Inductively coupled plasma processing (ICPP) is regarded as an unrivaled technique in the field of aspheric and freeform optics fabrication for its non-contact chemical etching and high efficiency. In this paper, to evaluate the obliquely incident machining behavior of removal function during inductively coupled plasma, we did some plasma beam line scanning test treatments on the fused silica surface with different obliquely incident angles in two vertical directions. Test results show that the full width at half maximum (FWHM) of the footprint of removal function increases from 13.1699 mm to 14.8368 mm with the increase of the obliquely incident angle from 0° to 30° along the X-direction line scanning processing, and that of another direction only increases from from 13.1699 mm to 14.0598 mm. Furthermore, the material removal rate in both directions reduces in a small range with the increase of the obliquely incident angle less than 10° under our processing condition. Therefore, test results demonstrate that the three-axis machining system can be effective supposing that the local slopes of the part to treat are less than about 10°. The presented conclusions can provide technical guidance for fused silica aspheric and free-form optical surface machining.
In this paper, from two aspects of abrasion of grinding disk and stability of removal function, this paper compares the machining methods of planet movement and smooth running. On the basis of the Preston hypothesis, based on the kinematics theory, the grinding disk theory wear model of planet movement and smooth running is established, and the three-dimensional model of grinding disk wear under two kinds of motion is simulated by MATLAB. The correctness of the theoretical wear model and three-dimensional simulation wear distribution model of the grinding disk is verified by experiments. The experiment found that the wear of the grinding disc under smooth running tends to be uniform, and the wear of the grinding disc under the planet movement increases along the direction of the radius increasing. It is assumed that with the continuous abrasion of the grinding disk, the degree of fit between the grinding plate and the workpiece surface becomes worse, and the removal quantity of workpiece material is affected, which will affect the stability of the removal function. Through the removal function experiment of an hour, we find that the stability of the volume removal rate of the removal function fluctuates within 7% and the stability of the peak removal rate fluctuates within 6% under the smooth running, while the stability of the volume removal rate of the removal function fluctuates within 29% and the stability of the peak removal rate fluctuates within 12.3% under the planet movement. The results show that the wear of the smooth running is uniform and the removal function is stable. Therefore, the smooth running is more suitable for high-precision modification than planet movement.
The ion beam figuring(IBF) process can produce high accuracy optical surfaces, but the material removal rate is usually lower than 5nm/s and it usually can’t reduce the surface roughness and the middle frequency. This paper study on material removal characteristic of reactive ion beam figuring(RIBF) for optics mirrors, the RIBF process combines physical and chemical effects to remove material, including physical sputtering, spontaneous chemical etching and simultaneous ion bombardment-enhanced desorption. The experiment results indicated that the RIBF process improved the surface quality for optics mirrors by decreased the surface roughness and the middle frequency, and it increased the removal efficiency compare with the IBF process. The research hopes to establish a combined process of RIBF and IBF, and aim to obtain high removal rate and high accuracy surfaces for complex optics mirrors.
During the conventional optical shaping process of fused silica, lapping is generally used to remove grinding damage layer. But this process is of low efficiency, it cannot meet the demand of large aperture optical components. Therefore, Inductively Coupled Plasma Processing (ICPP) was proposed to remove grinding damage layer instead of lapping. ICPP is a non-contact, deterministic figuring technology performed at atmospheric pressure. The process benefits from its ability to simultaneously remove sub-surface damage (SSD) while imparting the desired figure to the surface with high material remove rate. The removing damage capability of ICPP has preliminarily been confirmed on medium size optical surfaces made of fused silica, meanwhile serious edge warping was found. This paper focused on edge effect and a technique has been designed to compensate for these difficulties. Then it was demonstrated on a large aperture fused silica mirror (Long320mm×Wide370mm×High50mm), the removal depth was 30.2μm and removal rate got 6.6mm3/min. The results indicate that ICPP can rapidly remove damage layer on the fused silica induced by the previous grinding process and edge effect is effective controlled.
