Enhanced Laser Damage Threshold in Optically Addressable Light Valves via Aluminum Nitride Photoconductors

Abstract

Optically addressable light valves (OALVs) are specialized optical components utilized for spatial beam shaping in various laser-based applications, including optics damage mitigation, and enhanced functionality in diode-based additive manufacturing requiring high intensities. Current state-of-the-art OALVs employ photoconductors such as Bismuth Silicon Oxide (BSO) or Bismuth Germanium Oxide (BGO), which suffer from limited laser-induced damage thresholds (LiDT) and inadequate thermal conductivities, thus restricting their use in high peak and average power applications. Aluminum nitride (AlN), an emerging ultra-wide band gap (UWBG) III–V semiconductor, offers promising optoelectronic properties and superior thermal conductivity (>300 Wm⁻¹K⁻¹ at 298° K, compared to BSO's 3.29 Wm⁻¹K⁻¹). In this study, the first AlN-based OALVs are designed, fabricated, and experimentally demonstrated using commercially available single-crystal AlN substrates. These AlN-based OALVs have shown clear superiority over BSO and BGO-based devices. Design considerations for OALVs incorporating UWBG photoconductors are discussed, and the photoresponsivity from defect-mediated sub-bandgap absorption in AlN crystals is verified as sufficient for OALVs operating under high light fluences. The optimum driving voltage for the AlN-based OALV is determined to be ≈ 45 V_pp at 100 Hz, achieving a transmittance of 91.3%, an extinction ratio (ER) of more than 100, and a 51:1 image contrast.