Optical Masers and Their Possible Applications to Biology

Abstract

Optical masers of useful performance will probably be available to a number of research workers in the course of the next one or two years. Their characteristics have already been sufficiently tested to make them predictable with considerable confidence from theoretical expectations. Potential research applications of the coherent form of light produced by optical masers seem interesting enough to warrant pointing out here the characteristics of masers to biologists and biophysicists. An optical maser can either amplify light waves or produce coherent oscillations at optical frequencies by use of stimulated emission from excited atoms or molecules. The process of stimulated emission as a result of interaction between electromagnetic waves and excited atoms is just the reverse of absorption, and dominates when there are more atoms in an excited state than in a lower state to which transitions may occur. If a coliection of suitably excited atoms are placed, for example, between two parallel reflecting plates, a light wave traveling perpendicularly to the plates will be amplified between each successive reflection. If the amplification is greater than the loss on reflection, the light wave will build up into a coherent oscillation, and some of it may be drawn off into a beam if one of the reflecting plates is partially transparent. There are many ways of providing excited atoms, and many different detailed arrangements of the optics involved, which will not be discussed here. Rather, we shall point out briefly the characteristics of the waves produced. The resulting radiation is extremely monochromatic; masers oscillating in the near infrared region at a frequency of about 3 x 1014 cycles per second have been shown to produce radiation with a frequency width, over short times, as small as a few thousand cycles per second. The path length over which such a wave would show interference phenomena is about 100 Km, as compared with a path length of about 1 meter for the most monochromatic light produced by other methods. We may expect from theory that light which is even more monochromatic can be produced by masers. The emitted light is remarkably directional. The wave emitted from the surface of one of the parallel plates may be coherent over the entire surface of the plate. Hence it will be almost a plane parallel wave, and will have as an angle of divergence