data were fitted to a Sellmeier-type dispersion equation which permits refractive index interpolation within several parts in 10. The index of SrF2 is compared graphically with that of BaF, and CaF2.

The development of fluorides for high power laser optics, J. F. Ready, H. Vora, R. A. Skogman, K. M. Leung, and E. Bernal, SP541, pp. 59-64 (Dec. 1978).

Key words: fluorides; forging; laser windows; lithium fluoride; mechanical properties; optical properties; ultraviolet transmission.

The development of improved optical materials with low nonlinear refractive index and good vacuum ultraviolet transparency is needed for future laser systems to heat fusion targets. This program has produced lithium fluoride windows through isostatic forging of single crystalline material. For reductions around 60%, forging yields finegrained material with considerably increased yield strength and fracture energy. The ultraviolet transparency of the material is not degraded by the forging.

This paper will describe the improvement of yield strength and fracture energy as a function of forging parameters. It will discuss measurements of optical homogeneity, optical scattering and visible and ultraviolet transmission for both the original material and the forged material.

Optical properties of KCl forged between optically polished dies, R. H. Anderson and J. M. Bennett, SP541, pp. 65-69 (Dec. 1978).

Key words: alkali halides; backward scattering; forward scattering; grain boundaries; isostatic forging; optical figure; optical homogeneity; single crystal; Talystep traces.

Plano-plano and plano-concave KCl optical elements have been isostatically forged using a two-step forging process in a closed die. No optical polishing was required for the finished surfaces. The initial forging was performed between teflon sheets, the sample was then water polished, and the final forging was done between optically figured fused quartz or pyrex dies. Forgings were typically done in the 200 to 275 °C temperature range in a helium atmosphere at 29.65 MN/m2 (4000 psi). Measurements on the finished samples include optical figure, homogeneity, internal strain, total integrated forward and backscattering, surface texture (Nomarski microscopy), and surface roughness. The results of these measurements are compared with similar measurements on optically polished single-crystal and press-forged KCl samples.

Bulk optical properties of fine grained forged calcium fluoride, R. H. Anderson, R. A. Skogman, J. F. Ready, and J. M. Bennett, SP541, pp. 70-77 (Dec. 1978).

Key words: calcium fluoride; forging; laser windows; optical properties; scattering.

Single crystals of CaF, having < 111>, <100>,<112>, and < 113 > orientations have been routinely isostatically forged in a helium atmosphere at 750 °C. The crystals were deformed 60 percent to ensure a uniform grain size of less than 15 μm. A fine cloudiness of "veiling" occurs when the forging is done below the recrystallization temperature of about 800 °C for CaF2. Nomarski micrographs show that voids are distributed within the bulk of the forgings. Polariscope photographs show internal stress. Total integrated forward scattering measurements have been made on the sample immersed in a cell containing index matching fluid to eliminate scattering from the sample surfaces. These measurements show

variations cannot be definitely correlated with the positions of veils in the CaF2.

CW laser damage in AR coated alkaline earth fluorides at 3.8 μm, J. A. Detrio and R. D. Petty, SP541, pp. 78-85 (Dec. 1978).

Key words: antireflection coatings; calcium fluoride; cw laser damage; DF laser; fusion cast; laser damage; laser window; single crystal; strontium fluoride.

We have measured the damage threshold of AR coated SrF, and oriented single crystals of CaF, using a cw chemical laser operating at approximately 3.8 μm. The samples were irradiated for three seconds up to a total power of 8.4 kW. The specimens all failed at a power density of 22 kW/cm2 over a 0.3 cm2 area. The failure mode was not catastrophic and is believed to consist of plastic deformation due to compressive loading in the center of the irradiated region on the exit surface. The surface absorption is the dominant contributor to the failures. A novel statistical approach to defining the damage threshold and assessing the confidence level of the data was used.

Lattice absorption, phonon assignments, and image spoiling properties of CVD ZnS in the infrared, C. Klein, B. diBenedetto, R. Donadio, T. Kohane, and J. Pappis, SP541, pp. 86-97 (Dec. 1978).

Key words: characteristic phonons; chemical-vapor deposition; image spoiling; infrared imaging; lattice absorption; zinc sulfide.

