Influence Of Doppler Effect On The Phenomenon Of Electromagnetically Induced Transparency

Electromagnetically induced transparency(EIT)is a significant nonlinear optical phenomenon.EIT has many applications,such as slow light,quantum information storage,quantum teleportation,and so on.In this article,we present a theoretical study of a Doppler broadened cascade type three-level system,based on density matrix approach,to investigate the influence of temperature.When considering the influence of the Doppler effect of probe field,the results showed that thermal motion will influence the appearance of EIT greatly and makes EIT is relate to temperature further.An obvious transparent window can be observed only when the temperature is less than 50 K.With the increase of temperature,the depth of EIT window decreases quickly until to disappear.At room temperature,we can only see the double peaks of Aulter-Townes with strong coupling field.In addition,we have also observed an interesting phenomenon that with the increase of frequency detuning of the coupling field,the peak that is away from the resonant frequency will develop into an ultra narrow one.Thermal motion will make this narrow peak disappear.Just then,the height of the whole absorption profile increases and the line width of it decreases with the increase of frequency detuning.The frequency of the laser field due to the atom is related to the direction of light propagation.For EIT system,the Doppler effect disappears the EIT window at the resonant frequency when the coupling and the probe laser beams copropagate.While as the two laser beams counter-propagate,especially when the two lasers are with the same wavelength,we can get a broadened Doppler absorptive profile and a narrowed EIT window.The width of the EIT window decreases with the increase of temperature.But if the frequency of the two lasers are diff erent,the EIT window at resonant point will be instead by a broadened dip.This dip will disappear gradually with the increase of the frequency difference.Thus at thermal environment,when we perform the investigation associated with EIT,we ought to not only let two laser beams counterpropagate,but also select an atomic system owns a cascade equal energy interval as far as possible.In the previous study,most of people regard the probe field as a weak field,using perturbation method to solve the density matrix equation and get absorption curve.In this article,we solved the exact solution of the density matrix equations to explore the EIT effect when the probe field is strong.As the intensity of the detection field increases,an absorption peak appears at the bottom of the absorption curve at the resonant position,showing a “mollow” like curve.In the end,due to the broadening of the power of the detection field,the absorption peak of the resonant position gradually disappears and becomes an absorption peak similar to that of the two-level system.