To improve the beam quality and output powers of driving optical components for Inertial Confinement Fusion (ICF) laser facilities, this paper introduces the construction, operation and performance enhancement of SG series laser facilities in China. It reviews the research working and developments of optical components for the ICF laser facilities in recent years. These workings involve the preparation of raw materials, such as high purity metal hafnium(Hf) and Potassium Dihydrogen Phosphate(KDP), and the melting, processing and growing of four kinds main materials, including neodymium glass, high purity KDP, fused quartz and KDP/DKDP (doped deuterium KDP). For fabrication of the optical components, it describes the cold machining technology for neodymium glass, white glass, KDP crystals and the coating technology for dielectric films and chemical films. Finally, the paper also focuses on some key test technologies of the large diameter optical components in process inspection and final inspection. These key technologies and machining processing proposed in this paper meet the most requirements of the optical components in whole machining process and improve the development and production capacities of optical components in ICF laser facilities.

This paper reviews the advances in fabricating large-aperture Beam Sampling Grating (BSG) made of fused silica for Shenguang laser facility. A chemical mechanical polishing process for large-aperture BSGs is proposed. The efficiency uniformity of BSGs with an aperture of 430 mm× 430 mm is successfully controlled within a rms of 5% , which meets the specification of the large-aperture BSGs. For threshold characteristics of BSGs, the contamination and its cleaning of large-aperture BSGs are characterized with second ion mass spectroscopy quantitatively, and the cleaning flow of BSGs is developed and optimized. To remove the subsurface damage of fused silica, the fused silica substrate processing based on hydrofluoric acid and inductively coupled plasma etching is investigated. For improving the laser-induced damage threshold of the BSGs, it suggests that the HF acid etching method for large-aperture fused silica BSGs and the preparation method for BSGs integrated with sub-wavelength antireflection gratings should be developed in the future.

For the requirements of Inertial Confinement Fusion(ICF) facility for large aperture transport mirrors with higher performance, key technologies and special processing involved in mirror machining are explored. Some kinds of machining technologies, including the manufacturing of K9 glass blanks, optics cold processing, coating for transport mirrors and laser conditioning are investigated. The precision annealing process of 400 mm aperture K9 glass blank is proposed to implement the high precision optical finishing. Moreover, Low-defect coating is achieved. A preprocessing device for the larger aperture optical element is established and a laser conditioning platform for large aperture transport mirror is also realized. Finally, the paper reviews main achievements of development of large aperture transport mirrors. A 400 mm aperture transport mirror with an incidence angle of 45° shows its surface roughness to be higher than 99.8%, surface figure(PV value) lower than λ/3, and the laser-induced damage threshold higher than 30 J/cm2 (5 ns) at 1 053 nm. The large aperture transport mirrors have been successfully used in the higher power laser equipment of SG ICF facility, which supports the stable operation of the facility.

The research and achievements of high performance polarizer coatings by many scholars around the world are reviewed, including the spectral properties, laser damage threshold and stress control. For the performance requirements of polarizer coatings in China Shenguang series facilities, it describes the investigation of spectral properties, laser damage threshold, and figure accuracy of the polarizer coatings based on electron beam depolarization by Shanghai Institute of Opitcs and Fine Mechanics of the Chinese Academy of Sciences(SIOM). Much work and achievements on design, preparation and past-treatment of the coating are given. On the basis of the research achievements, high performance thin films polarizer with low defect density and low stress have obtained. The Brewster angle thin film polarizer developed by our team has participated in the International Laser Damage Competition held on the SPIE 2012 Laser Damage & SPIE 2013 Laser Damage Symposium. The p-polarized LIDT( Laser Induced Damage Threshold) as well as the average of p-polarized and s-polarized LIDT achieves the best results. The stress-induced crazing of large aperture polarizer coating is also solved, by which the manufacturing of large aperture polarizer is implemented in China, showing the spectral properties of TP>98%,RS>99% and the flux property of 17 J/cm2(9 ns).Now, the prepared large aperture polarizer has supported the stable operation of ShenguangII-UP laser facility.

