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A Technique for Increasing the Optical Strength of Single-Crystal NaCl and KCl Through Temperature Cycling

Description: This thesis relates a technique for increasing the optical strength of NaCl and KCl single-crystal samples. The 1.06-μm pulsed laser damage thresholds were increased by factors as large as 4.6 for a bulk NaCl single-crystal sample. The bulk laser damage breakdown threshold (LDBT) of the crystal was measured prior to and after heat treatment at 800*C using a Nd:YAG laser operating at 1.06 μm. Bulk and surface LDBTs were also studied on samples annealed at 400° C. These samples showed differences in damage morphology on both cleaved and polished surfaces, and the cleaved surfaces had improved damage thresholds. However, neither the polished surfaces nor the bulk showed improved threshold at the lower annealing temperature.
Date: May 1983
Creator: Franck, Jerome B. (Jerome Bruce)
Partner: UNT Libraries

Wide Area Thermal Processing of Light Emitting Materials

Description: Laboratory laser materials synthesis of wide bandgap materials has been successfully used to create white light emitting materials (LEMs). This technology development has progressed to the exploration on design and construction of apparatus for wide area doping and phase transformation of wide bandgap material substrates. The objective of this proposal is to develop concepts for wide area doping and phase transformation based on AppliCote Associates, LLC laser technology and ORNL high density pulsed plasma arc technology.
Date: October 1, 2011
Creator: Duty, Chad E; Joshi, Pooran C; Jellison Jr, Gerald Earle; Angelini, Joseph Attilio & Sabau, Adrian S
Partner: UNT Libraries Government Documents Department

Development of large scale production of Nd-doped phosphate glasses for megajoule-scale laser systems

Description: Nd-doped phosphate glasses are the preferred gain medium for high-peak-power lasers used for Inertial Confinement Fusion research because they have excellent energy storage and extraction characteristics. In addition, these glasses can be manufactured defect-free in large sizes and at relatively low cost. To meet the requirements of the future mega-joule size lasers, advanced laser glass manufacturing methods are being developed that would enable laser glass to be continuously produced at the rate of several thousand large (790 x 440 x 44 mm{sup 3}) plates of glass per year. This represents more than a 10 to 100-fold improvement in the scale of the present manufacturing technology.
Date: May 1, 1996
Creator: Ficini, G. & Campbell, J.H.
Partner: UNT Libraries Government Documents Department

Large area damage testing of optics

Description: The damage threshold specifications for the National Ignition Facility will include a mixture of standard small-area tests and new large-area tests. During our studies of laser damage and conditioning processes of various materials we have found that some damage morphologies are fairly small and this damage does not grow with further illumination. This type of damage might not be detrimental to the laser performance. We should therefore assume that some damage can be allowed on the optics, but decide on a maximum damage allowance of damage. A new specification of damage threshold termed {open_quotes}functional damage threshold{close_quotes} was derived. Further correlation of damage size and type to system performance must be determined in order to use this measurement, but it is clear that it will be a large factor in the optics performance specifications. Large-area tests have verified that small-area testing is not always sufficient when the optic in question has defect-initiated damage. This was evident for example on sputtered polarizer and mirror coatings where the defect density was low enough that the features could be missed by standard small- area testing. For some materials, the scale-length at which damage non-uniformities occur will effect the comparison of small-area and large-area tests. An example of this was the sub-aperture tests on KD*P crystals on the Beamlet test station. The tests verified the large-area damage threshold to be similar to that found when testing a small-area. Implying that for this KD*P material, the dominate damage mechanism is of sufficiently small scale-length that small-area testing is capable of determining the threshold. The Beamlet test station experiments also demonstrated the use of on-line laser conditioning to increase the crystals damage threshold.
Date: April 26, 1996
Creator: Sheehan, L.; Kozlowski, M. & Stolz, C.
Partner: UNT Libraries Government Documents Department

Recent advances in phosphate laser glasses for high power applications. Revision 1

Description: Recent advances in Nd-doped phosphate laser glasses for high-peak-power and high-average-power applications are reviewed. Compositional studies have progressed to the point that glasses can be tailored to have specific properties for specific applications. Non-radiative relaxation effects can be accurately modeled and empirical expressions have been developed to evaluate both intrinsic (structural) and extrinsic (contamination induced) relaxation effects. Losses due to surface scattering and bulk glass absorption have been carefully measured and can be accurately predicted. Improvements in processing have lead to high damage threshold (e.g. Pt inclusion free) and high thermal shock resistant glasses with improved edge claddings. High optical quality pieces up to 79 x 45 x 4 cm{sup 3} have been made and methods for continuous melting laser glass are under development.
Date: May 1, 1996
Creator: Campbell, J.H.
Partner: UNT Libraries Government Documents Department

