larger size of the laser guide star is caused by the large optical aberration on the primary mirror of LLT due to the heat stress generated at the trigonal support points. We are making a plan to repair this problem during June and the second laser launching test will start around this summer.

  8. Robust remote-pumping sodium laser for advanced LIDAR and guide star applications

    NASA Astrophysics Data System (ADS)

    Ernstberger, Bernhard; Enderlein, Martin; Friedenauer, Axel; Schwerdt, Robin; Wei, Daoping; Karpov, Vladimir; Leisching, Patrick; Clements, Wallace R. L.; Kaenders, Wilhelm G.

    2015-10-01

    The performance of large ground-based optical telescopes is limited due to wavefront distortions induced by atmospheric turbulence. Adaptive optics systems using natural guide stars with sufficient brightness provide a practical way for correcting the wavefront errors by means of deformable mirrors. Unfortunately, the sky coverage of bright stars is poor and therefore the concept of laser guide stars was invented, creating an artificial star by exciting resonance fluorescence from the mesospheric sodium layer about 90 km above the earth's surface. Until now, mainly dye lasers or sumfrequency mixing of solid state lasers were used to generate laser guide stars. However, these kinds of lasers require a stationary laser clean room for operation and are extremely demanding in maintenance. Under a development contract with the European Southern Observatory (ESO) and W. M. Keck Observatory (WMKO), TOPTICA Photonics AG and its partner MPB Communications have finalized the development of a next-generation sodium guide star laser system which is available now as a commercial off-the-shelf product. The laser is based on a narrow-band diode laser, Raman fiber amplifier (RFA) technology and resonant second-harmonic generation (SHG), thus highly reliable and simple to operate and maintain. It emits > 22 W of narrow-linewidth (≈ 5 MHz) continuous-wave radiation at sodium resonance and includes a re-pumping scheme for boosting sodium return flux. Due to the SHG resonator acting as spatial mode filter and polarizer, the output is diffraction-limited with RMS wavefront error < λ/25. Apart from this unique optical design, a major effort has been dedicated to integrating all optical components into a ruggedized system, providing a maximum of convenience and reliability for telescope operators. The new remote-pumping architecture allows for a large spatial separation between the main part of the laser and the compact laser head. Together with a cooling-water flow of less than 5 l

  9. Wide baseline optical interferometry with Laser Guide Stars

    SciTech Connect

    Gavel, D. T., LLNL

    1998-03-01

    Laser guide stars have been used successfully as a reference source for adaptive optics systems. We present a possible method for utilizing laser beacons as sources for interferometric phasing. The technique would extend the sky coverage for wide baseline interferometers and allow interferometric measurement and imaging of dim objects.

  10. Laser systems for the generation of sodium layer guide stars

    SciTech Connect

    Friedman, H.; Erbert, G.; Kuklo, T.; Salmon, T.; Thompson, G.; Wong, N.; Malik, J.

    1996-03-05

    Laser generated guide stars in the mesosphere at 90 km provide an effective beacon for adaptive optics schemes which compensate the effects of atmospheric turbulence. This report discusses the attributes of the laser systems which are desirable from a point of view of overall adaptive optics system performance and operation ease.

  11. Desing of a Laser Guide Star System for the Keck II Telescope

    SciTech Connect

    Friedman, H.W.; Erbert, G.V.; Kuklo, T.; Thompson, G.R.; Wong, N.J.; Gavel, D.T.; Salmon, J.T.; Feldman, M.

    1997-09-11

    A laser guide star system similar to that deployed at the Lick Observatory has been designed for the Keck II 10 m telescope on Mauna Kea, Hawaii. The subaperature size on the primary is comparable to that at Lick, and at the same observational wavelength centered about the K band, so that the average power requirements of the laser system are also comparable, at about 20 W. One major difference is that the seeing at Mauna Kea is about a factor of two better than at Lick so that the spot diameter requirements are smaller and this can give rise to reduced back scatter resulting from saturation effects in the sodium layer. To reduce the peak flux in the sodium layer and obtain a smaller spot diameter, the output beam diameter has been increased along with the repetition rate of the laser. As with the Lick laser system, a dye laser is pumped by a series of frequency doubled YAG lasers which are remotely located and coupled to the dye laser on the telescope by optical fibers. The laser system has a full set of beam control optics as well as launch telescope and safety systems. A computer system couples the laser system to the User Interface and Supervisory Control system of the main telescope. The laser system is due to be shipped to Keck during the fall of 1997 where it will be integrated with the telescope at Mauna Kea. The Adaptive Optics and Optics Bench systems will be integrated first and be ready for integration with the laser in the summer of 1998. 1 ref., 8 figs.

  12. Guiding effect of quantum wells in semiconductor lasers

    SciTech Connect

    Aleshkin, V Ya; Dikareva, Natalia V; Dubinov, A A; Zvonkov, B N; Karzanova, Maria V; Kudryavtsev, K E; Nekorkin, S M; Yablonskii, A N

    2013-05-31

    The guiding effect of InGaAs quantum wells in GaAs- and InP-based semiconductor lasers has been studied theoretically and experimentally. The results demonstrate that such waveguides can be effectively used in laser structures with a large refractive index difference between the quantum well material and semiconductor matrix and a large number of quantum wells (e.g. in InP-based structures). (semiconductor lasers. physics and technology)

  13. Indication of Local Laser Pump Depletion via Transmitted Self-Guided Laser Light

    SciTech Connect

    Pak, A. E.; Marsh, K. A.; Ralph, J. E.; Lu, W.; Clayton, C. E.; Joshi, C.

    2009-01-22

    In recent experiments it has been shown that an ultra-intense, ultra-short laser pulse can be self-guided over tens of Rayleigh lengths in an underdense plasma where {tau}(FWHM of the laser pulse) is on the order of the plasma wavelength ({lambda}{sub p}). Using an imaging spectrograph, the frequency of the transmitted laser pulse was spatially and spectrally resolved at the exit of 3, 5, and 8 mm long plasmas. The mechanism of laser pump depletion was studied by observing the amount that the transmitted laser pulse's spectrum was red shifted in wavelength through the interaction with the self-guiding plasma wave.

  14. Status of the GRAAL system development: very wide-field correction with 4 laser guide-stars

    NASA Astrophysics Data System (ADS)

    Paufique, J.; Argomedo, J.; Arsenault, R.; Conzelmann, R.; Donaldson, R.; Hubin, N.; Jochum, L.; Jost, A.; Kiekebusch, M.; Kolb, J.; Kuntschner, H.; Le Louarn, M.; Madec, P.-Y.; Siebenmorgen, R.; Tordo, S.

    2012-07-01

    We recall the design and present the development status of GRAAL, the Ground-layer adaptive optics assisted by Laser, which will deliver wide-field (10 arcmin), enhanced images to the HAWK-I instrument on the VLT, with an improved seeing. GRAAL is an adaptive optics module, part of the Adaptive optics facility (AOF), using four Laser- and one natural guide-stars to measure the turbulence, and correcting for it by deforming the adaptive secondary mirror of a Unit telescope in the Paranal observatory. GRAAL is in the laboratory in Europe and the integration of its laser guide-star optics is completed. The first wave-front sensor camera will be ready for its integration in the coming weeks, allowing the first system tests to start.

  15. Improving sodium laser guide star brightness by polarization switching.

    PubMed

    Fan, Tingwei; Zhou, Tianhua; Feng, Yan

    2016-01-01

    Optical pumping with circularly polarized light has been used to enhance the brightness of sodium laser guide star. But the benefit is reduced substantially due to the precession of sodium atoms in geomagnetic field. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to improve the return. With ESO's laser guide star system at Paranal as example, numerical simulation shows that the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 50% at 90°. The proposal is significant since most astronomical observation is at angle between 60° and 90° and it only requires a minor addition to the delivery optics of present laser system. PMID:26797503

  16. Improving sodium laser guide star brightness by polarization switching

    PubMed Central

    Fan, Tingwei; Zhou, Tianhua; Feng, Yan

    2016-01-01

    Optical pumping with circularly polarized light has been used to enhance the brightness of sodium laser guide star. But the benefit is reduced substantially due to the precession of sodium atoms in geomagnetic field. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to improve the return. With ESO’s laser guide star system at Paranal as example, numerical simulation shows that the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 50% at 90°. The proposal is significant since most astronomical observation is at angle between 60° and 90° and it only requires a minor addition to the delivery optics of present laser system. PMID:26797503

  17. Laser guide star experiment at Lawrence Livermore National Laboratory

    SciTech Connect

    Max, C.E.; Friedman, H.W.; Brase, J.B.; Avicola, K.; Bissinger, H.; Gavel, D.T.; Horton, J.A.; Morris, J.R.; Olivier, S.S.; Presta, R.W.; Rapp, D.A.; Salmon, T.J.; Waltjen, K.

    1993-01-01

    An overview of the Laser Guide Star feasibility experiment at Lawrence Livermore National Laboratory is presented. The goal of the project is to demonstrate a closed-loop adaptive optics system using a sodium-layer laser guide star to correct wavefront aberrations caused by atmospheric turbulence. The laser beam is projected upwards from a beam director located 5 meters from a half-meter telescope and forms a spot about 2 meters in diameter in the mesospheric sodium layer at an altitude of about 95 km. The laser beam is approximately fifth magnitude and is visible to the unaided eye at the top of the Rayleigh-scattered laser beam. A Shack-Hartmann wave front sensor measures the aberrated wave front and a continuous sheet deformable mirrow will correct the wave front in a closed loop control system at a bandwidth fast enough to follow changes in the atmosphere. In this paper, the authors present an overview of the methodology for the design of the experiment and the requirements of the laser source. The long term goal of this effort is to develop laser guide stars and adaptive optics for large astronomical telescopes and to this end, a summary of laser issues relevant to future sites is presented.

  18. Polarization competition in quasi-index-guided laser diodes

    SciTech Connect

    Amann, M.; Stegmueller, B.

    1988-03-15

    The mechanism of polarization competition in laser diodes with a lateral quasi-index-guiding (QIG) structure is analyzed generally by way of the effective index approximation using a simplified QIG laser model. The influence of the relevant waveguide parameters on the polarization-dependent threshold current of QIG laser diodes is investigated in detail by example of lambda = 1.3-..mu..m ridge-waveguide lasers. Thereby, it is found that for intermediate values of the effective index step, the TM mode exhibits a higher gain and lower threshold current, whereas for pure gain guiding or strong index guiding, the TE mode prevails. This behavior, which compares excellently to published experimental results, is proven as a basic feature of the two-dimensional waveguiding mechanism in QIG devices. Accordingly, the effect of stress-induced anisotropy of the optical gain has been found to be of minor importance as the origin for TM-polarized QIG lasers made from lattice-matched heterostructures. It is further demonstrated that, for certain device parameters, the QIG lasers with a small effective index step exhibit somewhat higher threshold currents than the purely gain-guided devices of identical geometry.

  19. Guide for preparing initial reports and model change reports on lasers and products containing lasers

    SciTech Connect

    Not Available

    1985-09-01

    Manufacturers of products subject to performance standards under the Radiation Control for Health and Safety Act of 1968 are required to furnish various reports to the Center for Devices and Radiological Health (FDA). The guide is for use by manufacturers of lasers and products containing lasers in preparating initial and model change reports. The format of the guide incorporates changes from the 1985 amendments to the standard and supersedes previous editions. Much of the instructional material for use in completing this form has been moved to the companion publication Compliance Guide for Laser Products.

  20. MRI-guided laser ablation of neuroendocrine tumor hepatic metastases

    PubMed Central

    Perälä, Jukka; Klemola, Rauli; Kallio, Raija; Li, Chengli; Vihriälä, Ilkka; Salmela, Pasi I; Tervonen, Osmo

    2014-01-01

    Background Neuroendocrine tumors (NET) represent a therapeutically challenging and heterogeneous group of malignancies occurring throughout the body, but mainly in the gastrointestinal system. Purpose To describe magnetic resonance imaging (MRI)-guided laser ablation of NET liver metastases and assess its role within the current treatment options and methods. Material and Methods Two patients with NET tumor hepatic metastases were treated with MRI-guided interstitial laser ablation (LITT). Three tumors were treated. Clinical follow-up time was 10 years. Results Both patients were successfully treated. There were no local recurrences at the ablation site during the follow-up. Both patients had survived at 10-year follow-up. One patient is disease-free. Conclusion MRI-guided laser ablation can be used to treat NET tumor liver metastases but combination therapy and a rigorous follow-up schedule are recommended. PMID:24778794

  1. Sodium laser guide star system at Lawrence Livermore National Laboratory: System description and experimental results

    SciTech Connect

    Avicola, K.; Brase, J.; Morris, J.

    1994-03-02

    The architecture and major system components of the sodium-layer kw guide star system at LLNL will be described, and experimental results reported. The subsystems include the laser system, the beam delivery system including a pulse stretcher and beam pointing control, the beam director, and the telescope with its adaptive-optics package. The laser system is one developed for the Atomic Vapor Laser Isotope Separation (AVLIS) Program. This laser system can be configured in various ways in support of the AVLIS program objectives, and was made available to the guide star program at intermittent times on a non-interference basis. The first light transmitted into the sky was in July of 1992, at a power level of 1. 1 kW. The laser pulse width is about 32 ns, and the pulse repetition rate was 26 kHz for the 1. 1 kW configuration and 13 kHz for a 400 W configuration. The laser linewidth is tailored to match the sodium D{sub 2} absorption line, and the laser system has active control of beam pointing and wavefront quality. Because of the short pulse length the sodium transition is saturated and the laser power is not efficiently utilized. For this reason a pulse stretcher was developed, and the results of this effort will be reported. The beam is delivered via an evacuated pipe from the laser building to the guide star site, a distance of about 100 meters, and then launched vertically. A beam director provides the means to track the sky in the full AO system, but was not used in the experiments reported here. The return signal is collected by a 1/2 meter telescope with the AO package. This telescope is located 5 meters from the km launch tube. Smaller packages for photometry, wavefront measurement, and spot image and motion analysis have been used. Although the unavailability of the AVLIS laser precluded a full AO system demonstration, data supporting feasibility and providing input to the system design for a Lick Observatory AO system was obtained.

  2. 75 FR 76015 - Compliance Policy Guide Sec. 393.200 Laser(s) as Medical Devices for Facelift, Wrinkle Removal...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-07

    ... the Federal Register of August 9, 2010 (75 FR 48180 at 48233), FDA included the Compliance Policy... HUMAN SERVICES Food and Drug Administration Compliance Policy Guide Sec. 393.200 Laser(s) as Medical... Administration (FDA) is announcing the withdrawal of Compliance Policy Guide Sec. 393.200 Laser(s) as...

  3. The laser guide star program for the LBT

    NASA Astrophysics Data System (ADS)

    Rabien, S.; Ageorges, N.; Angel, R.; Brusa, G.; Brynnel, J.; Busoni, L.; Davies, R.; Deysenroth, M.; Esposito, S.; Gässler, W.; Genzel, R.; Green, R.; Haug, M.; Lloyd Hart, M.; Hölzl, G.; Masciadri, E.; Pogge, R.; Quirrenbach, A.; Rademacher, M.; Rix, H. W.; Salinari, P.; Schwab, C.; Stalcup, T., Jr.; Storm, J.; Strüder, L.; Thiel, M.; Weigelt, G.; Ziegleder, J.

    2008-07-01

    Laser guide star adaptive optics and interferometry are currently revolutionizing ground-based near-IR astronomy, as demonstrated at various large telescopes. The Large Binocular Telescope from the beginning included adaptive optics in the telescope design. With the deformable secondary mirrors and a suite of instruments taking advantage of the AO capabilities, the LBT will play an important role in addressing major scientific questions. Extending from a natural guide star based system, towards a laser guide stars will multiply the number of targets that can be observed. In this paper we present the laser guide star and wavefront sensor program as currently being planned for the LBT. This program will provide a multi Rayleigh guide star constellation for wide field ground layer correction taking advantage of the multi object spectrograph and imager LUCIFER in a first step. The already foreseen upgrade path will deliver an on axis diffraction limited mode with LGS AO based on tomography or additional sodium guide stars to even further enhance the scientific use of the LBT including the interferometric capabilities.

  4. Smithsonian Astrophysical Observatory's minicomputer vs. the laser. [computer predictions for laser tracking stations

    NASA Technical Reports Server (NTRS)

    Cherniack, J. R.

    1973-01-01

    Review of some of the problems encountered in replacing a CDC 6400, that was used for supplying a network of laser tracking stations with predictions, by an 8K Data General 1200 minicomputer with a teletype for I/O. Before the replacement, the predictions were expensive to compute and to transmit, and were clumsy logistically. The achieved improvements are described, along with every step it took to accomplish them, and the incurred costs.

  5. A sodium laser guide star coupling efficiency measurement method

    NASA Astrophysics Data System (ADS)

    Feng, Lu; Shen, Zhi-Xia; Xue, Suijian; Li, Yang-Peng; Jin, Kai; Otarola, Angel; Bo, Yong; Zuo, Jun-Wei; Bian, Qi; Wei, Kai; Hu, Jing-Yao

    2016-09-01

    A large telescope's adaptive optics (AO) system requires one or more bright artificial laser guide stars to improve its sky coverage. The recent advent of a high power sodium laser is perfect for such application. However, besides the output power, other parameters of the laser also have a significant impact on the brightness of the generated sodium laser guide star, mostly in non-linear relationships. When tuning and optimizing these parameters it is necessary to tune based on a laser guide star generation performance metric. Although return photon fluxis widely used, variability of the atmosphere and sodium layer makes it difficult to compare results from different sites or even within a short time period for the same site. A new metric, coupling efficiency, is adopted in our field tests. In this paper, we will introduce our method for measuring the coupling efficiency of a 20W class pulse sodium laser for AO application during field tests that were conducted during 2013–2015.

  6. Sodium-layer laser-guide-star experimental results

    SciTech Connect

    Avicola, K.; Brase, J.M.; Morris, J.R.

    1994-02-01

    The authors describe a series of experiments to characterize the sodium-layer guide star that was formed with the highpower laser developed for the Lawrence Livermore National Laboratory Atomic Vapor Laser Isotope Separation program. An emission spot size of 3.0 m was measured, with an implied laser irradiance spot diameter of 2.0 m. The rms spot motion at the higher laser powers, with active beam-pointing control, was less than 0.5 arcsec and had little effect on the observed spot size under these conditions. The authors measured the resonant backscatter from the sodium layer as a function of laser power to obtain a saturation curve. With a transmitted power of 1100 W and an atmospheric transmission of 0.6, the irradiance from the guide star at the ground was 10 (photons/cm{sup 2})/ms, corresponding to a visual magnitude of 5.1. The implications for the performance of wave-front sensors with a laser guide star of this magnitude and resulting closed-loop adaptive-optics performance are discussed. 13 refs., 9 figs.

  7. Diffused guides for distributed-feedback lasers

    NASA Technical Reports Server (NTRS)

    Elachi, C.

    1975-01-01

    Proposed waveguide is hollow cylindrical pipe. Inside channel surface is infused with gas or metal molecules, forming periodic cross sections along entire length. Light is scattered at periodic infusions, resulting in distributed feedback. Configuration is suited for capillary gas lasers.

  8. [Laser navigation guided cleft lip repair].

    PubMed

    Bing, Shi

    2016-06-01

    A new method using the ideal mid-facial line as the navigating reference was introduced to improve the outcome of cleft lip repair. Using the verticle coordinate crossing the middle point of the intercanthus line, surgeons could observe and correct the distortion of the fine structures in labial-nasal area. This laser projecting mid-facial-line navigation was repeatable, while not interfere the operating. In conclusion, generalizing laser navigation is a valuable supplementary for cleft lip repair. PMID:27526442

  9. Transurethral ultrasound-guided laser-induced prostatectomy

    NASA Astrophysics Data System (ADS)

    Babayan, Richard K.; Roth, Robert A.

    1991-07-01

    A transurethral ultrasound-guided Nd:YAG laser delivery system has been developed for use as an alternative approach to the treatment of benign prostatic hyperplasia. The TULIP system has been extensively tested in canine models and is currently undergoing FDA trials in humans.

  10. Observing techniques for astronomical laser guide star adaptive optics

    SciTech Connect

    Max, C.E.; Macintosh, B.; Olivier, S.S.; Gavel, D.T.; Friedman, H.W.

    1998-05-01

    We discuss astronomical observing requirements and their implementation using sodium-layer laser guide star adaptive optics. Specific issues requiring implementation include the ability to place the astronomical object at different locations within the field of view; reliable subtraction of Rayleigh-scattered light; efficient focusing; and stable point-spread-function characterization.

  11. Laser Electro-Optic Technology. Florida Vocational Program Guide.

    ERIC Educational Resources Information Center

    University of South Florida, Tampa. Dept. of Adult and Vocational Education.

    This program guide identifies primary considerations in the organization, operation, and evaluation of a laser electro-optic technology program. An occupational description and program content are presented. A curriculum framework specifies the exact course title, course number, levels of instruction, major course content, laboratory activities,…

  12. Laser Electro-Optic Engineering Technology. Florida Vocational Program Guide.

    ERIC Educational Resources Information Center

    University of South Florida, Tampa. Dept. of Adult and Vocational Education.

    This program guide identifies particular considerations in the organization, operation, and evaluation of laser electro-optic engineering technology programs. Contents include an occupational description and information on the following: program content, including a curriculum framework that details major concepts and intended outcomes and a list…

  13. Tesla coil discharges guided by femtosecond laser filaments in air

    NASA Astrophysics Data System (ADS)

    Brelet, Yohann; Houard, Aurélien; Arantchouk, Leonid; Forestier, Benjamin; Liu, Yi; Prade, Bernard; Carbonnel, Jérôme; André, Yves-Bernard; Mysyrowicz, André

    2012-04-01

    A Tesla coil generator was designed to produce high voltage pulses oscillating at 100 kHz synchronisable with a nanosecond temporal jitter. Using this compact high voltage generator, we demonstrate reproducible meter long discharges in air at a repetition rate of 1 Hz. Triggering and guiding of the discharges are performed in air by femtosecond laser filaments.

  14. Laser needle guide for the sonic flashlight.

    PubMed

    Wang, David; Wu, Bing; Stetten, George

    2005-01-01

    We have extended the real-time tomographic reflection display of the Sonic Flashlight to a laser guidance system that aims to improve safety and accuracy of needle insertion, especially for deep procedures. This guidance system is fundamentally different from others currently available. Two low-intensity lasers are mounted on opposite sides of a needle aimed parallel to the needle. The needle is placed against a notch in the Sonic Flashlight mirror such that the laser beams reflect off the mirror to create bright red spots on the flat panel display. Due to diffuse reflection from these spots, the virtual image created by the flat panel display contains the spots, identifying the projected destination of the needle at its actual location in the tissue. We have implemented our design and validated its performance, identifying several areas for potential improvement. PMID:16685901

  15. Experimental studies of laser guiding in plasma channels

    SciTech Connect

    Volfbeyn, P.; Leemans, W.P.

    1998-07-01

    The authors present results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme is proposed and experimentally tested in hydrogen and nitrogen. It makes use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows, creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a > 5 {times} 10{sup 17} W/cm{sup 2}, 75 fs laser pulse.

