Electric field measurement for a 320GHz wave by Rydberg-atom based sensor

Research on Rydberg-atom based sensers, which realize the SI-traceable measurements for the electric field of Terahertz wave, have been started. The ladder-type EIT (Electromagnetically Induced Transparency) signals were observed by counterpropagating lasers of two distinct wavelength lasers corresponding to the $S-P-D$ transitions of Cesium (Cs) atoms enclosed in a cylindrical glass cell. Irradiation of a 320GHz wave whose frequency matched the $D-F$ transition then results in an observed Autler-Townes (AT) splitting of the EIT signals. The electric field strength was calculated by frequency measurement of the splitting separation.