Precise Mirror Research Articles

Line–planes deflectometry

The key issue in phase measurement deflectometry is the solution of incident light which is used to determine the surface normal. To restore the 3D mirror surface information, line–planes deflectometry is proposed to determine the surface normal from the reflected light and the incident light planes containing incident light. To this end, a point light source is used to replace the continuous surface light source of traditional deflectometry. Accordingly, the incident light is calculated by the intersection of incident light planes which are determined by two or more projected lights of a point light source. Finally, the precise mirror surface is restored through the radial basis function interpolation from the gradient which is transformed from the normal information. To verify the proposed method, a line–planes deflectometry system is developed with two projectors and one camera. The system can be applied for two measurement modes concerning different measurement requirements: the ‘line–plane model’ and the ‘line–planes model’. The ‘line–plane model’ can be inferred with a measurement error of less than 0.25 mm to measure objects with low accuracy and non-connectivity. In contrast, the ‘line–planes model’ can be used to measure objects with high accuracy and good area connectivity, and the measurement error is about 1 µm.

Fabrication of a precise ellipsoidal mirror for soft X-ray nanofocusing.

In X-ray focusing, grazing incidence mirrors offer advantages of no chromatic aberration and high focusing efficiency. Although nanofocusing mirrors have been developed for the hard X-ray region, there is no mirror with nanofocusing performance in the soft X-ray region. Designing a system with the ability to focus to a beam size smaller than 100 nm at an X-ray energy of less than 1 keV requires a numerical aperture larger than 0.01. This leads to difficulties in the fabrication of a soft X-ray focusing mirror with high accuracy. Ellipsoidal mirrors enable soft X-ray focusing with a high numerical aperture. In this study, we report a production process for ellipsoidal mirrors involving mandrel fabrication and replication processes. The fabricated ellipsoidal mirror was assessed under partial illumination conditions at the soft X-ray beamline (BL25SU) of SPring-8. A focal spot size of less than 250 nm was confirmed at 300 eV. The focusing tests indicated that the proposed fabrication process is promising for X-ray mirrors that have the form of a solid of revolution, including Wolter mirrors.

Precise mirror alignment and basic performance of the RICH detector of the NA62 experiment at CERN

The Ring Imaging Cherenkov detector is crucial for the identification of charged particles in the NA62 experiment at the CERN SPS. The detector commissioning was completed in 2016 by the precise alignment of mirrors using reconstructed tracks. The alignment procedure and measurement of the basic performance are described. Ring radius resolution, ring centre resolution, single hit resolution and mean number of hits per ring are evaluated for positron tracks. The contribution of the residual mirror misalignment to the performance is calculated.

A Spectral Analysis of Feedback Regulation Near and Beyond Nyquist Frequency

A fundamental challenge in sampled-data control arises when a continuous-time plant is subject to disturbances that possess significant frequency components beyond the Nyquist frequency of the feedback sensor. Such intrinsic difficulties create formidable barriers for fast high-performance controls in modern and emerging technologies such as additive manufacturing and vision servo, where the update speed of sensors is low compared with the dynamics of the plant. This paper analyzes spectral properties of closed-loop signals under such scenarios, with a focus on mechatronic systems. We propose a spectral analysis method that provides new understanding of the time- and frequency-domain sampled-data performance. Along the course of uncovering spectral details in such beyond-Nyquist controls, we also report a fundamental understanding on the infeasibility of single-rate high-gain feedback to reject disturbances not only beyond but also below the Nyquist frequency. New metrics and tools are then proposed to systematically quantify the limit of performance. Validation and practical implications of the limitations are provided with experimental case studies performed on a precision mirror galvanometer platform for laser scanning.

Study on Surface Roughness of Modified Silicon Carbide Mirrors polished by Magnetorheological Finishing

In order to obtain high precision and high surface quality silicon carbide mirrors, the silicon carbide mirror substrate is subjected to surface modification treatment. In this paper, the problem of Silicon Carbide (SiC) mirror surface roughness deterioration by MRF is studied. The reasons of surface flaws of “Comet tail” are analyzed. Influence principle of MRF polishing depth and the surface roughness of modified SiC mirrors is obtained by experiments. On this basis, the united process of modified SiC mirrors is proposed which is combined MRF with the small grinding head CCOS. The united process makes improvement in the surface accuracy and surface roughness of modified SiC mirrors.

