A reference beam is a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

beam used to read and write

hologram Holography is a technique that allows a wavefront to be recorded and later reconstructed. It is best known as a method of generating three-dimensional images, and has a wide range of other uses, including data storage, microscopy, and interf ...

s. 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 (namely its angle of incidence, beam profile and

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

) must be reproduced exactly as when it was used to write the hologram. As a result, usually reference beams are

Gaussian beam In optics, a Gaussian beam is an idealized beam of electromagnetic radiation whose amplitude envelope in the transverse plane is given by a Gaussian function; this also implies a Gaussian intensity (irradiance) profile. This fundamental (or ...

s or spherical wave beams (beams that radiate from a single point) which are fairly easy to reproduce. The other beam used to write a hologram is the signal beam or object beam.

References

Works cited

* Holography {{optics-stub