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To restrain surface deliquescence which directly influences surface quality and machining efficiency of polishing KDP crystal, this paper presents a novel water-dissolution magneto-rheological finishing process by controlling fluid-crystal temperature difference. Deliquescence mechanism is revealed from the perspective of deliquescence circle. Micro-condensation is proved as the main cause of deliquescence, which is restrained by fluid-crystal synergistic heating. Case test on KDP crystal verified that the humidity threshold of anti-deliquescence rises from 40% to 80%, which has realized synchronous improvements of machining efficiency as well as surface roughness and laser induced threshold on KDP crystal during the process of water-dissolution magneto-rheological finishing. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive model for the motorized spindles in machine tools. The proposed model consists of a thermo-mechanical dynamic model and a milling stability model. The thermo-mechanical dynamic model is establishedbased on finite element method with the consideration of the transfer function at cutting point, which is coupled with the milling stability model. The influences of thermo-mechanical coupled factors (TMCF) on the transfer function at the cutting point and the milling stability of the system are discussed and validated, and the influences of the parameters of the material properties and machining process on the milling stability are acquired. The theoretical and experimental results are useful to the dynamic analysis and design for motorized spindle machine tools. [ABSTRACT FROM AUTHOR]

Traditional measurement methods of squareness for ultra-precision motion stage have many limitations, especially the errors caused by the inaccuracy of standard specimens. On the basis of error separation, this paper presents a novel method to measure squareness with an optical square brick. The angles between the guideways and the four lines of brick section are measured based on the fact that sum of interior angle of a quadrilateral is 2π, and the squareness is obtained. A squareness measurement experiment was performed on a profilometer with a modified optical square brick. Experimental results show that the squareness accuracy between X and Y axes is not influenced by the accuracy of brick, and the measurement repeatability reaches 0.22 arcsec. Finally, a verification experiment to the proposed method was carried out with a high accurate standard specimen, and the error between the two methods is 1.06 arcsec. According to the error results and simulation analysis of the measurement system, the measurement error based on error separation is 0.06 arcsec. The proposed method is able to achieve a very high accurate squareness measurement with auxiliary components of normal accuracy, and can be applied to measure the accuracy class of sub-arcsec squareness. [ABSTRACT FROM AUTHOR]

• The phenomena of laser energy deposition and light-field enhancement caused by ripple structures was cleared through FEM simulation. • A combined technique of low–stress CCOS and IBF was used to polishing ripple–structure optical surface, and its suitability was verified for fused silica laser optics. • The changes of anti-laser damage characteristics at different processing stage were studied. The correlation between processing parameters, photo-thermal absorption, laser induced damage threshold was cleared. In AMRF (arrayed magnetorheological finishing) process of fused silica laser optics, ripple structures would generate on the optical surface. The ripple structures could cause nonlinear self-focusing and localized energy deposition, finally induced laser damage. In this work, the removal of ripple structures and the improvement of anti-laser damage characteristics were studied. First, the heat deposition and light-field enhancement induced by ripple structures were analyzed by finite element simulation method, and the negative impact of ripple structures was clarified. Then, the ripple-structure surface was polished by a combined technique of low-stress CCOS (computer control optical surfacing) and ion beam finishing (IBF). After the combined polishing process, the ripple structures and the hydrolyzed layer on the surface were removed, the photo-thermal absorption decreased from 0.736 ppm to 0.124 ppm, and the laser induced damage threshold (LIDT) increased from 6.3 J/cm2 to 7.4 J/cm2. In this work, the combined technique was able to remove the ripple structures while maintaining the processing efficiency, and it also could improve the anti-laser damage characteristics of the optics. The relative research results had important reference value for ultra-precision manufacturing of large-aperture laser optics. [ABSTRACT FROM AUTHOR]

