The equivalent foil thickness principle, S. M. El-Soudani, SP431, pp. 273-276 (Jan. 1976).

Stereological method for estimating relative membrane surfaces in freeze-fracture preparations, E. R. Weibel, G. A. Losa, and R. P. Bolender, SP431, pp. 277-280 (Jan. 1976).

Application of various stereological methods to the study of the grain and the crack structure of concrete, P. Stroeven, SP431, pp. 281-286 (Jan. 1976).

The use of quantitative metallography and stereological methods to describe composite materials, J. L. Chermant and M. Coster, SP431, pp. 287-290 (Jan. 1976).

A definition of the two-dimensional size of irregular bodies, G. M. Timčák, SP431, pp. 291-294 (Jan. 1976).

Stereometric microstructure and properties of two-phase materials, G. Ondracek, SP431, pp. 295-298 (Jan. 1976).

Use of mathematical morphology to estimate comminution efficiency, P. Cauwe, SP431, pp. 299-303 (Jan. 1976).

Microscopy, radial distribution analysis, and sortability, R. M. Doerr, SP431, pp. 305-308 (Jan. 1976).

Size distribution analysis in situ on individual or interconnected phases by image analyses, C. Gateau and J. M. Prévosteau, SP431, pp. 309-314 (Jan. 1976).

Stereological determination of the proportional volume of dendrites in cast iron by measuring plan micrographs, R. Wlodawer, SP431, pp. 315-318 (Jan. 1976).

Morphometry, stereometry and stereology applied to cancer development in the large intestine of man, H. Elias, D. Bokelmann, and R. Vögtle, SP431, pp. 321-326 (Jan. 1976).

Analysis of the heterogeneous composition of central nervous tissue, S. Eins and J. R. Wolff, SP431, pp. 327-330 (Jan. 1976).

Stereological analysis of the heterogeneous composition of central nervous tissue: Synapses of the cerebral cortex, J. R. Wolff, SP431, pp. 331-334 (Jan. 1976).

The development of myelinated fibers in the visual cortex of cats, H. Haug, SP431, pp. 335-336 (Jan. 1976).

Studies on the partially-oriented surfaces of skeletal muscle mitochondria, N. T. James and G. A. Meek, SP431, pp. 367370 (Jan. 1976).

Determination of the number of cells with multiple nucleoli in histological sections, A. Schleicher, H. J. Kretschmann, F. Wingert, and K. Zilles, SP431, pp. 371-374 (Jan. 1976).

Combined light and electron microscopy of serially sectioned cells and tissues, Y. Collan, SP431, pp. 375-378 (Jan. 1976). Morphometric "organelle profiles" as metabolic indicators, S. Malamed and L. C. Zoller, SP431, pp. 379-384 (Jan. 1976).

A quantitative analysis of some ultrastructural aspects of seed development, C. E. Hughes and L. G. Briarty, SP431, pp. 385388 (Jan. 1976).

The brain as a "stereological device," T. Radil-Weiss and J. Radilová, SP431, pp. 389-391 (Jan. 1976).

Stereological analysis of neural organogenesis in the chick embryo, O. Mathieu and P. E. Messier, SP431, pp. 393-396 (Jan. 1976).

Application of stereological methods to the study of preimplantation embryogenesis in mice, R. L. Deter, SP431, pp. 397400 (Jan. 1976).

The determination of size distribution on lymphoblasts in acute leukemia, E. Feinermann and G. A. Langlet, SP431, pp. 401-404 (Jan. 1976).

A morphometric study of human placentae of different gestational ages from normal and triplet pregnancies, I. Bhargava, K. Kamashki, and Y. Dodge, SP431, pp. 405-408 (Jan. 1976).

The effects of optical resolution on the estimation of stereological parameters, H. J. Keller, H. P. Friedli, P. Gehr, M. Bachofen, and E. R. Weibel, SP431, pp. 409-410 (Jan. 1976).

Quantification of rarely occurring structures in electron microscopy, U. Pfeifer, SP431, pp. 411-414 (Jan. 1976).

The morphometry and stereology of cerebral arterial bifurcations, P. B. Canham, J. G. Walmsley, and J. F. H. Smith, SP431, pp. 415-418 (Jan. 1976).

