Microwave studies of the dynamic Stark shift

A study of the dynamic Stark effect for the (J,K)=(1,1) and (3,3) inversion spectral lines of NH 3 is presented. When the gas in the waveguide absorption cell is strongly driven by off-resonant microwave radiation and probed by a second weak source of radiation, the absorption line profiles are both broadened and shifted. Investigations of this effect in the microwave region have previously been hindered by an inability to separate the weak probe radiation from the strong pump radiation. This experiment uses a balanced-bridge technique to prevent the pump radiation reaching the crystal detector used to monitor the probe radiation. Theoretical calculations of the Stark shifts, which take in to account the variation of electric field across the cell and the M-degeneracy of an inversion level, agree closely with the measured values.