Several kinds of important preparation processes of synthetic optical silica glass are elaborated, such as Chemical Vapor Deposition (CVD), Plasma Chemical Vapor Deposition (PCVD) and indirect synthetic method. The raw materials and characteristics for the optical silica glass, as well their applications in different fields are given. Then, developing situations and tendencies of these preparation processes are reviewed. It compares their advantages and shortcomings in detail. Among them, the CVD is the most mature and commercial technology. It prepares the synthetic silica glass with a diameter of 600 mm or beyond, its optical uniformity is better than 2×10-6, and the laser damage threshold is 30 J/cm2@355 nm. The PCVD processes synthetic silica glass of full-spectrum transmittance. It shows excellent internal quality, its hydroxyl content is less than 5×10-6, and the spectral transmittance of T190-4000 nm is more than 80%. Furthermore, the indirect synthetic method prepares the synthetic silica glass with an absorption coefficient less than 1×10-6/cm@1064 nm, its hydroxyl content is less than 1×10-6, and the spectral transmittance of T157-4000 nm is more than 80%. Moreover, the indirect synthetic method is beneficial to doping and controlling the defects of synthetic silica glass, which achieves all kinds of special functional silica glass. It suggests that each of these preparation processes of synthetic optical silica glass has its own advantages and disadvantages, so proper preparation processes could be adopted for different application requirements of modern high-end photoelectron technological fields.

The main properties of high-power Nd∶laser glass in China and abroad and its development situations were compared. Then, the physical properties of large aperture N41 Nd∶glass developed by Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences(SIOM) were analyzed and its gain characteristics in a segment amplification system with an aperture of 400 nm was investigated. An optimized technological scheme was used to measure the small-signal net-gain parameters of N41 glass and N31-42 glass and the gain homogeneity of large aperture glass under the same condition. The results indicate that the several key parameters of N41 glass are better than that of the N31 glass. Under the same pumping condition, the average small-signal net-gain parameters for N41 glass and N31 glass are 5.3% and 5.16%, respectively, much better than the online experimental result of N31-35 glass used in Shenguang-Ⅲ. Moreover, the gain homogeneity of N41 glass with an aperture of 385 mm is 1.085∶1, and its cladding glass meets the requirement of Shenguang-Ⅲ. It concludes that the gain characteristics of the N41 glass have been improved greatly as compared with that of the N31 glass. When the amplifier structure is optimized, the N41 glass can be used in the Shenguang system in the future.

To further increase the laser-induced damage threshold of the fused silica elements, the effect of Magnetorheological Finishing( MRF) technology on the laser damage properties of fused silica elements was investigated under the condition of Hydrogen Fluoride(HF) acid dynamic etching process. Firstly, the fused silica samples were prepared by different processes and their surface roughnesses were measured. Then, the contents and depths of metal impurity elements before and after MRF processing were measured by Time of Flight- Secondary Ion Mass Spectroscopy (TOF-SIMS). The damage threshold was measured by 1-on-1 test method, and the damage morphology was observed and statistically analyzed. Finally, the reasons of increasing the laser-induced damage threshold of the fused silica by the MRF were analyzed. The experimental results were compared with that of the fused silica without the MRF. It shows that the MRF can increase the laser damage threshold of fused silica by 23.3%. Moreover, the content of metal impurity elements is significantly reduced, especially the Ce element which has a significant impact on the laser damage performance of fused silica is completely eliminated. It concludes that the MRF process can be used as a pre-treatment process for HF acid dynamic etching process.

Research progress of laser conditioning technology and its applications in China is reviewed in this paper. The physical mechanisms, effects and key techniques of laser conditioning on 1ω dielectric coatings and potassium dihydrogen phosphate(KDP)and doped deuterium KDP (DKDP) crystals are studied. A laser conditioning platform for large-aperture optics is constructed to increase the laser damage resistance of critical optics used in high power laser systems. The laser conditioning for large-aperture 1ω dielectric coatings is realized on engineering working. The influences of laser pulse lengths on the laser damage performance of DKDP crystals are compared. It demonstrates that there no intrinsic damage during nanosecond laser irradiation until 14 J/cm2(5 ns) can be observed in sub-nanosecond conditioned DKDP crystals, so that the scheme proposed in the paper is verified to be feasibility. Finally, it points out that the sub-nanosecond laser conditioning will be the key technology to implement the anti-laser damage performance of the high laser harmonic generation crystals.

