Pre-stabilization of a distributed feedback diode laser for locking to a high-finesse cavity

An ultra-stable laser based on frequency doubling of a distributed feedback (DFB) semiconductor laser has been built for interrogation of the 674-nm clock transition in Sr
⁺
. The DFB laser is pre-stabilized using an all-fiber interferometer that reduces the linewidth from the 1 MHz regime down to a few kHz and enables reliable locking of the laser to a 30-cm reference cavity with a finesse of 270 000 at 674 nm The laser will be used in a Sr
⁺
single-ion clock that should reach a fractional frequency uncertainty of a few parts in 10
^-18
.