Laser intensity modulation by nonabsorbing defects

Description: Nonabsorbing defects can lead to laser damage. Defects such as voids, microcracks, and localized stressed concentrations, even if they differ from the surrounding medium only by refractive index, can serve as positive or negative lenses for the incident laser light. The resulting interference pattern between refracted and diffracted light can result in intensity increases on the order of a factor of 2 some distance away from a typical negative microlens, and even larger for a positive microlens. Thus, the initial damage site can be physically removed from the defect which initiates damage. The parameter that determines the strength of such lensing is (Ka){sup 2}{Delta}{epsilon}, where the wavenumber K is 2{pi}/{lambda}, 2a is the linear size of the defect, and {Delta}{epsilon} is the difference in dielectric coefficient between matrix and scatterer. Thus, even a small change in refractive index results in a significant effect for a defect large compared to a wavelength. Geometry is also important. Three dimensional (e.g. voids) as well as linear and planar (e.g. cracks) microlenses can all have strong effects. This paper evaluates intensification due to spherical voids and high refractive index inclusions.
Date: November 20, 1996
Creator: Feit, M.D., Rubenchik, A.M.
Partner: UNT Libraries Government Documents Department

Effective index model predicts modal frequencies of vertical-cavity lasers

Description: Previously, an effective index optical model was introduced for the analysis of lateral waveguiding effects in vertical-cavity surface-emitting lasers. The authors show that the resultant transverse equation is almost identical to the one typically obtained in the analysis of dielectric waveguide problems, such as a step-index optical fiber. The solution to the transverse equation yields the lateral dependence of the optical field and, as is recognized in this paper, the discrete frequencies of the microcavity modes. As an example, they apply this technique to the analysis of vertical-cavity lasers that contain thin-oxide apertures. The model intuitively explains the experimental data and makes quantitative predictions in good agreement with a highly accurate numerical model.
Date: April 18, 2000
Partner: UNT Libraries Government Documents Department

Trends in packaging of high power semiconductor laser bars

Description: Several different approaches to packaging high power diode laser bars for pumping solid state lasers or for direct diode laser applications are examined. The benefit and utility of each package is strongly dependent upon the fundamental optoelectronic properties of the individual diode laser bars. Factors which influence these properties are outlined and comparisons of packaging approaches for these materials are made.
Date: July 1, 1997
Creator: Solarz, R.W.; Emanuel, M.A.; Skidmore, J.A.; Freitas, B.L. & Krupke, W.F.
Partner: UNT Libraries Government Documents Department

Dual-rod Cr:LiSAF oscillator/amplifier for remote sensing applications

Description: A dual rod configuration is used to achieve 16W average power operation from a flashlamp-pumped Cr:LiSAF laser oscillator. A double-pass dual-rod amplifier configuration was used to amplify 141{mu}J pulses from a Q-switched diode-pumped LiSAF oscillator by a factor of {approximately}120. This experiment established a small signal gain of 13.4% per cm at 820 nm. Improved slope efficiency (7.4% electrical-to-light) and pulse repetition frequency (40Hz) were achieved with a single-rod oscillator using improved Cr:LiSAF material.
Date: April 1996
Creator: Early, J. W.; Lester, C. S. & Cockroft, N. J.
Partner: UNT Libraries Government Documents Department

Scatter Loss From Environmental Degradation of KDP Crystals

Description: Severe scattering losses from KDP crystals have been correlated with the exposure of porous sol AR coated crystals to ambient humidity. The scattering is attributed to formation of etch pits which develop under the coating on the KDP surface along crystallographic axes. This high angle scattering can in turn produce laser damage of downstream optics either through modulation of the beam or by optic contamination from ablation of adjacent metal structures. We have developed a simple tool to characterize the evolution of scatter from sol-coated KDP surfaces. We have measured the rate of etch pit formation as a function of relative humidity and surface treatment using both microscopy and scattering. We will discuss various surface treatments which can be utilized to retard or eliminate the environmental degradation of KDP crystals.
Date: December 17, 1999
Creator: Wheeler, E.K.; McWhirter, J.; Whitman, P.K.; Thorsness, C.; De Yoreo, J.; Thomas, I. et al.
Partner: UNT Libraries Government Documents Department

The origin and evolution of the optics specifications for the National Ignition Facility

