To examine the reflections we bounced a tiny 3 mm in diameter highly collimated pencil beam of light at 45 degrees to the screen and photographed the reflected beams, which appear as overlapping circles in the photos below. (displaymate.com)
Participated in commissioning procedures in two IBA treatment gantries for pencil beam scanning (PBS) (jobhero.com)
The accelerator produces a small, intensely concentrated beam of electrons called a pencil beam. (sciencedaily.com)