Combined computer-generated hologram for testing steep aspheric surfaces

A novel type of a combined (or multiplex) computer-generated hologram (CGH) and a method for interferometric testing of steep axially symmetric aspheres is presented. The method is based on a hybrid CGH containing two different diffractive structures. The presented new type of Diffractive Fizeau Null Lens (DFNL) design eliminates the transmitted wavefront distortion (TWD) of the CGH substrate and increases the accuracy of the surface test. The method was approved by testing a spherical reference mirror with an f-number of f/0.65.

Polar coordinate laser pattern generator for fabrication of diffractive optical elements with arbitrary structure

A precision laser pattern generator for writing arbitrary diffractive elements was developed as an alternative to Cartesian coordinate laser/electron-beam writers. This system allows for the fabrication of concentric continuous-relief and arbitrary binary patterns with minimum feature sizes of less than 0.6 microm and position accuracy of 0.1 microm over 300-mm substrates. Two resistless technologies of writing on chromium and on amorphous silicon films were developed and implemented. We investigated limit characteristics by writing special test structures. A 58-mm f/1.1 zone plate written directly is demonstrated at a lambda/50 rms wave-front error corresponding to a 0.06-microm pattern accuracy. Several examples of fabricated diffractive elements are presented.