Atomic excited-state Faraday anomalous dispersion optical filter in the reflection configuration

An excited-state Faraday anomalous dispersion optical filter (ES-FADOF) operating in a reflection configuration at a wavelength of 917 nm is experimentally demonstrated based on the cesium (¹³³Cs) 6S_1/2 → 6P_3/2 → 6D_5/2 (852 nm + 917 nm) ladder-type atomic system. The 852 nm laser acts as the pump light populating Cs atoms from the 6S_1/2 ground state to the 6P_3/2 intermediate state, while the frequency of 917 nm laser as the signal light is scanned across the 6P_3/2 → 6D_5/2 transition, so an ES-FADOF spectral signal is obtained. Experimental results show that the performance of ES-FADOF remains nearly identical whether the pump and signal light beams are co-propagating or counter-propagating within the atomic vapor cell. Building on this observation, a reflection-type ES-FADOF is achieved for the first time, which allows signal light to pass through the atomic medium twice round trip, doubling the effective length of the vapor cell, so its peak transmission is obviously improved compared to popular ES-FADOF, where the signal light beam passes through the atomic vapor only once. This technique can be applied to the other FADOF systems, especially suitable for atomic media with high melting points.