Energy levels for the stable isotopes of atomic helium(<sup>4</sup>He I and<sup>3</sup>He I)

Morton, Donald C.; Wu, Qin; Drake, G. W. F.

doi:10.1139/p06-009

Cited by 134 publications

(165 citation statements)

References 66 publications

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“…This means that we can neglect stimulated emission by the high-energy photons in Eqs. (48) and (49). Given these considerations, the net rate of two-photon transitions can be written in the following form, valid for both ν < ν n1 and ν > ν n1 :…”

Section: B Two-photon Decays and Raman Scatteringmentioning

confidence: 99%

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HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

2011

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We present a state-of-the-art primordial recombination code, HyRec, including all the physical effects that have been shown to significantly affect recombination. The computation of helium recombination includes simple analytic treatments of hydrogen continuum opacity in the He I 2 1 P o − 1 1 S line, the He I] 2 3 P o − 1 1 S line, and treats feedback between these lines within the on-the-spot approximation. Hydrogen recombination is computed using the effective multilevel atom method, virtually accounting for an infinite number of excited states. We account for two-photon transitions from 2s and higher levels as well as frequency diffusion in Lyman-α with a full radiative transfer calculation. We present a new method to evolve the radiation field simultaneously with the level populations and the free electron fraction. These computations are sped up by taking advantage of the particular sparseness pattern of the equations describing the radiative transfer. The computation time for a full recombination history is ∼ 2 seconds. This makes our code well suited for inclusion in Monte Carlo Markov chains for cosmological parameter estimation from upcoming high-precision cosmic microwave background anisotropy measurements.

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Section: B Two-photon Decays and Raman Scatteringmentioning

confidence: 99%

“…For the equilibrium calculations, the He I level energies and are obtained from the NIST database (itself based on the compilation of Ref. [49]). The bound-bound Einstein coefficients are obtained from Ref.…”

Section: Helium Recombinationmentioning

confidence: 99%

HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

2011

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“…The 4 He ionization potential (up to an integer multiple of f rep ) is derived from these measurements by adding the excited state ionization energy of the 4p and 5p. The energy of these states is known with an accuracy better than 20 kHz based on theoretical calculations [25].…”

mentioning

confidence: 99%

Extreme Ultraviolet Frequency Comb Metrology

et al. 2010

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The remarkable precision of frequency-comb (FC) lasers is transferred to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), a frequency region previously not accessible to these devices. A frequency comb at XUV wavelengths near 51 nm is generated by amplification and coherent upconversion of a pair of pulses originating from a near-infrared femtosecond FC laser. The phase coherence of the source in the XUV is demonstrated using helium atoms as a ruler and phase detector. Signals in the form of stable Ramsey-like fringes with high contrast are observed when the FC laser is scanned over P states of helium, from which the absolute transition frequency in the XUV can be extracted. This procedure yields a 4 He ionization energy at h Â 5 945 204 212ð6Þ MHz, improved by nearly an order of magnitude in accuracy, thus challenging QED calculations of this two-electron system. Mode-locked frequency-comb (FC) lasers [1,2] have revolutionized the field of precision laser spectroscopy. Optical atomic clocks using frequency combs are about to redefine the fundamental standard of frequency and time [3]. FC lasers have also vastly contributed to attosecond science by providing a way to synthesize electric fields at optical frequencies [4], made long distance absolute length measurements possible [5], and have recently been employed to produce ultracold molecules [6]. FC based precision spectroscopy on simple atomic systems has provided one of the most stringent tests of bound state quantum electrodynamics (QED) as well as upper bounds on the drift of fundamental constants [7]. Extending these methods into the extreme ultraviolet (XUV, wavelengths below 100 nm) spectral region is highly desirable since this would, for example, allow novel precision QED tests [8].Currently the wavelength range below 120 nm is essentially inaccessible to precision frequency metrology applications due to a lack of power of single frequency lasers and media for frequency up-conversion. Spectroscopic studies on neutral helium using amplified nanosecond laser pulses [9,10] are notoriously plagued by frequency chirping during amplification and harmonic conversion which limits the accuracy. These kind of transient effects can be avoided if a continuous train of high power laser pulses (produced by a FC) can be coherently up-converted. This would transfer the FC modes, at frequencies f n ¼ f CEO þ nf rep , where f CEO is the carrier-envelope offset frequency, f rep is the repetition frequency of the pulses, and n an integer mode number, to the XUV. Similar to what was shown in the visible [11,12], the up-converted pulse train could be used to directly excite a transition, with each of the up-converted modes acting like a single frequency laser.By amplification of a few pulses from the train, and producing low harmonics in crystals and gasses, sufficient coherence has been demonstrated down to 125 nm to perform spectroscopic experiments [13,14]. To reach wavelengths below 120 nm in the extreme ultraviolet or even x rays, high harmonic generati...

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“…Most importantly, accurate determination of the 3 1 D-3 3 D separation in 3 He is critical to resolve the 7.4 σ discrepancy between the theories and experiments [23].…”

Section: Resultsmentioning

confidence: 99%

Doppler-free intermodulated fluorescence spectroscopy of 4He 23P–31,3D transitions at 588 nm with a 1-W compact laser system

Luo

Feng

et al. 2015

Appl. Phys. B

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Abstract:We have demonstrated Doppler-free intermodulated fluorescence spectroscopy of helium 2 3 P-3 1,3 D transitions in an rf discharged sealed-off cell using a compact laser system at 588 nm. An external cavity diode laser at 1176 nm was constructed to seed a Raman fiber amplifier. Laser power of more than one watt at 588 nm was produced by frequency doubling of the fiber amplifier output using a MgO:PPLN crystal. A doubling efficiency of 23 % was achieved. The power-dependent spectra of the 2

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Energy levels for the stable isotopes of atomic helium(⁴He I and³He I)

Cited by 134 publications

References 66 publications

HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

Extreme Ultraviolet Frequency Comb Metrology

Doppler-free intermodulated fluorescence spectroscopy of 4He 23P–31,3D transitions at 588 nm with a 1-W compact laser system

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Energy levels for the stable isotopes of atomic helium(4He I and3He I)

Cited by 134 publications

References 66 publications

HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

HyRec: A fast and highly accurate primordial hydrogen and helium recombination code

Extreme Ultraviolet Frequency Comb Metrology

Doppler-free intermodulated fluorescence spectroscopy of 4He 23P–31,3D transitions at 588 nm with a 1-W compact laser system

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Product

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Energy levels for the stable isotopes of atomic helium(⁴He I and³He I)