Abstract
Stimulated Raman scattering (SRS) allows chemical identification of substances based on their third-order nonlinear vibrational susceptibility χ(3)(ω). In its standard single-frequency implementation, SRS can only access the imaginary part of χ(3)(ω). Here we introduce interferometric SRS (iSRS), which has the capability to measure both the real and the imaginary parts of the nonlinear susceptibility. With respect to a standard SRS setup, iSRS simply requires the insertion of a few optical elements in the Stokes(pump) beam pathway to generate an intrinsically phase-coherent local oscillator. While preserving the acquisition speed and the simplicity of single-frequency SRS, iSRS considerably increases its information content by providing access to the vibrational phase, which allows one to distinguish overlapping species in congested spectra and is more robust with respect to noise.
Highlights
Coherent Raman scattering (CRS) encompasses a class of nonlinear spectroscopy and microscopy techniques for label-free identification of molecules and solids based on their characteristic vibrational fingerprints, which find a growing range of applications in life and materials sciences [1,2]
In coherent anti-Stokes Raman scattering (CARS) [3] the nonlinear signal is at the anti-Stokes frequency, ωaS = ωp + Ω, while in stimulated Raman scattering (SRS) [4] the signal is emitted at the Stokes/pump frequency, resulting in Stokes amplification and pump attenuation, called stimulated Raman gain (SRG) and stimulated Raman loss (SRL), respectively
The pump pulse is modulated at high frequency and the pump-induced variation of the Stokes energy, i.e. the SRG, is synchronously detected with a photodiode combined with a lock-in amplifier. interferometric SRS (iSRS) requires the addition of a few elements to this standard setup
Summary
Coherent Raman scattering (CRS) encompasses a class of nonlinear spectroscopy and microscopy techniques for label-free identification of molecules and solids based on their characteristic vibrational fingerprints, which find a growing range of applications in life and materials sciences [1,2]. Stokes (at frequency ωS ) pulses, whose frequency difference matches a vibrational frequency Ω of the molecule, CRS sets up a vibrational coherence which drives a nonlinear signal many orders of magnitude stronger than in the case of spontaneous Raman. The CRS signal depends on the third-order nonlinear vibrational susceptibility, which can be written as χ (3) (ω) = χ (3) R + χ (3) NR , where χ (3) R (ω )
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