Study, Development and Optimization of Laser Resonant Photo-Ionization processes applied to species of interest for the Isolpharm-SPES project

The principle of resonance laser photo-ionization is used to selectively ionize elements of interest in isotope separation online (ISOL) facilities. The work presents the study of two-step resonance photo-ionization of silver atoms in the context of selective production of exotic species (SPES) at INFN-LNL. Using a hot ablation plume of silver atoms in a time of flight mass spectrometer (TOF-MS), Doppler-suppressed and Doppler-broadened resonance frequency profile of the transition steps. It is shown that a Doppler-suppressed resonance profile can be achieved in a two-step resonant transition by introducing an angular separation as low as 8.5° between the two resonant laser beams. In the case of collinear injection of these laser beams, Doppler broadening is observed and the effect of the laser linewidth in a Doppler-broadened resonance profile is also studied. A silver hollow cathode lamp has also been used to study the same resonant transitions. Two kinds of opto-galvanic signals i.e. slow signal and fast signal are used to detect the resonance in this case. Using the hollow cathode lamp, strong evidence of high-lying Rydberg states of silver around the energy value of 7.56 eV (60945.32 cm$^{-1}$). First-time characterization of the SPES laser ion source (LIS) at ISOLDE Offline 2 is also presented. The SPES-LIS is a hot tubular tantalum cavity inside which laser beams with frequencies tuned to the electronic transitions of particular elements are made to interact with the vapor of the element. Important parameters such as thermal stability of the ion source, time structure of the ion beam, laser enhancement of the ion yield, and resonance laser ionization efficiency have been measured in relation to the production of the gallium ion beam. The effect of the electrostatic axial field on the movement of the ions along the length of the ion source is discussed. The dependence of the laser enhancement of the ion yield on the ion source temperature and the total ion current has been studied too. At a high ion source temperature of 2200°C, the laser enhancement of the ion yield at different total ion currents is found relatively stable compared to lower ion source temperatures. A new TOF-MS has been designed and assembled in the online laser lab at the SPES facility. Two independent sources of atomic beam viz. an effusion cell and an ablation target system, are employed in the system. This new TOF-MS should aid in scheme developments for the photo-ionization of several elements and also provide the geometry for high-resolution laser resonant spectrometry.