mccown_1982
===========

A\. W\. McCown, M\. N\. Ediger and J\. G\. Eden, "Two\-photon ionization of xenon at 193 nm", Phys\. Rev\. A 26, 3318\-3324 \(1982\)

`Source record <https://github.com/LupoLab/optmat/blob/main/src/optmat/data/sources/mccown_1982.toml>`__ · :doc:`Catalogue </the-data/sources>` · :doc:`Review register </register>`

DOI: `10\.1103/PhysRevA\.26\.3318 <https://doi.org/10.1103/PhysRevA.26.3318>`__

**Source kind:** measurement

**Recorded technique:** Two\-photon ionisation of Xe by an ArF laser at 193 nm, the photoelectrons detected by an X\-band microwave bridge \(pp\. 3319\-3321\)\. ArF laser\: 'linewidth = 5\.2 Angstrom or ~140\-cm^\-1 full width at half maximum \(FWHM\); beam randomly polarized' \(p\. 3319\), focused to a line \(0\.02 x 2\.9 cm2 at the focus, p\. 3320\) by a 7 cm cylindrical lens on the axis of a sealed Suprasil cell \(20 mm inner diameter, 6\.5 cm long, 1\-500 Torr of research\-grade Xe, barium\-gettered; one cell per pressure\); 25 to 175 mJ per pulse 'or ~20 to 146 MW cm^\-2 \(at the focus\) in a 13 ns FWHM pulse' \(p\. 3319\), the pulse monitored by a vacuum photodiode calibrated against a pyroelectric detector and an energy meter, corrected for the lens \(93 %\) and cell\-wall \(91 %\) transmissions\. The cell sits in a 15 cm cylindrical waveguide \(TE11, a = 1\.27 cm\) in one arm of a 9\.252 GHz bridge; the phase shift and attenuation give the plasma frequency and the momentum\-transfer collision frequency \(Eqs\. 1\-8, with the filling factor F = 1/150 from the measured beam profile, Eq\. 7\)\. nu\_m measured at 300 Torr\: \(3\.9 \+\- 1\.0\) x 10^10 s^\-1 \(p\. 3321\); thereafter the single\-pass attenuation alone gives the absolute peak electron density\. Minimum detectable n ~ 4 x 10^11 cm^\-3 \(footnote 19\); waveguide cutoff limits n to ~2 x 10^13 cm^\-3; wall photoelectrons \< 2 % at the highest intensities, corrected \(footnote 20\)\. Peak electron density against peak intensity at 100 and 300 Torr \(Fig\. 2\)\: slope 2, and the I^2 law observed down to 10 Torr \(p\. 3322\)\. alpha from Eq\. \(10\) with the time integral of the squared photodiode waveform\: 'Over several trials, int I^2 dt for a 100\-mJ pulse was found to be 9\.7 x 10^7 W^2 s cm^\-4', 100 mJ corresponding to 84 MW/cm2 at the focus \(p\. 3322\)\.

**Materials in structured entries:** Xe

**Dataset quantities:** multiphoton\_ionization\_cross\_section

**Contents:** 4 datasets; 0 formulas.

Curation notes
--------------

Journal pp\. 3318\-3324 = PDF pages 1\-7 \(a scan with a text layer\)\. Identity checked against the first page \(Physical Review A, volume 26, number 6, December 1982; received 24 June 1982\) on 2026\-10\-08\.

THE DEFINITION \(p\. 3322, Eq\. 9\)\: 'dn/dt = alpha \[Xe\] I^2 / hbar omega \- beta\_1 \[Xe\+\] n \- beta\_2 \[Xe2\+\] n, where \[ \] denote particle concentrations, alpha is the two\-photon ionization coefficient and has the units of cm^4 W^\-1'\. Recombination is negligible at the peak of n \(risetime ~12 ns, e^\-1 decay ~1 us at 100 Torr\), so \(Eq\. 10\) 'n = \(alpha \[Xe\] / hbar omega\) int I^2 dt', with ground\-state depletion negligible\. alpha is thus the ionisation rate per atom times hbar omega / I^2\: the generalised two\-photon cross section on the photon flux \(sigma\_2 = W / Phi^2, Phi = I / hbar omega in cm^\-2 s^\-1, the convention of uiterwaal\_1998 and mckenna\_2004\) is sigma\_2 = alpha hbar omega, 4\.11e\-50 cm4 s at the line centre \(two photons 103 466 cm^\-1, p\. 3321; hbar omega = 6\.414 eV\)\. Not printed by the paper\: a register finding\. Santra and Greene quote this measurement as 'about 4 x 10^\-50 cm^4 s' \(santra\_2004, preprint p\. 7\), the same conversion \(tools/extract/mccown\_1982\.py checks it\)\.