Ion beam figuring (IBF) provides a highly deterministic method for the final precision figuring of optical components. According to the Sigmund sputtering theory, the mass of incident ions is an important factor to the sputtering rate and the optical surface quality. Both Ar+ and Kr+ are alternative ions in IBF, but the mass of Kr+ equals two times that of Ar+. In order to achieve the nanometer and sub-nanometer precision fabrication with IBF, the optical material removal property of Ar+ and Kr+ ions was researched. The bombardment process had been simulated with the software TRIM, and the sputtering yield of Ar+ and Kr+ ions for different incident angles was calculated. Then the removal function experiments on Si were conducted. The simulations and experiments result indicated that Ar+ ion beam achieves higher removal rate at 0° incident angle, but Kr+ ion beam performs more efficiently when the incident angle gets across a critical point.
Nd doped phosphate glass is widely used as gain media in high power laser system. It is traditionally polished with the annular polishing technology. The edge effect is inevitable in annular polishing process and it results in the low manufacturing efficiency. Ion Beam Figuring (IBF) is a highly deterministic, non-contact method for the ultra-precision optics fabrication. So the edge effect is avoided. Nanometer and sub-nanometer precision is realizable in IBF. In this paper, Nd doped phosphate glass was polished with IBF, and the evolvement of surface roughness was emphasized. The roughness of surface polished with ion beam at normal and oblique incidence was researched. The oblique incident angle was 45°. The surface roughness was measured with the white light interferometer. No evident change was observed. This means that the pre-finish roughness can be preserved in IBF. The results denote that IBF is a feasible method to correct the contour errors of Nd doped phosphate glass, and the roughness will not be coarsened.
Ion beam figuring (IBF) is a deterministic and powerful optical figuring process to high-end optics. To perform an IBF process, some computations are inevitably involved, such as to extract beam removal functions, to calculate dwell times, to determine scan velocities and to recognize the removal rate. These computations influence the process time and the process result of the IBF. In this paper, the computations involved in an IBF process are introduced and the software IBFCAM, which is developed by us to implement all the computations, is also introduced. IBFCAM is well designed and it consists of 6 modules, including IBFCAM. Read, IBFCAM. Removal, IBFCAM.BRF, IBFCAM. Time, IBFCAM. Code and IBFCAM. PostAnalysis. Each module deal with a relatively independent function. Particularly, The IBFCAM. Post Analysis is newly added to IBFCAM in version 5.0. It is used to recognize the actual the removal rate. especially useful to a new material or a new optics. This is very useful to a new optics, especially to a new material.
Specifications made on optical components are becoming more and more stringent with the performance improvement of modern optical systems. These strict requirements not only involve low spatial frequency surface accuracy, mid-and-high spatial frequency surface errors, but also surface smoothness and so on. This presentation mainly focuses on the fabrication process for square aspheric window which combines accurate grinding, magnetorheological finishing (MRF) and smoothing polishing (SP). In order to remove the low spatial frequency surface errors and subsurface defects after accurate grinding, the deterministic polishing method MRF with high convergence and stable material removal rate is applied. Then the SP technology with pseudo-random path is adopted to eliminate the mid-and-high spatial frequency surface ripples and high slope errors which is the defect for MRF. Additionally, the coordinate measurement method and interferometry are combined in different phase. Acid-etched method and ion beam figuring (IBF) are also investigated on observing and reducing the subsurface defects. Actual fabrication result indicates that the combined fabrication technique can lead to high machining efficiency on manufaturing the high-precision and high-quality optical aspheric windows.
An ion beam figuring system (KDIBF2000) for final figuring of large size optics has been designed and built by National University of Defense Technology in China. It can figure optics up to the maximum dimensions of 2.0m×2.0m×0.4m with five axes of servo-motion used to control ion source movement. For operational facility, there are two vacuum chambers with main work chamber and a small supplementary chamber isolated by a flapper valve. The main chamber has two work zones, which can meantime hold a large optics with Φ1.5m and a small optics with 0.4m. The small optics can be transferred through supplementary chamber with a moving vehicle. By this way, it is very convenient and economical to gain the material removal function and check the system’s process performance. Now, this system has been gone into running to figure large SiC off-axis aspheric optics. Next step, a 1.2m SiC aspheric primary mirror will be figure by this system.
