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[en] There has been substantial recent experimental interest in the ratio of double-to-single photoionization of He near threshold following several theoretical observations that earlier measurements appear to overestimate the ratio, perhaps by as much as 25%, in the first several hundred eV above threshold. The authors recent measurements are 10%-15% below these earlier results and more recent results of Doerner et al. and Samson et al. are yet another 10% lower. The authors will compare these measurement with new data, not yet analyzed, and available theory
[en] New experimental results on the photoexcitation of Cd and In spin isomers by real and virtual photons (electrons) in the threshold energy region are presented. Measurements have been performed using the INR LUE-8 electron linac. The results are compared with theoretical calculations within the phenomenological models. There is a discrepancy between experimental data and theoretical calculations.
[en] The Sturmian expansions of the multiphoton transition matrix elements diverge in the case of above-threshold ionization (ATI). To get convergent expressions one must use the analytical continuation methods. The method proposed in this paper is based on the analytical continuation of the radial transition matrix elements developed earlier for the two-photon ATI and is proved to be valid for the number of photons up to nine with one additional photon involved. Transition rates for ATI of atomic hydrogen in the ground state with one extra photon by linearly polarized light are calculated. A good agreement with experiments is obtained. 19 refs.; 8 figs.; 1 table
[en] Full text: The optical breakdown in air of atmospheric pressure has been investigated at the wavelengths 1064 nm and 532 nm, and using a combination of both radiations, as well. To achieve this goal, a commercial Q-switched flash lamp pumped Nd:YAG laser with a pulse length of 5.6 ns FWHM was frequency doubled via a KTP crystal. Conversion efficiencies of up to 60 % have been obtained. The dominant process for the optical breakdown of gases is the electron avalanche process, where electrons absorb energy from the electrical field of the laser radiation by inverse bremsstrahlung. If the electron energy overcomes the ionization potential an atom or molecule can be ionized by impact ionization and a second free electron is generated. So the number of free electrons exponentially grows. To start this process, initial free electrons are required which can originate from aerosols or are generated by multiphoton ionization. The obtained thresholds for optical breakdown at 1064 nm and 532 nm have been compared and lie in good agreement with theory. The generated plasmas have been characterized by their amount of scattered laser light, energy transmission and temporal transmission. (author)
[en] Charge storage in injection lasers under transient forward bias has been found to be responsible for the difference in the observed threshold for a driving current pulse with and without another pulse preceding it. Estimated relative threshold currents of two successive pulses as a function of pulse spacing based on the charge storage model agreed reasonably well with the experiment. (U.S.)