Karyo-interkaryometry as a periodic control for clinical prognosis, E. C. Craciun and C. Tasca, SP431, pp. 419-422 (Jan. 1976).

Nucleic acids content-nuclear volume correlation as a quantitative parameter in cellular malignancy, C. Tasca and E. C. Craciun, SP431, pp. 423-426 (Jan. 1976).

Is there an unrecognized systematic error in the estimation of surface density of biomembranes?, A. Reith and T. Barnard, SP431, pp. 427-428 (Jan. 1976).

Quantitative studies with the optical and electronic microscope of the pathological cells of the acute leukemia and chronic lymphocytic leukemia, J. L. Binet, P. Debré, P. d'Athis, D. Dighiero, and F. de Montaut, SP431, p. 429 (Jan. 1976).

Simple devices for stereology and morphometry, H. Elias and E. Botz, SP431, pp. 431-434 (Jan. 1976).

The edema syndrome in motion pictures, O. C. Jaffee, SP431, p. 435 (Jan. 1976).

Overview, R. T. DeHoff, SP431, pp. 439-443 (Jan. 1976).

Probabilistic foundations of stereology, R. E. Miles and P. Davy, SP431, pp. 443-445 (Jan. 1976).

Volume fraction analysis, H. E. Exner, SP431, pp. 446-448 (Jan. 1976).

Surface area, E. R. Weibel, SP431, pp. 448-455 (Jan. 1976). Length of lineal features in space, R. T. DeHoff, SP431, pp. 455-457 (Jan. 1976).

The area tangent count and the total curvature, R. T. DeHoff, SP431, pp. 457-459 (Jan. 1976).

Granulometry for isolated particles or connected media, J. Serra, SP431, pp. 460-461 (Jan. 1976).

Statistics of measurement, W. L. Nicholson, SP431, pp. 461464 (Jan. 1976).

Introduction remarks, B. H. Kaye, SP431, pp. 467-468 (Jan. 1976).

Stereology and particle technology, H. E. Exner, SP431, pp. 469-470 (Jan. 1976).

Representation of particle size and shape, B. Scarlett, SP431, pp. 471-47 6(Jan. 1976).

The application of stereology to particle technology, B. Scarlett and P. J. Lloyd, SP431, pp. 477-482 (Jan. 1976).

Techniques for particle measurement using image analysis, R. R. A. Morton, SP431, pp. 483-486 (Jan. 1976).

Microscopic characterization of fine powders, P. Ramakrishnan, SP431, pp. 487-490 (Jan. 1976).

Stereology of paint films, B. H. Kaye and I. Robb, SP431, pp. 491-492 (Jan. 1976).

Concluding remarks, B. H. Kaye, SP431, p. 493 (Jan. 1976).

Estimation of linear properties of spherical bodies in thin foils from their projections, F. Piefke, SP431, pp. 497-498 (Jan. 1976).

On size distribution methods, F. A. L. Dullien and K. S. Chang, SP431, pp. 499-502 (Jan. 1976).

Size distribution of retained austenite phase in a quenched stainless steel, A. V. Samudra and O. Johari, SP431, pp. 503506 (Jan. 1976).

Analysis of a set of spherical cells relative to their volume, P. d'Athis, SP431, pp. 507-508 (Jan. 1976).

Appendix - Basic stereology, E. E. Underwood, SP431, pp. 509-512 (Jan. 1976).

SP432. NBS time and frequency dissemination services, S. L. Howe, Ed., (Supersedes NBS Special Publication 236, 1974 and previous editions), Nat. Bur. Stand. (U.S.), Spec. Publ. 432, 32 pages (Jan. 1976) SD Catalog No. C13.10:432.

Key words: broadcast of standard frequencies; frequency calibration; high frequency; low frequency; standard frequencies; television color subcarrier; time calibration; time signals.

Detailed descriptions are given of the time and frequency dissemination services of the National Bureau of Standards. These services include the broadcasts from radio stations WWV, WWVH, WWVB, and WWVL, and new time and frequency

calibration services using television. This publication shows the services available on January 1, 1976. It will be updated only when the services are revised or when new services are added. A list of other publications available about the Time and Frequency Division is also included.

