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Diode laser-based dual-wavelength light sources are experimentally compared in individual and common operation. First, a Y-branch distributed Bragg reflector diode laser is presented. It consists of two laser cavities with a single output waveguide. The device provides 180 mW and dual-wavelength laser emission around 785 nm. The measured spectral widths and spectral distance are 20 pm and 0.6 nm, respectively. Resistors implemented next to the gratings allow changing the wavelength spacing within a range of 0.0 nm - 1.7 nm. Lateral far field profiles show a strong modulation and a lateral shift of 1° between both far fields indicates beam steering. Second, a multimode interference coupler-based master oscillator power amplifier is presented. It provides 500 mW dual-wavelength laser emission. Within the available power range, spectral widths of 20 pm and nearly constant peak emission wavelengths are measured. In comparison to quasicontinuous wavelength tuning obtained for the Y-branch laser, the MMI MOPA enables non-continuous wavelength tuning. As an example, selected spectral distances of 0.0 nm, 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated in individual operation. Beam steering is successfully eliminated. Near field widths of 5 μm and far field angles of 15° result in beam propagation ratios of M2 = 1.2 at the 1/e2 level in all operation modes. This enables easy beam shaping or efficient single-mode fiber coupling. Both devices are suitable for spectroscopic applications such as Raman spectroscopy and shifted excitation Raman difference spectroscopy as well as for the generation of THz radiation by photomixing.
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