High power laser beam delivery monitoring for laser safety

Abstract

The output of high power lasers used for material processing present extreme radiation hazards. In normal operation this hazard is removed by the use of local shielding to prevent accidental exposure and system design to ensure efficient coupling of radiation into the workpiece. Faults in laser beam delivery or utilisation can give rise to hazardous levels of laser radiation. Two methods for controlling hazards are possible: i) A passive hazard control strategy requiring the laser system to be enclosed such that the full laser power cannot burn through the housing under fault conditions. Usually this approach is too restrictive, ii) Active control strategies in which a fault condition is detected and the laser beam terminated This reduces the requirements for protective housing. Active controls can be thought of as reactive or pro-active. Reactive strategies rely upon detecting the effects of an errant laser beam whereas pro-active strategies can anticipate and detect fault conditions. This prevents hazardous situations arising. A pro-active strategy in which the laser beam is sampled at the final turning mirror is described in this work. Two control systems have been demonstrated; the first checks that beam power is within preset limits, the second monitors incoming beam power and position, and radiation reflected back from the cutting head. In addition to their safety functions the accurate monitoring of power provides an additional benefit to the laser user.The output of high power lasers used for material processing present extreme radiation hazards. In normal operation this hazard is removed by the use of local shielding to prevent accidental exposure and system design to ensure efficient coupling of radiation into the workpiece. Faults in laser beam delivery or utilisation can give rise to hazardous levels of laser radiation. Two methods for controlling hazards are possible: i) A passive hazard control strategy requiring the laser system to be enclosed such that the full laser power cannot burn through the housing under fault conditions. Usually this approach is too restrictive, ii) Active control strategies in which a fault condition is detected and the laser beam terminated This reduces the requirements for protective housing. Active controls can be thought of as reactive or pro-active. Reactive strategies rely upon detecting the effects of an errant laser beam whereas pro-active strategies can anticipate and detect fault conditions. This prevents hazar...