Transformation of gaussian to coherent uniform beams by inverse-gaussian transmittive filters

Several plano-convex aluminum thin films, ~30 nm thick in the center and ~2 mm in diameter, were deposited on microscope cover slides to function as inverse-Gaussian transmittive filters. By placing one of these filters in front of the Gaussian He-Ne laser, we can modify the beam intensity profile in the downstream direction. To yield a uniform beam, the position of the filter must be aligned in the transverse plane for maximum intensity at the output of the filter. These filters are easy to fabricate and are inexpensive. Most important, they can help produce collimated phase-coherent uniform beams, which are useful in high-precision fringe-analysis techniques.