  16. Recent developments in aircraft protection systems for laser guide star operations

    NASA Astrophysics Data System (ADS)

    Stomski, Paul J.; Murphy, Thomas W.; Campbell, Randy

    2012-07-01

    The astronomical community's use of high power laser guide star adaptive optics (LGS-AO) systems presents a potential hazard to aviation. Historically, the most common and trusted means of protecting aircraft and their occupants has been the use of safety observers (aka spotters) armed with shut-off switches. These safety observers watch for aircraft at risk and terminate laser propagation before the aircraft can be adversely affected by the laser. Efforts to develop safer and more cost-effective automated aircraft protection systems for use by the astronomical community have been inhibited by both technological and regulatory challenges. This paper discusses recent developments in these two areas. Specifically, with regard to regulation and guidance we discuss the 2011 release of AS-6029 by the SAE as well as the potential impact of RTCA DO-278A. With regard to the recent developments in the technology used to protect aircraft from laser illumination, we discuss the novel Transponder Based Aircraft Detection (TBAD) system being installed at W. M. Keck Observatory (WMKO). Finally, we discuss our strategy for evaluating TBAD compliance with the regulations and for seeking appropriate approvals for LGS operations at WMKO using a fully automated, flexibly configured, multi-tier aircraft protection system incorporating this new technology.

  17. 25 W Raman-fiber-amplifier-based 589 nm laser for laser guide star.

    PubMed

    Feng, Yan; Taylor, Luke R; Calia, Domenico Bonaccini

    2009-10-12

    We report on a 25 W continuous wave narrow linewidth (< 2.3 MHz) 589 nm laser by efficient (> 95%) coherent beam combination of two narrow linewidth (< 1.5 MHz) Raman fiber amplifiers with a Mach-Zehnder interferometer scheme and frequency doubling in an external resonant cavity with an efficiency of 86%. The results demonstrate the narrow linewidth Raman fiber amplifier technology as a promising solution for developing laser for sodium laser guide star adaptive optics. PMID:20372636

  18. Guiding cold atoms in a hollow laser beam

    NASA Astrophysics Data System (ADS)

    Xu, Xinye; Minogin, V. G.; Lee, Kwanil; Wang, Yuzhu; Jhe, Wonho

    1999-12-01

    The theory of atom guiding in a far blue-detuned hollow laser beam (HLB) is developed for the dipole interaction scheme described by a three-level Λ model. The complete kinetic description of atomic motion based on the Fokker-Planck equation for the atomic distribution function is presented. The dipole gradient force, radiation pressure force, and momentum diffusion tensor are then derived. It is found that even for a far-detuned laser beam, the optical potential for a three-level Λ atom is not generally reduced to a sum of two independent potentials associated with the two two-level interactions in the Λ scheme. The theory developed here is also compared with the experimental guiding of cold 85Rb atoms in the HLB. The experimental results are found to be in good agreement with the Monte Carlo simulations based on the three-level Λ model. We observe that the guiding efficiency depends strongly on the intensity and the detuning of the HLB and the initial temperature of atoms. In particular, the experimental results show that, at small detunings, the guiding efficiency is deteriorated strongly by the radiation pressure force. The Monte Carlo simulations also indicate that the efficiency of guiding versus detuning depends strongly on the direction of the HLB propagation with respect to that of atomic motion. Under optimal conditions, the guiding efficiency was found to be about 20%.

  19. Performance results on the laser portion of the Keck laser guide star system

    SciTech Connect

    Cooke, J B; Danforth, P M; Erbert, G V; Feldman, M; Friedman, H W; Gavel, D T; Jenkins, S L; Jones, H E; Kanz, V K; Kuklo, T; Newman, M J; Pierce, E L; Presta, R W; Salmon, J T; Thompson, G R; Wong, N J

    1998-09-29

    The Laser Guide Star (LGS) system for the Keck II, 10 m telescope consists of two separate but interconnected systems, the laser and the adaptive optics bench. The laser portion of the LGSl is a set of five frequency doubled YAG lasers pumping a master oscillator-power amplifier dye chain to produce up to 30 W of 589 p at 26 kHz of tuned light. Presently the laser system has been set up at the Keck facility in Waimea, HI and is undergoing test and evaluation. When it will be set up on the Keck II telescope, the pump lasers, dye master oscillator and associated control equipment will be located on the dome floor and the dye laser amplifiers, beam control system and diagnostics will be mounted directly on the telescope as shown in Fig. 1, Extensive use of fiber optics for both transmission of the oscillator pulse and the pump laser light has been used.

  20. Laser Triggered Electron Injection into a Channel Guided Wakefield Accelerator

    NASA Astrophysics Data System (ADS)

    Nakamura, K.; Filip, C.

    2005-10-01

    Laser-plasma accelerators have demonstrated the generation of narrow energy spread (˜ few %) electron beams with considerable amount of charge (>100 pC). Stability of laser-plasma accelerators, as in the conventional accelerators, requires highly synchronized injection of electrons into the structured accelerating field. The Colliding Pulse Method[1] with pre-formed plasma channel guiding [2] can result in jitter-free injection in a dark-current-free accelerating structure. We report on experimental progress of laser triggered injection of electrons into a laser wakefield, where an intense laser pulse is guided by a pre-formed plasma channel. The experiments use the multi-beam, multi-terawatt Ti:Al2O3 laser at LOASIS facility of LBNL. The ignitor-heater method is used to first produce a pre-formed plasma channel in a hydrogen gas jet. Two counter propagating beams (wakefield driver:100-500mJ-50fs, injector:50-300mJ-50fs) then are focused onto the entrance of the channel. Preliminary results indicate that electron beam properties are affected by the second beam. Details of the experiment will be presented. [1]G.Fubiani, et al, Phys. Rev. E 70, 016402 (2004). [2]C.G.R. Geddes et al, Nature 431, 538 (2004). This work is supported by DoE under contract DE-AC02-05CH11231.

  1. Research aims at development of laser-guided electron beam

    NASA Astrophysics Data System (ADS)

    Kozicharow, E.

    1985-02-01

    The U.S. Department of Defense is conducting a technology development program that may result in the stationing of a laser-guided electron beam weapon, at ionospheric altitudes of 80-600 km, for the interception and destruction of Soviet ICBMs at ranges of more than 1000 miles. This research program is pursuing the principle of ion-focused propagation, which resolves the problem of atmospheric beam scattering by ionizing a channel in the atmospheric medium with a laser. Also discussed is the development status of space-based particle beams and lasers, ground-based laser systems employing orbiting mirror platforms for beam aiming, and nuclear device-powered directed energy weapons.

  2. Precise Gravity Measurements for Lunar Laser Ranging at Apache Point Observatory

    NASA Astrophysics Data System (ADS)

    Crossley, D. J.; Murphy, T.; Boy, J.; De Linage, C.; Wheeler, R. D.; Krauterbluth, K.

    2012-12-01

    Lunar Laser Ranging (LLR) at Apache Point Observatory began in 2006 under the APOLLO project using a 3.5 m telescope on a 2780 m summit in New Mexico. Recent improvements in the technical operations are producing uncertainties at the few-mm level in the 1.5 x 10^13 cm separation of the solar orbits of the Earth and Moon. This level of sensitivity permits a number of important aspects of gravitational theory to be tested. Among these is the Equivalence Principle that determines the universality of free fall, tests of the time variation of the Gravitational Constant G, deviations from the inverse square law, and preferred frame effects. In 2009 APOLLO installed a superconducting gravimeter (SG) on the concrete pier under the main telescope to further constrain the deformation of the site as part of an initiative to improve all aspects of the modeling process. We have analyzed more than 3 years of high quality SG data that provides unmatched accuracy in determining the local tidal gravimetric factors for the solid Earth and ocean tide loading. With on-site gravity we have direct measurements of signals such as polar motion, and can compute global atmospheric and hydrological loading for the site using GLDAS and local hydrology models that are compared with the SG observations. We also compare the SG residuals with satellite estimates of seasonal ground gravity variations from the GRACE mission. Apache Point is visited regularly by a team from the National Geospatial-Intelligence Agency to provide absolute gravity values for the calibration of the SG and to determine secular gravity changes. Nearby GPS location P027 provides continuous position information from the Plate Boundary Observatory of Earthscope that is used to correlate gravity/height variations at the site. Unusual aspects of the data processing include corrections for the telescope azimuth that appear as small offsets at the 1 μGal level and can be removed by correlating the azimuth data with the SG

  3. Photon Return On-Sky Test of Pulsed Sodium Laser Guide Star with D2b Repumping

    NASA Astrophysics Data System (ADS)

    Jin, Kai; Wei, Kai; Feng, Lu; Bo, Yong; Zuo, JunWei; Li, Min; Fu, HanChu; Dai, XiaoLin; Bian, Qi; Yao, Ji; Xu, Chang; Wang, ZhiChao; Peng, QingJun; Xue, XiangHui; Cheng, XueWu; Rao, ChangHui; Xu, ZuYan; Zhang, YuDong

    2015-08-01

    Sodium laser guide star (LGS) system has become one of the critical components in modern astronomical adaptive optics system (AOS), especially for the next-generation extremely large telescopes, such as the Thirty Meter Telescope and the European Extremely Large Telescope. Since the wavefront detection performance of AOS is directly related to the brightness of LGS, it is important for AOS to maximize its photon generation efficiency by all means. Sodium D2b line repumping is such a technique that can greatly increase the returned photons for either sodium continuous wave (CW) laser or pulsed laser. This technique has been studied theoretically and field tested with a 20 W CW laser by European Southern Observatory team. However, field test results of a 20 W class pulsed laser with D2b repumping have not been reported yet. In this paper, our latest field test results with theoretical comparison of D2b repumping with a 20 W quasi-continuous wave (QCW) pulsed laser will be presented. With a linearly polarized beam, approximate 40% photon return enhancement was achieved when 10% of laser power was detuned to D2b line, which agreed well with results from a rate equation-based Monte Carlo photon return simulation program. Both experiment and simulation results indicate that with a higher laser intensity projected at the sodium layer, the D2b repumping will be more effective.

  4. Guiding of laser beams in plasmas by electromagnetic cascade compression

    NASA Astrophysics Data System (ADS)

    Kalmykov, S.; Shvets, G.

    2006-10-01

    The near-resonant beatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few- femtosecond electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red- and blue-shifted by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser phase, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. Thus, a train of high intensity radiation spikes with continually evolving longitudinal profile can be self- guided over several Rayleigh lengths in homogeneous plasma. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW show that achieving GeV energy is possible under realistic experimental conditions.

  5. Guiding of Laser Beams in Plasmas by Radiation Cascade Compression

    NASA Astrophysics Data System (ADS)

    Kalmykov, Serguei; Shvets, Gennady

    2006-11-01

    The near-resonant heatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few-fs electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the beat frequency. Consequently, the cascade of sidebands red- and blue-shifted from the fundamental by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion [S. Kalmykov and G. Shvets, Phys. Rev. E 73, 046403 (2006)]. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser frequency, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the multi-frequency laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. A train of high-intensity radiation spikes with continually evolving longitudinal profile can be self-guided over several Rayleigh lengths in homogeneous plasmas. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW [using the code WAKE by P. Mora and T. M. Antonsen Jr., Phys. Plasmas 4, 217 (1997)] show that achieving GeV electron energy is possible under realistic experimental parameters.

  6. Guiding of Laser Beams in Plasmas by Radiation Cascade Compression

    SciTech Connect

    Kalmykov, Serguei; Shvets, Gennady

    2006-11-27

    The near-resonant heatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few-fs electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the beat frequency. Consequently, the cascade of sidebands red- and blue-shifted from the fundamental by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion [S. Kalmykov and G. Shvets, Phys. Rev. E 73, 046403 (2006)]. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser frequency, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the multi-frequency laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. A train of high-intensity radiation spikes with continually evolving longitudinal profile can be self-guided over several Rayleigh lengths in homogeneous plasmas. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW [using the code WAKE by P. Mora and T. M. Antonsen Jr., Phys. Plasmas 4, 217 (1997)] show that achieving GeV electron energy is possible under realistic experimental parameters.

  7. New process for screen cutting: water-jet guided laser

    NASA Astrophysics Data System (ADS)

    Perrottet, Delphine; Amorosi, Simone; Richerzhagen, Bernold

    2005-07-01

    Today's OLED manufacturers need high-precision, fast tools to cut the metal screens used to deposit the electroluminescent layers onto the substrate. Conventional methods -tching and dry laser cutting - are not satisfying regarding the demands of high-definition OLED displays. A new micro machining technology, the water jet guided laser - a hybrid of laser and water jet technologies that has been actively used in recent years in the electronic and semiconductor field - is now available to OLED manufacturers. This technology represents a significant improvement in screen, mask and stencil cutting, as it combines high precision and high speed. It is able to cut small apertures with totally clean edges (no dross or slag), as the water jet removes the particles and a thin water film is maintained on the material surface during the process. Because the water jet cools the material between the laser pulses, the cut material is free of any thermal stress. The water jet guided laser is also a very fast process: as an example, rectangular slots can be cut in 30 to 50 microns thick stainless steel or nickel at a rate between 25'000 and 30'000 holes per hour.

  8. Fluorescence enhancing mechanism of optical repumping in sodium atoms for brighter laser guide star.

    PubMed

    Lihang, Li; Wang, Hongyan; Hua, Weihong; Ning, Yu; Xu, Xiaojun

    2016-04-01

    With quantum Bloch equations and sodium cell based experiment, we systematically resolved optical repumping mechanism of sodium atoms, a path to brighter sodium laser guide star (SLGS) that would be accepted by worldwide observatories. Besides the former studies, we detailed the population distribution of sodium atoms with and without repumping, which makes the repumping mechanism easy to understand. Experimental results based on a buffer gas free sodium cell and a single frequency laser implies that the optimum repumping frequency offset is 1712 MHz, and the repumping power fraction should be 10-18%. The light intensity depended character of repumping is also carried out. We learned that future SLGS pumped by higher effective light intensity would benefit more from repumping. To the best of our knowledge, this is the first systematic investigation of repumping mechanism using a single mode sum-frequency laser, which gives thorough support for previous numerical work and shows that the lab bench experiment could be used as an intermediate link between theoretical modeling and on-sky test. PMID:27136991

  9. High-gain reverse guide field free electron lasers

    SciTech Connect

    Tsui, K.H.

    1995-10-01

    Electron beam trajectories under circularly polarized external wigglers in free electron laser devices with axial guide fields are reconsidered by introducing the self-fields of the electron beam. The competition between the self-fields and the wiggler field plus the action of the guide field are not only responsible for the known positive guide field singularity, but also the new reverse guide field singularity. The physics of the new reverse field singularity relies on the fact that an azimuthal magnetic field uniform in {ital z} is able to generate steady-state helical beam orbits just as if it were a transverse wiggler. According to this theory, the handness of the circularly polarized microwave should depend on the guide field configuration. High-gain strong pump equations coupled to these trajectories are used to account for the Massachusetts Institute of Technology reverse guide field results [Phys. Rev. Lett. {bold 67}, 3082 (1991)]. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  10. Microfluidics-Based Laser Guided Cell-Micropatterning System

    PubMed Central

    Erdman, Nick; Schmidt, Lucas; Qin, Wan; Yang, Xiaoqi; Lin, Yongliang; DeSilva, Mauris N; Gao, Bruce Z.

    2014-01-01

    The ability to place individual cells into an engineered microenvironment in a cell-culture model is critical for the study of in vivo-relevant cell-cell and cell-extracellular matrix interactions. Microfluidics provides a high-throughput modality to inject various cell types into a microenvironment. Laser guided systems provide the high spatial and temporal resolution necessary for single-cell micropatterning. Combining these two techniques, the authors designed, constructed, tested, and evaluated 1) a novel removable microfluidics-based cell-delivery biochip and 2) a combined system that uses the novel biochip coupled with a laser guided cell-micropatterning system to place individual cells into both 2D and 3D arrays. Cell-suspensions of chick forebrain neurons and glial cells were loaded into their respective inlet reservoirs and traversed the microfluidic channels until reaching the outlet ports. Individual cells were trapped and guided from the outlet of a microfluidic channel to a target site on the cell-culture substrate. At the target site, 2D and 3D pattern arrays were constructed with micron-level accuracy. Single-cell manipulation was accomplished at a rate of 150 μm/s in the radial plane and 50 μm/s in the axial direction of the laser beam. Results demonstrated that a single-cell can typically be patterned in 20-30 seconds, and that highly accurate and reproducible cellular arrays and systems can be achieved through coupling the microfluidics-based cell-delivery biochip with the laser guided system. PMID:25190714

  11. Guiding-center equations for electrons in ultraintense laser fields

    SciTech Connect

    Moore, J.E.; Fisch, N.J.

    1994-01-01

    The guiding-center equations are derived for electrons in arbitrarily intense laser fields also subject to external fields and ponderomotive forces. Exhibiting the relativistic mass increase of the oscillating electrons, a simple frame-invariant equation is shown to govern the behavior of the electrons for sufficiently weak background fields and ponderomotive forces. The parameter regime for which such a formulation is valid is made precise, and some predictions of the equation are checked by numerical simulation.

  12. Guiding-center equations for electrons in ultraintense laser fields

    SciTech Connect

    Moore, J.E.; Fisch, N.J. )

    1994-05-01

    The guiding-center equations are derived for electrons in arbitrarily intense laser fields also subject to external fields and ponderomotive forces. Exhibiting the relativistic mass increase of the oscillating electrons, a simple frame-invariant equation is shown to govern the behavior of the electrons for sufficiently weak background fields and ponderomotive forces. The parameter regime for which such a formulation is valid is made precise, and some predictions of the equation are checked by numerical simulation.

  13. Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars.

    PubMed

    Marc, Fabien; Guillet de Chatellus, Hugues; Pique, Jean-Paul

    2009-03-30

    The possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis. PMID:19333251

  14. ARGOS: the laser guide star system for the LBT

    NASA Astrophysics Data System (ADS)

    Rabien, S.; Ageorges, N.; Barl, L.; Beckmann, U.; Blümchen, T.; Bonaglia, M.; Borelli, J. L.; Brynnel, J.; Busoni, L.; Carbonaro, L.; Davies, R.; Deysenroth, M.; Durney, O.; Elberich, M.; Esposito, S.; Gasho, V.; Gässler, W.; Gemperlein, H.; Genzel, R.; Green, R.; Haug, M.; Hart, M. L.; Hubbard, P.; Kanneganti, S.; Masciadri, E.; Noenickx, J.; Orban de Xivry, G.; Peter, D.; Quirrenbach, A.; Rademacher, M.; Rix, H. W.; Salinari, P.; Schwab, C.; Storm, J.; Strüder, L.; Thiel, M.; Weigelt, G.; Ziegleder, J.

    2010-07-01

    ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.

  15. Experimental research on water-jet guided laser processing

    NASA Astrophysics Data System (ADS)

    Li, Ling; Wang, Yang; Yang, Lijun; Chu, Jiecheng

    2007-01-01

    The water-jet guided laser processing is a new compound micro-machining process in which the laser beam passes through the water-jet by full reflection onto the workpiece. In this paper, a new key component:the coupling unit was designed and which would form a long, slim, high-pressure and stable water-jet. The couple unit made the fluid field in the chamber symmetry; the coupling quality of the laser beam and the water-jet could be easily detected by CCD camera. For its excellent surface quality, the nozzle with a \\fgr 0.18mm hole got better machining effect than other nozzles. Aiming at finding optimum machining parameters, experiments were carried out. The results showed the attenuation of laser energy bore relation to water-jet stability. The energy intensity distributed over the water-jet cross section nearly homogeneous and the laser energy nearly did not decrease in long working distance. When water-jet pressure was high, efficient cooling of the workpiece prevented burrs, cracks and heat affected zone from forming. During cutting Si wafer process, nearly no cracking was found; Adjusting reasonable laser parameters grooving 65Mn, the machining accuracy would combine with the speed.

  16. Return flux budget of polychromatic laser guide stars.

    PubMed

    Guillet de Chatellus, Hugues; Pique, Jean-Paul; Moldovan, Ioana Cristina

    2008-02-01

    The polychromatic laser guide star (PLGS) is one of the solutions proposed to extend the sky coverage by large telescopes to 100% by enabling a complete knowledge of all perturbation orders of the wavefront. The knowledge of the tip-tilt is deduced from the monitoring of the chromatic components of the PLGS, from 330 nm to the visible or near infrared. Here we study the original scheme to create the PLGS by resonant excitation of the mesospheric sodium by two pulsed lasers (tens of kilohertz repetition rate, tens of watts average power, tens of nanoseconds pulse duration), at 589 and 569 nm, respectively. The efficiency of this process is investigated numerically by means of both Bloch equation and rate equation models. The influence of numerous laser parameters is studied. In the best case, having optimized all laser parameters, the return flux at 330 nm should not exceed 7x10(4) photons/s/m2 for 2x18 W laser average power at the mesosphere. This maximum is obtained for a modeless laser whose spot diameter corresponds to 4 times the diffraction limit. For a diffraction-limited spot, the return flux falls down to 4x10(4)photons/s/m2. PMID:18246174

  17. Optical guiding and beam bending in free-electron lasers

    SciTech Connect

    Scharlemann, E.T.

    1987-01-01

    The electron beam in a free-electron laser (FEL) can act as an optical fiber, guiding or bending the optical beam. The refractive and gain effects of the bunched electron beam can compensate for diffraction, making possible wigglers that are many Rayleigh ranges (i.e., characteristic diffraction lengths) long. The origin of optical guiding can be understood by examining gain and refractive guiding in a fiber with a complex index of refraction, providing a mathematical description applicable also to the FEL, with some extensions. In the exponential gain regime of the FEL, the electron equations of motion must be included, but a self-consistent description of exponential gain with diffraction fully included becomes possible. The origin of the effective index of refraction of an FEL is illustrated with a simple example of bunched, radiating dipoles. Some of the properties of the index of refraction are described. The limited experimental evidence for optical beam bending is summarized. The evidence does not yet provide conclusive proof of the existence of optical guiding, but supports the idea. Finally, the importance of refractive guiding for the performance of a high-gain tapered-wiggler FEL amplifier is illustrated with numerical simulations.

  18. Laser Research and Development Studies for Laser Guide Star Systems

    SciTech Connect

    Pennington, D.; Beach, R.; Ebbers, C.; Erbert, G.; Nguyen, H.; Page, R.; Payne, S.; Perry, M.

    2000-02-23

    In this paper we consider two CW solid state laser approaches to a 589 nm LGS system. Both are based on the technique of sum-frequency generation, but differ in the cavity architecture. Both technologies are very promising and are worth of further consideration. This preliminary proposal is intended to encompass both designs. A down select shall be performed early in the project execution to focus on the most promising option. The two design options consist of: (1) A dual-frequency resonator with intra-cavity doubling in LB0 offers the promise of a simple architecture and may scale more easily to high power. This design has been shown to be highly reliable, efficient and high power when used in frequency-doubled Nd:YAG lasers for programs at LLNL and in commercial products. The challenge in this design is the demonstration of a high power13 18 nm oscillator with adequate suppression of the 1064 nm line. (2) A MOPA based design uses commercial low power oscillators to produce both wavelengths, then amplifies the wavelengths before doubling. This design requires the demonstration of a 1318 nm amplifier, though the design is scaled from a kW CW amplifier already delivered to a customer at a different wavelength. The design must also demonstrate high power scaling of sum-frequency generation in the relatively new nonlinear material, PPLN. The first step in the process would be to further evaluate the two conceptual options for technical feasibility, cost and constructability. Then a down selection to one design would be conducted. Finally, R&D on that design would then proceed. Minimal testing should be required for this selection. The majority of the funding received would be allocated to development of the design selected.

  19. On Sky Validation of the Polychromatic Laser Guide Star Concept

    NASA Astrophysics Data System (ADS)

    Girard, J.

