Cross-correlation frequency-resolved optical gating coherent anti-Stokes Raman scattering with frequency-converting photonic-crystal fibers

Abstract

Photonic-crystal 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 photonic-crystal fiber 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 (XFROG CARS).

Frequency shifting and pulse shaping with photonic‐crystal fibers for coherent nonlinear spectroscopy

“…3(b)), the CARS signal can be conveniently separated from the pump and probe beams with a pinhole, designed to reject all light except the beam along the wave vector k CARS D k 1 k PCF C k 0 1 (where k 1 and k 0 1 are the wave vectors of second-harmonic beams and k PCF is the wave vector of the PCF output), corresponding to the phase-matched CARS signal. The spatially filtered CARS signal was spectrally resolved with diffraction gratings, which allowed us to measure the intensity of this signal, I a , as a function of the frequency ω a and the delay time (XFROG CARS 15 ). The results of these measurements were represented as two-dimensional spectrograms I a ω a , ), visualizing Raman resonances in the nonlinear response of the medium under study.…”

“…14 Coherent nonlinear spectroscopy and microscopy open up a vast area for applications of PCF light sources and frequency shifters. Efficient frequency conversion and supercontinuum generation in PCFs have been shown to enhance the capabilities of chirped-pulse coherent antiStokes Raman scattering (CARS) 15 and coherent inverse Raman spectroscopy. 16 Cross-correlation frequency-resolved optically gated CARS (XFROG CARS) has been recently demonstrated 17 using specially designed PCF frequency converters for ultrashort laser pulses.…”

Two‐beam multiplexed CARS based on a broadband oscillator

“…[9 -11] The advent of specialty fibres has led to novel and rather simple schemes for generating subpicosecond broadband (BB) pulses suitable for CARS spectroscopy. [12] Furthermore, by employing such fibres as supercontinuum sources within one arm of the interferometer (two-beam geometry), the system setup for BB CARS microscopy has also been simplified and its spectral coverage dramatically broadened. [13 -15] However, when an extremely BB pulse such as supercontinuum is used, the efficiency of the Raman process can be rather low, giving rise to serious degradation of the vibrational spectra due to the presence of the NRB.…”

Dispersion‐compensated supercontinuum generation for ultrabroadband multiplex coherent anti‐Stokes Raman scattering spectroscopy

“…The idea of chirped-pulse CARS using the supercontinuum has been proposed and experimentally demonstrated. 21,22 The CARS process occurs when the pump and the Stokes laser pulses overlap at the sample position temporally as well as spatially. Therefore, the wide range of the vibrational resonance cannot be excited efficiently if the supercontinuum has the large group delay dispersion (GDD).…”