The heart of a laser cutting machine is the cutting head in which the laser lens is placed. This is needed to bundle the laser beam. Only in this way does the beam achieve the necessary power to melt metals. After bundling, the beam is about 2,500 times stronger than before.
The laser lens for a cutting system is not made of glass as in the case of magnifying glasses or binoculars, for example. Glass lenses could not withstand the strong thermal stress long enough. The laser lenses therefore consist of zinc selenide (ZnSe). This material is heat-resistant up to a temperature of 1,500°C and gives the laser lenses their typical orange colour.
In addition, the lenses are coated with a thin layer of thorium fluoride. Despite the colouring, laser lenses are absolutely transparent for light in the infrared range. Our Co2 lasers work in this spectral range, which is invisible to the human eye.
Danger through decomposition
Thorium fluoride is a chemical compound that can withstand very high heat. For this reason, it is extremely important to protect lenses from contamination. If particles have settled on the lenses, the energy cannot be fully released again. Depending on how dirty the lens is, it disintegrates completely.
When the lens is destroyed, decomposition products such as zinc oxide, selenium oxide and thorium on its surface are released. Thorium and selenium compounds are very toxic and cause serious health problems when inhaled or in contact with skin.
For this reason, lenses should be checked and maintained regularly.