A new ion beam figuring (IBF) technique, obliquely incident IBF (OI-IBF), is proposed. In OI-IBF, the ion beam bombards the optical surface obliquely with an invariable incident angle instead of perpendicularly as in the normal IBF. Due to the higher removal rate in oblique incidence, the process time in OI-IBF can be significantly shortened. The removal rates at different incident angles were first tested, and then a test mirror was processed by OI-IBF. Comparison shows that in the OI-IBF technique with a 30 deg incident angle, the process time was reduced by 56.8%, while keeping the same figure correcting ability. The experimental results indicate that the OI-IBF technique is feasible and effective to improve the surface correction process efficiency.
Ion beam figuring (IBF) provides a nanometer/subnanometer precision fabrication technology for optical components, where the surface materials on highlands are gradually removed by the physical sputtering effect. In this deterministic method, the figuring process is usually divided into several iterations and the sum of the removed material in each iteration is expected to approach the ideally removed material as nearly as possible. However, we find that the material removal programming in each iteration would influence the surface error convergence of the figuring process. The influence of material removal programming on the surface error evolution is investigated through the comparative study of the contour removal method (CRM) and the geometric proportion removal method (PRM). The research results indicate that the PRM can maintenance the smoothness of the surface topography during the whole figuring process, which would benefit the stable operation of the machine tool and avoid the production of mid-to-high spatial frequency surface errors. Additionally, the CRM only has the corrective effect on the area above the contour line in each iteration, which would result in the nonuniform convergence of the surface errors in various areas. All these advantages distinguish PRM as an appropriate material removal method for ultraprecision optical surfaces.
This paper proposes a new chemical mechanical polishing (CMP) process method for CaF2 single crystal to get ultraprecision surface. The CMP processes are improving polishing pad and using alkaline SiO2 polishing slurry with PH=8, PH=11 two phases to polish, respectively, and the roughness can be 0.181nm Rq (10μm×10μm). The CMP process can’t get high surface figure, so we use ion beam figuring (IBF) technology to obtain high surface figure. However, IBF is difficult to improve the CaF2 surface roughness. We optimize IBF process to improve surface figure and keep good surface roughness too. Different IBF incident ion energy from 400ev to 800ev does not affect on the surface roughness obviously but the depth of material removal is reverse. CaF2 single crystal can get high precision surface figure (RMS=2.251nm) and still keep ultra-smooth surface (Rq=0.207nm) by IBF when removal depth is less than 200nm. The researches above provide important information for CaF2 single crystal to realize ultra-precision manufacture.
An ion-enhanced atmospheric pressure plasma machining (IAPPM) method is introduced to improve the processing efficiency of SiC. The argon inductively coupled plasma is generated in designed the IAPPM machine. SF6 chosen as the reactive gas is injected into the argon plasma where SF6 is broken down into fluorine radicals. The reactive atoms are delivered onto the surface of SiC, and SiF4 is generated which is exhausted in the gaseous form. The material removal rate is increased by bringing in the energetic ions bombardment. Three linear trenches were etched onto the S-SiC sample. The etch rate is 3μm/min. The surface becomes rough after the IAPPM process.
Ion beam figuring (IBF) provides a highly deterministic method for high-precision optical surface fabrication, whereas ion-induced microscopic morphology evolution would occur on surfaces. Consequently, the fabrication specification for surface smoothness must be seriously considered during the IBF process. In this work, low-energy ion nanopatterning of our frequently used optical material surfaces is investigated to discuss the manufacturability of an ultrasmooth surface. The research results indicate that ion beam sputtering (IBS) can directly smooth some amorphous or amorphizable material surfaces, such as fused silica, Si, and ULE® under appropriate processing conditions. However, for IBS of a Zerodur® surface, preferential sputtering together with curvature-dependent sputtering overcome ion-induced smoothing mechanisms, leading to the granular nanopatterns’ formation and the coarsening of the surface. Furthermore, the material property difference at microscopic scales and the continuous impurity incorporation would affect the ion beam smoothing of optical surfaces. Overall, IBS can be used as a promising technique for ultrasmooth surface fabrication, which strongly depends on processing conditions and material characters.
