Studies On Dynamics Of Optical Parametric Amplification Based On Four-wave-mixing Processes In The Regime Of Electromagnetically Induced Transparency

Electromagnetically induced transparency is a quantum interference effect based on the resonance interaction between coherent laser and multi-level atoms,which can greatly reduce the absorption of signal field by the medium.The dispersion property of medium can be modified dramatically by adjusting the intensity of the control field,and then the group ve-locity of signal can be manipulated.Four-wave mixing is a parametric third-order nonlinear process.Compared with traditional four-wave mixing,electromagnetically induced trans-parency provides a feasible scheme to realize enhanced coherent four-wave mixing in weak field.Electromagnetic induced transparency can enhance the nonlinearity near the resonance frequency,which makes it easier to realize nonlinear processes without strong driving field,then it is convenient to process quantum information.We now introduce the main content of this paper.Under the framework of semiclassical theory,we theoretically study the propagation dynamics of optical parametric amplification by coherent four-wave mixing in the regime of electromagnetically induced transparency.Electromagnetically induced transparency can greatly suppress the linear absorption,at the same time,enhance the nonlinear effect.Using the nonlinear gains of four-wave mixing to increase the intensity of the signal and idle fields.The highlight of our work is the explore for the dynamics of four-wave-mixing process.The previous research work mostly focused on the steady state of system,while the discusses of pulse propagation dynamics in the medium are rare so that the understanding was not perfect and the results were not accurate enough.We consider a three-level lambda-type atomic system driven by two-color fields.Only using a few approximation conditions,we accurately simulate the propagation dynamics of signal and idle pulses in medium by numerically solving Maxwell-Liouville equation.The results show that the generation of idle pulse is a slow process rather than a sudden one.The generated idle pulse is extremely weaker than signal(10^-4).The idle and signal lights propagate in fast and slow modes,respectively.The width of signal pulse is almost same as that of slow light without four-wave mixing,while the idle pulse is obviously broadened,and the broaden increases rapidly with optical depth.On the basis of previous research,we consider a four-level double-lambda atomic system for adjusting the coupling strength between light fields and atoms more conveniently.And then the four-wave mixing will be enhanced and the signal will be amplified.The numerical method is also used to simulate the dynamic evolution processes of signal and idle pulses in medium.The results show that the idle pulse is generated and amplified slowly.The intensity of the paired pulses increases with optical depth and the corresponding deformation coefficients tend to be the same with the increase of pump field.The intensity of pump and optical depth must be both large enough to realize optical amplification.The gain rate of idle is larger than that of signal when pump strength and optical depth are both increased.By analyzing the susceptibility,we find the reason for the different increasing rate between signal and idle pulses,the Raman gain is mixed in four-wave mixing process which enhances the group velocity dispersion of signal pulse,and then the pulses become wider and wider with optical depth increasing.