Common Resources: Optics Cleaning Basics

Basic Optics Cleaning

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 and ensure their continued performance. For cleaning optics with Bare Gold or other soft metal coatings, please refer to our article entitled "Cleaning Bare Gold Optics".

General Tips

If it’s not dirty, don’t clean it! Handling optics increases their chances of getting dirty or damaged, so you should clean optics only when necessary.

You should handle optics in a clean, low-dust environment while wearing powder-free acetone-impenetrable Gloves or Finger Cots. Since oil and debris from your hands or from used lens tissue can stain or damage optical coatings, you should not touch any transmissive or reflective surface of your optic and never reuse a lens tissue. Remember that lens tissues are inexpensive compared to the price of an optic.

Inspect an optic for dust and stains by holding it near a bright visible-light source. Viewing the optic at different angles allows you to see scattering from dust and stains.

Step 1. Use a clean-air duster:
Dusting is always the first step in cleaning your optics. Wiping a dusty optic is like cleaning it with sandpaper. So always dust with either a canned air duster, or low-pressure compressed and filtered air or nitrogen before wiping any optic. If the dusted optic has no visible stains after you dust it, then remember: “If it’s not dirty, don’t clean it.” If it’s still not clean, proper use of solvents and lens tissue can often do the trick.

Step 2. Use solvent and lens tissue. The way to use them depends on the optic, but always wipe slowly and clean the edges first.

Glass-cleaning solvents will streak, and tissue paper or a t-shirt will scratch, so always clean optics with reagent or spectrophotometric grade solvent and a low-lint tissue manufactured for cleaning optics. Always use lens tissue with a solvent, because dry lens tissue can scratch optical surfaces. A good solvent to use is a mix of 60% acetone and 40% methanol. Acetone alone dries too quickly to dissolve all of the debris. The methanol in the solution slows the evaporation time, and also dissolves debris that acetone alone would not clean. Isopropyl alcohol is safe and effective, but its relatively slow evaporation rate can leave drying marks on the optic. Cleaning your optic’s edges before cleaning its faces prevents dirt from being drawn up onto the face. Wiping slowly allows the solvent to evaporate without streaking. Remember, slow and steady cleans the optic.

NOTE: Always use acetone-impenetrable gloves when using acetone.

The “Drop and Drag” Technique

The “drop and drag” technique is ideal for light cleaning of unmounted optics, such as our optical filters.

Place your optic on a clean, non-abrasive surface, such as a clean-room wiper. After blowing off the dust using compressed air or nitrogen, lay a piece of unfolded lens tissue over the optic, drop on some solvent, and slowly drag the soaked tissue across the optic’s face. Remember to clean the edges of your optic before you clean the face.

The “Brush” Technique

Use the “brush” technique for small optics, such as our 5CGA-### series of Colored-Glass Alternative Filters.

Make a lens-tissue brush by folding the lens tissue so that the fold is as wide as the optic to be cleaned. Do not touch any part of the tissue that will touch the optic. With a hemostat or tweezers, grip the folded tissue parallel to and near the fold. Wet the “brush” with acetone and shake off any excess liquid.

Blow off the dust. Place the brush on the optic surface, apply slight pressure with the hemostat, and slowly wipe straight across, from one edge of the optic surface to another.

The “Immersion” Technique

For softer coatings, which damage more easily, we recommend using the “immersion” technique. Simply remove any dust from the optic and then immerse it in acetone. If the optic is very dirty, you can use an ultrasonic bath. Rinse and immerse the optic in fresh solvent a number of times until it’s clean. To dry the optic, carefully blow the solvent off (from one direction to avoid leaving drying marks) with low-pressure compressed and filtered air or nitrogen.