Abstract: A branching mirror and a transfer mirror receiving a laser beam reflected on the branching mirror and outputting a laser beam in a direction parallel to the laser beam coming into the branching mirror are fixed to and mounted on one mirror holder. The mirror holder is movably provided between a branching position at which the branching mirror is located in a light path of the laser beam and an escaping position at which the branching mirror is located outside the light path of the laser beam, and while the mirror holder is located at the beam branching position, a laser beam from a laser oscillator can be introduced to the branching mirror.

Abstract: 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 and a drive gas supply port in the external cylinder at the laser supply side of the head. An annular piston is formed at the laser beam application side end of the movable lens holder, that is disposed in the annular groove. The piston may be pressed toward the nozzle side of the head by the pressure of drive gas supplied through the drive gas supply port. The drive gas pressure and the area of the piston is selected to define an offsetting pressure for reducing the effect of the cutting gas on the lens and lens holder.