Supermirrors

Author: the photonics expert Dr. Rüdiger Paschotta

Definition: laser mirrors with a very high reflectivity

More general term: mirrors

Category: article belongs to category photonic devices photonic devices

DOI: 10.61835/w54 Cite the article: BibTex plain text HTML

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.

More to Learn

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Suppliers

The RP Photonics Buyer's Guide contains seven suppliers for supermirrors. Among them:

LASEROPTIK

So-called supermirrors for ring laser gyroscope assemblies or certain scientific applications require coated optics with extremely low losses (i.e. absorption and scattering). These mirrors also have a maximum reflectivity with R > 99.998% and total losses < 10 ppm.

LASEROPTIK uses a modified IBS machine that is capable to produce coatings on superpolished substrates. The cleanliness of the machine and environment is maintained in a dedicated super-clean room, where also the extensive substrate pre- and after-treatment takes place.

Measurement devices such as white light profilometers and high resolution microscopes (up to × 1000) for the inspection procedures are in place. A custom built cavity ring-down setup allows to determine the reflection with a precision of up to four decimal places and to refer back to the losses.

Bibliography

[1]	O. Schaerpf, “Comparison of theoretical and experimental behaviour of supermirrors and discussion of limitations”, Physica B: Phys. Cond. Matter 156, 631 (1989); https://doi.org/10.1016/0921-4526(89)90750-3
[2]	R. P. Stanley et al., “Ultrahigh finesse microcavity with distributed Bragg reflectors”, Appl. Phys. Lett. 65, 1883 (1994); https://doi.org/10.1063/1.112877
[3]	C. J. Hood, H. J. Kimble, and J. Ye, “Characterization of high-finesse mirrors: Loss, phase shifts, and mode structure in an optical cavity”, Phys. Rev. A64 (3), 033804 (2001); https://doi.org/10.1103/PhysRevA.64.033804
[4]	A. Schliesser et al., “Complete characterization of a broadband high-finesse cavity using an optical frequency comb”, Opt. Express 14 (13), 5975 (2006); https://doi.org/10.1364/OE.14.005975
[5]	A. Muller et al., “Ultrahigh-finesse, low-mode-volume Fabry–Pérot microcavity”, Opt. Lett. 35 (13), 2293 (2010); https://doi.org/10.1364/OL.35.002293
[6]	G. D. Cole et al., “Tenfold reduction of Brownian noise in high-reflectivity optical coatings”, Nature Photonics 7, 644 (2013); https://doi.org/10.1038/nphoton.2013.174
[7]	G. D. Cole et al., “High-performance near- and mid-infrared crystalline coatings”, arxiv.org 1604.00065

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