Operation of a frequency-narrowed high-beam quality broad-area laser by a passively stabilized external cavity technique.

The average spectral bandwidth of a 2 W broad-area diode laser was narrowed to 5 GHz with wavelength tunability of up to 12 nm at a center wavelength of 790 nm with the use of a Littman-Metcalf external cavity in a displaced configuration. The use of lens and combined lens-laser transformation systems allowed precise alignment of the beam shaping optics, which led to significant improvements of the beam quality and an enhanced suppression of the free-running laser modes. We characterize the spatial beam quality of our external cavity diode laser by measuring the M2 quality factor and relate this to our measured bandwidths. Our external cavity can be configured over a range of cavity lengths and is modular in design, enabling access to a broad frequency spectrum for a wide range of applications that require high-power, narrow bandwidth operation.