Beam Shape And Quality Control Base On Hybrid Holograms

The energy of the laser beam is generally Gaussian.This non-uniform distribution of energy will cause the material to accumulate heat locally,affect the consistency of processing results,and greatly limit the development of laser technology.The laser beam shaping technology can change the shape and energy distribution of the beam,which can effectively reduce the thermal effect and improve the processing quality.In this paper,a beam shape and quality control method based on hybrid hologram is presented.The main research contents are as follows:Firstly,the common Gauss and flat top beam model is analyzed and the transfer characteristics of the flat top beam in the near field and far field are discussed.The influence of the transmission distance on the energy distribution of the flat-topped beam is researched in the transmission of the optical ABCD optics with no aperture limitation.Secondly,the modulation principle of the liquid crystal spatial light modulator is explained by the electronic controlled birefringence effect and the phase change effect of the liquid crystal molecules.After analyzing the diffraction characteristics of binary gratings,blazed gratings and sinusoidal gratings,the diffraction characteristics between grating element and the liquid crystal grating is compared and appropriate analyzed.According to the above analysis,the hybrid hologram is designed,and the principle of beam shaping based on the hybrid hologram is also described.Thirdly,the experimental system is designed and set up.A diffraction effect around the shaped beam has been significantly reduced.Beam profiles of arbitrary shape,such as square,ring,triangle,pentagon and hexagon,can be conveniently obtained by loading the corresponding holograms on the SLM.The shaped beam can be reconstructed in the range of 0.5 mm at the image plane.Ablation on a polished stainless steel sample at the image plane are consistent with the beam shape at the diffraction near-field.The ±1st order and higher order beams can be completely removed when the grating period is smaller than 160?m.The local energy ratio of the shaped beam observed by the CCD camera is up to 77.67%.Dynamic processing at 25 Hz using different shapes has also been achieved.Finally,in order to improve the energy efficiency of the shaped beam,a binary grayscale grating mask is designed to achieve precise control of the shape and intensity distribution of the shaped beam.The effect of different gratings on the quality of the shaped beam is researched.The experimental results show that when the blazed grating period is 120?m,the corresponding local energy ratio reaches a maximum of 91.86%,and the uniformity of the beam RMSE reaches the minimum value of 0.039.A flat top beam with a shaping efficiency of 48% has been successfully obtained by using a hybrid hologram combined with a blazed grating with a period of 120?m and a binary grayscale grating mask.