Due to the complexity and inhomogeneity of the distribution of the middle-spatial frequency errors (MSFE), the existing theoretical models cannot realize the manufacturability prediction of the smoothing process for the MSFE on the largeaperture optical components. Therefore, based on the parameterized time-domain smoothing model and the idea of regional division, a prediction algorithm suitable for the smoothing process of the MSFE in complex periods is proposed in this paper. The relevant verifiable experiments are carried out. The prediction results are in good agreement with the real data, which indicates that the prediction algorithm proposed in this paper can be applied to predict the smoothing process of the MSFE of large-aperture optical components and guide the polishing process.
By virtue of the characteristics of high machining certainty, fast surface shape convergence and less subsurface damage, magnetorheological finishing (MRF) has been widely applied in ultra-precision machining for optics. However, the convolution of tool influence function (TIF) and the regular movement track make it difficult to avoid the deterioration of mid-spatial frequency (MSF) errors in the MRF process, which will affect the optical properties of optics. In this paper, the main factors affecting the MSF errors in grating path processing are theoretically analyzed. Under the condition of determinate polishing spot, the main influencing factors are the removal depth and processing spacing of a single scan. Through experimental research, the influence of removal depth and processing spacing of a single scan on the MSF errors in the MRF process is acquired. On this basis, the preferred parameters of removal depth and processing spacing of a single scan under specific processing conditions in the MRF process are obtained with the MSF errors of 1 nm as the evaluation index. It provides a theoretical basis and reference value for suppressing the deterioration of MSF errors of optics during MRF process and obtaining high quality optical surfaces.
The high-precision aspheric optics is difficult to achieve batch production because of its high complexity and cost in manufacturing process. Bonnet polishing is an efficient and precision polishing technology that has been widely used in aspheric optics manufacturing process. The existing aspheric bonnet polishing is mostly based on the five-axis CNC machine, but its cost is high. With the development of robot technology, it is a new, economical and effective attempt to combine robotic technology with bonnet polishing technology and apply it to manufacture the precision aspheric optics. In this paper, the research on robot-based bonnet polishing technology of aspheric optics is carried out. Firstly, the robotbased bonnet polishing equipment is introduced. Then, the control model of the robot-based bonnet polishing technology of aspheric optics is established. Finally, the aspheric polishing verification experiments are completed, and the good results are obtained. In this paper, the high-efficiency and high-precision manufacture of aspheric optics by robot-based bonnet polishing technology is realized, which greatly reduces the cost of aspheric precision manufacturing equipment, and provides a new technology choice for the high-precision, low-cost and batch production of aspheric optics.
Continuous phase plate (CPP) is the vital diffractive optical element in large laser devices. It is extremely difficult to manufacture owing to its random and small feature structures. Bonnet polishing (BP) has obvious advantage of high efficiency, and has great potential in high-efficient manufacturing of large optics. In the paper, BP techniques have been developed to manufacture CPP. Firstly, the relationship between the process parameters and tool influence functions (TIFs) has been analyzed, and the adjustable ranges of TIF size and efficiency have been determined. Then, a surface topography simulation model for the forecast of CPP residual errors has been established. Based on the model, the influence of TIF size on the accuracy of CPP has been simulated and analysed, meanwhile the optimized TIF has been determined. Finally, an experiment has been carried out by a 300mm×300mm CPP element. The result has shown that the residual root-mean-square (RMS) of CPP is 26 nm. Based on the optimized TIF of BP, it has been realized the high-efficient and high-precision processing of CPP in this paper, and a new technical reference for the CPP manufacturing has been provided simultaneously.
Magnetorheological finishing (MRF) is a deterministic optical element polishing method that achieves material removal by means of the sheared and rheo-logical behavior of magnetorheological fluids. To realize high precision fabrication of large-aperture optical components, MRF technology had been explored in this paper. The main factors affecting the removal efficiency were investigated by orthogonal experiment. It indicated that the influence of the immersion depth and the thickness of ribbon on removal efficiency was more remarkable than the other parameters. The process of MRF machining component is established. Finally, the 590mm × 400mm plane optical element are manufactured using the MRF, and the result are very good.
