Broadband antireflective subwavelength structures for infrared detection

Enhancing infrared window transmittance of zinc sulfide (ZnS) is an effective way to improve the infrared detection imaging quality. In this study, the antireflective subwavelength structure (ASS) is designed and fabricated on ZnS substrate, aiming to suppress surface Fresnel reflection and achieve high transmittance within the far-infrared band. The structure parameters of ASS such as height, period, and fill factor are initially set based on the effective medium approximation theory, and are optimized via the rigorous coupled-wave analysis (RCWA) method. Moreover, the antireflective ASS mechanism is explored by using the local light field selective enhancements in structures for capturing incident photons. In addition, a femtosecond laser Bessel beam is used to experimentally fabricate the designed ASS on the ZnS substrate for obtaining large array height, resulting in transmittance enhancement in the far-infrared region. Ultimately, the broadband and wide-angle ASS with the anti-laser damage properties and hydrophobicity is achieved on the optical window. Hence, the clarity of the infrared image captured by the infrared detection system is improved.