R. C. Williams

OPTICAL MASERS (LASERS).

The possibility of constructing an oscillator using Microwave Amplification by means of Stimulated Emission of Radiation MASER was discussed at a symposium at the University of Illinois in May 1951 by A. H. Nethercot, a colleague of C. H. Townes of Columbia University. A year later, independently and almost simultaneously, J. Weber of the University of Maryland and N. G. Basov and A. M. Prokhorov of the Lebedev Institute discussed the basic ideas and theoretical possibilities of making a molecular generator ( 1 ) . The first molecular oscillator was reported by Townes and his colleagues of Columbia University in 1954 (2). Further contributions by Schawlow and Townes (3), demonstrated the feasibility of extending the maser principle to shorter wavelengths by using solid state devices; Maiman (4) achieved a notable technological wbreak through<< in 1960 when he succeeded in producing stimulated optical emission in a ruby crystal. This stimulated radiation in the visible region of the electromagnetic spectrum (694.3 mp) suggested the acronym LASER (L for light) as an alsternate for the nomenclature, optical maser, suggested by Townes. Rapid advances in the applications of lasers to military problems, communicattions, medicine, and basic research ( 5 ) have resulted in a need to investigate the biological effects of intense beams of photons, especially the ocular hazards associated with the widespread use of laser sources in laboratories throughout the world. Solon (6), (7) and Zaret (8), (9) have published

The Effect of Threshold Macular Lesions and Subthreshold Macular Exposures on Visual Acuity in the Rhesus Monkey

The purpose of this research program was to evaluate retinal threshold burns and subthreshold exposures of the mammalian macula in terms of visual acuity. Rhesus monkeys {Macaca mulatto) were trained by a reward system to respond to the automated presentation of Landolt rings. After appropriate training, these animals were exposed to threshold and subthreshold levels of retinal energy density ranging from 3.2 to 10.7 J/cm2, exposure time approximately 135 ms. spectral quality approximately that of color temperature 6000° K with wavelengths above 900 nm removed,, and image sizes on the retina of about 1 mm in diameter, covering a major portion of the monkey macular area. Results, in terms of visual acuity decrement (monocular), indicated that energy densities on the retina below 5 J/cm2 were not statistically significant, whereas energy densities greater than 5 J/cm2 produced losses in visual acuity (monocular) which were significant. These results indicate that, at levels of energy density on the retina w...

Effects of acute and protracted ionizing radiation on the rabbit lens.

With the advancement of manned space exploration, potentially hazardous exposure levels to ionizing radiation deriving from the continuous fields of the van Allen belt to less predictable exposures from solar flares have been of concern. While the former can be avoided to some degree by selected orbital flight patterns, solar flares may present some problems. Since the eye is a superficially located organ and its lens is a relatively sensitive biological structure, responding to ionizing radiation with characteristic changes easily observable under in vivo biomicroscopy, it lends itself particularly well to studying effects of selected dose and energy levels. T o accomplish this goal, the following investigations were conducted:

LASER RADIATION PROTECTION

Abstract Although most health physicists and others in the field of radiation protection have confined their efforts primarily to the hazards from the so-called ionizing radiations (X-rays, gamma-rays, neutrons, high energy particles, etc.), an increasing number of workers in this field are being called upon to protect personnel from laser radiation. The phenomenal development of laser technology during the past three years has introduced new hazards for industry, for governmental agencies, particularly the military and space agencies, and for universities and medical schools. The necessity for such criteria will be examined. Since the eye is the most vulnerable organ of man to laser radiation, the effects of wavelength, pulse duration, intensity of irradiation (power density), energy density, and other factors on the eye will be given. Current data from several laboratories will be reviewed briefly. Finally, protective practices and equipment in current use in the United States will be discussed.