The impact which has been made on spectroscopy by lasers, and by this route on major segments of physics and chemistry, has received ample documen tation in the past several years. Two principal themes emerge from examina tion of the numerous books and monographs now available on this subject: first, an increase in spectral resolution to levels previously undreamed of; and, second, the generation of nonlinear phenomena as a result of the intense radiation fields available from laser devices. There is one additional property of laser radiation which, although used extensively in experiments,...