Self-pulsed Tm:GdScO3 laser amplifier for near-diffraction-limited nanosecond pulse generation

Achieving high-peak-power, narrow pulse width 2 μm lasers with near-diffraction-limited beam quality is critical for precision micromachining, minimally invasive surgery, and sensitive gas sensing, as this wavelength coincides with a strong water absorption peak. Conventional master oscillator power amplifier (MOPA) systems exhibit inherent limitations in compactness and complexity due to their reliance on external active modulators and associated driving electronics. In this work, we demonstrate a simplified MOPA architecture centered on a self-pulsed thulium-doped oscillator. By leveraging intrinsic dynamic loss mechanisms, this oscillator directly generated high-quality nanosecond pulse trains without external modulators, thereby eliminating the primary source of system bulk, cost, and complexity. In experiments, the self-pulsed oscillator achieved a minimum pulse duration of 348.2 ns and a beam quality factor M2 < 1.1. After single-pass amplification using a 3 mm gain crystal, the pulse peak power reached 55.7 W while maintaining near-diffraction-limited beam quality. This work establishes a self-modulation-based pathway for high-performance miniaturized pulsed lasers, while guiding the development of monolithically integrated chip-scale sources.