Figure 3

EIT spectra at different interaction lengths l. a). Unnormalized EIT spectra at different interaction lengths l. Bottom X-axis (\(\Delta _{\text{c}}\)) is the detuning of the coupling laser, and Y-axis (\({T}_{\text{p}}\)) is probe transmission. The EIT spectra at different interaction lengths are added with a 5 MHz horizontal shift by hand sequentially to display each spectrum clearly (solid line). A blue dot mark the point of maximum transmission for each spectrum (\(A_{\text{EIT}}\)). The blue dashed line is a linear fit to the maximum transmission as a function of the interaction length (upper X-axis). b). Normalized EIT spectra at different interaction lengths l. Y-axis (\(T_{\text{p}}\)) is normalized probe transmission