Fig. 1. Comparison of (a) impulsive stimulation and (b) interpulse stimulation in the frequency domain. (c) Interpulse stimulation in the time domain. (d) Principle of interpulse stimulation FT-CARS.

Fig. 2. Simulated comparison of the spectral coverage of interpulse stimulation FT-CARS and impulsive stimulation FT-CARS. (a) Excitation spectrum of the interpulse stimulation scheme. (b) Excitation spectrum of the impulsive stimulation scheme. (c) Assumed spectrum without (dark black) and with (light gray) nonresonant background of the simulated sample. (d) Retrieved spectra of the interpulse and impulsive stimulation FT-CARS.

Fig. 3. Experimental setup of interpulse stimulation FT-CARS. HWP: half-wave plate; PBS: polarizing beam splitter; M: mirror; R: retroreflector; L: lens; F: filter; DM: dichroic mirror; PCF: photonic crystal fiber; BS: beam splitter; PD: photodetector; OBJ: objective lens; APD: avalanche photodiode.

Fig. 4. Spectra of the (a) pump and (b) Stokes; autocorrelation of the (c) pump and (d) Stokes.

Fig. 5. (a) Unaveraged interferogram of DMSO rescaled to relative delay. (b) Unaveraged FT-CARS spectrum of DMSO in the high-wavenumber region.

Fig. 6. Measured interpulse stimulation FT-CARS spectra of (a) methanol in the high-wavenumber region and (b) polyethylene terephthalate (PET) in the upper part of the fingerprint region without averaging (top) and with 20 spectra averaged (middle). Both resonant spectra (shaded areas) and nonresonant-background-affected spectra (unshaded lines) are illustrated. The Raman spectra are shown (bottom) as reference. (c) Quantitative analysis of DMSO in water together with the quadratic fit with R2=0.984.