SP433. MFPG-Success by design: Progress through failure analysis. Proceedings of the 21st Meeting of the Mechanical Failures Prevention Group, held at the National Bureau of Standards, Gaithersburg, MD, Nov. 7-8, 1974, T. R. Shives and W. A. Willard, Eds., Nat. Bur. Stand. (U.S.), Spec. Publ. 433, 229 pages (July 1976) SD Catalog No. C13.10:433.

Key words: design; engineering education; failure analysis; failure analysis case histories; failure prevention; reliability; safety.

These Proceedings consist of a group of twenty-two submitted papers and discussions from the 21st meeting of the Mechanical Failures Prevention Group which was held at the National Bureau of Standards in Gaithersburg, Maryland on November 7-8, 1974. The central theme of the Proceedings was improvement in design through failure analysis. Emphasis was on design philosophy, the use of failure analysis case studies as an educational tool, successful redesign through failure analysis, and design oversights. These proceedings include the following papers (indented):

Creative student engineering design, P. S. De Jong, SP433, pp. 3-5 (July 1976).

The designer's contribution in the development of new products, J. J. Lesko, SP433, pp. 7-14 (July 1976).

Successful redesign and launch performance of the ERTS/Nimbus adapter after an acceleration test failure, V. T. Sweet and W. B. Keegan, SP433, pp. 19-72 (July 1976).

Agricultural equipment for underdeveloped countries, C. W. Suggs, SP433, pp. 74-81 (July 1976).

Safety success through design, D. W. Logan, SP433, pp. 8387 (July 1976).

Reliability, pollutants and aluminum raw material, V. D. Matney, SP433, pp. 89-101 (July 1976).

Rotor burst protection program, G. J. Mangano, SP433, pp. 103-119 (July 1976).

Airframe "crashworthiness" experiments, N. N. Shapter, SP433, pp. 122-128 (July 1976).

Redesign and assembly of anti-friction bearing housings for improved life, G. D. Xistris and D. C. Watson, SP433, PP. 131-142 (July 1976).

Case history of failures in a hammer mill, J. K. L. Bajaj, SP433, pp. 144-158 (July 1976).

Solution of an art restoration problem, E. Passaglia, SP433, pp. 159-161 (July 1976).

Elimination of failures of U-bolts in farm tractor dual wheels, B. P. Bardes, SP433, pp. 164-165 (July 1976).

Structural in-flight wing failures, M. L. Marx, SP433, pp. 166-177 (July 1976).

Use of cases in engineering education - Their special value, H. O. Fuchs, SP433, pp. 180-182 (July 1976).

What can be learned from cases, G. Kardos, SP433, pp. 183187 (July 1976).

Student written design case studies, C. O. Smith, SP433, pp. 188-190 (July 1976).

Teacher feedback on the use of engineering case studies, B. J. Pelan, SP433, pp. 192-198 (July 1976).

Some thermal problems in the design of fluid film bearings, D. D. Fuller, SP433, pp. 205-211 (July 1976).

Never overlook notches, C. O. Smith, SP433, pp. 212-213 (July 1976).

Innovation or reliability, H. O. Fuchs, SP433, pp. 214-215 (July 1976).

The "model" designer, R. E. Maringer, SP433, pp. 216-217 (July 1976).

The misuse of tensile strength as a design parameter, T. J. Dolan, SP433, pp. 218-219 (July 1976).

Inspection consideration at the design stage, J. F. Erthal, SP433, p. 222 (July 1976).

SP434. Hydrocarbons for fuel-75 years of materials research at NBS, G. T. Armstrong, Nat. Bur. Stand. (U.S.), Spec. Publ. 434, 20 pages (May 1976) SD Catalog No. C13.10:434.

Key words: coal; energy; fuel; graphite; hydrocarbons; metering; methane; natural gas; petroleum; physical properties; standard reference materials.

In this historical review the NBS work on hydrocarbons is discussed in terms of the three major classes of natural hydrocarbonaceous fuels: natural gas, petroleum, and coal. The work done on the measurement of properties of the pure components has included measurement of the values of the properties themselves and development of practical and accurate measurement procedures and instruments. In addition, combustion energies, densities, viscosities, vapor pressures, refractive indices, elemental compositions and other parameters have been determined for complex fuel mixtures and correlated to find methods of estimating properties. Extensive standard reference data tables have been compiled and a number of standard reference materials have been developed.

