定义：具有非常高反射率的激光反射镜。

光学超反射镜是一种电介质反射镜，具有非常高的反射率，极限情况下甚至大于99.9999%。这表示反射损耗小于1 ppm。两个这种反射镜可以组成一个法布里-珀罗干涉仪，精细度大于300万，在腔内具有很强的场增强效应。超反射镜腔的Q因子大于1011。 
超反射镜可以用于一些量子光学实验和一些极高精度测量中，例如高精细度干涉仪或者陀螺仪中。 
超反射镜更长用于X射线和中子反射镜。在该领域，最初很难实现很高的反射率。然后发展了多层反射镜，能够得到高很多的反射率。 

Definition: laser mirrors with a very high reflectivity

More general term: mirrors

An optical supermirror is a Bragg mirror (typically a dielectric mirror) that is optimized for an extremely high reflectance – in extreme cases, larger than 99.9999%. This means that the reflection losses are below 1 ppm. Two such ultra-high reflectance mirrors form a Fabry–Pérot interferometer with a finesse larger than 3 millions and a strong field enhancement within the cavity. The Q factor of a supermirror cavity can be above 10¹¹.

Although most supermirrors are dielectric mirrors (often with Ta₂O₅/SiO₂ layers made by ion beam sputtering), there are also crystalline mirrors [6] with very high peak reflectivities of e.g. 99.9997% [7].

Supermirrors can be used in certain quantum optics experiments and for some measurements with extremely high precision, e.g. involving high-finesse interferometers or optical gyroscopes.

The term supermirror is also common for X-ray and neutron reflectors. In that field, it was originally very difficult to achieve high reflectance values. Multilayer mirrors have then been developed, which offer much better performance. Still, the achieved peak reflectivities are far lower in this regime, comparing with optical supermirrors.

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