  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 $500\times 500$~$\mu$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$^2$.
