Focal switch of astigmatic Hermite-Gaussian beams

The focal switch of astigmatic Hermite-Gaussian (H-G) beams passing through a system with the aperture and lens separated is studied. Closed-form expressions for the axial irradiance of focused astigmatic H-G beams are derived based on the Collins formula and recurrence relation. The influence of astigmatism on the behavior of the focal switch is stressed. It is found that the astigmatism affects the axial maximum irradiance, relative focal shift and transition height, but does not affect the turning point, where the focal switch can take place. In addition, there exists not only a critical maximum truncation parameter alpha(c,max), but also a critical minimum truncation parameter alpha(c,min), within the region of alpha(c,min), < alpha < alpha(c,max) the focal switch can appear. (C) 2004 Elsevier B.V. All rights reserved.