Laser Beam Homogenization Method Of Controllable Divergence Angle And High Energy Efficiency

The flat top laser beam with uniform energy distribution is the energy distribution form of the necessary light source in the fields of projection lithography,laser medical treatment and quantum correlation imaging.Therefore,shaping the laser beam with Gaussian energy distribution into a flat top laser beam has important application value.Traditional laser beam homogenization methods include aspheric lens,diffractive optical element,microlens array（MLA）and so on.MLA is favored by researchers because of its high diffraction efficiency,wide band applicability and high filling factor.When the MLA is used to homogenize the laser beam,the microlens unit divides the incident laser beam into a series of sub beams,which are superimposed on each other and form a homogenized spot on the target surface.However,due to the high coherence of the laser and the same phase modulation factor between sub beams,the target spot produces interference fringes,and the homogenized spot is distributed in periodic strong points,which seriously affects the beam homogenization effect.To solve the above problems,thesis proposes to design a new random Rectangular dense array MLA to realize the homogenization of high coherence laser beam.By introducing random structural parameters into the MLA,the coherence between sub beams is reduced,so as to obtain a rectangular homogenized spot with controllable angle and high energy utilization.The main research contents of thesis are as follows:（1）Thesis analyzes the development status of laser beam homogenization methods at home and abroad,and solves the problem of spot size and angle when MLA is used for beam homogenization from the perspective of geometric optics by using matrix optics theory;Fourier optics is used to understand the distribution and change of light field in the transmission process from the perspective of diffractive optics,and the theory is verified by simulation.（2）The causes of interference point array in laser beam homogenization are analyzed.By designing the MLA with random structural parameters,the phase control of the laser beam is realized,and the divergence angle of the spot is controlled by using the constraint relationship of the geometric structure of the sub lens unit;An iterative segmentation algorithm is proposed to solve the dense arrangement problem of MLA to improve the filling factor of the array,and the algorithm is verified by simulation.（3）Study the preparation technology of microlens,and break through the bottleneck of the preparation technology of random MLA with multi focus.By studying the nonlinear relationship between photoresist exposure dose and exposure depth,the mathematical model of exposure depth and exposure dose is obtained.The design method of mask is studied,and the nonlinear correction of mask is carried out according to the obtained mathematical model.In the specific preparation process,the influence of the physical parameters of each process link on the surface shape of MLA is studied in order to achieve a simple and efficient method with high filling factor,high surface fidelity and preparation.（4）Finally,the optical path is built to test the random MLA,explore the evaluation system of homogenization spot,and test the homogenization effect,energy utilization,wide-band applicability and divergence angle of spot respectively.At the same time,the effects of random structural parameters of MLA,surface preparation error and experimental alignment error on the final homogenization effect are discussed.