Optical performance of heated laser mirrors for high power lasers

Industrial laser are a universal tool for cutting, welding, drilling and many other applications. For the focusing optics gold coated mirrors are used which have to withstand the high power laser radiation. For a 2 kw laser and a 99% high reflection coating the absorbed energy is 20 W. A heating up of the mirror and a correlated thermal expansion will result from the absorbed laser energy. To avoid optical distortion, defocusing, etc. the focusing mirrors made out of copper have to be cooled down to a temperature tolerance of ± 1 Kelvin. Using ceramics instead of metal allows alternative less sophisticated solution. The laser mirror is heated up to the operating temperature, where it has its optimum optical performance. The heating by the laser beam is supported by electrical heating to keep the operating temperature constant. The new concept is proved by simulation and a first test is performed.