    2005-10-01

    The atmospheric turbulence affects image quality and causes angular resolution losses at the focus of large ground based optical telescopes. Real time adaptive optics (AO) corrects wave front distortions measured with at least one bright reference source located within a tiny isoplanatic angle from the science object. At visible wavelengths, the probability to find one such natural star is ridiculously small. The laser guide star (LGS) solves the problem but the overall wavefront slope (referred here as tilt) remains undetermined. The Polychromatic Laser Guide Star will allow the use of AO with full sky coverage. Based on the tilt chromaticity, a multicolor reference spot is created in the upper atmosphere and the differential tilt is measured between two wavelengths to retrieve the tilt itself. In the present thesis, I describe ATTILA, an experiment designed to prove the feasibility of the concept in astronomical conditions. Observations carried on at Observatoire de Haute Provence on natural stars allowed us to establish the proportionality law that links the tilt and the differential tilt for the first time. A temporal monitoring of the two signals shows a good correlation. The accuracy obtained on the slope (about one Airy disk ) let us be optimistic for the future full ELP-OA demonstrator with lasers. This work required an in-depth characterization of a detector featuring the novel EMCCD technology as well as the implementation and tests of pendular seismometers dedicated to measure telescope angular vibrations.

  20. ISIS Topside-Sounder Plasma-Wave Investigations as Guides to Desired Virtual Wave Observatory (VWO) Data Search Capabilities

    NASA Technical Reports Server (NTRS)

    Benson, Robert F.; Fung, Shing F.

    2008-01-01

    Many plasma-wave phenomena, observed by space-borne radio sounders, cannot be properly explained in terms of wave propagation in a cold plasma consisting of mobile electrons and infinitely massive positive ions. These phenomena include signals known as plasma resonances. The principal resonances at the harmonics of the electron cyclotron frequency, the plasma frequency, and the upper-hybrid frequency are well explained by the warm-plasma propagation of sounder-generated electrostatic waves, Other resonances have been attributed to sounder-stimulated plasma instability and non-linear effects, eigenmodes of cylindrical electromagnetic plasma oscillations, and plasma memory processes. Data from the topside sounders of the International Satellites for Ionospheric Studies (ISIS) program played a major role in these interpretations. A data transformation and preservation effort at the Goddard Space Flight Center has produced digital ISIS topside ionograms and a metadata search program that has enabled some recent discoveries pertaining to the physics of these plasma resonances. For example, data records were obtained that enabled the long-standing question (several decades) of the origin of the plasma resonance at the fundamental electron cyclotron frequency to be explained [Muldrew, Radio Sci., 2006]. These data-search capabilities, and the science enabled by them, will be presented as a guide to desired data search capabilities to be included in the Virtual Wave Observatory (VWO).

  1. ISIS topside-sounder Plasma-wave investigations as guides to desired Virtual Wave Observatory (VWO) data search capabilities

    NASA Astrophysics Data System (ADS)

    Benson, R. F.; Fung, S. F.

    2008-12-01

    Many plasma-wave phenomena, observed by space-borne radio sounders, cannot be properly explained in terms of wave propagation in a cold plasma consisting of mobile electrons and infinitely massive positive ions. These phenomena include signals known as plasma resonances. The principal resonances at the harmonics of the electron cyclotron frequency, the plasma frequency, and the upper-hybrid frequency are well explained by the warm-plasma propagation of sounder-generated electrostatic waves. Other resonances have been attributed to sounder-stimulated plasma instability and non-linear effects, eigenmodes of cylindrical electromagnetic plasma oscillations, and plasma memory processes. Data from the topside sounders of the International Satellites for Ionospheric Studies (ISIS) program played a major role in these interpretations. A data transformation and preservation effort at the Goddard Space Flight Center has produced digital ISIS topside ionograms and a metadata search program that has enabled some recent discoveries pertaining to the physics of these plasma resonances. For example, data records were obtained that enabled the long-standing question (several decades) of the origin of the plasma resonance at the fundamental electron cyclotron frequency to be explained [Muldrew, Radio Sci., 2006]. These data-search capabilities, and the science enabled by them, will be presented as a guide to desired data search capabilities to be included in the Virtual Wave Observatory (VWO).

  2. Assembly and test results of the AOF laser guide star units at ESO

    NASA Astrophysics Data System (ADS)

    Hackenberg, W.; Bonaccini Calia, D.; Buzzoni, B.; Comin, M.; Dupuy, C.; Gago, F.; Guidolin, I. M.; Guzman, R.; Holzloehner, R.; Kern, L.; Kirchbauer, J.-.; Lewis, S.; Lizon, J.-.; McLay, S.; Pfrommer, T.; Quattri, M.; Quentin, J.; Ridings, R.

    2014-08-01

    The Four Laser Guide Star Facility (4LGSF) is part of the ESO Adaptive Optics Facility, in which one of the VLT telescopes, UT4, is transformed in an adaptive telescope-equipped with a deformable secondary mirror, two adaptive optics systems at the Nasmyth focii and four sodium laser guide star modular units. In this paper we present the design, the assembly and validation test performed so far in Europe on the first laser guide star unit.

  3. Analysis of Capillary Guided Laser Plasma Accelerator Experiments at LBNL

    SciTech Connect

    Nakamura, K.; Esarey, E.; Leemans, W. P.; Gonsalves, A. J.; Panasenko, D.; Toth, Cs.; Geddes, C. G. R.; Schroeder, C. B.; Lin, C.

    2009-01-22

    Laser wakefield acceleration experiments were carried out by using a hydrogen-filled capillary discharge waveguide. For a 15 mm long, 200 {mu}m diameter capillary, quasi-monoenergetic e-beams up to 300 MeV were observed. By de-tuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. For a 33 mm long, 300 {mu}m capillary, a parameter regime with high energy electron beams, up to 1 GeV, was found. In this regime, the electron beam peak energy was correlated with the amount of trapped electrons.

  4. Analysis of Capillary Guided Laser Plasma Accelerator Experiments at LBNL

    SciTech Connect

    Advanced Light Source; Nakamura, Kei; Gonsalves, Anthony; Panasenko, Dmitriy; Lin, Chen; Toth, Csaba; Geddes, Cameron; Schroeder, Carl; Esarey, Eric; Leemans, Wim

    2008-09-29

    Laser wakefield acceleration experiments were carried out by using a hydrogen-filledcapillary discharge waveguide. For a 15 mm long, 200 mu m diameter capillary, quasi-monoenergetic e-beams up to 300 MeV were observed. By de-tuning discharge delay from optimum guiding performance, self-trapping was found to be stabilized. For a 33 mm long, 300 mu m capillary, a parameter regime with high energy electron beams, up to 1 GeV, was found. In this regime, the electron beam peak energy was correlated with the amount of trapped electrons.

  5. Transurethral ultrasound-guided laser prostatectomy: initial Luebeck experince

    NASA Astrophysics Data System (ADS)

    Thomas, Stephen; Spitzenpfeil, Elisabeth; Knipper, Ansgar; Jocham, Dieter

    1994-02-01

    Transurethral ultrasound guided laser prostatectomy is one of the most promising alternative invasive treatment modalities for benign prostatic hyperplasia. The principle feature is an on- line 3-D controlling of Nd:YAG laser denaturation of the periurethral tissue. Necrotic tissue is not removed, but sloughs away with the urinary stream within weeks. The bleeding hazard during and after the operation is minimal. By leaving the bladder neck untouched, sexual function is not endangered. Thirty-one patients with symptomatic BPH were treated with the TULIP system and followed up for at least 12 weeks. Suprapubic bladder drainage had to be maintained for a mean time of 37 days. Conventional TURP was performed in four patients due to chronic infection, recurrent bleeding, and poor results. Our initial experience with the TULIP system shows it to be very efficient and safe. A longer follow up of a larger patient population is necessary to compare the therapeutic efficiency to conventional transurethral resection.

  6. Laser-assisted guiding of electric discharges around objects

    PubMed Central

    Clerici, Matteo; Hu, Yi; Lassonde, Philippe; Milián, Carles; Couairon, Arnaud; Christodoulides, Demetrios N.; Chen, Zhigang; Razzari, Luca; Vidal, François; Légaré, François; Faccio, Daniele; Morandotti, Roberto

    2015-01-01

    Electric breakdown in air occurs for electric fields exceeding 34 kV/cm and results in a large current surge that propagates along unpredictable trajectories. Guiding such currents across specific paths in a controllable manner could allow protection against lightning strikes and high-voltage capacitor discharges. Such capabilities can be used for delivering charge to specific targets, for electronic jamming, or for applications associated with electric welding and machining. We show that judiciously shaped laser radiation can be effectively used to manipulate the discharge along a complex path and to produce electric discharges that unfold along a predefined trajectory. Remarkably, such laser-induced arcing can even circumvent an object that completely occludes the line of sight. PMID:26601188

  7. Laser-assisted guiding of electric discharges around objects.

    PubMed

    Clerici, Matteo; Hu, Yi; Lassonde, Philippe; Milián, Carles; Couairon, Arnaud; Christodoulides, Demetrios N; Chen, Zhigang; Razzari, Luca; Vidal, François; Légaré, François; Faccio, Daniele; Morandotti, Roberto

    2015-06-01

    Electric breakdown in air occurs for electric fields exceeding 34 kV/cm and results in a large current surge that propagates along unpredictable trajectories. Guiding such currents across specific paths in a controllable manner could allow protection against lightning strikes and high-voltage capacitor discharges. Such capabilities can be used for delivering charge to specific targets, for electronic jamming, or for applications associated with electric welding and machining. We show that judiciously shaped laser radiation can be effectively used to manipulate the discharge along a complex path and to produce electric discharges that unfold along a predefined trajectory. Remarkably, such laser-induced arcing can even circumvent an object that completely occludes the line of sight. PMID:26601188

  8. Laser induced electron acceleration in an ion-channel guiding

    SciTech Connect

    Esmaeilzadeh, Mahdi; Taghavi, Amin; Hanifpour, Maryam

    2011-09-15

    Direct electron acceleration by a propagating laser pulse of circular polarization in an ion-channel guiding is studied by developing a relativistic three-dimensional single particle code. The electron chaotic dynamic is also studied using time series, power spectrum, and Liapunov exponent. It is found that the electron motion is regular (non-chaotic) for laser pulse with short time duration, while for long enough time duration, the electron motion may be chaotic. In the case of non-chaotic motion, the electron can gain and retain very high energy in the presence of ion-channel before reaching the steady-state, whereas in the case of chaotic motion, the electron gains energy and then loses it very rapidly in an unpredictable manner.

  9. A novel laser angioplasty guided hollow fiber using mid-infrared laser

    NASA Astrophysics Data System (ADS)

    Yoshihashi-Suzuki, Sachiko; Yamada, Shinya; Sato, Izuru; Awazu, Kunio

    2006-02-01

    We have proposed selective removal of cholesterol ester by infrared laser of wavelength with 5.75 μm irradiation; the wavelength of 5.75 μm correspond with the ester bond C=O stretching vibration. The flexible laser guiding line and a compact light source are required for our proposal. We used a compact mid-infrared tunable laser by difference frequency generation; DFG laser was developed for substitute light source of free electron laser. In the present work, first, we have developed hollow optical fiber with a diamond lens-tip to deliver DFG laser in the blood vessel and evaluated the transmission of DFG laser from 5.5 μm to 7.5 μm. The transmission of 5.75 μm is about 65%, the DFG beam was focused on the tip of fiber by diamond lens-tip. Secondly, we performed the selective removal experiment of cholesterol ester using the hollow optical fiber with diamond lens-tip and DFG laser. The sample used a two layer model, cholesterol oleate and gelatin. The cholesterol oleate was decomposed by 5.75 μm DFG irradiation with 3.8 W/cm2.

  10. Time transfer between the Goddard Optical Research Facility and the U.S. Naval Observatory using 100 picosecond laser pulses

    NASA Technical Reports Server (NTRS)

    Alley, C. O.; Rayner, J. D.; Steggerda, C. A.; Mullendore, J. V.; Small, L.; Wagner, S.

    1983-01-01

    A horizontal two-way time comparison link in air between the University of Maryland laser ranging and time transfer equipment at the Goddard Optical Research Facility (GORF) 1.2 m telescope and the Time Services Division of the U.S. Naval Observatory (USNO) was established. Flat mirrors of 25 cm and 30 cm diameter respectively were placed on top of the Washington Cathedral and on a water tower at the Beltsville Agricultural Research Center. Two optical corner reflectors at the USNO reflect the laser pulses back to the GORF. Light pulses of 100 ps duration and an energy of several hundred microjoules are sent at the rate of 10 pulses per second. The detection at the USNO is by means of an RCA C30902E avalanche photodiode and the timing is accomplished by an HP 5370A computing counter and an HP 1000 computer with respect to a 10 pps pulse train from the Master Clock.

  11. From Dye Laser Factory to Portable Semiconductor Laser: Four Generations of Sodium Guide Star Lasers for Adaptive Optics in Astronomy and Space Situational Awareness

    NASA Astrophysics Data System (ADS)

    d'Orgeville, C.; Fetzer, G.

    This presentation recalls the history of sodium guide star laser systems used in astronomy and space situational awareness adaptive optics, analysing the impact that sodium laser technology evolution has had on routine telescope operations. While it would not be practical to describe every single sodium guide star laser system developed to date, it is possible to characterize their evolution in broad technology terms. The first generation of sodium lasers used dye laser technology to create the first sodium laser guide stars in Hawaii, California, and Spain in the late 1980's and 1990's. These experimental systems were turned into the first laser guide star facilities to equip medium-to-large diameter adaptive optics telescopes, opening a new era of LGS AO-enabled diffraction-limited imaging from the ground. Although they produced exciting scientific results, these laser guide star facilities were large, power-hungry and messy. In the USA, a second-generation of sodium lasers was developed in the 2000's that used cleaner, yet still large and complex, solid-state laser technology. These are the systems in routine operation at the 8-10m class astronomical telescopes and 4m-class satellite imaging facilities today. Meanwhile in Europe, a third generation of sodium lasers was being developed using inherently compact and efficient fiber laser technology, and resulting in the only commercially available sodium guide star laser system to date. Fiber-based sodium lasers will be deployed at two astronomical telescopes and at least one space debris tracking station this year. Although highly promising, these systems remain significantly expensive and they have yet to demonstrate high performance in the field. We are proposing to develop a fourth generation of sodium lasers: based on semiconductor technology, these lasers could provide the final solution to the problem of sodium laser guide star adaptive optics for all astronomy and space situational awareness applications.

  12. Study of optimal wavefront sensing with elongated laser guide stars

    NASA Astrophysics Data System (ADS)

    Thomas, S. J.; Adkins, S.; Gavel, D.; Fusco, T.; Michau, V.

    2008-06-01

    Over the past decade, adaptive optics (AO) has become an established method for overcoming the effects of atmospheric turbulence on both astronomical imaging and spectroscopic observations. These systems are now beginning to make extensive use of laser guide star (LGS) techniques to improve performance and provide increased sky coverage. Sodium LGS AO employs one or more lasers at 589-nm wavelength to produce an artificial guide star through excitation of sodium atoms in the mesosphere (90 km altitude). Because of its dependence on the abundance and distribution of sodium atoms in the mesosphere, this approach has its own unique set of difficulties not seen with natural stars. The sodium layer exhibits time-dependent variations in density and altitude, and since it is at a finite range, the LGS images become elongated due to the thickness of the layer and the offset between the laser projection point and the subapertures of a Shack-Hartmann wavefront sensor (SHWFS). Elongation causes the LGS image to be spread out resulting in a decrease in the signal-to-noise ratio which, in turn, leads to an increase in SHWFS measurement error and therefore an increased error in wavefront phase reconstruction. To address the problem of elongation, and also to provide a higher level of readout performance and reduced readout noise, a new type of charge-coupled device (CCD) is now under development for Shack-Hartmann wavefront sensing called the polar coordinate CCD. In this device, discrete imaging arrays are provided in each SHWFS subaperture and the size, shape and orientation of each discrete imaging array are adjusted to optimally sample the LGS image. The device is referred to as the polar coordinate CCD because the location of each imager is defined by a polar coordinate system centred on the laser guide star projection point. This concept is especially suited to Extremely Large Telescopes (ELTs) where the effect of perspective elongation is a significant factor. In this

  13. Laser micromachining in microelectronic industry by water-jet-guided laser

    NASA Astrophysics Data System (ADS)

    Sibailly, Ochelio; Wagner, Frank; Richerzhagen, Bernold

    2004-07-01

    The water jet guided laser technology (laser Microjet«) has been developed since 10 years now and is used for several applications in the semiconductor industry. In this unique laser cutting technique, a thin stable water jet is used as a waveguide for a high-power Nd:YAG laser, that may be frequency doubled or tripled. This presentation gives an overview of the semiconductor machining applications of this technique and relates the different applications to alternative techniques and the different functions of the water jet. The water jet cools the sample when the laser is not emitting, it expels the melt very efficiently, and it avoids that the few generated particles can attach to the wafer surface. The strengths of Laser Microjet« machining are free shape cutting and cutting of thin wafers. In free shape cutting the system leads to much better results in terms of fracture strength and process simplicity than the classical laser cutting methods. In thin wafer cutting astonishing cutting speeds are obtained at very good cut quality (200 mm/s in 50 micron thick wafers). Due to the free shape cutting possibilities drilling and slotting with aspect ratios of up to 5 is also possible resulting in the same edge quality as standard cutting.

  14. Photometric observations of a polychromatic laser guide star.

    PubMed

    Foy, R; Tallon, M; Tallon-Bosc, I; Thiébaut, E; Vaillant, J; Foy, F C; Robert, D; Friedman, H; Biraben, F; Grynberg, G; Gex, J P; Mens, A; Migus, A; Weulersse, J M; Butler, D J

    2000-12-01

    We report the photometric observation of a polychromatic laser guide star (PLGS) using the AVLIS laser at the Lawrence Livermore National Laboratory (LLNL). The process aims at providing a measurement of the tilt of the incoming wave front at a telescope induced by atmospheric turbulence. It relies on the two-photon coherent excitation of the 4D5/2 energy level of sodium atoms in the mesosphere. We used two laser beams at 589 and 569 nm, with a maximum total average output power of approximately 350 W. For the purpose of photometric calibration, a natural star was observed simultaneously through the same instrument as the PLGS at the focus of the LLNL 50-cm telescope. Photometric measurements of the 330-nm return flux confirm our previous theoretical studies that the PLGS process should allow us at a later stage to correct for the tilt at wavelengths as short as approximately 1 microm at good astronomical sites. They show also that, at saturation of two-photon coherent absorption in the mesosphere, the backscattered flux increases by a factor of approximately 2 when the pulse repetition rate decreases by a factor of 3 at constant average power. This unexpected behavior is briefly discussed. PMID:11140483

  15. Adaptive interferometric velocity measurements using a laser guide star

    NASA Astrophysics Data System (ADS)

    Czarske, J.; Radner, H.; Büttner, L.

    2015-07-01

    We have harnessed the power of programmable photonics devices for an interferometric measurement technique. Laser interferometers are widely used for flow velocity measurements, since they offer high temporal and spatial resolutions. However, often optical wavefront distortions deteriorate the measurement properties. In principle, adaptive optics enables the correction of these disturbances. One challenge is to generate a suitable reference signal for the closed loop operation of the adaptive optics. An adaptive Mach Zehnder interferometer is presented to measure through a dynamic liquid-gas phase boundary, which can lead to a misalignment of the interfering laser beams. In order to generate the reference signal for the closed loop control, the Fresnel reflex of the phase boundary is used as Laser Guide Star (LGS) for the first time to the best of the authors' knowledge. The concept is related to the generation of artificial stars in astronomy, where the light transmitted by the atmosphere is evaluated. However, the adaptive interferometric flow velocity measurements at real world experiments require a different concept, since only the reflected light can be evaluated. The used LGS allows to measure the wavefront distortions induced by the dynamic phase boundary. Two biaxial electromagnetically driven steering mirrors are employed to correct the wavefront distortions. This opens up the possibility for accurate flow measurements through a dynamic phase boundary using only one optical access. Our work represents a paradigm shift in interferometric velocity measurement techniques from using static to dynamic optical elements.

  16. A Monte Carlo simulation for predicting photon return from sodium laser guide star

    NASA Astrophysics Data System (ADS)

    Feng, Lu; Kibblewhite, Edward; Jin, Kai; Xue, Suijian; Shen, Zhixia; Bo, Yong; Zuo, Junwei; Wei, Kai

    2015-10-01

    Sodium laser guide star is an ideal source for astronomical adaptive optics system correcting wave-front aberration caused by atmospheric turbulence. However, the cost and difficulties to manufacture a compact high quality sodium laser with power higher than 20W is not a guarantee that the laser will provide a bright enough laser guide star due to the physics of sodium atom in the atmosphere. It would be helpful if a prediction tool could provide the estimation of photon generating performance for arbitrary laser output formats, before an actual laser were designed. Based on rate equation, we developed a Monte Carlo simulation software that could be used to predict sodium laser guide star generating performance for arbitrary laser formats. In this paper, we will describe the model of our simulation, its implementation and present comparison results with field test data.

  17. Experimental assessment of the matched filter for laser guide star wavefront sensing.

    PubMed

    Conan, Rodolphe; Lardière, Olivier; Herriot, Glen; Bradley, Colin; Jackson, Kate

    2009-02-20

    Laser guide star wavefront sensing comes with several limitations. When imaged with a Shack-Hartmann wavefront sensor, the laser guide star is seen as extended sources elongated in the directions given by the lenslet locations and the laser axis. A test bed has been built in the Adaptive Optics Laboratory of the University of Victoria that reproduces this effect as seen on extremely large telescopes. A new wavefront sensing algorithm, the matched filter, has been implemented and its performance assessed with the test bed. Its ability to mitigate laser guide star aberrations by tracking the sodium layer fluctuations in a closed loop adaptive optics system is shown. PMID:23567582

  18. Large scale Tesla coil guided discharges initiated by femtosecond laser filamentation in air

    NASA Astrophysics Data System (ADS)

    Arantchouk, L.; Point, G.; Brelet, Y.; Prade, B.; Carbonnel, J.; André, Y.-B.; Mysyrowicz, A.; Houard, A.

    2014-07-01

    The guiding of meter scale electric discharges produced in air by a Tesla coil is realized in laboratory using a focused terawatt laser pulse undergoing filamentation. The influence of the focus position, the laser arrival time, or the gap length is studied to determine the best conditions for efficient laser guiding. Discharge parameters such as delay, jitter, and resistance are characterized. An increase of the discharge length by a factor 5 has been achieved with the laser filaments, corresponding to a mean breakdown field of 2 kV/cm for a 1.8 m gap length. Consecutive guided discharges at a repetition rate of 10 Hz are also reported.

  19. High-Precision Lunar Ranging and Gravitational Parameter Estimation With the Apache Point Observatory Lunar Laser-ranging Operation

    NASA Astrophysics Data System (ADS)

    Johnson, Nathan H.

    This dissertation is concerned with several problems of instrumentation and data analysis encountered by the Apache Point Observatory Lunar Laser-ranging Operation. Chapter 2 considers crosstalk between elements of a single-photon avalanche photodiode detector. Experimental and analytic methods were developed to determine crosstalk rates, and empirical findings are presented. Chapter 3 details electronics developments that have improved the quality of data collected by detectors of the same type. Chapter 4 explores the challenges of estimating gravitational parameters on the basis of ranging data collected by this and other experiments and presents resampling techniques for the derivation of standard errors for estimates of such parameters determined by the Planetary Ephemeris Program (PEP), a solar-system model and data-fitting code. Possible directions for future work are discussed in Chapter 5. A manual of instructions for working with PEP is presented as an appendix.

