Mirror Material Research Articles

Effect of background gases at reduced pressures on the laser treated surface morphology, spectral emission and characteristics parameters of laser produced Mo plasmas

Molybdenum owing to its high melting point and high reflectivity over a broad range of wavelengths has been used as first mirrors in EAST and HL-2A tokomaks and is also a candidate material for ITER mirrors. The effect of atmospheric conditions of Ar, N2 and He at reduced pressure (2.0×10−4 to 5mbar) on the physical processes of the atomic and background emission, mass ablation, electron density and temperature of a laser produced Mo plasma has been investigated in order to adapt Laser Induced Breakdown Spectroscopy (LIBS) for in situ diagnostic and cleaning of the first mirrors. The obtained results strongly indicate that pressure and physical properties of the background gases play a crucial role to interpret the emission (line and continuum background) and characteristic parameters (electron density and temperature) of the plasma. The plasma shielding effect was found less pronounced for He environment and it leads to enhancement of the material evaporation from the target surface.

Low-energy helium irradiation on in-vessel mirror materials

Many metallic mirrors will be used for optical diagnostics in ITER. This study investigates the effects of low-energy helium (He) irradiation on the reduction in optical reflectance for molybdenum (Mo) and tungsten (W). When the surface temperature of the materials was sufficiently low, (i.e., lower than 700K for W and 600K for Mo), optical reflectance did not change; however, at higher temperatures, optical reflectance decreased significantly due to the He irradiation. Surface analysis indicated that the reduction in optical reflectance was caused by the morphology change, likely due to the formation of He bubbles. Based on the experimental results, the influences of He irradiation on the diagnostic mirrors in ITER are discussed.

The Aharonov-Bohm effect in graphene rings with metal mirrors

We measured the Aharonov-Bohm (AB) effect in graphene rings with superconducting-(Al) and normal-metal (Au) mirrors. The mirrors were deposited either on additional stubs connected to the rings in the transverse direction or on the ring bias lines. A significant enhancement of the visible phase coherence was observed in the latter case, in which we observed even the third harmonic of the AB oscillations. The superconductivity of the mirrors appears to be unimportant for the improved coherence in graphene. A large Fermi energy mismatch between graphene and the mirror material is sufficient for this effect. In addition, a transport gap was observed in our graphene structures at the gate voltage close to the Dirac point. The value of the gap can be reproduced by assuming the occurrence of Coulomb blockade effects in graphene.

Multilayer structures for the water-window spectral range on the basis of scandium

The problems of creating multilayer structures for the soft X-ray range are discussed. The search for an absorbing material for multilayer mirrors and phase shifters based on scandium for the water-window spectral range (wavelength of 2.3–4 nm) is performed. A comparison of the reflection characteristics of normal-incidence mirrors and the properties of phase shifters during numerical simulation of different pairs of materials shows the possibility of using cobalt as an absorbent in a pair with scandium.

Drift-Free Micromirror Arrays Made of Monocrystalline Silicon for Adaptive Optics Applications

In this paper, we report on the heterogeneous integration of monocrystalline silicon membranes for the fabrication of large segmented micromirror arrays for adaptive optics applications. The design relies on a one-level architecture with mirrors and suspension formed within the same material, employing a large actuator gap height of up to 5.1 μm to allow for a piston-type mirror deflection of up to 1600 nm. Choosing monocrystalline silicon as actuator and mirror material, we demonstrate a completely drift-free operation capability. Furthermore, we investigate stress effects that degrade the mirror topography, and we show that the stress originates from the donor silicon-on-insulator wafer. The novel heterogeneous integration strategy used in this work is capable of reducing this stress to a large extent.