To figure out the causes of cavity mirror defects in a Chemical Oxygen-iodine Laser (COIL), the surface defects on the cavity mirror were studied. A Scanning Probe Microscopy (SPM) was used to observe the surface defects on the cavity mirror, and its micro topography was analyzed. The shapes of the surface defects and the reasons why the defects appeared were discussed. Then, a simplified model of cavity mirror with defects was established. The ring beam irradiating the cavity mirror was simulated by using COMSOL Multiphysics. The relationship between the defect size, power density and the surface temperature of the cavity mirror was given and the influence of an adsorption layer on the melting damage of the cavity mirror was analyzed. The calculated results show that when the defect area is a constant, the larger the laser radiation power is and the faster the temperature grows, the more the melting damage of film surface is. Moreover, the mirror film has the possibility of melting damage at the defect radius of 2.3 mm. The absorption coefficient of the absorption layer increases by 1%, then the maximum temperature of the mirror increases about 210 K. The conclusion provides a reference for the analysis of the causes of cavity mirror damage and the replacement of the cavity mirror in the COIL system.

The Laser-induced Damage Thresholds (LIDTs) of fused silica optical elements would be deteriorate, when it suffers the 355 nm laser irradiation. This paper proposes a method to improve their LIDTs. A silica element was immersed into two types of HF-based etchants: 1.7%wt. HF acid and buffer oxide etchant (BOE: the mixture of 0.4%wt. HF and 12%wt. NH4F)to be treated in the same experimental condition , respectively. The etching rate was calculated by measuring the weight variation of the etching element during the etching process, and the surface roughness of the element was tested by a Zygo contourgraph. Then, the LIDT characteristics of the fused quartz element under the 355 nm laser irradiation were studied. The damage testing shows that the LIDT is relative to the depth of material removal. Both the etchants increase the LIDT at a certain depth of material removal, but further removal of material lowers the LIDT markedly. The etching rates of both etchants keep steady in our processing procedure, they are ~85.9 nm/min and ~58.6 nm/min, respectively. The micro-surface roughness (RMS&PV) increases as etching time extended. Furthermore, the hardness and Young's modulus of the fused silica etched were measured by a nano-indenter, and there is no solid evidence that LIDT can be related to hardness or Young's modulus.

The structure of a grating polarizer in common 1053 nm lasers was optimized for high power laser systems. The diffraction characteristics and extinction ratio of the grating polarizer were investigated by using rigorous coupled-wave theory. The results show when the grating period, duty cycle and the groove depth of the grating are 600 nm, 0.535-0.55 and 1 395-1 420 nm at a wavelength of 1053 nm, respectively, the extinction ratio could be more than 1500, and the optical transmittance of the TM-polarized wave could be over 95%. Based on the above analysis, a high quality photoresist grating mask was made by holographic lithography. Then, it was transferred to the fused silica substrate by tilted rotating ion beam etching and reactive ion beam etching to fabricate a grating polarizer with the period of 600 nm, bottom duty cycle of 0.54 and the groove depth 1 400 nm. Experimental measurements on the grating polarizer show that the optical transmittance is 92.9% and the extinction ratio is 160. Compared with other fabricating methods for the grating polarizer, the proposed method only requires a single layer of photoresist grating mask, which simplifies the fabricating process, enjoys low costs and guarantees the high damage threshold of the grating. As the method can fabricate large scale gratings, it is suitable for applications to the high power laser systems.

This paper focuses on the continuous melting technology of neodymium laser glass carried out by Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences since 2005. It describes the research progress and some achievements of the technology. The continuous melting processing of N31 laser Nd glass is given, continuous melting of phosphate glass is simulated and a lots of experiments on the design, establishment, improvement and verification of the continuous melting line are carried out. A series of key technologies of continuous melting such as hydroxylation removal, Pt-inclusion removal, and transition metal impurity control, large size casting and birefringence control in lehr annealing are solved and the mass production of N31 laser glass is realized. The experimental achievements show that the fluorescent lifetime, laser attenuation at 1 053 nm, optical homogeneity and other properties of the continuous melted laser glass meet the requirements of the Shenguang facility. The comparison experiments show that the optical parameter homogeneity and absorption coefficient at 400 nm of the continuous melted laser glass are superior to those of the pot melted glass. Moreover, the absorption coefficient at 3 333 nm and larger laser damage threshold caused by platinum inclusion of the N31 laser glass are better than those of LHG-8 glass used in Lawrence Livermore National Laboratory in the United States.

