Small-angle diffusing screens for photolithographic camera illumination systems

A method is described for producing transmitting screens that diffuse light into small angles. With these screens, the amount of small-angle diffusion can be controlled while light loss from large-angle scattering is kept to a minimum. The diffusers are fabricated from two glass substrates that are ground, etched, and cemented together. There is a controlled mismatch between the optical index of the cement and that of the substrates. The screens were primarily designed for photolithographic camera illumination systems that involve a tradeoff between luminance and uniformity.