Abstract

The output profile of the most of the conventional laser resonators is gaussian in natur e. In the recent past, a number of beam shaping techniques has been reported for converting the gaussian profile to any profile useful for some specific applications. The simplest technique for getting a uniform flat-top profile is to truncate the beam by an aperture. A neutral density filter having suitable transmittance profile may also be used for the same purpose. A laser beam with flat-top profile has many applications in optical processing, laser micro -fabrication and laser surgery. Unfortunately, most of these techniques suffer from a serious limitation of having very low energy efficiency. Binary diffraction gratings may also be used to get a desired beam profile. However, this technique is also associated with limited diffraction efficiency. Aspheric reflective mirrors or aspheric lenses redistributes energy of a gaussian beam and are highl y energy efficient. But the fabrication of these elements is very difficult and related applications are limited to only circular beam shaping geometry. A phase -only filter in this respect seems to be highly effective since its theoretical energy efficienc y may approach 100%. The present communication reports our study on the design of a phase -only laser beam shaper. Such filters when placed at the fractional Fourier transform plane of a two lens Fourier transform setup, produces a new profile at the Fourie r transform plane.

© 2003 Optical Society of America