MRF is capable of producing smooth surface without incurring serious mechanical defects. Thus it is employed to machine fused silica in the hope of reducing mechanical defects on the optical components. The MRF-polished surface was damage-tested with 355nm 8ns pulsed laser and it is found that the laser induced damage threshold was not improved (31.2J/cm2 ) even if the surface contains almost no mechanical defects. However, the damage threshold is increased to 45J/cm2 after slight HF-solution etching (~1μm material removal). On the other hand, the ion beam etching (IBE) was also investigated to find out the potential effects on the laser damage performance of fused silica. The laser damage threshold of IBE processed fused silica is 26.5J/cm2 while the threshold rose to 55J/cm2 after slight chemical etching (~1μm material removal) with HF solution. For comparison, the control samples finished with conventional pad polishing process were also tested. The thresholds prior to and following HF wet etching (~1μm material removal) are 29 J/cm2 and 42 J/cm2 , respectively. From the experimental results, it is clear that slight HF wet etching can enhance the damage resistance of fused silica irrespective of the finishing techniques. Neither MRF nor IBE finished fused silica surface behave better than conventionally polished surface whilst IBE-finished surface appears to have stronger damage resistance after HF etching. HF etching can improve the laser damage threshold by >107% for IBE finished fused silica.
Magnetorheological finishing (MRF) is a deterministic optical element polishing method that achieves material removal by means of the sheared and rheo-logical behavior of magnetorheological fluids. For the magnetorheological processing optics, an experimental study of the magnetorheological processing force was carried out. It was obtained that the relationship between the process parameters and element forces in magnetorheological polishing .The process parameters in MRF are the rotation speed of the polishing wheel, the magnetic field strength, the liquid flow rate, and the immersion depth. For MRF-600 magnetorheological polishing machine with polishing wheel Φ300mm, the normal forces range from 2N to 32N.According to the fitting curve between the magnetic field and the normal forces, the force is 6 times larger than that under the zero magnetic field condition. At the same time, the polished spots were collected under different magnetic field intensity. The law of the removal rate of polishing spots was obtained.
The wave front gradient is a key parameter to the low frequency wave front of the aspherical components, which ultimately affects the focusing performance of the optical system. CCOS(Computer Controlled Optical Surfacing)is a technique widely used in precision polishing of aspherical lens. First of all, the reasons for the deterioration of the gradient are analyzed. Secondly, the control technology is designed for various main factors. This paper also found a technological scheme that could inhibit the error of the wave pattern in theory. Finally, combined with the actual conditions of engineering processing, the results of control process methods are verified. The results show that GRMS value of a large aperture(400mm × 400mm)aspheric element is reduced from 0.013 λ/cm to 0.008λ/cm.
Based on the theoretical removal function model, the internal relation between the fluid dynamic pressure parameters and the processing parameters of the magnetorheological removal function is analyzed. The main technological parameters affecting the removal function are clarified. The single-factor influence experiment was carried out for four technological parameters (liquid flow, concentration of polishing liquid, immersion depth and thickness of ribbon).The relationship curve between the single factor parameter and the removal function volume and the single factor parameter and the removal area is given. The influence of different single-factor parameters on magnetorheological removal function is obtained. The processing of a concave mirror is guided by this rule. High quality optical elements are obtained.
As a kind of Computer Controlled Optical Surfacing(CCOS) technology. Ion Beam Figuring(IBF) has obvious advantages in the control of surface accuracy, surface roughness and subsurface damage. The superiority and characteristics of IBF in optical component processing are analyzed from the point of view of removal mechanism. For getting more effective and automatic tool path with the information of dwell time, a novel algorithm is proposed in this thesis. Based on the removal functions made through our IBF equipment and the adaptive tool-path, optimized parameters are obtained through analysis the residual error that would be created in the polishing process. A Φ600 mm plane reflector element was used to be a simulation instance. The simulation result shows that after four combinations of processing, the surface accuracy of PV (Peak Valley) value and the RMS (Root Mean Square) value was reduced to 4.81 nm and 0.495 nm from 110.22 nm and 13.998 nm respectively in the 98% aperture. The result shows that the algorithm and optimized parameters provide a good theoretical for high precision processing of IBF.