Chemical-vapor-deposited zinc sulfide (CVD ZnS) has been established as a highly promising material for advanced infrared imaging applications and is attracting attention as a potential window material at HF/DF laser wavelengths. The present contribution concerns work that has been carried out in the context of assessing the optical characteristics of CVD-ZnS blanks, particularly with regard to: (a) lattice absorption. Careful examination of transmission traces at wavelengths up to 25 μm indicates that multiphonon processes dominate at frequencies below 1000 cm-1; peak-absorption assignments in terms of zone-boundary phonons have been made on the basis of best available inelastic neutron-scattering results for zincblende ZnS. (b) Temperature dependence. Absorption coefficients at temperatures up to 600 K have been investigated in light of spectral transmittance and emittance measurements supplemented by calorimetric data at HF, DF, CO, and CO,laser wavelengths. (c) Image spoiling. Line-spread functions in conjunction with index-inhomogeneity maps demonstrate that wavefront distortions resulting from the presence of a CVD-ZnS window do not inject any detectable degradation in contrast transmittance.

Laser induced damage in fluoride glasses: A status report, S. E. Stokowski, D. Milam, and M. J. Weber, SP541, pp. 99-108 (Dec. 1978).

Key words: damage thresholds; fluoroberyllate glass; fluorophosphate glass; inclusions; pulse duration.

Bulk and surface damage thresholds of fluorophosphate and fluoroberyllate glasses have been measured for 1-ns 1064-nm laser pulses. For crystal-free samples, threshold values for fluoride glasses are comparable to those measured in optical quality fused silica and borosilicate glasses. However, for many samples investigated the presence of solid inclusions results in low damage thresholds. Some examples of solid inclusions are shown and discussed. Surface damage thresholds in FK-51 fluorophosphate glass are uniformly high and exhibit an approximate square root dependence on pulse duration in the range of 0.1-1.0 ns.

Liquids for high repetition rate glass laser systems, J. M. Rinefierd, S. D. Jacobs, D. C. Brown, J. A. Abate, O. Lewis, and H. Appelbaum, SP541, pp. 109-121 (Dec. 1978).

Key words: Abbé value; coolants, dn/dT; index matching liquids; neodymium glass lasers; nonlinear refractive index; thermal conductivity; viscosity.

We present physical properties data for a number of liquids currently being used for cooling and/or index matching of components in high peak power, low repetition rate Nd:glass laser systems. Liquids examined include saturated water solutions of ZnCl, and ZnBr2, TCP, benzene, DMSO, glycerol, ethylene glycol, FC-104, DowCorning 710, and Cargille 5040 and 5610. Thermal properties (conductivity, diffusivity), mechanical properties (viscosity, density), chemical properties (pH, materials compatibility), and optical properties (refractive index Abbé value, nonlinear index, dn/dT, optical transparency) are tabulated and compared to projected liquid properties requirements for high repetition rate systems.

Physical and optical properties of surfaces generated by diamond-turning on an advanced machine, D. L. Decker and D. J. Grandjean, SP541, pp. 122-130 (Dec. 1978).

Key words: absorption; diamond-turning; scattered light; surface roughness.

A superprecision, two-axis, air-static bearing, diamondturning machine of advanced design has been previously described at this conference and is now operational. The microtopography and other physical characteristics of surfaces turned by this machine will be examined in detail. Some effects of machining parameters will be briefly discussed. The ability of this machine to turn surfaces with very small slope errors (<103) and small rms roughness (~10 Å) is discussed with relation to the resulting optical absorption, scattering, and laser damage resistance. The characteristics of the machine which permit these high quality surfaces are identified, and some projections are given to the future application of diamond-turned optics at near infrared or visible wavelengths.

Optical and metallurgical characterization of molybdenum laser mirrors, S. M. Wong, G. Krauss, and J. M. Bennett, SP541, pp. 132-163 (Dec. 1978).

Key words: laser mirror; metallurgical characterization; microstructures; molybdenum; optical characterization.

A study has been performed to determine the correlation between the microstructure, metallurgical processing, and surface finish of eight specially selected molybdenum (Mo) specimens from various sources. Samples of bar and plate stock produced from pure Mo either arc-cast or pressed and sintered, and TZM (Ti-Zr-Mo) Mo alloy were examined in the form of optically polished 1 1/2-inch- (3.86cm-) diameter discs. Metallurgical characterization included hardness measurements, grain size and shape determinations from polished and etched sections, scanning electron microscopy, and Auger electron spectroscopy. Optical characterization consisted of measurements of total integrated scattering, rms roughness, height distribution functions, and autocovariance. In some cases, the surface roughness of as-polished mirror surfaces could be directly related to grain structure and substructure as revealed by etching. These observations and their implications for the selection of Mo starting stock to be used in the production of low-scatter laser mirrors will be discussed.

