Spectrally smoothed supercontinuum generation by using unstably mode-locked laser pulses

We report on a simple approach to obtain spectrally smoothed supercontinuum (SC) by using unstably mode-locked femtosecond laser pulses. The spectrum smoothing effect is due to the averaging of the supercontinua generated in a nonlinear photonic crystal fiber by modulated pulses. Theoretical analysis based upon solving the generalized nonlinear Schrodinger equation is presented, which qualitatively agrees well with the experimental observation. Finally, the application of the smoothed SC to broadband coherent anti-Stokes Raman scattering spectroscopy is demonstrated, which can result in a relatively smooth nonresonant background and suppress spurious peaks.