Description: In the second half of the 1990`s, LLNL and others will be designing and beginning construction of the National Ignition Facility (NIF). At more than 10 times the power and size of the Nova laser system, this new laser will be capable of producing the worlds first controlled fusion ignition and burn, completing a vital milestone on the path to Fusion Energy. In order to optimize the performance of the laser system for a minimum cost, the designers have been conducting a campaign to properly specify the optical properties of the more than 7,500 large optical components to be deployed in the NIF. The draft optics specifications derived from this effort will be presented. The evolution of these specifications, both in language and in content, will be discussed, specifically transmitted wavefront (both P-V and PSD), scratch/dig, surface roughness, bubbles and inclusions specifications.
Date: June 27, 1995
Creator: Aikens, D.
Partner: UNT Libraries Government Documents Department

Continuous-wave diode-pumped Cr:YAG laser

Description: We describe a diode-pumped Cr{sup 4+}:YAG laser operating at 1.45 {mu}m. The laser outputs xxx mW when pumped by a 2 W single-transverse-mode 980 nm InGaAs diode.
Date: July 1, 1995
Creator: Carrig, T.J.; Cockroft, N.J.; Pollock, C.R. & Walpole, J.N.
Partner: UNT Libraries Government Documents Department

Large-aperture, high-damage-threshold optics for beamlet

Description: Beamlet serves as a test bed for the proposed NIF laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of our previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, we discuss the properties and characteristics of the large-aperture optics used on Beamlet.
Date: February 23, 1995
Creator: Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.; Kozlowski, M.R.; Maney, R.T.; Montesanti, R.C. et al.
Partner: UNT Libraries Government Documents Department

Femtosecond Laser Materials Processing

Description: The use of femtosecond lasers allows materials processing of practically any material with extremely high precision and minimal collateral damage. Advantages over conventional laser machining (using pulses longer than a few tens of picoseconds) are realized by depositing the laser energy into the electrons of the material on a time scale short compared to the transfer time of this energy to the bulk of the material, resulting in increased ablation efficiency and negligible shock or thermal stress. The improvement in the morphology by using femtosecond pulses rather than nanosecond pulses has been studied in numerous materials from biologic materials to dielectrics to metals. During the drilling process, we have observed the onset of small channels which drill faster than the surrounding material.
Date: March 6, 2000
Creator: Banks, P.S.; Stuart, B.C.; Komashko, A.M.; Feit, M.D.; Rubenchik, A.M. & Perry, M.D.
Partner: UNT Libraries Government Documents Department

Modeling of High-Energy Pulsed Laser Interactions with Coupons

Description: We describe a computational model of laser-materials interactions in the regime accessed by the solid state heat capacity lasers (SSHCLs) built at LLNL. We show that its predictions compare quite favorably with coupon experiments by the 10 kW SSHCL at LLNL. The body of this paper describes the following topics, listed by section number: (2) model in quiescent air, (3) comparison with experiments in quiescent air, (4) effects of air flow, (5) comparison with experiments involving air flow, (6) importance of material properties, (7) advantage of pulsed lasers over CW lasers, and (8) conclusions and recommendations.
Date: February 6, 2003
Creator: Boley, C D & Rubenchik, A M
Partner: UNT Libraries Government Documents Department

Reduced polarization decay due to carrier in-scattering in a semiconductor active medium

Description: The in-scattering processes, which reduce the decay of the active medium polarization, should be included in a consistent treatment of semiconductor laser gain. The in-scattering processes affect the laser gain by decreasing the influence of the high k-states, which contribute absorption to the spectrum. A theory, based on the semiconductor-Bloch equations with the effects of carrier-carrier scattering treated at the level of the quantum kinetic equations in the Markov limit, predicts gain spectra that do not exhibit absorption below the renormalized band gap, in agreement with experiment. When compared to gain calculations where the in-scattering contribution is neglected, the theory predicts markedly different properties for intrinsic laser parameters, such as peak gain, gain bandwidth, differential gain and carrier density at transparency, especially at low carrier densities.
Date: July 1, 1996
Creator: Hughes, S.; Knorr, A.; Koch, S.W. & Chow, W.W.
Partner: UNT Libraries Government Documents Department

InAlGaP vertical cavity surface emitting lasers (VCSELs): Processing and performance

Description: (Al{sub y}Ga{sub 1{minus}y}){sup 1{minus}x}In{sub x}P semiconductor alloys lattice-matched to GaAs are widely used in visible optoelectronic devices. One of the most recent developments in this area is the AlGaInP-based red vertical cavity surface emitting laser (VCSEL). These lasers, which employ AlGaInP active regions and AlGaAs distributed Bragg reflectors (DBRs), have demonstrated continuous-wave (CW) lasing over the 630--690 nm region of the spectrum. Applications for these lasers include plastic fiber data communications, laser printing and bar code scanning. In this paper, the authors present an overview of recent developments in the processing and performance of AlGaInP based VCSELs. This overview will include a review of the general heterostructure designs that have been employed, as well as the performance of lasers fabricated by both ion implantation and selective oxidation.
Date: June 1, 1997
Creator: Crawford, M.H.; Choquette, K.D.; Hickman, R.J. & Geib, K.M.
Partner: UNT Libraries Government Documents Department

