Online Condition Measurement of High Power Solid State Laser Cutting Optics using Ultrasound Signals

AbstractThe occurrence of thermally induced focal shifts in high power solid state laser cutting applications has been reported. A fraction of laser light is absorbed in transmissive optical elements and at optical surface contaminations, leading to a temperature rise of the optical elements. The object of this study is experimental identification of temperature changes in laser cutting head optics during processing, and development of a novel method utilizing ultrasound to measure the bulk temperature online for every optical element in the cutting head. A thermal model is provided for each optical element and allows to estimate the absorbed laser power, the condition and focal shift of the optics. The novel method is compared to existing techniques using thermopiles as temperature sensors. Our measurement system facilitates a closed loop focal shift compensation control and enables a fast reacting emergency shutdown when the temperature of an optical element reaches a damage threshold