Optically pumped frequency standard with reduces AC stark shift

An apparatus for generating a stabilized frequency signal is disclosed. The apparatus includes a quantum absorber having first, second, and third energy states. The quantum absorber is irradiated by a first radiation source that generates electromagnetic radiation having a frequency, nuL, that induces transitions between the first and third energy states. The quantum absorber is also irradiated by a second radiation source that generates electromagnetic radiation having a frequency, nuM, that induces transitions between the first and second energy states. A detector that generates a detector signal indicative of the level of radiation leaving the quantum absorber in a frequency range including nuL is used by a number of servo loops. One of the servo loops determines the value of nuL that minimizes or maximizes the detector signal and a second servo loop determines an offset signal that reduces the dependence of nuM on the intensity of the first radiation source.