THE ENERGY\. Two ArF photons, 103 466 \+\- 70 cm^\-1 \(12\.83 eV\), lie above the Xe\+ 2P3/2 limit the paper quotes \(97 834 cm^\-1; ~0\.7 eV excess\) and below the 2P1/2 limit\: the autoionising region between the two thresholds\. The authors argue \(pp\. 3322\-3323\) that the 7d'\[1 1/2\] \(J = 2\) autoionising state, expected near the J = 1 state at 103 419 cm^\-1 \(47 cm^\-1 from twice the line centre\), is excited within the 140 cm^\-1 laser linewidth, and conclude that 'two\-photon excitation of one or more autoionization states is occurring' with a Xe\+ \(2P3/2 core\) ion and a ~0\.7 eV electron as products \(p\. 3323\)\. The value is therefore an average over the ArF spectrum across a resonance, not a smooth continuum value\. The first one\-photon allowed level, 6s\[3/2\]1 at 8\.4 eV, is ~2 eV above one photon\: no near\-resonant intermediate state \(p\. 3323\)\.

ACCURACY\. No uncertainty of alpha is printed \(one significant figure\)\. Pressure effects are expected to be negligible\: I^2 at every pressure, n roughly linear in the Xe pressure \(p\. 3323\)\.

CONSISTENCY\. Eq\. \(10\) with the printed int I^2 dt \(9\.7 x 10^7 W^2 s cm^\-4 for the 100 mJ pulse of 84 MW/cm2\) and the slope\-2 lines of Fig\. 2 \(read on the library's figure image at its native resolution, the frame calibrated to the axes' end ticks\: n = \(I / 12\.2\)^2 x 10^12 cm^\-3 at 300 Torr and \(I / 21\.15\)^2 x 10^12 at 100 Torr, I in MW/cm2\) gives alpha = 5\.1e\-32 cm4 W\-1 at both pressures for the gas at 296 K \(the fill temperature is not stated\)\: 1\.3 times the printed 4 x 10^\-32\. The paper does not say how its value was reduced from the data\. The two lines differ by a factor 3\.0 at one intensity \('almost a factor of 3', p\. 3322\)\. Fig\. 2's points are not digitised\: the paper prints its result\.

WHAT IS TAKEN\. Table I \(p\. 3322, tbl\_0641e78d7d33; the cells checked against the table image\), xenon\: the present measurement \(alpha\_Xe\) and, as checks with reproduced\_from, the three values the paper compares with\: Bischel et al\.'s estimate \(Ref\. 11\), Hodges, Lee and Moseley's lower limit \(Ref\. 12\) and McGuire's calculation \(Ref\. 13, mcguire\_1981 in the library\)\. The originals of Refs\. 11 and 12 are not in the library; these rows are the only copies at hand, and they disagree with the measurement by two orders of magnitude, which is the point of the comparison\. Not taken\: propane's row \(1\.2 x 10^\-31 here; 3\.0 x 10^\-31 from Lee and Bischel, Ref\. 23\), not a curated material; nu\_m, a transport property\.

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

Datasets
--------

mccown\_1982/alpha\_Xe
~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "alpha_Xe",
     "material": "Xe",
     "file": "Xe/mccown_1982__alpha_Xe.csv",
     "table": "tbl_0641e78d7d33",
     "quantity": "multiphoton_ionization_cross_section",
     "unit": "cm4 W-1",
     "scale": 1e-32,
     "abscissa_unit": "nm",
     "use": "primary",
     "uncertainty": {
       "level": "not stated"
     },
     "parameters": {
       "photons": 2,
       "polarization": "natural",
       "polarization_printed": "beam randomly polarized (p. 3319)",
       "method": "absolute photoelectron density by microwave-bridge attenuation (nu_m measured), ArF laser, Xe at 10-300 Torr; alpha from Eq. (10) and the slope-2 lines of Fig. 2",
       "definition": "dn/dt = alpha [Xe] I^2 / hbar omega (Eq. 9), so n = (alpha [Xe] / hbar omega) int I^2 dt (Eq. 10); alpha in cm4 W-1 (p. 3322)",
       "wavelength_nm": 193,
       "two_photon_energy_cm1": 103466,
       "two_photon_energy_uncertainty_cm1": 70,
       "linewidth_cm1": 140,
       "linewidth_definition": "FWHM, '5.2 Angstrom or ~140-cm^-1' (p. 3319)",
       "pulse_ns": 13,
       "pulse_definition": "FWHM (p. 3319)",
       "intensity_range_mw_cm2": [
         20,
         146
       ],
       "intensity_definition": "peak intensity at the focus, '~20 to 146 MW cm^-2' for 25 to 175 mJ (p. 3319)",
       "pressure_range_torr": [
         10,
         300
       ]
     }
   }