SP435. Laser induced damage in optical materials: 1975. Proceedings of a Symposium sponsored by: National Bureau of Standards, American Society for Testing and Materials, Office of Naval Research, Energy Research and Development Administration, NBS Boulder, CO, July 29-31, 1975, A. J. Glass and A. H. Guenther, Eds., Nat. Bur. Stand. (U.S.), Spec. Publ. 435, 437 pages (Apr. 1976) SD Catalog No. C13.10:435.

Key words: avalanche ionization; IR windows and mirrors; laser damage; laser materials; multiphoton processes; selffocusing; thin films.

The Seventh ERDA-ASTM-ONR-NBS Symposium on Laser Induced Damage in Optical Materials was held at the National Bureau of Standards in Boulder, Colorado, on July 29-31 of this year. These Symposia are held as part of the activities in Subcommittee II on Lasers and Laser Materials, of the ASTM. Subcommittee II is charged with the responsibilities of formulating standards and test procedures for laser materials, components, and devices. The Chairman of Subcommittee II is Haynes Lee, of Owens-Illinois, Inc. Co-chairmen for the Damage Symposia are Dr. Arthur Guenther, Chief Scientist of the Air Force Weapons Laboratory, and Dr. Alexander J. Glass, Head, Theoretical Studies, Y Division, Lawrence Livermore Laboratory.

Over 150 attendees at the Symposium heard 42 papers on topics relating fabrication procedures to laser induced damage in optical materials; on metal mirrors; in infrared window materials; the multipulse, wavelength and pulse length dependence of damage thresholds; damage in dielectric films and at exposed surfaces; as well as theoretical discussions on avalanche ionization and multiphoton processes of importance at shorter wavelengths. Of particular importance was the sealing relations developed from several parametric studies relating fundamental properties (refractive index, surface roughness, etc.) to the damage threshold. This year many of the extrinsic influences tending to reduce a material damage resistance were isolated such that a measure of its egregious nature could be quantified. Unfortunately, it was evident that much still needs to be accomplished to improve processing and fabrication procedures to allow a measurable approach to a materials intrinsic strength to be demonstrated. These proceedings include the following papers (indented):

Fabrication of laser optics at Lawrence Livermore laboratory, N. J. Brown, SP435, pp. 3-9 (Apr. 1976).

Key words: chamfering; continuous polishing; grinding; metal polishing; optical fabrication.

This paper summarizes fabrication techniques in use at Lawrence Livermore Laboratory for laser discs, windows, and mirrors, and polishing techniques used with metal surfaces.

Standard industrial polishing of high energy laser optics, W. J. Spawr, SP435, pp. 10-13 (Apr. 1976).

Key words: copper; molybdenum; optician; polishing; surfaces; zinc selenide.

The polishing and figuring of optical materials to produce state-of-the-art surface quality is truly an art, a scientific art, but an art nonetheless.

To attain success, the optician must have a clear mental model of the processes and associated techniques, and use this model as his most important tool. Second only to that is the combination of discipline and determination that no harmful or deleterious influences are allowed to effect the processes. New sophisticated polishing machines used in "Metrology Laboratory" environments are of little or no assistance. Polishing machines built 50 years ago work as well as the latest designs.

Today, moderately skilled technicians routinely produce 30 Å RMS surfaces on copper, molybdenum, and zinc selenide. These surfaces are free of orange peel, scratches, and digs; and are produced on conventional polishing machinery. Such surfaces are shown to exhibit exceedingly high laser damage thresholds from 1.06 to 10 μm. This is accomplished on a daily basis in a time frame comparable to the commercial polishing of ordinary optical glasses.

Ion planing and coating of sodium chloride, R. A. Hoffman, W. J. Lange, and W. J. Choyke, SP435, pp. 14-19 (Apr. 1976). Key words: arsenic trisulphide; ion planing; protective films; moisture resistance: sodium chloride.

