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Stimulated Raman spectroscopy using optical fibers

31 May | By Sebastian Karpf
Stimulated Raman spectroscopy using optical fibers
Time-Encoded (TICO) stimulated Raman spectroscopy technique
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Researchers from University of Lübeck in Germany and University of California, Los Angeles (UCLA) in the USA have presented a system for fiber-based high-resolution stimulated Raman spectroscopy. Their findings have been published in the Journal of Spectroscopy "Shot-Noise Limited Time-Encoded Raman Spectroscopy". The system employs the previously introduced time-encoded (TICO) Raman technique which makes use of the broadband coverage of swept-source lasers to obtain broadband Raman spectra. In the non-linear stimulated Raman scattering (SRS) technique, the effect height is increased by orders of magnitude with respect to the traditional spontaneous Raman technique by employing two lasers sources rather than just one pump laser. The second laser is often called probe or Stokes-laser, because the energy difference between the two wavelengths drives the Stokes-Raman transition. The new hurdle in SRS is thus to tune this energy difference between the pump and the Stokes laser. Here the researchers around Prof. Robert Huber were able to rapidly increase tuning speeds by employing a swept-source Fourier Domain Mode-Locked (FDML) laser, which can reach sweep speeds of up to MHz while covering up to 1000cm-1 of Raman bandwidth. In their new paper the researchers analyze the sensitivity of their detection. A two step approach employing analogue and digital balancing ultimately reduces the detection noise down to the shot-noise limit. This sensitivity makes the approach promising for applications in biomedical spectroscopy and in vivo molecular imaging. The most striking advantage, however, is the fiber-based approach making it already now suitable for endoscopic applications. This is enabled by two quasi monochromatic light sources which circumvent most of the problems that are currently hindering the application of the powerful non-linear Raman approach to endoscopic imaging. 
Category: Spectroscopy
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