Hyperfine structure and collisions in three-photon Rydberg electromagnetically induced transparency

Multiphoton electromagnetically induced transparency (EIT) of atomic vapors involves several intermediate atomic levels. The substructure of these levels and their collisional interactions can drastically alter experimental EIT signals. Here we report on hyperfine structure and collision effects in three-photon Rydberg EIT on the cascade $5{S}_{1/2}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}5{P}_{1/2}\ensuremath{\rightarrow}5{D}_{3/2}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}25{F}_{5/2}$ in a room-temperature $^{85}\mathrm{Rb}$ vapor cell. In our measurements of EIT spectra, we identify two types of EIT signatures that correspond with distinct excitation pathways and atomic velocity classes in the atomic vapor. The $5{D}_{3/2}$ hyperfine structure and Autler-Townes splittings lead to complex patterns in the EIT spectra, which we analyze with the aid of 10-level EIT simulations. Adding 50 mTorr of Ar gas alters the EIT spectra and induces an additional, third EIT mode. Based on our simulation results, we attribute these changes to hyperfine collisions in the Rb $5{D}_{3/2}$ level. Our study may become useful in quantum technologies involving Rydberg EIT and hyperfine collisions in vapor cells, including noninvasive spatiotemporally resolved electric-field sensing of electric fields in low-pressure plasmas.