1064-nm laser damage thresholds of polished glass surfaces as a function of pulse duration and surface roughness, D. Milam, SP541, pp. 164-167 (Dec. 1978).

Key words: BK-7 glass; fused silica; laser damage; polished surfaces; pulse duration dependence of damage; surface roughness.

Laser damage thresholds were measured for four polished glass surfaces, using linearly polarized 1064-nm pulses with durations of 0).17 ns, 1.0 ns, 1.6 ns, and 3.2 ns. Thresholds scaled approximately as the square root of pulse duration, but were insensitive to variations in surface roughness when the roughness was < 25 Å rms. Careful cleaning increased the damage threshold at 3.2 ns by removing particulates.

Large giant and free-running laser pulse energy and power densities through optical fibers, M. J. Landry, SP541, pp. 168-189 (Dec. 1978).

Key words: free-running laser pulses; giant laser pulse; optical fiber damage; pulsed Nd3+ laser damage; single and multiple element fibers; surface threshold damage.

The surface threshold damage levels (STDL) and coupling efficiencies, e, (ratio of output-to-input energy) have been determined for single and multiple optical fibers of five manufacturers. For giant laser pulses of 30) nsec duration, the largest STDL's were observed in American Optical Company fibers for single and multiple laser shots with values of 48.2 and 31.6 J/cm2, respectively. For freerunning laser pulses of 100 μsec duration, the largest STDL was observed in Corning Glass Works fibers for single laser shots with a value of 4.66 kJ/cm2. For multiple laser shots increased energy caused the initial damage sites in the binding or fiber cladding materials to increase in size and cause new sites in these materials at lower STDL's than for single laser shots. The giant laser pulses caused the most severe surface damage. There is no evidence to suggest that the observed decrease in was caused by other than the increase in damage to the input surface of the fibers.

Ultraviolet damage resistance of laser coatings, B. E. Newnam and D. H. Gill, SP541, pp. 190-202 (Dec. 1978).

Key words: damage thresholds; electric fields; laser damage; nanosecond pulses; pulsewidth dependence; standing waves; thin-film coatings; two-photon absorption; ultraviolet wavelength scaling.

The damage resistance of several thin-film materials used in ultraviolet laser optics was measured at 266 nm and 355 nm. The coatings included single, quarter-wave (QW) layers of NaF, LaF,, MgF2, ThO2, Al2O3, HfO2, ZÃO2, Y2O, and SiO2, plus multilayer reflectors composed of some of these materials. The substrates were uv-grade fused silica. Single-shot thresholds were obtained with 22-ns and 27-ns (FWHM) pulses at 266 and 355 nm, respectively. One of the samples had previously been tested using 20-ps pulses, providing a pulsewidth comparison.

At 266 nm the coating with the highest damage threshold was a QW layer of NaF at 10.8 J/cm2 (450 MW/cm2), whereas for a maximum reflector of Al2O3/NaF the value was 3.6 J/cm2 (154 MW/cm2). At 355 nm the QW layer of NaF could not be damaged at 38 J/cm2 (1390 MW/cm2), and the threshold of the maximum reflector was 12.2 J/cm2 (470 MW/cm2).

The results were analyzed to determine correlations with standing-wave electric fields and linear and two-photon absorption. Scaling relationships for wavelength, refractive index and atomic density, and pulsewidth were found. Multithreshold evaluation of 100-nsec pulsed laser damage to coating materials at 2.7- and 3.8-μm wavelengths, J. O.

Porteus, T. M. Donovan, J. L. Jernigan, and W. N. Faith, SP541, pp. 202-211 (Dec. 1978).

Key words: absorption; antireflection coatings; damage thresholds; impurities; laser-induced damage; thermal damage.

