ABSOLUTE FREQUENCY CONTROL OF A 1560 NM (192-THZ) DFB LASER LOCKED TOA RUBIDIUM ABSORPTION-LINE USING A 2ND-HARMONIC-GENERATED SIGNAL

We demonstrate second-harmonic generation from a DFB laser at 1560 nm in a type I critically phase-matched KNbO3 crystal. We obtain 2.2 nW a t 780 nm with 11.3 mW at 1560 nm incident on the crystal, The conversi on efficiency is 17.2 pW/(mW)(2). The 780 nm beam is used to interroga te a resonance of the Rb-87-D-2 line at 780 nm and lock the laser freq uency. To characterize the absolute frequency stability, two 1560 mm D FB lasers are respectively stabilized on a Doppler resonance of the Rb -87-D-2 line (780.246 nm) and of the Rb-85-D-2 line (780.244 nm). The square root of the Allan variance measured from the beat note is aroun d 1.5 x 10(-9) for averaging times between 3 and 100 s. To improve the precision of the frequency locking, we realize a setup to observe a s aturated absorption profile: We use a 780 nn stabilized laser as a pum p and the SHG signal as a probe. A saturated absorption profile is obs erved over the Doppler envelope. Work is under progress to use this sa turated resonance for an improved frequency control.