Two-photon excitation/ionization of deep shells of multiply charged atomic ions

Absolute values and the shape of cross sections for two-photon one-electron excitation/ionization of the 1s shell of Ne⁶⁺ and Ne⁸⁺ ions, taking into account the relaxation of the atomic core in the field of resulting vacancies, are calculated. The many-particle stabilization of a deep vacancy in moving from a neutral atom to multiply charged ions is taken into account. The calculations are made for linear and circular polarizations of the incident laser beam. The results of the calculations are predictive.     

Coincidence studies of electron impact ionization of atomic inner shells

We consider (e,2e) processes on the 2s and 2p shells of argon and magnesium. We present triple differential cross sections in coplanar asymmetric geometry calculated in the Plane Wave Born, 1st Born and Distorted Wave Born approximations. We show that the currently available relative experiments can not easily distinguish between these approximations. We make proposals for relative experiments where the difference between these approaches can be more readily observed.     

Two-photon excitation of atomic oxygen in a flame

Atomic oxygen has been detected in a lean acetylene/oxygen flame using the 2p⁴³P₂-2p³3p³P two-photon transition at 226 nm and fluorescence detection at 845 nm.     

Two-photon excitation of atomic oxygen using a Raman-shifted ArF-excimer laser

A novel method for exciting the two-photon 2p ³ 3p ³ P 2p ^{4 3} P atomic oxygen transition is reported. The transition energy is provided by the combined photon energies of the second and third Stokes orders of a deuterium-filled Raman shifter pumped by an ArF-excimer laser. The ArF-excimer-pumped Raman shifter performance is characterized and the approach is demonstrated in an atomic oxygen population created by molecular oxygen absorption and predissociation in room air.     

Two-photon excitation and ionization of the 2s shell of the argon atom

The absolute values and the form of the cross section for two-photon one-electron excitation and ionization of the deep 2s shell of the Ar atom are calculated taking into account the many-body effects of relaxation of the atomic core in the fields of arising virtual vacancies and the decay of vacancies via the Auger and (or) radiative channels. The one-electron wave functions are calculated in the nonrelativistic approximation. The appearance of the Cooper minimum in the two-photon absorption cross section is established. The calculations are carried out for the linear and circular polarizations of photons of an incident laser beam.     

Influence of multi-photon excitation on the atomic above-threshold ionization

Using the time-dependent pseudo-spectral scheme, we solve the time-dependent Schr ¨odinger equation of a hydrogenlike atom in a strong laser field in momentum space. The intensity-resolved photoelectron energy spectrum in abovethreshold ionization is obtained and further analyzed. We find that with the increase of the laser intensity, the abovethreshold ionization emission spectrum exhibits periodic resonance structure. By analyzing the population of atomic bound states, we find that it is the multi-photon excitation of bound state that leads to the occurrence of this phenomenon, which is in fairly good agreement with the experimental results.     

Enhanced plasmon excitation in inner level ionization in Si and Mg

The low energy satellite structure of the ionization peak of Si and Mg has been studied. It is found that plasmon losses associated to the L₂₃ ionization level have intensities comparable to those of the main peak. By relating these observations to the plasmon losses in the elastic peak, it is concluded that plasmon creation by an incident electron beam is enhanced by ionization processes.     

Internal conversion in inner shells of atomic ions and relativistic ionic potentials

Internal conversion coefficients for inner shells of atomic ions of Sn are calculated for various degrees of ionization and compared with neutral atom predictions. The relativistic version of an analytic perturbation theory is used to include screening effects.     

Collisional alignment and orientation of atomic outer shells. III. Spin-resolved excitation

The review generalizes the formalism of the first part of this series [N. Andersen, J.W. Gallagher and I.V. Hertel, Phys. Rep. 165 (1988) 1–188] on electron-atom collisions to cases where the spin polarization of the electron is investigated at least once, i.e., before and/or after the collision. In addition, the target atom may be spin polarized. The preparation of initially polarized beams and/or the analysis of photon and spin polarization in the final state significantly increase the number of cases where a “perfect scattering experiment” can be performed. The connection between the scattering amplitudes and the generalized Stokes and STU parameters is analyzed. Favorable scattering geometries for perfect experiments and possibilities for consistency checks are pointed out. Recommendations are made about directions of future work.     

The relative role of shake-up and shake-off processes in additional monopole excitation of L and M electrons due to inner atomic shell ionization

The probabilities of additional monopole excitation (shake-up) and ejection (shake-off) processes for electrons of the L and M shells upon K and L ionization for atoms with 3 ≤ Z ≤ 38 are calculated in the sudden perturbation approximation. With increasing atomic number, the portion of the nl-electron shake-offs in the total probability of monopole shake-up/shake-off processes increases from several percent in the beginning of the nl subshell population to above 50% after its filling. Within one shell, the shake-off processes are relatively more probable for electrons with smaller orbital quantum numbers.     

Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

Two-photon resonant three-photon ionization with ultrashort pulses

The problem of two-photon resonant three-photon ionization is analysed for the case of ultrashort ionizing pulses. An analytic solution to the problem is obtained and discussed. A simple experiment is proposed which would demonstrate the effect of optical nutation on the photoelectron flux.     

Two-photon spectroscopy in a fast atomic beam

We suggest the use of a fast atomic beam to obtain resonance enhancement in Doppler-free two-photon spectroscopy. The method requires only one laser frequency thus avoiding the complications due to a residual Doppler shift.     

Two-photon near- and far-field fluorescence microscopy with continuous-wave excitation

We report on scanning far- and near-field two-photon microscopy of cell nuclei stained with DAPI and bisbenzimidazole Hoechst 33342 (BBI-342) with the 647-nm laser line of a cw ArKr mixed-gas laser. Two-photon-excited fluorescence images are obtained for 50-200 mW of average power at the sample. A nearly quadratic dependence of fluorescence intensity on laser power confirmed the two-photon effect. The nonlinearity was further supported by evidence of three-dimensional sectioning in a scanning far-field microscope. We find that the cw two-photon irradiation sufficient for imaging within typically 5 s does not significantly impair cell cycling of BBI-342-labeled live cells. Finally, high-resolution imaging in scanning near-field microscopy with good contrast is demonstrated.