Reducing the danger of flare images in laser focusing objectives

In an earlier publication [J. Appl. Phys. 36, 2598 (1965)] attention was drawn to the danger of a flare image, found in or near the material of the objective, causing failure when a pulse of energy is passed through the lens. At the time no details were given of the basic problem of avoiding flare images or designs to achieve this effect as the studies were confidential to a commercial organization. G. & E. Bradley, Ltd., have now authorized publication, and since the subject still attracts some attention, the basic principles are illustrated with a particular design. While antireflection coatings are still advisable, design of a flare-free or flare-reduced objective will reduce the stringent specifications otherwise required, and the effects of coating failures are much reduced.