Search results for "IONIZATION"
showing 10 items of 1255 documents
Piecewise static Hamiltonian for an atom in strong laser field
2009
We show that it is possible to use a piecewise constant Hamiltonian to describe the main features of the dynamics of an atom interacting with a laser field. In particular we show that using this approximation we are able to give a good description of the ionization signal, of the HHG spectra and of the attosecond pulses generated by the radiating electron. Finally, we give an explicit formula to evaluate the ionization rate in the time dependent laser field. This formula, which is a generalization of the Landau formula for the ionization rate of an atom in a static electric field, fairly well reproduces the numerical ionization rates for a broad range of laser frequency and intensity. The m…
First Observation of Atomic Levels for the Element Fermium (Z=100)
2003
The atomic level structure of the element fermium was investigated for the first time using a sample of $2.7\ifmmode\times\else\texttimes\fi{}{10}^{10}$ atoms of the isotope $^{255}\mathrm{F}\mathrm{m}$ with a half-life of 20.1 h. The atoms were evaporated from a filament and stored in the argon buffer gas of an optical cell. Atomic levels were sought by the method of resonance ionization spectroscopy using an excimer-dye-laser combination. Two atomic levels were found at wave numbers $(25\text{ }099.8\ifmmode\pm\else\textpm\fi{}0.2)$ and $(25\text{ }111.8\ifmmode\pm\else\textpm\fi{}0.2)\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}1}$. Partial transition rates to the $5{f}^{12}7{s}…
Rydberg and autoionizing states of tellurium studied by laser resonance ionization spectroscopy
2019
Multistep laser-resonance-ionization spectroscopy of tellurium (Te) has been performed at TRIUMF's off-line laser ion source test stand. Six clean and regular even-parity Rydberg series $5{p}^{3}$ $({^{4}S}_{3/2}^{\ensuremath{\circ}})$ $np\phantom{\rule{4pt}{0ex}}^{3}P_{0,1,2}$, $np\phantom{\rule{4pt}{0ex}}^{5}P_{1,2}$, and $nf\phantom{\rule{4pt}{0ex}}^{3}F_{2}/^{5}F_{1,2}$ were observed. The ionization potential of Te was extracted from the measured series as $72669.114{(56)}_{\mathrm{stat}}{(45)}_{\mathrm{sys}}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Excited from two different intermediate levels, seven odd-parity autoionization Rydberg series converging to the $5{s}^{2}…
Determination of the first ionization potential of technetium
2010
Using resonance ionization spectroscopy the first-ionization potential of actinium has been determined by analyzing different Rydberg series in two-color resonant laser excitation. Three individual Rydberg series were investigated, converging toward the ionic ground state and toward the first- and second-excited state of the actinium ion, respectively. A combined analysis of the convergence limits leads to a consistent value for the first-ionization potential of Ac of $43\phantom{\rule{0.16em}{0ex}}394.45\phantom{\rule{0.16em}{0ex}}(19)\phantom{\rule{0.28em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$, equivalent to $5.380\phantom{\rule{0.16em}{0ex}}226\phantom{\rule{0.16em}{0ex}}(24)$ eV.
Towards Laser Spectroscopy of Superheavy Elements
2016
The sensitivity of laser spectroscopic methods has been increased over the past two decades dramatically so that today the spectroscopy of superheavy elements appears on the horizon as a realistic option. For elements with Z > 100 no experimental atomic or ionic level structure information is known so far. These elements cannot be bread in high flux nuclear power reactors via successive neutron capture and \(\beta ^-\) decay but must be produced in accelerator-based nuclear fusion-evaporation reactions. Laser spectroscopic investigations at low rates take advantage of the storage of ions or atoms in rare gas traps. A first successful experiment was conducted only recently for the element no…
Total angular momenta of even-parity autoionizing levels and odd-parity high-lying levels of atomic uranium
2002
Using three-step resonance ionization spectroscopy, over 200 even-parity autoionizing (AI) levels of atomic uranium, including Rydberg series converging to the second lowest ionic level (6L 11/2o), were observed in the 49 930–51 200 cm−1 energy range. Total angular momenta (J values) of these levels were determined by a polarization combination method as well as a method based on the J-momentum selection rule. Using the AI levels of which J values were determined unambiguously, unique J values were also assigned for about 70 high-lying odd-parity levels. The observed J-dependence on autoionization linewidth is interpreted as being due to a centrifugal potential barrier.
Wavelength dependence of multiphoton ionization of xenon
2004
We have studied the multiphoton ionization of xenon atoms by $160\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ pulses at intensities of $5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ and $1.3\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ and present photoelectron kinetic energy and angular distribution spectra measured with a photoelectron imaging spectrometer. A noncollinear optical parametric amplifier allows us to tune the wavelength of the laser pulse over a range between 500 and $700\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Resonant and nonresonant processes as well as channel switching effects have been observed in this intensity and wavel…
Ionization of Rb and Na Rydberg atoms by blackbody radiation
2007
This work presents the results of the numerical calculations of (blackbody radiation) BBR-induced photoionization rates of Rb and Na Rydberg nS, nP and nD atoms with n = 8-65 at the ambient temperatures of 77, 300 and 600 K.
The role of synchrotron self-absorption in the late radio emission of SN1993J
2001
The standard model for radio supernovae considers that the observed synchrotron radio emission arises from the high-energy shell that results from the strong interaction between the expanding supernova ejecta and the circumstellar medium. This emission is considered to be only partially absorbed by ionized thermal electrons in the circumstellar wind of the progenitor star. Based on a study of the radio light curves of the type II supernova SN1993J, we present evidence of synchrotron self-absorption. Our modeling of the radio light curves requires a large initial magnetic field, of about 30 Gauss, and the existence of an (initially) highly-relativistic population of electrons. We also show t…
Results from Droxo
2007
AIMS. We study the variability of the Fe 6.4 KeV emission line from the Class I young stellar object Elias 29 in the Rho-Oph cloud. METHODS. We analysed the data from Elias 29 collected by XMM during a nine-day, nearly continuous observation of the Rho-Oph star-forming region (the Deep Rho-Oph X-ray Observation, named Droxo). The data were subdivided into six homogeneous time intervals, and the six resulting spectra were individually analysed. RESULTS. We detect significant variability in the equivalent width of the Fe 6.4 keV emission line from Elias 29. The 6.4 keV line is absent during the first time interval of observation and appears at its maximum strength during the second time inter…