A Dichroic Beamsplitter for the Laser Protection of Infrared Detectors

The design and fabrication approach of a dichroic beamsplitter to meet the protection requirements of infrared detectors for blinding laser weapons is presented. The dichroic beamsplitter must protect against 1064 and 532 nm lasers and have high transmittance in the detection beam band of 3.6–4.7 µm. In order to realize the protection and antireflection (AR) functions of the dichroic beamsplitter, Ta2O5, which has a wide band gap and high thermodynamic stability, was selected as the high-refractive-index material. A multilayer stack was deposited on a silicon substrate by ion-assisted electron beam evaporation. The manufactured dichroic beamsplitter features a high laser-induced damage threshold (LIDT), excellent spectral characteristics in the requested spectral region, and good environmental stability.