Research On Technology For Laser Beam Shape Parameters Detection

As the high-precision test equipment, the test of the measured is passed directly by the precision of the laser design and processing, the accuracy of the output parameters, the deviation from the design values, the stability during operation, so the test of the laser output parameters itself is particularly important. This paper is to use four-wave lateral shearing interferometry to detect the laser beam parameters, the way of which has advantages of high resolution, strong maneuverability, high stability, non-sensitive to vibration, and compact structure.The basic principle of the four-wave lateral shearing interferometry is introduced in detail in the paper based on thorough research and discussion of currently the commonly-used wave-front detection methods. The two-dimensional diffraction grating is the key device to realize the principle, which is based on the traditional Hartmann wave-front sensor mask, processing a phase grating of certain amount of phase shift. The four-wave lateral shearing interferometry system is consisted of the two-dimensional diffraction grating and a CCD camera. When the laser beam enters the two-dimensional diffraction grating, there will produce shearing spots at receiving screen of the CCD camera, which forms an interference pattern. The method of spatial carrier frequency can be adopted to extract the intensity and phase information, with no special requirements on the device. With the interferogram processing technology, the phase is extracted and unwrapped, and the differential information of two orthogonal directions is obtained, and the method of Zernike polynomials least squares fitting is used for wave-front reconstruction to get the original wave-front.In order to verify the feasibility, the four-wave lateral shearing interferometry is applied to test the wave-front in the paper. The wave-front of 532nm semiconductor laser was tested in the experiments, and the laser measurement data is compared with the nominal parameters drawn. Besides, the compared test is done both by using the four-wave lateral shearing interferometry and ZYGO-GPI interferometer, within the test accuracy of RMS 15nm and the repeatability accuracy of 8nm. The experimental results show that the four-wave lateral shearing interferometry is of accurate and quick testing, which provides a good research method for laser wave-front detection.