Microrelief diffraction structure recording in LC reactive mesogen

Abstract

Reactive liquid crystal (LC) mesogen (trade mark C6M of Merck) is shown to possess efficient relief formation properties. Photosensitive formulation was made by mixing of the reactive LC mesogen C6M with 2% of photoinitiator (Irgacure 651). Photosensitive layer (thickness 70 micrometers ) was obtained by melting the formulation in the gap between two glass substrates. One of the substrates contained a photosensitive silver-halide layer, in which the amplitude mask was recorded with the resolution Fequals40 lines/mm. The amplitude function of the mask represented a phase function of the desired CO<SUB>2</SUB> laser focusing element, designed for wavelength 10.6 micrometers and 45 degrees incidence . Exposure of the reactive mesogen layer through the mask was carried out at elevated temperature of Tequals85 degrees C by UV source (wavelength 365 nm). Immediately after exposure a substrate with photomask was removed and the relief structure in the exposed layer was measured to be ca. hequals1 micrometers deep. After that a dark self-development was allowed resulting in the increase of relief depth h up to 15 micrometers within several hours. The desired hequals7.5 micrometers needed for the most efficient performance of CO<SUB>2</SUB> laser focusing element at 10.6 micrometers and 45 degrees incidence, was stabilized by interrupting self-development with uniform UV exposure of the recorded structure.