Characterize the VUV laser triangular modulation parameters used during 229Th excitation scans

Determine the exact amplitude and phase of the ~5 GHz triangular frequency modulation applied to the vacuum-ultraviolet (VUV) laser during the 229Th isomer excitation scans, so that this modulation can be incorporated explicitly into the detuning model δf_n(x) used in the lineshape analysis and thereby reduce modeling uncertainty in bounds on ultralight dark matter–induced frequency variations.

Background

In their lineshape analysis of the 229Th isomer excitation spectrum, the authors account for uncertainties in the laser detuning, including a triangular frequency modulation applied to the VUV laser during data taking. Because the precise modulation characteristics were not available, this effect was modeled as an added detuning uncertainty rather than being explicitly included in the detuning function δf_n(x).

Identifying the exact modulation amplitude and phase would enable a more accurate forward model of the excitation rate, potentially tightening the derived limits on periodic variations of the 229Th transition frequency and improving sensitivity to ultralight dark matter couplings to the strong sector.