Composite Mirror Research Articles

Test of the CLAS12 RICH large-scale prototype in the direct proximity focusing configuration

A large area ring-imaging Cherenkov detector has been designed to provide clean hadron identification capability in the momentum range from 3 GeV/c up to 8 GeV/c for the CLAS12 experiments at the upgraded 12 GeV continuous electron beam accelerator facility of Jefferson Laboratory. The adopted solution foresees a novel hybrid optics design based on aerogel radiator, composite mirrors and high-packed and high-segmented photon detectors. Cherenkov light will either be imaged directly (forward tracks) or after two mirror reflections (large angle tracks). We report here the results of the tests of a large scale prototype of the RICH detector performed with the hadron beam of the CERN T9 experimental hall for the direct detection configuration. The tests demonstrated that the proposed design provides the required pion-to-kaon rejection factor of 1:500 in the whole momentum range.

Mathematical model of composite mirror adjustment process

Mathematical model of composite mirror adjustment process

Ionic polymer metal composite for an optical zoom in a compact camera.

The reflective method is utilized in the optical zoom function of a thin camera for the advantage of folding the optical path. An ionic polymer metal composite deformable mirror used in a reflective zoom system achieves large deformations to change optical power with a low bias voltage. Polydimethylsiloxane is used as a buffer layer to improve surface roughness. The surface roughness of this layer is about 17 nm. The optical focusing power of the deformable mirror reaches 73.8 m(-1) diopters with 3 volts. A complete reflective camera module is fabricated using two ionic polymer metal composite deformable mirrors in the zoom function. The zoom ratio is about 1.6 × .

空间遥感器高体份SiC/Al复合材料反射镜组件设计

空间遥感器高体份SiC/Al复合材料反射镜组件设计

Tests of innovative photon detectors and integrated electronics for the large-area CLAS12 ring-imaging Cherenkov detector

A large area ring-imaging Cherenkov detector has been designed to provide clean hadron identification capability in the momentum range from 3GeV/c to 8GeV/c for the CLAS12 experiments at the upgraded 12GeV continuous electron beam accelerator facility of Jefferson Lab. Its aim is to study the 3D nucleon structure in the yet poorly explored valence region by deep-inelastic scattering, and to perform precision measurements in hadron spectroscopy. The adopted solution foresees a novel hybrid optics design based on an aerogel radiator, composite mirrors and a densely packed and highly segmented photon detector. Cherenkov light will either be imaged directly (forward tracks) or after two mirror reflections (large angle tracks).Extensive tests have been performed on Hamamatsu H8500 and novel flat multi-anode photomultipliers under development and on various types of silicon photomultipliers. A large scale prototype based on 28 H8500 MA-PMTs has been realized and tested with few GeV/c hadron beams at the T9 test-beam facility of CERN. In addition a small prototype was used to study the response of customized SiPM matrices within a temperature interval ranging from 25 down to −25°C. The preliminary results of the individual photon detector tests and of the prototype performance at the test-beams are here reported.

The large-area hybrid-optics CLAS12 RICH detector: Tests of innovative components

A large area ring-imaging Cherenkov detector has been designed to provide clean hadron identification capability in the momentum range from 3GeV/c to 8GeV/c for the CLAS12 experiments at the upgraded 12GeV continuous electron beam accelerator facility of Jefferson Lab to study the 3D nucleon structure in the yet poorly explored valence region by deep-inelastic scattering, and to perform precision measurements in hadronization and hadron spectroscopy. The adopted solution foresees a novel hybrid optics design based on an aerogel radiator, composite mirrors and densely packed and highly segmented photon detectors. Cherenkov light will either be imaged directly (forward tracks) or after two mirror reflections (large angle tracks). The preliminary results of individual detector component tests and of the prototype performance at test-beams are reported here.

Tailoring Reflections From Thin Composite Metamirrors

We propose an effective route to fully control the phase of plane waves reflected from electrically (optically) thin composite sheets. This becomes possible using engineered artificial full-reflection layers (metamirrors) formed by arrays of electrically small resonant bi-anisotropic particles. In this scenario, fully reflecting mirrors do not contain any continuous ground plane, but only arrays of small particles. Bi-anisotropic omega coupling is required to get asymmetric response in reflection phase for plane waves incident from the opposite sides of the composite mirror. It is shown that with this concept one can independently tailor the phase of electromagnetic waves reflected from both sides of the mirror array.

