Design and fabrication of composite structures in ZnSe providing broadband mid-infrared anti-reflection.

Abstract A comparative study of anti-reflection microstructures (ARMs) and ARMs with Al 2 O 3 coatings (Al 2 O 3 /ARMs) on zinc selenide (ZnSe) has been carried out. The transmittance and electric field intensities were analyzed and presented using finite-difference time-domain (FDTD) simulations. ARMs were successfully fabricated on ZnSe surfaces by reactive ion etching and an Al 2 O 3 layer was deposited onto the ARMs by an ion beam sputtering method. The theoretical analysis and experimental results showed that the transmittance of Al 2 O 3 /ARMs-treated ZnSe had a close relationship with the thickness of Al 2 O 3 layer and was higher than that of ARMs-treated ZnSe in the 2–5 μm wavelength range, which was due to the fact that the Al 2 O 3 /ARMs had a better graded refractive index profile. The angle-dependent reflectance of ZnSe with Al 2 O 3 /ARMs was lower than that with ARMs. A difference of the spatial distribution of the electric field intensity between ARMs and Al 2 O 3 /ARMs was observed due to the surface Al 2 O 3 coating, which predicted qualitative laser damage thresholds for both structures. The results of this study provide potential applications in high-efficiency IR optoelectronic devices and high power mid-infrared laser systems. Highlights • The transmittance of Al 2 O 3 /ARMs on ZnSe is enhanced by the more graded refractive index profile. • The composite antireflective structures allowed a significant improvement in omni-directional antireflective properties. • A change of the spatial distribution of the electric field intensity between ARMs and Al 2 O 3 /ARMs is observed. [ABSTRACT FROM AUTHOR]