According to the surface characteristics of continuous phase plates with small feature structures on high surface gradients and extensive mid-to-high spatial frequencies, several factors influencing the machining accuracy of the phase plates are analyzed. These factors include raster scanning pitch, material removal programming, positioning precision and material removal. The analysis points out that the optimal pitch can be selected according to the Nyquist sampling theorem to achieve the effective imprinting of feature structures with different sizes. When the surface errors in all spatial frequency ranges are controlled effectively , the stable dwell time can be achieved during the raster scanning process by the optimized material removal programming. Furthermore, when the surface matching method is used to correct the measurement errors , the accurate material removal information can be obtained. When the positioning precision of the removal accuracy is increased, the machining accuracy of the element with small feature structures can be improved significantly. Finally, on the basis of eliminating of different process errors, the Ion Beam Fabrication(IBF) is adopted to imprint the complex phase structures with characteristic dimensions as small as 1.5 mm, surface peak-to-valley (PV) smaller than 200 nm and surface gradient as large as 1.8 μm/cm. The results show that the matching error between figured surface and desired surface has been controlled down to 8.1 nm (Root-Mean-Square, RMS) of design specifications. The experimental results verify the reliability of the error analysis.

A composite transmission pulse compression grating was proposed for femto-second Ti∶sapphire lasers. The composite transmission grating with 700-900 nm bandwidth worked at a center wavelength of 800 nm was consisted of two gratings with groove densities 1 250 line/mm and 3 300 line/mm and they were integrated in a fused silica plate. The 1 250 line/mm grating was used for compressing laser pulse. The 3 300 line/mm anti-reflection grating was conductive to decreasing the reflection loss and avoiding the wave-front distortion by using a high frequency grating structure to replace the anti-reflection film on the surface of the fused silica plate. Completely being made of fused silica, the composite pulse compression grating has a high laser damage threshold. The composite transmission grating was designed based on the rigorous coupled wave theory. The optimization calculation results show that the -1st order diffraction efficiency of the 1 250 line/mm grating is up to 98% (@800 nm) and the transmission of the 3 300 lp/mm grating is up to 99.7% at 700-900 nm bandwidth. Finally, the composite transmission pulse compression grating(Φ65 mm×1 mm ) was fabricated by holographic recording and ion bean etching and its diffraction efficiency is coincident with that of the theoretical analysis.

This paper focuses on the spectral properties and the impact resistances of composite quartz tubes and cerium doped quartz tubes used in the driving optical components of Inertial Confinement Fusion (ICF) laser facility. The spectral transmittances were tested on the selected samples, new composite quartz tube, new cerium doped quartz tube, 14 000 shot composite quartz tube and 14 000 shot cerium doped quartz lamp tube and their spectral properties were compared. It show that the spectral properties of the composite quartz tube and cerium doped quartz tube have all reached spectral index of the high power pulse xenon lamp, and the spectral propeprty of cerium doped quartz tube is about 1% higher than that of composite quartz tube. A composition test of composite quartz tube and cerium doped quartz tube was carried out to verify the tested results.It indicates that the content of metal impurities in cerium doped quartz tube is lower than that of composite quartz tube, which is one of the reasons to explain the phenomenon mentioned above. Finally, the xenon lamp discharge operation was simulated, the impact resistance tests for the composite quartz tube and the cerium doped quartz tube were carried out. The experimental result demonstrates that the shock resistance of the composite quartz tube is about 6% higher than that of cerium doped quartz tube.

To realize the low aberration of pulse compression gratings (PCGs) applied in chirped pulse amplification and compression, a Deformable Mirror (DM) with small deformation was designed and fabricated to compensate the sub-micron static wavefront aberration induced by a large diameter grating substrate. The DM contains 19 piezoelectric actuators and its effective diameter is 80 mm and thickness is 5mm. The response function of each actuator was measured with an interferometer to construct the stiffness matrix of the DM. The least square was used to resolve the control voltage required of each actuator to obtain the target surface. By combination of the global optimization and local optimization, the target surface of the DM was controlled effectively. Finally, the DM was used to construct an active holographic optical recording system and a substrate with bigger aberration was selected to perform the compensation experiment for the grating. The experimental results show that: for about 0.93λ aberration of grating substrate, the PV of residual wave-front aberration of the PCG is near to 0.14λ (@ 633 nm) after employing the DM. It demonstrates that the DM can be effectively applied in the fabrication of low aberration PCGs.

