Nickel Mirror Research Articles

Evaluation of a composite nickel mirror as a back mirror of a flashlamp-pumped Nd:YAG laser system in free running regime

Evaluation of a composite nickel mirror as a back mirror of a flashlamp-pumped Nd:YAG laser system in free running regime

An approach to determine radiative properties of solid struts of open-cell foams by pore scale identification from macro scale measurements

Open-cell foams consisting of interconnected struts are widely used in thermal applications such as volumetric solar receivers. The thermal performance of foams strongly relies on their radiative behaviors which intrinsically depends on the radiative properties of struts. This study proposed a feasible approach to determine the radiative properties of solid struts by a pore scale identification from a macro scale measurement. First, the normal-hemispherical transmittance and reflectance spectra of two nickel foams were measured by an experimental system. Second, a pore scale forward calculation was conducted by a combination of Monte Carlo Ray-tracing method and real foam structures obtained from micro-computed tomography technique. Last, an Adaptive Particle Swarm Optimization algorithm was adopted to retrieve the spectral reflectivity and specularity of nickel struts from the measured spectra. The results show that it is unreasonable to assume the reflection behavior of strut surface simply as either specular or diffused, and also, it is unreliable to assign the reflectivity of strut surface directly by Fresnel's law. Within the investigated wavebands 0.4–2.2 μm, the average reflectivity of nickel struts is 12% lower than that of a nickel mirror. The proportion of specular reflection at nickel strut surface is between 37%–52%, almost increasing with wavelengths.

Two-color spatial and temporal temperature measurements using a streaked soft x-ray imager.

A dual-channel streaked soft x-ray imager has been designed and used on high energy-density physics experiments at the National Ignition Facility. This streaked imager creates two images of the same x-ray source using two slit apertures and a single shallow angle reflection from a nickel mirror. Thin filters are used to create narrow band pass images at 510 eV and 360 eV. When measuring a Planckian spectrum, the brightness ratio of the two images can be translated into a color-temperature, provided that the spectral sensitivity of the two images is well known. To reduce uncertainty and remove spectral features in the streak camera photocathode from this photon energy range, a thin 100 nm CsI on 50 nm Al streak camera photocathode was implemented. Provided that the spectral shape is well-known, then uncertainties on the spectral sensitivity limits the accuracy of the temperature measurement to approximately 4.5% at 100 eV.

A new streaked soft x-ray imager for the National Ignition Facility.

A new streaked soft x-ray imager has been designed for use on high energy-density (HED) physics experiments at the National Ignition Facility based at the Lawrence Livermore National Laboratory. This streaked imager uses a slit aperture, single shallow angle reflection from a nickel mirror, and soft x-ray filtering to, when coupled to one of the NIF's x-ray streak cameras, record a 4× magnification, one-dimensional image of an x-ray source with a spatial resolution of less than 90 μm. The energy band pass produced depends upon the filter material used; for the first qualification shots, vanadium and silver-on-titanium filters were used to gate on photon energy ranges of approximately 300-510 eV and 200-400 eV, respectively. A two-channel version of the snout is available for x-ray sources up to 1 mm and a single-channel is available for larger sources up to 3 mm. Both the one and two-channel variants have been qualified on quartz wire and HED physics target shots.

Fabrication of metallic micromirror using electroplating technology

A nickel micromirror array was designed and successfully fabricated using a thick photoresist as a sacrificial layer and as a mold for nickel electroplating. It was composed of two address electrodes, two support posts and a nickel mirror plate. The mirror plate, which is supported by two nickel posts, is overhung about 10 μm from the silicon substrate. The nickel mirror plate is actuated by an electrostatic force generated by electrostatic potential difference applied between the mirror plate and the address electrode. Optimized fabrication processes have been developed to reduce residual stress in mirror plate and prevent contact between the mirror plate and the substrate, which ensure a reasonable flat and smooth micromirror for operation at low actuation voltage.

