Tunable and Robust Mid‐Infrared Saturable Absorber Employing Tungsten Doping Cadmium Oxide

Abstract

Mid‐infrared (MIR) pulsed lasers operating at 2–5 µm have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser‐induced damage threshold (800 nm, 134 mJ cm−2) and broadband saturable absorption (2.0–3.9 µm) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)‐doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W‐dopant level. Based on these findings, the robust CdO‐SAs with customizable parameters are realized and Q‐switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 µm. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high‐performance MIR ultrafast lasers.