Mirror Material Research Articles

Some problems of the material choice for the first mirrors of plasma diagnostics in a fusion reactor

We present the results of simulation experiments on the effect of the fusion reactor environment on the optical properties of the first mirrors for spectroscopy and laser diagnostics. We found the greatest effect on the degradation of mirror optical properties was due to charge exchange atoms. These atoms can affect mirror quality in two ways: by sputtering and by redeposition of material sputtered from other inner components of the vacuum chamber. The degradation rates of mirrors made of different metals and subjected to long-term bombardment by ions from hydrogen or deuterium plasmas are compared. From analysis of all data, we concluded that special experiments will have to be conducted in order to make a correct choice of a first mirror material. These tests should include the following: (1) study the role of swelling on mirror surface modification; (2) find the multimillion shot laser-induced-damage threshold of metal mirrors; and (3) develop and test methods to protect the first mirrors from redeposition. In addition, a model should be developed for the charge exchange atom flux and energy distribution that represents real data from operating tokamaks.

On the choice of materials for the first mirrors of plasma diagnostics in a fusion reactor

The reflectivity coefficient, R, of mirrors fabricated from different metals (Al, Cu, Mo, Ta, W) in the wavelength range 0.25–0.65 μm was investigated under long-term sputtering with ions of ECR plasma of hydrogen or deuterium, and R values versus thickness of sputtered layer were measured. For copper mirrors the influence of ion energy and ion energy spectrum on optical reflectivity was investigated in detail. Because a strong effect was found, the comparative test of mirrors made of different metals was carried out using ions with a wide energy distribution (0.1–1.5 keV) to have a more adequate simulation of fusion reactor environment conditions. The results obtained show that, with the exception of Al, the decrease of reflectivity coefficient with thickness of sputtered layer has approximately similar rate for metal tested. Thus, mirrors made of materials having lower sputtering coefficient, Y, will withstand a higher charge exchange atom fluence, in qualitative agreement with R/ Y criterion suggested by the authors earlier.

Evaluation of structural reliability of mems device in digital video disk systems

In this paper, we describe the reliability evaluation for MEMS devices, especially designed tbr DVD(Digital Video Disk) application. These MEMS devices are fabricated as a mirror plane (shutter plane) used in DVD data picking up. This micromachined annular shutter mirror (ASM) acts as an adjusting means of the numerical aperture. The electrostatic force can drive the upper plane up and down for focusing or defocusing of incident laser beam to the selected recording plane. So we need to evaluate the micromechanical properties of thin film structural materials to ensure the reliability of those MEMS devices. For those, we perfl)rm the fatigue tests onto the devices in the conditions of much accelerated than those of normal driving. The applied electrostatic force can induce the change of the thin film properties, and those are observed by direct and indirect methods (XRD and electrical system). And then, we compare the fatigue effects with electrical, optical data from the intentionally-fatigue-applied specimen and as-fabricated one under accelerated conditions. Consequently, we can estimate the structural reliability and will provide the effective suggestion data for the fabrication of stable mirror material before commercialization.

Optical constants of in situ-deposited films of important extreme-ultraviolet multilayer mirror materials

We have performed angle-dependent reflectance measurements of in situ magnetron sputtered films of B(4)C, C, Mo, Si, and W. The Fresnel relations were used to determine the complex index of refraction from the reflectance data in the region of approximately 35-150 eV. In the cases of Si, C, and B(4)C we found excellent agreement with published data. However, for Mo and W we found that the optical properties from 35 to 60 eV differed significantly from those in the literature.

Handbook of glass in construction

This handbook covers uses, specifying, manufacture, and testing of sealed insulating glass units and windows. It includes all types of glass and insulation glass, including single and dual sealed systems, heat mirror materials, sealant compounds, swiggle strip and metal edge compounds.

