Speaker
Description
Precision spectroscopy in few-body atomic systems, like hydrogen and helium, enables the testing of the quantum electrodynamics(QED) theory and determination of the fundamental physical constants, such as the Rydberg constant, the proton charge radius, and the fine-structure constant.We perform an laser spectroscopy measurement of the $2^3$S-$2^3$P transition of $^4He$ in an atomic beam.The new centroid frequency of the $2^3$S-$2^3$P may lead to a determination of the nuclear charge radius of He($r_{He}$) with a relative accuracy of $10^{-3}$,once the theoretical calculations for m$\alpha^7$ corrections have been accomplished. This will enable a comparison of the $r_{He}$ values obtained from electronic and from muonic helium in the future.
In order to further improve the accuracy of the measurement of the $2^3$S-$2^3$P transition, for both $^4He$ and $^3He$, to the level of sub-kilohertz. We have recently improved the set up. By optimise the vacuum structure, we have effectively increased the beam intensity of the meta-stable helium atom by a factor of 10. By adding the zeeman slower system, the longitudinal velocity of the helium atom is actively reduced to about 100m/s, and the influence of the first-order Doppler effect is further reduced. In addition, we recently present an experimental and theoretical study of the light-force shift in the measurements of the $2^3$S-$2^3$P transition frequency. The systematic shift in the extrapolated result at the zero-field limit was analyzed. As a consequence of this effect, a correction of +0.50(80)kHz was added to our previous result on the $2^3$S-$2^3$P transition frequency. Methods to suppress the light-force shift were also discussed, which will be applied in our new setup to improve the accuracy of the atomic helium spectroscopy. A more accurate determination of the $2^3$S-$2^3$P transition frequency of $^4He$ and $^3He$ may help to resolve the present disagreements in the $^4He$ and $^3He$ nuclear charge radius difference.
