Abstract
We demonstrate coherent Raman spectroscopy (CRS) using a tunable excitation source based on a single femtosecond
fiber laser. The frequency difference between the pump and the Stokes pulses was generated by soliton
self-frequency shifting in a nonlinear optical fiber. Spectra of C─H stretches of cyclohexane were measured simultaneously
by stimulated Raman gain (SRG) and coherent anti-Stokes Raman scattering (CARS) and compared.
We demonstrate the use of spectral focusing through pulse chirping to improve CRS spectral resolution. We analyze
the impact of pulse stretching on the reduction of power efficiency for CARS and SRG. Due to chromatic
dispersion in the fiber-optic system, the differential pulse delay is a function of Stokes wavelength. This differential
delay has to be accounted for when spectroscopy is performed in which the Stokes wavelength needs to be
scanned. CARS and SRG signals were collected and displayed in two dimensions as a function of both the time
delay between chirped pulses and the Stokes wavelength, and we demonstrate how to find the stimulated Raman
spectrum from the two-dimensional plots. Strategies of system optimization consideration are discussed in terms
of practical applications.