The principle radiation damage effects occurring in optical materials, particularly those produced by energetic particles and gamma rays, are described phenomenologically. Included is a description of the basic processes whereby radiation interacts with non-metals. Emphasized are: 1) ionization induced electron and hole formation and migration processes and, 2) the displacement and ionization damage effects that are responsible for atoms being displaced from their normal lattice positions. In nonmetals, the principal radiation damage effect produced by these processes is the creation of color centers. In turn, it is shown that the radiation induced color center formation, as well as the changes that occurs after an irradiation is terminated, are described by a particularly simple theory. Radiation damage in transparent crystals and glasses is illustrated by measurements made with unique equipment fn making optical measurements during and after irradiation. One arrangement utilizes a 60 Co gamma-ray source and the other a 3.0 MeV electron accelerator. The illustrations include: 1) Measurements on F-center formation during irradiation--and the changes that occur after irradiation--on LiF, NaC1, and KC1 synthetic crystals. 2) Studies on the radiation induced F-center and Na metal colloid formation occurring in natural rock salt (NaCl) from potential radioactive waste repository sites. 3) The growth during irradiation and decay after irradiation of color centers in glasses irradiated at different temperatures. Lastly, the radioluminescence emitted during irradiation, as well as the absorption spectrum changes and the thermoluminescence emission that is observed when irradiated samples are heated, is illustrated by studies on natural quartz.
The nature of defects in transparent crystals is reviewed from the perspective of general measures that can be taken to minimize the effects of radiation damage in a particular spectral or temporal range. The data reproduced here emphasize transient optical absorption associated with ionizing radiation pulses. Photochemical generation of lattice damage by ionizing radiation is described, with particular attention to a new mechanism which seems to provide the first satisfactory accounting of intrinsic vacancy-interstitial pair creation at both high and low temperature in alkali halides and, by inference, in alkaline-earth fluorides.
The natures of radiation-induced defects and defect generation processes in optical glasses are critically reviewed. Materials of interest here include silica, silicates, and fluorides, hence encompassing glasses now in use or contemplated for fiber optics, lenses, mirrors, windows, and other optical applications. The most extensive discussions are devoted to pure fused silica because of its wide application and extensive literature and its value as a simple prototype for beginning to understand more complex systems. Emphasis is placed on the atomic scale structure of point defects, as gleaned mainly from the technique of electron spin resonance, although such important properties as optical absorption, luminescence, and volume change are also discussed.
Persistent spectral hole-burning (PHB) is a photoinduced process in low temperature solids that may lead to a possible future application, frequency domain optical storage. The feasibility of such a data storage device depends critically upon having recording materials that undergo spectral hole-burning with certain well-defined characteristics. It is a stimulating challenge for the laser spectroscopist, photochemist, and physicist to find suitable materials and to devise detection techniques that make this application possible.
The optical properties of fiber waveguides can be degraded by exposure to nuclear radiation, primarily through the generation of color centers in the fiber core. This paper will review recent studies of the radiation-induced absorption in state-of-the-art fiber optics. Particular emphasis is placed on the development of more radiation resistant pure and doped silica core waveguides and on the understanding of the damage processes in these materials. The results of studies of radiation damage in high birefringent, polarization-maintaining fibers and in heavy metal fluoride glasses and fibers will also be reviewed.
Fiber optics have been utilized in a variety of sensor and data transmission roles, some of which are complicated by the presence of ionizing radiation. In this paper, transient radiation effects in fibers are reviewed. The paper by E. J. Friebelel (in this same Conference) concentrates on longer term radiation effects, but includes selected transient effects data as well. Several literature reviews and conferences have covered related topics.2-5
A review of the behavior of state-of-the-art optical fiber waveguides in high dose (≥ 105 rad), steady state radiation fields is presented. The influence on radiation-induced transmission loss due to experimental parameters such as dose rate, total dose, irradiation history, temperature, wavelength, and light intensity, and material parameters such as dopant type, concentration, and OH content is described. Recommendations for future work in high dose environments are given.
Bulk laser-induced damage to optical materials is reviewed. Recent evidence indicates that laser-induced breakdown (LIB) of very transparent optical materials is due to extrinsic factors (e.g., defects and impurities). The role of self-focusing in LIB is reviewed and the results of recent studies are presented.
A summary is given of the principal aspects of laser-induced damage to polished optical surfaces and dielectric, thin-film, high-reflectivity and antireflective coatings. Methods for producing porous, antireflective surfaces and coatings and their damage properties are also reviewed. Finally, new areas of basic research to solve current and future problems are addressed.
The rapidly expanding field of optoelectronics includes a wide variety of both military and non-military applications in which the systems must meet radiation exposure requirements. Herein, we review the work on radiation effects on sources and detectors for such optoelectronic systems. For sources the principal problem is permanent damage-induced light output degradation, while for detectors it is ionizing radiation-induced photocurrents.
The present knowledge of radiation damage effects in spacecraft solar cells is reviewed. The photovoltaic effect and the effects of particle radiation on photovoltaic materials and devices is described for the more useful semiconductors, viz. silicon and gallium arsenide. The improvements in silicon solar cells since their development in 1954 have resulted in steady improvements in photovoltaic conversion efficiency, voltage, current density, and radiation hardness, and an increasing compendium of solar cell performance as a function of environmental factors such as temperature, light intensity, and radiation fields has been developed. However, as new technology constantly develops, there is a continuing need to study radiation effects in new solar cell structures and to attempt to understand fully the basic mechanisms of radiation interactions at the atomic level in order to explain their effects on solar cell performance at the macroscpoic level.
A review is given of the effect of the space environment on the external surfaces of satellites. The early development of thermal control materials in the 1960's and the 1970's is summarized. Selected recent results, based on flight experiments from the SCATHA satellite (P78-2) of the Space Test Program and the Space Shuttle, are reviewed along with Laboratory experiments designed to understand the often unexpected results of the flight experiments. The topics include long-term stability of thermal control materials, contamination, spacecraft charging, and the effect of oxygen atoms on materials. Several areas of future research are proposed.