Multiphoton Ionization Of Rare Gases Research Articles

Autocorrelation measurement of subpicosecond pulses by using multiphoton ionization of rare gases

Autocorrelation measurement of subpicosecond pulses by using multiphoton ionization of rare gases

Photoelectron imaging spectrometry: Principle and inversion method

A new photoelectron spectrometer has recently been used to analyze the energy and spatial distribution of photoelectrons produced by multiphoton ionization of rare gases. It is based on the analysis of the image obtained by projecting the expanding electron cloud resulting from the ionization process onto a two-dimensional position sensitive detector by means of a static electric field. In this article, we present the principle of this imaging spectrometer and the relevant equations of motion of the charged particle in this device, together with an inversion method that allows us to obtain the energy and angular distribution of the electrons. We present here the inversion procedure relevant to the case where the electrostatic energy acquired in the static field is large as compared to the initial kinetic energy of the charged particles. A more general procedure relevant to any regime will be described in a following article.

Photoelectron-spectroscopy of multi-photon ionization of rare gases with circularly and linearly polarized light

Above-threshold multiphoton ionization of xenon, krypton, and argon was studied with circularly and linearly polarized light (photon energy 1.17 eV and 2.33 eV). With linearly polarized light photoelectrons are preferentially ejected along the direction of the polarization vector. With circularly polarized light a strong suppression of ejected photoelectrons was observed; the measured yield of photoelectrons was reduced by factors of up to 80 depending on the laser intensity and the photon energy. The experimental results are compared with theoretical calculations based on a multiphoton-detachment model.

Multiphoton ionization of rare gases using multichannel-quantum-defect theory.

We apply multichannel-quantum-defect theory (MQDT) to multiphoton ionization of rare gases in lowest-order perturbation theory. We determine MQDT parameters of J = 1,3 odd-parity states, J = 0,2 even-parity states in xenon and krypton by fitting experimental energy levels and constructing Lu-Fano plots. We present calculations of two- and three-photon ionization of xenon and krypton in the autoionization region between the two thresholds. We compare autoionization spectra and also photoelectron angular distributions to experimental data (S. T. Pratt, P. M. Dehmer, and J. L. Dehmer, Phys. Rev. A 35, 3793 (1986); J. L. Dehmer, S. T. Pratt, and P. M. Dehmer, ibid. $fat 36: , 4494 (1987)). Agreement between theory and experiment is reasonable, especially for krypton.

Multiphoton ionization of many‐electron atoms

AbstractWe review the main experimental results obtained in the multielectron multiphoton ionization of rare gases. Multiple ionization is interpretated as a sequential process. We study the influence of many‐electron effects in multiphoton ionization within the framework of the random phase approximation. This is applied to a calculation of the two‐photon ionization cross section of xenon. Finally, the role of screening effects in the multiphoton stripping of heavy atoms (Xe) is estimated.

Laser-intensity effects in the energy distributions of electrons produced in multiphoton ionization of rare gases

The energy spectra of electrons produced in multiphoton ionization of rare gases display a large number of peaks corresponding to the absorption of much more than a minimum number of photons required to ionize the atom. A retarding-potential method has been used to analyze the energy of electrons produced in the multiphoton ionization of He, Ne, and Xe at 1064 and 532 nm in a broad range of laser intensities (1013–1015 W cm−2). The intensity dependence of energetic electrons emphasizes the validity of the IM law, where M is the total number of photons absorbed. The shape of the electron energy distribution can be completely changed when the laser intensity is increased. The maximum of the energy distribution is switched from the slowest electron peak to faster electron peaks. The distortion of the energy distribution is generally strongly asymmetric, with a steep gradient at the low-energy edge. At 1064 nm, this leads to the disappearance of the first peak in Xe at 4 × 1013 W cm−2, whereas in Ne the first three peaks disappear at 4.3 × 1014W cm−2 and the first thirteen peaks disappear at 7.8 × 1014W cm−2. These effects are still more marked in He in comparison with other higher-Z atoms. The present experimental results could be explained by a model based on continuum–continuum transitions.

Multiphoton ionization of rare gases by a tunable-wavelength 30-psec laser pulse at 1.06 μm

Multiphoton ionization of xenon, krypton, and argon atoms has been investigated by using a tunable-wavelength bandwidth-limited 30-psec laser pulse of ${10}^{13}$ W/${\mathrm{cm}}^{2}$ at 1.06 \ensuremath{\mu}m. The laser linewidth is 0.8 ${\mathrm{cm}}^{\ensuremath{-}1}$, and the laser wavelength can be tuned over a range of 80 \AA{}. No resonant effects have been observed within this wavelength range, although resonance conditions are satisfied. The absence of resonance effects could be explained in terms of the short laser pulse duration. Laser light polarization effects were still measured. Moreover, the ionization energy of krypton has been observed to be lowered by 86\ifmmode\pm\else\textpm\fi{}6 ${\mathrm{cm}}^{\ensuremath{-}1}$ under the influence of a laser electric field of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{8}$ ${\mathrm{Vcm}}^{\ensuremath{-}1}$.

Multiphoton Ionization of Rare Gases at Very High Laser Intensity (1015W/cm2) by a 30-psec Laser Pulse at 1.06 μm

Multiphoton Ionization of Rare Gases at Very High Laser Intensity (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mn>10</mml:mn></mml:mrow><mml:mrow><mml:mn>15</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>W/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">cm</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>) by a 30-psec Laser Pulse at 1.06 μm

Multiphoton ionization of rare gases at 1.06µ and 0.53µ

The interaction between an intense focused beam of optical photons and matter in gaseous form at low pressure (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> torr) brings into play some strongly nonlinear processes. These multiphoton processes occur through the simultaneous absoprtion of several quanta by an atom that may be thus either excited or ionized. The orders of nonlinearity of the interaction of a multimode <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched laser beam with rare gas atoms were measured with laser intensities up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> W ċcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at 1.06μ and up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> W ċcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at 0.53μ. The energy of the number of quanta corresponding to the order of nonlinearity is always close to the energy of an atomic level. The results seem to emphasize the particularly important role performed by bound states during the ionization process. Thus a two-stage ionization process seems far more probable than a single direct transition between the ground state and the continuum spectrum. Experimental values of multiphoton ionization probabilities are also given after having precisely determined the spatiotemporal intensity distribution function.

Multiphoton ionization of rare gases at 1.06 μ and 0.53 μ

The order of the non-linear processes appearing upon the interaction of 1.06 μ and 0.53 μ laser beams with rare gases has been determined. Excited levels seem to play a dominant role in this multiphoton ionization.