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 · Catalogue · Review register
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#
{
"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#
{
"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#
{
"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#
{
"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 review register for the checks and decisions.