Enhancement of Quantum Efficiency and Resolution for an Image Intensifier in the VIS-NIR Band Using a Grating With High Local Electric Field

The near-infrared performance of Gen-II+ image intensifiers is limited by the low resolution and quantum efficiency and of the Na₂KSb photocathodes. Previous studies have demonstrated that diffractive grating can effectively enhance the absorption of photocathodes. However, existing reports have not explicitly addressed the resolution of image intensifiers with a S25 photocathode. This paper presents a novel photocathode design based on a hexagonal nanograting structure to enhance the overall imaging performance of Gen-II+ image intensifiers. Experimental results demonstrate that the grating‑based photocathode increases the quantum efficiency from 15.90% to 22.44% in visible band and from 12.31% to 19.15% in near-infrared band, improves the spatial resolution from 64 lp/mm to 72 lp/mm, and reduces the halo diameter from 0.78 mm to 0.69 mm. The guided‑mode resonance effect induced by the grating enhances the local optical field, leading to higher absorption and quantum efficiency, particularly in the 480-850 nm range. The improved signal‑to‑noise ratio, resulting from the higher quantum efficiency, contributes to better imaging resolution and halo suppression. Discrepancies between simulated and measured results in the 400-480 nm range are attributed to non‑ideal grating morphology and interfacial effects, which more significantly affect short wavelengths. This work provides an effective approach for enhancing the overall performance of image intensifiers and identifies directions for further optimization.