Reference beam
A reference beam is a laser beam used to read and write holograms. It is one of two laser beams used to create a hologram. In order to read a hologram out, some aspects of the reference beam must be reproduced exactly as when it was used to write the hologram. As a result, usually reference beams are Gaussian beams or spherical wave beams which are fairly easy to reproduce.
The other beam used to write a hologram is the signal beam or object beam.
