Abstract: An apparatus for determining the position of the focal point of a laser beam in a laser machining system in which the laser beam is transmitted via an optical fiber to the work-piece to be machined by the laser beam. The z coordinate position of the focal point is determined by a mirror for reflecting some of the laser radiation back towards the end surface of the optical fiber, and a detector is arranged between the laser and the outgoing fiber for measuring the radiation reflected back through the fiber.

Abstract: An optical fiber cable of the type comprising a fiber (3) having a central core and a surrounding cladding and made for transmitting optical high-power, specifically power exceeding 1 kW. At least one of the fiber ends is provided with cooling means for optical power loss comprising a cavity with a flowing coolant (2) surrounding the envelope surface of the fiber end. Incident radiation that falls outside the fiber comes into the coolant, preferably a liquid coolant such as water, where it is at least partially absorbed. At least one of the limiting wall surfaces of the cavity is completely or partially non-absorbing for the incident radiation, while the other limiting wall surfaces are arranged to absorb such radiaton that is still present and transmitted through the flowing coolant (2). As these surfaces are in direct contact with the coolant an efficient cooling is obtained.