HOW LARGE PHOTON RECOIL CAN MAKE COLD ATOMS LASE

We calculate the weak probe field absorption spectrum for ultracold three-level atoms in a Raman gain configuration in the limit of the recoil shift exceeding the natural linewidth and the Doppler broadening. Our results show that even in the limit of very large recoil gain persists with its maximum shifted toward the red of the atomic line by the recoil energy, as is the spontaneous emission line. Some preliminary calculations suggest the possibility of a cw deep uv laser, based on cooled metastable helium atoms. © 1995 The American Physical Society.