Role of oxygen in laser-induced contamination at diamond-vacuum interfaces

Many modern-day quantum science experiments rely on high-fidelity measurement of fluorescent signals emitted by the quantum system under study. A pernicious issue encountered when such experiments are conducted near a material interface in vacuum is “laser-induced contamination” (LIC): the gradual accretion of fluorescent contaminants on the surface where a laser is focused. Fluorescence from these contaminants can entirely drown out any signal from, e.g., optically probed color centers in the solid state. Crucially, while LIC appears often in this context, it has not been systematically studied. In this work, we probe the onset and growth rate of LIC for a diamond nitrogen-vacancy center experiment in vacuum, and we correlate the contamination-induced fluorescence intensities to micron-scale physical buildup of contaminant on the diamond surface. Drawing upon similar phenomena previously studied in the space optics community, we use photocatalyzed oxidation of contaminants as a mitigation strategy. We vary the residual oxygen pressure over 9 orders of magnitude and find that LIC growth is inhibited at near-atmospheric oxygen partial pressures, but the growth rate at lower oxygen pressure is nonmonotonic. Finally, we discuss a model for the observed dependence of LIC growth rate on oxygen content and propose methods to extend in situ mitigation of LIC to a wider range of operating pressures.