Microstructure fibers as frequency-tunable sources of ultrashort chirped pulses for coherent nonlinear spectroscopy

Microstructure fibers are shown to allow the creation of new tunable sources for femtosecond nonlinear spectroscopy. These fibers provide a high efficiency of frequency upconversion of regeneratively amplified femtosecond pulses of a Cr:forsterite laser, permitting the generation of subpicosecond anti-Stokes pulses with a smooth temporal envelope and a linear positive chirp. These pulses from a microstructure fiber were used to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene solution by cross-correlating these pulses with the femtosecond second-harmonic output of the Cr:forsterite laser in boxcars geometry (XFROG CARS). PACS 42.65.Wi; 42.81.Qb