Modulation transfer in an electromagnetically induced transparency system

Near the condition of electromagnetically induced transparency in a three-level system, the absorption experienced by the weak probe laser beam interacting with one transition is very sensitive to the frequency detuning of the strong-coupling laser beam coupled to another transition. When the frequency detuning of the coupling laser is modulated at different frequencies, the resulting change in probe absorption as a function of that modulation frequency can be described by a transfer function. The effects on the transfer function from various experimental parameters are calculated numerically. Experimental measurements are shown to be in good agreement with the predicted behavior.