Continuous-wave coherent Raman spectroscopy for improving the accuracy of Raman shifts.

Raman spectroscopy is an appealing technique that probes molecular vibrations in a wide variety of materials with virtually no sample preparation. However, accurate and reliable Raman measurements are still a challenge and require more robust and practical calibration methods. We demonstrate the implementation of a simple low-cost continuous-wave (cw) stimulated Raman spectroscopy scheme for accurate and high-resolution spectroscopy. We perform shot noise-limited cw stimulated Raman scattering as well as cw coherent anti-Stokes Raman scattering on polystyrene samples. Our method enables accurate determination of Raman shifts with an uncertainty below 0.1  cm. The setup is used for the characterization of reference materials required for the calibration of Raman spectrometers. Compared with existing standards, we provide an order of magnitude improvement of the uncertainty of Raman energy shifts in a polystyrene reference material.