Ion planing of single crystal sodium chloride, using low energy Xe ions at grazing incidence, is effective in removing scratches from surfaces when the sample is rotated. Surface features which develop, probably due to defects such as polishing grit and dislocations, can be minimized and the scratches eliminated by optimizing the amount of material removed. Ion planing and depositing overcoating films "in situ" greatly improves film adherence and protection of sodium chloride substrates against moisture attack.

Polishing studies and backscatter measurements on alkali-halide windows, M. J. Soileau, H. E. Bennett, J. M. Bethke, and J. Shaffer, SP435, pp. 20-28 (Apr. 1976).

Key words: alkali-halide; KCl; laser windows; optical figure; polishing; scattered light; surface absorption.

Surface absorption, optical figure, and optical scatter from windows are particularly important in high energy lasers. Surface absorption can result in window failure due to thermal distortion and in some cases catastrophic failure. Excellent optical figure is required for each component in the laser system optical train in order to maintain maximum on axis intensity of the focused laser beam. Backscatter from windows and other optical components can cause depumping of the active medium, and in the case of amplified chains, catastrophic damage to the laser amplifiers. A technique for polishing alkali-halide and quantitative measurements of backscatter for alkali-halide windows from the visible to 10.6 μm will be presented. This polishing procedure produces alkali-halide surfaces which have less than 1×10-4 surface absorption, are parallel to less than 3 seconds of arc and are flat to better than a quarter wave in the visible. Scattering levels below 10-4 at 10.6 μm have been achieved.

1.06 um 150 psec laser damage study of diamond turned, diamond turned/polished and polished metal mirrors, T. T. Saito, D. Milam, P. Baker, and G. Murphy, SP435, pp. 29-40 (Apr. 1976).

Key words: copper mirror; damage threshold; dark field photography; diamond turned optics; 1.06 μm polishing.

Using a well characterized 1.06 μm 150 psec glass laser pulse we have studied the damage characteristics for diamond turned, diamond turned/polished, and polished copper and silver mirrors less than 5 cm diameter. Although most samples were tested with a normal angle of incidence, some were tested at 45° with different linear polarization showing an increase in damage threshold for S polarization. Different damage mechanisms observed will be discussed. Laser damage is related to residual surface influence of the fabrication process. Our first attempts to polish diamond turned surfaces resulted in a significant decrease in laser damage threshold. The importance of including the heat of fusion in the one dimensional heat analysis of the theoretical damage threshold and how close our samples came to the theoretical damage threshold will be discussed.

Pulsed laser damage to uncoated metallic reflectors, I. Goldstein, D. Bua, and F. A. Horrigan, SP435, pp. 41-48 (Apr. 1976).

Key words: angle of incidence; polarization; pulsed laser damage; thermal model.

Threshold damage measurements were made on a variety of polished bulk copper and thin gold film reflectors using a TEM∞o mode Q-switched Nd:YAG laser. Results correlate well with a simple thermal model based on the assumed existence of a critical surface temperature. Direct confirmation of this thermal model was obtained through systematic variations of the polarization and angle of incidence of the incident laser beam and calorimetric measurements of the surface optical absorption coefficients. The "Damage Threshold" was defined through a careful procedure of attenuating the incident beam and varying all parameters (e.g., focus, position on the surface) until the sample no longer could be "damaged" as assessed visually with a microscope. In one striking case the damage threshold of two "identical" samples was shown to correlate with the measured surface absorption and not with the visual surface quality.

́The implications of these results to the design of high power optical systems which use large angles of incidence (e.g., axicon or toric optical elements) are discussed. In particular, for the polarization associated with Brewster's phenomenon the damage threshold was found to remain constant over wide variations of the angle of incidence, e.g., from 0 to 70° or 80°.

Diamond-turned mirrors, H. E. Bennett, M. J. Soileau, and P. C. Archibald, SP435, pp. 49-56 (Apr. 1976).

Key words: diamond turning; laser damage; metal mirrors; micromachining; optical figure; scattered light.