First mirrors in ITER: material choice and deposition prevention/cleaning techniques

We present here our recent results on the development and testing of the first mirrors for the divertor Thomson scattering diagnostics in ITER. The Thomson scattering system is based on several large-scale (tens of centimetres) mirrors that will be located in an area with extremely high (3–10%) concentration of contaminants (mainly hydrocarbons) and our main concern is to prevent deposition-induced loss of mirror reflectivity in the spectral range 1000–1064 nm. The suggested design of the mirrors—a high-reflective metal layer on a Si substrate with an oxide coating—combines highly stable optical characteristics under deposition-dominated conditions with excellent mechanical properties. For the mirror layer materials we consider Ag and Al allowing the possibility of sharing the Thomson scattering mirror collecting system with a laser-induced fluorescence system operating in the visible range. Neutron tests of the mirrors of this design are presented along with numerical simulation of radiation damage and transmutation of mirror materials. To provide active protection of the large-scale mirrors we use a number of deposition-mitigating techniques simultaneously. Two main techniques among them, plasma treatment and blowing-out, are considered in detail. The plasma conditions appropriate for mirror cleaning are determined from experiments using plasma-induced erosion/deposition in a CH4/H2 gas mixture. We also report data on the numerical simulation of plasma parameters of a capacitively-coupled discharge calculated using a commercial CFD-ACE code. A comparison of these data with the results for mirror testing under deuterium ion bombardment illustrates the possibility of using the capacitively-coupled discharge for in situ non-destructive deposition mitigation/cleaning.

Mg–Ni thin-film composition dependence of durability of electrochromic switchable mirror glass in simulated environment

Mg–Ni thin films as a switchable mirror material are promising for application in energy-saving windows because they can change their state between reflective and transparent by hydrogenation and dehydrogenation. In our previous work, we found that electrochromic switchable mirror glass based on a Mg 4Ni thin film is affected by environmental factors such as temperature and humidity. In this work, we investigated the effects of the environment on the optical switching properties of electrochromic switchable mirrors with Mg–Ni thin films of various compositions suitable for a broad range of applications and operating environments. When the mirror devices were kept in a simulated environment with a constant temperature 40 °C and a constant relative humidity of 80%, controlled by a thermostat/humidistat bath, their optical switching properties degraded. The degradation was found to be related to the change in the Mg–Ni thin films into nonmetallic states of oxides and hydroxides. The device with a Mg 6Ni thin film kept in the bath for 7 days showed no optical switching property. The mechanism of degradation in the bath was strongly affected by the composition of the Mg–Ni thin-film optical switching layer. The device constructed with an optical switching layer having high magnesium content degraded more rapidly in the test.

Reflectivity measurement inside small hollow mirrors using an x-ray tube

Small hollow x-ray mirrors are manufactured by several techniques. The mirror material—the reflecting surface itself—can be either a simple metal, such as Au or Ni, or a multilayer. The development of a manufacturing technique, however, requires a simple way of measuring the mirror reflectivity curves. This may be done using a pencil beam at the synchrotron, but it is rather difficult to make it in a laboratory using an x-ray tube. This paper describes the development of a method of carrying out absolute reflectivity measurements inside these mirrors using only a typical laboratory source. Thus, we provide a fast, convenient and inexpensive way to perform mirror characterization. The method was tested in a laboratory and verified in synchrotron experiments in the case of conical micromirrors, while tests for other mirror shapes are under way. The method utilizes only an x-ray tube, an x-ray camera and linear motorized stages. The tube and the camera are moving relative to the mirror in a predefined way taking images of the peak. Detected images are then automatically processed in order to obtain a reflectivity curve. A fully automatic measurement including automatic focusing is also possible and is under development. A typical manual measurement takes approximately 1–2 h for one reflectivity curve at present.

Ultra-Lightweight Design and Analysis of a 1.25m SiC Segmented Mirror

In order to explore the feasibility of large ultra-lightweight deployable optical systems, a 1.25m SiC segmented mirror is investigated. According to analysis and comparison, the mirror's material, ultra-lightweight structure pattern and support location are determined respectively. By FEM, an ultra-lightweight structure with areal density of 40kg/m2 is gotten. The results show that the self-weight deformation is 4.8nm RMS/22.6nm PV under supports, and the ultra-lightweight mirror has the enough strength to bear the stress at launch. The study may provide a technical scheme to develop the large ultra-lightweight deployable optical system.

