Abstract
The direct access to atomic transitions between close by quantum states employing standard spectroscopic methods is often limited by the size of the necessary radio-frequency cavities. Here we report on a new tool for fundamental spectroscopy measurements that can overcome this shortcoming. For this, a Sona transition unit was used, i.e., two opposed solenoidal coils that provide an oscillating field in the rest frame of the through-going atomic beam. In this way, we were able to control the induced photon energy down to 10 neV or f sim MHz. The tuneable parameter is the velocity of the atomic beam. For illustration of the method, we report a measurement of the hyperfine splitting energies between the substates with F=1 and m_F = -1, 0, +1 of 2S_{1/2} metastable hydrogen atoms as function of a magnetic field.Graphic
Highlights
Nowadays, 2-photon spectroscopy [1] reaches a relative uncertainty of the spectral energies of 4.5 · 10−15 and allows, for example, a precise measurement of the hyperfine-splitting energy of the 2S1/2 state of EHF S = 177.556860(16) MHz [2]
It should be mentioned that the wavelength λ of the static magnetic field oscillation is not a linear function of the distance between the Sona coils
If the distance between the coils surpasses a limit, the radial magnetic field at the zero-crossing will develop a second maximum like it is shown in Fig. 2c. (ii) Alternatively, one can exploit the nonlinearity of the well-known binding energies of the hyperfine substates α2 as function of the magnetic field to calibrate the frequency f1 and the magnetic field
Summary
2-photon spectroscopy [1] reaches a relative uncertainty of the spectral energies of 4.5 · 10−15 and allows, for example, a precise measurement of the hyperfine-splitting energy of the 2S1/2 state of EHF S = 177.556860(16) MHz [2]. Measurements of even smaller transition energies are limited by the size of such cavities that must ensure the overlap of the atomic trajectories and the radio-frequency waves. Up to now the measurement of the hyperfine-splitting energy of the 2S1/2 state by Rothery and Hessels [3] with a cavity of about 1 m length sets the limit with EHF S = 177.556785(29) MHz ∼ 7.34·10−7 eV, a similar precision as in 2-photon spectroscopy
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