Stray-light Suppression for the MIRACLS Proof-of-principle Experiment

The Multi-Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), currently under development at ISOLDE/CERN, aims to combine the high resolution of fluorescence-based collinear laser spectroscopy (CLS) with a high sensitivity. This will be achieved by confining 30-keV ion bunches in a Multi-Reflection Time-of-Flight (MR-ToF) device which allows laser spectroscopic probing for several thousand times. An MR-ToF setup operating at ∼ 1.5 keV beam energy has been adapted for a proof-of-principle experiment. Thus, efforts had to be undertaken to reduce the laser stray light as the leading source of background of this apparatus, not originally designed for CLS. These measures enabled CLS of $^{24,26}$Mg$^+$ ions in single-path mode, i.e. without ion trapping, which is the reference point to gauge the gain in sensitivity of the MIRACLS technique.