One of the first applications of lasers was for surgery on the retina of the eye. That, and the evident analogy to the old dreams of powerful heat rays, led many to predict that lasers would quickly be used for all kinds of cutting and welding, including surgical applications. It was soon apparent that laser sur gery could be performed in ways that caused little bleeding. Nevertheless, other surgical applications have been slower to arrive. One difficulty has been the enormous range of possibilities provided by the many different kinds of lasers. Infrared, visible, and ultraviolet light beams each interact very differently with human tissues. Light pulses of enor mously great peak powers became available from lasers, but their effects dif fered in surprising ways from those obtained with continuous beams. That provided both opportunities (i.e., treating or removing a very thin surface layer without affecting the underlying tissue) and problems with undesired side effects. Moreover, techniques were needed to deliver a precisely con trolled amount of energy just where it was desired. Lasers also had to be engineered and manufactured with the desired power levels and a high reliability."