Correlated spontaneous emission laser

Quantum-beat lasers are a particular form of correlated spontaneous emission lasers (CEL s) [43-49]. Quantum-beat is formed by creating coherence between near degenerate atomic states, either excited states or ground states. In particular, a beam of three-level atoms in Vee configuration emit photons into two modes. The atomic upper levels are initially prepared in a coherent superposition or are coupled by a coherent field [13-17]. The fluetuations of the relative phase and the relative amplitude drop to the vacuum levels. In addition to this, as a different form, correlated spontaneous emission can be formed by creating eoherenee between a pair of states between which lasing transitions occm. One such example is a two-photon CEL [13-17] with a beam of three-level atoms in cascade configuration. The top and bottom states are initially prepared in a coherent superposition state. It was predicted that the phase noise is reduced by 50% below the vacuum noise level. 

N. Lu and S. Y. Zhu. Quantum theory of two-photon correlated-spontaneous-emission lasers Exact atom-field interaction Hamiltonian approach. Physical Revew A 1989 Nov 15 40(10) 5735-5752. 

J. Bergou, C. Benkert, L. Davidovich and et al. Double two-photon correlated-spontaneous-emission lasers as bright sources of squeezed light. Physical Revew A 1990 Nov l 42(9) 5544-5552. 

M. O. Scully. Correlated Spontaneous-Emission Lasers Quenching of Quantum Fluctuations in the Relative Phase Angle. Physical Review Letters 1985 Dec 16 55(25) 2802-2805. 

U. W. Rathe and M. O. Scully. Phase coherence and decoherence in the correlated-spontaneous-emission laser. Physical Revew A 1995 Oct 52 (4) 3193-3200. 

H. Xiong, M. O. Scully, M. S. Zubairy. Correlated Spontaneous Emission Laser as an Entanglement Amplifier. Physical Review Letters 2004 Jul 21 94(2) 023601(4). 

Shahid Qamar, Han Xiong, M. Suhail Zubairy. Influence of pump-phase fluctuations on entanglement generation using a correlated spontaneous-emission laser. Physical Revew A 2007 0ct3 75(6) 062305(10). 

Finally that intriguing application yielding the laser. In luminescence the radiative decay of the excited state to the ground state occurs by spontaneous emission, i.e. the emission processes on different activator ions are not correlated. If, by some means, the majority of the luminescent ions are in the excited state (this situation is called population inversion), a single spontaneously emitted photon (quantum of radiation) may stimulate other excited ions to emit. This process is called stimulated emission. It is monochromatic, coherent and non-divergent. Laser action depends on emission by a stimulated process. Actually the word la.ser is an acronym for light amplification by stimulated emission of radiation. This book does not deal with lasers or laser physics. However, we will deal with the material where the stimulated emission is generated if this is useful for our purpose. F.very laser material is after all also a luminescent material. 

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