Particular attention is paid to the laser lenses, which focuses the laser beam to a point.
It is this focusing that allows the beam to reach the power output necessary for laser cutting metals and after it has been focussed it is around 2,500 times stronger than before focussing. For this reason, it is extremely important to protect lenses from dirt. If particles have settled on the lens, the energy cannot be fully re-discharged.
Depending on how dirty the lens is, it decomposes through to complete destruction. The lenses for a laser machine are not made of glass, for example, like the lenses of telescopes. They are made of zinc selenide.
The material is heat resistant up to 1,500°C and lends the lens its typical colour. The lenses are also finished with a thin layer of thorium fluoride. Thorium is a radioactive metal, which withstands very high heat.
If the lens is destroyed, decomposition products such as zinc oxide, selenium oxide, and the thorium on the surface, are released. Thorium and selenium compounds are very toxic cause serious health problems if they are inhaled or in case of skin contact. For this reason the lenses are checked and serviced regularly.