Tensor polarizability of the ground-state hyperfine structure of thallium

The atomic-beam magnetic-resonance technique has been used to measure the hyperfine-structure tensor polarizability (quadratic Stark effect) in the 6²P1/2 ground state of atomic thallium. Electric fields of up to 460 kV/cm were used to lift the degeneracy between the mF=0 and the mF=±1 substates in the absence of an external magnetic field, and focusing transitions between these Stark-separated states were observed. Measurements were also made between Zeeman-separated substates. The results are αT=-(3.74±0.09)×10^-8 Hz/(V/cm)², or k=-(5.62±0.14)×10^-8 Hz/(V/cm)², where δν=kE² is the Stark shift of the (mF=0)↔(mF=-1) "flop-in" transition.