Protected Aluminum Mirrors, Protected Silver, Protected Gold, Mirrors

Technical Coating Data for:

• Protected Aluminum Mirrors (PAL)
• Protected Silver Mirrors (PAG)
• Protected Gold Mirrors (PAU)

Metallic coated optical mirrors are coated with various metals to provide reflectivity across the UV, VIS, and IR spectra making them an excellent choice for a wide range of applications. When choosing a metallic coating, one should carefully consider the following:

Intended wavelength of use
Required reflectance
Environment in which the mirror will be used

Advanced Optics manufactures optical mirrors that offer reflectivity from 190nm – 20µm. Please visit our technical bare (unprotected) metallic coatings page to learn more about mirrors without a protective overcoat.

Please visit our optical mirrors page to see a full list of our capabilities and our in-stock optical mirrors.

Protected Aluminum Mirrors (PAL)

Protected aluminum mirrors are coated with aluminum and a ½ wave of either silicon monoxide or silicon dioxide overcoat. The choice of overcoat may need to be considered due to the thermal implications of how each is applied and the wavelength of intended use. Either overcoat provides abrasion resistance for the soft aluminum underneath, which should otherwise not be touched or cleaned. The protective overcoat also keeps the aluminum from oxidizing over time.

Protected aluminum is a popular choice in the visible spectrum due to its low cost and good reflectivity with R_avg >85% from 400 – 700nm. It continues to provide good reflectivity into the NIR spectrum with R_avg >90% 400 – 2000nm making it an excellent choice for many broadband applications.

Protected Aluminum with ½ Wave of Silicon Monoxide

The disadvantage of this common, general-purpose coating is the dip in reflectivity at 880nm, which is due to the aluminum and enhanced by the overcoat. However, protected aluminum mirrors can be customized by centering the coating at a specific wavelength to maximize reflectivity where it matters most to your application. This makes protected aluminum mirrors not only economical but flexible enough to be used in a wide range of applications.

Advanced Optics fabricates protected aluminum mirrors in almost any configuration from commercial grade down to 1/20 wave. For further information on how we can help you design the proper optical mirror for your application please visit our optical manufacturing capabilities page.

Enhanced Aluminum Mirrors

Enhanced aluminum mirrors are overcoated with a thin dielectric layer that provides protection and durability to the fragile aluminum underneath, which otherwise should not be touched or wiped. Enhanced aluminum mirrors can be specifically tailored to improve reflectivity in either the UV or the visible spectrum, thereby extending their application range.

UV and DUV Enhanced Aluminum Mirrors Enhancing the aluminum in the UV spectrum provides R_avg >90% 250 – 450nm and R_avg >85% 250 – 700nm.

UV Enhanced Aluminum Coating

In addition to our standard UV enhanced aluminum coating, Advanced Optics offers a deep UV enhanced aluminum coating for use down to 190nm.

Visible Spectrum Enhanced Aluminum Mirrors

Enhancing the aluminum in the visible spectrum provides R_avg of 93% 400 – 700nm, which peaks at 95 – 96% at 520nm.

Enhanced Aluminum Coating

As with our standard protected aluminum coatings, Advanced Optics can design UV enhanced aluminum and visible spectrum enhanced aluminum coatings centered at a specific wavelength to maximize reflectivity in the area of the spectrum that matters most to your application. Advanced Optics fabricates enhanced aluminum mirrors in almost any configuration from commercial grade down to 1/20 wave. Please visit our optical manufacturing capabilities page to see how we can help you meet your requirements.

Protected Silver Mirrors (PAG)

Protected silver mirrors have a thin dielectric overcoat that provides durability and prevents the silver underneath from rapid oxidation. These mirrors offer higher reflectivity over a broader spectral range than aluminum coated mirrors with R_avg > 97.5% from 450 – 2000nm and R_avg > 98% from 2 – 20µm. This makes them ideal for applications that require high, fairly flat reflectivity over the visible and NIR spectrum.