Single-crystal silicon is an important material in the high precision reflector, and its processing quality directly affects the overall performance index of the reflector. Aiming at the problem of "comet tail" defect produced by the magnetorheological machining process, the process parameters are controlled by the combination of experiments and simulations, and the surface roughness changes after different scanning speeds under the same removal depth are compared and analyzed. The results show that under the same process parameters, the probability of "comet tail" defects are related to density and surface quality. The main factors affecting the occurrence probability and density of "comet tail" defects are process parameters. In actual processing, it is necessary to establish a threshold of process parameters, so that the "Comet tail" defect is less within the threshold and can be quickly removed. The final threshold range is: buffing wheel speed< 220rpm, flow rate< 80L/min, depth coefficient< 0.25, magnetic field strength< 7A. By discussing the "Comet tail" defect suppression method and key technology, it provides technical support for the realization of high precision control manufacturing of single-crystal silicon. [ABSTRACT FROM AUTHOR]

• A PSD (Power Spectral Density) analysis method based on the contour of removal function was proposed for AMRF technique. • A new polishing path called "non-equal-interval parallel raster path" customized for AMRF technique was proposed and applied to control mid-spatial-frequency ripple error. • Simulation and actual experiment verified the effects of analysis method and polishing path. With the continuous development of high-power laser systems, laser optics gradually changed towards large-aperture, high-quality. To adapt to the fabrication of large-aperture laser optics, a new-type array magnetorheological finishing (AMRF) technique was developed and had made initial progress. However, AMRF technique would introduce more obvious ripple structures (such as 1 mm−1 of spatial frequency) compared to original MRF technique while adopting conventional raster path, and the ripple structures might affect laser beam transmission. For the further application of AMRF technique, the formation mechanism of ripple structures was studied, and a method based on the contour of removal function was proposed to analyze the changes of spatial frequency and evaluate the effect of different polishing paths. According to the analysis method, non-equal-interval parallel raster path was chosen and applied into AMRF process, along with maintaining efficiency while controlling ripple structures. In general, this work could provide a valuable support for the AMRF process of large-aperture laser optics and had a certain significance for the high-power laser system. [ABSTRACT FROM AUTHOR]

• Infrared optical properties optimization of various Si lattice structures are investigated. • Close-to-atomic method(IBF and CMP) is imported to regulate various lattice layers on Si surface. • Removal of amorphous layer above the low-density layer improve the reflectivity notable. • Low-density(about 1 nm) layer and transition layer(about 1 nm) are conducive for optimize the infrared optical properties(reflectivity and photo-thermal absorption). A fundamental challenge in optimizing the infrared optical properties of monocrystalline Si(1 0 0) reflectors is achieving high infrared reflection and low photo-thermal absorption. These requirements have been traditionally satisfied by removing various surface defects to obtain a perfect lattice structure. To supersede the traditional logic of "non-defect surfaces," a surface lattice structure scheme, "Si lattice layer regulation," is proposed. This paper presents a close-to-atomic-scale method for regulating multilayer Si lattices. First, a "multilayer lattice" (disordered, low-density, and transition layers) is introduced by ion beam figuring as a regulation base. Subsequently, the infrared optical properties are improved by reducing the disordered layer above the low-density layer using chemical–mechanical polishing. An experimental comparison proves that the scheme is effective: the reflectivity of the new surface developed in this study increases by 10 % (from 900 to 1500 nm (testing band)), and the photo-thermal absorption of the surface is controlled at 0.116 ppm. Therefore, the optical properties of monocrystalline Si can be optimized by regulating the thickness of the Si atomic layers with different densities. A lattice layer based on the field of materials science (e.g., material band gap and electronic property regulation) is introduced to an optical field with high infrared optical properties on Si surfaces. This allows the optical processing to enter an emerging "close-to-atomic-scale" manufacturing dimension. This work also opens up advanced prospects in the fields of high-energy optics and X-rays and directs research on atomic structure regulation toward a completely new area of optics. [ABSTRACT FROM AUTHOR]

