Memory correlation effects on quantum noise in lasers and masers.
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We demonstrate how spontaneous-emission noise in lasers and masers can be reduced through memory effects of the lasing atoms. We show that for short measurement times the spontaneous-emission noise can be smaller than the usual Schawlow-Townes limit. We discuss a general model for atomic memory effects and derive expressions for the noise correlation function, phase diffusion, and the emitted spectrum. Furthermore, we allow for a frequency distribution over the lasing atoms and hence account for Doppler broadening or a selective excitation of the atoms. 1990 The American Physical Society.