Spectral broadening induced by intense ultra-short pulse in 4H–SiC crystals

Abstract

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 be 1.88×10 −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.

Dispersion of nonresonant third-order nonlinearities in Silicon Carbide

“…Moreover, the assumption of nonparabolicity for both conduction and valence bands is demonstrated to be critical in order to match the experimental data. Indeed, our simulations indicate a considerable discrepancy between our theoretical n 2 dispersion and the measurements of refs 15 and 33, if the hypothesis of parabolicity or nonparabolicity only for the conduction band is adopted. Some problems that are linked to the parabolicity hypothesis are: (1) a reduction in the position ( λ peak ) of the n 2 peak; (2) creation of a smaller tail in the n 2 shape at higher photon energy, and (3) a reduction in the mid-IR asymptotic value.…”

“…5 the Kerr refractive index ( n 2 ) spectra are sketched for 4H-SiC material and the TE polarization, showing a very good agreement with experimental data1533. In the simulations we have assumed a fitting factor C np  = 4.3 × 10 3 (see Eq.…”