Investigation on nonlinear absorption and optical limiting properties of Tm:YLF crystals

Nonlinear optical limiting has recently attracted significant attention, thanks to the continuous development of laser technology. In order to explore more potential functional materials, the spectral and nonlinear optical properties of yttrium lithium fluoride doped with thulium (Tm:YLF) crystals are reported. Absorption and emission spectra of Tm:YLF are measured, and the absorption peaks correspond to the energy transition of Tm3+. Nonlinear absorption measurements are performed on crystals with different thulium doping concentrations (2.0 %, 2.5 %, and 3.0 %). The Z-scan results indicate the presence of two-photon absorption processes at 1064 nm pulse laser. Additionally, we measured the nonlinear transmittance of Tm:YLF crystals with various thulium doping concentrations and lengths to evaluate their nonlinear optical limiting performance. For the 2.5 % doped Tm:YLF crystal with 20 mm length, the maximum transmittance at low laser intensity is 73.9 %, and the minimum transmittance at high laser intensity is 38.1 %. These experimental results suggest that Tm:YLF crystals may have potential as solid-state nonlinear optical limiting materials.