The influence of multiple scattering of resonance radiation on ODR signals was observed in a dense atomic beam of Ca at a Zeeman splitting of 2.5 GHz. The experiment yielded a limit of narrowing Ɗνlim = [MATH]Ɗνnat and a maximum time of flight shift δv/v= -0.28 %.
Level-crossing effects have been detected non-optically with the use of a Rabi-type atomic-beam method. The sodium beam was excited by intense linearly polarised radiation from a CW narrow-band dye laser. Several superimposed resonances were observed in the atomic-beam signal when scanning the magnetic field around zero. The two narrower resonances are interpreted as high-order non-linear effects. They arise from the coupling of laser-induced Zeeman coherences in the ground state (including a hexa-decapole moment) with the populations of the Zeeman sublevels.
In the present study we have investigated three-photon ionization in Ca in which autoionizing states are engaged. The two-photon resonant process (from the Ca ground state 4s 2 1 S 0 ) occurred through or at least in the vicinity of one of the following states: 4s4d 1 D 2 , 4p 2 3 P 2 , 4s6s 1 S 0 , 4p 2 1 D 2 and 4p 2 1 S 0 , with the third photon either reaching the continuum directly or one of the autoionizing states. The three-photon resonant transitions to 3d m p, m f: 1 P 1 , 3 P 1 and 3 D 1 autoionizing states for m up to 21 have been observed. Some of the autoionizing resonances which we have found had not been observed before in a high-resolution one-photon absorption experiment (for J = 1) and in multiphoton experiments (for J = 3). We have compared the ionization signal as a function of the laser detuning and the laser intensity with theoretical curves obtained within a simple model (three-level atom + one-mode laser field). This gives information about the order of magnitude of the three-photon ionization probability through autoionizing states.
Characterization of the trap rf induced a.c. Zeeman shift is essential for achieving high accuracy in optical ion clocks. In this work, we demonstrate the experimental characterization of this shift using highly charged Ca14+. The transverse component of the a.c. magnetic field is measured using the Autler-Townes splitting of the equally-spaced Zeeman components of the 3P1 when the Zeeman splitting is close to resonance with the trap rf drive frequency. We observe the resulting modulation by performing quantum logic spectroscopy using the co-trapped Be+. The longitudinal component is measured from probing the Be+ magnetic field-insensitive hyperfine transition ∣F=2,mF=0⟩→∣F=1,mF=0⟩. We confirm the small influence of the a.c. Zeeman shift in highly charged ions. The employed techniques can easily be transferred to other multi-level atomic systems.
From resonance equations using density matrix formalism, we obtain several features of rf or mw optical double resonance experiments at zero field. Resonance signal intensity formulas are derived. The question of the spatial and polarization dependence is then reduced to a minimum number of parameters through the use of multipole tensors; the effect of a resonance within the excited state is formulated as a redistribution of excited state multipole moments. In the case of transitions between hyperfine sublevels which are separated on the order of the natural linewidth, coherence is produced by interference between different rf-optical transition pathways. Depending on the method of detection, such interference may lead to a dispersion-shaped contribution to the ODR line shape, as observed in the experiments on the NO A state (Bergeman and Zare, accompanying paper). Second order radiation field corrections for multiplet transitions (generalizations of the Bloch-Siegert shift) are also derived.
We report an experimental study of one- and two-photon Rabi oscillations and other coherent effects in microwave transitions between Rydberg states of calcium. Selective field ionization allows us to observe the time evolution of both the initial and final states with high discrimination. The experiments include measurements of the dependence of the one- and two-photon oscillation frequencies on microwave power and detuning from resonance. We have used the off-resonant behavior of the two-photon oscillation frequency to measure the ac Stark shift. In a magnetic field we have also observed the free evolution of the magnetic sublevels and the effect of Zeeman splitting on the one-photon Rabi oscillations. The theory for these experiments is presented; our results are in excellent agreement.