Foci-multiplexed optical printing of high-transmittance infrared subwavelength-structured surface

The anti-reflective subwavelength structures achieved by converting the abrupt refractive index change at the interface into a gradual variation, have emerged as a viable solution to enhance light transmittance. Nevertheless, to produce these structures on the hard and brittle infrared windows remains a formidable challenge. This paper presents a method for creating micro-nanostructures on the surface of an infrared window using femtosecond laser direct writing technology. By employing a quite simple foci-multiplexed technique during the scanning process, we have achieved double-sided antireflective subwavelength structures on zinc sulfide (ZnS). The light transmittance exceeds 90% within the wavelength range of 7.3-12.1 μm, with a peak transmittance of 96% at 10 μm, about 20% higher than untreated ZnS. The method is highly versatile for a variety of materials, paving the way for practical antireflection in the future.