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The 28th annual symposium on optical materials for high‐power lasers (Boulder damage symposium) was held at the National Institute of Standards and Technology in Boulder, CO, 7–9 October 1996. The symposium was held under the joint sponsorship of Bennett Optical Research, the Center for Research and Education in Optics and Lasers (CREOL) at the Center for Research and Education in Optics and Lasers (CREOL) at the University of Central Florida, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Sandia National Laboratories, and SPIE—The International Society for Optical Engineering. Over 130 scientists attended the symposium, including representatives from France, Germany, Japan, Russia, South Africa, Hungary, Armenia, Israel, the UK, and the US. The symposium was divided into sessions concerning materials and measurements, surfaces and mirrors, thin films, fundamental mechanisms, and a mini‐symposium on ‘Laser‐Induced Damage in Optical Fibers,’ organized by R. E. Setchell and Sandia National Laboratories. As in previous years, the emphasis of the papers presented at the symposium was directed toward new frontiers and new developments. Particular emphasis was given to materials for high‐power laser systems. The wavelength range of prime interest was from 10.6 μm in the infrared to the UV region. Highlights included surface characterization, thin film/substrate boundaries, and advances in fundamental laser‐matter interactions and mechansims. Harold E. Bennett of Bennett Optical Research, Inc., Arthur H. Guenther of Sandia National Laboratories, Mark R. Kozlowski of the Lawrence Livermore National Laboratory, Brian E. Newnam of the Los Alamos National Laboratory, and M. J. Soileau of the University of Central Florida were co‐chairs of the symposium. The 29th annual symposium is scheduled for 6–8 October 1997 at the National Institute of Standards and Technology, Boulder, CO. An added feature will be a wholly self‐contained mini‐symposium on ‘Damage in Laser Diodes’ organized by David Welch of Spectra Diode Laboratories.

The twelfth annual Symposium on Optical Materials for High Power Lasers (Boulder Damage Symposium) was held at the National Bureau of Standards in Boulder, Colorado, 30 Sept.-l Oct., 1980. The symposium was held under the auspices of ASTM Committee F-l, Subcommittee on Laser Standards, with the joint sponsorship of NBS, the Defense Advanced Research Projects Agency, the Department of Energy, the Office of Naval Research, and the Air Force Office of Scientific research. Over 150 scientists attended the symposium, including representatives of the United Kingdom, France, Japan, and West Germany. The symposium was divided into sessions concerning materials and measurements, mirrors and surfaces, thin films, and finally fundamental mechanisms. As in previous years, the emphasis of the papers presented at the symposium was directed toward new frontiers and new developments. Particular emphasis was given to materials for high power systems. The wavelength range of prime interest was from 10.6 microm to the UV region. Highlights included surface characterization, thin film-substrate boundaries, and advances in fundamental laser-matter threshold interactions and mechanisms. The scaling of damage thresholds with pulse duration, focal area, and wavelength was discussed in detail. Harold E. Bennett of the Naval Weapons Center, Alexander J. Glass of the Lawrence Livermore National Laboratory, Arthur H. Guenther of the Air Force Weapons Laboratory, and Brian E. Newnam of the Los Alamos National Laboratory were cochairmen of the symposium. The thirteenth annual symposium is scheduled for 17-18 Nov. 1981 at the National Bureau of Standards, Boulder, Colorado.

The tenth annual Symposium on Optical Materials for High Power Lasers (Boulder Damage Symposium) was held at the National Bureau of Standards in Boulder, Colorado, 12-14 September 1978. The symposium was held under the auspices of ASTM Committee F-1, Subcommittee on Laser Standards, with the joint sponsorship of NBS, the Defense Advanced Research Project Agency, the Department of Energy, and the Office of Naval Research. About 175 scientists attended, including representatives of the United Kingdom, France, Canada, Japan, West Germany, and the Soviet Union. The symposium was divided into sessions concerning the measurement of absorption characteristics, bulk material properties, mirrors and surfaces, thin film damage, coating materials and design, and breakdown phenomena. As in previous years, the emphasis of the papers presented was directed toward new frontiers and new developments. Particular emphasis was given to materials for use from 10.6 microm to the UV region. Highlights included surface characterization, thin film-substrate boundaries, and advances in fundamental laser-matter threshold interactions and mechanisms. The scaling of damage thresholds with pulse duration, focal area, and wavelength was also discussed. In commemoration of the tenth symposium in this series, a number of comprehensive review papers were presented to assess the state of the art in various facets of laser induced damage in optical materials. Alexander J. Glass of Lawrence Livermore Laboratory and Arthur H. Guenther of the Air Force Weapons Laboratory were co-chairpersons. The eleventh annual symposium is scheduled for 30-31 October 1979 at the National Bureau of Standards, Boulder, Colorado.

