  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 build-up of contaminant on the diamond
surface. Drawing upon similar phenomena previously studied in the space optics
community, we use photo-catalyzed 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 non-monotonic. 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.
