Fig. 1. (a) Photo of the freestanding vacuum-assisted filtrated h-BN film. (b) TEM image of the prepared h-BN nanosheets by drop coating the ball-milled h-BN solution on a carbon-coated copper grid. (c) HRTEM image of the h-BN nanosheets with five layers. (d) Laser patterned micro-pattern of an Australian map on a free-standing h-BN film.

Fig. 2. (a) FTIR spectra of the pristine h-BN film (blue line) and laser irradiated h-BN film (red line). (b) Raman spectra with laser excitation at the wavelength of 532 nm of the pristine h-BN film (blue line) and laser irradiated h-BN film (red line). (c) Atomic structure of pristine h-BN film and localized oxidation area after laser irradiation (red dash area).

Fig. 3. (a) UV-VIS absorption characterization in the pristine h-BN film (blue line) and the laser patterned area (red line). (b) The refractive index (n₀) of the pristine h-BN film (blue line) and laser patterned area (red line). (c) The extinction coefficient (ĸ) of the pristine h-BN film (blue line) and laser patterned area (red line).

Fig. 4. (a) Open aperture Z-scan results before laser oxidation. (b) Close aperture Z-scan results before laser oxidation. (c) Open aperture Z-scan results after laser irradiated optical breakdown. (d) Close aperture Z-scan result after laser oxidation.

Fig. 5. (a) The measured nonlinear absorption coefficient β and (b) nonlinear refractive index n₂ of the pristine h-BN film. (c) The measured nonlinear absorption coefficient β and (d) nonlinear refractive index n₂ of the laser oxidized h-BN film.

Fig. 6. FWM spectra of the h-BN film excited with pump wavelengths (865 nm, 1200 nm), compared to that of a standard gold film.

Table 1. The compared results of different kinds of h-BN with their nonlinear absorption coefficient β, nonlinear refractive index n₂, the imaginary part Imχ⁽³⁾ and the real part Reχ⁽³⁾ and the effective third-order susceptibility |χ⁽³⁾| of complex third-order susceptibility χ⁽³⁾.