We have measured the magnetic dipole (M1) and electric quadrupole (E2) amplitudes in the D1 transition of rubidium atoms placed in a static electric field, ${\mathit{scrE}\ensuremath{\rightarrow}}_{\mathit{s}}$. The interference of the Stark induced M1 and E2 amplitudes with the normal E1 amplitude gives the atomic absorptivity a linear dependence on ${\mathit{scrE}\ensuremath{\rightarrow}}_{\mathit{s}}$ and on the atomic spin polarization. We find that the fractional change in absorptivity due to the Stark interference is
aM1+
aE2=(-2.37\ifmmode\pm\else\textpm\fi{}0.37\ifmmode\pm\else\textpm\fi{}0.28)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ (kV/cm${)}^{\mathrm{\ensuremath{-}}1}$.
Dipole-dipole interactions between helium atoms in Rydberg-Stark states with principal quantum number
n=53 and approximately linear Stark energy shifts, resulting from induced electric dipole moments of approximately 7900 D, have been investigated experimentally. The experiments were performed in pulsed supersonic metastable helium beams, with particle number densities of up to $\ensuremath{\sim}{10}^{9}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. In the presence of amplitude-modulated, radio-frequency electric fields, changes in the spectral intensity distributions associated with the transitions to these states that are attributed to dipole-dipole interactions within the ensembles of excited atoms have been observed. The experimental results are in excellent agreement with calculations of the Rydberg energy level structure carried out using Floquet methods, and excitations shared by up to four atoms. The use of these Rydberg-Stark states as sensors for nonresonant broadband radio-frequency electrical noise is also discussed.
We have discovered an interference which results in the vanishing of some electric dipole transition amplitudes. A transition-matrix element
T between certain
S and
P sublevels with the same value of
MF vanishes when an applied magnetic field satisfies ${X}_{s}+{X}_{p}=\ensuremath{-}2{M}_{F}$, where $X={\ensuremath{\mu}}_{B}{g}_{J}\frac{B}{A}$, and
A is the hfs constant. There must be an avoided crossing between the two states of the same
MF which can only occur when one of the hyperfine manifolds has an inverted Zeeman effect. These conditions imply
MF<0 and
I>J. We observed the vanishing of
T in
23Na for one of the $\ensuremath{\Delta}{M}_{F}=0$ optical transitions of the $3{S}_{\frac{1}{2}}(F=1)\ensuremath{\rightarrow}3{P}_{\frac{1}{2}}(F=1)$ manifold. Absorption of cw laser light was monitored by observing total fluorescence perpendicular to both the atomic and laser beams, and absorption vanished near an applied field of 155 G.
T vanishes for a large number of cases including rf and microwave frequencies and is a rather general consequence of angular momentum selection rules and perturbation theory. This phenomenon may have application in optical pumping, Lamb-shift measurements, and atomic weak neutral-current experiments.
Quantum interference between an electric-quadrupole transition and a Stark--induced-dipole-transition amplitude leads to a net orientation of an atomic excited state. When the barium 6
s2 1S-6s5d
1D transition is excited in the presence of an electric field, we find the induced orientation of the 6s5d
1D state to be (2.86\ifmmode\pm\else\textpm\fi{}0.59)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$(V/cm${)}^{\mathrm{\ensuremath{-}}1}$.
The wavefunctions, matrix elements, and probabilities of radiative transitions between Stark sub-levels of atomic multiplets are calculated as a function of the strength of a dc electric field. The general expressions for the wavefunction of a multiplet state in a field obtained by perturbation theory for close-lying levels with the use of completely reduced Green’s function allow one to determine the field dependence of both the dipole-allowed and dipole-forbidden radiation amplitudes. A decomposition of the second-order amplitude for the transition between fine-structure sublevels of two levels of equal parity into irreducible components is obtained. Numerical calculations of the probabilities of radiative transitions between triplet states of helium show the possibility of experimental observation of the emergence and vanishing of Stark lines of radiative transitions in the vicinity of anticrossing fields.
An externally applied static electric field, by mixing opposite-parity states, can add electric-quadrupole and magnetic-dipole transition amplitudes to an allowed electric-dipole transition. The resulting interference among the amplitudes causes the absorption of resonance radiation to depend linearly on the static field and on the atomic polarization state. We present a calculation of this effect for the 254-nm line of Hg where the atomic polarization is specified by the ground-state nuclear spin, and the excited-state hyperfine structure is resolved. Possible experiments to measure this effect are pointed out.