  20. Guiding of intense laser pulse in uniform plasmas and preformed plasma channels

    SciTech Connect

    Wang Jingwei; Lei, A. L.; Wang Xin; Yu Wei; Yu, M. Y.; Senecha, V. K.; Wang, X. G.; Murakami, M.; Mima, K.

    2010-10-15

    Guiding of laser pulse in uniform plasmas and preformed plasma channels is investigated. The self-guiding mechanisms for these two cases are quite different. It is found that an intense laser pulse can be steadily self-guided in underdense plasmas with nearly a constant spot size if the self-consistently generated electron cavity has a sufficiently steep density gradient at the edge. In a preformed plasma channel, however, laser guiding is maintained mainly by the balance between the light diffraction and focusing. The latter is induced by the wall plasmas which greatly reduce the local dielectric constant. It is shown that the self-guiding of a laser pulse in uniform plasmas requires tens of terawatts power, but those that are in preformed channels can be realized with only a terawatt power.

  1. Development of laser guide stars and adaptive optics for large astronomical telescopes

    SciTech Connect

    Max, C.E.; Avicola, K.; Bissinger, H.; Brase, J.M.; Gavel, D.T.; Friedman, H.; Morris, J.R.; Olivier, S.S.; Rapp, D.; Salmon, J.T.; Waltjen, K.

    1992-06-29

    We describe a feasibility experiment to demonstrate high-order adaptive optics using a sodium-layer laser guide star. We use the copper-vapor-pumped dye lasers developed for LLNL's atomic Vapor Laser Isotope Separation program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser bream is projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot 1-2 meters in diameter at the atmospheric sodium layer (95 km altitude). We describe the overall system architecture and adaptive optics components, and analyze the expected performance. Our long-term goal is to develop sodium-layer laser guide stars and adaptive optics for large astronomical telescopes. We discuss preliminary design trade-offs for the Keck Telescope at Mauna Kea.

  2. Development of laser guide stars and adaptive optics for large astronomical telescopes

    SciTech Connect

    Max, C.E.; Avicola, K.; Bissinger, H.; Brase, J.M.; Gavel, D.T.; Friedman, H.; Morris, J.R.; Olivier, S.S.; Rapp, D.; Salmon, J.T.; Waltjen, K.

    1992-06-29

    We describe a feasibility experiment to demonstrate high-order adaptive optics using a sodium-layer laser guide star. We use the copper-vapor-pumped dye lasers developed for LLNL`s atomic Vapor Laser Isotope Separation program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser bream is projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot 1-2 meters in diameter at the atmospheric sodium layer (95 km altitude). We describe the overall system architecture and adaptive optics components, and analyze the expected performance. Our long-term goal is to develop sodium-layer laser guide stars and adaptive optics for large astronomical telescopes. We discuss preliminary design trade-offs for the Keck Telescope at Mauna Kea.

  3. Feasibility experiment for sodium-layer laser guide stars at the Lawrence Livermore National Laboratory

    SciTech Connect

    Max, C.; Avicola, K.; Bissinger, H.; Brase, J.; Gavel, D.; Friedman, H.; Morris, J.; Oliver, S.; Salmon, J.T.; Waltjen, K.

    1992-03-09

    We are developing a feasibility experiment to demonstrate closed-loop adaptive optics using a sodium-layer laser guide star. We will use the copper-vapor-pumped dye lasers developed for LLNL's Atomic Vapor Laser Isotope Separation Program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser beam will be projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot about a meter in diameter at the atmospheric sodium layer (at an altitude of 95 km). Details of the adaptive optics components and an analysis of the expected performance will be presented in companion papers for this Workshop. Here we summarize the overall architecture and system objectives. The long-term goal of our effort is to develop laser guide stars and adaptive optics for large astronomical telescopes.

  4. Laser spectroscopy of atoms guided by evanescent waves in micron-sized hollow optical fibers

    SciTech Connect

    Ito, H.; Nakata, T.; Sakaki, K.; Ohtsu, M.; Lee, K.I.; Jhe, W.

    1996-06-01

    We report the first laser spectroscopic experiments on the Rb beam guided by blue-detuned evanescent waves in micron-sized hollow fibers. The two-step photoionization spectra show the long-range dispersive properties of dipole interaction between guided atoms and evanescent waves. A large enhancement factor of 20in in the transmitted atomic flux is obtained at optimal conditions and the total guidance efficiency is estimated to be above 40{percent}. The state- and species-selective guide with proper frequency detunings of the guide laser realizes in-line spatial separation of two stable Rb isotopes. {copyright} {ital 1996 The American Physical Society.}

  5. Reporting guide for laser-light shows and displays (21 CFR 1002)

    SciTech Connect

    Not Available

    1988-05-01

    The guide is to be used for reporting laser-light shows or displays incorporating Class IIIb or Class IV lasers only. Separate reports are not required for shows or displays that incorporate Class I, IIa, II, or IIIa laser-projection systems. Such show descriptions must be included in the user instructions and the report for the laser projector. Laser projectors used in any light shows or displays regardless of the class of the projector must be certified by the manufacturer and reported using the guide titled, Guide for Preparing Initial Reports and Model Change Reports on Lasers and Products Containing Lasers, HHS Publication FDA 86-8259. These guides assist manufacturers in providing the information that the Center for Devices and Radiological Health (CDRH) needs to determine how laser-light-shown projections and laser-light shows comply with the Federal standard for laser products (21 CDR 1040.10 and 1040.11) and with the conditions of an approved variance.

  6. Split atmospheric tomography using laser and natural guide stars.

    PubMed

    Gilles, Luc; Ellerbroek, Brent L

    2008-10-01

    Laser guide star (LGS) atmospheric tomography is described in the literature as integrated minimum-variance tomographic wavefront reconstruction from a concatenated wavefront-sensor measurement vector consisting of many high-order, tip/tilt (TT)-removed LGS measurements, supplemented by a few low-order natural guide star (NGS) components essential to estimating the TT and tilt anisoplanatism (TA) modes undetectable by the TT-removed LGS wavefront sensors (WFSs). The practical integration of these NGS WFS measurements into the tomography problem is the main subject of this paper. A split control architecture implementing two separate control loops driven independently by closed-loop LGS and NGS measurements is proposed in this context. Its performance is evaluated in extensive wave optics Monte Carlo simulations for the Thirty Meter Telescope (TMT) LGS multiconjugate adaptive optics (MCAO) system, against the delivered performance of the integrated control architecture. Three iterative algorithms are analyzed for atmospheric tomography in both cases: a previously proposed Fourier domain preconditioned conjugate gradient (FDPCG) algorithm, a simple conjugate gradient (CG) algorithm without preconditioning, and a novel layer-oriented block Gauss-Seidel conjugate gradient algorithm (BGS-CG). Provided that enough iterations are performed, all three algorithms yield essentially identical closed-loop residual RMS wavefront errors for both control architectures, with the caveat that a somewhat smaller number of iterations are required by the CG and BGS-CG algorithms for the split approach. These results demonstrate that the split control approach benefits from (i) a simpler formulation of minimum-variance atmospheric tomography allowing for algorithms with reduced computational complexity and cost (processing requirements), (ii) a simpler, more flexible control of the NGS-controlled modes, and (iii) a reduced coupling between the LGS- and NGS-controlled modes. Computation

  7. Comparative Study of Remote Fiber Laser and Water-Jet Guided Laser Cutting of Thin Metal Sheets

    NASA Astrophysics Data System (ADS)

    Hock, Klaus; Adelmann, Benedikt; Hellmann, Ralf

    This article presents a comparison between remote laser cutting with a fiber laser and water-jet guided laser cutting using a 532 nm solid state laser. Complex contours are processed in stainless steel and brass sheets (thickness ≤ 100 μm), respectively. Results for achievable quality and productivity as well as possible applications for both systems are shown and discussed. We sustained dross free cuts with almost no heat affected zone and small kerf width for the water-jet guided process, whereas small dross, notable heat affected zone and varying kerf width where observed for remote cutting. However, process times for the water-jet guided process where considerably higher than those for remote cutting.

  8. Laser ablation of basal cell carcinomas guided by confocal microscopy

    NASA Astrophysics Data System (ADS)

    Sierra, Heidy; Cordova, Miguel; Nehal, Kishwer; Rossi, Anthony; Chen, Chih-Shan Jason; Rajadhyaksha, Milind

    2016-02-01

    Laser ablation offers precise and fast removal of superficial and early nodular types of basal cell carcinomas (BCCs). Nevertheless, the lack of histological confirmation has been a limitation. Reflectance confocal microscopy (RCM) imaging combined with a contrast agent can offer cellular-level histology-like feedback to detect the presence (or absence) of residual BCC directly on the patient. We conducted an ex vivo bench-top study to provide a set of effective ablation parameters (fluence, number of passes) to remove superficial BCCs while also controlling thermal coagulation post-ablation to allow uptake of contrast agent. The results for an Er:YAG laser (2.9 um and pulse duration 250us) show that with 6 passes of 25 J/cm2, thermal coagulation can be effectively controlled, to allow both the uptake of acetic acid (contrast agent) and detection of residual (or absence) BCCs. Confirmation was provided with histological examination. An initial in vivo study on 35 patients shows that the uptake of contrast agent aluminum chloride) and imaging quality is similar to that observed in the ex vivo study. The detection of the presence of residual tumor or complete clearance was confirmed in 10 wounds with (additional) histology and in 25 lesions with follow-up imaging. Our results indicate that resolution is sufficient but further development and use of appropriate contrast agent are necessary to improve sensitivity and specificity. Advances in RCM technology for imaging of lateral and deep margins directly on the patient may provide less invasive, faster and less expensive image-guided approaches for treatment of BCCs.

  9. Design of an infrared camera based aircraft detection system for laser guide star installations

    SciTech Connect

    Friedman, H.; Macintosh, B.

    1996-03-05

    There have been incidents in which the irradiance resulting from laser guide stars have temporarily blinded pilots or passengers of aircraft. An aircraft detection system based on passive near infrared cameras (instead of active radar) is described in this report.

  10. Laser Guiding at Relativistic Intensities and Wakefield ParticleAcceleration in Plasma Channels

    SciTech Connect

    Geddes, C.G.R.; Toth, Cs.; van Tilborg, J.; Esarey, E.; Schroeder, C.B.; Bruhwiler, D.; Nieter, C.; Cary, J.; Leemans, W.P.

    2005-05-01

    High quality electron beams with hundreds of picoCoulombs ofcharge inpercent energy spread above 80 MeV were produced for the firsttime in high gradient laser wakefield accelerators by guiding the drivelaser pulse.

  11. Follow the yellow-orange rabbit: a CCD optimized for wavefront sensing a pulsed sodium laser guide star

    NASA Astrophysics Data System (ADS)

    Beletic, James W.

    2004-09-01

    Most large telescopes are now implementing sodium laser guide star (LGS) adaptive optics (AO) systems. Most of these systems plan to use the Shack-Hartmann approach for wavefront sensing. In these systems, the laser spots that are imaged in the Shack-Hartmann subapertures suffer spot elongation due to the 10 km extent of the sodium layer. The spot elongation extends radially from the projection point, and increases linearly with the distance the subaperture is separated from the laser. For 8-meter class telescopes with laser projection behind the secondary mirror, the spot elongation is ~1 arc sec at the edge of the pupil, and does not significantly affect the performance of the AO system. However, for the coming generation of extremely large telescopes, sodium LGS spot elongation will significantly degrade the quality of wavefront measurement. Attention should now be given to the development of technologies that can reduce or eliminate the spot elongation problem. The laser spot elongation can be greatly reduced by projecting the sodium laser in a series of short (1-3 µsec) pulses. The Lawrence Livermore National Laboratory (LLNL) has been funded to develop a pulsed fiber laser. In parallel, a new kind of wavefront sensor detector must be developed to properly sense the pulsed laser return. In this paper, we present our project that will develop a novel CCD which is optimized for sensing the return from a pulsed sodium LGS. Our CCD design uses custom pixel morphology that aligns the pixels of each subaperture with the radial extension of the LGS spot. This pixel geometry will allow each subaperture to follow the yellow-orange rabbit (i.e. the 589 nm laser pulse) as it traverses the sodium layer, providing optimal sampling of a limited number of detected photons. This CCD will attain photon-noise limited performance at high frame rates, using MOSFET amplifiers that exist today (2-3 electrons noise). However, we seek even lower noise amplifiers, and as part of

  12. A laser guide star wavefront sensor bench demonstrator for TMT.

    PubMed

    Lardiere, Olivier; Conan, Rodolphe; Bradley, Colin; Jackson, Kate; Herriot, Glen

    2008-04-14

    Sodium laser guide stars (LGSs) allow, in theory, Adaptive Optics (AO) systems to reach a full sky coverage, but they have their own limitations. The artificial star is elongated due to the sodium layer thickness, and the temporal and spatial variability of the sodium atom density induces changing errors on wavefront measurements, especially with Extremely Large Telescopes (ELTs) for which the LGS elongation is larger. In the framework of the Thirty-Meter-Telescope project (TMT), the AO-Lab of the University of Victoria (UVic) has built an LGS-simulator test bed in order to assess the performance of new centroiding algorithms for LGS Shack-Hartmann wavefront sensors (SH-WFS). The design of the LGS-bench is presented, as well as laboratory SH-WFS images featuring 29x29 radially elongated spots, simulated for a 30-m pupil. The errors induced by the LGS variations, such as focus and spherical aberrations, are characterized and discussed. This bench is not limited to SH-WFS and can serve as an LGS-simulator test bed to any other LGS-AO projects for which sodium layer fluctuations are an issue. PMID:18542656

  13. Nonlinear study of an ion-channel guiding free-electron laser

    SciTech Connect

    Ouyang, Zhengbiao; Zhang, Shi-Chang

    2015-04-15

    A nonlinear model and simulations of the output power of an ion-channel guiding free-electron laser (FEL) are presented in this paper. Results show that the nonlinear output power of an ion-channel guiding FEL is comparable to that of an axial guide magnetic field FEL. Compared to an axial guide magnetic field FEL, an ion-channel guiding FEL substantially weakens the negative effect of the electron-beam energy spread on the output power due to its advantageous focusing mechanism on the electron motion.

  14. Laser-guided placement of the tibial guide in the transtibial technique for anterior cruciate ligament reconstruction.

    PubMed

    Takahashi, Toshiaki; Takeda, Haruhiko; Watanabe, Seiji; Yamamoto, Haruyasu

    2009-02-01

    In anterior cruciate ligament (ACL) reconstruction, it is important to determine the location and direction of the femoral bone tunnel when using the transtibial technique. Accurately identifying the anatomic location at which to make the femoral bone tunnel for double-bundle ACL reconstruction is not a straightforward procedure. We describe a new method in which the centrum of the femoral tunnel is marked with an awl and a laser beam-guided technique is used to place the tibial pin. This procedure allows us to mark the desired location of the femoral tunnel before drilling the tibial bone tunnel when using the transtibial technique. This is the first report of a laser-guided technique used in arthroscopic surgery. We used a laser beam to determine the location of the femoral tunnel--the anatomic site needed to perform the intra-articular drilling in the tibia. In this technique, a laser pointer is set at the tibial guide, which reflects the laser beam and illuminates the point where the femoral bone tunnel should be made. Our method offers an easy and accurate way to reconfirm the tibial placement before drilling. PMID:19171283

  15. Competency-Based Curriculum Guide for Laser Technology. September 1980-June 1981.

    ERIC Educational Resources Information Center

    Fioroni, John J.

    This document contains materials developed by a project to provide a competency-based curriculum guide for laser technology at the community college level. An abstract of the final report is included. Next, the 17 job competencies determined as necessary to meet the job description of laser technician are listed. A career ladder and qualifications…

  16. Systematic design and analysis of laser-guide-star adaptive-optics systems for large telescopes

    SciTech Connect

    Gavel, D.T.; Morris, J.R.; Vernon, R.G.

    1994-02-01

    The authors discuss the design of laser-guided adaptive-optics systems for the large, 8-10-m-class telescopes. Through proper choice of system components and optimized system design, the laser power that is needed at the astronomical site can be kept to a minimum. 37 refs., 9 figs., 3 tabs.

  17. Installation of two high-sensitivity laser strainmeters in a new underground geodynamical observatory (GEODYN) at Canfranc (Spain)

    NASA Astrophysics Data System (ADS)

    Crescentini, L.; Botta, V.; Amoruso, A.; Bettini, A.

    2012-04-01

    High-sensitivity wide-band strain measurements allow an advanced study of different geodynamic phenomena, both local and global, in a spectrum ranging from short period seismic waves to tectonic deformation. Among the latest results produced by the few high-sensitivity wide-band laser interferometers operating allover the world, the analysis of the strain recorded by the Gran Sasso (Italy) laser interferometers before and after the 2009 L'Aquila earthquake allowed putting tight constraints on earthquake nucleation processes and other pre-seismic phenomena, and detecting the slow diffusive propagation of an aseismic rupture during the first hours following the main event.The Gran Sasso interferometers are operating since several years, proving their high reliability. An improved version of the Gran Sasso interferometers have been recently installed in the Canfranc (Spain) underground Laboratory (LSC). The LSC is located at depth in one of the most seismically active areas in Western Europe, at the Pyrenean chain that marks the boundary between the European plate and the Iberian microplate. These features make it particularly suitable and interesting for hosting an advanced integrated geodynamic observatory (GEODYN), of which the interferometers are part. The first tests on strain data evidence a much lower noise level with respect that the Gran Sasso installations, expecially in the frequency band 0.0001 to 0.1 Hz, suggesting the capability of producing clear records of low-frequency seismic waves, Earth free oscillations, and possible local aseismic stress release. We will give a technical description of the installation, show some examples of recordings, and discuss the local distortion of the deformation field, as obtained by comparing Earth tide predictions and observations.

  18. Advancing adaptive optics technology: Laboratory turbulence simulation and optimization of laser guide stars

    NASA Astrophysics Data System (ADS)

    Rampy, Rachel A.

    optimizing the laser beacons used to bring AO correction to parts of the sky that lack a naturally bright light source for measuring atmospheric distortion. Long pulse length laser guide stars (LGS) that use fluorescence from the D 2 transition in mesospheric sodium are valuable both due to their high altitude, and because they permit Rayleigh blanking and fratricide avoidance in multiple LGS systems. Bloch equation simulations of sodium-light interactions in Mathematica show that certain spectral formats and pulse lengths (on the order of 30 μs), with high duty cycles (20-50%), should be able to achieve photon returns within 10% of what is seen from continuous wave (CW) excitation. Utilizing this recently developed code (called LGSBloch), I investigated the time dependent characteristics of sodium fluorescence. I then identified the optimal format for the new LGS that will be part of the upgrade to the AO system on the Shane 3 meter telescope at the Lick Observatory. I discuss these results, along with their general applicability to other LGS systems, and provide a brief description of the potential benefits of uplink correction. Predictions from the LGSBloch simulation package are compared to data from currently operating LGS systems. For a CW LGS, the return flux measurements and theory show reasonable agreement, but for short pulse lasers, such as those at the Lick and Keck Observatories, the code seems to be overestimating the data by a factor of 2--3. Several tactics to explicate this discrepancy are explored, such as verifying parameters involved in the measurements and including greater detail in the modeling. Although these efforts were unsuccessful at removing the discrepancy, they illuminated other facets of the problem that deserve further consideration. Use of the sophisticated LGSBloch model has allowed detailed study of the evolution of the energy level populations and other physical effects (e.g. Larmor precession, atomic recoil, and collisions). This has

  19. Noise-like pulse in a gain-guided soliton fiber laser.

    PubMed

    Zhao, L M; Tang, D Y; Wu, J; Fu, X Q; Wen, S C

    2007-03-01

    We report on the operation of a passively mode-locked fiber ring laser made of purely positive dispersion fibers and mode-locked by using the nonlinear polarization rotation technique. It was experimentally found that apart from the gain-guided soliton operation the laser can also emit a kind of noise-like pulse. We show numerically that the noise-like pulse emission is caused by the peak power clamping effect of the laser cavity on the gain-guided soliton. PMID:19532451

  20. Noise-like pulse in a gain-guided soliton fiber laser

    NASA Astrophysics Data System (ADS)

    Zhao, L. M.; Tang, D. Y.; Wu, J.; Fu, X. Q.; Wen, S. C.

    2007-03-01

    We report on the operation of a passively mode-locked fiber ring laser made of purely positive dispersion fibers and mode-locked by using the nonlinear polarization rotation technique. It was experimentally found that apart from the gain-guided soliton operation the laser can also emit a kind of noise-like pulse. We show numerically that the noise-like pulse emission is caused by the peak power clamping effect of the laser cavity on the gain-guided soliton.

  1. Variable Curvature Mirrors for ELT Laser Guide Star refocusing systems

    NASA Astrophysics Data System (ADS)

    Challita, Zalpha; Hugot, Emmanuel; Ferrari, Marc; Madec, Fabrice; Le Mignant, David; Cuby, Jean-Gabriel

    2011-09-01

    The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, LGS defocusing is one of the system issues that can be tackled using active refocusing mirrors such as Variable Curvature Mirrors (VCM). Indeed, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope, and induces a large defocusing at the LGS wave-front sensor focal plane. To compensate for that, we propose an original concept including a VCM specifically designed to keep a focused spot on the wave-front sensor: the mirror is made of a thin meniscus bend using a pressure applied on its back face. Due to the large defocusing, the LGS-VCM must be able to change its shape from F/12.5 to F/5, leading to more than 1 mm sag. The VCM benefits of a specific shape with a variable radial thickness distribution, allowing keeping an optical quality better than λ/5 over this very large range of deformation. The work presented here details the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Two prototypes have been manufactured to compare the real behaviour of the mirror and the simulations data. Results obtained on the prototypes show that the deformation of the VCM is very close to the simulation, and leads to a realistic concept.

  2. Guided wave generation and sensing system using a single laser source and optical fibers

    NASA Astrophysics Data System (ADS)

    Lee, Hyeonseok; Park, Hyun-Jun; Sohn, Hoon; Kwon, Il-bum

    2010-04-01

    Structural health monitoring (SHM) techniques based on guided waves have been of great interests to many researchers. Among various SHM devices used for guided wave generation and sensing, lead zirconate titanate (PZT) transducers and fiber Bragg grating (FBG) sensors have been widely used because of their light weight, non-intrusive nature and compactness. To best take advantage of their merits, combination of PZT-based guided wave excitation and FBG-based sensing has been attempted by a few researchers. However, the PZT-based actuation and the FBG-based sensing are basically two independent systems in the past studies. This study proposes an integrated PZT/FBG system using a single laser source. Since power and data delivery is based on optical fibers, it may alleviate problems associated with conventional wire cables such as electromagnetic interference (EMI) and power/data attenuation. The experimental procedure for the proposed system is as follows. First, a tunable laser is used as the common power source for guided wave generation and sensing. The tunable laser beam is modulated and amplified to contain an arbitrary waveform. Then, it is transmitted to the PZT transducer node through an optical fiber for guided wave actuation. The transmitted laser beam is also used with the FBG sensor to measure high-speed strain changes induced by guided waves. Feasibility of the proposed technique has been experimentally demonstrated using aluminum plates. The results show that the proposed system could properly generate and sense the guided waves compared to the conventional methods.

  3. Transendoscopic application of CO2 laser irradiation using the OmniGuide fiber

    NASA Astrophysics Data System (ADS)

    Tate, Lloyd P., Jr.; Elce, Yvonne A.

