摘要： Coherent Raman scattering (CRS) is a powerful label-free spectroscopic technique that allows fingerprinting of molecules based on their intrinsic vibrational response. The vibrational transitions can be described using Lorentzian functions, whose superposition gives rise to a complex third-order resonant nonlinear susceptibility. Its direct experimental access would allow a very rich spectroscopic information, especially in the presence of mixtures of molecular species. Unfortunately, standard CRS techniques do not allow to fully extract it: stimulated Raman scattering (SRS) only measures the imaginary part of the nonlinear susceptibility, while coherent anti-Stokes Raman scattering (CARS) retrieves a mixture of real and imaginary parts, as the signal is proportional to the square of the nonlinear susceptibility plus a real, frequency-independent non-resonant term. The complex susceptibility can in principle be retrieved using: (1) analytic techniques, but they require the full spectrum of the nonlinear susceptibility, often not available; (2) interferometric SRS, employing a pulse shaper to generate two replicas of the broadband Stokes pulse, but the use of a spectrometer limits the modulation frequency of the pump and thus the SRS detection sensitivity; (3) interferometric CARS, employing a local oscillator (LO) field collinearly combined with the anti-Stokes field and at the same frequency, but it is technically very demanding as it requires three synchronized and phase-coherent light beams. Recently, we introduced a novel technique based on Fourier-transform (FT) spectroscopy able to detect in the time domain both the Stokes and the SRS broadband spectra. It employs an interferometer, based on a passive birefringent delay line, and a single-channel lock-in amplifier. Here we introduce a simple modification, which we call interferometric FT-SRS (IFT-SRS), allowing the retrieval of the full complex nonlinear susceptibility of the sample. In IFT-SRS a birefringent plate placed before the sample generates a reference LO beam anticipated by a few picoseconds (so that it does not experience any nonlinear interaction) and with perpendicular polarization with respect to the pump/Stokes pulses. After the sample, a delay line, consisting of a pair of birefringent wedges with optical axis rotated by 90° with respect to the first birefringent plate, is used to vary the overall delay between the pump and the LO from zero to a few picoseconds. Their interference on a photodetector (after projection to a common polarization direction by a linear polarizer) is sent to a lock-in amplifier which records both the linear and differential interferograms, whose FT provides simultaneously real and imaginary parts of the nonlinear susceptibility, as shown for ethanol, acetone and isopropanol solvents. They display well-resolved spectra in the real part of the FT, which are in good agreement with the spontaneous Raman spectra of the solvents, as well as the expected dispersive lineshapes in their imaginary parts.