Rare-earth ions-doped mid-infrared (2.7-3 μm) bulk lasers: a review [Invited]

Mid-infrared (MIR) laser sources operating in the 2.7-3 mu m spectral region have attracted extensive attention for many applications due to the unique features of locating at the atmospheric transparency window, corresponding to the "characteristic fingerprint" spectra of several gas molecules, and strong absorption of water. Over the past two decades, significant developments have been achieved in 2.7-3 mu m MIR lasers benefiting from the sustainable innovations in laser technology and the great progress in material science. Here, we mainly summarize and review the recent progress of MIR bulk laser sources based on the rare-earth ions-doped crystals in the 2.7-3 mu m spectral region, including Er3+ -, Ho3+-, and Dy3+-doped crystalline lasers. The outlooks and challenges for future development of rare-earth-doped MIR bulk lasers are also discussed.