Third-Order Nonlinear Characteristics and the Temperature-Dependent Refractive Index of Sm/Tm: YCa₄O(BO₃)₃ for Use in Quasi-Parametric Chirped Pulse Amplification

Quasi-parametric chirped pulse amplification (QPCPA) can achieve efficient broadband signal output by using rare earth (RE)-doped yttrium calcium oxyborate (YCOB). However, a systematic study on the optical properties and the thermal refractive index of RE:YCOB crystal is rare, which causes difficulties in the design of QPCPA. Herein, we systematically investigated absorption spectra, Raman spectra, third-order nonlinear properties, and temperature-dependent refractive index of RE:YCOB. The effective gain factors in QPCPA were analyzed based on the absorption spectra. Raman spectroscopy showed that RE3+ will not change the vibration mode of the YCOB crystal when it enters the crystal by replacing Y3+. The nonlinear refraction values range from 0.2–3 × 10–5 and 5–16 × 10–7 cm2/GW for 532 and 1064 nm, respectively. Meanwhile, the refractive index of Sm:YCOB at different temperatures was investigated and the thermal-dependent Sellmeier equation was fitted. Moreover, the effect of the refractive index changes with temperature on QPCPA was investigated.