# Reference beam

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A '''reference beam''' is a [laser](/source/laser) beam used to read and write [hologram](/source/hologram)s.{{sfn|Vacca|2001|pp=4, 31–32}} It is one of two laser beams used to create a hologram.{{sfn|Vacca|2001|p=4}} In order to read a hologram out, some aspects of the reference beam (namely its [angle of incidence](/source/angle_of_incidence_(optics)), beam profile and [wavelength](/source/wavelength)) must be reproduced exactly as when it was used to write the hologram. As a result, usually reference beams are [Gaussian beam](/source/Gaussian_beam)s or [spherical wave](/source/spherical_wave) beams (beams that [radiate](/source/Radiation) from a single point) which are fairly easy to reproduce.

The other beam used to write a hologram is the [signal beam](/source/signal_beam) or object beam.{{sfn|Vacca|2001|p=4}}

==References==
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===Works cited===
* {{cite book |last=Vacca |first=John R. |date=2001 |title=Holograms & Holography: Design, Techniques, & Commercial Applications |publisher=Charles River Media |isbn=1-886801-96-7}}

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Category:Holography

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