Abstract

A laser beam illuminating a straightedge at normal incidence produces on an observation screen a bright spot and a luminous line perpendicular to the edge. In the diffraction edge wave context, the bright spot corresponds to the geometrical wave, while the luminous line belongs to the edge wave, and diffraction fringes appear where these two waves overlap. Takenaka and Fukumitsu¹ gave an analytical expression for the diffraction edge wave produced by a Gaussian beam incident on a half-plane. According to these results the edge wave is a cylindrico-Gaussian wave having its origin on the edge of the half-plane. The interesting point is that this edge wave has an intensity proportional to the intensity of the laser beam at the edge location. So, by measuring the intensity of the edge wave produced by a scanning blade it is an easy matter to determine, in real time, the spatial profile of a laser beam. The main advantage of this method is that it does not require any inversion procedure for the knife-edge data as is the case when one monitors the direct beam.² In fact, our light detector is positioned completely outside the direct beam, thus allowing only the edge wave to come in. As far as we know, this new method, based on diffraction, is the first one which allows direct profiling of a micron-sized beam.

© 1985 Optical Society of America