Performance of high-density cast silicon carbide in the extreme ultraviolet

The normal-incidence reflectance of high-density cast silicon carbide (SiC) is evaluated in the extreme ultraviolet (EUV) spectral region. High reflectivity in the EUV is achieved. High reflectivity and the relatively low-cost manufacturing process make high-density cast SiC a promising mirror material for EUV applications.

On the influence of fusion reactor conditions on optical properties of metallic plasma-viewing mirrors

This paper presents the results of imitation experiments concerning the effects of fusion reactor conditions on the properties of mirrors Made of stainless steel, copper and beryllium. The neutron irradiation was imitated using MeV energy range ions. To imitate the effects of charge exchange atoms (CXA) bombardment, keV energy range D + and He + ions were used. From the data obtained it was concluded that not only the reflectivity but also the resistance to CXA sputtering have to be taken into account when choosing the materials for the first mirrors of a fusion reactor.

Application of interferometry and Faraday rotation techniques for density measurements on the next generation of tokamaks

The next generation of tokamaks present unique challenges to plasma diagnostic design due to the physical size of the devices and the radiation environment. The need for a density measurement for density feedback control for a prototype reactor such as ITER is well established and several proposals for line average measurements have been put forward. In this article, a design for a line average density diagnostic for ITER using collinear interferometry and Faraday rotation measurements will be presented. Plasma effects on both types of measurements and density resolution will be discussed along with the possibility of combining the information from the two collinear measurements to improve the reliability and quality of the density profile. Survivability of the plasma facing mirrors, in particular the surface flatness and surface roughness, are critical issues and preliminary analysis suggests these may limit the wavelength of probing beams. Thermal and stress analysis of the plasma facing mirrors will be presented along with a discussion of mirror material selection based on thermal, nuclear, and sputtering considerations.

Photon-Stimulated Ion Desorption Measurement of Organosilicon Resist Reactions in Extreme Ultraviolet Lithography

In extreme ultraviolet (EUV) lithography, a surface-imaging process using an organosilicon resist is essential. Since the binding energies of Si core-level electrons coincide with the photon energy of the light source of EUV-lithography, we have analyzed the effect of their excitation on the decomposition of an organosilicon resist. We have also investigated a design policy for optical systems in terms of selecting the multilayer mirror materials to use organosilicon resists in EUV lithography. A photon-stimulated ion desorption (PSID) analysis of poly(cyclohexylmethylsilane) (PCHMS) that was exposed to monochromatic synchrotron radiation was carried out. We found that decomposition of the Si–Si backbone of PCHMS is enhanced by EUV exposure to wavelengths that excite the Si 2p and 2s electrons. In addition, the yield of CH3+ desorbed from the side-chain methyl of PCHMS is increased at a photon energy of 108 eV (a 11.5-nm wavelength), which presumably excites Si 2p electrons into the Si–C σ* state. Calculated reflectivities of a multilayer mirror suggest that the reflectivity of a multilayer mirror which does not contain Si, such as Mo/Be, realizes excellent reflectivity at the wavelength that excites the Si 2p electron.

Optimized axial support topologies for thin telescope mirrors

Thin and highly flexible telescope mirrors need to be supported carefully to avoid undesirable elastic deformations and a reduction of their optical quality. In this study, a wide variety of support topologies are examined to provide a basic set of optimized point supports for these telescope mirrors. This is carried out for mirrors without a central hole, with circular and annular entrance pupils. Efficient topologies introducing a small amount of zenith-angle-dependent defocusing are also proposed. The number of supporting points ranges between 3 and 36. Optimal forces and locations of point supports are calculated using thin-plate bending theory. Numerical methods include a linear least-squares method for determining the best forces, and a downhill simplex algorithm to optimize the support locations. The robustness of the proposed solutions is tested by simulated annealing. Scaling laws are briefly reviewed, and support efficiencies are given for each optimized topology. Results show that taking into account the central obscuration ratio (annular pupil) and tolerating a homologous (paraboloidal) deformation of the mirror allows an improvement of efficiency of up to 50% over the case of an unobscured pupil where defocus is not permitted. This work includes a study of support efficiencies versus the Poisson's ratio of the mirror material. Wavefront errors are also estimated in the case of a defective cell, to specify tolerances on forces and support locations.

