New mechanism for continuous-wave two-photon amplification
A probe-laser beam is amplified using a laser-driven, high-density potassium atomic beam in the presence of a weak magnetic field. Two σ + -polarized beams tuned near the 4S 1/2 -4P 1/2 transition form an electromagnetically induced trapped state by optically pumping the atoms in the 4S 1/2 state. Two-photon amplification of the z-polarized probe beam occurs when the atom makes a transition from the 4S 1/2 trapped state to the 4S 1/2 state in the presence of a σ - -polarized pump-beam. In this two-photon Raman process, two photons are annihilated and two z-polarized probe photons are created. Analysis of the quantum pathways reveals that they add constructively, whereas other geometries or laser beam polarizations can lead to destructive interference between pathways.