Ion beam figuring(IBF) is commonly used during the process of fine optical fabrication. According to sputtering theory, material removal rate varies with the ion inject angle and the surface curvature. During the process of figuring high gradient aspherical surface, the removal function of ion beam figuring should be calibrated strictly to guarantee the accuracy of the figuring results. In this paper, we describe the influence of ion density distribution and surface curvature on material removal rate. Since the removal function varies from point to point within the ion bombed region for high gradient surface, rectification matrix was proposed to fix the disparity between the practical removal function and flat removal function. Experiments were implemented with high gradient aspherical surface to prove the rectification matrix can fit the variety of the material removal rate effectively.
Ion beam figuring technology is ultra-high precision optical processing method. This paper introduces the independent FSGJ800-IBF five axis ion beam figuring equipment. According to the requirement of ion beam motion system dynamic performance of complex optical surface ion beam figuring, the design and control scheme of 3-RPS+XY mobile platform based on hybrid mechanism form five axis motion system was finished. Firstly, the radio frequency (RF) ion beam source was use in this machine. The Ion Beam Figuring System with Five-Axis Hybrid Mechanism was introduced especially the 3-RPS parallel mechanism. The process of polishing complex optical curved surface by ion beam is analyzed. The most close to the spherical surface processing strategy based on the experiments of high gradient lens was done. The aperture of the lens is 44mm and the R/# is 0.705, after a round of ion beam polishing, surface error of optical components RMS from the initial 0.019 lambda (lambda =632.8nm) converges to 0.006 lambda. The experiments verified the availability of the Five-Axis Hybrid Mechanism for high precision complex optical surface error correction.
Ion beam figuring (IBF) is an advanced and deterministic method for optical mirror surface processing. The removal function of IBF varies with the different incident angles of ion beam. Therefore, for the curved surface especially the highly steep one, the Ion Beam Source (IBS) should be equipped with 5-axis machining capability to remove the material along the normal direction of the mirror surface, so as to ensure the stability of the removal function. Based on the 3-RPS parallel mechanism and two dimensional displacement platform, a new type of 5-axis hybrid machine tool for IBF is presented. With the hybrid machine tool, the figuring process of a highly steep fused silica spherical mirror is introduced. The R/# of the mirror is 0.96 and the aperture is 104mm. The figuring result shows that, PV value of the mirror surface error is converged from 121.1nm to32.3nm, and RMS value 23.6nm to 3.4nm.
The high precision off-axis asphere mirrors are quite usefull in the modern sapce optical system.in this paper, the
ion beam figuring is researched to accomplish the final surface accuracy. Firstly, The IBF machine we used is introduced
simplely. The correction method for the distortion in off-axis mirror interference measurement is studied. Beacasue of
the curve shape of the off-axis mirror, the changing of the removal function was analyzed simply. In order to testify the
reaserch, a 1100mm×800mm off-axis aspheric mirror is finished by ion beam figuring. After 2 times polishing, the
surface error was corrected to RMS 9nm in full aperture and achieved 6.3nm in sub- aperture.
The high precision optical mirrors are quite important for the modern optical system. In this paper, a novel
Magnetic Medium Assistant Polishing technology and device is researched for optical finishing. The key element of the
device is a designed magnetic wheel and accessorial magnetic component. The solid magnetic powder arranged with the
magnetic field distribution and became a flexible polishing brush tool. The solid magnetic medium tool working with a
high rolling speed and the polishing liquid with abrasive was injected to contact region of the optical surface. The
magnetic powder tool is reforming with the magnetic field all the time, and this feature made the removal rate and
distribution of the removal function invariable. The device is connected to the polishing machine. The fabrication
experiments were completed. The distribution of the removal function is like a raindrop and asymmetry in one
orientation. The removal stability of the tool was quite good and achieves 95% sameness of peak value in one hour. The
primary experiments shown that the technology can be used in the practical fabrication.
Computer Controlled Optical Surfacing (CCOS) is widely used for making optical aspheric mirrors. In the practical
fabrication, edge effect is an important problem which restricts the fabrication efficiency and accuracy seriously. In this
paper, the edge effect is solved by working out the edge removal function and compensate with dwell time function. Skin
Model is used to describe the pressure distribution when the tool hangs over the work-piece. The calculation model of
edge removal function is derived from Skin Model theoretically. A removal function experiment is completed. The
difference between the theoretical model and the experiment results is less than 5%. It means that the calculation model
is suit for the practical fabrication. Than the dwell time is solved with edge effect compensation by matrix-based
algorithm. In the end, actual experiment was done to validate the edge effect compensation method.
In Computer Controlled Optical Surfacing (CCOS), polishing tool-path is the base of solving other control parameters
such as dwell time. In order to improve the fabrication results of polishing off-axis aspheric, a novel method to optimize
the tool-path is discussed in this paper. The optimizing method named weighted-iterative algorithm is according to the
balance principle of the particle system. The power factor of each dwell point represents the requirement of dwell density.
Considering the factors which influence the polishing result, the power factors cosist of three elements include constant,
error distribution and dwell distance of workpiece edge. The tool-path is solved by numerical iterative method. In the
end, an error data is simulated with actual parameters using the matrix-based algorithm with two different tool-paths.
The one is X-Y uniform spacing model and the other one is to optimize it based on the first. The comparison shows that
the results of the optimized one are much better than traditional one, especially the rms convergence rate. Theory of the
algorithm is simple and exercisable, and it satisfies practical requirement as well.
Annular subaperture stitching interferometric technology can test large-aperture, high numerical aperture aspheric surfaces with high resolution, low cost and high efficiency without auxiliary null optics. In this paper, the basic principle and theory of the stitching method are introduced, the reasonable mathematical model and effective splicing algorithm are established based on simultaneous least-squares method and Zernike polynomial fitting. The translation errors are eliminated from each subaperture through the synthetical optimization stitching mode, it keeps the error from transmitting and accumulating. The numerical simulations have been carried on by this method. As results, the surface map of the full aperture after stitching is consistent to the input surface map, the difference of PV error and RMS error between them is -0.0074 λ and -0.00052 λ (λ is 632.8nm), respectively; the relative error of PV and RMS is -0.53% and -0.31%; and the PV and RMS of residual error of the full aperture phase distribution is 0.027 λ and 0.0023 λ, respectively. The results conclude that this splicing model and algorithm are accurate and feasible. So it provides another quantitive measurement for test aspheric surfaces especially for large aperture aspheres besides null-compensation.