A Review of Near 3 μm Er3+/Ho3+-Doped Solid-State Lasers: From Continuous-Wave to Q-Switched Operation

Laser radiation near 3 μm overlaps with a strong water absorption band and is useful for medicine, materials processing, and mid-infrared frequency conversion. This review examines continuous-wave (CW) and Q-switched Er3+- and Ho3+-doped solid-state lasers in this wavelength region, with emphasis on the relationships between ion spectroscopy, host thermal properties, and laser performance. The advantages and limitations of different gain media and doping systems are compared in terms of lower-level depletion, energy transfer, pump absorption, and heat removal. Er3+ systems can use upconversion to deplete the lower laser level and recycle energy, whereas Ho3+ systems commonly employ Pr3+ codoping to reduce self-termination. Progress in CW and Q-switched operation is reviewed for individual host materials, and the roles of pumping geometry, gain-medium structure, and Q-switching method are discussed. The reported results highlight the need to assess CW power and efficiency together with pulse energy, duration, and repetition rate under their respective operating conditions. Future improvements require coordinated optimization of energy-level dynamics and pump utilization, host selection and thermal management, and pulse-generation devices. Long-term stability, damage resistance, wavelength control, and compact integration are also important for practical near-3-μm sources.