Applications of photonic-crystal fibers in nonlinear spectroscopy

Photonic-crystal fibers (PCFs) offer attractive and practical recipes for the enhancement of nonlinear-optical interactions of ultrashort pulses. In this work, it is demonstrated that 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, ideally suited for femtosecond coherent nonlinear spectroscopy. These pulses from a PCF were cross-correlated in our experiments with the femtosecond second-harmonic output of the Cr:forsterite laser in toluene solution, used as a test object, in boxcars geometry to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene molecules.