One of the most ubiquitous items on the optical table is the beam block. It gets moved around, sometimes to block a stray reflection, at other times to block a “what if” beam. (What if I miss the mirror?) But despite the beam block’s omnipresence, I could find only two or three vendors who actually sell them. There are many commercial beam dumps — devices designed to terminate primary beams on the optical bench. These even come in two flavors, air- and water-cooled — one’s choice depending on the amount of power they are expected to dissipate. However, the beam blocks I am writing about are mostly homemade devices, intended to block stray, accidental or secondary beams and reflections.

They usually are made of aluminum and often bent into an “L” shape, and they come in a variety of sizes. The larger ones — a foot or more on a side — are really perimeter guards and not intended to stop a particular beam. They are more like a fort — a protective wall around the optical setup (Figure 1). Other beam blocks are cards that obstruct the residual transmission through a beam-steering mirror or shrouds over an optical system that keep the laser light in and room light out...