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Raman spectroscopy of heterogenous samples requires measurements with larger spot size and herewith larger excitation power. The former leads to an increase of collected background light. Shifted excitation Raman difference spectroscopy, which requires two neighboring excitation wavelengths, is a powerful technique to spectrally separate Raman signals from the background. Master oscillator power amplifier systems using a Y-branch distributed Bragg reflector ridge waveguide diode laser as master oscillator and tapered laser as power amplifier can meet the spectral and power requirements. In this work, a comparison of 785 nm micro-integrated dual-wavelength master oscillator power amplifiers on 5 mm x 25 mm micro-optical benches is presented. To study the impact of potential back reflections from the amplifier into the master oscillator, Y-branch lasers with front facet reflectivity of 5% and 30% are investigated. The branches of the master oscillators are operated subsequently during characterization. At 25°C and 50 mW pump power, the master oscillator power amplifiers provide 2.7 W of near-diffraction limited dual-wavelength laser emission. Spectral widths < 20 pm and spectral distances of 0.6 nm (10 cm-1) between both laser wavelengths are measured, suitable for shifted excitation Raman difference spectroscopy. A higher front facet reflectivity significantly reduces feedback related mode hopping. Additional longitudinal modes still measured in both cases are separated by 30 pm, corresponding to the free spectral range of the master oscillators. These modes remain within spectral windows < 0.15 nm (< 3 cm-1) along the entire power ranges, sufficient to resolve Raman signals of most solid and liquid samples. As expected, the integration a compact 30 dB optical isolator eliminates the observed optical feedback effects.
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