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Magnetorheological polishing technology is a high-deterministic, high-precision optical ultra-precision processing technology, which is widely used in the polishing of large-aperture flat optical elements. The accuracy of magnetorheological removal function is a key factor that determines the accuracy and efficiency of magnetorheological polishing. In the process of making the removal function, it is easy to introduce spurious fringes when an interferometer is used for surface shape test. The spurious fringes will reduce the extraction accuracy of the removal function, and affect the certainty of magnetorheological polishing. In addition, the introduced spurious fringes contain complex mid- and high-frequency structures, which seriously affect the evaluation of the ability to remove function modification. In order to eliminate the spurious fringes, this paper proposes a method of removing the spurious fringes of the removal function based on the characteristic spectrum band-stop filter. First, the ZooMFFT algorithm is used to amplify the frequency spectrum to realize the effective identification of the spectral characteristics of the spurious fringes; secondly, a specific algorithm is used to eliminate only the frequency spectrum of the spurious fringes, completely retaining the frequency spectrum of the removal function itself, and does not change the valid shape of the removal function, making the spurious fringes are removed. And the Quad Flip operation is used in spectral filtering to improve the filtering accuracy. The magnetorheological making spot experiment uses a fused silica plate element with a diameter of 50mm. A static interferometer is used to measure the component wavefront data, and the tested result data contains obvious spurious fringes. Using the method described in this article, the spurious fringes are completely removed, and the morphological and removal efficiency of the removal function remains unchanged. Compared with the traditional frequency domain band-stop filter, the residual surface RMS of the spurious fringes separation is reduced from 5.45nm to 1.98nm; improve the extraction accuracy of the removal function. It can be effectively used to eliminate the spurious fringes of the magnetorheological removal function.

Magnetorheological polishing technology is a new type of ultra-precision processing technology. It has many advantages such as no sub-surface defects, easy realization of numerical precision control, high machining accuracy, and high polishing efficiency; and its small removal function size makes it very suitable for processing optical elements with complex geometric structures. It has been widely used in phase optical processing. In order to realize the processing of phase optical elements with a small space periodic structure, a smaller removal function is required. The traditional magnetorheological fluid circulation system structure is difficult to achieve stable control of the magnetorheological fluid flow under small flow conditions. Therefore, it is difficult to obtain a stable small size removal function. This paper analyzes the characteristics of the peristaltic pump, and aiming at the problem of strong pulse in its output flow; uses a pulsation damper and a variable-diameter back pressure pipeline to eliminate the flow pulse, realizes the stable and smooth output of the peristaltic pump flow. On this basis, this paper proposes a new type of magnetorheological fluid circulation system structure, which realizes the stable control of the flow rate under small flow rate conditions. The magnetorheological fluid flow fluctuation error of the magnetorheological fluid circulation system was from more than 25% reduced to less than 2%, realizing high stability control of magnetorheological fluid flow. Use small size removal function to process Continuous Phase Plates (CPP) with large depth and small periodic structure. The CPP is designed with a PV of 5μm and a minimum space period of 3mm. After processing, the residual error RMS of the CPP from 830nm converges to 24.5nm, realize high-precision processing of phase components with large depth and small structure.

In the interference test process of a parallel flat optical element, the light beam after multiple reflections on the front and rear surfaces of the element with the wavefront to be measured often cause multi-surface interference, forming spurious fringes on the interferogram, which will introduce large errors to the wavefront measurement. Spurious fringes mainly have a great impact on the parameters such as wavefront gradient root mean square (GRMS) and mid-spatial-frequency power spectral density (PSD). The RMS value of the wavefront containing spurious fringes is generally significantly larger than the true value, which will affect the accurate measurement and evaluation of the wavefront quality of optical components. Existing spurious fringes suppression methods often have the disadvantages of multiple adjustment steps in the test process or high hardware requirements, and it is difficult to match the requirements for rapid and high-efficiency test of high-precision optical flat components. This paper proposes a method for removing spurious fringes in interference test based on characteristic spectrum band-stop filter, which can achieve accurate removal of spurious fringes. First, by using the ZoomFFT algorithm to zoom up the spectrum of the wavefront data points, the effective identification of the spectral characteristics of the spurious fringe is realized; then the band-stop filter in a specific area is used according to the spectral characteristics of the spurious fringes, only the frequency spectrum of the spurious fringes is removed, and the wavefront data of the component to be tested is completely retained without changing its own shape; the Quad-Flip operation and error function filter window are used for spectrum filtering, which effectively reduces Gibb's noise in the frequency domain due to the sudden truncation of the input data edge during FFT transformation. The transmitted wavefront of a fused silica element with a diameter of Φ100mm was tested on the ZYGO static interferometer, and the test results contained a large number of spurious fringes. After processing by this method, the spurious fringes were removed. The mid-spatial-frequency wavefront RMS of the component is reduced from 5.365nm to 3.678nm. The method does not need to add additional hardware and tedious measurement and adjustment operations, the calculation is fast, and the spurious fringes removal is accurate.

