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.

Random lattices provide a natural framework to study the effect on critical phenomena caused by randomness. We use the histogram Monte Carlo renormalization-group method to study percolation processes on two-dimensional random lattices. We locate the transition thresholds and evaluate the thermal and field scaling powers. Our results show that randomness enhances the occurrence of percolations, and the values of scaling powers indicate that the idea of universality can be extended to two-dimensional random lattices. [S0163-1829(97)05941-9].