The advancing precision of modern atomic spectroscopy is beginning to afford optical tests of fundamental physics in helium through, for instance, nuclear charge radii determinations. Helium therefore provides a testbed as appealing as Hydrogen for spectroscopic tests of QED. Among outstanding discrepancies between predicted and observed Helium transition lines are the 7.5σ difference in the n = 3 singlet-triplet splitting and the 93σ difference between Martin’s measurements of the 23P2 → 53S1 and 23P2 → 53D transitions values, and recent predictions by Drake [3]. We contribute to both of these by measuring five transitions from the 23P2 state, improving on Martin’s measurements with an order of magnitude greater precision, and making the first observation of the spin-forbidden 23P2 → 51D2 transition in Helium. Our measurements constrain the 53D and 51D ionization energies of 4He[4] to 150 parts per billion, and the 53S to 28 parts per billion.
We report a new measurement for the 413 nm tune-out wavelength for metastable helium (He*); the optical wavelength at which the light does not interact with the atom, whose accurate determination provides a sensitive test of QED independent of transition energy measurements. Mitroy and Tang have shown[1] that the 413nm tune-out wavelength of the metastable 23S1 state of helium is particularly sensitive to QED effects, and a measurement of this tune-out to 175MHz accuracy would constitute the most precise measurement of transition rate information made in Helium.
Intense, highly collimated sources of atoms have many potential applications. Bright beams will be important for competitive high flux and high resolution direct-write techniques in lithography, with the added advantage of parallel writing through laser manipulation. Intense sources will also be useful in other atom optic devices e.g. for loading atoms into hollow fiber waveguides. In atomic physics, many collision processes can only be measured with the sensitivity offered by such high flux sources. We report progress on the development of an intense, collimated beam of metastable helium atoms which improves the brightness generated by conventional nozzle discharge sources by several orders of magnitude. The system uses diode lasers to transversely collimate and then to longitudinally slow the atoms, using Zeeman tuning to compensate for the changing Doppler shift. The slowed, collimated beam is then compressed in a 2D magneto-optic trap before a final collimation stage, to achieve the required increase in intensity. Initial experiments using the helium source for some of the applications above are described.
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