Metals have a strong spectral reflectance over a wide range of wavelengths. Silver has the highest reflectance in the visible and infrared regions of the spectrum of all metals, making Ag coatings ideal for highly reflective component applications like reflectors. Unprotected Ag coatings, on the other hand, are susceptible to environmental impacts, and their high reflectivity quickly deteriorates owing to oxidation.
For reflector applications, Ag coatings with one or more protective layers are required to avoid this. Protected silver mirror coatings are available from Alfa Chemistry to support your varied optical applications and research. To keep the Ag coating from oxidizing and lowering reflectivity, we apply a protective Si3N4 coating on top of it, which functions best in low-humidity conditions, with good aqueous solution resistance and minimal mechanical stress.
Applications and Benefits of Protected Silver Mirror Coating
The Ag coating's protective layer must be highly resistant to liquid solutions (acid and alkali resistance). In addition, it should also have low mechanical stress. Both tensile and compressive loads can cause cracks in the protective layer and delamination to the point where the protected silver coating is compromised.
Fig 1. The removal rate in nm / h of the SiO2 layers "SiO2_20Ar" and "SiO2_35Ar" (a) and the Si3N4 layers (b) in a basic solution (pH-value between 12.5 and 13), expressed through the negative slope m. (Schwinde S, et al. 2019)
Protective layers of Si3N4 are deposited by Alfa Chemistry using reactive sputtering. Protective layers of Si3N4 are deposited by Alfa Chemistry using reactive sputtering. Our protected silver mirror coating offers a highly visible and near-infrared reflectivity, as well as outstanding polarized and unpolarized light reflection. To protect the Ag coating from oxidation or abrasion in the air, the protective Si3N4 exterior coating provides outstanding anti-oxidation capabilities. Digital camera mirror optics, laser mirrors, medical equipment, gold mirror replacements, and more applications employ our coatings.
Alfa Chemistry Standard Optical Coating
Our protected silver mirror coating has a high optical reflectivity for infrared light and has a broad optical reflectivity in the visible spectrum. Unlike dielectric mirror coatings, our silver coatings' reflectivity is essentially unaffected by the polarization of incident light. For great imaging quality, our protective silver mirror coating is overlaid with a high-quality glass substrate.
Our coating is appropriate for various medical applications that demand high reflectivity at a low cost due to its superb high reflectivity. It's also perfect for femtosecond pulsed lasers.
| Wavelength Range | 450-2000 nm; 2000-10000 nm |
| Reflection Specifications | Ravg >98%; Ravg >98% |
| Typical Energy Density Limit | 0.5 J/cm2 @ 532nm & 1064nm, 10ns |
| Coating Construction | Silver, protected by Si3N4 coating |
| Substrate Material | Select mirror-grade glass; Other glass substrate materials available upon request |
| Standard Glass Thicknesses | 1.00 mm ± 0.10 |
| Standards | Adherence according to MIL-M-13508C
Hardness according to MIL-M-13508C |
Environmental forces and incorrect handling can cause damage to silver plated coatings. Fingerprints, improper contact, and high humidity/high temperature settings can all compromise the protective coating's effectiveness. Follow the normal guidelines for treating optical components when employing silver mirrors.
For tiny one-off orders, Alfa Chemistry can provide a choice of unique optical coatings. Contact us if you need custom optical sizes, geometries, substrate materials, or coatings. Please contact technical support for further information or to inquire about customisation.
Reference
- Schwinde S, et al. (2019). "Protected Silver Coatings for Reflectors." International Conference on Space Optics. 11180: 111804M.
