One of the most commonly asked questions we get here at North American Coating Laboratories is “how do we clean an anti-reflective coated part once we receive it?” This question is especially important in the high-end precision optics realm, as small particulate on top of a coated surface can disrupt numerous optical systems that operate behind the coated substrate.
The reason anti-reflective coatings are difficult to clean is due to their “peak and valley” microstructure that is a catalyst for destructive interference of light. In general terms an anti-reflective coating is a series of dielectric layers with varying refractive indices that when viewed under a microscope form a structure very similar to a mountain range with peaks and valleys. In some cases airborne dirt and lint, and or residue from packaging get trapped in these valleys and are not easy to remove.
Because anti-reflective coatings are not chemically resistive certain cleansers could attack the film structure and begin to stress the film over time. This is why we recommend the following process for cleaning an anti-reflective coated lens.
In a small clean glass or plastic container mix 1 part isopropyl alcohol to 3 parts clean distilled water.
Use this solution to wet the entire coated surface.
With a soft cotton or microfiber cloth wipe the coated surface dry. Applying pressure while you wipe to any specific area with high amounts of particulate is fine./li>
After the substrate is dried, examine the coated optic with standard ambient lighting against a black background. This will be a true indicator of how clean the coating is after the cleaning process.
Due to the amount of inquiries we receive from our customers and other members of the optics community concerning cleaning coated optics North American Coating Laboratories has developed our own thin-film cleaner that we can provide in either a 6 ounce or 3.5 ounce spray bottles. If you don’t want to go through the trouble of creating your own cleaning mixture we would be more than happy to provide our formula to assist your inspection staff in the cleaning process.
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