We propose a deterministic figuring method for fabricating high-precision optical surfaces by combining ion beam material adding (IBA) and material removal [ion beam figuring (IBF)] technology. The IBA is first utilized to improve the accuracy and quality of the optical surface by deterministically adding material to the local pits, and then the IBF is applied to further improve the surface accuracy through removing the local protuberances. Compared with current IBF technology, this combined method can realize the uniform convergence of the surface errors and simultaneously increase the convergence rate of the figuring process.
In deterministic ion beam figuring (IBF) technology, the application of small ion beam enhances the corrective capability for mid-to-high spatial frequency errors on the optical surface, which directly determines the surface accuracy of the figuring process. But when the diameter of the ion beam becomes smaller, the machining errors will have a stronger influence on the final figuring result, so these errors must be controlled through corresponding methods. We investigate the corrective principle in IBF for surface errors of different spatial frequencies and establish the selection criterion for removal function in different figuring stages to realize the rapid convergence of surface accuracy. Then, through analyzing and controlling the machining errors in the figuring process, high-precision mirrors can be rapidly obtained. Finally, experiments on fused silica planar and spherical samples are conducted on our self-developed IBF system, and their final surface accuracy are both smaller than 1.1 nm RMS (root-mean-square) and 12.0 nm PV (Peak-to-Valley) after several iterations within 20 min.
Ion beam figuring (IBF) Technology to fabricate optical materials with a high thermal expansion coefficient, such as BK7, we were aware that the thermal effect is a troublesome problem that generates high thermal stress. If the thermal stress is over the component mechanical stress limit, the component may crack or break. We discuss this problem in detail and set up a thermal model. Using this model, we gain the machined component temperature field and its corresponding thermal stress field. A filtered IBF method is created to correct the thermal stress field which that gain a more even thermal stress distribution and decrease the thermal stress about 20%.
Aspheric optics are being used more and more widely in modern optical systems, due to their ability of correcting
aberrations, enhancing image quality, enlarging the field of view and extending the range of effect, while reducing the
weight and volume of the system. With optical technology development, we have more pressing requirement to large-aperture
and high-precision aspheric surfaces. The original computer controlled optical surfacing (CCOS) technique
cannot meet the challenge of precision and machining efficiency. This problem has been thought highly of by
researchers. Aiming at the problem of original polishing process, an optimized method for manufacturing large aspheric
surfaces is put forward. Subsurface damage (SSD), full aperture errors and full band of frequency errors are all in control
of this method. Lesser SSD depth can be gained by using little hardness tool and small abrasive grains in grinding
process. For full aperture errors control, edge effects can be controlled by using smaller tools and amendment model with
material removal function. For full band of frequency errors control, low frequency errors can be corrected with the
optimized material removal function, while medium-high frequency errors by using uniform removing principle. With
this optimized method, the accuracy of a K9 glass paraboloid mirror can reach rms 0.055 waves (where a wave is
0.6328μm) in a short time. The results show that the optimized method can guide large aspheric surface manufacturing
Ion beam figuring (IBF) is an optical fabrication technique that provides highly deterministic process to correct surface figure error of previously polished surfaces by using a directed, inert and neutralized ion beam to physically sputter material from the optic surface. Recently, an ion beam figuring system KDIFS-500 has been designed and built in National University of Defense Technology (NUDT) of the P.R. China. KDIFS-500 is capable of processing workpiece up to Φ500mm. Line scanning process was discussed in detail for estimating the parameters of the beam removal function (BRF) in process. Experiments were conducted to demonstrate that the BRF increases gradually in process and by employing a stability control, the BRF can be kept stable in process. Finally, a Φ95 mm plano optical sample of CVD coated SiC substrate has been figured in two process iterations for demonstrating the correction capability of the KDIFS-500. Their figure convergence ratios reached 5.8 and 2.1 respectively. The actual figure residual errors were basically consistent with the predicted error. These consistencies indicated that the IBF processes on KDIFS-500 are predictable deterministic processes.