Table I \(p\. 3322\), 'Present work'\: the two\-photon ionisation coefficient alpha of Xe at 193 nm, cm4 W\-1 as printed \(also in the abstract and the conclusions\)\. The source's own definition, not the photon\-flux cross section\: sigma\_2 = alpha hbar omega = 4\.11e\-50 cm4 s \(the record's notes\)\. Averaged over the 140 cm\-1 ArF spectrum, which spans an autoionising resonance \(the record's notes\)\. No uncertainty printed\.

mccown\_1982/bischel\_Xe
~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "bischel_Xe",
     "material": "Xe",
     "file": "Xe/mccown_1982__bischel_Xe.csv",
     "table": "tbl_0641e78d7d33",
     "quantity": "multiphoton_ionization_cross_section",
     "unit": "cm4 W-1",
     "scale": 1e-34,
     "abscissa_unit": "nm",
     "use": "check",
     "reproduced_from": [
       "W. K. Bischel, J. Bokor, D. J. Kligler and C. K. Rhodes, IEEE J. Quantum Electron. QE-15, 380 (1979)"
     ],
     "parameters": {
       "photons": 2,
       "polarization": "not stated",
       "method": "estimate (Ref. 11), as quoted by McCown et al.",
       "definition": "alpha of Eq. (9), cm4 W-1, as Table I compares it",
       "wavelength_nm": 193,
       "linewidth_cm1": 100
     }
   }

Table I \(p\. 3322\), 'Bischel et al\.' \(Ref\. 11\)\: an estimate of alpha 'assuming a laser linewidth of 100 cm\-1' \(p\. 3322\); Bischel et al\. noted that autoionising resonances 'could enhance the value of alpha \.\.\. by a factor of 10^2' \(quoted p\. 3322\)\. Not in the library\: this row is the only copy at hand\.

mccown\_1982/hodges\_Xe
~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "hodges_Xe",
     "material": "Xe",
     "file": "Xe/mccown_1982__hodges_Xe.csv",
     "table": "tbl_0641e78d7d33",
     "quantity": "multiphoton_ionization_cross_section",
     "unit": "cm4 W-1",
     "scale": 1e-34,
     "abscissa_unit": "nm",
     "use": "check",
     "reproduced_from": [
       "R. V. Hodges, L. C. Lee and J. T. Moseley, Int. J. Mass Spectrom. Ion Phys. 39, 133 (1981)"
     ],
     "parameters": {
       "photons": 2,
       "polarization": "not stated",
       "method": "measurement (Ref. 12), as quoted by McCown et al.",
       "definition": "alpha of Eq. (9), cm4 W-1, as Table I compares it",
       "wavelength_nm": 193,
       "limit": "lower"
     }
   }

Table I \(p\. 3322\), 'Hodges, Lee, and Moseley' \(Ref\. 12\)\: 'experimentally determined the lower limit for alpha to be 5 x 10^\-34 cm4 W\-1' \(pp\. 3318\-3319\)\: a lower limit, not a value\. Not in the library\: this row is the only copy at hand\.

mccown\_1982/mcguire\_Xe
~~~~~~~~~~~~~~~~~~~~~~~~

.. code-block:: text

   {
     "id": "mcguire_Xe",
     "material": "Xe",
     "file": "Xe/mccown_1982__mcguire_Xe.csv",
     "table": "tbl_0641e78d7d33",
     "quantity": "multiphoton_ionization_cross_section",
     "unit": "cm4 W-1",
     "scale": 1e-32,
     "abscissa_unit": "nm",
     "use": "check",
     "reproduced_from": [
       "mcguire_1981"
     ],
     "parameters": {
       "photons": 2,
       "polarization": "circular",
       "method": "calculation (Ref. 13), as quoted by McCown et al.",
       "definition": "alpha of Eq. (9), cm4 W-1, as Table I compares it",
       "wavelength_nm": 193
     }
   }

Table I \(p\. 3322\), 'McGuire' \(Ref\. 13, E\. J\. McGuire, Phys\. Rev\. A 24, 835 \(1981\)\)\: 'sigma \(circular polarization\) is found to be 8 x 10^\-32 cm4 W\-1 at 193 nm\. While the cross section for linear polarization is ~20% lower than this value, both are within a factor of 2 of the result reported here' \(p\. 3322\); above 184\.3 nm McGuire's sigma drops rapidly, Xe\+ 2P1/2 being out of two\-photon reach\. McCown et al\.'s reading of McGuire's calculation, kept as a check of the mcguire\_1981 record\.

Formulas
--------

No formulas are recorded.

Corrections
-----------

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.