Ho 3+ -doped CALGO crystals for high-power ultrafast 2.1-µm lasers [Invited]

Ho 3+ -doped disordered CaAlGdO 4 (CALGO) crystals have recently emerged as a promising gain material platform for next-generation high-power ultrafast 2.1-µm laser systems. This laser gain material offers a unique combination of high-gain, small quantum defect, inhomogeneously broadened spectra, and good thermal conductivity, enabling ultrashort pulse generation and amplification at high-average power and high pulse energy. Many systems, including mode-locked oscillators and amplifiers with state-of-the-art performance, have been demonstrated in the last few years that promise to meet growing application demands for efficient ultrafast laser technology in this wavelength region. In this review paper, we summarize recent achievements using this gain material both in oscillators and amplifiers and place these results in the state-of-the-art of 2-µm ultrafast laser technology, present detailed spectroscopic characterization of this material, and discuss future perspectives of further performance scaling of Ho:CALGO lasers.