Two-Phase Lorentz Coils and Linear Halbach Array for Multiaxis Precision-Positioning Stages With Magnetic Levitation

In this paper, a new framework for linear permanent-magnet (PM) machines with applications in precision motion control is proposed and validated. A single forcer generating two independent force components in two perpendicular directions is the fundamental unit of the framework. Each forcer consists of two planar Lorentz coils separated by a 90° or 270° phase difference and parallel to a Halbach magnet array. Many coil pairs can be assembled to the same platen to move over a common magnet matrix, forming a linear or planar PM motor. Advantages of this framework include a linear system model, the capability to magnetically levitate the mover in multiaxis stages, and that to generate long translational motion range. The framework developed herein is validated by a six-degree-of-freedom magnetically levitated (maglev) stage. The dimension of the moving platen's frame is $\text{14.3}{\,\text{cm}}\times \text{14.3}{\,\text{cm}}$ , and its total mass is 0.75 kg. The achieved positioning resolution in translations along $X,Y$ , and $Z$ is 10 nm. The positioning resolution in out-of-plane rotation is $\text{0.1}\,\mu {\text{rad}}$ , which is a record in the literature. The maximum travel range in $XY$ with laser interferometers is ${\text{56}\,\text{mm}}\times \text{35}\,{\text{mm}}$ , limited by the size of the precision mirrors. With the coils’ total mass of only 0.205 kg, the achieved acceleration is 1.2 m/s2. Experimental results exhibit reduced perturbations in other axes of in-plane motions.

Conception and design of a control and monitoring system for the mirror alignment of the CBM RICH detector

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-proton and Ion Research (FAIR) will investigate the phase diagram of strongly interacting matter at high net-baryon density and moderate temperature in A+A collisions. One of the key detectors of CBM to explore this physics program is a Ring Imaging CHerenkov (RICH) detector for electron identification. For a high performance of the RICH detector precise mirror alignment is essential. A three-step correction cycle has been developed, which will be discussed: First a qualitative, fast check of the mirror positions, second a quantitative determination of possible misalignments and third a software correction routine, allowing a proper functioning of the RICH under misalignment conditions.

Development of precision mirrors for X-ray nanofocusing and nanoimaging

Development of precision mirrors for X-ray nanofocusing and nanoimaging

Image quality method as a possible way of in situ monitoring of in-vessel mirrors in a fusion reactor.

The plasma-facing (first) mirrors in ITER will be subject to sputtering and/or contamination with rates that will depend on the precise mirror locations. The resulting influence of both these factors can reduce the mirror reflectance (R) and worsen the transmitted image quality (IQ). This implies that monitoring the mirror quality in situ is an actual desire, and the present work is an attempt towards a solution. The method we propose is able to elucidate the reason for degradation of the mirror reflectance: sputtering by charge exchange atoms or deposition of contaminated layers. In case of deposition of contaminants, the mirror can be cleaned in situ, but a rough mirror (due to sputtering) cannot be used anymore and has to be replaced. To demonstrate the feasibility of the IQ method, it was applied to mirror specimens coated with carbon film in laboratory conditions and to mirrors coated with contaminants during exposure in fusion devices (TRIAM-1M and Tore Supra), as well as to mirrors of different materials exposed to sputtering by plasma ions in the DSM-2 plasma stand (in IPP NSC KIPT).

Research on Formation Mechanism of Grinding Wheel Oxide Film in ELID Ultra Precision Mirror Grinding

The characteristics, structural characteristics and composition of the grinding wheel oxide film is revealed by the theoretical analysis and simulating test in pre-dressing process of the ELID ultra precision mirror grinding, and the validity of oxide film formation mechanism analysis is verified by ELID experiments. Mirror grinding of hard brittle materials can be realized by on-line real-time control of the thickness of the oxide film.

Development of high-order harmonic focusing system based on ellipsoidal mirror.

We have developed a focusing system for extreme ultraviolet light produced by high-order harmonic generation. An ellipsoidal mirror with a precise surface shape was fabricated and installed into the focusing system. A rigid mirror manipulator and a beam profiler were employed to perform precise and stable mirror alignment. As a demonstration of the focusing performance, high-order harmonics in the wavelength range of 13.5-19.5 nm were successfully focused into a 2.4 × 2.3 μm(2) spot.

Extremely unbalanced interferometer for precise wavefront control in stellar coronagraphy

We propose to use an extremely unbalanced interferometer (EUI) as a wavefront correcting input to a stellar coronagraph for direct exoplanet observation. Since wavefront error causes incomplete suppression of stellar light, an EUI aims to precisely correct the wavefront incident on the coronagraph to a level better than λ/5000 in the visible wavelength range. Compared to the previous unbalanced interferometer, which incorporated a nulling function, the proposed EUI does not introduce the nulling function. EUI does not use a precise deformable mirror. It increases the accuracy of a wavefront control effectively because of the coherent summation with an amplitude imbalance. It enables obtaining the desirable 10−9 coronagraphic contrast for Earth-like exoplanet imaging.

Precise measurement of branching ratios in theβdecay ofCa38

We present the full description of a measurement of the branching ratios for the $\ensuremath{\beta}$ decay of $^{38}\mathrm{Ca}$. This decay includes five allowed ${0}^{+}\ensuremath{\rightarrow}{1}^{+}$ branches and a superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ one. With our new result for the latter, we determine its $ft$ value to be $3062.3\ifmmode\pm\else\textpm\fi{}6.8$ s, a result whose precision (0.2%) is comparable to the precision of the 13 well-known ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ transitions used up until now for the determination of ${V}_{\text{ud}}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix. The $^{38}\mathrm{Ca}$ superallowed transition thus becomes the first addition to this set of transitions in nearly a decade and the first for which a precise mirror comparison is possible, thus enabling an improved test of the isospin-symmetry-breaking corrections required for the extraction of ${V}_{\text{ud}}$.

