| As an important part of the solar pumped laser project,this paper optimized a circleshaped Fresnel lens with large aperture.It was a simulation design of light tracing conducted in Matlab.The optimized Fresnel lens design made of polymethyl methacrylate(PMMA)had a circle size of 1000mm×1000mm.It is conducted under three conditions of focal length—1000mm,1100 mm,and 1200 mm.This paper analyzed parameters of light spot size,light intensity distribution and optical efficiency in size of one or two diffraction limitation under four conditions—monochromatic parallel light,parallel spectrum light,divergent monochromatic light and sunlight.The optimized plan was based on the theoretical framework of Fresnel lens general design proposed by professor Guo in 1991.Based on this theory,this paper also took hight of the grooves in Fresnel lens into design consideration.The angles of the grooves in the Fresnel lens were calculated by simulated light tracing which went through the center of each groove.In this way,the light spot generated by the light of each groove had a diameter of groove width.In this way,this paper applied the general theory into Fresnel design with higher optical efficiency.In conducting Matlab simulation,this paper analyzed the weight of each wavelength in AM1.5 sun spectrum reported by NASA.Through careful analysis and trials,this paper successfully simulated light with same spectrum with the sun.In this design,beams of 550 nm wavelength was used and Fresnel reflection was considered.When the coaxial annular rings had the same width of 0.3mm with focus length of 1200 mm,the result indicated that the optimized lens could converge sunlight to a 78.7%optical efficiency within diffraction limit of 11.8mm.However,under the same condition,the Fresnel lens that based on spherical lens cutting could only obtain a 30.4% optical efficiency.This result showed that by optimization,Fresnel lens could obtain higher optical efficiency and light intensity. |
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