NONADIABATIC BEHAVIOR OF THE POLARIZATION OF ELECTRIC-FIELD-INDUCED LYMAN-ALPHA RADIATION

The linear polarization of Lyman-± radiation emitted when hydrogen atoms in the metastable 2s1/2 state traverse an external electric field is studied as a function of the effective rise time of the field for field strengths extending from very small values up to 6 keV/cm. With decreasing rise time, the measured polarization exhibits a transition from adiabatic to sudden behavior. The transition region is centered at a rise time which is approximately equal to the characteristic time associated with the 2s1/2-2p1/2 Lamb splitting in the unperturbed hydrogen system. The experimental data are well described by the results of a time-dependent theory. © 1990 The American Physical Society.