Polarization instabilities in a two-photon laser

We describe the operating characteristics of a new type of quantum oscillat or that is based on a two-photon stimulated emission process. This two-phot on laser consists of spin-polarized and laser-driven K-39 atoms placed in a high-finesse transverse-mode-degenerate optical resonator and produces a b eam with a power of similar to0.2 muW at a wavelength of 770 nm. We observe complex dynamical instabilities of the state of polarization of the two-ph oton laser, which are made possible by the atomic Zeeman degeneracy. We con jecture that the laser could emit polarization-entangled twin beams if this degeneracy is lifted.