All-solid-state 3-µm single-frequency Er:CaF2 laser with a stable and switchable wavelength

We have demonstrated a 3-µm all-solid-state single-frequency laser with a stable center frequency and a switchable wavelength using the intra-cavity Fabry-Perot etalon method. Experimentally, the central wavelengths of the laser for the single-longitudinal mode are 2728 and 2794 nm, with maximum output powers of 268 and 440 mW, respectively. The corresponding single-longitudinal mode linewidths are 25 and 11 MHz. In particular, the central wavelengths of the single-longitudinal mode laser remain almost constant as the incident pump power increases. To the best of our knowledge, this study represents the first instance of using a laser diode to directly pump Er:CaF₂ block single crystals for single-frequency lasers in the 3 µm region. Additionally, it achieves the highest output power of a 3-µm all-solid-state single-longitudinal mode.