Novel measurement method of infrared laser beam divergence angle based on two linear array CCDs

Abstract

In the practical application of infrared lasers, an infrared linear laser beam of 90°×2° is shaped to meet special demand. So it is very important to test its beam divergence angle which reflects long-distance transmission characteristics. Many approaches are proposed, such as area array CCD single imaging method, two plate reflecting mirrors multi imaging method, distorted diffraction grating multi imaging method and so on. Nevertheless, these methods only can be used to detect infrared laser beam whose spot shape is small and elliptical. Actually if the view angle of the infrared linear laser beam is greater than 90° in the horizontal direction, the area array CCD cannot detect the whole light spot. So we proposed a two linear array CCDs scanning imaging measurement method. The two linear array CCDs are placed at Z 1 position of near field and Z 2 position of far field respectively, and they are separated by an angle Φ. Beam width in two positions can be calculated by light intensity distribution curves which are measured by linear array CCD. Meanwhile, beam width fits linear equation in the far field, so beam divergence angle can be obtained by two point line fitting. This method is based on a real-time and automatic measurement system which consists of infrared laser optical transmitter, control module, imaging system and data processing. The infrared laser optical transmitter is controlled by control module to rotate every one degree. After scanning is completed, we can acquire the spot image and beam divergence angle curve by imaging system and data processing. This novel arrangement provides a precise and comprehensive measurement. Compared to other methods, this method can not only be used for measuring beam divergence angle of infrared linear laser beam, but also for detecting the uniformity of energy distribution and assembling laser optical transmitter. Experimental results indicate that measurement values are in the acceptable range, measurement accuracy is 1', and repeatability precision is 2.36%. Theory analysis and experiment shows the method is reasonable and efficient.