Diffractive phase elements

Micro- and nanostructuring of surfaces with UV-emitting excimer lasers is especially useful for fast and cost-efficient production of diffractive optical components. Examples are gratings, spot-array generators, beam-shapers etc. To realize a particular optical function, a diffractive structure has to be patterned on some substrate surface. Substrate materials for diffractive components working in transmission geometry can be all those materials which are absorbing at UV wavelengths yet transparent at the operation wavelengths. Examples are many plastics and optical glasses. By using an F2-laser emitting at 157 nm in the vacuum-UV region it is possible to pattern diffractive structures into fused silica – a material that is transparent from the deep UV to the near IR. Diffractive components working in reflection can be fabricated as well. Metals, whose micro- or nanostructuring with nanosecond laser pulses is problematical because of thermal effects, can be patterned with UV-emitting picosecond or femtosecond lasers.

Sinusoidal relief grating on fused silica with 400 nm period	Grating on fused silica with rectangular profile, 2 µm period

Typically, the production of diffractive optics works with mask projection techniques. A suitable mask placed in the laser beam is projected on the surface to be patterned at a specified demagnification. The form of the mask, energy density and total energy accumulated during exposure determine the ablation profile. Large-area structures can be made by moving the work piece with the help of motorized precision stages.

Diffractive optical elements made from sapphire

Further information:

J.-H. Klein-Wiele, J. Békési, P. Simon, J. Ihlemann
Fabrication of SiO2 phase gratings by UV laser patterning of silicon suboxide layers and subsequent oxidation
Journal of Laser Micro/Nanoengineering 1, 221 (2006)

J. Ihlemann, R. Weichenhain-Schriever
Laser Based Rapid Fabrication of SiO2-phase Masks for Efficient UV-laser Micromachining
Journal of Laser Micro/Nanoengineering 4, 100 (2009)