In this time and wavelength regime optical coatings typically fail from thermal damage. Unlike catastrophic damage resulting from dielectric breakdown, one finds disparity among the thresholds for one or more of the following damage characteristics: delamination, cracking, flow, erosion, perforation, ion emission, and light emission. Comparison of the different thresholds provides useful information on how damage proceeds, and how the absorbed energy is distributed in the coating layer. Comparison of multithreshold damage data at the two different

wavelengths permits evaluation of the importance of impurities which absorb preferentially at one of the wavelengths, such as water. Comparing thresholds at the two wavelengths after N/1 conditioning provides detection of preferentially absorbing impurities which are laserdesorbed. Complementary information may be obtained from laser calorimetry. The following materials, prepared as single-layer, antireflection coatings, were evaluated: NaF, SiO,, AlOŽ, ZnS, As,S3, and Si. Samples of the first three were prepared in ultra-high vacuum, in addition to the usual standard vacuum preparation. Thresholds are expressed in terms of the theoretical energy per unit area in the coating layer in order to permit a practical intercomparison of materials for multilayer coating design.

Multithreshold damage measurements on As̟S, As̟Se, and NaF at HF and DF wavelengths, T. M. Donovan, J. O. Porteus, J. L. Jernigan, and E. J. Ashley, SP541, pp. 212-217 (Dec. 1978).

Key words: absorption; arsenic selenide; arsenic trisulfide; defects; laser damage; sodium fluoride.

We previously reported on the deposition, absorption, and CO2-laser damage threshold for As,S ̧, As̟Se ̧, and NaF coatings. It was shown that the damage threshold was much lower for coated than uncoated substrates and that the mechanism for damage was different in the coatings than in the substrates. We speculated that the damage in the coatings was related to the presence of micron-sized crystalline defects distributed in the amorphous chalcogenide matrix. In this paper we report the results of damage measurements on these materials at 2.8 and 3.8 μm and identify two operating damage processes: "uniform" damage, which we associate with the amorphous chalcogenide matrix, and "selective" damage, which we associate with the crystalline defects. For single-layer films, we find that N/1 conditioning generally produces an increase in the damage thresholds. The wavelength dependence of multithreshold results in single-layer coatings of As2S, and NaF suggests that improvement in threshold results from the thermal desorption of contaminating layers of water at 2.7 μm. However, for a dielectrically enhanced reflector containing quarter-wave layers of As,Se, and NaF, N/1 conditioning promoted crystallite growth which resulted in a definite deterioration of N/1 thresholds.

TEM investigation of effects of a barrier layer on damage to 1.064 μ Ar coatings, C. K. Carniglia, J. H. Apfel, G. B. Carrier, and D. Milam, SP541, pp. 218-225 (Dec. 1978).

Key words: antireflection coatings; electron microscopy; laser damage; optical coatings; thin films.

Silica/titania 4 layer AR coatings on BK-7 glass, with and without a half-wave silica barrier layer, have been damaged at 1.064 μ by 150 ps laser pulses. The damage sites have been examined by TEM replica techniques at a magnification of 70,000. The size of the damage sites appears to be "quantized." Most sites consist of a 1 μ nucleus which leads to a 3 μ crater in a fully developed site. The mechanical properties of the films appear to play a role in the morphology of the damage sites. The titania layers seem to fracture while the silica layers seem to melt or tear. A series of micrographs of near threshold damage sites shows the development of the sites from a rupture which appears to occur at or near the substrate surface. Evidence of heating in the substrate is also present, although it is difficult to pinpoint the exact starting point of the damage mechanism.

Optical techniques for the determination of pulsed laser damage in thin films, T. W. Walker, A. H. Guenther, and P. E. Nielsen, SP541, pp. 226-234 (Dec. 1978).

Key words: laser damage; optical probe technique; radiation scattering; thin films.

Two techniques, to determine the occurrence of pulsed laser induced damage in thin film dielectric coatings, were compared and evaluated against normally employed methods. One of the new techniques utilized near back scattered radiation from the damaging pulse and proved to be as sensitive as the best existing optical probe method while being experimentally facile. The second new method recorded a time delayed probe pulse which was reflected from the thin film damage site. This method appears to be more sensitive to a local index of refraction change in the thin film rather than increased reflectance/scattering from the damage site. Preliminary test results show that most of the morphological damage occurs after the damaging pulse has passed.

A statistical analysis of absorptive laser damage in dielectric thin films, A. B. Budgor and K. F. Luria-Budgor, SP541, pp. 235-248 (Dec. 1978).

