This paper describes the advances in the state of the art solid-state laser technology made by researchers at Lawrence Livermore National Laboratory and their contractors. Analyses and experiments indicate that a good understanding of the design and implementation of the thermal optical control of laser plates required for high power, high brightness operation is in hand. Significant advances in the strengthening of Nd:glass and the growth of large size, good quality Nd:G:GSGG crystal show that there are at least two ways to increase laser power, brightness and efficiency simultaneously without increasing laser size and weight.
In an unstable laser resonator, spontaneous emission, which is emitted by the gain medium just as the laser resonator rises above threshold, propagates around the resonator while being coherently amplified and eventually becomes the outcoupled light. The approximate output pattern of pulsed, collimated unstable resonators can be determined by the sizes of and distance between the output aperture and the image of the spontaneous emission source, as viewed from the output aperture by looking back through the optical chain of the unstable resonator. In this paper, a detailed analysis of the time dependent output pattern of two common, positive-branch unstable resonators is presented in geometrical optic regime. The effect of a dot outcoupler and multiple internal apertures on the output pattern is investigated and some simple rules for analyzing other resonators are also presented.
In order to maintain a good beam quality on a high power, high repetition rate Q-switched Nd:YAG laser, a complete understanding of the thermal effects present in such a system is necessary. A model was developed to investigate two schemes which compensate the thermally induced birefringence and bifocal lensing effect. Tne experimental results agree very well with this model. The resulting laser can produce short Q-switched pulses (less than ins) with an energy greater than 100mJ and 35mJ at 1064nm and 532nm respectively, at a repetition rate as high as 1100Hz.
Lazar 'Lnc. has recently put on the market a new set of desk top Codes suitable for the Macintosh Plusnt that will allow the optical designer, systems analyst, or anyone that may be interested in the temperature transient when a reflective optical element is subjected to either continuous wave or repetitive pulsed laser radiation.
In previous work  we reported that the power of importance in self-focusing experiments using Gaussian spatial profile is the second critical power, P2, defined by P2=3.77 P1 rather than the often quoted P1=Cλ2/(32π22). Here n2 is the nonlinear refractive index, c the speed of light and A the wavelength (both in vacuum). The factor of 3.77 is a numerical factor coming from computer calculations as discussed by Marburger . We also presented a method by which we could obtain n2 at irradiances very near to damage In addition, we showed the experimental conditions under which self-focusing is unimportant in damage experiments. We have now extended these results so that in damage experiments where self-focusing is important we can estimate the reduced spot size within the bulk at damage and, thus, obtain the damaging electric field magnitude. This we do by observing the far field time integrated spatial irradiance distribution. We present data for Si02, NaCl, BK-7, and CS2.
This paper is directed at proposing a new technique for building high energy optical components that will permit the use of heat transfer techniques that will remove substantially more thermal load than is presently possible. This paper will describe the use of impingement and nucleate boiling heat transfer in concert with an optical component that is made up of optical cells. The optical component is made up of optical cells which will permit the designer to fabricate an optic of any size. The basic design of the cells and how they are fit together are shown in drawings and schematics. The optical cells may be figured and polished either as a unit or individually. Of particular value is the ability of changing out optical cells without having to disturb the rest of the optical component. The faceplate of the optical cell may be virtually whatever the designer wishes. Of particular interest would be the failure due to damage of a section of the optic. Instead of having to refigure and polish the whole component, one may only have to change out the optical cell(s) as required and replace with a new cell(s). Equations and curves are provided to show how the technique is accomplished and the resulting temperature gradients for various faceplate materials that may be used.
We discuss the application of self-phase modulation and grating pulse compression to the generation of temporally trapezoidal optical pulses for controlling the electron beam emittance and energy spread in an FEL photoelectric injector. Pulse compression in a single-stage pulse compressor, with background reduction based on the nonlinear birefringence of the optical fiber, yields 3-ps, compressed pulses without background pedestals or sidelobes. Trapezoidal, flat-topped pulses with 20-ps FWHM and 4-ps risetime have been obtained through self-phase modulation and group-velocity dispersion of the 3-ps pulses in a second fiber. Pulse shaping through Fourier transform amplitude and phase masking in the frequency domain and the amplification of the trapezoidal pulses are also discussed.
We present an overview of the development of laser optics utilizing liquid crystals. Devices discussed include wave plates, circular polarizers, optical isolators, laser blocking notch filters and laser beam apodizers. Issues addressed include fabrication methods and laser damage resistance.
Two figures of merit, the threshold power (Pth) and the limiting volume (Vmin) can be used to compare the relative efficiency and economy of new harmonic generating crystals. The properties of barium metaborate and L-Arginine phosphate are used to illustrate the effect of nonlinearity, birefringence, and damage threshold on these figures of merit.
