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Layered target burnthrough experiments using 50 nsec KrF laser pulses

Description: Experiments have been performed on two types of planar layered targets using the Sprite KrF laser. The targets lused were: (1) 0.25 to 3.0 microns of Al deposited on an SiO/sub 2/ substrate and (2) 0.25 to 3.0 microns of CH (parylene-N) deposited on 0.20 microns of Al on an SiO/sub 2/ substrate. The laser was characterized by a pulse length of 50 nsec FWHM, an intensity of 2 x 10/sup 10/ watts/cm/sup 2/ and a wavelength of 248.5 nm. A filtered photoiodide and a streak camera, each operating in the visible, viewed the rear of the target. We measured the time from the beginning of the laser pulse to the onset of the visible light signal as seen by the photoiodide at the rear of the initially opaque target. This time is referred to as the burnthrough time. We obtain an estimate of the mass ablation by plotting the mass ablation depth (mass density times target thickness in ..mu..gm/cm/sup 2/) versus the burnthrough time. These results are consistent with earlier mass loss measurements and with analytic and hydro-code calculations (LASNEX). The streak camera data shows emission at target positions larger than the laser focal spot, and thus are consistent with 1-D and 2-D calculations which show target surface ablation to be primarily driven by reradiated photons from the hot laser produced plasma.
Date: January 1, 1986
Creator: Kephart, J.F.; Dingus, R.S.; Gitomer, S.J.; Kopp, R.A. & Shaw, M.J.
Partner: UNT Libraries Government Documents Department

Laser Interactions for the Synthesis and In Situ Diagnostics of Nanomaterials

Description: Laser interactions have traditionall been at thec center of nanomaterials science, providing highly nonequilibrium growth conditions to enable the syn- thesis of novel new nanoparticles, nanotubes, and nanowires with metastable phases. Simultaneously, lasers provide unique opportunities for the remote char- acterization of nanomaterial size, structure, and composition through tunable laser spectroscopy, scattering, and imaging. Pulsed lasers offer the opportunity, there- fore, to supply the required energy and excitation to both control and understand the growth processes of nanomaterials, providing valuable views of the typically nonequilibrium growth kinetics and intermediates involved. Here we illustrate the key challenges and progress in laser interactions for the synthesis and in situ diagnostics of nanomaterials through recent examples involving primarily carbon nanomaterials, including the pulsed growth of carbon nanotubes and graphene.
Date: January 1, 2014
Creator: Geohegan, David B.; Puretzky, Alexander A.; Yoon, Mina; Eres, Gyula; Rouleau, Christopher; Xiao, Kai et al.
Partner: UNT Libraries Government Documents Department

Field Evaluation of the U.S. Army Engineer Topographic Laboratories' Laser Dam Alignment Instrument

Description: Summary: Several series of laser instrument alignment surveys were made at the exterior roadway deck level and within the interior inspection gallery of Keystone Dam, Oklahoma, and compared with theodolite surveys over the same lines and under similar conditions.
Date: April 1973
Creator: Davis, Carl D.
Partner: UNT Libraries Government Documents Department

Review of long-pulse laser development

Description: A brief review of some present techniques to obtain long-pulse laser action in excimer discharge devices will be presented. An attempt will be made to point out the strengths and weaknesses of these techniques. 18 refs., 15 figs.
Date: January 1, 1989
Creator: Sze, R.C.
Partner: UNT Libraries Government Documents Department

Stable 1 --> 0 carbon monoxide laser

Description: A stable carbon monoxide laser capable of oscillation on transitions in the fundamental 1 ..-->.. 0 band is described. This laser is also capable of a quasi-continuous tunability in the range of 4.7 to 8 microns.
Date: July 1, 1978
Creator: Gerlach, R. & Amer, N.M.
Partner: UNT Libraries Government Documents Department

Polymeric-host sulforhodamine-B lasers: Doubled Nd:YAG pumped

Description: Solid-state dye lasers, pumped by a doubled Nd:YAG laser, were evaluated as a function of concentration, output coupler reflectivity and oscillator dimensions. A slope efficiency of up to 62% was achieved. A maximum irradiance of 59 MW/cm{sup 2} to the dye laser cavity was achieved. 7 refs., 2 figs., 4 tabs.
Date: January 1, 1991
Creator: Gettemy, D.J.; Hermes, R.E. (Los Alamos National Lab., NM (USA)) & Barnes, N.P. (National Aeronautics and Space Administration, Hampton, VA (USA). Langley Research Center)
Partner: UNT Libraries Government Documents Department

