Questions about Chalcogenides
While the chalcogenides family of glasses is typically more difficult to process than crystalline IR materials, the range of benefits (listed below) often outweigh process issues in optical applications.
- Low weight
- Relatively low overall cost
- Higher transmission across the entire IR spectrum
- Variable fabrication approaches
- High refractive index
Chalcogenides are considered ideal in applications where weight and athermalized substrate materials are factors driving success. Designers are able to achieve more favorable athermal performance, while still maintaining a high degree of flexibility in terms of fabrication techniques. The relatively low change in refractive index to temperatures and an operating temperature range of -40 C to +60 C allows engineers to leverage chalcogenides for a broad spectrum of applications including moldable infrared optics like lenses, optical fibers, lasers, planar optics and integrated circuits among others.
Chalcogenides, while offering exceptionally favorable optical properties present unique difficulties during the manufacturing and coating process. Featuring amorphous less-robust structures, chalcogenides are markedly different from other infrared materials resulting in low adhesion between the glass and thin-film layers. They are also softer and prone to scratches and other surface-level defects, making it vital to perfect the ability to add protective layers of coating. Creating an extremely durable low stress coating for high-performance infrared (IR) applications has posed a challenge for manufacturers for years. The ideal parameters for achieving a high-performance coating are narrow and can be notoriously difficult to achieve, particularly when you attempt to coat chalcogenides with Diamond-Like Carbon (DLC) for specific applications.
DLC is notoriously difficult to utilize as a material for coating chalcogenides due to its tendency towards tiny defects called pinholes and the challenges with achieving uniform coating thickness. Poor coating adhesion and high compressive stress plague DLC applications on chalcogenides, which can lead to failures between the base material and the coating. Uncontrolled coating stress often results in “crazing” resulting in short and long-term failures.
The process of coating chalcogenides with DLC is what many might call a temperamental process — too few layers and you fail to meet the required durability levels, while too many layers can lead to undue stress and premature rupture. Finding the ideal balance has been a challenge but, here at Dynasil, we have developed a proprietary technique that produces dependable, long-lasting DLC coatings on chalcogenides at scale with virtually zero pinholes.