Interferometric Fourier-Transform Stimulated Raman Scattering

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 χ
⁽³⁾
_R
(ω). 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 |χ
⁽³⁾
_R
(ω)+χ
⁽³⁾
_NR
(ω)|
²
, where χ
⁽³⁾
_NR
(ω) is a real, frequency-independent non-resonant term.