High-Precision Collinear Laser Spectroscopy - Towards All-Optical Nuclear Charge Radius Determination

In recent measurements with the Collinear Apparatus for Laser Spectroscopy and Applied Physics (COALA) at TU Darmstadt, the rest-frame transition frequencies of Ba${}^{+}$ ions were determined with unprecedented accuracy. This precision will be used in the future to test precise atomic many-body calculations and especially for the determination of nuclear charge radii from an all-optical approach by the spectroscopy of Li-like light ions. Such ions will be produced in an Electron Beam Ion Source (EBIS) with a rather large energy spread and a widely broadened spectral linewidth is expected. A so-called pump-and-probe procedure will be used to reduce the experimentally observed linewidth. Here, only one velocity class is selected with a laser through optical pumping in a first step. Afterwards, only the selected ions are probed with a second laser and a largely reduced linewidth will be observed. This procedure has been demonstrated with In${}^{+}$ ions and the results are presented in this talk.