Abstract

Amplification without inversion (AWI) rests on the possibility of inducing interference of atomic states by means of intense classical fields. Two types of mechanisms have been identified¹ in a three-level medium with E₃ >> E₂ > E₁. The most common mechanism relies on the occurrence of trap states. If the transition 1–2 is driven by an external field, the trap state is an antisymmetric combination of states 1 and 2. No transition is allowed between the trap state and the upper state 3. Amplification requires only that there are more atoms in state 3 than in the untrap state N₁ + N₂ − N_t. This can be verified with N₃ smaller than N₂ and N₁, in which case we have AWI. If one optical transition, 3−1 for instance, is forbidden, another mechanism is possible, which implies anti-Stokes scattering and quantum interference to induce a coherence between states 3 and 1 despite the forbidden direct transition.

© 1994 IEEE