785 nm dual-wavelength Y-branch DBR-RW diode laser with electrically adjustable wavelength distance between 0 nm and 2 nm

Shifted excitation Raman difference spectroscopy is a powerful tool to separate the weak Raman lines from disturbing background light like fluorescence, day light or artificial light. When exciting the sample alternatingly with two slightly shifted wavelengths, the Raman lines follow the change whereas the background remains unchanged. Therefore, background free Raman spectra can be obtained measuring the two Raman spectra, subtracting the two signals and applying a reconstruction algorithm. When the spectral distance between the two wavelengths is the width of the Raman lines under study best signal-to-noise ratios can be achieved. In this work, monolithic dual wavelength Y-branch DBR ridge waveguide diode lasers with resistor heaters over the DBR gratings will be presented. The devices have a total length of 3 mm and a RW stripe width of 2.2 mu m. The wavelengths are defined and stabilized using 500 mu m long 10 th order gratings with a designed spectral distance of 0.62 nm. Using the resistor heaters, this distance can be adjusted. The monolithic devices reach optical output powers up to 180 mW. Over the full range, they operate in single mode. The emission width is smaller than 13 pm (FWHM). At an output power of 50 mW the conversion efficiency is 0.22, which only slightly decreases down to 0.18 at maximal power. At an output power of 100 mW and with heater currents smaller than 600 mA, the spectral distance can be tuned from 0 nm up to 2 nm. The spectra remain single mode.