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Abstract

High precision measurements of isotopic shifts in noble gases can provide a very good test of relativistic and quantum electrodynamic effects. In our experiment, we measured the isotopic shift between ³⁶Ar and ⁴⁰Ar for the 3s²3p⁵ (²P_3/2 → ²P_1/2) transition for singly ionized argon atoms. We measured the shift by implementing a Ramsey scheme using two ultra-short (~ 6fs) laser pulses. The first laser pulse excites the system in a coherent superposition of the aforementioned states. This superposition leads to a spinorbit wave packet whose dynamics can be investigated by applying a second delayed probe pulse. In order to increase the precision of a measurement, we modified a Mach-Zehnder interferometer, to introduce a long time delay of 3.97ns between the two pulses. To detect the ions of different argon isotopes we used a reaction microscope spectrometer (REMI). The isotopic shift is found to be (1.22 ± 0.10) x 10^-7eV and it is the first time it has been measured for this transition to the best of our knowledge.