Watt-level 100-fs-class pulses from the first GHz femtosecond Tm-based bulk laser oscillator

We report, to the best of our knowledge, the first fundamentally GHz femtosecond Tm-based bulk laser oscillator. The compact 1.006-GHz Kerr-lens mode-locked Tm:KYW resonator combines direct multimode in-band diode pumping with dry-air operation. The oscillator demonstrates the highest reported combination of short pulse duration and peak power among GHz Tm-based oscillators and, more broadly, among directly diode-pumped GHz bulk oscillators operating near 2 µm. In a power-optimized configuration, it delivers 134-fs pulses at 1.35 W of average output power, corresponding to 9 kW of peak power and 38% optical-to-optical efficiency with respect to absorbed pump power. In a second configuration optimized for pulse shortening, it generates 100-fs pulses at 0.90 W, corresponding to approximately 8 kW of peak power and 31% efficiency. These results establish the first watt-level, 100-fs-class performance from a GHz Tm-based oscillator, with up to a fourfold reduction in pulse duration and approximately an order-of-magnitude increase in peak power relative to previous GHz Tm oscillator benchmarks. More broadly, the demonstrated performance represents a major advance in compact, directly diode-pumped GHz ultrafast oscillators near 2 µm, substantially narrowing the performance gap with systems relying on specialized high-brightness and comparatively expensive pump lasers. The high-performance output achieved with a compact GHz design and multi-mode diode pumping makes this source a highly practical platform for compact, cost-effective, and power-scalable GHz 2-µm frequency-comb systems.