Key words: laser damage; probability; statistical analysis; thin films; Weibull distribution.

The Weibull distribution arises as an example of the theory of extreme events. It is commonly used to fit statistical data arising in the failure analysis of electrical components and in DC breakdown of materials.

This distribution is employed to analyze time-to-damage and intensity-to-damage statistics obtained when irradiating thin film coated samples of SiO,, ZrO2, and Al2O, with tightly focused laser beams. The data used is furnished by Milam. The fit to the data is excellent; we often obtain least squared correlation coefficients greater than 0.9.

It is found almost universally that statistical models of breakdown, such as the lucky electron theory, oversimplify the damage process by neglecting nonlinear interactions and anisotropies induced by impurities. Thus, the fundamental intensity I relation on pulse length t, often deviates from the classical t,-1/2 dependence resulting from 2photon absorption without diffusion, or from linear absorption with diffusion, to dependencies as high as t, 22 for the former to to 0.44 for the latter. This fact, coupled with the experimental nonobservability of higher than 2-photon absorption seems to imply that the avalanche mechanism is the most likely initiator of the plasma requisite for lattice meltdown.

Statistical confidence bands for material survivability as a function of laser intensity and pulse length can be con

structed; this lends high practical utility to the Weibull distribution as an engineering diagnostic tool.

New coating materials for IR laser optical components, R. C. Pastor, J. A. Harrington, L. E. Gorre, and R. K. Chew, SP541, pp. 249-256 (Dec. 1978).

Key words: infrared laser windows; materials purification; reactive atmosphere process (RAP) chemistry; thin film coating materials.

Six materials (LaF3, PrF3, CeF,, BiF,, KGaF, and Bil,) were prepared and optical evaluated for use as thin film coating materials at 3.8 and 9.27 μm.

Improved PbF, coatings for the infrared, P. Baumeister, G. P. Arnold, and D. F. Edwards, SP541, pp. 257-258 (Dec. 1978).

Key words: antireflection coatings; CdSe; coating substrate; damage resistant; Ge; PbF2; pulsed HF laser.

A technique is described for reproducibly depositing single layer PbF, antireflection coatings for CdSe that have a damage threshold of about 50 MW/cm2 for 2.87 μm laser radiation. This is an 8-fold increase in damage resistance over coatings made by other methods. These same coatings applied to Ge have a damage threshold of about 22 MW/cm2. The coated Ge value is less probably due to the index mismatch between the PbF, and the Ge.

Graded index coatings of cubic thallium iodide (TII) and lead fluoride (PbF2), T. J. Moravec and R. A. Skogman, SP541, pp. 259-265 (Dec. 1978).

Key words: graded index; lead fluoride; polymorphism; thallium iodide; thin films.

We present a new technique for producing graded index films from alternating very thin layers of two materials. During deposition the thickness of the layers is adjusted so that the resulting average index matches the index of the profile for that total thickness. This method shows great promise for making films with any desired complicated index profile in a very straightforward manner. Results are presented for graded index AR films near 10 μm made from Til and PbF2. The 10.6 μm absorption of these films was similar to that of discrete, multilayer AR films composed of the same materials.

The alternating layer method also takes advantage of the polymorphism of TII in thin layers to produce films in the cubic phase. We show by x-ray and optical measurements that each TII layer possesses the CsCl structure at room temperature. It thus appears that each layer of TII is ignorant of the existence of the previous layer of TII due to the layer of buffer material (PbF2).

Simple expressions for calculating the effect of volume or interface absorption in thin films on the performance of high reflectance or antireflectance multilayer coatings, H. E. Bennett and D. K. Burge, SP541, pp. 266-277 (Dec. 1978).

Key words: absorption; antireflectance coatings; high reflectance coatings; interface absorption; multilayer films; scattering.

Approximate closed-form expressions are developed for predicting the effect of volume and interface absorption in thin films on the performance of quarter-wave multilayer coatings. For highly reflecting coatings on dielectric substrates the volume absorption expressions are equivalent to those obtained by Sparks using a perturbation approach. The results are extended to metal substrates by introducing the concept of a generalized substrate index. An approxi

mate expression for scattering losses for high reflectance coatings is included. Multiple quarter-wave antireflectance coatings are also analyzed using admittance theory. A technique for experimentally separating and determining interface and volume absorption in single-layer films has recently been reported. The expressions developed in this paper make it possible to predict the performance of high reflectance and antireflectance multilayer stacks from these single-film measurements without recourse to a computer.