Proc. SPIE 0895, Nonlinear Optical Properties Of Strained GaAs-In[sub]x[/sub]Ga[sub]1-x[/sub]As Multiple Quantum Well Structures Using A Titanium Sapphire Laser Probe, 0000 (27 June 1988); doi: 10.1117/12.944440
The nonlinear saturation of the excitonic absorbtion in a GaAs-InxGa 1-xAs multiple quantum well sample consisting of 80 wells was investigated in the vicinity of the excitonic resonance at 991 nm using a tuneable titanium sapphire laser probe. This characterization yields a saturation intensity s of less than 50 kW/cm and a maximum off-resonance nonlinear refractive index of 6.42 x 10-7 cm2/W. It is shown that this dispersion can lead to practical optically bistable etalons fabricated from these multiple quantum well structures.
A general theory for three-wave-mixing valid for both type I and type II is presented. Analytic expressions for the SHG efficiencies are compared with the numerical exact solution. The effects of beam walk-off and spatial profile overlap for various polarizations are included. System parameters such as deff, E-number, F-number and angular sensitivity are calculated for type I and II BBO crystals. The integrated efficiency for divergent pump beam is calculated for various ratio of beam divergence and crystal angular acceptance width. Experimental data for SHG of 1064 nm (YAG-laser) are presented and compared for type I and type II BBO crystal. From our measured data, we conclude that the simple model based upon the ratio of P( laser power) and the beam quality (Q) or inverse-square of the angular sensitivity overestimates the effects of beam quality on the efficiency. A rigorous model including the complicated coupling between P, Q and the efficiency is presented which correctly explains our data.
Based upon the spectral expansions of output intensity and amplitude of light of electro-optic modulation (EON), the mode of EOM is studied for both external and internal modulations. The normalized harmonic distortions are introduced, and the conditions under which E0M, can be approximated to amplitude modulation (.00 or intensity modulation (IM) are obtained at different dc biases. The harmonic components of output light intensity and amplitude of intra-cavity EOM are numerically caculated for the first time. And the modulation index versus dc bias is obtained. The experiments of CO2 EOM using a CdTe crystal shower an agreement with the taeory.
Until recently all laser glasses were characterized by a high density of microscopic metallic platinum inclusions which became macroscopic fracture sites when the glass was used in high fluence applications. These inclusions are directly related to the utilization of metallic platinum in the construction of optical glass melters, a practice of critical importance if the resultant glass castings are to be produced with the high homogeneity required for laser applications. Substantial improvements have been made in reducing the number and size distribution of metallic platinum particles in many phosphate laser glasses. This reduction in platinum particle density has been achieved without compromising the physical, optical, or laser properties of these glasses.
Many of the damage problems experienced by intracavity laser optics, particularly for discharge-pumped and electron-beam-pumped laser systems, arise from the electronic interactions of low-energy electrons, ions and ultraviolet photons with the surface and near-surface regions of the optical material. We shall describe results of recent experiments which display some of the electronic mechanisms involved in these processes, through which incident electronic energy is absorbed, localized, transformed and ultimately dissipated in ways which change the surface composition and electronic structure of model wide bandgap optical materials. We consider discuss recent experimental results on the metallization of dielectric surfaces, the effects of adsorbed overlayers in inhibiting desorption of excited neutral atoms, and the effects of glass processing on response to electron and ion irradiation. We also point out some of the ways in which the changes in the optical surfaces wrought by the low-energy and low-intensity irradiation arising from the laser pumping mechanism can influence thermal, chemical and plasma properties of the surface in ways which alter the surface response to intense laser radiation.
The application of Raman spectroscopy to the analysis of dielectric films with respect to phase composition and homogeneity has been reported during the past several years. Interfacial strain at the film-substrate interface, which influences chemical bonding, also perturbs the vibrational spectrum and can be quantified from measured frequency shifts. Recent work has shown that this inelastic light scattering technique can be used as an in situ probe of chemical bonding during film deposition and under conditions where the film undergoes catastrophic degradation caused by high energy particle or high pulse energy laser irradiation. Examples will be presented in this review which demonstrate the utility of this technique for understanding molecular structural changes which result during sol-gel or plasma processing of films. Real-time measurements of thin films subjected to high temperature and pressure environments will also be emphasized.
We are building an optical laboratory in which three complementary optical techniques: Raman scattering, sur-face second harmonic generation and photoluminescence, will be used to observe in-situ, in real-time the cumulative structural changes that occur during repeated illumination of solid surfaces. Such changes may be beneficial as in sem-iconductor processing but in general are detrimental, as in laser-induced damage of optical components. The evolution of stress, crystallinity, surface electronic properties and of the type and number of defects will be correlated with the appearance of damage spots during illumination sequences with below threshold pulses. From this, the mechanisms of multiple pulse damage will emerge and prediction of failure in components will become possible.