Study of Space Big Aperture New Materials Mirror and its Technology

In order to keep step with new materials mirrors and its technology of developed of international space optics system, and promote research level of national new material mirror, the optimization methods of new mirror materials were introduced, and the application of new material mirrors was elaborated. The researching technologies and methods of new materials mirror substrate were recommended. The researching technologies and methods of new materials mirror were narrated. And at same time, the new materials mirror technology and directions of our country were pointed out.

射流式水冷镜结构优化设计

Factors which have influences on the deformation of the water jet cooled mirror were analyzed. Numerical simulations of corresponding structural parameters were then made to explore general design laws of the water jet cooled mirror and an optimized scheme was achieved. The results show that, the maximum mirror surface deformation can be reduced to 0.07 μm under the conditions of 100 W net absorption power and 25 mm spot diameter, when the water jet cooled mirror is 80 mm in diameter with silicon as mirror material.

聚变堆第一镜材料块体金属玻璃表面特性

聚变堆第一镜材料块体金属玻璃表面特性

Degradation of optical reflectivity of in-vessel mirror materials by helium bombardment

The effect of helium irradiation on in-vessel mirror materials, i.e. molybdenum and rhodium, are investigated experimentally. By the exposure to helium plasmas with low incident ion energy (∼50eV) at different surface temperatures, the optical reflectivity of molybdenum and rhodium decreases significantly. From the surface analysis, it is shown that fiberlike nanostructure is formed on molybdenum surface when the surface temperature is high (at 1500K), while rough surface is observed when the surface temperature is low (<1000K). The decrease in the optical reflectivity is significant particularly for short wavelength ranges, typically, less than 300nm. The results indicate that the helium irradiation should be taken into account for in-vessel mirror materials for the optical diagnostics in ITER.

Comparison of InP- and GaSb-based VCSELs emitting at 2.3 μm suitable for carbon monoxide detection

Carbon monoxide (CO) is a prominent and toxic gas mainly generated by imperfect burning in fires or ovens. For trace gas monitoring and fire detection a compact, long term stable and calibration-free CO sensor is desirable. One very interesting measuring method is Tuneable Diode Laser Absorption Spectroscopy (TDLAS), which utilizes the unique properties of Vertical-Cavity Surface-Emitting Lasers (VCSELs). Two approaches to reach the required wavelength range for the absorption lines of CO at around 2350nm are discussed in this paper. The first approach is an expansion of the emission wavelength range of the now well-established lasers based on InP and a second and new one is fabricating VCSELs based on GaSb. From the epitaxial point of view the gain of the active material and the realization of a tunnel junction as well as optical, thermal and electrical characteristics of the mirror materials are important issues. For a proper choice of the device design the structuring of the used materials also plays a fundamental role— in particular the substrate removal. With simultaneous considerations of all these crucial issues, devices on InP and GaSb substrates have been fabricated. Both types work in continuous-wave mode, generating light in single-mode emission at the desired wavelength of the CO absorption line, which enables CO measurements down to a concentration limit of 2ppm.

Characterization of Silicon Carbide Films Prepared by Chemical Vapor Deposition

Silicon carbide prepared by chemical vapor deposition (CVD) is one of the important candidate materials for space mirror and high-power mirror such as laser mirror, because of its superior performances such as low density, high melting point and homogeneity. In this paper, the SiC coatings were deposited on the substrates of reaction bonded silicon carbide (RB-SiC) by CVD process. Then, the morphologies of the deposits were examined with scanning electron microscopy. The crystalline phase of the as-deposited films was confirmed with X-ray diffractometry. And the adhesion between the CVD film and the substrate was rated with scraping method. As a result, the morphologies of the deposits, i.e. whiskers at 1050°C or films at 1100°C, are different from that of the substrate. And the mean diameter of the deposits at 1100°C is larger than that at 1050°C. Furthermore, the crystalline phase of the as-deposited film is determined as β-SiC and the adhesion is firm enough not to be peeled off with the scraping test.