Protected Silver Coating

The disadvantage of choosing a protected silver mirror is its propensity to oxidize over time. The protective dielectric overcoat is helpful but these mirrors will eventually tarnish, and environmental factors such as humidity will accelerate the process.

Advanced Optics fabricates protected silver mirrors in almost any configuration from commercial grade down to 1/20 wave. Please visit our optical manufacturing capabilities page for additional information

Enhanced Silver Mirrors

Silver can be enhanced to provide 99% reflectivity at a specific wavelength between 400nm – 20µm. However, the overall curve is not as flat as standard protected silver as illustrated in the curve below, which is optimized at 520nm.

Enhanced Silver Mirror Coating

Advanced Optics fabricates protected silver mirrors in almost any configuration from commercial grade down to 1/20 wave. For further information on how we can help you design the proper optical mirror for your application please visit our optical manufacturing capabilities page.

Protected Gold Mirrors (PAU)

Protected gold mirrors have a thin dielectric overcoat that provides durability for the soft gold underneath, which otherwise should not be touched or cleaned. When your application requires high reflectivity in the NIR or IR spectrum, these mirrors excel with R_avg >96% from 700 – 2000nm and R_avg >98% from 2 - 10µm.

Protected Gold Coating

The disadvantage of a protected gold coating is that it does not reflect well in the visible spectrum.

Advanced Optics can help you customize your protected gold coating to meet your reflectivity requirements. We fabricate protected gold mirrors in almost any configuration from commercial grade down to 1/20 wave. Please visit our optical manufacturing capabilities page to see how we can help you meet your requirements.

Summary of Protected Metal Coatings

Coating Type	Reflectivity/Wavelength Range	Usage/Advantages	Disadvantages
Protected Aluminum (PAL)	Ravg >85% from 400 – 700nm Ravg >90% 400 – 2000nm	Popular, low cost, general-purpose visible spectrum coating Does not oxidize over time like protected Ag Provides good reflectivity into the NIR and IR spectrum Can be customized at a specific wavelength to meet exact reflectivity requirements Can be coated with silicon monoxide or dioxide depending on application	Reflectivity of the standard coating dips below 80% at 880nm Does not reflect well below 350nm as it starts to absorb, UV enhanced Al is recommended
Enhanced Aluminum	UV Enhanced Al R_avg >90% 250 – 400nm R_avg >85% 250 – 700nm Deep UV enhanced Al coating with reflectivity down to 190nm Enhanced Al R_avg 93% from 400 – 700nm with a peak of 95 – 96% at 520nm	Optimized for UV reflection down to 190nm Standard coating does not dip as low at 880nm as does standard protected aluminum Provides enhanced reflectivity over protected Al. Does not oxidize like protected Ag. Can be customized at a specific wavelength to meet exact reflectivity requirements	Lower reflectivity than protected Al in the visible spectrum Compared to protected Ag, it does not provide a high, flat reflectivity over the visible and IR spectrum
Protected Silver (PAG)	R_avg > 97.5% for 450 – 2000nm R_avg > 98% for 2 – 20µm	Provides high broadband reflectance extending into the IR spectrum Can be customized at a specific wavelength to meet exact requirements Provides fairly flat reflectivity after 550nm	Will oxidize over time, especially under harsh environmental conditions More costly than protected Al and enhanced Al
Enhanced Silver	R=99% were centered	Can be optimized to provide 99% reflectivity in the region where the coating is centered	Overall reflectivity not as flat as standard protected Ag More costly than standard protected Ag
Protected Gold (PAU)	R_avg >96% from 700 – 2000nm R_avg>96% from 2 – 10µm	High reflectivity in the NIR and IR spectrum Gold is chemically inert and highly corrosion resistant Can be customized at a specific wavelength to meet exact reflectivity requirements	Low reflectivity in the visible spectrum which falls off dramatically at 700nm