Magneto-optical polarization rotation in a ladder-type atomic system for tunable offset locking

We demonstrate an easily tunable locking scheme for stabilizing frequency-sum of two lasers on a two-photon ladder transition based on polarization rotation in warm rubidium vapors induced by magnetic field and circularly polarized drive field. Unprecedented tunability of the two-photon offset frequency is due to strong splitting and shifting of magnetic states in external field. In our experimental setup we achieve two-photon detuning of up to 700 MHz.