Diamond-turned, micromachined metal mirrors offer a new approach to optical fabrication and may have significant advantages for use as laser components. A laser mirror must have (1) excellent optical figure, (2) low scattered light, (3) high reflectance, (4) high damage threshold, and (5) good environmental resistance. We have measured optical figures as good as 1/20th wave over a 3.86-cm diameter sample and better than a wave over a 10.2-cm diameter sample on micromachined mirrors produced by Oak Ridge National Laboratories. Scattered light levels in the infrared can be as low or lower than those obtained on conventional mirrors and values as low as 2×10-5 have been observed at a wavelength of 10.6 μm. Infrared reflectance values as high or higher than those of conventional evaporated or sputtered coatings have been achieved and one mirror had an absorption at 10.6 μm of 0.006. The laser damage threshold of micromachined mirrors may well be higher than that obtainable by other techniques, but this question and the environmental resistance and "coatability" of a micromachined surface require further investigation.

Results of optical measurements of surface quality and figure of diamond-turned mirrors, R. E. Sladky and R. H. Dean, SP435, pp. 57-65 (Apr. 1976).

Key words: blur circle; circular diffraction grating: diamond-turned mirrors; diffraction pattern; machine cusp; scattered light; surface figure.

During the past year, the Oak Ridge Y-12 Plant has diamond turned mirrors for the LASL High-Energy Laser and for other projects. The largest of these mirrors are flat, elliptical in shape, and 654 mm (25.5 in) on the major axis and 394 mm (15.5 in) on the minor axis. The concave mirrors are 394 mm OD. These mirrors were inspected for surface finish and figure. Results of this work will be summarized. In addition, blur circle was measured. Measurements of scattered light have also been made. In some cases, the diffraction pattern was related to the waves formed in the surface by the machining process. This information has been useful to the engineers doing research on the diamond turning of laser materials.

Dielectric coated diamond turned mirrors, J. R. Buckmelter, T. T. Saito, R. Esposito, L. P. Mott, and R. Standlund, SP435, pp. 66-74 (Apr. 1976).

Key words: adherence; diamond machining; dielectric mirror; electroplating; laser damage resistance; stress relief.

Adherence of multilayer dielectric enhanced mirror coatings to diamond turned metallic surfaces was discovered to be a problem. Initial coating results demonstrated peeling and erratic optical properties for a variety of coating designs deposited on ERDA diamond turned copper, silver, and gold. The same coating designs deposited on polished molybdenum had excellent adherence and consistent optical properties. The adherence problem was determined to derive from two factors intimately connected

with the diamond turning process, namely, oil adsorption and stress in the electroplated metal surface. These factors can be eliminated by stress relief in a heated oil bath followed by thorough clening in freon or trichloroethylene prior to coating. Procedures used to investigate dielectric coated diamond turned mirrors included absorption calorimetry, damage measurements with a 10 kW laser and Auger Spectroscopy.

Slide-position errors degrade machined optical component quality, J. B. Arnold, P. J. Steger, and R. R. Burleson, SP435, pp. 75-89 (Apr. 1976).

Key words: controlled environment; diamond machining; machined optics; nondistortion part support; position errors; quality and compatible part material; quality diamond tools.

An ultraprecision lathe is being developed at the Oak Ridge Y-12 Plant to fabricate optical components for use in high-energy laser sytems. The lathe has the capability to produce virtually any shape mirror which is symmetrical about an axis of revolution. Two basic types of mirrors are fabricated on the lathe; namely, (1) the mirrors which are machined using a single slide motion (such as flats and cylinders), and (2) the mirrors which are produced by two-coordinated slide motions (such as hyperbolic reflectors; large, true-radius reflectors, and other contoured-surface reflectors). The surface-finish quality of typical mirrors machined by a single axis of motion is better than 13 nm, peak to valley, which is an order of magnitude better than the surface finishes of mirrors produced by two axes of motion. Surface finish refers to short-wavelength-figure errors that are visibly detectable. The primary cause of the inability to produce significantly better surface finishes on contoured mirrors has been determined as positional errors which exist in the slide positioning systems. The correction of these errors must be accomplished before contoured surface finishes comparable to the flat and cylinder can be machined on the lathe.

Ultrasonic cleaning of optical surfaces, W. E. K. Gibbs and A. D. McLachlan, SP435, pp. 90-97 (Apr. 1976).

Key words: laser damage; metal mirrors; subsurface structure; ultrasonic cleaning.