In the process of computer-controlled optical surfacing (CCOS), the key of correcting the surface error of optical components is to ensure the consistency between the simulated tool influence function and the actual tool influence function (TIF). The existing removal model usually adopts the fixed-point TIF to remove the material with the planning path and velocity, and it considers that the polishing process is linear and time invariant. However, in the actual polishing process, the TIF is a function related to the feed speed. In this paper, the relationship between the actual TIF and the feed speed (i.e. the compensation relationship between static removal and dynamic removal) is determined by experimental method. Then, the existing removal model is modified based on the compensation relationship, to improve the conformity between simulated and actual processing. Finally, the surface error modification correction test are carried out. The results show that the fitting degree of the simulated surface and the experimental surface is better than 88%, and the surface correction accuracy can be better than 1/10 λ (Λ=632.8nm).
The surface chemical composition and atomic emission spectroscopy of F atoms and CF2 molecules involved in the
processing of Atmospheric Pressure Plasma Jet (APPJ) produced from CF4 precursor has been explored. The XPS
spectra illustrated that small amount of radicals including C-CFn and CF-CFn could be introduced onto the fused silica
surface during the CF4 plasma process, the fluorocarbon radicals were generated during CF4 plasma ionization.
Moreover, the relative concentrations of excited state species of F atoms and CF2 molecules, which play significant role
in remove and fluorocarbon radicals, were acquired for CF4 plasma. The densities of F atoms increased dramatically with
increasing applied RF power, whereas CF2 molecules decreased monotonically over the same power range, the
subsequent electron impacted decomposition of plasma species after CF4 precursor fragmentation. The spectrum of the F
atoms and CF2 molecules fallowed the same tendency with the increasing concentration of gas CF4, reaching the
maximum at the 20sccm and 15sccm respectively, and then the emission intensity of reactive atoms decreased with more
CF4 molecules participating. Addition certain amount O2 into CF4 plasma resulted in promoting CF4 dissociation, O2 can
easily react with the dissociation product of CF2 molecules, which inhibit the compound of the F atoms, so with the
increasing concentration of O2, the concentration of the CF2 molecules decreased and the emission intensities of F atoms
showed the maximum at the O2/CF4 ratio of 20%. These results have led to the development of a scheme that illustrates
the mechanisms of surface chemistry reaction and the affection of plasma parameters in CF4 plasma systems with respect
to F and CF2 gas-phase species.
The surface chemistry reaction involved in the processing of Atmospheric Pressure Plasma Jet (APPJ) produced from CF4 precursor has been explored. The atomic emission spectroscopy of F atoms and CF2 molecules was investigated as they contribute to substrate etching and FC film formation during APPJ processing. Optical emission spectroscopy (OES) spectra were acquired for CF4 plasma, relative concentrations of excited state species of F atoms and CF2 molecules were also dependent upon plasma parameters. The densities of F atoms increased dramatically with increasing applied RF power, whereas CF2 molecules decreased monotonically over the same power range, the subsequent electron impacted decomposition of plasma species after CF4 precursor fragmentation. The spectrum of the F atoms and CF2 molecules fallowed the same tendency with the increasing concentration of gas CF4, reaching the maximum at the 20sccm and 15sccm respectively, and then the emission intensity of reactive atoms decreased with more CF4 molecules participating. Addition certain amount O2 into CF4 plasma resulted in promoting CF4 dissociation, O2 can easily react with the dissociation product of CF2 molecules, which inhibit the compound of the F atoms, so with the increasing concentration of O2, the concentration of the CF2 molecules decreased and the emission intensities of F atoms showed the maximum at the O2/CF4 ratio of 20%. These results have led to the development of a scheme that illustrates the mechanisms of surface chemistry reaction and the affection of plasma parameters in CF4 plasma systems with respect to F and CF2 gas-phase species.
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