Single-colour resonant multiphoton ionization transitions of atomic gadolinium have been investigated by resonance ionization mass spectrometry. A total of 72 transitions have been found in the wavelength range of 530 - 635 nm. The wavelengths, relative intensities, linewidths and isotope shifts have been obtained for most of these transitions. In addition, the initial state for each transition has also been assigned employing the multicolour pump - probe technique. From the analysis of these transitions, it is found that most of the observed transitions arise from the three-photon process via the resonant first or second state and their isotope shifts correspond well with those of the resonant states. Based on these results, we have proposed new high-lying states and have determined isotope shifts of several excited states.
The multiphoton excitation of rubidium has been investigated over the 4600-6500-\AA{} wavelength region with a tunable dye-laser source having a linewidth better than 0.1 \AA{} and a space-charge ionization detector sensitive to a few ions per second. Multiphoton transitions have been observed to occur both through intermediate atomic states and through intermediate continuum states of the rubidium molecule. In the former case two-photon transitions have been observed from the
52S ground state of atomic rubidium to higher-lying
n2D levels for values of
n ranging from 9 to 34 and to
n2S levels for values of
n from 11 through 20. The fine-structure intervals of the
n2D levels for
n=9toc13 were measured together with the line-strength ratios and were found to be in good agreement with the predictions of a simple theoretical model. At the shorter wavelengths hybrid two-photon resonances were observed to be excited through resonant intermediate continuum states of
Rb2. As a result the dispersion curve for two-photon absorption in rubidium showed what appears to be resonant intermediate $p\ensuremath{\pi}(^{3}\ensuremath{\Sigma}_{u1})$ and
0g+ terms dissociating to give a
5P23 atom and resulting in the strong development of features corresponding to the $5^{2}P_{\frac{3}{2}}\ensuremath{\rightarrow}n^{2}D_{\frac{3}{2},\frac{5}{2}}$ part of the diffuse series, for $n\ensuremath{\le}50$ in absorption and the $5^{2}P_{\frac{3}{2}}\ensuremath{\rightarrow}n^{2}S_{\frac{1}{2}}$ part of the sharp series. Components to
322D and
302S were recorded to a precision of 0.3 ${\mathrm{cm}}^{\ensuremath{-}1}$ and quantum defects for these previously unobserved terms were derived. The corresponding hybrid two-photon resonances involving intermediate states dissociating to give a
52P21 atom were not observed in the wavelength interval available in this experiment.
This work reports the multiphoton ionization of cesium atoms, via resonance with the
6F level, by interaction with a single transverse and longitudinal mode neodymium-glass laser beam. At a low rate of ion production, when the laser frequency is tuned through resonance, the laser intensity necessary to create a constant number of ions passes through a minimum, as expected, for a three-photon energy equal to the unperturbed $6S\ensuremath{\rightarrow}6F$ transition energy. But for a higher ionization rate, involving larger laser intensities, a departure from expectation is observed which is interpreted as a consequence of an energy shift of the transition. The level shifts are demonstrated in another way by their strong effect on the experimental order of nonlinearity of the interaction,
Kexpt. A sharp variation of
Kexpt is observed when the energy shift of the $6S\ensuremath{\rightarrow}6F$ transition exactly compensates the wavelength detuning of the laser. The latter method gives shift values which are found to be independent of the large variations of the interaction volume under conditions of resonance. Both methods give a linear dependence of the shifts on the laser intensity. Identification of these shifts with energy shifts of the $6S\ensuremath{\rightarrow}6F$ transition is subject to theoretical reservations and needs further experimentation.
By focusing an excimer pumped dye laser on an atomic beam, the authors have observed multiphoton multiple ionisation of the neutral strontium atom in the tuned wavelength range 532-41 nm. Sr + and Sr ++ yields were measured with a time of flight spectrometer. At least three photons are required to produce Sr + and eight photons to produce Sr ++ . As a function of the wavelength, the Sr + yield exhibits resonances which correspond to two-photon excitation of bound states (5s 2 -5p 2 1 D 2 and 5s 2 -5p 2 1 S 0 ) and three-photon excitation of autoionising states 4d5f J=1 and J=3 of the neutral atom. The Sr ++ yield exhibits four broad smooth resonances that they interpret, from known spectroscopic data, as two-photon (5p 1/2 -4f), three-photon (5s-6p 1/2, 3/2 ) and four-photon (5s-7d) resonances in the singly charged ion. The latter transitions start from a singly charged ion in the 5s or 5p 1/2 state reached after three- or four-photon ionisation of the neutral ground state. The variation of the Sr ++ pattern as a function of the dye laser beam intensity shows that resonances are shifted and broadened when the intensity is increased. These features have been interpreted by a perturbative treatment of Sr + ionisation based on the use of an effective Hamiltonian which takes into account higher-order terms involved in the calculation of resonance effects. Calculated multiphoton ionisation probabilities are in good agreement with experimental data.
Multiphoton ionization of strontium in the wavelength range of \AA{}558-590 nm is studied via the fluorescence from excited
Sr+(5p2P23,21) ions. The fine-structure sublevels in the singly charged ion are fully resolved and are found to be nonstatistically populated. Four- and five- (or more) photon processes are observed to populate
Sr+(5p2P) in the intensity regime of $I\ensuremath{\sim}1\ensuremath{-}50$ GW/
cm2, but no emission is detected from higher-lying states of
Sr+.
We present the first measurements of the [Xe]4f75d16s6p$\;^{11}{F_J}$11FJ excited state hyperfine coefficients and isotope shifts of spin-forbidden transitions of atomic gadolinium (Gd) at 726 and 743 nm in a hollow cathode gas discharge. In addition, we performed a King Plot analysis to determine specific mass shift and field shift constants for these lines. Moreover, we observed King Plot nonlinearity for the 743 nm transition, which is an effect recently proposed to aid in searches for hypothetical new light bosons. Spectroscopic results obtained from this study will facilitate the development of more efficient isotope separation techniques, enable narrowband laser cooling of Gd for novel dipolar physics investigations, and foster technological advances in high precision atomic clocks and quantum enhanced metrology.