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 29–31 July 1975. These Symposia are held as part of the activities in ASTM Subcommittee II on Lasers and Laser Materials, which 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 Arthur Guenther of the Air Force Weapons Laboratory and Alexander J. Glass of Lawrence-Livermore Laboratory. Over 150 attendees at the Symposium heard forty-five papers on topics relating fabrication procedures to laser induced damage in optical materials; on metal mirrors; in ir 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 were the scaling 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 materials damage resistance were isolated such that measures of their egregious nature could be quantified. 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.

The Sixth ASTM-ONR-NBS Symposium on Laser Induced Damage in Optical Materials was held at the National Bureau of Standards in Boulder, Colorado on 22–23 May 1974. Over 150 attendees at the Symposium heard thirty-one papers on topics relating to laser induced damage in crystalline and nonlinear optical materials, at dielectric surfaces, and in thin film coatings as well as discussions of damage problems in the ir region due both to cw and pulsed irradiation. In addition, several reports on the theoretical analysis of laser–materials interaction relative to the damage progress were given, along with tabulations of fundamental materials properties of importance in evaluation of optical material response to high-power laser radiation. Attention was given to high-power laser system design considerations that relate to improved system performance and reliability when various damage mechanisms are operable in such systems. A workshop on the machining of optics was held, and nine papers on various facets of the topic were presented dealing with machining procedures, surface characterization of machined elements, coating of machined components, and the polishing and damage resistance of polished, coated, and bare metal reflectors.

The dependence of a single-shot laser-induced damage on certain film properties is investigated. Variable stress films are produced by mixing pure components with similar damage thresholds; a definite stress dependence is shown. Films formed from mixtures of high and low threshold components are investigated and found to have damage thresholds between the high and low component values. The damage thresholds of multilayer and periodic inhomogeneous film systems are compared. The results confirm that the damage threshold is almost entirely material-dependent and equal to the threshold of the lowest threshold component for highly reflecting multilayers. Multilayers deposited at different vapor incidence angles are compared. A definite dependence is shown.

During the 1973 Symposium on Damage in Laser Materials several specific topics received considerable attention. The papers presented to the approximately 135 specialists in attendance can logically be separated into categories on self-focusing damage, surface damage, coating damage, infrared component damage, and theory and fundamental properties. Highlighting the meeting were papers on small scale self-focusing, the importance of surface or near-surface absorbing impurities as a major extrinsic influence in reducing the intrinsic damage level of coated and uncoated surfaces, development of new instrumental methods for evaluation of material properties important in the damage process, initial attempts at cataloging these important properties, and, finally, several reports on the frequency and temporal aspects of laser-induced damage in a variety of materials, from the visible to the infrared, and from subnanosecond pulsed to continuous wave exposures.

In the application of high-power lasers, damage to active laser materials, and to components of laser system, generally determines the limit of useful laser performance. Accordingly, there is great interest in reducing the susceptibility of optical elements ot damage. Damage in transparent dielectrics arises from three major causes, particulate inclusions or microinhomogeneities in the material, self-focusing within the materials, and surface damage due to plasma formation. The state of understanding of these phenomena, and the thresholds observed, where they have been determined, will be discussed. Dependence on pulse length will also be considered. Although most of the research accomplished to date on laser damage has concentrated on Nd-glass, the advent of very high-powered gas lasers has stimulated interest in the development of damage resistant component materials for use in the ir. Crystalline dielectrics appear to be the most likely candidate materials for ir windows. Nonlinear optics materials are particularly susceptible to damage, since they are generally exposed to high intensity radiation. Asa final item, damage in thin film dielectric coatings are considered.

The laser damage threshold of various thin film coatings has been assessed using 1.06 μm radiation at a pulse length of 6ns FWHM. Samples of conventional coatings of several materials have been tested as a function of film thickness and spot size. Beam diameters employed range from approximately 9μm and larger. From these preliminary data, previously observed scaling has been verified, i.e., thinner films are more damage resistant, while smaller spot sizes yield higher damage thresholds, as expected. The samples employed in these tests were conventional coatings of ThF 4 , ZrO 2 and HfO 2 as well as specially prepared "low defect" coatings of Cerac and RAP grown ThF 4 . These "low defect" coatings are initial efforts and unfortunately showed no advantage over conventional coatings in terms of damage threshold.

