Al the plenary session held December 4, 1985 during the annual MRS Fall Meeting in Boston, Dr. Gerold Yonas was the keynote speaker. He was introduced to the packed ballroom by 1985 MRS President Elton N. Kauftnann.

Kaufmann: To introduce our plenary address this evening, I would like to make a few remarks on the context in which it is being presented. Iam sure you are all aware that materials research, as most fields of science, is a field where it is rare indeed that one can cleanly separate the technical aspects of a program from the social, economic, and political aspects. This evening's topic is certainly no exception. It involves the U.S. government's Strategic Defense Initiative, or SDI for short. It has broad technical and political implications and has raised highly contentious issues of both technical feasibility and political appropriateness. It is in every source of news available today. This evening we want to focus on those technical aspects of SDI which involve materials and which should therefore be of interest to this audience.

Recently, in Space Business News, John McTague, Acting Director of OSTP (Office of Science and Technology Policy), indicated that “the technology of Swords and the technology of Plowshares have much in common.” Of course the degree of commonality between the Swords and the Plowshares becomes greateras one goes to more fundamental research. In the same article Gerold Yonas indicated that “several aspects of SDI are likely to have enormous implications in the private sector with spinoffs directed into every part of the economy.” In addition to the technical materials aspect of the program those larger issues will certainly impact our lives. In that spirit we want to make this presentation so you can evaluate the program with a maximum amount of information. Of course, because this is a publicly controversial issue, I need to stress that the Society is not endorsing one particular view or another. But, we are strongly advocating the wide dissemination of information on a topic such as this.

The usefulness of infrared (IR) radiation has been recognized for many years and is today the basisof an expanding technology. The development of the laser, particularly the IR laser, has further fueled this technology expansion. Optical materials have always played a critical role in IR technology, primarily as transmissive and reflective optical components. Often, the lack Of an adequate IR optical material has delayed the implementation of applications Until appropriate materials or quality of materials were developed. While the developed material may satisfy the basic requirements of the application, often its other physical properties and/or cost are not desirable. The limited number of IR optical materials combined with the growing humber of applications has kept their development essential to our technological growth.

This paper reviews some current research and developmen t trend s in IR optical materials primarily for transmissive components. These IR components include geometric optics, windows and domes, optical fibers, high energy laser optics, and coatings. The emphasis is on optical materials for applications involving wavelengths in the 2-14 μm region.

Intrinsic Attenuation

Intrinsic attenuation defines the fundamental limits to light propagation in a transmissive material. It is composed of electronic or bandgap absorption, lattice vibration or multiphonon absorption, and Rayleigh and Brillouin scattering. Bandgap absorption results from the promotion of an electron from the valence to the conduction band by direct absorption of a photon or indirectly involving a phonon and the appropriate change in k-vector. The onset of absorption occurs at photon energies greater than or equal to the bandgap.

Damage to optical materials under intense photon irradiation has always been a major problem in the design and operation of high-energy and high-average-power lasers. In short-wavelength lasers, operating at visible and ultraviolet wavelengths, the problem appears to be especially acute; presently attainable damage thresholds seriously compromise the engineering design of laser windows and mirrors, pulsed power trains and oscillator-amplifier systems architecture. Given the present interest in ultraviolet excimer lasers and in short-pulse, high-power free-electron lasers operating at visible and shorter wavelengths, the “optical damage problem” poses a scientific and technological challenge of significantdimensions. The solution of this problem even has significant implications outside the realm of lasers, for example, in large space-borne systems (such as the Hubble Telescope) exposed to intense ultraviolet radiation.

The dimensions of the problem are illustrated by the Large-Aperture krypton-fluoride laser amplifier Module (LAM) shown schematically in Figure 1. This device, now operating at the Los Alamos National Laboratory, is typical of current and planned large excimer lasers for fusion applications. The LAM has an active volume of some 2 m3, and optical surfaces (resonator mirror and windows) exceeding 1 m2 in size; the fabrication of these optical elements was the most expensive and time-consuming single item in the construction of the laser. During laser operation, a population inversion in an Ar-Kr-F2 mix ture is created through electron-beam excitation of the laser gas by two 400 kA beams of 650 keV electrons from a cold cathode discharge. The electron trajectories in the gas are constrained by a 4 kG magnetic field transverse to the optical axis produced by a pair of large Helmholtzcoils.

The Center for Laser Studies (CLS) is a research organization within the School of Engineering at the University of Southern California. Since its founding in 1973, CLS has grown to about a dozen full-time research scientists working with about 35 graduate students on projects funded by a wide range of government and industrial agencies. Because studies of and research with lasers are frequently interdisciplinary ventures, close ties are maintained with academic departments within the University such as Electrical Engineering, Physics, Materials Science, Chemistry, Mechanical Engineering and Chemical Engineering. The need to cross traditional university department lines was one of the reasons for establishing CLS. The CLS researchers share an extensive equipment and knowledge base, which also serves as a resource facility for cooperative research with industry. This approach has led to over 200 publications in major journals and has given the Center national prominence.

Six faculty members conduct a majority of their research at CLS and an approximately equal number have experiments in residence. Examples of some of the current research projects of the primary faculty are given below:

1. Professor Elsa Garmire, Director, is studying nonlinear optical devices in a variety of materials with particular emphasis on using semiconductor nonlinearities in optically bistable devices and in optical phase conjugation. This group first demonstrated mid-infrared bistability in In As with a 3 mW threshold, the lowest threshold for any bistability reported at that time. Optical bistability occurs when a semiconductor etalon is illuminated near its bandgap. The nonlinear refractive index combined with reflection feedback causes the transmission or reflection to have two stable outputs at a single value of the input, depending on the device irradiation history. Typical results are shown in Figure 1. Currently under investigation is optical phase conjugation by means of degenerate four wave mixing with two wave mixing recently observed in Cr-doped GaAs.