We propose a B-integral management strategy for manipulating the nonlinear effects by employing a discrete single-crystal fiber (SCF) configuration, enabling direct amplification of 2-μm femtosecond pulses at high repetition rates without additional pulse picking, stretching and compression. The system delivers an average power of more than 56 W at 75.45 MHz with extremely high extraction efficiency (>55%) and near-diffraction-limited beam quality (M2 < 1.2). The dynamic evolution of the optical spectra and temporal properties in the power amplifier reveals that detrimental nonlinear effects are largely suppressed due to the low accumulated nonlinear phase shift in the discrete SCF layout. This straightforward, compact and relatively simple approach is expected to open a new route to the amplification of 2-μm ultrashort pulses at MHz and kHz repetition rates to achieve high average/peak powers, thereby offering exciting prospects for applications in modern nonlinear photonics.

We report on a high-efficiency, high-power tandem Ho:YAG single-crystal fiber (SCF) laser in-band pumped by a Tm-doped fiber laser at 1907 nm. In addition to the uniform heat distribution resulting from the large surface-to-volume ratio of this fiber-like thin-crystal rod, the long gain region provided by the tandem layout of two SCFs enables high lasing efficiency and power handling capability. More than 100 W output power is achieved at 2.1 μm, corresponding to a slope efficiency of 70.5% and an optical-to-optical efficiency of 67.6%. To the best of our knowledge, this is the highest output power and efficiency ever reported from SCF lasers in the 2-μm spectral range.

We report on a high-power Ho:YAG single-crystal fiber (SCF) laser inband pumped by a high-brightness Tm-fiber laser at 1908 nm. The Ho:YAG SCF grown by the micro-pulling-down technique exhibits a propagation loss of $0.05\pm 0.005~\text{cm}^{-1}$ at $2.09~\unicode[STIX]{x03BC}\text{m}$. A continuous-wave output power of 35.2 W is achieved with a slope efficiency of 42.7%, which is to the best of our knowledge the highest power ever reported from an SCF-based laser in the 2 $\unicode[STIX]{x03BC}\text{m}$ spectral range.