Thermodynamic Optimization of Atomically Thin Iron-Based Compounds for Mid-Infrared Laser Power Scaling

Mid-infrared pulsed lasers are pivotal for biomedical engineering and atmospheric remote sensing, yet power scaling is severely bottlenecked by poor thermal stability and low damage thresholds of conventional saturable absorbers. Here, we address this limitation through a thermodynamic optimization strategy applied to atomically thin iron-based crystals grown by space-confined chemical vapor deposition. Screening anionic chalcogens (Se, S, and O) paired with Fe identifies iron oxide as the most stable matrix, while Mn doping further stabilizes the matrix and modulates carrier dynamics. Mn incorporation enhances the laser-induced damage threshold approximately 3-fold and accelerates carrier relaxation to 23.63 ps. Consequently, a record-high average output power exceeding 1.0 W was achieved in an Er3+-doped fiber laser at 2.8 μm, accompanied by nanosecond pulse compression and operation stability over 30 days. Our findings establish lattice thermodynamics as a material route to high-energy mid-infrared pulsed lasers and highlight its potential for on-chip long-wave terahertz photonic devices.