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

• Published in: Chinese physics B Vol. 25; no. 6; pp. 254 - 258
• Main Author: 徐春华 闫腾飞 王刚 王文军 梁敬魁 陈小龙
• Format: Journal Article
• Language: English
• Published: 01.06.2016
• Subjects: Crystals; Lasers; Modulation; Nonlinearity; Refractive index; Refractivity; Silicon carbide; Spectra; 碳化硅晶体; 脉冲展宽; 诱导; 超短; 输出光谱; 非线性折射率; 非线性极化率; 飞秒激光脉冲
• ISSN: 1674-1056; 2058-3834; 1741-4199
• DOI: 10.1088/1674-1056/25/6/064206

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-1on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm2.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 n2 is estimated to be1.88×10-15cm2/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.