Engineering study on the auto-measurement of divergence angle of the laser beam with the variable diaphragms

Far-field divergence angle of laser beams is an important parameter in the evaluation of laser quality in the laser radiometer. According to the definition of far-field divergence angle and the international practice, the automated measurement system with the variable diaphragms was developed in the practical engineering application. It was used in the far-field divergence angle testing of laser. In the measurements, the pulse laser spots were captured with the special image processing, and the center position of laser spot was calculated by the first order moment for the center of gravity. By then the center of laser could be aligned with the center of variable diaphragms. With the automated measurement system, the diaphragms would be automatically changed from smaller to bigger, and the laser energy would be measured by the probe at the same time. It would be fitted for the chart of diameter of the diaphragm with the laser beam width, and when the part of total energy passing the diaphragm reached 1/e² percent of total beam energy, the fitting diameter of the diaphragm would be the laser beam waist width. Finally, the far-field divergence angle of the laser beam can be calculated. This automated far-field divergence angle measuring system was based on the technology of virtual instruments. It had been passed by the customers' tests and proved by the practical utilization.