bergeson_1998

S. D. Bergeson, A. Balakrishnan, K. G. H. Baldwin, T. B. Lucatorto, J. P. Marangos, T. J. McIlrath, T. R. O’Brian, S. L. Rolston, C. J. Sansonetti, J. Wen, N. Westbrook, C. H. Cheng and E. E. Eyler, “Measurement of the He ground state Lamb shift via the two-photon 1 1S-2 1S transition”, Phys. Rev. Lett. 80, 3475 (1998)

Source record · Catalogue · Review register

DOI: 10.1103/PhysRevLett.80.3475

Source kind: measurement

Recorded technique: Doppler-free two-photon spectroscopy of the He 1 1S - 2 1S transition at 120 nm: a pulse-amplified cw Ti:sapphire laser (842 nm, about 50 mJ), quadrupled in BBO and mixed with the fundamental in a 4:1 Kr/Ar cell (2 omega_4 - omega_1, about 30 nJ, 3 ns at 120 nm), focused to 40 um in a pulsed supersonic He jet and retroreflected (counter-propagating beams); the 2 1S atoms ionised by a 266 nm pulse 30 ns later and the ions counted by time-of-flight mass spectrometry. The frequency from a 75 MHz Fabry-Perot against a Ne saturated-absorption line, with the optical phase perturbation of the amplifier measured by heterodyne and the dependence on the omega_4 pulse energy extrapolated to zero.

Materials in structured entries: None recorded.

Dataset quantities: None recorded.

Contents: 0 datasets; 0 formulas.

Curation notes

Journal pp. 3475-3478 are PDF pages 1-4. Identity checked against the first page (Phys. Rev. Lett. 80, No. 16, 20 April 1998). The library’s text renders the binding energies on p. 3477 with the minus sign as ‘2’ and the parentheses as ‘s ... d’ (‘2960 332 041.01s15d’); the page image prints -960 332 041.01(15) MHz and -5 945 204 356(48) MHz (checked 2026-10-08).

NOTHING TAKEN. The result, ‘Our final number for the 1 1S-2 1S transition frequency is 4 984 872 315(48) MHz. The reported uncertainty represents 1 standard deviation’ (p. 3477), is a frequency; level_energy holds cm^-1 or eV, so it cannot be stored as printed (data rule 2: no hand conversion into data). Converted for comparison only (computed 2026-10-08, c exact): 4 984 872 315(48) MHz / 29 979.2458 MHz per cm^-1 = 166 277.44234(160) cm^-1 = 20.6157754 eV, against nist_asd_2026’s level_He_1s2s_1S0, 166 277.437635(63) cm^-1: Bergeson is higher by 0.00471 cm^-1 (141 MHz), 2.9 times its own standard uncertainty. The two-photon wavelength is 2c/nu = 120.2809 nm. The uncertainty budget (Table I, p. 3477, tbl_c5cf8a7fe6e5): ac Stark shift 0.7, Ne reference 5.6, free spectral range 6.3, frequency scan 10, optical phase perturbation 13, power extrapolation 44, combined 48 MHz (standard uncertainties). The extrapolation slope is 285 +- 34 MHz/mJ of omega_4 pulse energy (p. 3477).

The derived ground-state binding energy, -5 945 204 356(48) MHz relative to He+ (with the 2 1S binding energy -960 332 041.01(15) MHz from Drake and Martin and Sansonetti and Gillaspy, Refs. 15-16), is the He ionisation energy: 198 310.67118(160) cm^-1 = 24.5873896(2) eV (computed, CODATA h/e), against nist_asd_2026’s ie_He_I, 24.587389011(25) eV (198 310.66637 cm^-1): higher by 144 MHz (0.0048 cm^-1), 3.0 times Bergeson’s uncertainty; not taken for the same reason (MHz). The paper’s comparison: Eikema et al. (Phys. Rev. A 55, 1866 (1997), 1 1S-2 1P at 58.4 nm) give -5 945 204 236(45) MHz, 1.8 combined standard deviations away; Lamb shift 41 104(48) MHz against 41 224(45) MHz (Eikema) and the theory 41 233(35) MHz (p. 3478).

TWO-PHOTON QUANTITIES: none printed. No two-photon matrix element, cross section or excitation rate; the signal is ‘an order of 50 ions per laser pulse’ at line centre (p. 3476); the peak intensity in the interaction region is 10^6 W/cm^2, giving a worst-case ac Stark shift of 0.7 MHz (p. 3477); observed and modelled line widths 180 and 164 MHz (FWHM) against the 146 MHz transform limit of a 3 ns pulse and the 8 Hz natural width (Fig. 1, p. 3476). The 2 1S lifetime, 19 ms, is quoted from Van Dyck et al. (Ref. 9, p. 3475).

FURTHER TWO-PHOTON DATA CITED: none with values (the hydrogen 1S-2S measurements, Refs. 1-4 and 19, are frequencies).

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.