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. 
Micha{\l} Parniak, Adam Leszczy\'nski, Wojciech Wasilewski
physics.atom-ph physics.optics