| Optical freeform optics can considerably improve the performance of an optical system and simplify the system structure simultaneously.These components are widely applied in various modern high-end optical systems for high-performance imaging,il uminatio n,solar energy collection,and biomedical engineering.The fabrication technology and practical demands for freeform surfaces have significantly improved in recent years,thereby increasing the demand for metrology.However,high-accuracy measurement of these surfaces is always a great chal enge because of the arbitrary surface forms.Based on the digital Moiréinterferometric technique(DMIT)proposed by our research group,a novel non-null interferometry method for optical freeform surface measurement is proposed in this thesis.The proposed method is a versatile,vibration-resistant,and simple structure method for high-precision freeform surface measurement.The main work of the thesis are as follows.1.Researches on the design method of the key components,versatile partial compensator(PC),in non-null interferometry are conducted.The design method is always a problem caused by the diversity of the freeform surfaces.An on-axis refractive PC design method and an off-axis refractive PC design method based on vector aberration theory are raised for the measurement of rotational symmetry and non-rotational symmetry surface under test(SUT),respectively.For a complex SUT,a PC design method beased on deformable mirror and a novel computer generated hologram(CGH)based on the liquid crystal photoalignment technology are proposed.2.A two-step carrier-wave stitching method(TCSM)is proposed to solve the frequency spectrum aliasing caused by the wavefront bandwidth limit in the DMIT.The dynamic measurement range of DMIT is expanded to that of the phase shifting interferome tr y,eliminating the bandwidth limitations of the residual wavefront in DMIT.High precision surface figure error(SFE)can be solved by TCSM under the condition of frequency spectrum aliasing.The simulation results show that the PV of the point-to-point error between the solved SFE and the true value is less than 10-3?.3.To solve the freeform SUT calibration problem in the non-null interferome tr y measurement,a virtual interferometer calibration(VIC)method is proposed.No accurate adjustment mechanism is required to adjust the SUT in the real interferometer,and the alignment error is eliminated by digital Moirétechnique after adjusting the position and attitude of the SUT in the virtual interferometer.Multiple manual adjustment process is not needed,and VIC also reduces the requirements of the adjustment mechanism,while the SUT can be calibrated to any accuracy by algorithm.4.Pratical experiment of PC design and processing and the measurement of spherical,aspherical and freeform surfaces were conducted.Liquid crystal CGH fabrication experiment was carried out to fabricate grating CGH with different periods.The feasibility of the design method was verified by transmission wavefront detection and polarization microscope measurement.At the same time,a single PC was fabricated and spherical and off-axis paraboloid SUT with alignment error measurement experiments were conducted.Then the measurement experiments were carried out of a defocused spherical surface,paraboloid and the off-axis paraboloid SUT without PC with large residual wavefront.By the comparison of the measurement results between UA3P coordinate measuring machine and the proposed method,the point-to-point measurement accuracy is better than 1/10?.The RMS repeatability is better than 1/25?when the SUT and the interferometer are located on the separation platform,and 1/200?when located on the same platform.The actual experimental results verify the validity of VIC and TCSM algorithms.Through the work of this thesis,the proposed versatile PC design method,combined with TCSM and VIC algorithm is proved to be a high precision,simple structure,anti-environmental vibration and high versatility method for freeform surface measurement. |
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