Synergistic Integration of Disordered Tm:CaGdAlO₄ Single-Crystal Fibers with Oxidation-Resistant MXene for High-Performance 2 µm Lasers

Abstract

Mid-infrared lasers operating at ~2 µm are critical for photonic applications including precision sensing, machining, and biomedicine. Herein, we report the first integration of disordered Tm³⁺-doped CaGdAlO₄ (Tm:CGA) single crystal fibers (SCFs) with oxidation-resistant MXene (OR-Ti₃C₂Tₓ) saturable absorbers (SAs) for high-performance 2 µm lasers. The Tm:CGA SCFs feature a broad absorption bandwidth (FWHM: 19.4 nm at 793 nm) and low phonon energy (614 cm⁻¹), enabling efficient thermal management and high quantum efficiency. The OR-Ti₃C₂Tₓ SA exhibits strong nonlinear saturable absorption (modulation depth: 7.93%, saturation intensity: 7.32×10⁻⁵ GW•cm⁻²) and broadband transparency (0.4-6 µm). In a straight cavity, the hybrid system delivers a continuous-wave output of 3.338 W at 1982.8 nm with a slope efficiency of 27.3%. For passive Q-switching, it generates pulsed emission at 1978.5 nm with a peak power of 32.13 W and single-pulse energy of 15.74 µJ. This work highlights the synergistic combination of a spectrally broadened gain medium and a robust 2D nanomaterial saturable absorber, providing a scalable platform for next-generation mid-infrared photonic devices.