A device for focusing a laser beam includes a first telescopic
configuration and a second telescopic configuration. The first telescopic
configuration includes a collimating optical element for collimating the
laser beam and a downstream focusing optical element for focusing the
laser beam onto a focal point. The second telescopic configuration
includes a first lens and a downstream second lens disposed in the
divergent beam path upstream of the first telescopic configuration. The
first and second lenses of the second telescopic configuration are
moveable relative to each other in the beam direction.