Real-time Power Measure And Control System Of High Power CO₂ Laser

The stability and accuracy of laser power directly influence the quality of laser processing. During the course of laser processing, monitoring the variation of laser power and improving its stability and accuracy in real-time are very important for increasing the roduction rate.A new kind of power control system of CO2 lasers in real-time is developed to improve stability of laser power in this article, which is composed of two parts: sampling unit made of a high reflective mirror, an integrating sphere, an infrared detector and signal processing circuit, and feedback control unit based on Microcontroller Unit and a PID controller.In the sampling unit, an infrared detector is used to sampling the transmitted laser power out from the rear mirror of the resonator. Generally, the threshold of the incident laser power is milliwatt scale, so the detector can not be installed on the axis of the transmitted laser beam to respond the laser power face to face. In order to prevent the detector from damage by the higher incident laser power, and effectively and linearly sampling the real laser power, an integrating sphere is used to attenuate and homogenize the transmitted laser power. Then, the detector can receive and respond the small portion of the homogenized laser power, which just linearly represent the mean output laser power.The homogenization of laser power in the integrating sphere is explained as follow: After the transmitted laser beam enters into the integrating sphere, a multi-fold diffuse reflection process must happen. Due to the so fast laser velocity, the laser intensity at every point inside the sphere can be regarded to be same. So, sampling the laser radiation intensity at any inside position can linearly represent the mean output laser power, satisfiedly.The feedback control system compares the sampling signal of laser power with the reference input power, and sends a signal to the PID controller to automatically adjust the discharge current to make the output laser power stable around the setting power.The experimental results indicate that this system can automatically control the laser power on line, and greatly enhance the stability and accuracy of the laser power without any accessory inserted on the output laser path. This system has been successfully used in the 4kW fast-flow CO2 laser with much better output power stability of±0.1%.