Dust and stains on Optics can cause scattering, and impurities on the optic surface can react with incident laser light to damage optical coatings. With proper handling and cleaning of your optics, you can prevent damage, ensure their continued performance and extend the usable lifetime of your optics.
Optics should be handled in a clean, low-dust, temperature-controlled environment while wearing powder-free, acetone-resistant gloves or finger cots. Human sweat is highly corrosive, and oils or debris from hands or used lens tissues may damage optical coatings. Therefore, it is recommended to avoid direct contact with any transmissive or reflective optical surface. When necessary, optics may be held by their ground edges, handled with gloves or finger cots, or placed on clean lint-free wipes during inspection or cleaning. Lens tissues should never be reused, as their cost is minimal compared to the value of an optical component.
When removing optics from shipping or transport containers, note that these components are fragile. In a clean, temperature-controlled environment, carefully open the package to avoid unintended damage. Using gloves or finger cots, remove each optic and place it on a clean lint-free wipe or in a suitable optical storage container. For very small or delicate components, soft-tipped tweezers or suction tools may assist in handling. Metal tools should not be used. Regardless of the method, it is best to hold optics by their non-optical surfaces, such as ground edges. Many crystals are temperature-sensitive and may crack, so the package should be allowed to reach thermal equilibrium before handling. Certain surfaces—such as holographic and ruled gratings, first-surface unprotected metallic mirrors, and pellicle beamsplitters—are extremely delicate and may be damaged by any physical contact.
To inspect for dust or stains, hold the optic near a bright visible light source. Observing the surface from multiple angles helps reveal scattering caused by contamination.
Dust removal is the initial and essential step in optical cleaning. Wiping a dusty optic without first removing particulate is equivalent to abrading the surface; therefore, always use a canned air duster, compressed and filtered air, or dry nitrogen to remove loose dust before any wiping. After dusting, if no visible stains remain, follow the guideline “avoid any additional wiping or cleaning” to prevent unnecessary mechanical contact that may introduce scratches or residues. If contamination persists after dust removal, careful use of appropriate solvents together with fresh lens tissue or lint-free wipes can often restore the optic’s cleanliness.
The method for applying solvents and lens tissue varies depending on the specific optical component, but the general practice is to wipe slowly and clean the edges before addressing the optical surfaces.
Glass-cleaning household solvents tend to create streaks, and materials such as tissue paper or fabric can introduce scratches. For this reason, optics should only be cleaned using reagent-grade or spectrophotometric-grade solvents in combination with low-lint lens tissue designed specifically for optical cleaning. Lens tissue should always be used with solvent, as dry tissue may cause micro-abrasions on the surface. A commonly used cleaning mixture consists of 60% acetone and 40% methanol. Acetone alone evaporates too quickly to fully dissolve contaminants, while the addition of methanol both slows the evaporation and dissolves residues that acetone cannot remove. Isopropyl alcohol is also safe and effective, although its slower evaporation rate can leave drying marks.
For optics with edges that are difficult to access, a small cleaning brush can be prepared by wrapping a piece of lens tissue around the soft tip of a synthetic low-lint swab. In a single continuous motion, “paint” along the perimeter of the optic and then sweep across the center. Maintaining a continuous motion helps prevent the formation of drying marks.
(not recommended for metallic coatings)
This method is suitable when more intensive cleaning is required to remove persistent stains. Fold the lens tissue in the same manner as in the brush technique, but hold it directly with your gloved fingers rather than using a tool. Apply uniform pressure along the optic’s edge and slowly wipe across the optical surface. This technique is effective for removing stubborn contamination on coatings that are more resistant to mechanical contact.
After the cleaning process is complete, place the optic directly into its intended mount or wrap it individually in lens tissue and return it to its protective container. Each optic should be wrapped separately, and unwrapped optics should never be stored together in the same bag or box, as direct contact may lead to scratches or surface damage. Because optical components are fragile, avoid storing heavier items on top of them.
Cleaning the edges of the optic before the optical faces helps prevent contaminants from migrating onto the surface during wiping. Slow and steady wiping allows the solvent to evaporate cleanly without streaking.
For plastic optics or optics housed in plastic components, acetone should never be used, as it can damage the material. Only compressed air, reagent-grade alcohol, or de-ionized water should be used for cleaning plastic optics. When the optical coating or substrate is unknown, it is safer to rely on de-ionized water and mild dish soap to avoid potential chemical damage.