Abstract
We propose a new approach to broadband Stimulated Raman Scattering (SRS) spectroscopy and microscopy based on time-domain Fourier transform (FT) detection of the stimulated Raman gain (SRG) spectrum. We generate two phase-locked replicas of the Stokes pulse after the sample using a passive birefringent interferometer and measure by the FT technique both the Stokes and the SRG spectra. Our approach blends the very high sensitivity of single-channel lock-in balanced detection with the spectral coverage and resolution afforded by FT spectroscopy. We demonstrate our method by measuring the SRG spectra of different compounds and performing broadband SRS imaging on inorganic blends.
Highlights
Raman microscopy is gaining increasing recognition in biomedical optics [1] due to its capability of non-invasive, label-free imaging of tissues and cells, based on their intrinsic vibrational response [2,3]
The Stimulated Raman Scattering (SRS) interferogram is symmetric around time zero, but we limit our measurement to a single side of it because, with our wedge size, the maximum delay achievable by Translating-Wedge-based Identical pulses eNcoding System (TWINS) amounts to 1 ps, and this affords a better spectral resolution for the same scan length
We have introduced and demonstrated an original method to measure broadband SRS spectra by using Fourier transform (FT) spectroscopy
Summary
Raman microscopy is gaining increasing recognition in biomedical optics [1] due to its capability of non-invasive, label-free imaging of tissues and cells, based on their intrinsic vibrational response [2,3]. The main drawback of SR is its very weak scattering cross section, 10-12 orders of magnitude lower than that of absorption. This makes it difficult to separate the weak Raman-shifted light from the intense elastic scattering and from sample and substrate fluorescence, preventing probing dilute species and in vivo imaging, due to the long integration times needed. Coherent Raman Scattering (CRS) [5] can overcome these limitations, exploiting the thirdorder nonlinear optical response of the sample to pump and Stokes pulses in order to set up and detect a vibrational coherence within the ensemble of molecules inside the laser focus. CARS and SRS have both advantages and drawbacks and are actively developed for high-speed vibrational imaging
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