High average power excimer laser-pumped dye oscillators

Description: The design, construction, and testing of a high-average-power excimer laser-pumped dye oscillator is described. The system is designed to produce up to 75 watts of average power in the near uv at a pulse repetition rate of 500 Hz. 8 figs.
Date: January 1, 1988
Creator: Tennant, R.A.; Whitehead, M.C.; Tallman, C.R. & Basinger, R.W.
Partner: UNT Libraries Government Documents Department

Free-Electron Lasers: Present Status and Future Prospects

Description: Free-electron lasers as scientific instruments are reviewed. The present status and future prospects are delineated with attention drawn to the size, complexity, availability, and performance capability of this new tool. The Free-Electron Laser (FEL) was proposed by John Madey in 1970 (1), although earlier work, relevant to the concept, had been performed by Motz (2) and by Phillips (3). Experimental demonstration was achieved by Madey, et. al. in 1975 and 1976 (4). Since that time, FELs of diverse configurations have been operated at several laboratories around the world. At present, FEL development is focused in two directions: in constructing reliable FELs for scientific research and in extending FEL capability to vacuum ultra-violet (VUV) and even shorter wavelengths. In this article we shall only very briefly review the principles of an FEL, putting emphasis on those aspects that limit performance, after which we shall discuss the applications, present status and future prospects of FELs. Much material that we wish to present is in the form of Tables, and they are an essential part of this article.
Date: May 1, 1990
Creator: Kim, K.-J. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Limits to Electron Beam Emittance from Stochastic Coulomb Interactions

Description: Dense electron beams can now be generated on an ultrafast timescale using laser driven photo-cathodes and these are used for a range of applications from ultrafast electron defraction to free electron lasers. Here we determine a lower bound to the emittance of an electron beam limited by fundamental stochastic Coulomb interactions.
Date: August 22, 2008
Creator: Coleman-Smith, Christopher; Padmore, Howard A. & Wan, Weishi
Partner: UNT Libraries Government Documents Department

Fundamental mechanisms of optical damage in short-wavelength high-power lasers

Description: Evidence has been accumulating for many years that the physical mechanisms responsible for damage to optical materials in and from high-power, short-wave-length lasers (SWLs) differ in fundamental ways from the thermal processes identified in infrared and visible-wavelength laser damage problems. We propose that this difference stems primarily from the electronic nature of the absorption and excitation processes which occur when SWL photons strike an optical surface, and that electrons, ions and uv photons generated in the laser excitation cycle also contribute to optical damage. In this paper, we present recent experimental results which have pinpointed specific electronic excitation mechanisms which can operate in the high-power laser environment. In many optical materials of interest for SWLs, the deposition of electronic energy creates self-trapped excitons which decay through the energetic expulsion of atoms and molecules from the surface of the material. This erosion process is accompanied by the creation of permanent electronic defects which become nucleation sites for further damage. The relationship between these microscopic mechanisms and observed macroscopic damage phenomenology is discussed, along with evidence for the existence of a surface overlayer which may point the way to radically new techniques for protecting SWL optical elements from laser damage.
Date: October 1, 1985
Creator: Haglund, R.F. Jr.; Tolk, N.H. & York, G.W.
Partner: UNT Libraries Government Documents Department

FIRST DEMONSTRATION OF STAGED LASER ACCELERATION.

Description: Two independently-driven laser accelerators were operated together in series for the first time in a proof-of-principle experiment to demonstrate staging. The ability to stage together these devices is important for eventually building practical laser-driven accelerators. The laser accelerators consisted of two identical inverse free electron lasers (IFEL), where the first IFEL served as a prebuncher, which created {approx}3-fs long microbunches that were accelerated by the second IFEL. Precise and stable control of the phasing between the microbunches and laser wave inside the second IFEL was demonstrated. The effects of over-modulation of the prebuncher were also investigated. In all cases there was good agreement with the model. Additional details of the microbunch characteristics could be inferred by using the model. Plans for demonstrating monoenergetic laser acceleration are also presented.
Date: June 18, 2001
Creator: Kimura, W. D.; Campbell, L. P.; DILLEY,C.E.; Gottschalk, S. C.; Quimby, D. C.; BABZIEN,M. BEN-ZVI,I. et al.
Partner: UNT Libraries Government Documents Department

