RESUMO
In this Letter, we propose and demonstrate an external-cavity diode laser in second-order Littrow configuration. This topology utilizes a low-efficiency diffraction grating to establish a high-finesse external cavity, strong optical feedback, a high polarization discrimination, and a circular TEM00 output mode. In our proof-of-concept experiment, we realized a cavity with a finesse of 1855, being, to the best of our knowledge, the highest value ever reported for a three-port-grating-coupled cavity. With optical feedback, the laser threshold of the laser diode employed was reduced by a factor of 4.
RESUMO
We demonstrate the excellent spectral properties of a diode laser setup that combines good tunability with superb short-term frequency stability and controllability. It is based on merging two concepts, the diode laser with resonant optical feedback and the grating stabilized diode laser. To characterize the short-term performance we beat two essentially identical diode lasers and find a short-term linewidth of ~11 kHz. Phase locking between these lasers is achieved with a servo bandwidth as small as 46 kHz, although an analog phase detector is used that requires subradian residual phase error. Despite small phase error detection range and small servo bandwidth, cycle-slip-free phase locking is accomplished for typically many 10 min, and the optical power is essentially contained in a spectral window of less than 20 mHz relative to the optical reference. Due to the excellent performance this laser concept is well suited for atomic or molecular coherence experiments, which require phase locking of different lasers to each other, and as part of a flywheel for optical clocks.