Highlights • We present a novel flatness test which only using two flats. • Multi-shift and rotation steps are needed. • A pixel level spatial resolution can be achieved. • Analysis to tilt error and rotation error is presented. • Simulations and experimental absolute results are given. Abstract In classical three-flat test, error in reference surface can not be identified fully. What we obtain is only the absolute radial profile instead. In addition, at least three flats with similarly high accuracy are required. The test procedures are very complex and it takes a long time and requires high precision adjustment. In this paper, we proposed a new method for absolute test of flatness. There are only two flats used in our method and it does not need precise alignment of the specimens. The method requires multiple translations of the test surface and one 90° rotation step. The relative tilt during translation is measured by a compact wavefront interferometer. We analyze the effect of noise, tilt estimation error and rotation error on reconstruction result. The method is experimentally verified and compared with the direct interferometric result using high precision reference surface. [ABSTRACT FROM AUTHOR]

As the thickness of the adhesive layer between the mirror and the actuator decreases and the performance requirements of the unimorph deformable mirror (DM) increase, stricter control on the adhesive layer thickness and Young’s modulus is necessary. In this paper, a finite element model (FEM) for the unimorph DM with an adhesive layer is obtained. Based on the model, the influence of adhesive layer thickness and Young’s modulus on the deformation is studied. Also their influence on the adhesive’s maximum shear stress is analyzed. In the meantime, the design principles of the adhesive layer thickness and Young’s modulus are established with the restrictions of shear failure and the maximum displacement. As a result, different adhesive Young’s modulus has corresponding requirements for the upper and lower thicknesses (<20 μm) to obtain 85% maximum displacement. Then, DMs with four different mirror thicknesses are fabricated for verification experiments. The experiments results can be matched with the simulation results. Finally, the thickness in the spin coating process of adhesive layer is explored. The adhesive layer thickness can be controlled within 12.1 μm, and the deviation of uniformity is better than ±2%. [ABSTRACT FROM AUTHOR]

• The development of new-type arrayed MRF equipment was conducted through theoretical analysis, simulation and experiment. • High removal efficiency of 2.03 × 107 μm3/min and stability better than 5 % were achieved. • Actual experiment verified the effects of arrayed MRF equipment. Along with the continuous development of optical systems, the fabrication of optics gradually moved towards large aperture and high quality. To meet the requirements of optical systems, advanced technologies represented by magnetorheological finishing (MRF) were applied in the processing of optics. According to the background of high-efficiency processing, this work focused on the design of arrayed magnetorheological equipment, including magnetic field theoretical analysis, magnetic field simulation, equipment construction, removal function preparation and stability test. Through the study, arrayed MR (magnetorheological) equipment was preliminarily built and the removal function was prepared. The volume removal rate of arrayed removal function was 2.03 μm3/min after detection, which was 1.35 times of electromagnetic equipment under the same process parameters, and the stability of the removal function was better than 5 %. The results of two-dimensional removal experiment also verified that arrayed MR equipment could significantly improve materials removal efficiency. Based on the experimental results in this work, it is believed that arrayed MR equipment have certain advantages in the improvement of processing efficiency and surface quality, and it could meet the requirement of optical processing at the present stage. The relevant design theories and methods could provide reference to the follow-up research. [ABSTRACT FROM AUTHOR]

• Measurement of large area micro topography with subaperture stitching. • Detection of edge features with slope threshold and projection on OXY plane. • Fast correction of 2D lateral coordinates by solving a linear least-squares. • Correction of height coordinates by solving a linear least-squares problem. • No need for high precision scanning stages with "sliding" eliminated by stitching. Microstructured surfaces over large areas are typical in diffractive optics and biomimetic surfaces. The topography measurement is challenging due to the multi-scale nature. In this paper, an efficient stitching method is proposed for fusion of multiple subapertures to produce a large area topography. The first step is detecting edge features and then projecting them on the OXY plane. The next step is correction of lateral coordinates by registering the edge curves in overlapping regions. The change of lateral coordinates is linearly related to the lateral shifts and clocking angle which are estimated by simply solving a linear least-squares problem. In the final step, height change is also linearly related to the piston and tip-tilt of subapertures. Hence it is corrected by minimizing the height difference in overlapping regions, which is again modeled as a linear least-squares problem. The stitching method is experimentally verified on a holographic sample. Totally seven by seven subapertures are measured with an interference microscope and seamlessly stitched together. [ABSTRACT FROM AUTHOR]