During the formal proceedings of the 1975 Symposium on Laser Induced Damage in Optical Materials, Dr. A. H. Guenther presented some recent results on the degradation of polished optical surfaces by ultrasonic cleaning procedures. This information was supplied to him by Dr's. W. E. K. Gibbs and A. D. McLachlan of the Materials Research Laboratories of the Department of Defense, Commonwealth of Australia. Materials studied included OFHC copper, beryllium copper, zirconium copper, stainless steel, kanigen and fused quartz. Results indicate that ultrasonic cleaning degrades polished surfaces, and if the cleaning process is vigorous enough for a sufficient duration of time, subsurface fracture introduced in the grinding process is made quite evident. At the conclusion of the transmission of this correspondence, a discussion on the subject of ultrasonic cleaning ensued.

Thermal diffusivity of germanium gallium arsenide and cadmium telluride over the temperature range 80 K-900 K, R. Doussain, H. P. le Bodo, SP435, pp. 98-106 (Apr. 1976).

Key words: cadmium telluride; gallium arsenide; germanium; laser flash method; laser windows; thermal diffusivity.

The laser flash technique was used to determine the thermal diffusivity of germanium, gallium arsenide and cad um telluride over the temperature range 80 K-1000 K. The main features of the experimental equipment are described. Values of thermal diffusivity (80-900 K) are reported.

Damage to 10.6 μm window materials due to CO2 TEA laser pulses, K. M. Leung, M. Bass, and A. G. J. Balbin-Villaverde, SP435, pp. 107-117 (Apr. 1976).

Key words: KCl; NaCl; pulsed CO2 TEA laser damage; transmitted pulse; waveform distortion; ZnSe.

Laser irradiation induced damage to several materials of interest for use as 10.6 μm laser system windows was studied. A pulsed CO, TEA laser, operating in the TEM∞o mode was the irradiation source in these experiments. The light was focused onto the surfaces or into the bulk of the samples and the waveform of the transmitted pulse was monitored. Comparison of the incident and transmitted laser pulse waveforms shows the onset of laser induced damage as a distortion of the latter. Damage threshold data and a discussion of possible damage mechanisms for improved ZnSe, commercial and RAP grown KCl, and commercial NaCl are presented.

Improvements in the breakdown threshold in alkali halides at 10.6 μm, V. Wang, C. R., Giuliano, S. D. Allen, and R. C. Pastor, SP435, pp. 118-125 (Apr. 1976).

Key words: alkali halides; bulk damage; longitudinal mode control; pulsed 10.6 μm laser damage; RAP materials; transmitted pulse cutoff; variable pulse duration.

Evidence has been found that the threshold for laser-induced breakdown in the bulk of single crystals is strongly dependent upon processing. Potassium bromide, KCl, and NaCl have been examined over a range of pulse widths (from 0.2 μs to 6 μs) in selected cases and for a variety of pulse shapes using both single longitudinal mode and partially mode-locked multilongitudinal mode pulses. A breakdown threshold of over 12 GW/cm2 (2.5 MV/cm) for KCI far exceeds the best values obtained in previously available commercial material at these pulse lengths. A comparison of breakdown threshold for conventional and reactive atmosphere processed (RAP) halides is made with comment upon the present ambiguities in breakdown mechanism. In addition to the measurement of damage thresholds of materials from different sources, the temporal profile of transmitted pulses at the time of damage was monitored.

Optical distortion by laser heated windows, J. S. Loomis and E. G. Bernal, SP435, pp. 126-141 (Apr. 1976).

Key words: infrared lasers; interferometry; stress birefringence; thermal distortion; windows.

The optical distortion introduced in a collimated He-Ne beam by windows irradiated with a CO2 laser has been measured interferometrically. Materials measured included ZnSe, KCl, NaCl, CaF2, SrF2, and BaF2. Flux densities from the CO2 laser were in the range 10-60 KW/cm2 with total powers from 250 to 1000 watts for the ZnSe and the halides. The changes in the interferometric patterns observed can be attributed to a) isotropic phase shifts proportional to the local temperature, b) anisotropic effects due to induced birefringence that affect both the symmetry of the interferometric pattern and the visibility of the fringes, c) localized phase shifts at the entrance and exit points due to surface absorption.