Broadband metallic mirror coatings providing high reflectance across wide spectral ranges from deep UV to far infrared. Protected versions offer durability for practical optical systems.
Metallic coatings reflect light through free-electron interaction in the metal's conduction band. Unlike dielectric coatings that rely on interference, metals reflect intrinsically across broad wavelength ranges determined by their plasma frequency and interband transitions.
Aluminum is the most versatile metallic coating, offering 85-92% reflectance from deep UV (120nm) through the visible and into the infrared. When freshly deposited and protected with SiO2 or MgF2, aluminum maintains performance for years in normal environments.
Gold provides excellent reflectance (>98%) from 600nm through the far IR (>20μm), making it ideal for thermal imaging, spectrometer optics and laser systems operating in the near to mid-IR. Gold is chemically inert and does not require a protective overcoat.
Silver offers the highest visible and IR reflectance (>99% from 500nm to 20μm) of any metallic coating. Protected silver designs use dielectric barrier layers to prevent sulfidation, making them suitable for telescope mirrors and precision broadband optics.
| Parameter | Aluminum | Gold | Silver |
|---|---|---|---|
| Reflectance Range | 85-92% | 500nm-20μm: >98% | 500nm-20μm: >99% |
| UV Performance | Excellent (120nm+) | Poor (< 500nm) | Poor (< 400nm) |
| Visible | Good (85-92%) | Yellow tint | Excellent (>99%) |
| IR Performance | Good to 20μm | Excellent (>99%) | Excellent (>99%) |
| Chemical Stability | Needs protection | Inherent | Needs protection |
| Hardness | Soft | Very soft | Soft |
| Typical Protection | SiO2 or MgF2 overcoat | None needed | Dielectric barrier |
| LIDT | Available: 1-10 J/cm² | Available: 1-5 J/cm² | Available: 2-10 J/cm² |
| Type | Composition | Range | Application |
|---|---|---|---|
| Protected Aluminum | Al + SiO2/MgF2 | 180nm-2μm | General optics, UV-VIS |
| Enhanced Aluminum | Al + dielectric stack | 250nm-20μm | Broadband, telescopes |
| Protected Silver | Ag + dielectric barrier | 400nm-20μm | Telescopes, precision optics |
| Protected Gold | Au + protective layer | 500nm-20μm+ | IR optics, thermal |
| Bare Gold | Au (no protection) | 600nm-20μm+ | Vacuum IR, spectroscopy |
| Bare Silver | Ag (freshly deposited) | 350nm-20μm | Laboratory use |
Reflector telescopes use protected aluminum or silver coatings on primary and secondary mirrors. Enhanced aluminum designs improve IR performance for astronomical observations.
Systems operating across wide spectral ranges (UV-Vis-NIR) use enhanced aluminum mirrors for uniform broadband performance where dielectric mirrors would be too narrowband.
Gold-coated mirrors are standard for IR spectrometers, thermal imaging test systems and CO2 laser beam delivery due to excellent IR reflectance.
Concentrated solar power systems use silver or aluminum-coated mirrors for heliostats and parabolic troughs.
General-purpose reflectors in lighting, projectors and optical instruments use protected aluminum for cost-effective broadband reflection.
PhotonEdge offers coated optical components compatible with Metallic Coatings (Al/Au/Ag). Explore related products below.
Choose metallic when you need broadband performance across a wide spectral range, or when cost is a factor. Choose dielectric when you need >95% reflectance at a specific wavelength, high LIDT, or very narrow spectral control.
Modern protected silver coatings with dielectric barrier layers can maintain >98% reflectance for 10+ years in controlled environments. Telescope mirrors typically last 5-10 years before recoating is needed.
Yes. Bare metals (Al, Au, Ag) work well in vacuum and are actually preferred because there is no risk of oxidation or contamination. Bare gold is standard for space-based IR instruments.
Enhanced aluminum adds 2-4 dielectric layers over the aluminum base coat to boost reflectance in specific wavelength bands (e.g., visible) while maintaining reasonable UV performance. This gives 93-96% reflectance across 400-700nm vs 85-92% for standard protected Al.
Our optical engineers can help you select or design the optimal coating for your application.
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