Removal of single point diamond-turning marks by abrasive jet polishing

Single point diamond turning (SPDT) is highly controllable and versatile in producing axially symmetric forms, non-axially-symmetric forms, microstructured surfaces, and free forms. However, the fine SPDT marks left in the surface limit its performance, and they are difficult to reduce or eliminate. It is unpractical for traditional methods to remove the fine marks without destroying their forms, especially for the aspheres and free forms. This paper introduces abrasive jet polishing (AJP) for the posttreatment of diamond-turned surfaces to remove the periodic microstructures. Samples of diamond-turned electroless nickel plated plano mirror were used in the experiments. One sample with an original surface roughness of more than 400 nm decreased to 4 nm after two iterations abrasive jet polishing; the surface roughness of another sample went from 3.7 nm to 1.4 nm after polishing. The periodic signatures on both of the samples were removed entirely after polishing. Contrastive experimental research was carried out on electroless nickel mirror with magnetorheological finishing, computer controlled optical surfacing, and AJP. The experimental results indicate that AJP is more appropriate in removing the periodic SPDT marks. Also, a figure maintaining experiment was carried out with the AJP process; the uniform polishing process shows that the AJP process can remove the periodic turning marks without destroying the original form.

Single-point diamond turning of electroless nickel for flat X-ray mirror

X-ray mirrors require a super-smooth surface to prevent strong X-ray scattering. We examined the fabrication possibility of the X-ray mirror by single-point diamond turning (SPDT) for electroless nickel. The stable and unstable cutting modes for the electroless nickel were obtained by observing the relative position of a diamond tool for machining. A super-smooth surface of 0.95 nm rms was achieved within the stable cutting mode. The surface roughness of the electroless nickel mirror measured with an optical profiler was compared with the X-ray reflectivity measurement. The electroless nickel mirror could be successfully used as a soft X-ray reflector and a low-pass filter for the hard X-rays.

Wolter optics for neutron focusing

Focusing optics based on Wolter optical geometries developed for X-ray grazing incidence beams can be designed for neutron beams. Wolter optics are formed by grazing incidence reflections from two concentric conic sections (for example, a paraboloid and a hyperboloid). This has transformed observational X-ray astronomy by increasing the sensitivity by many orders of magnitude for research in astrophysics and cosmology. To increase the collection area, many reflecting mirrors of different diameters are nested with a common focal plane. These mirrors are fabricated using nickel-electroformed replication techniques. We apply these ideas to neutron focusing using nickel mirrors. We show an initial test of a conical mirror using a beam of cold neutrons.

Ultra light-weight and high-resolution X-ray mirrors using DRIE and X-ray LIGA techniques for space X-ray telescopes

We are developing novel ultra light-weight and high-resolution X-ray micro pore optics for space X-ray telescopes. In our method, curvilinear micro pore structures are firstly fabricated by silicon deep reactive ion etching (DRIE) or X-ray LIGA processes. Secondly, side walls of the micro structures are smoothed by magnetic field assisted finishing and/or hydrogen annealing techniques for high reflectivity mirrors. Thirdly, to focus parallel X-ray lights from astronomical objects, these structures are elastically or plastically bent into a spherical shape. Fourthly, the bent structures are stacked to form a multi-stage X-ray telescope. In this paper, we report on fabrication and X-ray reflection tests of silicon and nickel X-ray mirrors using the DRIE and LIGA processes, respectively. For the first time, X-ray reflections were confirmed on both of the mirrors. Estimated rms roughnesses were 5 nm and 3 nm for the silicon and nickel mirrors, respectively.

A Nickel Micro Switch Operating in a Wide Range of Torsion Angles

We report a nickel optical MEMS switch, being able to rotate through a large angle and to accommodate multiple channels. The proposed optical switch consists of a thin nickel mirror and two torsion springs supporting the mirror. The torsion springs are designed using a finite element method (FEM) such that plastic deformation of the thin nickel is avoided during the large torsion actuation. For switching speed improvement, transient vibration of the released mirror is suppressed by optimizing the mirror design and a fast switching response of <TEX>$200\;{\mu}s\;(pull-down)/300\;{\mu}s\;(pull-up)$</TEX> is demonstrated.

