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We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H–SiC single crystals.It is demonstrated that the full width at half maximum of output spectrum increases linearly with the light propagation length and the peak power density,reaching a maximum 870 cm~(-1)on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm~2.Such spectral broadening can be well explained by the self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index.The nonlinear refractive index n_2 is estimated to be1.88×10~(-15)cm~2/W.The intensity-dependent refractive index is probably due to both the nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process.Super continuum spectra could arise as crystals are long enough to induce the self-focusing effect.The results show that SiC crystals may find applications in spectral broadening of high power lasers.
We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H-SiC single crystals. It is the full width at half maximum of the output spectrum increase linearly with the light propagation length and the peak power density, reaching a maximum of 870 cm -1 on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW / cm ~ 2.Such spectral broadening can The well-explained self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index. The nonlinear refractive index n_2 is estimated to be 1.88 × 10 ~ (-15) cm ~ 2 / W. The intensity-dependent refractive index is probably due to both nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process. Supercontinuum spectra could arise as crystals are long enough to inducate The self-focusing effect. The results show that SiC crystals may find applications in spectral broadening of high power lasers.