Antireflection coating on organic nonlinear optical crystals using soft materials

Abstract

We have realized practical antireflection (AR) coatings for organic nonlinear optical crystals via dip coating of soft materials; specifically, the amorphous fluoropolymer Cytop. 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystals were coated with a Cytop solution; the coating thickness was controlled by the Cytop solution concentration. The Cytop coating did not show evidence of cracking or peeling after 200 days. The transmittance of AR-coated DAST crystals using a 5% Cytop solution was 90.9% at 1560 nm, an improvement of 17.8% compared to that before coating. High repeatability of the improvement was also confirmed. Moreover, the AR-coated DAST crystal was confirmed to have a stable transmittance over 720 minutes against the irradiation of a femtosecond laser with a power density of 3.6 GW/cm2. The ability to coat organic nonlinear optical crystals with an AR layer using soft materials is expected to have a wide range of optical applications.