HfO2 thin films were prepared by electron beam evaporation technique. Two kinds of post-treatment methods, anneal in oxygen and laser treatment, were employed to treat the samples under the oxygen condition. The procedures of post-treatment and corresponding treatment equipment were introduce and the optical transmittance, absorption and laser induced damage threshold of a HfO2 thin film sample at 355 nm were measured before and after the treatments. The treatment results on reducing absorption and improving the LIDT by above two post-treatment methods were compared, and their working principles were discussed. The experiments demonstrate that laser treatment decreases the sample absorption and improves the LIDT of HfO2 thin films. With one step(50% LIDT), the LIDT of the HfO2 film at 355 nm increases from 13 J/cm2 to 15 J/cm2. With two steps(50% LIDT and 80% LIDT ), the LIDT of the HfO2 film at 355 nm increases from 13 J/cm2 to 17.5 J/cm2, and the damage probability curve translates to a high flux area wholly.

To measure the transmissive wavefront of a long-focal length lens precisely, a novel Computer Generated Holography (CGH) was proposed by adding a binary diffractive optical element into the Zygo interferometer to provide a reference wavefront. The theory of transmissive wavefront measurement of large convex lens by using the CGH was introduced. A high precision computed holographic plane was designed and developed to apply in the measurement of the transmissive wavefront of the long-focal length lens. The theory analysis and practical test show that the proposed method has a lower systematic error, and the measuring repeatability of the CGH is better than 0.004λ (2σ RMS).The result is in agreement with that of common Fizeau interferometry, and verifies the feasibility of the proposed CGH. Finally, the measurement uncertainty due to the substrate error and hologram fabrication processes was analyzed, and the wavefront peak-valley error is less than λ/10. It concludes that the CGH method greatly shortens the airspace, improves measurement precision, and is of great importance for the wavefront measurement of long focal length lenses.

When a three Coordinate Measurement Machine is used to test the surface shape of an aspheric element in grinding and polishing, obtained result often shows astigmatism errors due to an imperfect compensation programming. This paper analyzes these measurement data, and points out that the astigmatism errors comes from the imprecise compensation programming for the radius of three-dimensional probe in the CMM. Then, It presents an off-line data processing method to compensate the measurement data and to eliminate the astigmatism. By calculation of the tangent vectors of row and column at the meshed central point, the normal vector of each point on the surface is obtained. By calculation of the offsets between the centers of probe and the contact points, the radius of the tree-dimensional probe in the CMM is compensated. The experiment of a standard sphere show that this method decreases the astigmatism PV(Peak-to-Valley) of the measurement result from 4.921 9 μm to 0.065 2 μm, eliminating basically the astigmatism errors and improving the accuracy of the coordinate measurement. Obtained results verify the effectiveness of the proposed compensation programming for the radius of tree-dimensional probe in the CMM.

To detect the bulk defects in crystal billet of a KDP(potassium dihydrogen phosphate)crystal quickly and exactly, a laser focusing scanning scattering imaging method was proposed and a corresponding high speed line scanning measurement setup was constructed. The principle of detection, image acquisition, image processing and the extraction of bulk defects were investigated. Based on laser scattering technique, a focused line laser beam was used to scan all parts of the crystal billet with a high-speed movement device. The scattering light caused by bulk defects such as bubbles and inclusions was collected by a linear array CCD. The adverse effect caused by rough surface was eliminated with the index-matching fluid. Combined with digital image processing technique, the captured image was processed in real time. An averaged background was subtracted from the original image, then the image was compared with a threshold to judge the existence of bulk defects. The image with bulk defects was binarized to exact the positions and sizes of bulk defects. Finally, the setup was used to test the crystal billet of a KDP, results show that the sensitivity by proposed method is superior to 40 μm. It verifies that this method provides supports for accurately cutting and making the most use of crystal billet and also saves a lot of costs.

