Adaptive shaping of a focused intense laser beam into a doughnut mode

We present a method to shape the intensity distribution of an intense laser beam in the focal region, by means of a bimorph adaptive mirror. We emphasize the advantages in terms of flexibility with respect of previous methods making use of specially designed retarding phase plates; however, the nature of the mirror imposes constraints on the accessible wavefronts, whose consequences are analyzed. We present an experimental demonstration of the feasibility of the scheme on a high intensity femtosecond laser system.