Development Of The Beam Divergence Measure System With Double Photo-Diodes

As the extensive application of the semiconductor laser diode (LD), it become more and more important to evaluate the quantity of laser beam. Far-field divergence angle of laser beams is an important parameter about value of laser quality. Not only the laser divergence peculiarity in the distance is reflected, but also quality of the correlative laser apparatus and the laser transmission is exactly known. In practical application,it is an impendent need to use the far-field small divergence angle of laser beams. Therefore, to measure exactly the far-field divergence angle of laser beams is highly important.A new method is given in this paper, which is used two photo-diode (PD) to measure the beam divergence. The laser power is detected through the PD's movement across the faculous region. When the value of the peak value of laser power is got, the power of the facular boundary points can be found according to definition of the facular boundary such as"1/ e~2"theory. Then the equation of the facular boundary can be made fitting by using the least square method, and calculate the beam divergence at last.Based on the method that we given, we design a detect system. PD is moving to detect the power of the laser, a simulated switch is selected to realize the divide control of the two photo-detectors; Incremental encoder is used to built the Closed-loop control of the step-motor; base on the Characteristic parameter of the laser diode, built the Mathematics model between the beam divergence and the temperature, to measure the result to carry on the temperature compensation. AT89C52 is selected as the controller of the measurement system. With programming, it realize the controlling of the device movement,boundary points determination and calculation and output of the laser beam divergence. Further more, it is analyzed the results and the elements which affect the experiments. And some new methods are given to improve the designed one.It's been proved by the experiments that detecting apparatus system can be used to detect the laser beam divergence. The detecting results are very close to the given, attain the certain accuracy.