Ambient‐Air, Room‐Temperature High‐Energy Thulium‐Doped Regenerative Amplifier

ABSTRACT High‐energy, high‐peak‐power 2 µm femtosecond pulses are essential for multiple applications in atmospheric sensing, material processing, and strong‐field physics. Tm:YAP offers a broader gain bandwidth than holmium‐doped media, enabling superior 2 µm femtosecond pulse generation. However, the central wavelength of conventional c‐cut Tm:YAP regenerative amplifiers operate at a central wavelength of 1.94 µm, where strong water‐vapor absorption occurs, necessitating nitrogen‐purged and low‐temperature environments to achieve high‐energy femtosecond pulses. Here, we demonstrate an ambient‐air, room‐temperature thulium‐doped regenerative amplifier that delivers high‐energy, high‐peak‐power 2 µm femtosecond pulses. This breakthrough is achieved by strategically shifting the emission peak to 1.98 µm, where water‐vapor absorption is significantly weaker, using an a‐cut Tm:YAP crystal, while mitigating thermal loading and enhancing the damage threshold through an optimized crystal design. The system delivers 2.6 mJ pulse energy at a 1 kHz repetition rate with excellent stability (1.58% RMS) and high beam quality ( M 2 < 1.1). In addition, it provides a spectral bandwidth exceeding 19 nm and a compressed pulse duration of 431 fs, yielding a peak power approaching 4.8 GW. These results represent the highest pulse energy and peak power achieved in thulium‐doped regenerative amplifiers, establishing an efficient, compact, and low‐cost approach for generating high‐energy, high‐peak‐power, broadband 2 µm femtosecond pulses.