1 Generation of Stochastic Electromagnetic Beams with prescribed Coherence and Polarization Properties by Means of Random Phase Screens and some Uses of Such Beams

Some years ago it was found by computer simulation that partially coherent beams may, in certain situations, behave better on propagation in random media than do coherent beams [1]. The reason for it, illustrated in Fig. 1, is the following: when fully coherent light is scattered, for example by refractive index fluctuations, it will generally produce, in some region of space, strong interference effects, somewhat analogous to speckles. Such effects are detrimental to resolution. An analogous phenomenon takes place when scattering from rough surface is involved. An example is given in Fig. 2. The Fig. 2a shows the image of a page illuminated by a laser beam. Fig. 2b shows the corresponding image when the page is illuminated with a more conventional beam, which has appreciably lower spatial coherence. It is seen that the image quality is much better in the second case. In the first part of our talk we will describe methods for producing stochastic electromagnetic beams with prescribed statistical properties, use in such applications. One such method consists of modulating a polarized coherent beam by a moving phase screen (see, for example Ref. [2]). The principle of the method is illustrated in Fig. 3. Fig. 1. Illustrating the difference in the interaction of fully coherent and partially coherent beams with random media