Fig. 1. (a) Crystal structure of CrPS₄; (b)–(d) optical images and AFM measurement results of CrPS₄ with different thicknesses. The insets are SEM images. (e) Absorption spectrum with energy diagram involved in the optical transitions and (f) Raman spectra of CrPS₄.

Fig. 2. Experimental schematic of (a) I-scan system and (b) nondegenerate pump-probe measurement.

Fig. 3. Nonlinear absorption of CrPS₄ with different thicknesses. (a) 1086 nm, (b) 510 nm, and (c) 105 nm. (d) TPA coefficient and saturable intensity, (e) imaginary part of χ⁽³⁾, and (f) FOM of CrPS₄.

Fig. 4. Time-resolved transmission signal of CrPS4 at different (a) pump intensities with the thickness of 1086 nm and (b) thicknesses with the pump intensity of 4.8 GW/cm2. (c) The peak amplitude of ΔT/T0 as a function of the pump intensity. (d) Schematic of the transition and relaxation processes for carriers in CrPS4. The relaxation time τ1 and τ2 as a function of (e) pump intensity and (f) thickness.

Fig. 5. (a) Normalized transmission signal of 1086 nm CrPS₄ at different pump intensities; (b) Raman spectra of 1086 nm CrPS₄ excited at 532 nm under the powers from 1.1 to 6.5 mW; (c) peak positions marked in (b) as a function of the incident power.