# Diffraction efficiency

Diffraction efficiency is the performance of diffractive optical elements – especially diffraction gratings – in terms of power throughput. It's a measure of how much optical power is diffracted into a designated direction compared to the power incident onto the diffractive element.

If the diffracted power is designated with $P$ and the incident power with $P_0$ the efficiency $\eta$ reads

$\eta = \frac{P}{P_0} \ .$

## 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. ^ "Diffraction Efficiency & Relationship between Diffraction Efficiency and Polarization". Shimadzu Corporation. 2012. Retrieved 1 November 2012.
2. ^ "Technical Note 10 – Guidelines for specifying diffraction gratings". Newport Corporation. Retrieved 1 November 2012.