Performance of upgraded thermal neutron guides with supermirrors at JRR-3

Thermal neutron guides at the JRR-3 reactor have been upgraded from natural nickel mirror guides to Ni/Ti supermirror ones with two times critical angle as large as that of natural nickel mirror. We have performed the characteristics experiment of neutron beams transmitted through the supermirror neutron guides. The neutron spectra have been measured at the end of the thermal neutron guide by the time-of-flight method. It was observed that the characteristic wavelength for the neutron beam was shifted from 2 to 1.3 A ̊ . Neutron flux at the end of the thermal neutron guide was measured by the gold foil activation method. It was measured 6.11×10 11 n/m 2 s and increases 4.32 times after upgrade. We have conducted Monte Carlo simulation in consideration of the reflectivity of fabricated supermirrors and their alignment errors for the purpose to examine the performance of supermirror neutron guides.

Performance of upgraded thermal neutron guides with supermirrors at JRR-3

Thermal neutron guides at the JRR-3 reactor have been upgraded from natural nickel mirror guides to Ni/Ti supermirror ones with two times critical angle as large as that of natural nickel mirror. We have performed the characteristics experiment of neutron beams transmitted through the supermirror neutron guides. The neutron spectra have been measured at the end of the thermal neutron guide by the time-of-flight method. It was observed that the characteristic wavelength for the neutron beam was shifted from 2 to 1.3Å. Neutron flux at the end of the thermal neutron guide was measured by the gold foil activation method. It was measured 6.11×1011n/m2s and increases 4.32 times after upgrade. We have conducted Monte Carlo simulation in consideration of the reflectivity of fabricated supermirrors and their alignment errors for the purpose to examine the performance of supermirror neutron guides.

Design and fabrication of low-cost X-ray mirrors

Traditional X-ray mirrors made from Zerodur and silicon carbide are quite expensive because of the fabrication cost involved in achieving a very high surface finish of the order of 15 Å or better. The cost of X-ray mirrors can be greatly reduced by using replication methods for producing the grazing-incidence type mirrors. This paper presents the optical and optomechanical design for a Wolter type I mirror and its mount, and the fabrication method used to produce a low-cost replicated nickel mirror. The finite element analysis results for this mirror are also presented. The design and fabrication steps for the aluminium master mandrel used for replication are also discussed. A surface finish of better than 15 Å was achieved for a such an electroformed mirror with a wall thickness of only 1 mm.

Neutron reflectivity measurements of different nickel mirrors

Neutron optical devices, such as neutron guides, apply mirrors where multiple total reflections of neutrons takes place. Materials more light and flexible than glass have never been used as a substrate of the neutron mirrors. The present work deals with neutron reflectivity measurements performed for three nickel mirrors. While one of them is a glass plate coated with a NiCr film, the other two mirrors are on plexiglas substrates coated by either NiCr or 58Ni films. The incident beam covered a neutron wavelength range from 0.05-0.4 nm. The results of the present measurements are in favour of the idea of using acrylic glass as a substrate for nickel mirrors.

Concentrations, distributions and seasonal variability of dissolved Cd, Co, Cu, Mn, Ni, Pb and Zn in the English Channel

Open ocean studies have shown that dissolved manganese, cobalt and lead exhibit vertical profiles that reflect external sources and short residence times due to scavenging on to particle surfaces. In contrast, dissolved cadmium, copper, nickel and zinc mirror, to different degrees, the profiles of the nutrients. The work reported here for three cruises (November–December 1985, May and July–August 1986) in a shallow shelf sea shows that seasonal variations are shown by metals of the scavenged group, whereas the metals whose cycling in the open ocean parallels those of the nutients, do not show these correlations and, in fact, show no measurable seasonal variability. Concentrations of manganese increased progressively from winter to summer [2.3 ± 0.7(mean± 1σ)to 5.0 ± 3.0 nmol l −1]. A surface enrichment in the upper mixed layer of the western Channel during summer was also observed. Concentrations of cobalt increased from winter to spring (from ≤0.02–0.50 to 0.08–0.71 nmol l −1), paralleling those of manganese, but then decreased into summer (to ≤0.08–0.56 nmol l −1). The regional distribution of lead changed during the spring, possibly reflecting removal by diatoms and decreased river inputs, although overall mean concentrations remained similar throughout the year (0.22 nmol l −1). Concentrations of cadmium (0.20 nmol l −1), copper (3.2 nmol l −1), nickel (3.8 nmol l −1) and zinc (7.6 nmol l −1), and their regional distributions, remained relatively uniform over the period of the observations.

Development of a Supermirror Neutron Guide Tube.

