A secondary reflection from a lens surface, window, filter or beamsplitter back side that carries a few percent or less of the main beam. Curved surfaces can focus a ghost to a tight spot inside another optic or on the operator's side of the table, and ghosts at a high-power laser can still exceed safe exposure. Good practice is to trace and block every ghost when building a setup.
There's a ghost off the lens going straight up toward the ceiling, put a block above it and tilt the lens a degree.
A ghost focused by a lens back into the previous optic is a classic cause of mysterious internal damage.
Also heard as
- ghost reflection
- ghost beam
Related terms
AR coating
Antireflection coating: thin dielectric layers that cut surface reflections from about 4 percent to a fraction of a percent.
Beam dump
A device that absorbs an unwanted or terminated laser beam completely and safely, without reflecting it.
Glint
A brief, bright reflection of a laser beam off a shiny object such as a tool, screw head, mount or jewelry.
Pickoff
An optic, usually an uncoated wedge, that samples a small fraction of a beam and sends it to a diagnostic.