Study of femtosecond laser writing in the bulk of Nd 3+ , Y 3+ co-doped CaF 2 crystals

We reported on the femtosecond (fs) laser induced permanent refractive index changes, stress-induced birefringence, and micro-photoluminescence properties of Nd3+, Y3+ codoped CaF2 crystals. Permanent changes in the linear optical properties were studied for various pulse energies (0.01 - 5 µJ) at two different repetition rates (10 kHz and 500 kHz). Optimum quantitative phase changes are close to - 1.7π radians within an irradiated area, surrounded by positive phase changes due to the stress field that can reach + 0.7π. Provided that, we avoid heat-accumulation at 500 kHz, written laser lines offer higher linear birefringence on the order of λ/4 at 200 nm. From the spectroscopic point of view, we observed the Raman changes and micro-photoluminescence spectra of irradiated fs-laser Nd3+, Y3+ doped CaF2.