# Diffraction efficiency

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Fraction of optical power diffracted by an optical element

In [optics](/source/Optics), **diffraction efficiency** is the performance of [diffractive](/source/Diffractive) optical elements – especially [diffraction gratings](/source/Diffraction_grating) – in terms of [power](/source/Power_(physics)) throughput. It's a measure of how much [optical power](/source/Optical_power) is diffracted into a designated direction compared to the power incident onto the diffractive element of grating.

If the diffracted power is designated with P and the incident power with *P*0, the efficiency η reads η = P P 0 . {\displaystyle \eta ={\frac {P}{P_{0}}}\ .}

## Grating efficiency

In the most common case – the diffraction efficiency of optical gratings (therefore also called *grating efficiency*) – there are two possibilities to specify efficiency:[1][2]

- The *absolute efficiency* is defined as above and relates the power diffracted into a particular order to the incident power.

- The *relative efficiency* relates the power diffracted into a particular order to the power that would be reflected by a mirror of the same coating as the grating, therefore attributing to inevitable reflection losses at the grating but not caused by inefficient diffraction itself.

## References

1. **[^](#cite_ref-1)** ["Diffraction Efficiency & Relationship between Diffraction Efficiency and Polarization"](http://www.shimadzu.com/products/opt/oh80jt0000001v0w.html). Shimadzu Corporation. 2012. Retrieved 1 November 2012.

1. **[^](#cite_ref-2)** ["Technical Note 10 – Guidelines for specifying diffraction gratings"](http://gratings.newport.com/library/technotes/technote10.asp). Newport Corporation. Retrieved 1 November 2012.

## External links

- Christopher Palmer (2020). ["Efficiency Characteristics of Diffraction Gratings"](https://www.gratinglab.com/Information/Handbook/Handbook.aspx). *Diffraction Grating Handbook (8th edition)*. MKS Newport. Retrieved 13 March 2020.

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