Fig. 2

a Schematic of the ND-CARS process of hBN b Raman spectrum of hBN and spectrum window of pump pulses c Time-resolved ND-CARS (ω₁, 910 nm; ω₂, 1040 nm; ω₃, 455 nm) and ND-FWM (ω₁, 810 nm; ω₂, 1040 nm; ω₃, 405 nm) of hBN flakes. The intensities are collected from time-resolved d ND-FWM (ω₁, 810 nm; ω₂, 1040 nm; ω₃, 405 nm) and e ND-CARS (ω₁, 910 nm; ω₂, 1040 nm; ω₃, 455 nm) images of hBN (cyan dotted circles). Time-resolved spectrum of f ND-FWM (ω₁, 810 nm; ω₂, 1040 nm; ω₃, 405 nm) and g ND-CARS (ω₁, 910 nm; ω₂, 1040 nm; ω₃, 455 nm) of hBN. The green arrows indicate the polarization direction. A logarithmic scale is used for d–g. The white scale bars correspond to 6 μm