    2005-04-01

    Transendoscopic laser surgery has been performed in large animals since 1984. It is used to treat many upper respiratory disorders, as well as urogenital diseases. Initially, the Nd:YAG laser was the laser of choice until the early 1990's, when smaller, more compact diode lasers entered the veterinary field. In the mid 1980's, several attempts were made to transmit CO2 laser energy transendoscopically. True success was not obtained until 2004 when the OmniGuide CO2 Laser Hollow Light Guide (fiber) was fabricated. Although there is attenuation of energy, this very flexible fiber allows the CO2 laser to be used transendoscopically for incision and ablation of tissue. Both healing and recuperation time are reduced, compared to other wavelengths transmitted through solid quartz fiber. The OmniGuide fiber can be coupled to the output ports of CO2 lasers commonly used in veterinary medicine. Transendoscopic application of the CO2 laser is advantageous in that there is no endoscopic white-out, no volume heating of tissue, and it provides accurate means of performing upper respiratory surgery in the standing large animal.

  4. A study on laser-based ultrasonic technique by the use of guided wave tomographic imaging

    SciTech Connect

    Park, Junpil Lim, Juyoung; Cho, Younho; Krishnaswamy, Sridhar

    2015-03-31

    Guided wave tests are impractical for investigating specimens with limited accessibility and coarse surfaces or geometrically complicated features. A non-contact setup with a laser ultrasonic transmitter and receiver is the classic attractive for guided wave inspection. The present work was done to develop a non-contact guided-wave tomography technique by laser ultrasonic technique in a plate-like structure. A method for Lam wave generation and detection in an aluminum plate with a pulse laser ultrasonic transmitter and a Michelson interferometer receiver has been developed. In the images obtained by laser scanning, the defect shape and area showed good agreement with the actual defect. The proposed approach can be used as a non-contact-based online inspection and monitoring technique.

  5. Controlled fundamental supermode operation of phase-locked arrays of gain-guided diode lasers

    NASA Technical Reports Server (NTRS)

    Kapon, E.; Margalit, S.; Yariv, A.; Katz, J.

    1984-01-01

    Uniform semiconductor laser arrays tend to oscillate in a superposition of their supermodes, thus leading to large beam divergence and spectral spread. Discrimination among the supermodes in phase-locked arrays is discussed theoretically. It is shown that supermode discrimination in gain-guided arrays, in favor of the fundamental supermode, is made possible by the near-field interference patterns which result from the complex optical fields of the gain-guided lasers. A fundamental supermode operation is demonstrated, for the first time, in GaAlAs/GaAs gain-guided laser arrays. This is achieved by control of the current (gain) profile across the array by means of individual laser contacts.

  6. Advancing adaptive optics technology: Laboratory turbulence simulation and optimization of laser guide stars

    NASA Astrophysics Data System (ADS)

    Rampy, Rachel A.

    optimizing the laser beacons used to bring AO correction to parts of the sky that lack a naturally bright light source for measuring atmospheric distortion. Long pulse length laser guide stars (LGS) that use fluorescence from the D 2 transition in mesospheric sodium are valuable both due to their high altitude, and because they permit Rayleigh blanking and fratricide avoidance in multiple LGS systems. Bloch equation simulations of sodium-light interactions in Mathematica show that certain spectral formats and pulse lengths (on the order of 30 μs), with high duty cycles (20-50%), should be able to achieve photon returns within 10% of what is seen from continuous wave (CW) excitation. Utilizing this recently developed code (called LGSBloch), I investigated the time dependent characteristics of sodium fluorescence. I then identified the optimal format for the new LGS that will be part of the upgrade to the AO system on the Shane 3 meter telescope at the Lick Observatory. I discuss these results, along with their general applicability to other LGS systems, and provide a brief description of the potential benefits of uplink correction. Predictions from the LGSBloch simulation package are compared to data from currently operating LGS systems. For a CW LGS, the return flux measurements and theory show reasonable agreement, but for short pulse lasers, such as those at the Lick and Keck Observatories, the code seems to be overestimating the data by a factor of 2--3. Several tactics to explicate this discrepancy are explored, such as verifying parameters involved in the measurements and including greater detail in the modeling. Although these efforts were unsuccessful at removing the discrepancy, they illuminated other facets of the problem that deserve further consideration. Use of the sophisticated LGSBloch model has allowed detailed study of the evolution of the energy level populations and other physical effects (e.g. Larmor precession, atomic recoil, and collisions). This has

  7. Laser altimetry simulator. Version 3.0: User's guide

    NASA Technical Reports Server (NTRS)

    Abshire, James B.; Mcgarry, Jan F.; Pacini, Linda K.; Blair, J. Bryan; Elman, Gregory C.

    1994-01-01

    A numerical simulator of a pulsed, direct detection laser altimeter has been developed to investigate the performance of space-based laser altimeters operating over surfaces with various height profiles. The simulator calculates the laser's optical intensity waveform as it propagates to and is reflected from the terrain surface and is collected by the receiver telescope. It also calculates the signal and noise waveforms output from the receiver's optical detector and waveform digitizer. Both avalanche photodiode and photomultiplier detectors may be selected. Parameters of the detected signal, including energy, the 50 percent rise-time point, the mean timing point, and the centroid, can be collected into histograms and statistics calculated after a number of laser firings. The laser altimeter can be selected to be fixed over the terrain at any altitude. Alternatively, it can move between laser shots to simulate the terrain profile measured with the laser altimeter.

  8. Scribing of GaN wafer for white LED by water-jet-guided laser

    NASA Astrophysics Data System (ADS)

    Nilsson, Thomas; Wagner, Frank; Housh, R.; Richerzhagen, Bernold

    2004-06-01

    In 1993, a laser light guiding water jet was successfully developed at the Institute of Applied Optics (EPFL, Lausanne, Switzerland; patented as Laser Microjet. The laser beam is focused into a nozzle from which a thin low-pressure water jet is emitted. The laser beam is injected in the water jet and guided in it by total internal reflection at the water/air interface similarly to a standard optical fiber. Normally a pulsed laser is used, so the continuous water jet is able to immediately cool the cut, reducing efficiently the heat-affected zone. The result is a very narrow, parallel, burr-free, clean cut, without detectable thermal damage. LED manufacturing is one example where thin layers need to be removed from well-defined regions on a wafer without damaging the neighboring structures. Compared with diamond saw cutting for which chipping and delaminating of the wafer cannot be avoided due to the strong shear forces; or compared with conventional laser cutting where low power irradiation of nearby functional structures occurs, the laser Microjet offers better edge quality and high precision. Compared to the main competitor, etching techniques combined with subsequent sawing of the substrate, the water jet guided laser is faster at similar edge quality.

  9. An Operations and Maintenance Overview of the Gemini North Artificial Guide Star Laser

    NASA Astrophysics Data System (ADS)

    Wyman, R.; Boccas, M.; D'Orgeville, C.; White, K.

    This is an overview of technical issues, and operational and maintenance activities for the Gemini North Guide Star Laser system that are specific to the laser itself, which currently operates in support of Laser Guide Star Adaptive Optics (LGS AO) science observations. Discussion will detail various issues with laser pump diode failures, failure analysis and reliability as well as techniques in spectral temperature tuning and laser diode procurements. Wavelength stability has been a major issue for operation of the laser and continuous monitoring of the laser is required to maintain power and wavelength within specification. Current investigation in to the problem will be reviewed along with the methods of managing the issue. The sum frequency generation PPSLT crystal will be discussed with respect to performance, maintenance and future testing plans to commission spare crystals in the laser system should they be needed. Various improvements in software and hardware will be briefly discussed along with an overview of diagnostics tools that are in place or being developed. Since the completion of science commissioning the operations model we follow to prepare and maintain the laser for LGS AO science observations has allowed for very good uptime. During this time it has been an intensive training for those operating the system and some of the experience will be discussed along with the current laser operations support model.

  10. Optimization of an Image-Guided Laser-Induced Choroidal Neovascularization Model in Mice

    PubMed Central

    Sun, Ye; Fu, Zhongjie; Liu, Chi-Hsiu; Evans, Lucy; Tian, Katherine; Saba, Nicholas; Fredrick, Thomas; Morss, Peyton; Chen, Jing; Smith, Lois E. H.

    2015-01-01

    The mouse model of laser-induced choroidal neovascularization (CNV) has been used in studies of the exudative form of age-related macular degeneration using both the conventional slit lamp and a new image-guided laser system. A standardized protocol is needed for consistent results using this model, which has been lacking. We optimized details of laser-induced CNV using the image-guided laser photocoagulation system. Four lesions with similar size were consistently applied per eye at approximately double the disc diameter away from the optic nerve, using different laser power levels, and mice of various ages and genders. After 7 days, the mice were sacrificed and retinal pigment epithelium/choroid/sclera was flat-mounted, stained with Isolectin B4, and imaged. Quantification of the area of the laser-induced lesions was performed using an established and constant threshold. Exclusion criteria are described that were necessary for reliable data analysis of the laser-induced CNV lesions. The CNV lesion area was proportional to the laser power levels. Mice at 12-16 weeks of age developed more severe CNV than those at 6-8 weeks of age, and the gender difference was only significant in mice at 12-16 weeks of age, but not in those at 6-8 weeks of age. Dietary intake of omega-3 long-chain polyunsaturated fatty acid reduced laser-induced CNV in mice. Taken together, laser-induced CNV lesions can be easily and consistently applied using the image-guided laser platform. Mice at 6-8 weeks of age are ideal for the laser-induced CNV model. PMID:26161975

  11. Upper limit power for self-guided propagation of intense lasers in plasma

    SciTech Connect

    Wang Weimin; Hu Zhidan; Chen Liming; Li Yutong; Sheng Zhengming; Zhang Jie; Zeng Ming; Liu Yue; Kawata, Shigeo; Zheng Chunyang; Mori, Warren B.

    2012-10-29

    It is shown that there is an upper-limit laser power for self-focusing of a laser pulse in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. This upper limit is caused by the transverse ponderomotive force of the laser, which tends to expel plasma electrons from the laser propagating area. Furthermore, there is a lower-limit plasma density for a given laser spot size, below which self-focusing does not occur for any laser power. Both the lower-limit density and the upper-limit power are derived theoretically and verified by two-dimensional and three-dimensional particle-in-cell simulations. It is also found that plasma channels may be unfavorable for stable guiding of lasers above the upper-limit power.

  12. Femtosecond laser guiding of a high-voltage discharge and the restoration of dielectric strength in air and nitrogen

    SciTech Connect

    Leonov, S. B.; Firsov, A. A.; Shurupov, M. A.; Michael, J. B.; Shneider, M. N.; Miles, R. B.; Popov, N. A.

    2012-12-15

    The use of a low energy, high peak intensity (>100 TW/cm{sup 2}) femtosecond laser pulse is investigated for guiding and control of a sub-microsecond high voltage discharge. Study of the laser induced plasma channel and measurements of the field required for breakdown in air and nitrogen at atmospheric pressure are presented. Direct imaging of the dynamics of the discharge breakdown shows effective laser guiding. The effectiveness of laser guiding is shown to be critically dependent on the laser focusing geometry, timing, and location relative to the electrodes.

  13. Femtosecond laser guiding of a high-voltage discharge and the restoration of dielectric strength in air and nitrogen

    NASA Astrophysics Data System (ADS)

    Leonov, S. B.; Firsov, A. A.; Shurupov, M. A.; Michael, J. B.; Shneider, M. N.; Miles, R. B.; Popov, N. A.

    2012-12-01

    The use of a low energy, high peak intensity (>100 TW/cm2) femtosecond laser pulse is investigated for guiding and control of a sub-microsecond high voltage discharge. Study of the laser induced plasma channel and measurements of the field required for breakdown in air and nitrogen at atmospheric pressure are presented. Direct imaging of the dynamics of the discharge breakdown shows effective laser guiding. The effectiveness of laser guiding is shown to be critically dependent on the laser focusing geometry, timing, and location relative to the electrodes.

  14. Laser active imaging-guided anti-tank missile system small-scale integration design

    NASA Astrophysics Data System (ADS)

    Yan, Mingliang; Shan, Xiangqian; Qu, Zhou

    2010-10-01

    At present, the domestic and international third-generation anti-tank missiles, laser-guided missiles are mostly divided into active laser-guided and laser semi-active guidance, this guidance system, there are vulnerable to electronic interference, can not be fully realized after launching deficiencies. Article based on this, an in-depth understanding of imaging-guided laser-active working principle, based on the pairs of third-generation anti-tank missile guidance system, boldly proposed to improve the anti-tank missiles, laser-active small-scale integration of imaging guidance system design, the main purpose is to improve a certain type of The optical target missile, TV angle measurement, laser-guided instruction transmission means, so that anti-tank missiles to achieve forward-looking, the next obstacle avoidance TV and multi-functional integration of the entire after launching smart missiles, and in theory be able to study the new antitank missiles play a certain reference.

  15. Self-Guiding of Ultrashort Relativistically Intense Laser Pulses to the Limit of Nonlinear Pump Depletion

    SciTech Connect

    Ralph, J. E.; Marsh, K. A.; Pak, A. E.; Lu, W.; Clayton, C. E.; Fang, F.; Joshi, C.; Tsung, F. S.; Mori, W. B.

    2009-01-22

    A study of self-guiding of ultra short, relativistically intense laser pulses is presented. Here, the laser pulse length is on the order of the nonlinear plasma wavelength and the normalized vector potential is greater than one. Self-guiding of ultrashort laser pulses over tens of Rayliegh lengths is possible when driving a highly nonlinear wake. In this case, self-guiding is limited by nonlinear pump depletion. Erosion of the pulse due to diffraction at the head of the laser pulse is minimized for spot sizes close to the blow-out radius. This is due to the slowing of the group velocity of the photons at the head of the laser pulse. Using an approximately 10 TW Ti:Sapphire laser with a pulse length of approximately 50 fs, experimental results are presented showing self-guiding over lengths exceeding 30 Rayliegh lengths in various length Helium gas jets. Fully explicit 3D PIC simulations supporting the experimental results are also presented.

  16. A guide to developing a laser standard operating procedure

    SciTech Connect

    Barat, K.

    1996-10-01

    The American National Standard Institute standard Z136.1 Safe Use of Lasers calls for the preparation of a standard operating procedure (SOP) with the use of class 3b and class 4 lasers. However, the ANSI Z 136.1 standard does not recommend or suggest a format for the SOP. The goal of this article is to outline, explain and suggest an SOP format that could be applied by a laser safety officer to a varied number of situations and laser uses.

  17. Guiding of high intensity ultrashort laser pulses in plasma channels produced with the dual laser pulse ignitor-heater technique

    SciTech Connect

    Volfbeyn, P.; Leemans, W.P.

    1998-07-01

    The authors present results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme is proposed and experimentally tested in hydrogen and nitrogen. It makes use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, is brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (160 ps long) is used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion creates a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allows creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a > 5 {times} 10{sup 17} W/cm{sup 2}, 75 fs laser pulse.

  18. Arecibo Observatory for All

    ERIC Educational Resources Information Center

    Bartus, P.; Isidro, G. M.; La Rosa, C.; Pantoja, C. A.

    2007-01-01

    We describe new materials available at the Arecibo Observatory for visitors with visual impairments. These materials include a guide in Braille that describes the telescope, explains some basic terms used in radio astronomy, and lists frequently asked questions. We have also designed a tactile model of the telescope. Our interest is in enabling…

  19. Current status of the laser guide star adaptive optics system for Subaru Telescope

    NASA Astrophysics Data System (ADS)

    Hayano, Yutaka; Takami, Hideki; Guyon, Olivier; Oya, Shin; Hattori, Masayuki; Saito, Yoshihiko; Watanabe, Makoto; Murakami, Naoshi; Minowa, Yosuke; Ito, Meguru; Colley, Stephen; Eldred, Michael; Golota, Taras; Dinkins, Matthew; Kashikawa, Nobunari; Iye, Masanori

    2008-07-01

    The current status and recent results, since last SPIE conference at Orlando in 2006, for the laser guide star adaptive optics system for Subaru Telescope is presented. We had a first light using natural guide star and succeed to launch the sodium laser beam in October 2006. The achieved Strehl ratio on the 10th magnitude star was around 0.5 at K band. We confirmed that the full-width-half-maximum of the stellar point spread function is smaller than 0.1 arcsec even at the 0.9 micrometer wavelehgth. The size of the artificial guide star by the laser beam tuned at the wavelength of 589 nm was estimated to be 10 arcsec. The obtained blurred artificial guide star is caused by the wavefront error on the laser launching telescope. After the first light and first launch, we found that we need to modify and to fix the components, which are temporarily finished. Also components, which were postponed to fabricate after the first light, are required to build newly. All components used by the natural guide star adaptive optics system are finalized recently and we are ready to go on the sky. Next engineering observation is scheduled in August, 2008.

  20. Integrated guided wave generation and sensing using a single laser source and optical fibers

    NASA Astrophysics Data System (ADS)

    Lee, Hyeonseok; Park, Hyun-Jun; Sohn, Hoon; Kwon, Il-Bum

    2010-10-01

    This study proposes an integrated lead zirconate titanate/fiber Bragg grating (PZT/FBG) system that can generate and measure guided waves for structural health monitoring (SHM) using a common laser source and optical cables. Among various SHM devices used for guided wave generation and sensing, PZT transducers and FBG sensors have been widely used because of their light weight, non-intrusive nature and compactness. To take the best advantage of the merits of these SHM devices, a combination of PZT-based guided wave generation and FBG-based sensing has been attempted by some researchers. However, the existing hybrid approaches have two independent systems: a wave generation system using electrical devices and a sensing system with optical devices. We have developed a fully integrated PZT/FBG system that uses a single laser source and optical cables. This system can alleviate problems associated with conventional electrical cables, such as electromagnetic interference, signal attenuation and vulnerability to noise. A tunable laser, the common power source for guided wave generation and sensing, is modulated and amplified to excite PZT. This laser is also used with FBG sensors for measuring high-speed strain changes induced by guided waves. The feasibility of this system has been experimentally demonstrated using an aluminum plate.

  1. Centroid gain compensation in Shack-Hartmann adaptive optics systems with natural or laser guide star

    PubMed

    Veran; Herriot

    2000-08-01

    In an adaptive optics system with an undersampled Shack-Hartmann wave-front sensor (WFS), variations in seeing, laser guide star quality, and sodium layer thickness and range distance all combine to vary WFS centroid gain across the pupil during an exposure. While using the minimum of 4 pixels per WFS subaperture improves frame rate and read noise, the WFS centroid gain uncertainty may introduce static aberrations and degrade servo loop phase margin. We present a novel method to estimate and compensate WFS gains of each subaperture individually in real time for both natural and laser guide stars. PMID:10935871

  2. Lick sodium laser guide star: performance during the 1998 LGS observing campaign

    SciTech Connect

    Bauman, B; Friedman, H; Gavel, D T

    1999-07-19

    The performance of a sodium laser guide star adaptive optics system depends crucially on the characteristics of the laser guide star in the sodium layer. System performance is quite sensitive to sodium layer spot radiance, that is, return per unit sterradian on the sky, hence we have been working to improve projected beam quality via improvements to the laser and changes to the launched beam format. The laser amplifier was reconfigured to a ''bounce-beam'' geometry, which considerably improves wavefront quality and allows a larger round instead of square launch beam aperture. The smaller beacon makes it easier to block the unwanted Rayleigh light and improves the accuracy of Hartmann sensor wavefront measurements in the A0 system. We present measurements of the beam quality and of the resulting sodium beacon and compare to similar measurements from last year.

  3. Self-guided laser wakefield acceleration beyond 1 GeV using ionization-induced injection.

    PubMed

    Clayton, C E; Ralph, J E; Albert, F; Fonseca, R A; Glenzer, S H; Joshi, C; Lu, W; Marsh, K A; Martins, S F; Mori, W B; Pak, A; Tsung, F S; Pollock, B B; Ross, J S; Silva, L O; Froula, D H

    2010-09-01

    The concepts of matched-beam, self-guided laser propagation and ionization-induced injection have been combined to accelerate electrons up to 1.45 GeV energy in a laser wakefield accelerator. From the spatial and spectral content of the laser light exiting the plasma, we infer that the 60 fs, 110 TW laser pulse is guided and excites a wake over the entire 1.3 cm length of the gas cell at densities below 1.5 × 10(18) cm(-3). High-energy electrons are observed only when small (3%) amounts of CO2 gas are added to the He gas. Computer simulations confirm that it is the K-shell electrons of oxygen that are ionized and injected into the wake and accelerated to beyond 1 GeV energy. PMID:20867526

  4. Direct analysis of gain-guided phase-locked semiconductor laser arrays

    NASA Technical Reports Server (NTRS)

    Marshall, W. K.; Katz, J.

    1986-01-01

    A method for analyzing arbitrary one-dimensional waveguides is described and applied to find the lateral modes of gain-guided laser arrays directly, without the need for a coupled-mode approximation. Detailed results are given for a four-element array for which experimental results are available, and the effect of varying device parameters on the relative gains of the modes is considered. The results show differences between gain-guided and real-index guided arrays which are not evident in prior analyses.

  5. Semiconductor laser having a non-absorbing passive region with beam guiding

    NASA Technical Reports Server (NTRS)

    Botez, Dan (Inventor)

    1986-01-01

    A laser comprises a semiconductor body having a pair of end faces and including an active region comprising adjacent active and guide layers which is spaced a distance from the end face and a passive region comprising adjacent non-absorbing guide and mode control layers which extends between the active region and the end face. The combination of the guide and mode control layers provides a weak positive index waveguide in the lateral direction thereby providing lateral mode control in the passive region between the active region and the end face.

  6. Feasibility experiment for sodium-layer laser guide stars at the Lawrence Livermore National Laboratory

    SciTech Connect

    Max, C.; Avicola, K.; Bissinger, H.; Brase, J.; Gavel, D.; Friedman, H.; Morris, J.; Oliver, S.; Salmon, J.T.; Waltjen, K.

    1992-03-09

    We are developing a feasibility experiment to demonstrate closed-loop adaptive optics using a sodium-layer laser guide star. We will use the copper-vapor-pumped dye lasers developed for LLNL`s Atomic Vapor Laser Isotope Separation Program to create the laser guide star. Closed-loop adaptive corrections will be accomplished using a 69-subaperture adaptive optics system on a one-meter telescope at LLNL. The laser beam will be projected upwards from a beam director approximately 5 meters away from the main telescope, and is expected to form a spot about a meter in diameter at the atmospheric sodium layer (at an altitude of 95 km). Details of the adaptive optics components and an analysis of the expected performance will be presented in companion papers for this Workshop. Here we summarize the overall architecture and system objectives. The long-term goal of our effort is to develop laser guide stars and adaptive optics for large astronomical telescopes.

  7. Design, layout, and early results of a feasibility experiment for sodium-layer laser-guide-star adaptive optics

    SciTech Connect

    Max, C.E.; Avicola, K.; Brase, J.M.

    1994-02-01

    The authors describe the design and the early results of a feasibility experiment for sodium-layer laser-guide-star adaptive optics. Copper-vapor-laser-pumped dye lasers from Lawrence Livermore National Laboratory`s Atomic Vapor Laser Isotope Separation program are used to create the guide star. The laser beam is projected upward from a beam director that is located {approximately}5 m from a 0.5-m telescope and forms an irradiance spot {approximately} 2 m in diameter at the atmospheric-sodium layer (at an altitude of 95 km). The laser guide star is approximately fifth magnitude and is visible to the naked eye at the top of the Rayleigh-scattered laser beam. To date, the authors have made photometric measurements and open-loop wave-front-sensor measurements of the laser guide star. They give an overview of the experiment`s design and the laser systems, describe the experimental setup, show preliminary photometric and open-loop wave-front-sensor data on the guide star, and present predictions of closed-loop adaptive-optics performance based on these experimental data. The long-term goal of this effort is to develop laser guide stars and adaptive optics for use with large astronomical telescopes. 26 refs., 17 figs., 2 tabs.