Damage resistance of coated optics

Description: Successful application of high energy lasers to national needs in strategic defense, inertial confinement fusion and isotope separation is contingent on the development of optical coatings that can withstand very intense radiation. Significant progress has been made in the development of damage resistant coatings over the past 15 years to support the needs of the inertial confinement fusion and isotope separation programs. However, the requirements evolving from the Strategic Defense Initiative (SDI) are much more severe and demand dramatic improvements in the performance of optical coatings beyond the current state of the art. The approach taken at Los Alamos towards solving the problems of optical coatings for SDI is presented.
Date: January 1, 1985
Creator: Wadt, W.R.
Partner: UNT Libraries Government Documents Department

A reliable low-maintenance flashlamp-pumped Ti:sapphire laser operating at 120 PPS

Description: Flashlamp-pumped Ti:sapphire lasers have been reported to produce high-energy pulses with broad tunability. However, with the flashlamps operated close to their explosion energy, and thermal loading effects in the laser rod, these lasers were restricted to low repetition rates (typically around 10 PPS). Higher repetition rates at constant laser pulse energy reduce the flashlamp lifetime drastically. The author reports on a reliable flashlamp-pumped Ti:sapphire laser that has been operating at 120 PPS for over 10{sup 9} shots with the only cavity or pump chamber maintenance being flashlamp changes less than every 2{times}10{sup 8} pulses -- the lowest maintenance reported. A specular dual-lamp pump chamber was used to pump a 4 mm {times} 6 inches, 0.1% doped Ti:sapphire rod. This resulted in a very low lasing threshold, which ensured a stable output at low pump levels. The criterion for pump power was to obtain a highly stable output at the edge of the selected tuning range, from 790 to 860 nm. The combination of flashlamp walls, flashlamp flow tubes, and rod solarization.
Date: March 1, 1994
Creator: Witte, K. H.
Partner: UNT Libraries Government Documents Department

A two-photon fluorescence autocorrelator for a Nd:YLF modelocked laser

Description: In this thesis, I discuss the design and implementation of an autocorrelator for an actively modelocked ND:YLF laser at wavelength 1.054{mu}m. A dye is used to generate a broadband two-photon fluorescence (TPF) signal at 570nm which is the autocorrelation of the laser pulses. Two different techniques are discussed. A colliding pulse scheme can be used to generate a TPF autocorrelation signal as a function of distance, or an interferometer technique can be used to generate an autocorrelation signal as a function of the delay in an interferometer arm. Experimental results are discussed, but they are inconclusive because of difficulties in interpreting the signal.
Date: May 1, 1991
Creator: Kner, P. A.
Partner: UNT Libraries Government Documents Department

Phase-locked arrays of vertical-cavity surface-emitting lasers

Description: Vertical Cavity Surface-Emitting Lasers (VCSELs) are of increasing interest to the photonics community because of their surface-emitting structure, simple fabrication and packaging, wafer-level testability and potential for low cost. Scaling VCSELs to higher power outputs requires increasing the device area, which leads to transverse mode control difficulties if devices become larger than 10-15 microns. One approach to increasing the device size while maintaining a well controlled transverse mode profile is to form coupled or phase-locked, two-dimensional arrays of VCSELs that are individually single-transverse mode. The authors have fabricated and characterized both photopumped and electrically injected two-dimensional VCSEL arrays with apertures over 100 microns wide. Their work has led to an increased understanding of these devices and they have developed new types of devices, including hybrid semiconductor/dielectric mirror VCSEL arrays, VCSEL arrays with etched trench, self-aligned, gold grid contacts and arrays with integrated phase-shifters to correct the far-field pattern.
Date: May 1, 1994
Creator: Warren, M. E.; Hadley, G. R.; Lear, K. L.; Gourley, P. L.; Vawter, G. A.; Zolper, J. C. et al.
Partner: UNT Libraries Government Documents Department

Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation

Description: Time resolved shadowgraph images were recorded of shockwaves and particle ejection from silicon during laser ablation. Particle ejection and expansion were correlated to an internal shockwave resonating between the shockwave front and the target surface. The number of particles ablated increased with laser energy and was related to the crater volume.
Date: May 6, 2006
Creator: Liu, C.Y.; Mao, X.L.; Greif, R. & Russo, R.E.
Partner: UNT Libraries Government Documents Department