Laboratory frequency metrology and the search for a temporal variation of the fine structure constant a on a cosmological time scale

The issue of the possibility of a temporal variation of the fundamental constants has been put high on the agenda of modern physics, now that accurately calibrated spectra of quasars become available. Such data allow for a comparison between the physical constants underlying the spectra fo today and those of 12 Billion years ago. Claims have been made that the fine structure constant a has changed outside a 5σ uncertainty [1]. More recent observations of quasar spectra, employing the Very Large Telescope of the European Southern Observatory contradict the claims of the Sydney group, that are based on observations with the Keck telescope; note that differing observations form the Northern and Southern hemisphere might point at space-time effects on spectroscopic properties. Up till now only 23 atomic (and ionic) transitions have been used following the socalled Many-Multiplet analysis, where for each line a q-parameter , representing the relativistic dependence of a variation of a on the transition frequency is calculated in atomic structure calculations. For test on variations of a more spectral lines can be used, but many important line positions of atomic transitions (mostly ionized atoms) are not known to sufficient accuracy [2]. Our group has started a line of research to produce accurate laboratory transition frequencies of some relevant species, also observed in quasars. For this purpose we perform high-resolution spectroscopy and calibrate the transitons with a frequency comb laser, built at the Laser Centre VU. First results on the resonance lines of atomic carbon (at 94.5 nm) and of atomic magnesium (at 202 nm) will be presented. Results include accurate determination of transition isotope shifts. Such effects are of importance to include in the data analysis, since differing isotopic abundances in the quasars may mimic variation of a. Knowledge of isotopic shifts also allows to study another important problem: isotopic evolution in the Universe. This provides a very sensitive test of models of nuclear processes in stars