HEAR & DLC Coating
HEAR and DLC Coating
HEAR and DLC coatings are used in specialized military and defense and scientific applications.
A High-Efficiency Anti-Reflective or HEAR coating is an optical coating applied to surfaces to reduce the amount of reflected light. It is typically used in optical applications where the coating is applied to the front of an interface between the medium (air) and a lens, glass, or a mirror. An AR coating is designed to maximize the amount of light that transmits or enters the medium while minimizing the light lost to reflection. The coating helps improve the efficiency of optical instruments, enhances contrast in imaging devices, and reduces scattered light that can interfere with the optical performance of telescopes, cameras, binoculars, and eyeglasses. An HEAR coating is an AR coating featuring reflection of <= 0.3% (per surface) and a transmission average of >= 98%. The process of coating optics with a HEAR coating has been well-established in the industry, providing superior durability and reliability but at an incremental cost.
While an HEAR coating ensures high-performance, it remains susceptible to harsh environmental conditions. HEAR coatings aren’t as durable when subjected to those conditions. Although this does not apply to every use case it can greatly reduce the viability of using HEAR-coated optics in certain applications.
A DLC coating offers an ideal solution for coating IR optics, creating an amorphous coating that is extremely durable, has exceptional abrasion resistance, a low coefficient of friction, is biologically compatible, electrically insulating and optically transparent — in short, nearly perfect in terms of an optical coating.
While an HEAR coating is straightforward for most manufacturers, ensuring a high-performance DLC coating consistent enough to withstand the harshest environmental conditions still poses significant challenges for some of the most established optical coating companies.
At Dynasil, we have designed a custom DLC coating chamber and developed a proprietary PE-CVD technique that produces dependable, long-lasting DLC coatings on virtually all IR substrates including Germanium (Ge), Silicon (Si), Zinc Sulfide (ZnS), Zinc Selenide (ZnSe) and Chalcogenides (As40 Se60) at scale with virtually zero pinholes.
We can help you eliminate the four most common coating issues – pinholes, uniformity, stress and adhesion. Everything from our chamber’s circular geometry, gas inputs, operating temperature, and even the coating direction has been carefully designed and calibrated to ensure that our coating stands up to the toughest military specs. We have successfully coated infrared optics for some of the most demanding commercial and military applications.
Ideal Substrate Materials for IR Wavelengths
SWIR // 0.9 – 2.7µ
Glass, Sapphire, Calcium Fluoride, Zinc Selenide, Zinc Sulfide
MWIR // 3.0 – 5.0µ
Sapphire, Calcium Fluoride, Silicon, Germanium, Zinc Selenide, Zinc Sulfide, Chalcogenides
LWIR // 7.0 – 14.0µ
Germanium, Zinc Selenide, Zinc Sulfide, Chalcogenides
MWIR-LWIR // 3.0 – 14.0µ
Germanium, Zinc Selenide, Zinc Sulfide (multi-spectral), Chalcogenides
Reflectance Chart for Germanium (8-12 µ)
Average Reflectance <= 0.3% at near normal AoI Transmission Average >= 98%
DLC Spectral Performance
Range: 8.0 – 11.5 µ
AOI: 0° – 20°
Transmission: >= 90% avg.
Range: 8.0 – 12.0 µ
AOI: 0° – 20°
Transmission: >= 88% avg.
MIL-Standard DLC Coatings
- Adhesion: Per MIL-M-13508C para 4.4.6 (fast pull)
- Abrasion: Per MIL-C-675C para 4.5.10. (severe abrasion 40 strokes)
- Humidity: Per MIL-C-675C para 4.5.8. Min 24 hours
- Solubility: Per MIL-C-675C para 4.5.7. Immersion for period of 24 hours in water/salt
- Salt Spray: Per MIL-C-675C para 4.5.9. Salt spray-fog test for a continuous period of 24 hours
- Temperature Cycle: Per MIL-M-13508C para 4.4.4.
- Wiper Test: No signs of removal when exposed to 5,000 revolutions sand/slurry mixture