Research on Cylindrical Precision Machining Adopting ELID Grinding Technology

In order to explore the new way to precision machining of the cylindrical, ELID precision mirror grinding technology are employed to precision ultra-precision grinding experiments. Given ELID precision mirror grinding technology has effectively solved the basis of many of the typical flat-precision machining difficult materials and efficient processing, through the conversion process equipment tools, and optimization of process parameters, obtained when the wheel speed in 16 ~ 20 m / s, when the grinding depth 10μm, cylindrical grinding state is best, which could obtain Ra0.025μm surface roughness of the machined surface.

The Absolute Measurement Deviation of Rotational Averaging Mirror Surface Based on the Finite Element Method

In order to obtain higher levels of surface form accuracy, it adopted rotational averaging method, analyzed the supporting position and rotation-angle deviation of the model via the finite element analysis technology. You can see that the mirror surface Peak Valley Value and Root Mean Square Value, increase with the increase of supporting and angle deviation. Thus, to realize high precision mirror surface detection, it should guarantee the supporting position and rotation-angle deviation of the model at the same time. The measurement precision of rotational averaging method absolute measurement can achieve one percent wavelength (λ=632.8nm),it is far superior to the other detection technology in absolute measurement.

Nano-accuracy measurements and the surface profiler by use of Monolithic Hollow Penta-Prism for precision mirror testing

We developed a Monolithic Hollow Penta-Prism Long Trace Profiler-NOM (MHPP-LTP-NOM) to attain nano-accuracy in testing plane- and near-plane-mirrors. A new developed Monolithic Hollow Penta-Prism (MHPP) combined with the advantages of PPLTP and autocollimator ELCOMAT of the Nano-Optic-Measuring Machine (NOM) is used to enhance the accuracy and stability of our measurements.Our precise system-alignment method by using a newly developed CCD position-monitor system (PMS) assured significant thermal stability and, along with our optimized noise-reduction analytic method, ensured nano-accuracy measurements. Herein we report our tests results; all errors are about 60nradrms or less in tests of plane- and near-plane- mirrors.

Far-Infrared Interferometric Telescope Experiment: Optical Adjustment System

We developed a balloon-borne, astronomical far-infrared interferometer telescope experiment (FITE), which is a Fizeau-type two-beam interferometer consisting of two off-axis parabolic mirrors. Therefore, it is important to establish a method by which the two beams can be simultaneously adjusted. A conventional Hartmann test was originally employed; however, it has two disadvantages in that we cannot simultaneously measure two beams, and it is time-consuming. We developed a new optical adjustment system that can simultaneously measure and evaluate two beams using a Shack-Hartmann wavefront sensor. In the first stage, the field-of-view (FOV) of a wavefront sensor is adapted to a full beam size of 40 cm (the beam diameter), and the mirror surface accuracy and mirror alignment are measured and adjusted for one beam. After the adjustment of both beams, both focuses coincide at the input aperture hole of the far-infrared sensor system by expanding the FOV of the wavefront sensor so that it includes both beams. Using this new method, we can realize the real-time measurement and analysis of converging beams, and can also achieve fast switching between the single- and double-beam modes. We demonstrated this new adjustment method by performing laboratory measurements; we have also designed a new optical adjustment system for FITE. To manufacture this system, we required a large and precise spherical mirror as the reference mirror with R = 300 mm and D = 300 mm to simultaneously calibrate the two beams using the wavefront sensor. We also manufactured an F/1 lens for the collimation of the two beams, a Keplarian beam expander and a beam-switching system. We will soon assemble this optical adjustment system and apply it to the optical adjustment of the FITE interferometer system.

Main approaches to formation of a thermal vacuum test program of precision mirror reflectors of space antennas

Main approaches to formation of a thermal vacuum test program of precision mirror reflectors of space antennas

A Study on the Analysis of Influential Factors for 300mm Wafer Final Polishing

In recent years, developments in the semiconductor and electronic industries have brought a rapid increase in the use of large size silicon. However, for many companies, it is hard to produce 400mm or 450mm wafers, because of excesive funds for exchange the equipments. Therefore, it is necessary to investigate 300mm wafer to obtain a better efficiency and a good property rate. Wafer final Polishing is one of the important methods in manufacturing of Si wafers and in thinning of completed device wafers. This research investigated the surface characteristics and optimum condition of applied pressure, polishing speed and slurry-mixed ratio to achieve the optimum condition of wafer final polishing by Taguchi method. By using optimum condition, it helps to achive an ultra precision mirror like surface.

Performance of an upgraded long trace profiler at NSRRC

Upgrading the long trace profiler at NSRRC has enabled measurements on mirrors in the beamlines with increased precision. The following working items are included: a 2D CCD detector and its upgraded software, improved straightness of the sliding stage of air bearings, calibration of the system linearity, control of air turbulence in the optical path and some upgraded optics. The factors influencing the stability and accuracy were studied and improved with engineering schemes. Measurements of highly precise flat mirrors and strongly curved mirrors were performed and are discussed.