White top-emitting organic light-emitting diodes with forward directed emission and high color quality

We demonstrate top-emitting organic light-emitting diodes (OLEDs) with white emission spectra, employing a three color hybrid cavity structure with two highly efficient phosphorescent orange-red and green emitters (iridium(III)bis(2-methyldibenzo-[f,h]chinoxalin)(acetylacetonate) (Ir(MDQ) 2(acac)) and tris(2-phenylpyridin)iridium(III) (Ir(ppy) 3)) and the stable blue fluorescent emitter 2,5,8,11-tetra-tert-butylperylene (TBPe). In contrast to Lambertian emission characteristics, our devices show enhanced emission in the forward direction up to angles of 50°. In order to optically adjust the balance of blue and red light in the emission spectra, the influence of two different anode mirror materials are studied. We further test varied electron blocking layer materials to improve the device performance. An optimized layer structure with a hybrid anode mirror yields luminous efficacies of 13.3 lm/W (4.9% external quantum efficiency (EQE)) for the blocker material 2,2′,7,7′-tetrakis-( N, N-diphenylamino)-9,9′-spirobifluoren (S-TAD) and 12.4 lm/W (5.3% EQE) for N, N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine (NPB), respectively, at approximate luminances of 1000 cd/m 2. Using an aluminum anode, the emission shows Commission Internationale d’Eclairage chromaticity coordinates (CIE 1931) of (0.420, 0.407) at approximately 1000 cd/m 2 and color rendering indices of up to 77.

Characterization of Silicon Carbide Grown on RB-SiC by Chemical Vapor Deposition

Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.

Progress in the development of deposition prevention and cleaning techniques of in-vessel optics in ITER

The lifetime of front optical components unprotected from reactor grade plasmas may be very short due to intensive contamination with carbon and beryllium-based materials eroded by the plasma from beryllium walls and carbon tiles. Deposits result in a significant reduction and spectral alterations of optical transmission. In addition, even rather thin and transparent deposits can dramatically change the shape of reflectance spectra, especially for mirrors with rather low reflectivity, such as W or Mo. The distortion of data obtained with various optical diagnostics may affect the safe operation of ITER. Therefore, the development of optics-cleaning and deposition-mitigating techniques is a key factor in the construction and operation of optical diagnostics in ITER. The problem is of particular concern for optical elements positioned in the divertor region. The latest achievements in protection of in-vessel optics are presented using the example of deposition prevention/cleaning techniques for in-machine components of the Thomson scattering system in the divertor. Careful consideration of well-known and novel protection approaches shows that neither of them alone provides guaranteed survivability of the first in-vessel optics in the divertor. Only a set of complementary prevention/cleaning techniques, which include special materials for mirrors and inhibition additives for plasma, is able to manage the challenging task. The essential issue, which needs to be addressed in the immediate future, is an extensive development of techniques tested under experimental conditions (exposure time and contamination fluxes) similar to those expected in ITER.

Chiral luminescent compounds as a perspective for cholesteric liquid crystal lasers

We present the synthesis and characterization of fluorene based materials for mirror less laser applications. Mirror less lasing is obtained from a cholesteric liquid crystals mixture, that acts as a resonator, doped with a photoluminescent dye, that acts as an active medium. We propose to use fluorene based compounds to combine two necessary properties to achieve laser emission: chirality and luminescence. Two different compounds, a trimer and an oligomer are synthesized. The trimer and the oligomer are both prepared with chiral moieties and, in addition, they are liquid crystalline compatible. More, oligofluorenes are good blue emitters and the emission quantum yield is around 0.8 in the violet–blue range. These fluorene based compounds are used in cholesteric liquid crystals mixtures as luminescent chiral dopants and a fine tuning of the laser emission is obtained. The dependence of lasing efficiency on concentration and the handedness of chiral luminescent dopants are investigated.

Realization of X-ray telescopes–from design to performance

For more than 45 years the building of X-ray telescopes for solar and astronomical observations has been practised with significant performance improvement. The various techniques applied are reviewed emphazising the impact of proper mirror material choice, grinding and polishing improvements and the role of metrology.