Frequency detuning and stabilization of a diode laser using the Zeeman shift of the saturated absorption signal of rubidium atoms

We observed saturated absorption spectra of the Rb-87 atom under a magnetic field of several millitesla with a diode laser oscillating at 780 nm. The spectra were compared with the theoretical ones obtained on the basis of Nakayama's four-level model. We numerically computed Zeeman splittings of the 5(2)P(3/2) excited state of the atom. As the magnetic field increased to 5 mT, the absorption peak of the F = 2-->F' = 3 transition shifted almost linearly up to about 62 MHz. The shift direction was reversed by changing the polarization combination of the pump and probe lasers. The measured frequency stability. when the laser was locked at the absorption peak, was better than sigma(y)(tau) = 1 x 10-(11)tau(-1/2) for the sampling time of 0.01s less than or equal to tau less than or equal to 10s.