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中国激光(英文版)

Cascade Two photon Correlated emission Optical Bistability

Huang Hongbin

Published Jan 1, 1998• 0 citations
OpenAlex

Abstract

A new kind of optical bistability, the cascade two photon correlated emission optical bistability (CEOB) studied. The results show that the cascade two photon CEOB can generate not only phase squeezings of light but also photon number squeezings of light in either nonresonant or resonant two photon CEOB. In any cases, the field squeezings are produced only in the lower branch of CEOB. It is also found that the field squeezings, the critical values of cooperativity C and the operations of CEOB are all affected by atomic coherences, atomic populations, and one photon detunings.

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A new kind of optical bistability, the cascade two photon correlated emission optical bistability (CEOB) studied. The results show that the cascade two photon CEOB can generate not only phase squeezings of light but also photon number squeezings of light in either nonresonant or resonant two photon CEOB. In any cases, the field squeezings are produced only in the lower branch of CEOB. It is also found that the field squeezings, the critical values of cooperativity C and the operations of CEOB are all affected by atomic coherences, atomic populations, and one photon detunings.
A new kind of optical bistability—the correlatedemission optical bistability(CEOB) in which coherently pumped atoms with n-1 almost degenerate lowlevels and m+1 almost degenerate upper levels are injected into a cavity randomly, and undergo multiple effective two-photon transitions in the cavity has been studies. The results show that the effective two-photon CEOB can generate phasesqueezed state of light from an ordinary vacuum only in the low branch of CEOB, and perfect photonnumber squeezings of light from a squeezed vacuum only in the high branch of CEOB. It is also find that the critical values of cooperativity C and the operations of CEOBs are all affected by atomic coherences and atomic populations.
I show that, in the case of both one- and two-photon resonances, a many-cascade two-photon correlated-spontaneous-emission laser can generate light exhibiting phase and photon-number squeezings. Optimizing the mean photon number in the cavity with respect to a phase factor sin[1/2(n-1)\ensuremath{\theta}]/sin(1/2\ensuremath{\theta}), we find that the maximized mean photon number and its squeezing increase with increasing the top populations ${\mathrm{\ensuremath{\rho}}}_{\mathit{n}\mathit{n}}^{\mathit{a}}$ of the active atoms. However, the photon-number squeezing may decrease, increase, or not change when increasing the number n-1 of lower, almost degenerate atomic levels, depending on the relative phase \ensuremath{\theta} of lower atomic states determined by the optimization conditions. The phase squeezing has a maximum value with increasing n-1 and ${\mathrm{\ensuremath{\rho}}}_{\mathit{n}\mathit{n}}^{\mathit{a}}$.
Both stationary and time-dependent regimes of operation, instabilities, and phase squeezing are investigated in the off-resonant two-photon correlated-spontaneous-emission laser by numerical calculation. Initial atomic coherence plays an essential role in lasing without population inversion, phase locking, and phase noise squeezing in the system. Under certain conditions, in the inverted and noninverted regimes alike, the output intensity exhibits bistable behaviors against the initial atomic coherence. Depending on the parameters, the whole or a portion of the upper or lower branch gives stable operations. In the inverted regime, even tristable behavior can be found in a narrow range of parameters. The field evolution and dynamics are studied. Furthermore, phase noise reduction near bistable areas is also investigated. In addition to the lower branch, where from previous studies, it has been known to exist, phase squeezing is also found on the upper branch both with and without population inversion, thus generating a bright source of phase noise squeezed light.
A quantum theory of two-photon correlated-spontaneous-emission lasers (CEL's) is developed, starting from the exact atom-field interaction Hamiltonian for cascade three-level atoms interacting with a single-mode radiation field. We consider the situation where the active atoms are prepared initially in a coherent superposition of three atomic levels and derive a master equation for the field-density operator by using a quantum theory for coherently pumped lasers. The master equation is transformed into a Fokker-Planck equation for the antinormal-ordering Q function. The drift coefficients of the Fokker-Planck equation enable us to study the steady-state operation of the two-photon CEL's analytically. We have studied both resonant two-photon CEL for which there is no threshold, and off-resonant two-photon CEL for which there exists a threshold. In both cases the initial atomic coherences provide phase locking, and squeezing in the phase quadrature of the field is found. The off-resonant two-photon CEL can build up from a vacuum when its linear gain is larger than the cavity loss (even without population inversion). Maximum squeezing is found in the no-population-inversion region with the laser intensities far below saturation in both cases, which are more than 90% for the resonant two-photon CEL and nearly 50% for the off-resonant one. Approximate steady-state Q functions are obtained for the resonant two-photon CEL and, in certain circumstances, for the off-resonant one.