Laser Optical Path Maintenance And Cleaning

Laser Optical Path:

The laser optical path, in simple terms, refers to the path through which the laser propagates. In practical applications, the laser often cannot directly meet the requirements, so various optical components are needed.

Common optical components on the laser optical path include beam expanders, optical mirrors, galvanometers, field lenses, etc.

Possible Results of Optical Path Issues:

• Laser Energy Attenuation: A common issue where optical lenses in the optical path are dirty, resulting in increased transmission rate and overall attenuation, leading to a decrease in the final processing power.

• Degraded Focus Spot Quality: The spot becomes elliptical, and the energy distribution of the spot is uneven.

• Multiple Foci: The optical path alignment is not calibrated properly, causing virtual focus.

• Thermal Drift: Different optical components have different qualities, and the degree of deformation due to heat varies, leading to different levels of thermal drift.

Methods for Optical Path Maintenance

Optical path maintenance mainly refers to the care of optical components in the optical path. Optical components are very fragile, and to achieve the best performance and lifespan during use, specific procedures must be followed. In daily use, optical components come into contact with dust, moisture, skin oils, and other contaminants. These pollutants increase scattering on the optical surface and also absorb incoming light, forming hotspots on the optical surface, which can cause permanent damage. Coated optical components are especially prone to such damage.

Never directly handle optical components with bare hands as skin oils may permanently damage the optical surface. The correct method is to wear gloves. For smaller optical components, optical tweezers or vacuum tweezers are more convenient. No matter what method is used to hold the optical components, always try to grip non-optical surfaces, such as matte edges, if possible.

01 Blowing Off Surface Dust of Optical Components

Before performing any other cleaning techniques, dust and other loose contaminants should typically be blown away. This method requires using an inert dust removal gas canister or a bulb blower. Do not blow directly on the optical component's surface with your mouth, as it could deposit saliva on the optical surface.

If using an inert dust removal gas, always keep the gas canister upright before and during use. Note: Do not shake the gas canister before or during use.

Follow these guidelines:

• Before blowing, aim the nozzle well away from the optical component. These steps help prevent the gas propellant from depositing on the optical surface.

• If using a gas canister, keep it about 6 inches away from the optical component and use short bursts of air.

• Rotate the nozzle of the inert gas canister to blow air at an oblique angle across the optical component.

• For large optical components, blow across the optical surface in the pattern shown below.

Since this cleaning method is non-contact and solvent-free, it should be the first step in cleaning nearly all optical components.

02 Cleaning Optical Components

First, contact the manufacturer for guidance. You can remove fingerprints and large dust particles by soaking the optical components in distilled water and optical soap. The immersion time for optical components should not exceed the time required to remove contaminants. Afterward, rinse the optical components with clean distilled water.

Depending on the type of optical component, you may use a wiping paper (coater) method to apply acetone, methanol, or another fast-drying solvent to the optical component to speed up drying. Avoid letting cleaning solvents form small droplets during the drying process, as this often leaves water stains on the optical surface.

03 Dragging Method

The dragging method can be used to clean any flat optical surface mentioned above.

Follow these steps:

• Inspect the optical component and determine the location of the contaminants. This will help you plan the direction of the drag, allowing you to lift the contaminants from the optical surface quickly, rather than dragging them across the surface.

• After inspection, place and hold the optical component firmly to ensure the lateral force on the surface is minimal, avoiding movement of the optical component. Take a new, clean lens paper and place it above the optical component (without direct contact), so that when you pull the lens paper, it will glide across the optical surface.

• Then, drop one or two drops of a fast-evaporating solvent onto the lens paper and position it above the optical component. The weight of the solvent will cause the lens paper to sag, making contact with the optical surface. Slowly and steadily drag the wet lens paper across the optical surface, being careful not to lift it during the process. Continue dragging the lens paper until it leaves the optical surface.

The correct amount of solvent will keep the lens paper moist throughout the entire drag, and no visible solvent marks will remain on the optical surface after the drag ends. Inspect the optical component, and if necessary, repeat the process. However, each piece of lens paper should only be used once. This cleaning method is the preferred choice for many applications because the lens paper only lightly contacts the optical surface. This method is effective at removing small particles and oils attached to the optical surface. Heavily concentrated contaminants may require multiple cleanings.

04 Using Tweezers with Lens Paper or Coater Method

This method is often used for fixed or curved optical components that need to be cleaned with solvents.

Follow these steps:

• Inspect the optical component to locate the source of contamination. Plan the wiping path to minimize the length of the path where large contaminants are dragged across the optical surface. If lens paper has been used before, fold it in half to ensure the side in contact with the optical component has not been used. Grip the lens paper with tweezers to smoothly wipe across the optical surface.

• Then, drop two drops of solvent onto the lens paper. The lens paper should be moist but not dripping; if too much solvent is added, shake the lens paper to remove the excess solvent. The lens paper should glide smoothly across the optical surface.

• During the wiping process, continuously and slowly rotate the lens paper. This ensures that different parts of the paper are in contact with the optical surface, keeping the areas with accumulated contaminants away from the surface.

• After wiping, inspect the optical component for any remaining contaminants or streaks. If needed, use a new piece of lens paper to continue cleaning the optical surface.

If too much solvent is used on the lens paper, or if streaks appear at the edges of the lens paper during the wiping process, use a larger coater or plan a continuous wiping path to eliminate streaks on the optical surface. If a spiral or winding wiping path is used, a slower-evaporating solvent may be necessary to ensure the optical surface does not dry before the cleaning is complete.