Broad-area laser diode with 0.02 nm bandwidth and diffraction limited output due to double external cavity feedback

External cavity feedback for a broad-area laser diode (BAL) with antireflection coating on the front facet was investigated experimentally. The feedback was created by a high-reflection mirror and a blazed grating, which reflected two parts of the laser emission back to the BAL, thereby forming an external resonator. When a Fabry-Perot etalon was inserted into the resonator, an output beam with a bandwidth of 0.02 nm and a power of 150 mW was obtained. The beam diffraction limited factor M2 is 1.16.