Experimental studies of perturbation of atoms by laser radiation under conditions when, due to the Stark effect, the energies of two neighboring levels become equal are reported for the first time.
Blackbody radiation is expected to produce a temperature-dependent Stark shift in atomic Rydberg states. Unfortunately, in "one-electron" atoms, all the Rydberg levels experience the same shift, and the effect is only observable on an optical transition from the ground state. However, in a many-electron atom the presence of valence-state perturbers leads to unequal shifts of the Rydberg levels. This should make it possible to observe the frequency shift of a transition between two neighboring Rydberg states at a frequency in the radio-frequency range. This eliminates the need for a very stable visible laser, which so far has been the major technical obstacle to the observation and utilization of the effect. We present as an example a specific case in Ba.
This is the first reported demonstration of the use of pair-absorption transitions for optically pumping lasers. In a mixture of barium and thallium metal vapors, single-photon absorption of 3867-A laser light caused simultaneous excitation of colliding ground-state atoms to the Ba(6s6p 1P1(o)) and Tl(6p 2P(3/2)(o)) excited states. Excited-state densities of about 10(14) cm(-3) were created, and subsequent laser emission on the Ba(6s6p 1PI(o)) - Ba(6s5d 1D2) atomic transition at 1.5 microm was observed.
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 6s2 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 Stark shift of the (6s)21S0\ensuremath{\rightarrow}(6s6p)1P1 transition in barium was measured using a laser to excite an atomic beam as it traversed a uniform electric field and a field-free region. The laser frequency was scanned across the transition while fluorescence produced by the radiative decay of the excited state was detected. The frequency scan was calibrated using an acousto-optic modulator which frequency shifted the laser by a specified amount. The Stark-shift rate was found to be -28.532\ifmmode\pm\else\textpm\fi{}0.060 kHz/(kV/cm)2. The hyperfine splitting of the 135,137Ba F=1/2 level relative to 138Ba of the (6s6p)1P1 state was determined to be -549.47\ifmmode\pm\else\textpm\fi{}0.12 MHz, where the minus sign indicates that the 138Ba transition is at a lower frequency.