Designing Algorithms And Actualizing Techniques For Diffractive Optics Elements In Beam Shaping

The research devoted to the thesis focuses on the design and applications of large aperture diffractive optical elements(DOE) that will be used to realize uniform illumination on focal plane for high power laser system.The primary research and achievements are listed as follows:1.When the DOE were designed with Input-Output(I-O) Algorithm,on focal area, the algorithm had the control of intensity feedback only in sampling locations.But in non-sampling locations,numeric calculations showed that Output intensity would surge sharp and fiercely.In numeric calculus,basing on the Nyquist-Shannon theory, intensity in non-sampling locations can be regenerated from those in sampling locations with interpolation formula.According to the interpolation method,we reform the I-O algorithm by appending the feedback control of non-sampling intensity,which can improve the effects of beam shaping because of the enhancement in illumination uniformity.Additionally,the reformed algorithm can give a better initial phase distribution of DOE stably.2.Previously,we devised DOE with less subcells,and the calculative extent was smaller.Subsequently,the target experiment validated that on focal plane,except for the primary facula,there also had faculas of other orders,which depress the diffractive efficiency of DOE obviously.According to the numeric analysis,the lack of DOE unit and the shortage of calculative extent are possibly the main causation that other orders faculas were engender obviously.To solving this issue,we increase the quality of DOE unit properly,and extend the computing area of output beam.The numeric analysis results show clearly that the facular intensity of other diffractive orders are reduced by this means.It is helpful to avoiding the expense of diffractive efficiency.3.We have tested a DOE of 70mm diameter with multi-step phasic distribution in the target experiment.The test results indicated that there was a sharp intensive protrusion produced in the center of primary diffractive facula,which was harmful to the uniformity of beam shaping.We processed the metrical data measured by step-scanner with surface fitting,and suggested the distribution model of etching error with spherical surface.The numeric analysis testified that such error distribution was the main reason that caused the intensive protrusion.Comparatively,in the same unbiased variance,random error influence DOE little.It is supporting to our following research and Ion Beam Etching(IBE) technique.4.When the etching error was investigated,it was separated into two parts.One was the random error,caused by etching environments,nonsignificantly.The other was etching system error,generated from intensive nonuniformity of ion beam,weightily and mainly researched.We suggested a parameter G to describe the system error deflection overall.Analysis attested that the purpose of DOE in beam shaping would meliorate evidently when G was converted to zero.According to this,we suggested a technical optimization for DOE in IBE progress by revising the etching time in specific intensive distribution of ion beam.The experiment showed that this method was apt to actualize.