Care and Cleaning of Laser Optics
The care and cleaning of optics is a very important aspect of the use and maintenance of high-power industrial lasers. The precision optics used in these lasers need to be clean in order to provide the greatest level of performance. Dirty optics can lead to premature failure of the optic itself, as well as overall system performance degradation.
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As explained in several other sections of this catalog, laser optics are produced in two different forms depending on their application: coated uncoated. Coated optics have one or more layers of vapor deposited materials on their surfaces, designed to produce specific levels of reflectivity at given wavelengths. The uncoated optics are intrinsically highly reflective at given wavelengths and are therefore simply ground and polished and left uncoated. The surfaces of all of the optics, coated or uncoated, are very susceptible to damage; some less so than others but all should be considered fragile. The fewer times an optic is cleaned and the less pressure applied during the cleaning, the better. When an optic gets dirty, there is foreign matter on its surface. This is bad for several reasons: the foreign matter will inhibit transmission and/or reflection and will absorb energy causing the optic to heat and potentially deform. If the energy absorption of the foreign matter is high enough, it may cause a burn on the surface of the optic, whether it is coated or not. When a burn mark appears on the surface of the optic, all the cleaning in the world will not remove it. If the optic is coated, several layers of the coating may be damaged.[/one_half][one_half_last]If it is uncoated, residue from the burn may permanently adhere to the surface of the optic. These burned areas absorb at a higher level than all the rest of the optic, thus creating a hot spot. This hot spot causes the optic to deform in a non-uniform fashion, which will affect the ability of the optic to do its job. The best way to avoid damaged optics is to keep them clean at all times. This is obviously easier said than done and, if all the optics are being cleaned too regularly, their life span can be dramatically shortened. The first thing to do is keep the laser system clean and in good working order, and inspect and clean your optics as needed. The second thing to do is follow the proper optics cleaning guidelines. Optics Kit (TST-10839): Materials included:
- Dropper bottle for reagent grade methanol (not included).
- Lens tissue; long fiber, low ash content with no chemical additives (50 sheets) (TST-11006)
- Clean air duster
- Finger cots (12)
- Cotton swabs (12)
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Procedure for cleaning optics
Applying drops of solvent to the optic and lens tissue
This optics cleaning procedure will minimize scratches and provide an effective means for removal of dust and dirt films which may have contaminated an optical component. Following these steps will develop good cleaning habits, which will contribute to a longer and more productive life for your optical components: A. Set aside a clean work area. B. For best results, optics to be cleaned should be removed from the laser system and their mounts. If the optic is mounted, it is impossible to use the recommended cleaning process. Further, the tendency to “scrub” the optic is significant, and will only lead to surface damage and premature failure.
It is impossible to get an optic thoroughly clean without removing it from the system and its mount. Holding it by its edges, inspect the surface to be cleaned by illuminating it with a high intensity light. This will highlight dust particles and films better than average room light. C. Using the clean air duster, blow the surface of the optic to dislodge any loose particles. D. Place the optic on a piece of clean lens tissue. E. The method recommended by Directed Light is the “drop and drag method.” This method depends on the surface tension of the solvent on the optic to create pressure. No other pressure is applied.
Dragging the lens tissue across the face of the optic, removing contaminants and leaving no residual solvent
The lens tissue is laid on the optic surface to be cleaned so that the optic is at one end of the tissue. Enough solvent is applied to make the entire surface of the optic wet, including the tissue. The lens tissue is now slowly pulled parallel to the surface being cleaned until the optic surface is completely dry. If the end of the tissue is reached before the optic is dry, the process should be repeated with slightly less solvent or a larger piece of tissue. Never reuse lens tissue! A curved optical surface is somewhat more difficult to clean as the surface tension of the solvent is not always strong enough to hold the lens tissue down to the surface. In this case, the process should simply be repeated until the optic is 100% clean. The lens tissue should not be reused.