Since operational lasers were first demonstrated in 1960, the field of laser/electro-optics has become an indispensable, rapidly expanding component of modern industry. With the emergence of numerous medical and telecommunication applications in the 1980s, including fiber-optics, the field of laser/electro-optics evolved into photonics, a broad field encompassing optoelectronics, micro-optics, lasers, digital imaging, spectroscopy, optical instruments, and optical systems. Today photonics is not only a technology field in and of itself but is also an enabler of nearly every other technology field, including microtechnology, measurement and materials processing, remote sensing, photolithography for semiconductors, nanotechnology, electro-optics displays and imaging, and national defense.

ICO coordinates the advancement and dissemination of scientific and technical knowledge in optics and photonics. Its Education Committee plans to survey, cross-reference and provide web links for syllabi, curricula, course materials, laboratory experiments and textbooks for K-12 through professional educational programs. We invite discussion and comment on near-term and long-term goals.

For the past 20 years, the Departments of Physics and Astronomy (P&A) and of Electrical and Computer Engineering (EECE) at the University of New Mexico have jointly administered a highly successful interdisciplinary, intercollegiate Ph.D. program in Optical Sciences. During this interval, over 75 Ph.D. degrees have been awarded to graduates who have become highly valuable members of optical industries and academia here and abroad. During this same period, the optics-related faculty has seen its numerical strength increase to nearly 30, and has expanded into several departments such as Biology, Chemistry, Mathematics and Statistics, Chemical Engineering, and Mechanical Engineering.

In direct response to the needs of the local optics and photonics sector, Albuquerque has established a comprehensive optics education program from middle school to post graduate. Individuals may enter and return to the workforce routinely as they ascend the degree chain. Quantitative details and progress will be presented as well as curricula.

University of New Mexico has developed a comprehensive plan for a new B.S. degree in Optical Science and Engineering, accompanied by teacher training and enhancement of K-12 optics education. The plan incorporates curriculum development, creation of new laboratories, development of optics courses for teachers, creation of outreach programs, and involvement of industry and government laboratories.

The completion of the report 'Harnessing Light: Optical Science and Engineering for the 21st Century' by COSE (Committee on Optical Science and Engineering) by the National Academy in 1998 has had a profound effect on optics related activities and the recognition of optics as a most pervasive and enabling field of technology. After a brief summary of the report - an update on its principal recommendations and other significant U.S. and global activities will be highlighted. © (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Since the advent of the communication revolution and global Internet system, the rate of creation of new knowledge is increasing at almost a geometric rate in diversity of applied fields. The global competitive economic system is driving everybody to rush into the technology innovation process. This is acutely apparent in all technology fields, and especially, in optics/photonics. Today's technology knowledge will become almost obsolete tomorrow. Then how do we create lasting textbooks for technicians? Different industry segments use same photonic sciences but for different applications and with different emphasis on different principles. Then how do you create textbooks that are customizable for different industry sectors? Rapid innovation and competition is also creating pressure on technicians to know and learn more with appropriate mathematical foundations that high schools are unable to provide. We will present concepts and ideas on how industries, professional societies and interested individuals can create a 'lasting' series of textbooks that are rapidly updateable along with extra, mathematically oriented examples to keep up with the technology changes and quickly customizable for different industry sectors. These concepts evolved through the experience of the NSF supported project, STEP (Science and technology Education in Photonics). The objective of STEP is to create a set of optics/photonics textbooks for technicians. The first overview text, 'Fundamentals of Photonics,' is already under field test. Explore cord.org on the web for more details.

Photonics is a critical enabling technology for the 21st century and photonics technicians are an integral part of the supporting workforce. This paper outlines a two-year AAS education program designed to product competent photonics technicians who can (1) enter the workforce directly upon graduation from the two-year program or (2) continue their education toward an appropriate four-year bachelor's degree program. As an appropriate foundation for the two-year AAS photonics program, consideration is given also to an optimal technology preparatory program for high school students who are moving towards careers in photonics.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

