Frequency stabilization of a diode laser on the Cs D2 resonance line by the Zeeman effect in a vapor cell

Hyperfine optical pumping of a Cs-vapor cell through a diode laser in frequency standards requires a high purity of the laser emission spectrum, and a high stability of the emission frequency. We present here a frequency-locking scheme that is able to produce a discrimination signal without any modulation, by using the dichroism induced by a magnetic field on the atomic vapor. The larger line-width of the reference signal (Doppler-broadened) is compensated by its larger amplitude, when compared with the saturated absorption signal. As a final result, the slope is similar, and the large line-width warrants a large locking range, making robust the lock against external perturbations. This error signal is used to lock the frequency of an external cavity diode laser, with a grating reflector in Littman configuration. A fast correction band is obtained by changing the cavity length through an intra-cavity electro-optic modulator. The possible sources of instabilities of the locking point are discussed and estimated through a simulation computer program. Received: 28 November 2000 / Revised version: 21 May 2001 / Published online: 18 July 2001