Effects of reflective coatings on performance of divergence-narrowed external-cavity laser-diode arrays

This study was conducted to experimentally investigate how reflective coatings on the front facets of laser-diode arrays (LDAs) affect the performance of external-cavity LDAs, devices that yield divergence-narrowed emission. We compared the performance of two external-cavity LDAs equipped with front facets coated with different reflective coatings (with a low or high reflectivity). Our results confirm that a low reflectivity yields a superior performance in a divergence-narrowed external-cavity LDA. At a high drive current of 39.9 A, the divergence angle of an LDA with a low-reflectivity coating of 3% was suppressed from 8.4 to 1.2 degrees at an available output power of 22.3 W.