Simplified description of dielectric reflectors, M. Sparks and M. Flannery, SP541, pp. 278-287 (Dec. 1978).

Key words: asymmetric absorptance; damage thresholds; dielectric reflectors; electric-field distribution; high-power; reflectance; spectral absorptance; theory.

The spectral reflectance, R(w), of a quarter-wave reflector is quite asymmetric in general as a result of absorption. The maximum electric field E in an infinite stack is in the center of the high-index (low-index) layer at the lowfrequency (high-frequency) end of the high-reflection band. Thus, the absorptance minimum of a stack having much greater absorption in the high-index material occurs at w>w (band center). Operation at w>w, could increase the damage resistance if the high-index material is easily damaged. At we, E decays rapidly. As a departs from we in an infinite reflector, E penetrates deeper into the coating, with no decay at the band edges. The peak-topeak distance in an infinite dielectric stack is constant for all frequencies in the band. By using the continuity of E and dE/dz, E can be obtained from E = 0 at the metallic substrate or, in an infinite stack, from E = 0 at the reflector surface for w=w, or E = 0 in the center of the highor low-index layer at the band edges. Simple closed-form approximations for the spectral absorptance and the phase of E are accurate and sufficient for present applications. Electric fields near coated surfaces: Application to damage protection, H. B. Rosenstock, SP541, pp. 288-295 (Dec. 1978).

Key words: damage threshold; electric fields; internal reflection; protective coatings.

Damage to transparent materials from intense light pulses usually begins at the exit surface. This is usually explained by "constructive" interference between incident and reflected waves: The total electric field may exceed the threshold for damage only upon reflection from the exit surface. However, in case of a surface coated with a thin film, interference may either increase or decrease the total electric field. Details depend on the optical constants, thickness, and wavelengths. A film designed to provide protection against excessive electric fields at one wavelength may not do so at other wavelengths. Also, attempts to minimize the field in the material proper may entail novel problems in the film, in which the damage mechanism may be an absorptive one.

Computer simulation of laser damage morphology in the alkali-halides, P. Kelly, D. Ritchie, P. Bräunlich, and A. Schmid, SP541, pp. 296-298 (Dec. 1978).

Key words: alkali-halides; laser pulse; pico-second; picosecond laser pulse.

A numerical model of the spatio-temporal behaviour of a pico-second laser pulse has been developed which allows the study of the interaction of macroscopic photons with electrons in an alkali-halide lattice. Trajectories of the photons are computed. Gradients in the refractive index

change the direction of the photons and this can lead to focusing or defocusing of the pulse. Rotational symmetry is assumed for both the pulse and background. Results obtained to date will be presented.

The relative role of impact and multiphoton ionization mechanisms in laser induced damage of transparent dielectrics, B. G. Gorshkov, A. S. Epifanov, and A. A. Manenkov, SP541, pp. 299-302 (Dec. 1978).

Key words: damage threshold; electron avalanche; frequency and pulse width dependencies of the critical field; multiphoton ionization.

The results of a theoretical analysis of the electron avalanche process at high frequencies of the electromagnetic field are presented. The dependence of the avalanche rate on radiation intensity and of the critical field on frequency are obtained for nanosecond and picosecond pulse durations. The relative role of electron avalanche and multiphoton ionization in laser damage of transparent dielectrics is discussed and it is shown that it is strongly influenced by the pulse widths.

Theory of laser damage in dielectric solids, S. Brawer and W. L. Smith, SP541, pp. 303-304 (Dec. 1978).

Key words: conduction band (CB) electrons; dielectric solids; electrons, conduction band (CB); laser damage.

In this theory a new approach to the interaction of conduction band (CB) electrons with damaging radiation is considered. We assume band gaps greater than 4 eV and radiation frequencies greater than 1 eV. Two processes are required for damage. First, the incident radiation rapidly excites a few "primer" electrons from trap levels to the bottom of the CB. Next these primer electrons can either cause enough energy to be absorbed to cause damage without avalanche, or they can trigger an electron avalanche and subsequent damage. In either case a mechanism for the excited-state absorption process is required.

