Optical Coating Degradation Problems

We use Nomarski phase interference contrast microscopy to identify damage and chemical attacks in anti-reflective coatings on optical elements. Here are four examples:

Optical Coating Example 1

Humidity acting upon an underlayer film in a multi-layer optical coating through a surface pinhole in the outer protective layer caused the damage above and the surface debris due to corrosive chemical reaction.
Humidity penetrated a pinhole in the outer protective layer. This damaged the underlayer film and created surface debris from a corrosive reaction.

Optical Coating Example 2

Underlayer chemical attack of anti-reflective optical coating
Moisture attacked an underlayer in a multi-layer anti-reflective coating. The attack followed a random path, likely due to lattice defects in an oxygen-deficient oxide.

Example 3

Damage caused to an anti-reflective coating upon attempted cleaning of high-value optical elements due to chemical attack through defects by the cleaning chemical.  The Nomarski method greatly enhances the visibility of the extensive underlayer damage.
Cleaning high-value optical elements caused damage to the anti-reflective coating. Cleaning chemicals attacked through defects. The Nomarski method revealed extensive underlayer damage.

Example 4

Delamination during a low-adhesion tape pull test. The coating was invisible to the naked eye but easily seen with Nomarski microscopy, which also showed the size, elongation, and completeness of the film failure.

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