Characterization and mid-infrared laser operation in Er:CaF2 single crystal fiber grown by the laser heated pedestal growth method

Abstract

Er:CaF2 crystals, characterized by low doping and high efficiency, are suitable materials for single-crystal fibers. 3 at.% Er:CaF2 single-crystal fibers (SCF) were grown using the laser heated pedestal growth (LHPG) method. Significant oxidation-induced whitening phenomena were observed during growth. Increasing the growth rate helped mitigate further deterioration due to oxidation. This is likely because higher growth speeds allow the SCF to quickly move away from temperature ranges conducive to oxidation. As oxidation progressed, the phonon energy of Er:CaF2 SCF increased, causing the emission intensity at ∼ 1 μm to decrease from 77 % in the initial source rod to 6 % in the fully whitened state. Additionally, the lifetime of the 4I11/2 level decreased by approximately 10 times, from 8.988 ms to 0.822 ms. Continuous laser output at ∼ 2.8 μm was achieved using the transparent portion of 3 at.% Er:CaF2 SCF. With an output mirror transmission of 2 %, a maximum output power of 251 mW and a slope efficiency of 15.9 % were obtained. Laser experiments demonstrated the potential application of LHPG-prepared Er:CaF2 SCF in ∼ 2.8 μm lasers, but further performance enhancement requires additional strategies to address oxidation issues. This work provides valuable insights into the preparation of Er:CaF2 SCF using the LHPG method.