Monolithic Y-branch DBR diode laser with emission at 633 nm as excitation light source for Raman and SERDS investigations

In this study, a dual-wavelength monolithic Y-branch distributed Bragg reflector (DBR) diode laser at 633 nm is demonstrated that is well-suited for Raman spectroscopy and especially shifted excitation Raman difference spectroscopy (SERDS). The device provides 30 mW optical output power with an electrical power consumption of less than 1 W. Its spectrally stabilized dual-wavelength laser emission is narrowband with spectral widths of 12 pm (0.3 cm-11). The spectral distance of the two emission wavelengths is 0.4 nm (10 cm-1 at 633 nm), as targeted for SERDS, and their side mode suppression ratios are in excess of 40 dB. SERDS measurements on soil, exemplarily chosen as highly fluorescent sample, showed a 17-fold improvement in the signal-to-background noise ratio in comparison to measured Raman spectra. Moreover, it revealed weak Raman signals, which were not detectable in Raman spectra and allowed for identification of quartz and calcite as selected soil constituents.