Few-Nucleon Charge Radii and a Precision Isotope Shift Measurement in Helium

Recent improvements in atomic theory and experiment provide a valuable method to precisely determine few nucleon charge radii, complementing the more direct scattering approaches, and providing sensitive tests of few-body nuclear theory. Some puzzles with respect to this method exist, particularly in the muonic and electronic measurements of the proton radius,~known as the proton puzzle. Perhaps this puzzle will also exist in nuclear size measurements in helium. Muonic helium measurements are ongoing while our new~electronic results will be discussed here.~~We measured precisely the isotope shift of the 2$^{\mathrm{3}}$S - 2$^{\mathrm{3}}$P transitions in~$^{\mathrm{3}}$He and~$^{\mathrm{4}}$He.~~The result is almost an order of magnitude more accurate than previous measured values.~~To achieve this accuracy, we implemented various experimental techniques. We used a tunable laser frequency discriminator and electro-optic modulation technique to precisely control the frequency and intensity.~ We select and stabilize the intensity of the required sideband and eliminate unused sidebands.~ The technique uses a MEMS fiber switch (t$_{\mathrm{s}}$~$=$ 10 ms) and several temperature stabilized narrow band (3 GHz) fiber gratings.~ A beam with both species of helium is achieved using a custom fiber laser for simultaneous optical pumping.~ A servo-controlled retro-reflected laser beam eliminates Doppler effects.~~Careful detection design and software are essential for unbiased data collection. Our new results will be compared to previous measurements.