How to clean laser optics with lens tissue: drop and drag, folded pad and first checks

To clean a fiber laser optic with lens tissue, blow the loose dust off first with oil free canned air, then lay a fresh sheet on the glass, wet it with a few drops of optical grade alcohol or acetone and drag it slowly across in one direction until it leaves the surface dry. Never wipe with dry tissue, never use the same sheet twice, and never touch the glass with bare fingers. For a window still sitting in its holder or a lens in a welding gun, fold the sheet into a pad, wet the folded edge and make a single straight pass from edge to edge.

Why the method matters more than the tissue

Lens tissue is soft and lint free, but on its own it does very little. Newport's optics cleaning note warns that dry lens tissue can scratch optical surfaces, and that wiping an optic before the dust is blown off can scratch it too. A grain of grit dragged across an anti reflection coating leaves a line, and on a fiber laser that line absorbs power, heats up and becomes a burn mark.

Precitec's optics manual adds that dust, fingerprints and adhering dirt cause burn marks even after short operating times. The solvent lifts the film; the single slow pass carries it off without spreading it.

Our lens tissue booklets hold 50 loose sheets each, 100 x 150 mm, which is large enough to fold into a pad for a 20 mm welding lens or lay flat over a 37 mm cutting head window. A 3 pack is see current price and a 10 pack is see current price.

What to have ready before you open the head

Gather everything first, so the beam path is open for as short a time as possible. Precitec asks for exactly that, and for openings in the beam path to be covered with protective film while the optic is out.

• Lens tissue, a fresh booklet kept closed in a clean drawer, not loose on the bench.
• Solvent: ethanol of at least 99.5 %, isopropyl alcohol or acetone at reagent or optical grade, the three Precitec lists. Newport notes that isopropyl alcohol dries slowly and can leave drying marks.
• Oil free canned air or a rubber blower. Never the shop air line: Precitec says standard industrial compressed air must not be used on optics, because the oil and dust in it cause burn marks.
• Powder free gloves or finger cots that the solvent does not dissolve. Newport specifies acetone impenetrable gloves when acetone is in use.
• Clean masking tape or protective film to cover the open slot in the head or the gun.
• A bright torch, plus a spare window and seal ring in case the inspection shows damage.

Leave out spectacle wipes and camera or contact lens cleaners. Precitec warns that the anti fog residue in spectacle wipes damages coatings and that camera and contact lens cleaners can contain water.

Inspect first: is this a cleaning job at all?

Hold the optic by its edge close to a bright light and look at it from several angles, which is the inspection Newport describes. Dust and films scatter the light and show up as bright points or haze.

Loose dust, light haze, fingerprints and spatter sitting on the surface come off with tissue and solvent. Burn pits, cracks, lifted or discoloured coating and fused spatter do not, and our guide on when to replace a fiber laser protective window covers those signs. If the window is damaged, skip the cleaning and fit a new one.

Method 1: drop and drag, for an optic out of its holder

This is the gentlest method and the one to use whenever the optic can be laid flat. Newport describes it for unmounted optics and Edmund Optics recommends the drag method because, done correctly, the solvent evaporates evenly without leaving streaks or spots.

• Blow the dust off. Hold the can upright and spray from at least 15 cm, the distance Precitec gives, so no propellant lands on the glass.
• Lay the optic down on a clean sheet, handling it by the edge only, and lay a fresh sheet over it, flat and unfolded, overhanging one side.
• Wet it. Put two or three drops of solvent on the tissue over the glass. It goes translucent and sticks lightly to the surface.
• Drag it slowly across the glass by the overhanging end, flat and in one direction, until the tissue has left the surface. Do not press down and do not scrub back and forth.
• Look again under the torch. If marks remain, repeat with a new sheet. A used sheet carries the dirt you just lifted.
• Turn it over and do the other face. Fiber protective windows are coated on both faces.

Method 2: the folded pad, for a window in its holder or a welding gun lens

When the optic is seated in a drawer, a cartridge or the lens holder of a handheld welding gun, you cannot drag a loose sheet across it. Fold the tissue into a pad instead. Newport calls this the brush technique when the pad is held in a hemostat or tweezers, and the wipe technique when it is held in the fingers.

