Measurement of light amplification in coherently pumped rubidium atoms

Abstract

We report the observation of steady-state amplification of a weak probe laser in Doppler broadened Λ-type rubidium atoms. With the weak probe laser and a strong coupling laser arranged in a Doppler cancellation configuration, and a third laser pumping Rb atoms to the probed upper level, Doppler-free probe amplification was observed and the measured spectral linewidth of the probe gain feature approaches the Rb natural linewidth. A theoretical analysis based on a three-level Λ-type model suggests that there is no population inversion in the bare states.