Multi beam laser target illumination

In order to compress matter to high densities by the application of intense pulses of laser energy it is necessary for the implosion of the target to be both stable and spherical. This imposes certain constraints on the uniformity of illumination of the target, and, this in turn places requirements on the illuminating optics and the laser beam quality. This report discusses the uniformity of illumination of a spherical target as provided by a variety of optical systems and for different numbers of laser beams and beam profiles. The results are compared with similar conclusions obtained by other workers. An alternative presentation of the calculations is given which is believed to be a more realistic estimate of the uniformity. Comments are made on the approximations that have been assumed and the results likely to be obtained from the full treatment are discussed. The effects of this non-uniform illumination on the target implosion are considered using the linear theory of the Rayleigh-Taylor instability. Finally, comments are made on other factors of a more practical nature which also govern the final choice of illumination system and the scope of experiments made possible by such a system. (author)