Processing parameters optimization for thermochemical writing of DOEs on chromium films

Computer-generated holograms are limited by conventional lithographic fabrication capabilities which rely on accurate deposition, exposure, and developing of photosensitive chemicals. We present an alternate fabrication technology that uses a focused laser beam to write patterns by inducing a thermochemical change in a bare metal film. The patterns are developed using a single etching step that dissolves the non-exposed metal. The thermochemical writing method allows holograms to be directly written onto large-diameter, thick, and non-flat substrates, requiring no intermediate steps that compromise the ultimate accuracy. Circular patterns for optical testing were written using a polar-coordinate laser writer. The laser power and control requirements are shown to be modest and the etching is shown to be tolerant of temperature and concentration variations. The technology is demonstrated with the fabrication of CGH's up to 136 mm in diameter used for optical testing.