Laser beam profilometry is an important scientific task with well-established solutions for beams propagating in air. It has, however, remained an open challenge to measure beam profiles of high-power lasers in ultra-high vacuum and in tightly confined spaces. Here we present a novel scheme that uses a single multi-mode fiber to scatter light and guide it to a detector. The method competes well with commercial systems in position resolution, can reach through apertures smaller than $500times 500$~$mu$m$^2$ and is compatible with ultra-high vacuum conditions. The scheme is simple, compact, reliable and can withstand laser intensities beyond 2~MW/cm$^2$.
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