Invisible blocker
Absorbs rays but stays hidden in exported figures.
Open in the canvas →In the real world
This element has no laboratory counterpart. It is a figure-making tool: a region that absorbs any ray entering it, drawn on the canvas while you work and then omitted from exported figures.
The need it answers is a real one, though. A ray tracer follows every branch it generates, including ones that are physically correct but irrelevant to the point a figure is making — a weak back-reflection wandering across the frame, a stray diffraction order, the ghost from a beamsplitter's second surface. On a bench you would put a card in the way and forget about it. The equivalent here is a blocker: it takes the unwanted branch out of the trace without adding a component to the drawing that a reader would have to interpret.
The honest framing is that this is a presentation control, not physics. If a stray beam exists in your setup it exists in reality too, and hiding it from a figure is a choice about what the figure is for. Use it to remove distractions from a teaching diagram; do not use it to make a setup look cleaner than it is, and never use it to hide a beam that would need terminating in the real build — see the safety notes on the beam dump page.
In OpticalSetup
The blocker is a rectangle whose faces all absorb. Any ray reaching it stops
there, exactly as with a beam dump — the difference is
purely in the drawing. It carries hideInExport, so it is visible on the
canvas while you compose and absent from SVG and PNG exports. In the exported
figure the blocked beam simply ends, with nothing to explain why.
Two controls set its width and height, and the blue handles resize it on the canvas, so it can be shaped to catch exactly the branch you want and nothing else.
Its bounds are still counted when a figure is fitted for export, so a blocker parked far from the setup will pad the exported crop with empty space even though it is not drawn. Keep it close to the beam it is catching, or use a figure frame to define the crop explicitly.
Absorption is perfect and total, like the beam dump's. The single thing to understand about this element is that it changes what a figure shows, not what the setup is: the trace it removes was a real branch of the light, and its absence from the exported drawing is your editorial decision rather than a physical result. A reader of the figure has no way to tell a blocker was used.