Interferometric Testing System For General & Digitizing Aspheric Testing

Aspherics can provide more degrees of freedom for aberration control. Use of aspherics helps to reduce the system size and weight while improving image quality. But due to their varieties of shapes and optical characteristics, aspheric testing has always been a great challenge for optical researchers.There are a good deal of aspheric testing methods, null interferometric test, nonnull interferometric test, profilometer, etc, for instance. Null compensator method and computer generated holograms method, which belong to null test, require one unique null optics for one asphere. They can both obtain high accuracy measurement, but the challenge in design, fabrication and certification of the null optics greatly limit their application. Aberration free methods, which employ auxiliary reflecting mirror, can perform general test for conics. However, the auxiliary mirror usually should have larger aperture than the test aspheric, and its surface figure limits the overall test accuracy. The profilometer is time consuming and also has the danger of damage the surface of the test aspheric. Nonnull tests, which employ long wavelength, multi-wavelength, shearing methods, etc, can also perform general test. But the retace error with nonnull configuration can greatly reduce the test accuracy.This dissertation mainly research on a general & digitizing nonnull interferometric aspheric testing system, include wavefront compensation, figure reconstruction, experimental data and image processing, etc. This research is of great contribution for aspheric testing, especially the general & digitizing aspheric testing method. The content of this dissertation include:After review of the various applications and the current fabrication methods of the aspherics, there is also a review over the current aspheric testing methods. And these reviews reflects the necessity of establishing a general & digitizing aspheric testing system.A type of novel partial null lens(PNL) is proposed to compensate for a range of aspherics. The design process of the PNL is discribed in detail and also the characteristics of the PNL are analyzed. The idea of using a series of PNLs to compensate for a larger range of aspherics is proposed and realized.The retrace error in nonnull interferometric aspheric testing system is analyzed in detail. The performance and its influence to the testing result are also analyzed and the correcting method is present.A matrix is proposed to represent the status of the aspheric under test. A reverse optimization figure reconstruction(ROR) process is proposed, which is based on system modeling and employs reverse optimization to reconstruct the figure of the aspheric form the wavefront detected on the detector. The performance of the ROR process is analyzed with lots of simulation.An interferometric system, which employs partial null lens and reverse optimization reconstruction process, is proposed to perform general aspheric testing. The system layout and figure construction process are present. System modeling and error analysis basing on the system model are also carried out. The error analysis provides important information for the modeling accuracy control of real experiment system.The validation experiment of the general & digitizing interferometric aspheric testing system has been established and the testing experiment for real paraboloid of 159mm aperture and 818.952mm vertex radius has been carried out with an accuracy of 1/30wave RMS. This dissertation is of great value for the accuracy enhancement of nonnull general aspheric testing.