  8. Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity.

    PubMed

    Hosokai, Tomonao; Kinoshita, Kenichi; Ohkubo, Takeru; Maekawa, Akira; Uesaka, Mitsuru; Zhidkov, Alexei; Yamazaki, Atsushi; Kotaki, Hideyuki; Kando, Masaki; Nakajima, Kazuhisa; Bulanov, Sergei V; Tomassini, Paolo; Giulietti, Antonio; Giulietti, Danilo

    2006-03-01

    We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (lambda=790 nm, 11 TW, 37 fs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak approximately 11.5 MeV[DeltaE/E approximately 10% (FWHM)] and with a narrow-cone angle (0.04pi mm mrad) of ejection is detected at a plasma density of 8 x 10(19) cm(-3). A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations. PMID:16605668

  9. Experimental studies of laser guiding and wake excitation in plasma channels

    NASA Astrophysics Data System (ADS)

    Volfbeyn, Pavel

    1998-12-01

    This thesis presents results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor- Heater scheme was proposed and experimentally tested in hydrogen and nitrogen. It made use of two laser pulses. The Ignitor, an ultrashort (<100 fs) laser pulse, was brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (100-200 ps long) was used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion created a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allowed, for the first time, creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a 5 × 1017 W/cm2, 75fs laser pulse. The guiding properties and transmission and coupling efficiency were studied as a function of relative position of the channel and the injection pulse focus. Whereas entrance coupling efficiency into the channel was lower than expected, channel coupling to continuum losses were found to be in good agreement with analytical predictions. We speculate that increased coupling efficiency can be achieved through better mode matching into the channel. Analytic and numerical one dimensional (1-D), nonrelativistic theory of laser pulse propagation in underdense plasma was presented, in the context of laser wakefield acceleration. The relation between the laser pulse energy depletion, longitudinal laser pulse shape distortion, and changes in the group velocity and center wavelength was explored. 1-D theory was extended to treat the case of a laser exciting a wake in a hollow plasma channel, by making

  10. Improved laser triggering and guiding of meqavolt discharges with dual fs-ns pulses

    SciTech Connect

    Mejean, Guillaume; Ackermann, Roland; Kasparian, Jerome; Salmon, Estelle; Yu Jin; Wolf, Jean-Pierre; Rethmeier, Kay; Kalkner, Wilfried; Rohwetter, Philipp; Stelmaszczyk, Kamil; Woeste, Ludger

    2006-01-09

    We demonstrate that the capacity of ultrashort high-power laser pulses to trigger and guide high-voltage discharges can be significantly enhanced by a subsequent visible nanosecond laser pulse. The femtosecond pulse induces a bundle of filaments, which creates a conducting channel of low density and cold plasma connecting the electrodes. The subsequent laser pulse photodetaches electrons from O{sub 2}{sup -} ions in the electrode leader. The resulting electrons allow efficient heating by Joule effect in a retroaction loop, resulting in a 5% reduction of the breakdown voltage.

  11. Series production of next-generation guide-star lasers at TOPTICA and MPBC

    NASA Astrophysics Data System (ADS)

    Enderlein, Martin; Friedenauer, Axel; Schwerdt, Robin; Rehme, Paul; Wei, Daoping; Karpov, Vladimir; Ernstberger, Bernhard; Leisching, Patrick; Clements, Wallace R. L.; Kaenders, Wilhelm G.

    2014-07-01

    Large telescopes equipped with adaptive optics require high power 589-nm continuous-wave sources with emission linewidths of ~5 MHz. These guide-star lasers should be highly reliable and simple to operate and maintain for many years at the top of a mountain facility. After delivery of the first 20-W systems to our lead customer ESO, TOPTICA and MPBC have begun series production of next-generation sodium guide-star lasers. The chosen approach is based on ESO's patented narrow-band Raman fiber amplifier (RFA) technology [1]. A master oscillator signal from a TOPTICA 50-mW, 1178-nm diode laser, with stabilized emission frequency and linewidth of ~ 1 MHz, is amplified in an MPBC polarization-maintaining (PM) RFA pumped by a high-power 1120-nm PM fiber laser. With efficient stimulated Brillouin scattering suppression, an unprecedented 40 W of narrow-band RFA output has been obtained. This is spatially mode-matched into a patented resonant-cavity frequency doubler providing also the repumper light [2]. With a diffraction-limited output beam and doubling efficiencies < 80%, all ESO design goals have been easily fulfilled. Together with a wall-plug efficiency of < 3%, including all system controls, and a cooling liquid flow of only 5 l/min, the modular, turn-key, maintenance-free and compact system design allows a direct integration with a launch telescope. With these fiber-based guide star lasers, TOPTICA for the first time offers a fully engineered, off-the-shelf guide star laser system for ground-based optical telescopes. Here we present a comparison of test results of the first batch of laser systems, demonstrating the reproducibility of excellent optical characteristics.

  12. Analysis of optical klystron wave guide free electron laser with betatron oscillation effects

    NASA Astrophysics Data System (ADS)

    Jain, Deepi; Mishra, G.

    2014-12-01

    In this paper, we analyze the effect of the betatron oscillation on spontaneous emission and gain spectrum of an optical klystron wave guide free electron laser. The analysis also includes the effects of length mismatch of the two undulator sections of the klystron configuration. We observe that intensity and gain can be change with length mismatch parameter without changing the central emission frequency.

  13. Laser System Technician. A Catalog of Performance Objectives and Performance Guides.

    ERIC Educational Resources Information Center

    Florida State Dept. of Education, Tallahassee. Div. of Vocational, Adult, and Community Education.

    This Vocational-Technical Education Consortium of States (V-TECS) catalog contains the state-of-the-art tasks and standards of performance for the occupation of laser system technician. It provides the curriculum specialist or instructor with the foundation for instructional development. Performance objectives and performance guides are provided…

  14. Laser guiding at relativistic intensities and wakefield particle acceleration in plasma channels

    SciTech Connect

    Geddes, C.G.R.; Toth, Cs.; van Tilborg, J.; Esarey, E.; Schroeder, C.B.; Bruhwiler, D.; Cary, J.; Leemans, W.P.

    2004-08-01

    Electron beams with hundreds of picoCoulombs of charge in percent energy spread at above 80 MeV, and with few milliradian divergence, have been produced for the first time in a high gradient laser wakefield accelerator by guiding the drive laser pulse. Channels formed by hydrodynamic shock were used to guide acceleration relevant laser intensities of at least 1E18W/cm2 at the guide output over more than 10 Rayleigh lengths at LBNL's l'OASIS facility (10TW, 2E19W/cm2). The pondermotive force of the laser pulse drove an intense plasma wave, producing acceleration gradients on the order of 100 GV/m. Electrons were trapped from the background plasma and accelerated. By extending the acceleration length using the guiding channel, the energy of the electron beam was greatly increased, and bunches of small energy spread and low emittance were formed. Experiments varying gas jet length as well assimilations indicate that the high quality beams were formed when beam loading turned off injection after an initial load, producing an isolated bunch, and when that bunch was subsequently accelerated to the dephasing length at which point it rotated in phase space to produce low energy spread.

  15. Performance of capillary discharge guided laser plasma wakefieldaccelerator

    SciTech Connect

    Nakamura, Kei; Esarey, Eric; Geddes, Cameron G.R.; Gonsalves,Anthony J.; Leemans, Wim P.; Panasenko, Dmitriy; Schroeder, Carl B.; Toth, Csaba; Hooker, S.M.

    2007-06-25

    A GeV-class laser-driven plasma-based wakefield acceleratorhas been realized at the Lawrence Berkeley National Laboratory (LBNL).The device consists of the 40TW high repetition rate Ti:sapphire LOASISlaser system at LBNL and a gas-filled capillary discharge waveguidedeveloped at Oxford University. The operation of the capillary dischargeguided laser plasma wakefield accelerator with a capillaryof 225 mu mdiameter and 33 mm in length was analyzed in detail. The input intensitydependence suggests that excessive self-injection causes increased beamloading leading to broadband lower energy electron beam generation. Thetrigger versus laser arrival timing dependence suggests that the plasmachannel parameters can be tuned to reduce beam divergence.

  16. Amateur Observatories

    NASA Astrophysics Data System (ADS)

    Gavin, M.

    1997-08-01

    A roundup of amateur observatories in this country and abroad, with construction and location details, concluding with a detailed description and architect's drawing of the author's own observatory at Worcester Park, Surrey. The text of the 1996 Presidential Address to the British Astronomical Association.

  17. Astronomical observatories

    NASA Technical Reports Server (NTRS)

    Ponomarev, D. N.

    1983-01-01

    The layout and equipment of astronomical observatories, the oldest scientific institutions of human society are discussed. The example of leading observatories of the USSR allows the reader to familiarize himself with both their modern counterparts, as well as the goals and problems on which astronomers are presently working.

  18. Ondrejov Observatory

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    The Ondrejov Observatory is located 20 miles from Prague in the village of Ondrejov. It was established in 1898 as a private observatory and donated to the state of Czechoslovakia in 1928. Since 1953 it has been part of the Astronomical Institute, Academy of Sciences of the Czech Republic; there are 40 astronomers....

  19. Laser to single-mode-fiber coupling: A laboratory guide

    NASA Technical Reports Server (NTRS)

    Ladany, I.

    1992-01-01

    All the information necessary to achieve reasonably efficient coupling of semiconductor lasers to single mode fibers is collected from the literature, reworked when necessary, and presented in a mostly tabular form. Formulas for determining the laser waist radius and the fiber mode radius are given. Imaging relations connecting these values with the object and image distances are given for three types of lenses: ball, hemisphere, and Gradient Index (GRIN). Sources for these lenses are indicated, and a brief discussion is given about ways of reducing feedback effects.

  20. Sky coverage modeling for the whole sky for laser guide star multiconjugate adaptive optics.

    PubMed

    Wang, Lianqi; Andersen, David; Ellerbroek, Brent

    2012-06-01

    The scientific productivity of laser guide star adaptive optics systems strongly depends on the sky coverage, which describes the probability of finding natural guide stars for the tip/tilt wavefront sensor(s) to achieve a certain performance. Knowledge of the sky coverage is also important for astronomers planning their observations. In this paper, we present an efficient method to compute the sky coverage for the laser guide star multiconjugate adaptive optics system, the Narrow Field Infrared Adaptive Optics System (NFIRAOS), being designed for the Thirty Meter Telescope project. We show that NFIRAOS can achieve more than 70% sky coverage over most of the accessible sky with the requirement of 191 nm total rms wavefront. PMID:22695611

  1. Microsurgery of the retina with a needle-guided 193-nm excimer laser.

    PubMed

    Lewis, A; Palanker, D; Hemo, I; Pe'er, J; Zauberman, H

    1992-07-01

    This article presents a method used to guide the beam from an argon fluoride excimer laser to make it suitable for microsurgical purposes and confine it to areas that can be varied in dimension from 1 micron to tens or hundreds of microns. This approach guides the excimer laser beam with an articulated mechanical arm and confines it with variable-diameter tapered tubes, possibly allowing the use of this laser in in vitro retinal surgery with endolaser techniques. Currently, because of the lack of a delivery and focusing system for the 193-nm argon fluoride beam and its absorption by biologic liquids, this laser is used exclusively in ophthalmology for topical applications, such as corneal sculpting. This new method resolves these problems in a unique way with impressive results. Specifically, it was shown that, with this needle-guided excimer laser, it is possible to remove retinal tissue accurately without detectable damage to surrounding cells. Applications of this new technique in retinal surgery are discussed. PMID:1634334

  2. Calibration method for a vision guiding-based laser-tracking measurement system

    NASA Astrophysics Data System (ADS)

    Shao, Mingwei; Wei, Zhenzhong; Hu, Mengjie; Zhang, Guangjun

    2015-08-01

    Laser-tracking measurement systems (laser trackers) based on a vision-guiding device are widely used in industrial fields, and their calibration is important. As conventional methods typically have many disadvantages, such as difficult machining of the target and overdependence on the retroreflector, a novel calibration method is presented in this paper. The retroreflector, which is necessary in the normal calibration method, is unnecessary in our approach. As the laser beam is linear, points on the beam can be obtained with the help of a normal planar target. In this way, we can determine the function of a laser beam under the camera coordinate system, while its corresponding function under the laser-tracker coordinate system can be obtained from the encoder of the laser tracker. Clearly, when several groups of functions are confirmed, the rotation matrix can be solved from the direction vectors of the laser beams in different coordinate systems. As the intersection of the laser beams is the origin of the laser-tracker coordinate system, the translation matrix can also be determined. Our proposed method not only achieves the calibration of a single laser-tracking measurement system but also provides a reference for the calibration of a multistation system. Simulations to evaluate the effects of some critical factors were conducted. These simulations show the robustness and accuracy of our method. In real experiments, the root mean square error of the calibration result reached 1.46 mm within a range of 10 m, even though the vision-guiding device focuses on a point approximately 5 m away from the origin of its coordinate system, with a field of view of approximately 200 mm  ×  200 mm.

  3. Thoracic Pedicle Screw Placement Guide Plate Produced by Three-Dimensional (3-D) Laser Printing.

    PubMed

    Chen, Hongliang; Guo, Kaijing; Yang, Huilin; Wu, Dongying; Yuan, Feng

    2016-01-01

    BACKGROUND The aim of this study was to evaluate the accuracy and feasibility of an individualized thoracic pedicle screw placement guide plate produced by 3-D laser printing. MATERIAL AND METHODS Thoracic pedicle samples of 3 adult cadavers were randomly assigned for 3-D CT scans. The 3-D thoracic models were established by using medical Mimics software, and a screw path was designed with scanned data. Then the individualized thoracic pedicle screw placement guide plate models, matched to the backside of thoracic vertebral plates, were produced with a 3-D laser printer. Screws were placed with assistance of a guide plate. Then, the placement was assessed. RESULTS With the data provided by CT scans, 27 individualized guide plates were produced by 3-D printing. There was no significant difference in sex and relevant parameters of left and right sides among individuals (P>0.05). Screws were placed with assistance of guide plates, and all screws were in the correct positions without penetration of pedicles, under direct observation and anatomic evaluation post-operatively. CONCLUSIONS A thoracic pedicle screw placement guide plate can be produced by 3-D printing. With a high accuracy in placement and convenient operation, it provides a new method for accurate placement of thoracic pedicle screws. PMID:27194139

  4. Thoracic Pedicle Screw Placement Guide Plate Produced by Three-Dimensional (3-D) Laser Printing

    PubMed Central

    Chen, Hongliang; Guo, Kaijing; Yang, Huilin; Wu, Dongying; Yuan, Feng

    2016-01-01

    Background The aim of this study was to evaluate the accuracy and feasibility of an individualized thoracic pedicle screw placement guide plate produced by 3-D laser printing. Material/Methods Thoracic pedicle samples of 3 adult cadavers were randomly assigned for 3-D CT scans. The 3-D thoracic models were established by using medical Mimics software, and a screw path was designed with scanned data. Then the individualized thoracic pedicle screw placement guide plate models, matched to the backside of thoracic vertebral plates, were produced with a 3-D laser printer. Screws were placed with assistance of a guide plate. Then, the placement was assessed. Results With the data provided by CT scans, 27 individualized guide plates were produced by 3-D printing. There was no significant difference in sex and relevant parameters of left and right sides among individuals (P>0.05). Screws were placed with assistance of guide plates, and all screws were in the correct positions without penetration of pedicles, under direct observation and anatomic evaluation post-operatively. Conclusions A thoracic pedicle screw placement guide plate can be produced by 3-D printing. With a high accuracy in placement and convenient operation, it provides a new method for accurate placement of thoracic pedicle screws. PMID:27194139

  5. Design of a fieldable laser system for a sodium-layer guide star

    SciTech Connect

    Friedman, H.W.; Erbert, G.V.; Kuklo, T.C.; Salmon, T.; Smauley, D.A.; Thompson, G.R.; Wong, N.

    1994-12-31

    A laser system to generate a sodium-layer guide star has been designed that incorporates state-of-the-art, solid-state pump lasers and well-developed dye lasers as the frequency tunable converter. With the use of efficient quartz fibers, the pump laser and dye master oscillator can be located far from the telescope, allowing simple thermal management and providing a stable environment for the coherent part of the laser system. The remainder of the system, consisting of single-pass dye amplifiers, is mounted directly on the telescope, thereby eliminating complex and inefficient beam-transport configurations. A key feature of this laser system is the scalability to higher powers, which will be required for observation wavelengths in the visible region. Most of the cost and complexity exist in this {open_quotes}front end{close_quotes} of the system. Adding another dye laser amplifier, which can be accommodated on the same laser table, and adding more pump lasers in the equipment area can raise the output power level to the hundred-watt range.

  6. Optical guiding of terawatt laser pulses in the plasma waveguide

    NASA Astrophysics Data System (ADS)

    Alexeev, I.; Fan, J.; Kim, K. Y.; Nikitin, S.; Milchberg, H. M.

    1999-11-01

    We report coupling and guiding of pulses of peak power 0.5 TW in 1.5 cm long preformed plasma waveguides generated in a high repetition rate argon gas jet. Greater than 50 percent coupling was measured in the injection of 50 mJ, 100 fs pulses, giving guided intensities up to 10^17 W/cm^2. For short delays between waveguide generation and pulse injection, refraction-induced pulse shortening occurred, with this effect reduced either by increasing the delay between waveguide generation and injection or by injecting a prepulse into the waveguide. We will also describe recent experiments which attempt to reduce the avalanche ionization threshold for the gases in which the waveguide is generated. This work is supported by the US Department of Energy (DEF G0297 ER 41039) and the National Science Foundation (PHY-9515509).

  7. Status of ARGOS - The Laser Guide Star System for the LBT

    NASA Astrophysics Data System (ADS)

    Raab, Walfried; Rabien, Sebastian; Gaessler, Wolfgang; Esposito, Simone; Antichi, Jacopo; Lloyd-Hart, Michael; Barl, Lothar; Beckmann, Udo; Bonaglia, Marco; Borelli, Jose; Brynnel, Joar; Buschkamp, Peter; Busoni, Lorenzo; Carbonaro, Luca; Christou, Julian; Connot, Claus; Davies, Richard; Deysenroth, Matthias; Durney, Olivier; Green, Richard; Gemperlein, Hans; Gasho, Victor; Haug, Marcus; Hubbard, Pete; Ihle, Sebastian; Kulas, Martin; Loose, Christina; Lehmitz, Michael; Noenickx, Jamison; Nussbaum, Edmund; Orban De Xivry, Gilles; Quirrenbach, Andreas; Peter, Diethard; Rahmer, Gustavo; Rademacher, Matt; Storm, Jesper; Schwab, Christian; Vaitheeswaran, Vidhya; Ziegleder, Julian

    2013-12-01

    ARGOS is an innovative multiple laser guide star adaptive optics system for the Large Binocular Telescope (LBT), designed to perform effective GLAO correction over a very wide field of view. The system is using high powered pulsed green (532 nm) lasers to generate a set of three guide stars above each of the LBT mirrors. The laser beams are launched through a 40 cm telescope and focused at an altitude of 12 km, creating laser beacons by means of Rayleigh scattering. The returning scattered light, primarily sensitive to the turbulences close to the ground, is detected by a gated wavefront sensor system. The derived ground layer correction signals are directly driving the adaptive secondary mirror of the LBT. ARGOS is especially designed for operation with the multiple object spectrograph Luci, which will benefit from both, the improved spatial resolution, as well as the strongly enhanced flux. In addition to the GLAO Rayleigh beacon system, ARGOS was also designed for a possible future upgrade with a hybrid sodium laser - Rayleigh beacon combination, enabling diffraction limited operation. The ARGOS laser system has undergone extensive tests during Summer 2012 and is scheduled for installation at the LBT in Spring 2013. The remaining sub-systems will be installed during the course of 2013. We report on the overall status of the ARGOS system and the results of the sub-system characterizations carried out so far.

  8. Guiding of intense femtosecond laser pulses in fully ionized plasma channels

    NASA Astrophysics Data System (ADS)

    Downer, M. C.

    2002-11-01

    Plasma waveguides capable of guiding relativistically intense fs laser pulses without optical distortion are essential to developing GeV-scale laser wakefield accelerators, coherent short-wavelength sources and lenses for fourth-generation x-ray sources. Various approaches to guiding terawatt pulses through preformed plasma fibers inside gas-filled solid capillaries [1], and in laser-generated cylindrical shock waves [2] will be compared. We report the first implementation of a laser-generated waveguide in a Helium plasma, which provides full ionization and minimization of ionization-induced distortions of the guided pulse up to relativistic guided intensity. 80 fs laser pulses were guided at near-relativistic intensity (0.2 x 10^18 W/cm^2) over 60 Rayleigh ranges (1.5 cm) with > 50% throughput, 20 Hz repetition rate and no detectable distortion of their spectrum or 16 micron-diameter TEM_00 mode structure [3]. Channels were generated by the method developed by Milchberg et al. [2], in which a filament of He gas (300-700 Torr) was ionized and heated by a powerful line-focused Nd:YAG laser pulse. To enable waveguide formation in Helium, the method was modified by slightly (0.1%) pre-ionizing the helium to seed inverse bremsstrahlung absorption, and by lengthening (100 to 400 ps) and strengthening (0.3 to 1 J) the channel-forming laser pulse. Recent femtosecond time-resolved pump-probe experiments inside the Helium channel will be reported. The issues involved, and current progress, in upgrading performance to fully relativistic guided intensity (10^18 W/cm^2) will be discussed. [1] Ehrlich et al., Phys. Rev. Lett. 77, 4186 (1996); Hosokai et al., Opt. Lett. 25, 10 (2000); Spence et al., Phys. Rev. E 63, 015401 (2001). [2] C. G. Durfee, III and H. M. Milchberg, Phys. Rev. Lett. 71, 2409 (1993); J. Fan, et al. Appl. Phys. Lett. 73, 3064 (1998). [3] E. W. Gaul et al., Appl. Phys. Lett. 77, 4112 (2000).

  9. Aero-thermal simulations of the TMT Laser Guide Star Facility

    NASA Astrophysics Data System (ADS)

    Vogiatzis, Konstantinos; Boyer, Corinne; Wei, Kai; Tang, Jinlong; Ellerbroek, Brent

    2014-08-01

    The Laser Guide Star Facility (LGSF) system of the Thirty Meter Telescope (TMT) will generate the artificial laser guide stars required by the TMT Adaptive Optics (AO) systems. The LGSF uses multiple sodium lasers to generate and project several asterisms from a laser launch telescope located behind the TMT secondary mirror. The laser beams are transported from a location below the primary mirror to the launch telescope using conventional optics to relay the beams along the telescope structure. The beams and relay optics are enclosed into hermetic ducts for safety reasons and to protect the optics against the environment. A Computational Solid Fluid Dynamics (CSFD) model of the LGSF ducts has been developed. It resolves the duct thickness, laser beam transfer lenses, mirrors and their framework for most of the laser beam path that is subject to significant temperature gradients and/or large vertical change. It also resolves the air inside the duct and its thermal interaction with the aforementioned components through conjugate heat transfer. The thermal interaction of the laser beam with the optics is also captured. The model provides guidance to the LGSF design team and a first estimate of the laser beam stability performance and requirement compliance. As the telescope structure design has evolved in the recent years, a new optical path has been proposed for the LGSF. Both the original and the new optical paths are compared against optical, mechanical and other telescope performance related criteria. The optical performance criteria include a first order analysis of the optical turbulence generated within the ducts. In this study simulations of the thermal environment within the ducts of the two candidate paths are performed and conclusions are drawn.