A supermirror neutron guide tube with a characteristic wavelength of 1.2 A was developed and installed at the Kyoto University Reactor (KUR). The apparent critical wavelength of the present supermirrors is about 250 A. The geometrical parameters of the guide tube are: 11.7 m total length, and 10 mm wide X74 mm high beam cross section. The supermirror neutron guide tube presents decisive advantages over the conventional nickel mirror guide tube higher transmission of neutrons, brought about through the contribution of neutrons of shorter wavelengths and of those presenting large divergent angles. The total neutron flux obtained from the KUR supermirror guide tube is about 5x107n/cm2·s, which is about 25 times what is obtainable with the conventional KUR nickel mirror neutron guide tube of the same geometrical parameters.

The neutron microguide as a probe for materials analysis

A system composed of curved totally reflecting nickel mirrors is described for the focusing of neutrons by the superposition of intensities transmitted through many thin-layer films, each of which points individually to the focus. This is achieved by stacking many curved mirrors on top of each other with their ends slightly overlapping, so that the projections of each microguide meet at the focal point. The maximum current density is obtained with a large number of microguide sheets of minimum thickness, a large radius of curvature, and a short focal length, though the thickness of the microguides may be dictated by more practical considerations. The length of the system should be as short as possible (∼ few cm) to reduce both reflection and scattering losses, consistent with the length of direct view. The major loss in transmission is caused by misalignment of the layers which will diffuse the focus from its theoretical maximum.

Transmission electron microscopy of Ni/Ti neutron mirrors

Transmission electron microscopy (TEM) is a revealing method to characterize the microstructure of multilayer thin film coatings. The performance of nickel mirrors, used for neutron spin polarization at grazing incident angles, may be enhanced by replacing the nickel coating with a Ni/Ti multilayer. Difficulties have historically arisen in fabricating defect-free multilayer structures. TEM of cross-sectioned multilayers provides a direct means to identify debilitating structural defects. During the sputter deposition of long-period Ni/Ti multilayers, an undesirable growth morphology has been prevalent, i.e. nodular. Modifications to sputter deposition processes have improved the quality of the multilayer coatings, hence their performance as efficient neutron mirrors should be improved as well. The origin of the nodular growth structure and the measures taken to curtail this morphology will be revealed in the TEM characterization of Ni/Ti neutron, multilayer mirrors.

Pulsed x-ray induced damage to metal and multilayer mirrors

The effects of intense pulses of laser-produced x rays upon the reflective and diffractive properties of metal mirrors and layered synthetic microstructure mirrors (artificial crystals) have been investigated. Laser pulses from a Nd–glass pulsed laser system of 25-ns pulse width and 50-J energy were focused onto a copper target to generate x-ray pulses. A polished planar nickel mirror reflected 0.98- to 1.3-keV x rays onto photographic film. The x-ray flux onto the mirror (at grazing incidence angles near 3.5°) was split into two adjacent fields with a beryllium filter over one field and with an equal thickness beryllium filter placed over the film holder covering the adjacent field. Thin pieces of Kimfol were used as debris shields ahead of the mirror sample. This technique provided an in situ normalization since both a low- and high-intensity irradiation can be simultaneously achieved on adjacent portions of the mirror. A similar technique was used to study reflection by a multilayer mirror of carbon–tungsten carbide layering with a 2d spacing of 3.92 nm. Experimental details and the results obtained are presented.

A cold-neutron spectrometer for inelastic-scattering studies

This paper contains a description of the cold-neutron spectrometer which is operated in the CAMEN centre at San Piero a Grado (Pisa). The apparatus was designed for use in classical and quantum-fluid research. The neutron beam of the 5 MW Galileo reactor enters, after passing trough a cold propane source, a rectangular guide tube, made of nickel mirrors. The dimensions of the tube have been optimized to give a maximum neutron current on the sample. The neutron-energy spectrum measured by the time-of-flight method confirmed the theoretical predictions. The average neutron flux in the beam is 7.7×10 5 n/cm 2sec. The neutrons emerging from the tube are “chopped” by a rotor giving a burst of 100 μsec. These neutrons are scattered by the samples along a convenient flight path and are collected by scintillation detectors. The analyser system consists of a PDP-11 computer with a special 8-input interface.