Evolution of a super-broadened spectrum in a filament generated by an ultrashort intense laser pulse in fused silica
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- Fang, XJ. & Kobayashi, T. Appl Phys B (2003) 77: 167. doi:10.1007/s00340-003-1176-9
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We report experimental and theoretical investigations of the evolution of super-broadened spectrum generation by intense 50-fs pulses propagating in bulk fused silica. Based on good agreement between the experimental results and numerical simulations, a mechanism of supercontinuum generation (SCG) is proposed. At first, both self-phase modulation (SPM) and stimulated Raman scattering (SRS) contribute substantially but slowly to the broadening before filament formation takes place. After filamentation, a plasma grows rapidly and asymmetric spectral broadening results in a blue-shifted spectrum extending to about 400 nm. A time-resolved experiment of the SCG was also performed using a double-pump technique. The temporal behavior suggests that the vibrational mode excited by the stimulated Raman process by the first pulse contributes to the occurrence of self-focusing.