Research On The Interference Detection Technology Of Partial Zero Astigmatism Compensation For Optical Free-form Surfaces

Compared with the traditional spherical and aspheric surfaces,freeform surfaces lose the rotational symmetry and have higher design freedom.It can better correct the off-axis aberrations and make the optical system move towards the direction of high image quality and miniaturization.At present,freeform optics has been used in imaging optical systems especially for those in off-axis reflective type,which raises urgent demand for the high precision metrology for surface figure of freeform optics.The test beam reflected from the freeform optics is strongly diverged due to its high departure from the best fit sphere,so the research on interferometric technique for freeform optics is still limited currently.In this thesis,a partial null astigmatism-compensated interferometry without using any null optics is proposed to measure a series of freeform optics with the same character as astigmatism-dominated mirrors.The oblique incidence configuration is utilized to compensate for astigmatism as the dominant contribution to the sag of the freeform mirror,to constrain the divergence of the test beam.By combining the accurate model building of the interferometric system with reverse optimization reconstruction technology the low-frequency component of surface figure error can be reconstructed and high-frequency component of surface figure error can be retrieved by using high-frequency retrieving technology according to the partial nulled interferograms.In this thesis,theoretical analysis,interferometric system design,simulation verification,experiment and error analysis are carried out.The concept is applied to measure a Zernike freeform mirror with the diameter of 44 mm and the basic radius of curvature of 500 mm.The sag of the freeform with the best fit sphere removed is 3.953 ?m and the PV value reduced to 0.549 ?m when the astigmatism and tilt is compensated.The experimental result is similar to that of computer-generated hologram(CGH)null test and the feasibility is verified.This method doesn't use any null optics and gives more flexibility than the CGH null test method because the astigmatism as the dominant contribution to the sag can be compensated by changing the tilt angle of the mirror under test.