High-performance anti-reflective subwavelength structures on diamond fabricated by double-pulse sequence Bessel beam

Abstract The optical loss in diamond infrared windows arises from the high refractive index of diamond and Fresnel reflection at the air-diamond interface. Drawing inspiration from the anti-reflective properties of moth eyes, this study investigates the anti-reflective subwavelength structures (ASS) on the diamond surface through numerical simulations and experiments, aiming to achieve broadband high transmittance in the long-wave infrared range. The geometrical parameters, including period, depth, and filling factor, of the ASS are optimized using the finite difference time domain method, effective medium theory, and thin-film theory. A three-dimensional femtosecond laser back-processing technique, exploiting double-pulse sequence Bessel beam, is employed to examine the effects of various laser and process parameters on the morphologies, enabling the fabrication of ASS square frustum arrays. The resulting structures achieve a maximum transmittance of 96.4% at a wavelength of 11.1 μ m, demonstrating significant potential for application in extreme environments.