• Fold the sheet so the folded edge is at least as wide as the optic. A 100 x 150 mm sheet folded three or four times gives a firm pad with a clean edge for a 20 mm welding lens; fold it fewer times for a 30 to 37 mm cutting head window.
• Hold it near the fold, with tweezers or a hemostat parallel to the folded edge. Do not touch the part of the tissue that will meet the glass.
• Wet the folded edge with solvent and shake off the excess. A dripping pad leaves solvent pooled at the rim of the holder, which dries into a ring.
• Make one pass, slowly and straight across from one edge to the other, with light, even pressure.
• Refold or throw it away. Each pass uses a clean face of tissue. Newport's rule is to never reuse a lens tissue.

Precitec adds: dab rather than rub. A second clean pass is safer than more pressure.

Handheld welding guns: clean the outside before you open it

Welding guns throw spatter at the protective lens all day. Durma's guidance for handheld welding heads is to wipe the area around the protective lens with a dust free cloth and alcohol before pulling the holder, then seal the holder window with clean masking tape or a dust cover while it is out. It traces black dots on the lens to lenses changed without that protection.

Our 20 x 3 mm protective lens for Ospri and Relfar guns comes in packs of 20 and 50. Check the seal ring at the same time; a flattened or burnt ring lets fume past the lens. The 21 x 15 x 3 mm seal ring for Ospri guns and the other handheld sizes are in our laser seals collection.

Cutting head windows and lenses

On a cutting head, the protective window is the optic you clean most. Raytools recommends cleaning the cover glass once a week in its BM115 manual, using absolute ethanol, a one direction wipe and a rubber blower. Pull the drawer, cover the slot, clean the window off the head by drop and drag, and clean the seat and seal ring before it goes back. Our protective window fitting guide walks through seating the window and seal.

Precitec is clear that a dirty window must never be turned over and refitted. Clean it properly or replace it. Turning it puts the contamination on the lens side, where it burns the lens above.

Collimating and focusing lenses cost many times more than a window. Open them only once the window is ruled out, and use the same two methods. For Raytools heads, our D30 lens sets and the rest of the laser lenses collection list the sizes and focal lengths.

This guide is for fiber laser optics: fused silica windows and lenses for 1,064 nm. CO2 lenses are zinc selenide, a softer material with its own cleaning procedure from the lens maker, and are not covered here.

Mistakes that undo the cleaning

• Wiping dry. Dry tissue drags grit across the coating. Always wet it.
• Skipping the canned air, or using the shop line. A loose particle becomes an abrasive under the tissue, and shop air carries compressor oil onto the optic.
• Blowing on the glass. Precitec and Newport both warn that breath leaves saliva on the surface, and Precitec says it causes burn marks.
• Reusing a sheet or wiping back and forth. Both put the dirt straight back on.
• Dipping into the bottle. A used pad or tweezers dipped into the bottle contaminates all of it. Decant a few drops for each job and keep the bottle closed.

After cleaning: first start checks

Remove the tape, close the holder fully, check the red pilot light is centred in the nozzle and run a short test cut on scrap. A cut no better than before points to damage you missed or a fault elsewhere, such as a worn nozzle. Our guide to making protective windows last covers the pierce and gas settings that send spatter up into the window in the first place.

Keep a closed booklet at each machine and gun, with spare windows and seal rings. Windows for Raytools, Precitec, Trumpf, Bystronic, BOCI and handheld guns are in our laser protective windows collection, and if you cannot find your size, send us the dimensions through our quote request page.

Frequently asked questions

Can I use lens tissue dry to wipe off dust?
No. Blow loose dust off with oil free canned air, then use the tissue wet with solvent. Newport warns that dry lens tissue can scratch optical surfaces.

Which solvent should I use on a fiber laser protective window?
Ethanol of at least 99.5 %, isopropyl alcohol or acetone, at reagent or optical grade, as Precitec lists for its optics.

How many times can I use one sheet?
Once. A used sheet carries the dirt it lifted and puts it back on the next pass.

How often should I clean the protective window?
Raytools recommends once a week for the BM115 head. A machine piercing thick plate all day needs the window inspected far more often, and cleaned whenever the inspection shows a film or loose spatter.

The marks will not come off. What now?
If two passes with fresh tissue leave a mark, it has burned into the coating. Replace the window rather than pressing harder.