Spherical-grating monochromator system with circular-polarization capability for the U5U undulator at Brookhaven

We plan to upgrade the U5U undulator beamline at Brookhaven with a 4-grating 3.5 m SGM (spherical-grating-monochromator) system offering the following enhancements in performance: (1) Improved imaging especially at the sample; (2) Small “expendable” gratings; and (3) Circular polarizer of the 4-reflection type. Ray tracing calculations are offered with emphasis on spot-size quality at the sample, and on the relative merits of scanning the exit- or entrance-slit to maintain focus. The excursion of the entrance slit coincides with the length of the undulator image. Calculations of the figure of merit TP 2 ( T = transmission, P = polarization) are presented for a 4-reflection circular polarizer using the candidate mirror materials Al, Ag, Au and Rh. Ag offers the widest range of coverage, hω = 10–150 eV, with reasonable throughput, TP 2 = 4–18%.

Normal-incidence reflectance of crystalline K_6C_60, Rb_6C_60, and Cs_6C_60

The structure factors and normal-incidence reflectances of the alkali-metal-doped fulleride crystals M(6)C(60) (where M = K, Rb, or Cs) were calculated, and the peak reflectances are in the 2-20% range for incident wavelengths of 9-17 Å, which indicates that C(60) may be a promising transmissive (spacer) material for normal-incidence mirrors that have relatively high normal-incidence reflectance in the x-ray region.

Epitaxial growth of W/Mo material by laser beam

High electrical conductivity metals are used in mirror materials for manipulating high-power CO2 laser beams. Although the reflectance of Mo and W is slightly lower than that of Cu, A1 and Ag due to their lower electrical conductivities, their melting points are much higher (2640 °C for Mo and 3410 °C for W), their thermal expansion coefficients are less than one-third of those of Cu, A1 and Ag, and they are very hard. Since the shape change due to temperature increase and deformation due to external stress are very small in Mo and W, they are widely used in mirror materials for high-power CO2 laser beams in manufacturing plants. However, their melting points are so high that they are fabricated in powder compaction at high temperature in vacuum, by vacuum arc melting or electron beam melting. W, especially, has the lowest thermal expansion coefficient and the highest melting point of all metals and its electrical conductivity and oxidation resistance are better than those of Mo. Therefore, W is preferred to Mo in mirror materials. In order that all light is reflected at the specular angle, a mirror should possess no surface irregularities of a size comparable with the wavelength. If the heights of the surface irregularities are of the order of a wavelength or more, the reflectance is mostly diffuse and depends strongly on the shape of the irregularities. However, if they are very small relative to the wavelength, most of the light is reflected specularly, the amount depending on the height of the irregularities. For a random height distribution of surface irregularities, the specular reflectance at normal incidence R~ is given by [1]

Chemical Vapor Deposited β-SiC for Optics Applications

AbstractThe fabrication, properties and optics applications of transparent and opaque Chemical Vapor Deposited (CVD) β-SiC are reviewed. CVD-SiC is fabricated by the pyrolysis of methyltrichlorosilane, in excess H2, in a low-pressure CVD reactor. The CVD process has been successfully scaled to produce monolithic SiC parts of diameter up to 1.5 m and thickness 2.5 cm. The characterization of CVD-SiC for important physical, optical, mechanical and thermal properties indicate that it is a superior material for optics applications. CVD-SiC properties are compared with those of the other candidate mirror and window materials. SiC process/property relationships are discussed, emphasizing the differences in process conditions, microstructure, and properties between transparent and opaque CVD-SiC.

