Enhanced saturable absorption of SFX-2,7-DDPA organic semiconductor in a passively <i>Q</i> -switched Tm:YAP laser

In this work, a saturable absorber (SA) was fabricated using the organic semiconductor material SFX-2,7-DDPA via spin-coating. Comprehensive microstructural analysis and optical characterization were conducted to evaluate both linear and nonlinear absorption properties. The SFX-2,7-DDPA SA exhibited outstanding saturable absorption behavior, with a measured modulation depth of 8.4%. Subsequently, the SA was successfully implemented as a modulator to realize a passively Q -switched (PQS) Tm:YAP laser. Under PQS operation, the laser achieved an average output power of 540 mW with a slope efficiency of 7.1%, emitting at a central wavelength of 1931.21 nm. The system generated stable pulses with durations below 315 ns at a repetition rate of 100.4 kHz, yielding single-pulse energies up to 5.38 µJ and peak powers reaching 17.1 W. High beam quality was confirmed by M 2 values of 1.11 and 1.06 along orthogonal axes, indicating near-diffraction-limited performance. This study presents a novel application of organic semiconductors as efficient modulators in 2-µm laser systems.