Squeezing in the many atom resonance fluorescence emitted in the forward direction : application to photon noise reduction

We show theoretically that the resonance fluorescence field radiated in the forward direction by an ensemble of many atoms exhibits squeezing. In a full quantum treatment we quantitatively evaluate this squeezing and the photon noise reduction which can be obtained by entering this squeezed field in a homodyne or heterodyne detector. The study is restricted to a dilute and thin atomic medium containing motionless two-level atoms but it includes all the cases of weak and saturating excitation, resonant and detuned excitation, homodyne and heterodyne detection. Our results show the importance of taking into account the field coherence properties for a correct evaluation of photon noise reduction.