Efficient diffractive optical elements from glass with continuous surface profiles

Abstract

Diffractive optical elements (DOE) play an important role for laser beam shaping in industry, for example in lithography or parallel laser material processing. Typically such applications require high damage threshold and low background illumination (high contrast and efficiency). Usual DOE with binary phase (step-like) profiles are made microlithographically and suffer from substantial scattering on profile derivative discontinuities. That gives also tendency to lower damage threshold as compared to intrinsic material values. The LIMO approach is based contrarily on a proprietary, non etching material processing and is suitable for manufacturing of high-precision free programmable continuous surface profiles in optical glasses and crystals. We report on linear symmetric diffractive beam splitter 1:11 with high homogeneity and efficiency > 95% and discuss also other DOE designs. The design data, simulations with measured surface profiles and experimental intensity distributions are in very good agreement. Furthermore we report on a new type of optical attenuator composed from two DOE gratings. Its dynamic transmission range is 0.3% to 98%. The required lateral DOE shift is only 5 - 10 μm in the present design, so that the device can be very fast and applicable for dynamic intensity stabilization.