The transient radiation-induced absorption in fused silica due to neutron and 7-ray irradiation has been investigated. Transient radiation-induced absorption coefficients (a) at 325 nm have been measured during and after pulsed reactor (TRIGA) irradiation. a increases very rapidly to a maximum value (am x)during a pulse and then decreases asymptotically to a permanent value afterwards. a wassound to reach a maximum value of 0.0070 cm-1 during a 0.5 MRad reactor pulse and to recover 99% of its initial value to 0.0001 cm-1 at a time of 1000 s after the reactor pulse.
We report the careful characterization of a passive monolithic ZnSe based optical fluence limiter that, in addition to protecting downstream optical components, also exhibits self-protection. The output energy is held to below 3 nJ using 30 ps 532 nm pulses while the low energy transmission is greater than 10% . This device has a useful wavelength range from 500 - 950 nm.
Presented are the experimental measurements of the absorptance characteristics of multilayer dielectric mirrors designed for operation at glancing angles of incidence. The characteristics are measured as a function of incidence angle (up to 89.5°), for both s and p-polarization, using photoacoustic calorimetry. An absorptance of 0.007% (99.993% R) at 89.5° is measured for a multilayer all-dielectric mirror designed for 514.5 nm light. The results of multilayer dielectric on metal mirrors are also given. Preliminary comparisons with theory show fair agreement with the data, but finer scale differences still need to be better understood.
The accumulation dependence of damage and laser induced damage morphologies on single crystal metal surfaces have been observed under Q-switched 1064 nm Nd:YAG laser irradiation at 10 nsec pulses at a 10 Hz rate. Several different damage morphologies were observed: slip-line formation, ripple patterns, flat-melting, and boiling. Damage probability versus fluence curves and accumulation curves are plotted to investigate damage behavior as it correlates with morphology. Accumulation curves showed different damage behavior for crystals of different orientation. Threshold decrease due to accumulation was the largest on (111) Cu and Al surfaces, whidh also had the lowest single shot damage threshold. The threshold reduction in accumulation follows the equation FN = F1 NS-1 where FN is the N-pulse damage threshold, N the pulse number, and S the slope of the accumulation curve. Accumulation appears to be the result of the storage cycle of thermal stress-strain energy induced by each laser pulse, and multi-pulse damage results from plastic slip and fatigue.
Pulsed laser induced damage of optical thin films is, in general, initiated by the absorption of laser radiation by imperfections in the films or at interfaces between film layers and/or the substrate. A heat flow analysis of this process stresses the importance that the thermal conductivity of both the thin film host and that of the substrate play in establishing the laser-induced damage threshold. Unfortunately, recent work which will be reviewed in this presentation, indicates that the thermal conductivity of thin films can be several orders of magnitude lower than that of a corresponding material in bulk form, as a consequence of the film structure resulting principally from the deposition process. The importance of thermal conductivity will be compared to parameters such as absorption mechanisms, film materials, composition, and other variables. Its implication for the ultimate optical strength of materials and the direction in which thin film research and processing should proceed will be highlighted.
The optical elements that define the resonant cavity in a laser must meet exacting standards of optical performance. Not only must the reflectance and transmittance be tailored to fit the gain characteristics of the laser cavity, but the absorption and scatter losses in the coatings must be limited to prevent degradation of laser performance. Current requirements for laser optics are diverse. Mirrors for tunable dye lasers must meet broadband requirements for reflectance and transmittance. In ion lasers, wavelength selection using cavity mirrors with narrow bandwidth characteristics has become practical. Laser isotope separation and free electron lasers have stimulated needs for optics with wavelength discrimination characteristics and extremely low absorption loss. This paper will discuss both generic requirements and specific coating types in the 240nm to 10 um spectral regime. A number of special cases where optical coatings provide unique solu-tions for evolving requirements will also be examined.
Graded index layers provide a greater flexibility for the design of optical coatings than "homogeneous" layers. A graded index layer can replace the whole or a part of a traditional multilayer stack of alternating thin films of high and low refractive index. This paper presents design examples for broadband antireflection coatings, narrowband high reflectors (also referred to as minus filters or rejection line filters), and non-polarizing beam splitters. Optimized refractive index profiles are derived for broadband antireflection coatings for various combinations of incident medium and substrate. The rejection line filter example uses a sinusoidal (rugate) index profile. The non-polarizing beamsplitter summarizes the topical contents of a paper presented in another conference at the same symposium.
The abrasion resistance of a porous silica antireflective coating prepared from a colloidal silica suspension was increased by the addition of a soluble siloxane binder to the suspension prior to application. After evaporation of the solvent this binder served to increase the adhesion between individual silica particles thereby increasing the coating strength. The optimum binder concentration was 20-30% and at this level the optical properties and laser damage threshold of the original silica coating were retained.
The design of mirror coatings for the oxygen iodine laser was complicated by the need for an alignment beam. Dual wavelength reflectors were required. A 2:1 stack design was a possible solution, which could be conveniently monitored in reflection. The achievement of particular phase shifts was a more difficult task and required the use of thin correc Live layers.