Many years spent in an industrial engineering laboratory have convinced me that there is ever-increasing need to present recent and current research in forms which can be easily assimilated by engineers, technical managers, and others concerned with applications and the development of new technology. There is a forbidding gap between the typical research paper, addressed by specialists to other specialists, and the popular-level account addressed to the layman. The second does not adequately prepare the engi­ neer for profitably studying the first; it does not impart sufficient depth of understanding to the manager who must make decisions on the relative merits of various approaches to a problem or on the potential contributions various specialists might make to his program. This book is the outgrowth of a review prepared to fill this need for engineers in a large corporation who were concerned with the industrial application of lasers. That review was written hurriedly, on a fixed budget, to a deadline; consequently, it contained oversimplifications and errors, not all of which were trivial. Nevertheless, the favorable response proved that such a review is indeed needed. It is hoped that this more finished work will prove useful to a wide variety of potential users of laser-centered devices and systems, and may even stimulate the generation of useful ideas.