On a subject of considerable import to the laser-induced damage community, a two day workshop on the topic, Thin Film Thermal Conductivity Measurement was held as part of the 13th Symposium on Thermophysical Properties at the University of Colorado in Boulder CO, June 25 and 26, 1997. The Workshop consisted of 4 sessions of 17 oral presentations and two discussion sessions. Two related subjects of interest were covered; 1) methods and problems associated with measuring thermal conductivity ((kappa) ) of thin films, and 2) measuring and (kappa) of chemical vapor deposited (CVD) diamond. On the subject of thin film (kappa) measurement, several recently developed imaginative techniques were reviewed. However, several authors disagreed on how much (kappa) in a film differs from (kappa) in a bulk material of the same nominal composition. A subject of controversy was the definition of an interface. In the first discussion session, several questions were addressed, a principal one being, how do we know that the values of (kappa) we obtain are correct and is there a role for standards in thin film (kappa) measurement. The second discussion session was devoted to a round-robin interlaboratory comparison of (kappa) measurements on a set of CVD diamond specimens and several other specimens of lower thermal conductivity. Large interlaboratory differences obtained in an earlier round robin had been attributed to specimen inhomogeneity. Unfortunately, large differences were also observed in the second round robin even though the specimens were more homogenous. There was good consistency among the DC measurements, however, the AC measurements showed much greater variability. There was positive feedback from most of the attenders regarding the Workshop with nearly all respondents recommending another Workshop in three or fewer years. There was general recognition that thin film thermal conductivity measurements are important for predicting the resistance of optical coating materials to laser damage.

The explosive photonics industry in the United States and elsewhere signals a critical need for comprehensive programs in education for the preparation of photonics technicians, engineers, and scientists. This paper outlines curricular plans in photonics education which begin at the ninth grade in high school and end generally at the fourteenth grade with an associate of applied science degree. Beginning with comprehensive lists of appropriate tasks for photonics technicians -- as identified by photonics-related industries - - extrapolation is made to specific courses, sequences of courses, and on to comprehensive high school/ post-secondary curricula, with appropriate emphasis on the necessary basics in mathematics, science communications, and introductory technology courses. The identification of a photonics core for technician education is a major part of this paper. In addition, a strategy for the development of the photonics core courses in modular form -- with the desired pedagogical organization of a typical module -- is discussed.

At present, previously developed curriculum materials designed to teach the technology of lasers and electro-optics for two- year postsecondary students are becoming outdated. In an effort to update technology-oriented curricula for the new and emerging applications of photonics, the authors are proposing a systemic process that would facilitate the interaction of educators in an innovative electronic format. The morphing process is NOT a listserve, but an established set of curriculum materials in laser/electro-optics that in print contain over 1900 pages and an excess of 1300 illustrations, all placed on the World Wide Web that would allow access to faculty only. The faculty will be allowed to make peer- reviewed changes to the curriculum via an e-mail submission process and submit ideas for lecture and laboratory techniques that will be hyperlinked to specific parts of the curriculum. The curriculum and the process will be available to optics/photonics faculty world-wide as recently proposed in a 3-year project with the U.S. Department of Education.

Herein is reviewed the utility of scaling relations and pitfalls to be avoided in their application. This is illustrated by recourse to a discussion of selected proposed scaling relationships including their range of validity, experimental foundation and efficacy in determining the basis of fundamental physical interaction processes. The latter is illustrated using the scaling of damage threshold with the duration of an incident laser pulse. It is shown that for a defect dominated pulsed laser interaction mechanism, the pulse length scaling dependence can change over a narrow range due to a variation of the characteristics of the defect which is most sensitive or easiest to damage under the experimental conditions of import even though the gross aspects of the interaction mechanism do not change appreciably.

New Mexico is very proud of its tri-cultural heritage -- Hispanic, Native American, and Anglo, but that simple description belies the technical richness of the state. If one is in technology and thinks of New Mexico, particularly if involved in the defense community, one thinks of organizations like Los Alamos National Laboratory, Sandia National Laboratories, White Sands Missile Range, and Phillips Laboratory. Phillips Laboratory is one of the new Air Force super laboratories and its activities are focused on space and missile technology. One should appreciate some statistical aspects of the impact of those organizations on New Mexico. In a recent National Science Foundation study, if one looks at R&D performance measured in dollars of activity, on an absolute scale, New Mexico ranks fourth nationally among the 50 states. It also ranks fourth nationally in the university sector in R&D performance. And those two numbers or rankings are not unrelated. You should come to appreciate how we have tried to leverage these strong technology organizations. The private sector ranks only twenty-first, and much of the economic development activity in New Mexico is now attempting to raise this standing by concentrating on the manufacturing sector. What this all means is that, among the 50 states, New Mexico ranks first in the ratio of R&D performance to gross state product. By that measure, technology is more significant to the State of New Mexico than it is to any other state in the Union.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laserinduced damage of optical materials due to the presence of radiation at two different frequencies has received little attention in the literature even though this is not an uncommon occurrence in the laboratory. Recent studies on the inultiphoton ionization of single atoms have shown that the ionization threshold depends strongly on the frequencies of the incident fields and their polarizations. In this paper we explore the extent to which these results can be applied to laserinduced damage. The results for a single atom are presented for the case where one field has a comparatively high frequency and low intensity. This field is responsible for the ionization. The other field has a higher intensity and much lower frequency such that it does not ionize by itself. However it substantially modifies the ionization threshold due to the first field. Both fields are circularly polarized. The behavior of the ionization rate near the thresholds is found to depend strongly on whether the fields have the same or opposite circular polarizations. We also speculate on how these results will influence laser induced damage thresholds.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A summary was not available at time of publication.

