A laser cutting head has a nozzle as well as a lens disposed in a holder that is moveable by a mechanical drive along the laser beam axis and has a working gas supply port at the nozzle side of the head. The head also has an annular groove that is defined by concentric internal and external cylinders...http://www.google.de/patents/US5298716?utm_source=gb-gplus-sharePatent US5298716 - Laser processing head and method for operation thereof
