Suppression of cross coupling in an external resonator for a diode laser bar with 19 single emitters.

We present an external cavity in a quasi-Littrow configuration for a diode laser bar with 19 single emitters and the individual spectral stabilization, ranging from wavelengths between 970 and 980 nm corresponding to each emitter. The imaging of the vertical waveguide mode onto a blazed grating acting as a diffractive optical element is realized with a beam transformation system that swaps the vertical and lateral axes. Along with a feedback intensity of <10%, the reduction of the divergence due to a beam expander results in high losses for cross coupling modes. We demonstrate the possibility to suppress cross coupling and that even a process-related small smile error has a positive effect on the quality of the spectral stabilization in a quasi-Littrow configuration.