Grating External Cavity Diode Lasers with Broad Tunable Range and Narrow Spectral Linewidth for High-Resolution Spectroscopy

A grating external cavity technique is used to improve the poor spectral qualities of commercially available semiconductor lasers in order to realize high-resolution spectroscopy. We describe a method of coating an anti-reflector onto the front facet of semiconductor lasers to suppress the intrinsic laser oscillation. The coated laser operates in an external cavity with a Littrow-mounted diffraction grating. The spectral linewidth of the resultant laser system is confirmed to be less than 250 kHz, and the system can be scanned over 25 nm. In order to demonstrate its improved tunability, we observed three resonance lines of two alkali-metal atoms, Rb-D2 (780.0 nm), K-D1 (769.9 nm) and K-D2 (766.5 nm), without replacing the laser chip.