Femtosecond coherent anti-stokes Raman scattering Spectroscopy using frequency-tunable chirped pulses produced and shaped in a photonic-crystal fiber

A new scheme of femtosecond coherent anti-Stokes Raman scattering spectroscopy using chirped pulses is proposed and experimentally implemented. A theory of this modification of coherent nonlinear spectroscopy is developed. We show that a linear time-frequency mapping defined by linearly chirped pulses allows the spectra of nonlinear response of a medium to be measured by varying the delay time between the pump pulses. Photonic-crystal fibers with a special dispersion profile are at the heart of the experimental implementation of this technique. Such fibers are ideally suited for the generation of frequency-tunable pulses with a smooth envelope and a controlled chirp. We present the results of experimental characterization of the envelope, spectrum. and chirp of anti-Stokes pulses generated in photonic-crystal fibers by Femtosecond Cr: forsterite-laser pulses. These frequency-tunable anti-Stokes pulses produced and shaped in photonic-crystal fibers are then employed for coherent anti-Stokes Raman scattering spectroscopy of toluene solution.