Abstract

The problem of controlling the parameters of laser radiation becomes particularly topical in view of the widespread use of lasers in medicine and technological processes. In this paper, we present the results of investigations of the possibility to form beams with different orders of super-Gaussian profile at the output of a stable laser cavity with the help of an active mirror. As shown in Ref.[1], in order to get these intensity profiles, it is necessary to construct specially calculated profiles of minor surface. As an example, on Fig.1 curve "A" represents such a surface profile. We tried to reproduce this shape with the help of a deformable bimorph minor (curve "B" on Fig.1). Since this profile was symmetrical, we used a minor with ring control electrodes. Such minor was a circular concave semipassive bimorph one with three electrodes. To minimize the root-mean-square (RMS) error between our profile and the necessary one, we combined the real (measured by interferometer) response functions of our minor with different weights. In practice, this amounts to applying a particular voltage to the electrodes of the deformable minor. As shown in Fig.1 (corresponding to a super-Gaussian of order 8), we were able to reproduce the appropriate minor profiles with a corresponding RMS enor of only 0.03% (curve "B"). Figure 2 compares the corresponding calculated near-field distributions (including saturation and edge diffraction effects) for a 2 m long stable cavity. The nearly identical associated far-fields are depicted on Fig. 3. A comparison with a conventional spherical resonator designed to yield a similar output beam divergence allows us to expect ≈ 30% power increase owing to the higher extraction efficiency of super-Gaussian beam profiles. Similar conclusions have been reached for a super-Gaussian of order 6. These calculations make us believe that our intracavity bimorph deformable mirror with only three control elements is able to reproduce super-Gaussian output radiation of the CW CO₂ laser with a stable cavity. An experiment to verify this is under way.

© 1996 IEEE