Effect of thermal motion on the phenomenon of electromagnetically induced transparency

Atoms and molecules are always in random thermal motion, especially in gas system. This paper investigated the effect of thermal motion on Electromagnetically induced transparency (EIT). During this course, we adopt the theory of density matrix equation for the description of a ladder-type three-level system. 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.