The inclusion dominated model of laser-induced damage is reexamined in order to explore the consequences of recent measured low values of thin film thermal conductivities. In the model absorption of radiation is assumed to only occur in the inclusion via Mie scattering. From the analysis two different values of the imaginary part of the index of refraction are predicted for a given damage threshold. Physical mechanisms are proposed for each value. Interestingly, varying the thermal conductivity of the both the host and inclusion over several orders of magnitude seem to have a less than expected influence on the damage threshold. However there is also proposed an effect of the index of refraction associated with a given damage threshold which is based upon two distinct absorption mechanisms. The results of this modified model are then compared with experimental data for damage thresholds of different thickness films.

A quantum rate analysis of laser‐induced breakdown in deuterium and helium gas was used to predict the dependence of the breakdown‐threshold intensity on gas pressure, laser‐pulse length, and the magnitude of an applied external magnetic field parallel to the direction of propagation of the laser beam. Diffusion, elastic and inelastic collisions, and multiphoton ionization of atomic and molecular states excited by electron impact were considered. The threshold data indicate the presence of three distinct regions: the pulse‐length dominated, intermediate, and the diffusion dominated, as well as the importance of a dimensionless parameter Ω in determining the magnitude of the magnetic field effect on the breakdown threshold for a given set of experimental conditions. The results are in excellent agreement with experimental data.

The acoustic velocities in polymethylmethacrylate have been measured with an ultrasonic pulse‐echo technique as functions of frequency, temperature, and pressure. At atmospheric pressure, data on the velocities and attenuation coefficients were obtained for the temperature range of 22°–75°C in the frequency range of 6–30 MHz. For the measurements of velocity and attenuation as a function of frequency, the complex adiabatic bulk modulus was calculated at room temperature and atmospheric pressure for the above frequencies. At temperatures of 25°, 40°, 55°, and 75°C, the pressure dependence of the longitudinal and shear velocity was determined to 150 kpsi at a frequency of 6 MHz. It was found that the measured velocities under increasing pressure conditions were generally lower than those of decreasing pressure by about 0.5% for the longitudinal measurements and about 1% for the shear measurements. However, measurements of the velocities at atmospheric pressure after the specimens had been exposed to 150 kpsi were usually within 0.1% of the initial values. A discussion is presented which compares the continuity of the present data with equation of state determinations in PMMA at elevated pressures.

The velocity and attenuation of longitudinal bulk waves in a solid epoxy foam were measured by an acoustic pulse technique in the frequency range of 0.667–4.0 Mc./sec. and in the temperature range from ambient to 150°C. The measurements are reported with the density of the solid epoxy and with aluminum impurity loading as parameters. Over the indicated temperature and frequency ranges, complete attenuation and velocity measurements are reported for one foam corresponding to a density of 0.325 g./cc. In the density range of 0.088–0.325 g./cc. for the unloaded foams, attenuation is reported at room temperature. It is observed that the longitudinal velocities for all the densities decrease with temperature by about 40% in a span of 100°C. and that an approximately linear relation exists with temperature. The velocities in the foams loaded with small percentages of aluminum and heat-treated at 250°C. exhibit temperature behavior which is dependent upon the combined effects of loading, density change, and epoxy properties. For the loaded foam with the highest density (1.068 g./cc.), velocity is reported to a temperature of about 250°C. The velocities of all the various density samples with the exception of the loaded foams exhibit inflections at a temperature of about 110°C. The attenuation–temperature measurements on the 0.325 g./cc. sample show similar behavior at this temperature except that the effect is much more pronounced than the velocity inflection, hence a better indication of the transition. The precision of the measurement is about 2% for the relative longitudinal velocities and about 20% for the attenuation.

