Development of an anti-reflection coating for optical windows in multimode electro-optical detection systems

As a critical component of integrated optoelectronic detection systems, multispectral ZnS windows enable multiband, common-path optical configurations. In this study, a broadband anti-reflection coating was designed and fabricated on multispectral ZnS substrates for multimodal detection applications covering the visible spectrum, the 905 nm laser band, and the long-wave infrared (LWIR) region. The residual stress, deposition process, coating design, and error sources of single-layer YbF₃ films were systematically investigated. By examining the effects of ion-source parameters on the stress of YbF₃ films, the optimal deposition conditions were determined to be a bias voltage of 150 V and a discharge current of 50 A. Initial experiments showed that the average transmittance in the visible band was only 73.35%. Inverse analysis indicated that this deviation was mainly caused by a systematic error in the tooling factor. After correcting the tooling-factor deviation and implementing an optimized monitoring strategy based on inverse spectral analysis, the layer-thickness error was effectively reduced, enabling precise control of highly thickness-sensitive layers. Normalized-coordinate analysis further revealed pronounced wavelength-dependent differences in spectral sensitivity between the visible and infrared regions. Therefore, a targeted single-band optimization strategy, combined with segmented monitoring of highly sensitive layers, was adopted to compensate for spectral shifts induced by cumulative thickness errors during multilayer deposition. The measured results show that, within an incidence-angle range of 0-15°, the average transmittance reached 93.57% at 450-1000 nm and 92.91% at 8000-12000 nm, satisfying the required performance specifications.