xenakis_1996
============

D\. Xenakis, O\. Faucher, D\. Charalambidis and C\. Fotakis, "Observation of two\-XUV\-photon ionization using harmonic generation from a short, intense laser pulse", J\. Phys\. B\: At\. Mol\. Opt\. Phys\. 29, L457\-L463 \(1996\)

`Source record <https://github.com/LupoLab/optmat/blob/main/src/optmat/data/sources/xenakis_1996.toml>`__ · :doc:`Catalogue </the-data/sources>` · :doc:`Review register </register>`

DOI: `10\.1088/0953\-4075/29/12/003 <https://doi.org/10.1088/0953-4075/29/12/003>`__

**Source kind:** measurement

**Recorded technique:** Ar ionised by two photons of the third harmonic \(82\.9 nm, 14\.96 eV\) of a hybrid dye\-KrF excimer laser \(248\.6 nm, about 450 fs by second\-order autocorrelation, 4 Hz, up to 14 mJ, bandwidth about 170 cm\-1, ASE contrast \< 1e\-6\), the harmonic made in a pulsed Xe jet \(about 70 mbar; up to 2e15 W cm\-2 at its focus\), selected and imaged into a pulsed Ar jet \(about 1\.0 mbar\) by a gold\-coated concave grating \(600 grooves/mm, 400 mm radius\) on the Rowland circle; Ar\+ detected by a 10 cm time\-of\-flight mass spectrometer and a microchannel plate \(pp\. 3\-4/L458\-L459\)\. Near\-resonant scheme \(Fig\. 1\)\: the first photon lies between the Ar 6s'\[1/2\]1 and 6s\[3/2\]1 levels, 'detuned by 486 and \-915 cm\-1' \(Fig\. 1's caption\: 485\.6 and \-915\.5 cm\-1\); the second reaches the continuum 0\.7 eV above Ar\+ 3s3p6 \(p\. 3/L458\)\.

**Materials in structured entries:** None recorded.

**Dataset quantities:** None recorded.

**Contents:** 0 datasets; 0 formulas.

Curation notes
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Journal pp\. L457\-L463 = PDF pages 2\-8 \(PDF p\. 1 is an IOPscience cover page\); journal page = PDF page \+ L455\. Identity checked on PDF p\. 2 \('J\. Phys\. B\: At\. Mol\. Opt\. Phys\. 29 \(1996\) L457\-L463\. Printed in the UK', Letter to the Editor; D Xenakis, O Faucher, D Charalambidis and C Fotakis, Heraklion and Dijon; received 23 January 1996, in final form 1 April 1996\) on 2026\-10\-09\. The PDF carries a text layer and vector figures\.

WHAT THE PAPER MEASURES\. The observation of Ar\+ when both jets run \(Fig\. 4\(c\)\) and not when either is off \(Figs\. 4\(a\), 4\(b\)\)\: 'a two\-XUV\-photon ionization of Ar utilizing subpicosecond XUV pulses' \(p\. 6/L461\); and the Ar\+ yield against the energy of the fundamental, log\-log, slope 3 \(Fig\. 4's insert\), 'instead of a slope of 6 that should be expected for a two\-XUV\-photon process', ascribed to 'saturation of the first step of the ionization process due to the near\-lying 6s resonances' \(pp\. 6\-7/L461\-L462\)\. The Xe and Kr one\-photon ion yields against the fundamental's energy also have slope 3, unsaturated to 1e15 W cm\-2 \(Fig\. 3, p\. 6/L461\)\. No two\-photon cross section is measured or deduced, absolute or relative\: the yields are in arbitrary units and the harmonic's intensity is not measured\.

THE INTENSITY AND ITS SCALE \(p\. 5/L460\)\: 'No absolute measurements were performed of the number of XUV photons produced\. Upper and lower limits for the third harmonic intensity were estimated by measuring the ion signal produced when the third harmonic was interacting with different rare gases such as Xe, Kr and He\. No two\-photon ionization could be observed in He\.' 'Using the known single\-photon ionization cross sections of Xe and Kr \(Berkowitz 1979\), the two\-photon ionization of He \(Starace et al 1987 and Cormier et al 1995\), the estimated ion extraction volume and the gas pressure in the interaction region in the third cell, the third harmonic intensity was estimated to be in the range of 10^5\-10^8 W cm^\-2 within this interaction region\.' The fundamental's scattered light there was 'of the order of a few kW cm^\-2'\. The duration of the harmonic pulse is not measured or stated \(the fundamental's is about 450 fs; the abstract says 0\.5 ps\)\.

NOT TAKEN \(no quantity of the vocabulary holds them honestly\)\: \(a\) the third harmonic's estimated intensity, 1e5\-1e8 W cm\-2\: a condition of the experiment, three decades wide, not a property of argon\. \(b\) The estimated resonant absorption cross section of the first step at 82\.9 nm, '~7 x 10^\-11 cm^2' for a Lorentzian line shape and g\_3p/g\_6s = 3, reduced to '~7 x 10^\-12 cm^2' for the detunings and the harmonic's bandwidth, and the range '10^\-10\-10^\-13 cm^2' for which the first step would saturate \(p\. 7/L462\)\: estimates from assumed line shapes, the authors stating 'the absorption cross section to these states is not known to us'; not a photoabsorption measurement\. \(c\) Figs\. 3 and 4\: ion yields in arbitrary units against the fundamental's pulse energy \(vector drawings\), and time\-of\-flight spectra\. \(d\) Fig\. 1's level energies \(14\.2 eV, 0\.7 eV, the detunings\)\: Moore's levels, quoted \(Moore 1971\)\.

FINDING\. The He two\-photon cross section used to bound the harmonic's intensity is cited to 'Starace et al 1987', listed as Starace A F and Tsin\-Fu Jiang, Phys\. Rev\. A 36, 1705 \(1987\) \(starace\_1987, TC\-878\); that paper computes argon only and says its approach 'is, however, applicable with minor modifications to He'\. The other source, Cormier et al 1995, is a private communication\. So the He value behind the 1e5\-1e8 W cm\-2 cannot be traced\. saenz\_1999 \(TC\-873\) cites this paper as 'Ar two\-photon at 15 eV' without a value \(saenz\_1999 notes\)\.

TWO\-PHOTON REFERENCES the paper cites \(data not in this record\)\: E\. Cormier, private communication \(He two\-photon\); D\. Charalambidis, P\. Lambropoulos, H\. Schroder, O\. Faucher, H\. Xu, M\. Wagner and C\. Fotakis, Phys\. Rev\. A 50, R2822 \(1994\) \(Xe ionisation saturation at 248 nm and 0\.5 ps, about 1e13 W cm\-2\); one\-photon cross sections\: J\. Berkowitz, Photoabsorption, Photoionization and Photoelectron Spectroscopy \(Academic, 1979\)\.

**Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.

Datasets
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No datasets are recorded.

Formulas
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No formulas are recorded.

Corrections
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No dataset errata are recorded in this source record.

Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register </register>` for the checks and decisions.