  10. Design and evaluation of a fiberoptic fluorescence guided laser recanalization system.

    PubMed

    Garrand, T J; Stetz, M L; O'Brien, K M; Gindi, G R; Sumpio, B E; Deckelbaum, L I

    1991-01-01

    Current angioplasty techniques for recanalization of totally occluded arteries are limited by the inability to cross the occlusion and by the risk of perforation. A fiberoptic fluorescence guided laser recanalization system was developed and evaluated in vitro for recanalization of 17 human femoral or tibial totally occluded arterial segments (length 1.9-6.8 cm, diameter 2.5-6.0 mm). A 400 or 600 micron silica fiber was coupled to a helium-cadmium laser (lambda = 325 nm) for fluorescence excitation and to a holmium: YAG laser (lambda = 2.1 micron) for tissue ablation. Fluorescence was recorded during recanalization after every other holmium laser pulse. During recanalization, each arterial segment was bent 30-90 degrees with respect to the fiber to simulate arterial tortuosity. Ablation continued with fiber advancement as long as the fluorescence confirmed that the target tissue was atherosclerotic. Arterial spectra were classified as normal or atherosclerotic by an on-line computerized fluorescence classification algorithm (sensitivity 93%, specificity 95%). Normal fluorescence necessitated redirection of the fiber greater than 30 times per segment to continue recanalization. Fifteen of 17 totally occluded arteries had multiple recanalization channels created following total energy delivery of 40-1,016 Joules per segment with no angiographic or histologic evidence of laser perforation. Two heavily calcified arterial occlusions were not recanalized due to inhibition of holmium: YAG laser ablation by the recording of normal fluorescence spectra. Therefore, this fluorescence guided laser recanalization system appears safe and effective for recanalization of totally occluded arteries and merits in vivo evaluation. However, the lower sensitivity of fluorescence detection of heavily calcified plaques may limit the efficacy (but not safety) of fluorescence guided recanalization of heavily calcified occlusions. PMID:2034008

  11. Laser-Guided Neuronal Tracing in Brain Explants

    PubMed Central

    Klug, Achim

    2016-01-01

    Short Abstract We describe a technique to label neurons and their processes via anterograde or retrograde tracer injections into brain nuclei using an in-vitro preparation. We modified an existing method of in-vitro tracer electroporation by taking advantage of fluorescently labeled mouse mutants and basic optical equipment in order to increase labeling accuracy. Long Abstract We present a technique which combines an in-vitro tracer injection protocol, which uses a series of electrical and pressure pulses to increase dye uptake through electroporation in brain explants with targeted laser illumination and matching filter goggles during the procedure. The described technique of in-vitro electroporation by itself yields relatively good visual control for targetting certain areas of the brain. By combining it with laser excitation of fluorescent genetic markers and their read-out through band-passing filter goggles, which can pick up the emissions of the genetically labeled cells/nuclei and the fluorescent tracing dye, a researcher can substantially increase the accuracy of injections by finding the area of interest and controlling for the dye-spread/uptake in the injection area much more efficiently. In addition, the laser illumination technique allows to study the functionality of a given neurocircuit by providing information about the type of neurons projecting to a certain area in cases where the GFP expression is linked to the type of transmitter expressed by a subpopulation of neurons. PMID:26649948

  12. On-Sky Tests of a High-Power Pulsed Laser for Sodium Laser Guide Star Adaptive Optics

    NASA Astrophysics Data System (ADS)

    Otarola, Angel; Hickson, Paul; Gagné, Ronald; Bo, Yong; Zuo, Junwei; Xie, Shiyong; Feng, Lu; Rochester, Simon; Budker, Dmitry; Shen, Shixia; Xue, Suijian; Min, Li; Wei, Kai; Boyer, Corinne; Ellerbroek, Brent; Hu, Jingyao; Peng, Qinjun; Xu, Zuyan

    2016-03-01

    We present results of on-sky tests performed in the summer of 2013 to characterize the performance of a prototype high-power pulsed laser for adaptive optics. The laser operates at a pulse repetition rate (PRR) of 600-800Hz, with a 6% duty cycle. Its coupling efficiency was found to be, in the best test case (using 18W of transmitted power), 231±14 photons s‑1 sr‑1 atom‑1 W‑1 m2 when circular polarization was employed and 167±17 photons s‑1 sr‑1 atom‑1 W‑1 m2 with linear polarization. No improvement was seen when D2b repumping was used, but this is likely due to the relatively large laser guide star (LGS) diameter, typically 10 arcsec or more, which resulted in low irradiance levels. Strong relaxation oscillations were present in the laser output, which have the effect of reducing the coupling efficiency. To better understand the results, a physical modeling was performed using the measured pulse profiles and parameters specific to these tests. The model results, for a 10 arcsec angular size LGS spot, agree well with the observations. When extrapolating the physical model for a sub-arcsecond angular size LGS (typical of what is needed for a successful astronomical guide star), the model predicts that this laser would have a coupling efficiency of 130 photons s‑1 sr‑1 atom‑1 W‑1 m2, using circular polarization and D2b repumping, for a LGS diameter of 0.6 arcsec Full Width at Half Maximum (FWHM), and free of relaxation oscillations in the 589 nm laser light.

  13. Near-IR Image-Guided Laser Ablation of Demineralization on Tooth Occlusal Surfaces

    PubMed Central

    Tom, Henry; Chan, Kenneth H.; Darling, Cynthia L.; Fried, Daniel

    2016-01-01

    Introduction Studies have shown that reflectance images at near-IR wavelengths coincident with higher water absorption are well-suited for image-guided laser ablation of carious lesions since the contrast between sound and demineralized enamel is extremely high and interference from stains is minimized. The objective of this study was to demonstrate that near-IR reflectance images taken at a wavelength range of 1,500–1,700 nm can be used to guide a 9.3 μm CO2 laser for the selective ablation of early demineralization on tooth occlusal surfaces. Methods The occlusal surfaces of ten sound human molars were used in this in vitro study. Shallow simulated caries lesions with random patterns and varying depth and position were produced on tooth occlusal surfaces. Sequential near-IR reflectance images at 1,500–1,700 nm were used to guide the laser for the selective removal of the demineralized enamel. Digital microscopy and polarization sensitive optical coherence tomography (PS-OCT) were used to assess selectivity. Results Images taken before and after lesion removal suggest that the demineralized areas were removed with high selectivity. Although the estimated volume of tissue ablated was typically higher than the initial lesion volume measured with PS-OCT, the volume of enamel removed by the laser correlated well with the initial lesion volume. Conclusion Sequential near-IR reflectance images at 1,500–1,700 nm can be used to guide a 9.3 μm CO2 laser for the selective ablation of early demineralization on tooth occlusal surfaces. PMID:26763111

  14. Electromagnetically Induced Guiding and Superradiant Amplification of Counter-Propagating Lasers in Plasma

    SciTech Connect

    Fisch, N.J.; Shvets, G.

    1998-08-01

    The interaction of counter-propagating laser pulses in a plasma in considered. When the frequencies of the two lasers are close, nonlinear modification of the refraction index results in the mutual focusing of the two beams. A short (of order the plasma period) laser pulse can be nonlinearly focused by a long counter-propagating beam which extends over the entire guiding length. It is also demonstrated that a short (< 1/ omega (sub p)) laser pulse can be superradiantly amplified by a counter-propagating long low-intensity pump while remaining ultra-short. Particle-in-Cell simulations indicate that pump depletion can be as high as 40%. This implies that the long pump is efficiently compressed in time without frequency chirping and pulse stretching, making the superradiant amplification an interesting alternative to the conventional method of producing ultra-intense pulses by the chirped-pulse amplification.

  15. Imaging performance analysis of adaptive optical telescopes using laser guide stars.

    PubMed

    Welsh, B M

    1991-12-01

    The use of laser guide stars in conjunction with adaptive optical telescopes offers the possibility of nearly diffraction-limited imaging performance from large, ground-based telescopes. We investigate the expected imaging performance of an adaptive telescope, using laser guide stars created in the mesospheric sodium (Na) layer. A 2-3-m class telescope is analyzed for the case of a single, on-axis guide star at an altitude of 92 km (the nominal height of the mesospheric Na layer). We analyze an annular telescope pupil with approximately 15 wave-front sensor subapertures and mirror actuators spanning the pupil diameter. The imaging performance is quantified in terms of the pupil-averaged rms wave-front error, the optical transfer function, the point spread function, the Strehl ratio, and finally the angular resolution. The performance analysis takes into account the degradation caused by the limitation of the wave-front sensor as well as the deformable mirror. These limitations include the finite spacing and size of the wave-front sensor subapertures and the spacing and influence function of the mirror actuators. The effects of anisoplanatism and shot noise are also included in the analysis. The results of the investigation indicate that a 3-m adaptive telescope using a single Na guide star is capable of achieving a Strehl ratio of 0.57 and an angular resolution nearly matching that of diffraction-limited performance (0.05 arcsec). This performance is achieved assuming that r(0) = 20 cm and a 5-W laser is used to create the guide star. The effect of variations in seeing conditions and guide star brightness is also investigated. PMID:20717316

  16. Intrinsic corrections to optical guiding in a free electron laser

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Jiuan; Scharlemann, E. T.; Sessler, A. M.

    1988-10-01

    The effect on optical guiding of the undulations of an electron beam in an FEL is investigated, and a model for a fully saturated FEL amplifier with no remaining gain is developed. The density of the electrom beam in the model fully includes the effects of both transverse and longitudinal undulation of the beam. The longitudinal density modulation is expressed in terms of the Bessel functions of ζ, where ζ = {a w2}/{2(1 + a w2}) is the shift of the electron phase in the electron bucket caused by its longitudinal undulation. The transverse density modulation is evaluated to second order in the ratio of undulation amplitude δr to beam radial scale length rb. The radiation field from the modeled beam is calculated in terms of spatial modes proportional to exp[i( k + δk + lkw) z - i ωt], where l is an arbitrary integer. Here, δk is the change of the wavenumber of the radiation caused by the electron bunches. Radially radiating modes with intensity on the order of ( {δk}/{k w)ζ 2} are found. Optical guiding is found to be modified by the transverse undulations of the beam at second order in {δr}/{r b}, and by the longitudinal undulations to first order in {δk}/{k w}. For the usual FEL parameters, the correction is quite small.

  17. Taosi Observatory

    NASA Astrophysics Data System (ADS)

    Sun, Xiaochun

    Taosi observatory is the remains of a structure discovered at the later Neolithic Taosi site located in Xiangfen County, Shanxi Province, in north-central China. The structure is a walled enclosure on a raised platform. Only rammed-earth foundations of the structure remained. Archaeoastronomical studies suggest that this structure functioned as an astronomical observatory. Historical circumstantial evidence suggests that it was probably related to the legendary kingdom of Yao from the twenty-first century BC.

  18. Design of guided-mode resonance mirrors for short laser cavities.

    PubMed

    Kondo, Tomohiro; Ura, Shogo; Magnusson, Robert

    2015-08-01

    A guided-mode resonance mirror (GMRM) consists of a waveguide grating integrated on an optical buffer layer on a high-reflection substrate. An incident free-space wave at the resonance wavelength is once coupled by the grating to a guided mode and coupled again by the same grating back to free space. The reflection characteristics of a GMRM are numerically calculated and theoretically analyzed. It is predicted that notch filtering or flat reflection spectra are obtained depending on the optical buffer layer thickness. Design of short cavities using a GMRM is discussed for potential application in surface-mount packaging of diode lasers onto a photonic circuit board. PMID:26367288

  19. Hydrogen isotope correction for laser instrument measurement bias at low water vapor concentration using conventional isotope analyses: application to measurements from Mauna Loa Observatory, Hawaii.

    PubMed

    Johnson, L R; Sharp, Z D; Galewsky, J; Strong, M; Van Pelt, A D; Dong, F; Noone, D

    2011-03-15

    The hydrogen and oxygen isotope ratios of water vapor can be measured with commercially available laser spectroscopy analyzers in real time. Operation of the laser systems in relatively dry air is difficult because measurements are non-linear as a function of humidity at low water concentrations. Here we use field-based sampling coupled with traditional mass spectrometry techniques for assessing linearity and calibrating laser spectroscopy systems at low water vapor concentrations. Air samples are collected in an evacuated 2 L glass flask and the water is separated from the non-condensable gases cryogenically. Approximately 2 µL of water are reduced to H(2) gas and measured on an isotope ratio mass spectrometer. In a field experiment at the Mauna Loa Observatory (MLO), we ran Picarro and Los Gatos Research (LGR) laser analyzers for a period of 25 days in addition to periodic sample collection in evacuated flasks. When the two laser systems are corrected to the flask data, they are strongly coincident over the entire 25 days. The δ(2)H values were found to change by over 200‰ over 2.5 min as the boundary layer elevation changed relative to MLO. The δ(2)H values ranged from -106 to -332‰, and the δ(18)O values (uncorrected) ranged from -12 to -50‰. Raw data from laser analyzers in environments with low water vapor concentrations can be normalized to the international V-SMOW scale by calibration to the flask data measured conventionally. Bias correction is especially critical for the accurate determination of deuterium excess in dry air. PMID:21290447

  20. CONTROL OF LASER RADIATION PARAMETERS. GENERATION OF ULTRASHORT PULSES: Mode locking in linear injection laser arrays with gain-guided waveguides

    NASA Astrophysics Data System (ADS)

    Nakwaski, W.

    1990-12-01

    The problem of mode locking in linear arrays of lasers with gain-guided waveguides is considered on the basis of a theoretical analysis of Basov, Belenov, and Letokhov for diffraction-coupled lasers and also using the Vaĭnshteĭn approximation for diffraction losses. A simple calculation procedure, enabling an easy determination of the maximum wavelength difference between adjacent elements of gain-guided arrays, is proposed.

  1. Multimodal scanning laser ophthalmoscopy for image guided treatment of age-related macular degeneration

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Ferguson, R. D.; Patel, Ankit H.; Iftimia, Nicusor V.; Mujat, Mircea; Husain, Deeba

    2009-02-01

    Subretinal neovascular membranes (SRNM) are a deleterious complication of laser eye injury and retinal diseases such as age-related macular degeneration (AMD), choroiditis, and myopic retinopathy. Photodynamic therapy (PDT) and anti-vascular endothelial growth factor (VEGF) drugs are approved treatment methods. PDT acts by selective dye accumulation, activation by laser light, and disruption and clotting of the new leaky vessels. However, PDT surgery is currently not image-guided, nor does it proceed in an efficient or automated manner. This may contribute to the high rate of re-treatment. We have developed a multimodal scanning laser ophthalmoscope (SLO) for automated diagnosis and image-guided treatment of SRNMs associated with AMD. The system combines line scanning laser ophthalmoscopy (LSLO), fluorescein angiography (FA), indocyanine green angiography (ICGA), PDT laser delivery, and retinal tracking in a compact, efficient platform. This paper describes the system hardware and software design, performance characterization, and automated patient imaging and treatment session procedures and algorithms. Also, we present initial imaging and tracking measurements on normal subjects and automated lesion demarcation and sizing analysis of previously acquired angiograms. Future pre-clinical testing includes line scanning angiography and PDT treatment of AMD subjects. The automated acquisition procedure, enhanced and expedited data post-processing, and innovative image visualization and interpretation tools provided by the multimodal retinal imager may eventually aid in the diagnosis, treatment, and prognosis of AMD and other retinal diseases.

  2. High contrast optical imaging methods for image guided laser ablation of dental caries lesions

    PubMed Central

    LaMantia, Nicole R.; Tom, Henry; Chan, Kenneth H.; Simon, Jacob C.; Darling, Cynthia L.; Fried, Daniel

    2014-01-01

    Laser based methods are well suited for automation and can be used to selectively remove dental caries to minimize the loss of healthy tissues and render the underlying enamel more resistant to acid dissolution. The purpose of this study was to determine which imaging methods are best suited for image-guided ablation of natural non-cavitated carious lesions on occlusal surfaces. Multiple caries imaging methods were compared including near-IR and visible reflectance and quantitative light fluorescence (QLF). In order for image-guided laser ablation to be feasible, chemical and physical modification of tooth surfaces due to laser irradiation cannot greatly reduce the contrast between sound and demineralized dental hard tissues. Sound and demineralized surfaces of 48 extracted human molar teeth with non-cavitated lesions were examined. Images were acquired before and after laser irradiation using visible and near-IR reflectance and QLF at several wavelengths. Polarization sensitive-optical coherence tomography was used to confirm that lesions were present. The highest contrast was attained at 1460-nm and 1500–1700-nm, wavelengths coincident with higher water absorption. The reflectance did not decrease significantly after laser irradiation for those wavelengths. PMID:24791129

  3. High contrast optical imaging methods for image guided laser ablation of dental caries lesions

    NASA Astrophysics Data System (ADS)

    LaMantia, Nicole R.; Tom, Henry; Chan, Kenneth H.; Simon, Jacob C.; Darling, Cynthia L.; Fried, Daniel

    2014-02-01

    Laser based methods are well suited for automation and can be used to selectively remove dental caries to minimize the loss of healthy tissues and render the underlying enamel more resistant to acid dissolution. The purpose of this study was to determine which imaging methods are best suited for image-guided ablation of natural non-cavitated carious lesions on occlusal surfaces. Multiple caries imaging methods were compared including near-IR and visible reflectance and quantitative light fluorescence (QLF). In order for image-guided laser ablation to be feasible, chemical and physical modification of tooth surfaces due to laser irradiation cannot greatly reduce the contrast between sound and demineralized dental hard tissues. Sound and demineralized surfaces of 48 extracted human molar teeth with non-cavitated lesions were examined. Images were acquired before and after laser irradiation using visible and near-IR reflectance and QLF at several wavelengths. Polarization sensitive-optical coherence tomography was used to confirm that lesions were present. The highest contrast was attained at 1460-nm and 1500-1700-nm, wavelengths coincident with higher water absorption. The reflectance did not decrease significantly after laser irradiation for those wavelengths.

  4. GeV electron beams from cm-scale channel guided laser wakefieldaccelerator

    SciTech Connect

    Nakamura,K.; Nagler, B.; Toth, Cs.; Geddes, C.G.R.; Schroeder,C.; Esarey, E.; Leemans, W.P.; Gonsalves, A.J.; Hooker, S.M.

    2007-02-20

    Laser-wakefield accelerators (LWFA) can produce electricfields of order 10-100 GV/m suitable for acceleration of electrons torelativistic energies. The wakefields are excited by a relativisticallyintense laser pulse propagating through a plasma and have a phasevelocity determined by the group velocity of the light pulse. Twoimportant effects that can limit the acceleration distanceand hence thenet energy gain obtained by an electron are diffraction of the drivelaser pulse and particle-wake dephasing. Diffraction of a focusedultra-short laser pulse can be overcome by using preformed plasmachannels. The dephasing limit can be increased by operating at a lowerplasma density, since this results in an increase in the laser groupvelocity. Here we present detailed results on the generation of GeV-classelectron beams using an intense femtosecond laser beamand a 3.3 cm longpreformed discharge-based plasma channel [W.P. Leemans et al., NaturePhysics 2, 696-699 (2006)]. The use of a discharge-based waveguidepermitted operation at an order ofmagnitude lower density and 15 timeslonger distance than in previous experiments that relied on laserpreformed plasma channels. Laser pulses with peak power ranging from10-50 TW were guided over more than 20 Rayleigh ranges and high-qualityelectron beams with energy up to 1 GeV were obtained by channelling a 40TW peak power laser pulse. The dependence of the electron beamcharacteristics on capillary properties, plasma density,and laserparameters are discussed.

  5. Combination of fiber-guided pulsed erbium and holmium laser radiation for tissue ablation under water

    NASA Astrophysics Data System (ADS)

    Pratisto, Hans; Frenz, Martin; Ith, Michael; Altermatt, Hans J.; Jansen, E. Duco; Weber, Heinz P.

    1996-07-01

    Because of the high absorption of near-infrared laser radiation in biological tissue, erbium lasers and holmium lasers emitting at 3 and 2 mu m, respectively, have been proven to have optimal qualities for cutting or welding and coagulating tissue. To combine the advantages of both wavelengths, we realized a multiwavelength laser system by simultaneously guiding erbium and holmium laser radiation by means of a single zirconium fluoride (ZrF4) fiber. Laser-induced channel formation in water and poly(acrylamide) gel was investigated by the use of a time-resolved flash-photography setup, while pressure transients were recorded simultaneously with a needle hydrophone. The shapes and depths of vapor channels produced in water and in a submerged gel after single erbium and after combination erbium-holmium radiation delivered by means of a 400- mu m ZrF4 fiber were measured. Transmission measurements were performed to determine the amount of pulse energy available for tissue ablation. The effects of laser wavelength and the delay time between pulses of different wavelengths on the photomechanical and photothermal responses of meniscal tissue were evaluated in vitro by the use of histology. It was observed that the use of a short (200- mu s, 100-mJ) holmium laser pulse as a prepulse to generate a vapor bubble through which the ablating erbium laser pulse can be transmitted (delay time, 100 mu s) increases the cutting depth in meniscus from 450 to 1120 mu m as compared with the depth following a single erbium pulse. The results indicate that a combination of erbium and holmium laser radiation precisely and efficiently cuts tissue under water with 20-50- mu m collateral tissue damage. wave, cavitation, channel formation, infrared-fiber-delivery system, tissue damage, cartilage.

  6. Performance of keck adaptive optics with sodium laser guide star

    SciTech Connect

    Gavel, D.T.; Olivier, S.; Brase, J.

    1996-03-08

    The Keck telescope adaptive optics system is designed to optimize performance in he 1 to 3 micron region of observation wavelengths (J, H, and K astronomical bands). The system uses a 249 degree of freedom deformable mirror, so that the interactuator spacing is 56 cm as mapped onto the 10 meter aperture. 56 cm is roughly equal to r0 at 1.4 microns, which implies the wavefront fitting error is 0.52 ({lambda}/2{pi})({ital d}/{ital r}{sub 0}){sup 5/6} = 118 nm rms. This is sufficient to produce a system Strehl of 0.74 at 1.4 microns if all other sources of error are negligible, which would be the case with a bright natural guidestar and very high control bandwidth. Other errors associated with the adaptive optics will however contribute to Strehl degradation, namely, servo bandwidth error due to inability to reject all temporal frequencies of the aberrated wavefront, wavefront measurement error due to finite signal-to-noise ratio in the wavefront sensor, and, in the case of a laser guidestar, the so-called cone effect where rays from the guidestar beacon fail to sample some of the upper atmosphere turbulence. Cone effect is mitigated considerably by the use of the very high altitude sodium laser guidestar (90 km altitude), as opposed to Rayleigh beacons at 20 km. However, considering the Keck telescope`s large aperture, this is still the dominating wavefront error contributor in the current adaptive optics system design.

