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High Temperature Anti-Reflective Coating

Background

Industry – Medical device

Requirement

An anti-reflective (AR) coating needed to be applied over a sapphire window and survive 1,000C high temperature braze processing. The coating of the sapphire could not show any physical delamination, crazing, or degradation of the optical properties such as transmission and/or reflectance in the specific spectral regions.

Materials Used

Titanium alloy – FDA approved
Optical window –Sapphire with AR coating

Challenges:

Sapphire is an excellent optical material for the visible range of the spectrum with a transmission of approximately 85%. The project required even greater transmission via application of an A/R coating.  Hermeticity requirements along with the 5,000 cycle autoclave ability meant no low temperature solder could be considered. Therefore, the whole assembly needed to be bonded by brazing. Typical, A/R coatings such as MgF2 and CaF2 cannot withstand these conditions.

The primary issue was how to ensure the selected A/R coating adheres to the sapphire without delamination, crazing or any changes of optical properties.

Solution:

Over the course of a few months IJ Research developed its own custom AR coating that withstands braze processing, shows minimal and predictable spectrum shift, and negligible degradation of transmission performance before and after brazing.

Results:

The resultant brazed assemblies with the new anti-reflective coating established an immediate market advantage for our customer. Our unique coating expertise was able to enhance the performance of their units well beyond that of any competition. This project demonstrated the diverse utility of IJ Research’s in-depth material science background to all projects and clients.