Design And Application Study Of The Refractive Off-axis System

JSJ Intergrating Inspection Instrument for Precision levels is a metrological standardinstrument with advantages of high precision and perfect function, and it has satisfied therequirement for inspecting various levels. The instrument automatically offersquasi-absolute horizontal line with a standard deviation of σ≤0.5″,which can be usedto establish the national level baseline. The leveling of the collimation axis of theinstrument is accomplished by the mechanism of plane external focusing, which ensuresthe high precision and stability of the instrument. The scuffing of the back cardinal plane ofthe objective and the center of the cross reticle collimation axis ensure the long-termstability of the collimation axis. A disadvantage, however, is brought because of theobscuration between the reticle and the objective, which results in a low-contrast image,when the inspected instrument has a small aperture, such as plumb aligner and centeringdevice; or which even makes the observation failed, when the aperture Φ＜20mm.This thesis is devoted to seeking solution to avoid the obscuration in the part of theobjective based on the original design. According to the intrinsic structure of the instrumentand the mechanism of plane external focusing, there is no way to add a prism or use thenon-coaxial system, so we try to deal with it by the off-axis of the pupil, which can beimplemented by further optimization on the basis of the coaxial structure. The primaryaberration theory and the method of modern optical design are described in detail at thefirst part of the paper. In the subsequently design procedure of the apochromatic objective,we show the difficult to meet the requirement of the aperture suitable for further off-axisprocessing. Analyzing the aberration characteristic of parabolic-mirror, we find that there ismore freedom to correct the off-axis aberration in double-separating lens than theparabolic-mirror in monochromatic system. On the other hand, we prefer to the lens systemrather than the mirror on the consideration of the maintenance of the original layout, so themost effort are paid on the research of the double-separating system. The method of theimage quality evaluation of off-axis system is analyzed. Three systems based on ZEMAXare given: the first result reaches to the limit of diffraction when the object is at infinity andmeets the requirements of the aberration tolerance when the object is at8m, and the backfocal length is also long enough. The third result is available when the object is at5m, butthe back focal length is too short. A triplet that is available when the object distance is5mand has a long-enough back focal length is also designed. In the process, we can learn thatthe harsh structural requirement needs a more complicated lens type, which is hard to assemble. So in the last part we introduce the free-form optical surface that has moredesign freedom and can be used to simplify the structure of the optical system. Most of ourwork is focused on the method of discretely defined surface, which is common innon-imaging optics. Besides，we found the correlation between this method and theimaging optics. Due to the finite working time and the limited technical information, wesimplified the mathematical model and only gave the results calculated by MATLAB in theend.