kobayashi_1998

Y. Kobayashi, T. Sekikawa, Y. Nabekawa and S. Watanabe, “27-fs extreme ultraviolet pulse generation by high-order harmonics”, Opt. Lett. 23, 64-66 (1998)

Source record · Catalogue · Review register

DOI: 10.1364/OL.23.000064

Source kind: measurement

Recorded technique: Autocorrelation of the ninth harmonic of a Ti:sapphire laser (10 Hz, run at 1 TW with 34-fs pulses; the harmonics generated in Xe in a 1-mm gas envelope 15 mm before the focus of a 1-m radius-of-curvature mirror, the beam split into two spatially separated halves in a delay line) by two-photon ionisation of He: the harmonics above the seventh selected by a beam splitter at 70 degrees and an Al mirror (f = 10 cm), focused into a pulsed gas jet (about 5 Torr) in a time-of-flight ion spectrometer, the ions counted by an electron multiplier (pp. 64-65). The ninth harmonic’s two-photon energy is above He’s ionisation energy, the seventh’s below; its role confirmed by an MgF2-coated mirror (which absorbs it) and by the quadratic dependence of the He+ yield on its intensity (slope 2.0, Fig. 3). The trace (Fig. 4) fitted with a sech^2 shape gives 27 fs (p. 66). Neither the fundamental’s wavelength nor the harmonic’s photon energy is stated.

Materials in structured entries: None recorded.

Dataset quantities: None recorded.

Contents: 0 datasets; 0 formulas.

Curation notes

Opt. Lett. 23(1), 64-66 (1 January 1998): PDF pages 1-3 = pp. 64-66, a digital text layer with the figures as embedded images. Identity checked on the first page (PDF p. 1: ‘OPTICS LETTERS / Vol. 23, No. 1 / January 1, 1998’, p. 64, Y. Kobayashi, T. Sekikawa, Y. Nabekawa and S. Watanabe, Institute for Solid State Physics, University of Tokyo; received August 1, 1997) on 2026-10-09. The library’s identity is VALIDATED_WITH_WARNINGS; the copy is the version of record.

WHY NOTHING IS TAKEN. The paper prints no two-photon cross section of He (or Ar), neither measured nor quoted from another paper, and uses none. Figs. 2-4 (raster images) are the time-of-flight spectrum, the number of He+ ions against the ninth harmonic’s intensity in arbitrary units (slope 2.0), and the autocorrelation trace; the one absolute comparison is with a Keldysh-Faisal-Reiss estimate of the ion number, not a cross section: ‘If we assume an intensity of 155 GW/cm2 and a pressure of 1 Torr, the number of ions expected per pulse is 60, whereas the number actually detected was ~20. This factor-of-3 difference may be due to the estimation of the size of the focal spot’ (p. 66; the theory is H. R. Reiss, Phys. Rev. A 22, 1786 (1980), ref. 13; its two-photon rate and the focal volume are not given). The photon energy is not stated either (the ninth harmonic of an unnamed Ti:sapphire wavelength).

NUMBERS IN THE TEXT (not data of any quantity): the harmonic energies in the ionisation region, fifth 17 nJ, seventh 7 nJ, ninth 13 nJ (50 nJ generated from 44 mJ of the fundamental; pp. 64-65); ‘more than 10 ions per pulse’ of He+ at about 5 Torr (p. 64); the slope 2.0 of the He+ (and Ar+, seventh or ninth harmonic) yield against the harmonic’s intensity (p. 65); the 27-fs pulse width (sech^2), against the fundamental’s 34 +- 5 fs and the 11 fs of tau / sqrt(q), and about 6 fs from the Fourier transform of the ninth harmonic’s spectrum; the autocorrelation contrast 1.7 against the usual 3 (p. 66). An Ar+ signal was seen with both the seventh and the ninth harmonics (p. 65).

FURTHER TWO-PHOTON DATA CITED: none (the cited works are on short-pulse lasers, harmonic generation and cross-correlation, and Reiss’s strong-field theory).

Recorded bibliographic identity status: VALIDATED_WITH_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.

Datasets

No datasets are recorded.

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.