Frequency stabilization of a diode laser at 1540 nm by locking to sub-Doppler lines of potassium at 770 nm

Abstract
An external cavity 1540-nm diode laser was frequency doubled in a 3-cm-long periodically poled LiNbO3 waveguide doubler with 150% W-1 conversion efficiency, thereby generating more than 3 μW at 770 nm. Second-harmonic light was used to detect and lock to sub-Doppler lines of the 39K D 1 transition.