Compact and versatile laser system for polarization-sensitive stimulated Raman spectroscopy

We demonstrate a compact and versatile laser system for stimulated Raman spectroscopy (SRS). The system is based on a tunable continuous wave (CW) probe laser combined with a home-built semi-monolithic nanosecond pulsed pump Nd:YVO₄ laser at 1064 nm. The CW operation of the probe laser offers narrow linewidth, low noise and the advantage that temporal synchronization with the pump is not required. The laser system enables polarization-sensitive stimulated Raman spectroscopy (PS-SRS) with fast high resolution measurement of the depolarization ratio by simultaneous detection of Raman scattered light in orthogonal polarizations, thus providing information about the symmetry of the Raman-active vibrational modes. Measurements of the depolarization ratios of the carbon-hydrogen (CH) stretching modes in two different polymer samples in the spectral range of 2825-3025 cm^-1 were performed. Raman spectra are obtained at a sweep rate of 20 nm/s (84 cm^-1/s) with a resolution of 0.65 cm^-1. A normalization method is introduced for the direct comparison of the simultaneously acquired orthogonal polarized Raman spectra.