Quasi-phase-matched frequency doubling in a waveguide of a 1560-nm diode laser and locking to the rubidium D₂ absorption lines

An external-cavity 1560-nm diode laser was frequency doubled in a 3-cm-long periodically poled LiNbO₃ waveguide doubler with 120% W^-1 conversion efficiency. The 780-nm light was used to detect the D₂ transitions of Rb, and the laser frequency was locked to Doppler-broadened lines of Rb. Furthermore, the ∼1 μW of second-harmonic power was sufficient for detecting the sub-Doppler lines of Rb, and the laser was locked to a ⁸⁷Rb crossover line.