制作平面全息光栅的离轴抛物镜/洛埃镜干涉系统

Off-axis parabolic/Lloyd mirror interferometric systems for manufacturing plane holographic gratings

设计和制作具有较高波前平面度和结构稳定的干涉曝光系统是研制高质量平面全息光栅的首要条件。对离轴抛物镜/洛埃镜系统、单透镜/洛埃镜系统、球面反射镜/洛埃镜系统和双分离透镜/洛埃镜系统等4种单反射镜干涉曝光系统产生的干涉条纹直线度进行了光线追迹。在干涉场中放置标准光栅,使用于曝光的两束平行光入射到光栅上,从而衍射光相干叠加产生莫尔条纹;并对上述4个系统产生的莫尔条纹做了模拟。利用Zernike多项式对莫尔条纹进行拟合得到干涉曝光系统的波前像差,比较了4个系统的差异。结果表明,采用离轴抛物镜/洛埃镜系统制作中、小口径平面全息光栅是最为合适的。在此基础上,研制了用于制作最大尺寸为110 mm×110 mm,刻线密度〉1 200 l/mm的平面全息光栅的离轴抛物镜/洛埃镜干涉曝光系统,在洛埃镜和离轴抛物镜面形精度为λ/8（λ=632.8 nm）的前提下,平面全息光栅的衍射波前像差为0.239 6λ（λ=550 nm）。此系统经过消除外界扰动和精细装调后,可用于制作衍射波前像差达λ/6~λ/7（λ=550 nm）以上的平面全息光栅。

The design and manufacturing of interferometric exposure systems with high wave-front flatness and structural stability is a paramount condition for development of high-quality holographic diffraction gratings.A ray-tracing was carried out on straightness of the interference fringes arisen from four kinds of interferometric exposure systems of Single Reflective Mirrors（SLR）,namely,off-axis parabolic/Lloyd mirror system,single lens/Lloyd mirror system,spherical mirror/Lloyd mirror system and the separation of pairs of lens/Lloyd mirror system.A standard grating was placed in the interferometric field to make two parallel light beams for exposure incident on the grating,so that the diffractive light was superpositioned to appear Moire fringes.Then,the Moire fringes metioned above were simulated.The Zernike polynomial was used to fit the Moire fringes to get wavefront aberration of interferometric exposure systems and to compare the differrences among the four systems.The results show that the off-axis parabolic/Lloyd mirror system is the most appropriate in production of small-caliber plane holographic gratings.On that basis,the off-axis parabolic/Lloyd mirror interferometric exposure system was manufactured to fabricate plane holographic gratings with a maximum size of 110 mm×110 mm and the engraved linear density greater than 1200 l/mm.The diffraction grating wave-front aberration produced by the plane holographic grating is 0.239 6λ（λ = 550 nm）,as the mirror face accuracy aberration between off-axis parabolic mirror and Lloyd mirror is λ / 8（λ = 632.8 nm）.This system can be used to produce plane holographic gratings with wave-front aberration in λ/6-λ/7（λ=550 nm）,if the external disturbance is overcome and finely tuned.