A frequency stabilization method for diode lasers utilizing low-field Faraday polarimetry

We present a method of diode laser frequency stabilization based on the Faraday rotation of linearly polarized light passing through an atomic sample in the presence of a very modest (1mT) magnetic field. Near the zero crossing of this spectroscopic feature, an optical system capable of very precise polarimetry detects and corrects for very small frequency fluctuations via a feedback system, which keeps the rotation signal at zero. In our application, we have demonstrated robust frequency stabilization over time scales from 10ms to 1h at the 1MHz level or below. We utilize this technique to lock our laser to a “forbidden” M1∕E2 transition in thallium at 1283nm, for which saturated absorption techniques are not straightforward. This technique has broad applicability to spectroscopy of various atomic systems as we also demonstrate using a Rb cell and a 780nm diode laser.