External cavity spectral beam combining of 4.6 µm emitting quantum cascade laser arrays

Spectral beam combining of linear arrays of quantum cascade (QC) lasers emitting at 4.6 µm is demonstrated as a viable approach towards power-upscaling. By using an external cavity setup equipped with a diffraction grating and a partially transmitting output mirror providing wavelength selective feedback to each emitter, up to 8 individual QC lasers are combined with an optical coupling efficiency of 60% for an array of 6 emitters. The resulting beam quality (M2<2 for both fast and slow axis) is close to that observed for single emitters.