The difference between the measurement angle and the use angle will produce measuring errors when the wavefront errors of the large reflective optics in a high power driving device are measured. So this paper proposes a method to convert the reflection wavefront in a measuring angle into the reflection wavefront in a use angle. Firstly, the cosine conversion method used in conversing the wavefront in an oblique incidence angle into the wavefront in the use angle was analyzed, and the calculation relationship of the wavefront errors between actual measurement angle and actual use angle was obtained. Then, the mid-frequency PSD1 (Power Spectral Density) error caused by the third interpolation algorithm itself was calculated, and it points out that the selected incident angle should be close to that the actual use angle as much as possible when the measuring condition meets the effective diameter measurement. Finally, the error analysis and experimental verification were carried out based on a 410 mm ×410 mm fused quartz reflector.Using this method, the 0° reflection wavefront was convered into the 45° reflection wavefront, and the measuring result after conversion was compared with that of the direction measuring result at 45°. The compared results show that the differences of PV values, RMS values and the PSD1 values are 0.01 λ, 0.003 λ and 0.08 nm, respectively. These results indicate that the method not only can calculate exactly the low frequency errors of reflection wavefront, but also can obtain the PSD1 mid-frequency error.

To improve the measuring accuracy of optical interferometry, the filtering methods to eliminate the noise in interference fringe patterns were researched. The results of different filtering methods were discussed in different wavefronts and different noises of the interferometer. By taking the effects of interferometric noise on fringe patterns and different wavefronts into account, four kinds of fringe patterns for defocus, astigmatism, coma, spherical aberration were established based on zernike polynomials by matlab simulation. The differences of PV and GRMS values before and after filtering were calculated for different wavefronts. The results on four kinds of wavefronts for defocus, astigmatism, coma, spherical aberration show that under the same kind of noise and filtering, the PV difference of the spherical aberration is largest, up to 0.11λ, which shows a poor filtering effect as compared with the 0.08λ from other wavefront differences under the multiplicative noise. Furthermore, the PV difference of the astigmatism wavefront is smallest, and it is down to 0.05λ excepting median filtering in the multiplicative noise, showing a better filter effect. Moreover, the result of coma wavefront filtering is slightly better than that of the defocus wavefront filtering. For the filter methods, low-pass filters offer high-stability and the differences of the PV is from 0.01λ to 0.04λ, showing a better filtering effect.

As the optical absorption coefficient of KDP or DKDP frequency doubling crystal in an Inertial Confinement Fusion (ICF) facility effects directly its frequency conversion efficiency and output energy, this paper researches the measurement methods of the absorption coefficients for two kinds of crystals. A measurement method based on LAMBERT-BEER law was proposed under oblique incidence for frequency doubling crystals. Then, the relationship between the polarization state of incident light and the propagation of light in the crystals under oblique incidence was analyzed. An iterative algorithm for calculating extraordinary refractive index of the crystals was presented. On the basis of the iterative algorithm, the extraordinary refractive index was obtained and the optical absorption coefficient of KDP or DKDP frequency doubling crystal was calculated by using the measured dada indirectly. The error sources were analyzed in detail. It shows that total measuring error of this method is less than 0.000 2 cm-1. Finally, a 40 mm×40 mm×60 mm crystal switch was measured and the obtained results were compared with that of spectrophotometry. The comparison indicates that the deviation of the two methods is less than 0.000 2 cm-1, which verifies that the proposed method can be used in absorption coefficient measurement of KDP or DKDP frequency doubling crystal in the ICF facility.

For the high efficient and high accuracy convergence of surface figure of a large aperture workpiece, the continuous polishing technology was investigated. As the convergence efficiency of surface figure of the workpiece was effected directly by the flatness of pitch lap in a continuous polisher, a high precision measurement equipment with repeatability accuracy of ±1 μm was designed and developed for measuring the flatness of the pitch lap. The change rules and correlation between the flatness of pitch lap and the PV value of surface figure for the workpiece were analyzed during continuous polishing, and relationship between the flatness data and the surface figure of the workpiece was obtained based on the measured data. The experiments indicate that when the diference between flatness and surface curve are larger, the shape of the workpiece is rapidly converged to about 1λ, meanwhile the polishing process transits from a rough polishing to a fine polishing. The high precision measurement equipment proposed by the paper implements precise measurement of the flatness for a large wet pitch lap and provides an important technical support for deterministic continuous polishing.

