Electromagnetically induced transparency in vacuum and buffer gas potassium cells probed via electro-optic frequency combs
David A. Long, Adam J. Fleisher, David F. Plusquellic, Joseph T. Hodges
Electromagnetically induced transparency (EIT) in 39K and 41K was probed using electro-optic frequency combs generated by applying chirped waveforms to a phase modulator. The carrier tone of the frequency comb served as the pump beam and induced the necessary optical cycling. Comb tooth spacings as narrow as 20 kHz were used to probe potassium in both buffer gas and evacuated cells at elevated temperatures. Features as narrow as 33(5) kHz were observed allowing for the 39K lower state hyperfine splitting to be optically measured with a fit uncertainty of 2 kHz. Due to the ultranarrow width of the EIT features, long-lived free induction decays were also observed which allowed for background-free detection.