  7. An ion guide laser ion source for isobar-suppressed rare isotope beams.

    PubMed

    Raeder, Sebastian; Heggen, Henning; Lassen, Jens; Ames, Friedhelm; Bishop, Daryl; Bricault, Pierre; Kunz, Peter; Mjøs, Anders; Teigelhöfer, Andrea

    2014-03-01

    Modern experiments at isotope separator on-line (ISOL) facilities like ISAC at TRIUMF often depend critically on the purity of the delivered rare isotope beams. Therefore, highly selective ion sources are essential. This article presents the development and successful on-line operation of an ion guide laser ion source (IG-LIS) for the production of ion beams free of isobaric contamination. Thermionic ions from the hot ISOL target are suppressed by an electrostatic potential barrier, while neutral radio nuclides effusing out are resonantly ionized by laser radiation within a quadrupole ion guide behind this barrier. The IG-LIS was developed through detailed thermal and ion optics simulation studies and off-line tests with stable isotopes. In a first on-line run with a SiC target a suppression of surface-ionized Na contaminants in the ion beam of up to six orders of magnitude was demonstrated. PMID:24689577

  8. Thermo-mechanical simulation of guided waves in pipes excited by laser pulses

    NASA Astrophysics Data System (ADS)

    Lim, Hyeong Uk; Hong, Jung-Wuk

    2013-04-01

    Ultrasonic guided waves have been widely utilized for the structural health monitoring (SHM) of structural components such as plates and pipes. In particular, the noncontact excitation of the pipe surfaces using laser pulses has shown several advantages in experiments by eliminating the bonding process of the dielectric patches on the curved surfaces and the complicated interpretation of the temperature effect on the bonding layers. However, the numerical simulation of the methodology requires thermo-mechanical coupling and large-scale computation. Therefore, the numerical efficiency of the spatial partitioning by deploying thermo-mechanical elements and mechanical elements is investigated. Then, the laser excitation on the surface is modeled in the form of heat flux, and the generated wave forms are observed. The formation and propagation of the guided waves are also represented numerically.

  9. Positioning method for a visual guiding system in a laser welding machine

    NASA Astrophysics Data System (ADS)

    He, Tao; Fan, Youqing; Xie, Yulang; Wu, Qinghua

    2013-10-01

    Combined with the development of guiding systems in laser welding, a visual guidance based positioning method for coaxial installation with a laser welding head is researched. A system calibrating method has been researched and designed, which is to install calibration cylinder in the part fixing a machined part, and test the calibration cylinder center coordinates works calibration of the system. A localization method based on template matching and characteristics of the target image are extracted as target image for templates, guiding two localizations both coarse positioning and fine positioning. Coarse positioning can reduce the influence of other information on the target image. Fine positioning is the second location of targets on the basis of the coarse positioning, reducing the information and keeping effect information of target image characteristics. And the method of sub-pixel localization based on least square method is fixed the center position of the target.

  10. An ion guide laser ion source for isobar-suppressed rare isotope beams

    SciTech Connect

    Raeder, Sebastian Ames, Friedhelm; Bishop, Daryl; Bricault, Pierre; Kunz, Peter; Mjøs, Anders; Heggen, Henning; Institute of Applied Physics, TU Darmstadt, Schlossgartenstr. 7, 64289 Darmstadt ; Lassen, Jens Teigelhöfer, Andrea; Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2

    2014-03-15

    Modern experiments at isotope separator on-line (ISOL) facilities like ISAC at TRIUMF often depend critically on the purity of the delivered rare isotope beams. Therefore, highly selective ion sources are essential. This article presents the development and successful on-line operation of an ion guide laser ion source (IG-LIS) for the production of ion beams free of isobaric contamination. Thermionic ions from the hot ISOL target are suppressed by an electrostatic potential barrier, while neutral radio nuclides effusing out are resonantly ionized by laser radiation within a quadrupole ion guide behind this barrier. The IG-LIS was developed through detailed thermal and ion optics simulation studies and off-line tests with stable isotopes. In a first on-line run with a SiC target a suppression of surface-ionized Na contaminants in the ion beam of up to six orders of magnitude was demonstrated.

  11. Laser Wakefield Acceleration at Reduced Density in the Self-Guided Regime

    SciTech Connect

    Ralph, J E; Albert, F; Glenzer, S H; Palastro, J P; Pollock, B B; Shaw, J L; Till, A; Froula, D H; Clayton, C E; Lu, W; Mori, W B; Pak, A E; Joshi, C; Martin, S; Silva, L O

    2009-11-18

    Experiments conducted using a 200TW 60 fs laser have demonstrated up to 720 MeV electrons in the self-guided laser wakefield regime using pure Helium gas jet targets. Charge and energy of the accelerated electrons was measured using an electron spectrometer with a 0.5T magnet and charge callibrated image plates. The self-trapped charge in a helium plasma was shown to fall off with decreasing electron density with a threshold at 2.5 x 10{sup 18} (cm{sup -3}) below which no charge is trapped. Self-guiding however is shown to continue below this density limitation over distances of 14 mm with an exit spot size of 25{micro}m. Simulations show that injection of electrons at these densities can be assisted through ionization induced trapping in a mix of Helium with 3% Oxygen.

  12. Effects of the irradiation of a finite number of laser beams on the implosion of a cone-guided target

    NASA Astrophysics Data System (ADS)

    Yanagawa, T.; Sakagami, H.; Nagatomo, H.; Sunahara, A.

    2016-03-01

    In direct drive laser fusion, the non-uniformity of the laser absorption on the target surface caused by the irradiation of a finite number of laser beams is a sever problem. GekkoXII laser at Osaka University has twelve laser beams and is irradiated to the target with a dodecahedron orientation, in which the distribution of the laser absorption on the target surface becomes non-uniform. Furthermore, in the case of a cone-guided target, the laser irradiation orientation is more limited. In this paper, we conducted implosion simulations of the cone- guided target based on GekkoXII irradiation orientation and compared the case of using the twelve beams and nine beams where the three beams irradiating the cone region are cut. The implosion simulations were conducted by a three-dimensional pure hydro code.

  13. Use of the carbon dioxide laser in guided tissue regeneration wound healing in the beagle dog

    NASA Astrophysics Data System (ADS)

    Rossmann, Jeffrey A.; Parlar, Ates; Abdel-Ghaffar, Khaled A.; El-Khouli, Amr M.; Israel, Michael

    1996-04-01

    The concept of guided tissue regeneration (GTR) allowing cells from the periodontal ligament and alveolar bone to repopulate the treated root surface has shown the ability to obtain periodontal new attachment. Healing studies have also shown that conventional GTR therapy still does not exclude all the epithelium. This epithelial proliferation apically interferes with the establishment of the new connective tissue attachment to the root surface. The objective of this research study was to examine whether controlled de-epithelialization with the carbon dioxide laser during the healing phase after periodontal surgery, would retard the apical migration of the epithelium and thereby enhance the results obtained through guided tissue regeneration. Eight beagle dogs were used, the experimental side received de-epithelialization with the CO2 laser in conjunction with flap reflection and surgically created buccal osseous defects. Selected defects on each side were treated with ePTFE periodontal membranes. The laser de-epithelialization was repeated every 10 days until removal of the membranes. The control side received the same surgical treatment without laser application. This experimental design allowed histologic study of the new attachment obtained in defects treated with flap debridement with or without laser de-epithelialization and with or without ePTFE membranes. A statistical analysis was performed on the histometric data from 48 teeth in the 8 dogs after 4 months of healing. The results showed significant amounts of new attachment obtained from all four treatment modalities with no statistically significant differences for any one treatment. However, the trend towards enhanced regeneration with the combined treatment of laser and membrane vs. membrane alone or debridement alone was evident. The histologic analysis revealed a significant amount of newly formed `fat cementum' seen only on the laser treated teeth. This feature was the most remarkable finding of the

  14. Free-running modes for gain-guided diode laser arrays

    NASA Astrophysics Data System (ADS)

    Hadley, G. Ronald; Hohimer, John P.; Owyoung, A.

    1987-06-01

    A numerical model for directly calculating the eigenmodes of multiple-stripe gain-guided diode laser arrays is presented which includes the effects of both carrier diffusion and heating in the active region. Comprehensive calculations of the eigenmodes of a CW gain-guided array using this model are directly compared to experimental observations on commercial ten-stripe arrays. These numerical and experimental results show that, contrary to popular wisdom, gain-guided arrays are characterized by a large number of eigenmodes, not limited to the number of elements in the array. In addition, the results show the importance of including the refractive index perturbation arising from junction heating, which dramatically alters both the character and the gain of the array modes.

  15. Keele Observatory

    NASA Astrophysics Data System (ADS)

    Theodorus van Loon, Jacco; Albinson, James; Bagnall, Alan; Bryant, Lian; Caisley, Dave; Doody, Stephen; Johnson, Ian; Klimczak, Paul; Maddison, Ron; Robinson, StJohn; Stretch, Matthew; Webb, John

    2015-08-01

    Keele Observatory was founded by Dr. Ron Maddison in 1962, on the hill-top campus of Keele University in central England, hosting the 1876 Grubb 31cm refractor from Oxford Observatory. It since acquired a 61cm research reflector, a 15cm Halpha solar telescope and a range of other telescopes. Run by a group of volunteering engineers and students under directorship of a Keele astrophysicist, it is used for public outreach as well as research. About 4,000 people visit the observatory every year, including a large number of children. We present the facility, its history - including involvement in the 1919 Eddington solar eclipse expedition which proved Albert Einstein's theory of general relativity - and its ambitions to erect a radio telescope on its site.

  16. 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

  17. 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.

  18. Suppression of Weibel Instabilities in Advanced Fast Ignition Laser Fusion Pellets by Two Cone-Guided Relativistic Laser Beams

    NASA Astrophysics Data System (ADS)

    Stefan, V.

    2007-11-01

    I propose utilization of two cone-guided relativistic laser beams in antiparallel interaction with the fusion pellet as a novel approach for the suppression of Weibel instabilities in the core of advanced fast ignition pellets.ootnotetextM. Tabak, J. Hammer, M.E. Glinsky, W.L. Kruer, S. C. Wilks, J. Woodworth, E. M. Campbell, and M.D. Perry, Phys. Plasmas 1 (5), 1626 (1994). The propagation of generated suprathermal electron beam toward the core may lead to the appearance of colossal (˜10MG), small scale (L˜velocity of light/local electron plasma frequencyootnotetextV. Stefan, Suppression of Weibel Instabilities by High-Harmonic Electron Bernstein Modes in Advanced Fast Ignition Laser Fusion Pellets.APS-2006. October 30-November 3, 2006; Philadelphia, Pennsylvania. magnetic fields. This would suppress the transport of magnetic fields into the core of the pellet and may eliminate the difficulties in the nonlinear-relativistic treatment of magnetized core plasma.

  19. Near-infrared image-guided laser ablation of dental decay

    PubMed Central

    Tao, You-Chen; Fried, Daniel

    2009-01-01

    Image-guided laser ablation systems are now feasible for dentistry with the recent development of nondestructive high-contrast imaging modalities such as near-IR (NIR) imaging and optical coherence tomography (OCT) that are capable of discriminating between sound and demineralized dental enamel at the early stages of development. Our objective is to demonstrate that images of demineralized tooth surfaces have sufficient contrast to be used to guide a CO2 laser for the selective removal of natural and artificial caries lesions. NIR imaging and polarization-sensitive optical coherence tomography (PS-OCT) operating at 1310-nm are used to acquire images of natural lesions on extracted human teeth and highly patterned artificial lesions produced on bovine enamel. NIR and PS-OCT images are analyzed and converted to binary maps designating the areas on the samples to be removed by a CO2 laser to selectively remove the lesions. Postablation NIR and PS-OCT images confirmed preferential removal of demineralized areas with minimal damage to sound enamel areas. These promising results suggest that NIR and PS-OCT imaging systems can be integrated with a CO2 laser ablation system for the selective removal of dental caries. PMID:19895146

  20. Near-infrared image-guided laser ablation of dental decay

    NASA Astrophysics Data System (ADS)

    Tao, You-Chen; Fried, Daniel

    2009-09-01

    Image-guided laser ablation systems are now feasible for dentistry with the recent development of nondestructive high-contrast imaging modalities such as near-IR (NIR) imaging and optical coherence tomography (OCT) that are capable of discriminating between sound and demineralized dental enamel at the early stages of development. Our objective is to demonstrate that images of demineralized tooth surfaces have sufficient contrast to be used to guide a CO2 laser for the selective removal of natural and artificial caries lesions. NIR imaging and polarization-sensitive optical coherence tomography (PS-OCT) operating at 1310-nm are used to acquire images of natural lesions on extracted human teeth and highly patterned artificial lesions produced on bovine enamel. NIR and PS-OCT images are analyzed and converted to binary maps designating the areas on the samples to be removed by a CO2 laser to selectively remove the lesions. Postablation NIR and PS-OCT images confirmed preferential removal of demineralized areas with minimal damage to sound enamel areas. These promising results suggest that NIR and PS-OCT imaging systems can be integrated with a CO2 laser ablation system for the selective removal of dental caries.

  1. Mesospheric sodium structure variability on horizontal scales relevant to laser guide star asterisms

    NASA Astrophysics Data System (ADS)

    Pfrommer, Thomas; Hickson, Paul

    2012-07-01

    Adaptive optics (AO) systems of modern telescopes use laser guide stars, produced by resonant excitation of sodium atoms in the mesosphere at around 92 km. Wavefront sensor subapertures, if sufficiently far away from the primary mirror center, resolve the internal structure of the sodium layer. The variability of this structure is caused by the influence of gravity waves and wind shear turbulence. The relevance of such dynamics to AO has been investigated over the past four years. A high-resolution lidar system, employed at the 6-m liquid mirror telescope, which is located near Vancouver, Canada, has been used to study mesospheric dynamics, such as the temporal behavior of the mean altitude. The main results from this study have been published elsewhere and will be summarized here. Along with the temporal variability, the mean altitude on horizontal scales of order IOs of meters has been studied by introducing a tip/tilt stage in the experimental setup. This enables us to swap the laser pulse within a 1 arcmin field of view. The horizontal mean altitude structure function has been measured on 10 observing nights between July and August 2011. Results reveal severe structural differences and a strong horizontal anisotropy. Individual laser beacons in a laser guide star asterism will therefore have at the same time significantly different focus heights. By propagating this 2d structure function to the entrance pupil of a 39 m telescope, we derive a differential focus wavefront error map.

  2. High quality electron beams from a plasma channel guided laser wakefield accelerator

    SciTech Connect

    Geddes, C.G.R.; Toth, Cs.; van Tilborg, J.; Esarey, E.; Schroeder, C.B.; Bruhwiler, D.; Nieter, C.; Cary, J.; Leemans, W.P.

    2004-07-08

    Laser driven accelerators, in which particles are accelerated by the electric field of a plasma wave driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV/m. These fields are thousands of times those achievable in conventional radiofrequency (RF) accelerators, spurring interest in laser accelerators as compact next generation sources of energetic electrons and radiation. To date however, acceleration distances have been severely limited by lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance results in low energy beams with 100% electron energy spread, limiting applications. Here we demonstrate that a relativistically intense laser can be guided by a preformed plasma density channel and that the longer propagation distance can result in electron beams of percent energy spread with low emittance and increased energy, containing >10{sup 9} electrons above 80 MeV. The preformed plasma channel technique forms the basis of a new class of accelerators, combining beam quality comparable to RF accelerators with the high gradients of laser accelerators to produce compact tunable high brightness electron and radiation sources.

  3. High-quality electron beams from a laser wakefield accelerator using plasma-channel guiding.

    PubMed

    Geddes, C G R; Toth, C S; Van Tilborg, J; Esarey, E; Schroeder, C B; Bruhwiler, D; Nieter, C; Cary, J; Leemans, W P

    2004-09-30

    Laser-driven accelerators, in which particles are accelerated by the electric field of a plasma wave (the wakefield) driven by an intense laser, have demonstrated accelerating electric fields of hundreds of GV m(-1) (refs 1-3). These fields are thousands of times greater than those achievable in conventional radio-frequency accelerators, spurring interest in laser accelerators as compact next-generation sources of energetic electrons and radiation. To date, however, acceleration distances have been severely limited by the lack of a controllable method for extending the propagation distance of the focused laser pulse. The ensuing short acceleration distance results in low-energy beams with 100 per cent electron energy spread, which limits potential applications. Here we demonstrate a laser accelerator that produces electron beams with an energy spread of a few per cent, low emittance and increased energy (more than 10(9) electrons above 80 MeV). Our technique involves the use of a preformed plasma density channel to guide a relativistically intense laser, resulting in a longer propagation distance. The results open the way for compact and tunable high-brightness sources of electrons and radiation. PMID:15457252

  4. Plasma Parameter of a Capillary Discharge-Produced Plasma Channel to Guide an Ultrashort Laser Pulse

    SciTech Connect

    Higashiguchi, Takeshi; Terauchi, Hiromitsu; Bai, Jin-xiang; Yugami, Noboru

    2009-01-22

    We have observed the optical guiding of a 100-fs laser pulse with the laser intensity in the range of 10{sup 16} W/cm{sup 2} using a 1.5-cm long capillary discharge-produced plasma channel for compact electron acceleration applications. The optical pulse propagation using the plasma channel is achieved with the electron densities of 10{sup 17}-10{sup 18} cm{sup -3} and the electron temperatures of 0.5-4 eV at a discharge time delay of around 150 ns and a discharge current of 500 A with a pulse duration of 100-150 ns. An energy spectrum of the accelerated electrons from a laser-plasma acceleration scheme showed a peak at 1.3 MeV with a maximum energy tail of 1.6 MeV.

  5. Intelligent Image Analysis for Image-Guided Laser Hair Removal and Skin Therapy

    NASA Technical Reports Server (NTRS)

    Walker, Brian; Lu, Thomas; Chao, Tien-Hsin

    2012-01-01

    We present the development of advanced automatic target recognition (ATR) algorithms for the hair follicles identification in digital skin images to accurately direct the laser beam to remove the hair. The ATR system first performs a wavelet filtering to enhance the contrast of the hair features in the image. The system then extracts the unique features of the targets and sends the features to an Adaboost based classifier for training and recognition operations. The ATR system automatically classifies the hair, moles, or other skin lesion and provides the accurate coordinates of the intended hair follicle locations. The coordinates can be used to guide a scanning laser to focus energy only on the hair follicles. The intended benefit would be to protect the skin from unwanted laser exposure and to provide more effective skin therapy.

  6. Tip-tilt reconstruction with a single dim natural guide star in multiconjugate adaptive optics with laser guide stars

    NASA Astrophysics Data System (ADS)

    Femenã­A, Bruno

    2005-12-01

    A solution to the problem of detecting the tip-tilt modes in multiconjugate adaptive optics (MCAO) with laser guide stars (LGS) is presented. This solution requires the presence of only a single relatively dim natural guide star (NGS) within the reconstructed field of view (FoV). The dim NGS is used for the reconstruction of the tip-tilt modes on the entire FoV, while the tomographic reconstruction of second-order and higher-order modes is made possible by having an LGS constellation with LGSs at different heights. Due to the relatively low brightness required for the tip-tilt NGS and the large corrected FoV (as compared with the case of conventional adaptive optics) the presented solution provides a means to achieve near-diffraction-limited performance of a 10-m-class telescope in the near infrared over a large portion of the sky. Sky coverage calculations assuming median seeing conditions indicate that this technique could be applied to 75% (95%) of the sky, achieving corrections with an average Strehl ratio -0.42(-0.33) in the 2.2 μm K band across the 1.5 - reconstructed FoV.

  7. MR-Guided Laser-Induced Thermotherapy of the Infratemporal Fossa and Orbit in Malignant Chondrosarcoma via a Modified Technique

    SciTech Connect

    Vogl, Thomas J.; Mack, Martin G.; Straub, Ralf; Eichler, Katrin; Zangos, Stephan

    2001-12-15

    A 76-year-old patient presented with a recurrent mass of a malignant chondrosarcoma in the right infratemporal fossa and in the left maxillary sinus with orbital invasion. The patient was treated with a palliative intention with MR-guided laser-induced thermotherapy using a modified applicator technique. Following treatment clinical symptoms improved and MRI revealed complete laser-induced tumor necrosis.

  8. Detection of superficial esophageal squamous cell neoplasia by chromoendoscopy-guided confocal laser endomicroscopy

    PubMed Central

    Huang, Jin; Yang, Yun-Sheng; Lu, Zhong-Sheng; Wang, Shuang-Fang; Yang, Jing; Yuan, Jing

    2015-01-01

    AIM: To evaluate the diagnostic potential of Lugol’s chromoendoscopy-guided confocal laser endomicroscopy (CLE) in detecting superficial esophageal squamous cell neoplasia (ESCN). METHODS: Between December 2008 and September 2010, a total of 52 patients were enrolled at the Chinese PLA General Hospital in Beijing, China. First, Lugol’s chromoendoscopy-guided CLE was performed in these patients and the CLE in vivo histological diagnosis was recorded. Then, chromoendoscopy-guided biopsy was performed in the same patients by another endoscopist who was blinded to the CLE findings. Based on the biopsy and CLE diagnosis, en bloc endoscopic resection was performed. The CLE in vivo diagnosis and the histological diagnosis of biopsy of ESCN were compared, using a histological examination of the endoscopic resection specimens as the standard reference. RESULTS: A total of 152 chromoendoscopy-guided biopsies were obtained from 56 lesions. In the 56 lesions of 52 patients, a total of 679 CLE images were obtained vs 152 corresponding biopsies. The sensitivity, specificity, negative predictive value and positive predictive value of chromoendoscopy-guided CLE compared with biopsy were 95.7% vs 82% (P < 0.05), 90% vs 70% (P < 0.05), 81.8% vs 46.7% (P < 0.05), and 97.8% vs 92.7% (P > 0.05), respectively. There was a significant improvement in sensitivity, specificity, negative predictive value, and accuracy when comparing chromoendoscopy-guided CLE with biopsy. CONCLUSION: Lugol’s chromoendoscopy-guided CLE is a real-time, non-invasive endoscopic diagnostic technology; the accuracy of the detection of superficial ESCN is equivalent to or may be superior to biopsy histology. PMID:26078575

  9. Robo-AO: Initial results from the first autonomous laser guide star adaptive optics instrument

    NASA Astrophysics Data System (ADS)

    Riddle, R. L.; Baranec, C.; Law, N. M.; Ramaprakash, A. N.; Tendulkar, S.; Hogstrom, K.; Bui, K.; Burse, M.; Chordia, P.; Das, H.; Dekany, R.; Kulkarni, S.; Punnadi, S.; Smith, R.

    2014-12-01

    Large surveys are discovering thousands of objects which require further characterization at high angular resolution. The demands on space-based observatories and large telescopes with AO systems leave them generally unavailable for large high angular resolution surveys. To address this gap, we have developed Robo-AO, the first robotic laser AO system, as an economical and efficient imaging instrument for 1-3 m class telescopes. Observations of over 200 stellar objects per night have routinely been performed, with target-to-target observation overheads of less than 1.5 minutes. Scientific programs of several thousands of targets can be executed in mere weeks, and Robo-AO has already completed the three largest AO surveys to date.

  10. Laser Station Design for the Global Light System for the Planned JEM-EUSO Extreme Universe Observatory

    NASA Astrophysics Data System (ADS)

    Geier, Christine; Burg, Martin; Bigler, Colton; Wiencke, Lawrence

    2014-03-01

    The JEM-EUSO Global Light System (GLS) will provide ground-based calibration and monitoring for the JEM-EUSO detector planned for the International Space Station (ISS). JEM-EUSO will use the atmosphere as a giant calorimeter to measure Ultra High Energy Cosmic Rays (UHECRs). The GLS will include twelve ground stations. All twelve will have calibration xenon flash bulbs and six will have steered lasers. The GLS laser stations will generate optical signatures by creating light tracks across the JEM-EUSO field of view. The lasers and xenon flashers will be used to benchmark the JEM-EUSO instrument during its mission since energy, duration and orientation of those sources can be controlled. In this presentation, we will describe a project to design and build a working prototype of a GLS laser station. In order to meet the specifications set forth in the design requirements, our design incorporates remote operation capability, solar power, and a controlled internal climate. These components are in addition to the laser and calibration system and steering mechanism. All components will be combined in a robust, durable design that can be deployed and operated in remote locations across the globe.