Residual Doppler Effect on Electromagnetically Induced Transparency in a Zeeman Sublevel System

We investigate the residual Doppler effect on the linewidth of electromagnetically induced transparency (EIT) in a Zeeman sublevel system where a careful experimental design ensures the smallest measurement error. The overall measurement error of the EIT linewidth is estimated to be less than 5%. We present the linear dependence of EIT resonance broadening at small angular deviation in detail. The theoretical analysis exploits the dependence of this feature and shows the qualitative agreement between numerical results and experimental results.