Modeling of laser damage initiated by surface contamination

Description: The authors are engaged in a comprehensive effort to understand and model the initiation and growth of laser damage initiated by surface contaminants. This includes, for example, the initial absorption by the contaminant, heating and plasma generation, pressure and thermal loading of the transparent substrate, and subsequent shockwave propagation, `splashing` of molten material and possible spallation, optical propagation and scattering, and treatment of material fracture. The integration use of large radiation hydrodynamics codes, optical propagation codes and material strength codes enables a comprehensive view of the damage process The following picture of surface contaminant initiated laser damage is emerging from our simulations.
Date: November 1, 1996
Creator: Feit, M.D.; Rubenchik, A.M.; Faux, D.R.; Riddle, R.A.; Shapiro, A.; Eder, D.C. et al.
Partner: UNT Libraries Government Documents Department

Monolithically integrated active waveguides and lasers using rare-earth doped spin-on glass

Description: This LDRD program No. 3505.230 explored a new approach to monolithic integration of active waveguides and rare-earth solid state lasers directly onto III-V substrates. It involved selectively incorporating rare-earth ions into spin-on glasses (SOGs) that could be solvent cast and then patterned with conventional microelectronic processing. The patterned, rare-earth spin-on glasses (RESOGs) were to be photopumped by laser diodes prefabricated on the wafer and would serve as directly integrated active waveguides and/or rare-earth solid state lasers.
Date: September 1, 1996
Creator: Ashby, C.I.H.; Sullivan, C.T. & Vawter, G.A.
Partner: UNT Libraries Government Documents Department

Effects of Accelerated Aging on Fiber Damage Thresholds

Description: Laser-induced damage mechanisms that can occur during high-intensity fiber transmission have been under study for a number of years. Our particular interest in laser initiation of explosives has led us to examine damage processes associated with the transmission of Q-switched, Nd:YAG pulses at 1.06 {micro}m through step-index, multimode, fused silica fiber. Laser breakdown at the fiber entrance face is often the first process to limit fiber transmission but catastrophic damage can also occur at either fiber end face, within the initial entry segment of the fiber, and at other internal sites along the fiber path. Past studies have examined how these various damage mechanisms depend upon fiber end-face preparation, fiber fixturing and routing, laser characteristics, and laser-to-fiber injection optics. In some applications of interest, however, a fiber transmission system may spend years in storage before it is used. Consequently, an important additional issue for these applications is whether or not there are aging processes that can result in lower damage thresholds over time. Fiber end-face contamination would certainly lower breakdown and damage thresholds at these surfaces, but careful design of hermetic seals in connectors and other end-face fixtures can minimize this possibility. A more subtle possibility would be a process for the slow growth of internal defects that could lead to lower thresholds for internal damage. In the current study, two approaches to stimulating the growth of internal defects were used in an attempt to produce observable changes in internal damage thresholds. In the first approach test fibers were subjected to a very high tensile stress for a time sufficient for some fraction to fail from static fatigue. In the second approach, test fibers were subjected to a combination of high tensile stress and large, cyclic temperature variations. Both of these approaches were rather arbitrary due to the lack of ...
Date: February 15, 1999
Creator: Setchell, R.E.
Partner: UNT Libraries Government Documents Department

High reflector absorptance measurements by the surface thermal lensing technique

Description: Surface thermal lensing is an alternate configuration of a photothermal deflection system that was used to measure low levels of optical absorption. The thermal lensing configuration facilitated the alignment of the pump and probe laser beams by using a larger diameter probe beam. This technique was applied to high performance optical coatings, specifically high reflectors at 511 nm, zero degrees angle of incidence. The absorptance of these coatings was previously measured using a high power copper vapor laser system. A high power copper laser beam is focused onto a -2 mm diameter spot. A thermal camera senses the temperature rise with respect to the rest of the coating. The temperature change, power density and beam diameter were used with an empirical formula that yields optical absorption. The surface thermal lensing technique was able to resolve absorption levels lower than that achieved with the copper laser method.
Date: November 1, 1996
Creator: Chow, R.; Taylor, J.R.; Wu, Z.L.; Krupka, R. & Yang, T.
Partner: UNT Libraries Government Documents Department