Excimer laser fabrication of diffractive optical elements

Abstract

Excimer lasers are well known for their ability to machine features on the micron scale. Recently, they have been used to fabricate diffractive optical elements (DOEs). These elements are patterns of pixels machined to the depth required, in order that a reconstructed pattern is formed in the image plane when the DOE is illuminated by a coherent source. The patterns are designed using computer phase retrieval code. These designs are used to create XY co-ordinate data files for conversion to machining routines where the pixels are machined individually. The laser used is an ArF excimer operating at 193 nm. We describe research undertaken on the fabrication and testing of some typical DOEs. The measurements include efficiency of reconstruction as well as the measurements of profile and surface roughness. The work compares the reconstruction results with the topographical measurements made on the DOE for 2, 4 and 8 phase-level designs. Newly developed simulation code was used to generate reconstructions without machining imperfections.