Laser-induced damage in semiconductors, Y. K. Danileiko, A. A. Manenkov, and A. V. Sidorin, SP541, pp. 305-308 (Dec. 1978).

Key words: laser induced breakdown; laser-induced damage threshold; nonequilibrium carriers; semiconductors, Ge, Si, GaAs.

The laser-induced bulk breakdown in Ge, Si and GaAs crystals at the 10.6 μm, 2.76 μm, and 2.94 μm radiation wavelengths of the pulsed CO2, Ca2F:Er3+ and YAG:Er3+ lasers is investigated. Generation of free carriers has been observed and their kinetics studied by the dc and microwave photoconductivity measurement techniques. In Si and GaAs, the laser-induced bulk damage has been observed and the damage threshold measured. In Ge, the damage was not observed due to a self-defocusing effect associated with the negative contribution of nonequilibrium electrons in the refractive index. Mechanisms of free carrier generation and laser-induced damage are discussed. Frequency dependence of breakdown fields in single-crystal NaCl and KCI, M. J. Soileau, M. Bass, and E. W. Van Stryland, SP541, pp. 309-317 (Dec. 1978).

Key words: breakdown fields; KCl; NaCl; spot-size dependence.

In this paper new observations of the breakdown fields in single-crystal NaCl and KCl are reported. Measurements were made of the wavelength and focal spot radius depen

dence of breakdown fields in NaCl and KCl at optical frequencies. The measurements at different focal spot radii were used to establish empirical scaling laws for these two materials over the range of focal spot radii studied. Correct application of these scaling laws gives directly comparable fields at all frequencies. The results indicate little dispersion in breakdown fields over the wavelength range of 10.6 to 0.53 μm. The ratio of the NaCl and KCl breakdown fields are found to depend on frequency and this implies that extrinsic phenomena were being probed by these experiments.

Investigation of surface breakdown mechanism in IR-optical materials, V. I. Kovalev and F. S. Faizullov, SP541, pp. 318326 (Dec. 1978).

Key words: adsorbed water; breakdown mechanism; frequency and time dependence of breakdown thresholds; IR window materials; NaCl; pressure; pulsed TEA CO, laser surface breakdown; spot size; surface absorption; transmitted pulse.

It has been found that with a decrease in ambient gas pressure, there takes place a decrease of surface breakdown threshold in IR-optical materials under TEA CO2laser radiation. To explain this fact, a new mechanism of the breakdown has been proposed, which is connected with evaporation of adsorbed water. The breakdown stage has been experimentally investigated and a theoretical analysis has been performed. The dependence of the surface breakdown in NaCl on ambient gas pressure, spot size, frequency and time have been studied. The dependence on the quantity of adsorbed water (surface absorption) has been studied as well. The breakdown thresholds have been measured with a calibrated, photon drag detector by the amplitude of the transmitted pulse. The results obtained are in good agreement with the proposed model.

SP542. Possible contributions of cement and concrete technology to energy conservation, G. Frohnsdorff, P. W. Brown, and J. R. Clifton, Nat. Bur. Stand. (U.S.), Spec. Publ. 542, 76 pages (May 1979) SN003-003-02059-1.

Key words: cement; concrete; energy saving opportunities; research needs.

A workshop on Possible Contributions of Cement and Concrete Technology to Energy Conservation by the Year 2000 was held at the National Bureau of Standards on October 3 and 4, 1977. The purpose of the workshop was to identify and record ideas on possible contributions of cement and concrete technology to energy conservation in the near term and by the Year 2000. This included consideration of current technology as well as areas in which technological advances might be realized.

The workshop was divided into working groups on cement composition, cement production, blending materials, concrete production, efficient use of concrete, and institutional factors. The essential results from the six working groups were statements of Energy-Saving Opportunities, Research Needs, and Unresolved Issues. The statements, which are the major part of this report, are presented without critical analysis. They suggest, however, that there are a large number of possible opportunities which should be evaluated for their ability to contribute to energy conservation in the cement and concrete industries. SP543. The technological knowledge base for industrializing countries. Proceedings of the NBS/AID UNCSTD Seminar held at the National Bureau of Standards, Gaithersburg, MD, Oct. 16-17, 1978, R. C. Sangster, Ed., Nat. Bur. Stand. (U.S.), Spec. Publ. 543, 239 pages (Apr. 1979) SN003-00302057-5.