Manufacturing of highly-dispersive, high-efficiency transmission gratings by laser interference lithography and dry etching

Abstract

Diffraction efficiency for transmission gratings with period-to-wavelength ratios smaller than 0.6 e.g. for laser pulse compression is mainly limited due to reflection losses from imperfect effective refractive index matching. In our contribution, different approaches for achieving high efficiencies by reducing these losses are discussed based on 1d and 2d rigorous coupled wave analysis. These include multilayers underneath the corrugation, sub-wavelength gratings and optimized non-binary profiles. Experimental results from the manufacturing of 1700 l/mm gratings for 1030 nm center wavelength using two-beam interference lithography and reactive ion beam etching are presented. Diffraction efficiencies of above 96% were achieved, significantly exceeding the theoretical limit for widely used monolithic binary profiles in this application.