Research On Beam Shaping Devices Based On Angular Spectrum Theory And G-S Algorithms

Laser has the advantages of high directivity,high coherence,high brightness and high monochrome.It plays an increasingly important role in biomedicine,information technology,laser processing,national defense industry and other fields.Usually the output mode of laser is fixed.However,the requirements of spot shape,size and beam energy distribution are different in various applications.Therefore,there is an urgent need to study beam shaping devices for specific light sources and different applications.Traditional beam shaping technology has many problems,such as low cost-effective,low energy efficiency and poor shaping effect for complex beams.Diffraction optical shaping elements have many advantages,such as small size,large degree of freedom in design,high diffraction efficiency,easy mass production and light weight.It provides an effective technical way for complex special beam shaping.The key technology of beam shaping has important scientific significance and practical value.Aiming at the problems of poor uniformity and large root mean square error of beam shaping devices based on diffractive optical elements,this paper studies the design method of beam shaping devices based on G-S algorithm,combining the theory of diffraction angle spectrum and fast Fourier transform.For visible He-Ne laser,the phase distribution of flat-topped beam shaping device is designed,and the beam shaping system based on spatial light modulator is built.The square spot with good uniformity is realized,and the design results are verified.According to the characteristics of laser beam produced by THz QCL,a terahertz Gauss beam shaping device is designed and fabricated.The main works of this paper are as follows:(1)The research status and analyzed development trend of beam shaping technology is investigated for Diffractive Optical Elements(DOEs).Aiming at the existing problems of DOEs,the research contents and purposes of this paper was proposed.(2)Based on G-S algorithm and angular spectrum theory,the design algorithm of diffractive beam shaping device is studied.The design software of beam shaping has been written with MATLAB.(3)The 8-bit phase distribution of flat-topped beam shaping device is designed for linearly polarized light with wavelength of 632.8 nm produced by He-Ne laser.The design target spot size is 4.7 mm×4.7 mm,the average intensity is 1.53(a.u.)and the non-uniformity is 0.1.A beam shaping system is constructed based on spatial light modulator,and produced 4.7mm×4.7mm square spot.The average intensity of the spot is 1.4(a.u.)and the non-uniformity is 0.328.Verified the proposed algorithm theoretically and experimentally.(4)For THz QCL with wavelength of 118.8 um,this paper designed a shaping and focusing lens to change the output beam of THz QCL with uneven shape and energy distribution into a Gauss beam.The size of the beam shaping device is 51.2 mm×51.2mm,and the diffraction distance is 25 cm.The theoretical simulation results show that the waist radius of the Gauss beam,peak intensity,and root mean square error are 1?,7.77×10~7(a.u.),and 0.18,respectively.And the spot shaping and focusing can be achieved in the range of 13.9 cm to 36.1 cm.The beam shaping device for THz QCL was fabricated by micro processing technology.