An experimental study was conducted to determine previously unavailable data showing the relationship between temperature and the velocity of longitudinal ultrasonic waves through several plastics. The ultrasonic frequencies used were between 1 and 10 Mc./sec., and the temperature range covered was between room temperature and 100°C. Velocity–temperature curves were determined for nylon, a high- and a low-density polyethylene, Plexiglas, Teflon, and for several reentry vehicle nose-cone materials, including chopped nylon phenolic, tape-wound nylon phenolic, Castable 124, Avcoat I, and Avcoat 19. Less complete data were obtained for Avco phenolic fiber glass, General Electric phenolic fiber glass, and oblique tape-wound refrasil. These layered materials are difficult to measure, and the velocity of acoustic waves is very dependent on the direction of propagation with respect to the laminations. For most of the materials studied the velocity was found to decrease more or less linearly with increasing temperature. Typically, the velocities at 100°C. were 9–31% less than at room temperature.

The influence of parameters affecting the laser triggering of a high voltage electrical sphere‐sphere gap has been experimentally investigated. Of primary interest was the delay time between arrival of the laser pulse and current flow across the gap. This delay was studied as a function of total laser beam power (0–80 MW); dielectric gas (SF6, N2, air); gas pressure (100–1400 Torr); electrode spacing (0.4–1.5 cm); gap electric field (10–100 kV/cm); and focus point location between two 5 cm diam stainless steel spheres. Delay times less than 10 nsec were observed in SF6 at atmospheric pressure with corresponding low jitter. For the cases studied delay times varied inversely with the electric field, gas pressure, and focus point distance from the anode surface. Above a certain laser beam power the delay time was not a significant function of laser power for the range studied. Applications of laser triggering are discussed with a description of current and future research areas.

A pulse‐transmission technique is described that allows the determination of small changes of the acoustic velocities in high‐loss materials. The technique employs phase comparison between a transmitted acoustic pulse and the input rf signal to establish a null pattern in the superimposed output. The method has useful applications in situations where it is necessary to detect changes as small as one part in 104 in the velocities. It has been used in ultrasonic investigations employing propagation frequencies higher than 10 MHz and for total attenuation losses as high as 50 dB. Data are presented illustrating the shear velocity as a function of one‐dimensional stress in polymethylmethacrylate.

The temperature dependence of acoustic shear velocities are reported for Poly-Penco nylon, type G Plexiglass [poly(methyl methacrylate)], TFE Teflon (tetrafluoroethylene), low- and high-density polyethylene, Lexan (polycarbonate), and Delrin Acetal (nylon). Most of the data were obtained at a frequency of 1 Mc./sec. over the temperature range of 25–100°C. In addition, previously unreported longitudinal velocities to ∼125°C. are reported for Lexan and Delrin Acetal.

The relationship of ultrasonic velocities to equations of state is addressed for two homogeneous isotropic plastics, polystyrene and polymethylmethacrylate. Ultrasonic velocities were measured at hydrostatic pressures up to 10 kbar and temperatures from ambient to 75°C at an acoustic frequency of 6 MHz. From these data the pressure and temperature dependence of the elastic moduli are calculated. In particular, the bulk modulus is used to compute an equation of state from models proposed by Birch and Murnaghan. The nonlinearity of the bulk modulus at pressures below 10 kbar favors the Birch model. Comparison with shock data shows that the Birch equation of state, determined ultrasonically, agrees quite well with the shock data to pressures well over an order of magnitude in excess of the 10‐kbar ultrasonic data for both polystyrene and polymethacrylate.

Ultrasonic longitudinal wave velocities in layered materials were measured as a function of the lamination angle at several temperatures. It was found that the longitudinal wave velocity versus lamination angle curve maintains the same shape (for a given material) for temperatures between 25 and 125°C. Furthermore, it was found that the wave velocity versus lamination angle curve can be predicted to within 2% by a theoretical equation involving only the lamination angle, & thetas; (taken as the angle between the grain of the sample and the direction of sound propagation); c (0°), the measured wave velocity at an angle of 0°; and c (90°) the measured wave velocity at an angle of 90°. Finally, it was found that the longitudinal wave velocity of certain materials varies as much as 25% between lamination angles of 0° and 90°, while other materials show less variation, and some none at all.