F2-laser microfabrication of multilevel diffractive optical elements

The 157nm F₂-laser drives strong and precisely controllable interactions with fused silica, the most widely used material for bulk optics, optical fibers, and planar optical circuits. A diffractive optical element (DOE) breaks apart wavefronts and redirects segmented beamlets through phase control for novel beam steering and shaping applications. This paper shows that precise excisions of 10-30 nm depth are available from the F₂ laser for the generation of efficient DOEs for the visible and ultraviolet spectrum. F₂-laser radiation was applied with beam homogenization optics and high-precision computer-controlled motion stages to shape up to 16-level, 256 × 256 pixel DOE devices on bulk glasses, with distinguishable level-tolevel spacing of ∼100 nm and surface roughness of ∼13 nm. The 1st order diffraction efficiency was ∼35%. The farfield pattern when illuminated with a HeNe laser was found to agree with simulations based on an iterative Fourier transform algorithm. Future improvements in the laser micromachining process and possible directions are also offered.