Multilayer mirrors and filters for imaging the earth's inner magnetosphere

We present guidelines for the performance of multilayer mirrors and filters for imaging the earth's inner magnetosphere by isolating the 304-Å He⁺ emission. Our analysis shows that the combination of filters and multilayer mirrors for an inner magnetosphere imager must attenuate the 1216-Å Lyman α emission by six orders of magnitude and the 584-, 834-, and 1026-Å background emissions by three orders of magnitude relative to the 304-Å signal. Multilayer mirrors with the highest possible reflectance at 304 Å are needed to preserve as much of the low-intensity 304-Å signal as possible. The design of multilayer mirrors is discussed, and the results of an exhaustive computer search for the best multilayer mirror design for 304-Å radiation are presented and analyzed. The theoretical performance of these new multilayer mirror designs is significantly better than that of designs currently used for imaging the solar 304-Å emission. Promising materials for normal-incidence multilayer mirrors for 304-Å radiation are B₄C, Be, Si, or SiC used with Al, Mg, or Mg2Si. Promising materials for a filter for this application are Te passivated with Si, or a combination of Al or Si with B or C.

Diamond Turning of Oxygen-Free Copper for Mirrors

This paper deals with machining tests, regarding oxygen-free copper (OFC) as one of the materials suitable for diamond turning. The machining tests were carried out to study the optimal cutting conditions for OFC, the selection of a suitable high-purity OFC material for mirrors and the mirror-finishing properties of the suitable OFC material over long cutting distances. The test results show the following. ( 1 ) The optimal cutting conditions are 9-17μm/rev for the feed rate and 15-20μm for the depth of cut. ( 2 ) The raw material produced by the processes of hot rolling, cold rolling and heat treatment is the most suitable with respect to the surface integrity. ( 3 ) The surface roughness is stable in the cutting distance range of 500 km. As for tool wear, crater wear, in particular, is remarkably large, while flank wear is negligible.

Thermal effects and mirror surface figure requirements for a diagnostic beamline at the advanced light source

Abstract An imaging beamline based on a Kirkpatrick-Baez mirror configuration has been designed to image the electron beam in the ALS storage ring, to measure its size and shape. The electron beam emittance will be small ( ϵ h = 3.4×10 −9 m rad) and the quality of the image is extremely sensitive to surface figure distortion of the mirrors. Thermal distortions and surface temperatures have been calculated for radiatively cooled mirrors of various materials in a search for a simple design which avoids water cooling. The choice of mirror material and the thermal and mechanical design is discussed.

Synchrotron radiation mirrors for high intensity beam lines

Most of the recently established synchrotron beam lines need optical components which are able to withstand high total heat loads. High beam power densities have to be tolerated without decreasing the optical quality. New mirror materials such as SiC and Si have been introduced into the optics manufacturer’s workshop, being in principle ideal for high quality optical surfaces. On the other hand, they are causing new problems resulting mainly from inherent material properties. Several possibilities of manufacturing mirrors for high intensity beam lines are discussed in this paper and related problems and possible solutions shown. Special remark is made on mirrors manufactured from a graphite core with chemical vapor deposition-SiC coating.

Mirrors for optical telescopes

From the viewpoint of up-to-date requirements, fundamental scientific and technological problems arising in the design and manufacture of optical reflecting telescopes are formulated as compared to those of the refracting systems. Nontraditional materials, such as beryllium, silicon, and silicon carbide, are shown to be capable of successful competition with traditional optical materials for the telescope mirror. A brief overview is given of the development of beryllium-based mirrors.

Elliptical-polarization measurements in the vacuum ultraviolet and soft x-ray regions with a reflection polarimeter

A complete polarization analysis has been successfully achieved for synchrotron radiation beams in the vacuum ultraviolet and soft x-ray regions using a reflection polarimeter. The Stokes parameters, which provide a full description of the polarization state of light, were experimentally determined along with three polarizing quantities of the polarimeter. The present result indicates the possibility of a simultaneous determination of the optical constants of mirror materials through polarization analyses.