Due to the characteristics of large depth, small period and high steepness, phase optical elements with complex structure need to use a small size removal function in magnetorheological processing, and use very small line spacing and step size values when planning the polishing path，so the dwell time matrix is very large, and the dwell time calculation speed is slow; besides, because of the complicated phase optical profile, it is difficult to achieve high-precision convergence of the dwell time. This paper proposes a fast and high-precision numerical iterative dwell time algorithm for complex structure phase optical elements. this paper proposes the concept of the dwell point matrix, which realizes the methods of the FFT convolution multi-core parallel algorithm to calculate the dwell time in the entire iterative calculation process. Also, to achieve high-precision convergence of the dwell time calculation, this paper proposes a calculation rule based on machine dynamic performance matching, when calculating the dwell time, the speed, acceleration, and speed smoothness of the machine were matched with the performance of the magnetorheological machine, which improves the stability of the machine. A large-diameter Continuous Phase Plate (CPP) is processed on a magnetorheological machine. The shape of the CPP contains a random structure of various periods. The initial RMS = 228.07nm, the CPP data matrix size is 2424 × 2424, and the line spacing is 0.6mm, the dwell time is calculated using the algorithm described in this article, the entire calculation process takes only 4.2 seconds, the calculation speed is about 3 times faster than the traditional iterative methods, the CPP residual error RMS converges to 10.2nm; After the CPP processing is completed, the CPP actual residual error RMS is reduced from the original 228.07nm to 15.6nm, and its convergence rate is 93.1%, which shows that the algorithm has high calculation efficiency and convergence accuracy.

The test of wavefront of large aperture continuous phase plate(CPP) is difficult to obtain by whole aperture once because of CPP’s characteristic such as large phase depth and large phase gradient,so sub-aperture stitching technique is often used to test the CPP’s wavefront in whole aperture.We analysed some problems in the traditional sub-aperture stitching test and put forward a new stitching model mathematically in order to improve the precision in CPP’s sub-aperture stitching test.We have found that this new model is available by a serial experiments.

The design and manufacure of Continuous Phase Plate(CPP) with a large aperture is very significant and useful to the Inertial Confinement Fusion(ICF) and some physical experiment related due to its several advantages such as high energy availability ratio and easily controllable focal spot's profile. Various processing errors will be inevitably introduced for the limitation of the fabrication technique and hence produce aberrated laser wavefront, which is very influential for the process of beam's propagation and focusing. In this paper we numerically simulate and compare the optical filed distributions of phase-aberrated super-Gaussian beam passing through both designed and manufactured CPP with a large aperture and deep phase. The simulation results prove the CPP's beam smoothing performance and high tolerance of the super-Gaussian beam's far-field focal plane intensity distributions,which has been added by the random phase screen, furthermore, the modulation influence of intermediate frequency phase error to the near-field light intensity distribution has also been simulated and proved, from which we can improve the fabrication technique and optimize the design method.

In this paper, a new focusing method adopting an axicon for the demand of the plasma measurements in inertial confinement fusion (ICF) drivers is presented. In order to improve the performance of this element, annular-aperture and Super-Guassian apodization are introduced to remove the on-axis oscillations. Meanwhile, the lateral width is optimized through choosing appropriate radius ratio of the inner ring to outer ring of the element. Furthermore, the feasibility is conformed by numerical evaluation of Fresnel diffraction integral .The results obtained are accordant with our designed intention. At last, as an example and for specific application, we designed an axicon, which has almost unchanged axial intensity, a focal depth more than 3mm, beam size smaller than 100μm and the maximal relative intensity of side lobe less than 2%. The performance of this element satisfies the requirements of plasma measurements in ICF drivers.

In the final optics assembly of ICF driver, Diffractive Optical Elements (DOEs) are applied to achieve some important functions. Due to the advantage of easy integration, DOEs that achieve different functions can be combined into one element, and thus the system structure and performance of ICF driver can be optimized. In this paper, we present a new means to fabricate color separation grating (CSG) and beam sampling grating (BSG) on two surfaces of one fused-silica substrate with two-surface exposure method. The mask for CSG can be fabricated with common optical method since the period of CSG is large; whereas the mask for BSG cannot be made with normal micro-fabrication system whose resolution cannot meet the requirement of fabrication precision of slowly changed BSG fringes (from 2μm to 4μm). Therefore, we use e-beam direct writing method to fabricate mask for BSG. The alignment of CSG and BSG is designed in accordance with the requirement of actual system. Thus the functions of harmonic wave separation and beam sampling are realized through one silica plate. The satisfying experimental results are illustrated.

Color Separating Grating (CSG) is one of the important Diffractive Optical Elements (DOE) used in the final optical system of high power laser system. Its periodic step-phase structure can separate the third harmonic frequency from base- and second-harmonic waves in the far field. But the structure abbreviations of CSG, caused by the fabrication process, generate great modulations to the laser beam, which may lead to severe optical damages to CSG itself and the system. In this paper, a comprehensive error model is built, in which each structural parameter of CSG is expressed as a variable, and the structural parameter error induced by fabrication process is expressed as minute disturb of relative variable. With this error model, the near field diffraction pattern of CSG is calculated based on Fresnel diffractive theory. Through simulation and analysis, we obtain the amplitude modulation of different harmonic waves in near field, and also the relationship between the amplitude modulation and the fabrication error. The results show that beam modulations are mainly caused by the stair depth error and the slope error. This study provides a convenient way to estimate the possibility of optical damages induced by CSG.