Intensity Modulation of Transmitted Light at the Ground-State Hyperfine Frequency ofK39

This paper discusses intensity modulation of transmitted light at 462 MHz due to coherence between sublevels of the ${\mathrm{K}}^{39}$ ground state. A concise theory of transmitted-light modulation is presented, using the density-matrix and monitoring-operator formalism. The theory and construction of an ultrahigh-frequency photodetection system is described. The auxiliary apparatus is also described, together with experimental conditions under which signals have been observed. It is suggested that a possible application of this technique is a wide-range magnetometer.