The magnetorheological processing was investigated to improve the machining precision of large aperture optical elements. The principle of magnetorheological processing and the mathematical model of removal function were introduced. On the basis of the characteristics of the magneticrheological processing, the whole processing flow of optical elements was established and the technological factors of element process were given. Then, the software for extracting laser spots was developed, the technological software was also proposed based on the orbit segment divided speed mode and functions of modules in the technological software were analyzed. Finally, an element with a length of 800 mm and a width of 400 mm was machined experimentally. The results in low, middle and high frequencies by a test equipment show that the PV value of reflective wavefront in low frequency is 34 nm, the PSD1(power spectrum density)value is 1.7 nm, and the roughness Rq value is 0.27 nm, respectively. These experimental results verify that it is feasible to machine the high precise large aperture optical elements by magnetorheological processing. Moreover, this paper expounds the advantages of magnetorheological processing in high power laser component applications.

By taking the effect of Tool Influence Function(TIF) used in the NC program on the polishing accuracy for optical elements into account, the method how to obtain the optimized TIF based on the aspheric parameters to be polished and polishing pad parameters is proposed. As the key to calculate the TIF of aspheric elements is to obtain accurately the dynamic pressure distribution between polishing pad and mirror, this paper analyzes the pressure distribution between polishing pad and mirror by finite element method and obtains the TIFs in different positions on the aspheric surface by classic Preston equation and planet motion. The variation tendency of the pitch polishing pad in polishing an aspheric element is analyzed in different polishing positions based on the dynamic pressure distribution model. The TIF spot experiment is carried out on an aspheric element with a curvature of 1 000 mm. The result shows that the shape of TIF simulated by the theory introduced in the paper is more similar with that of the actual situation, and the Pearson correlation coefficient reaches 0.977. It concludes that the method can obtain the pressure distribution conveniently by changing the parameter of polishing position and can optimize the TIFs, which provides a theoretical basis for improving polishing efficiency and polishing accuracy.

The fabrication and testing of a Ф420 mm fused silica high-order aspheric lens were presented. Current fabricating technologies were optimized, and robot grinding, polishing, and ion beam figuring were respectively applied to the fabrication of lens. For testing an aspheric lens, a spherical interferometer was used to test the concave surface of spheric lens, and the result shows that the test accuracy is 0.011λ-rms after the error of interferometer standard lens reference surface was removed. Furthermore, null compensators based on reflective auto-collimating method were taken to test the high-order convex aspherical surface,and the surface figure errors are 0.013λ-rms. Finally, a standard spherical mirror was used to test the transmission wavefront of processed aspheric lens with self-aplanatic form,and the transmission wavefront errors of aspheric lens is 0.013λ-rms. The testing results indicate that the entire specifications meet the requirements of design. The processing methods proposed by the paper are suitable for the fabrication of larger aspheric lenses and other larger aperture aspherical elements.

To control the mid-spatial frequency error of a flat optics by Magnetorheological Finishing(MRF), the correction ability of frequency error by the MRF removal function and the suppression method of residual error created by the MRF were investigated. Firstly, the changes of mid-spatial frequency PSD1 (Power Spectral Density 1)errors of the optics and the PSD curves before and after simulating the MRF were compared and the correctable frequency error range of the MRF removal function was analyzed. Then the effects of MRF processing parameters such as removal depth, tool-path intervals and the size of removal function on mid-spatial frequency PSD2 were analyzed based on uniform remove way and a method to suppress the mid-spatial frequency PSD2 error was established. Finally, the flat optics with a size of 400 mm×400 mm was polished by the MRF. Experimental results indicate that the wavefront PV of the flat optics is converged from 0.6 λ to 0.1 λ, the PSD1 error is converged from 5.57 nm to 1.36 nm, and the PSD2 error changes from 0.95 nm to 0.88 nm. It is concluded that the MRF has the abilities to control mid-spatial frequency error of large aperture flat optics by optimizing and choosing MRF processing parameters and corresponding strategies.