Optical Response of Metakaolin after Ultraviolet and High Energy Electron Exposure

Metakaolin, which is part of a class of inorganic polymers called geopolymers, is being tested currently for its use as a lightweight mirror material in spacecraft applications. Metakaolin, as with most geopolymers, has the advantages of low initial coefficient of thermal expansion, easy preparation at room temperature and pressure, and high specific strength. Even though metakaolin has been known as a structural material for millennia, it has not been properly vetted for use as a material in spacecraft applications, especially with respect to exposure to its environments. This research highlights one particular aspect of response to the space environment; that is, how do the optical properties of metakaolin change after subjugation to bombardment by ultraviolet and high energy electron radiation? These two radiation sources are common in low earth orbit and a primary cause of degradation of organic polymers in space. Photospectroscopic analysis showed that ultraviolet in combination with high energy electrons causes changes in the metakaolin which need to be accounted for due to their potential impacts on the thermal management of a spacecraft and during application in composite mirror structures.

Influence of ply misalignment on form error in the manufacturing of CFRP mirrors

We describe our study conducted within the framework of the design of composite mirrors for use in future generation astronomical telescopes. The work is also relevant to applications requiring lightweight optics and other unidirectional-ply fibre-composite-polymer constructs that require improved accuracy of form. Misalignment of layers (plies) in a composite laminate gives an astigmatic type deformation of the surface after cure. The influence of ply misalignment on surface form has been investigated via a series of finite element analyses. Thirty-two different layup sequences have been investigated: the angular increment between each ply, the number of plies and the number of sequence repeats were varied. Samples with random alignment errors have been simulated in order to compare the robustness of these different layup sequences toward ply misalignment; some design recommendations have been made. The finite element modelling method and results are presented here.

Composite mirror facets for ground based gamma ray astronomy

Composite mirrors for gamma-ray astronomy have been developed to fulfill the specifications required for the next generation of Cherenkov telescopes represented by CTA (Cherenkov Telescope Array). In addition to the basic requirements on focus and reflection efficiency, the mirrors have to be stiff, lightweight, durable and cost efficient. In this paper, the technology developed to produce such mirrors is described, as well as some tests that have been performed to validate them. It is shown that these mirrors comply with the needs of CTA, making them good candidates for use on a significant part of the array.

Versions of a composite high-aperture mirror objective of compact design

It is shown that using an afocal Mersenne system that possesses known anaberrational properties makes it possible to construct a number of compact mirror and mirror–lens systems that possess aplanatic, anastigmatic, and planastigmatic correction of the aberrations of the resulting image, with the length of the system being about a factor of 4 less than the diameter of its entrance pupil.

Finite element modeling and testing of a deformable carbon fiber reinforced polymer mirror

Thin-shelled composite mirrors have been recently proposed for use as deformable mirrors in optical systems. Large-diameter deformable composite mirrors can be used in the development of active optical zoom systems. We present the fabrication, testing, and modeling of a prototype 0.2 m diameter carbon fiber reinforced polymer mirror for use as a deformable mirror. In addition, three actuation techniques have been modeled and will be presented.

Arrays of large-area, tip/tilt micromirrors for use in a high-contrast projector

Arrays of two-degree of freedom analog micromirrors are designed for use within an high-contrast projector and fabricated using a multi-user MEMS fabrication process. We demonstrate a novel way of optimizing the tradeoffs between tilt angle and mirror size by subdividing the mirrors into smaller functional subsections that move synchronously. The mirror design employs multiple mirrors within a gimbal frame. The frame rotates around one axis, and each mirror within the frame rotates around a perpendicular axis, resulting in two-degree of freedom rotation. The design employs specific electrode shapes to allow one-layer connections. Using these fabricated mirrors, simultaneous actuation of mirrors within a composite structure is achieved. A prototype array of fabricated mirrors is described, with 6 × 5 mirrors each of 160 μm × 160 μm forming one composite mirror of an array, giving total active area of 960 μm × 800 μm. The mirrors can achieve a maximum tilt angle of 2.25°. The fill factor of this design is 68%.

Cryogenic optical testing of an 800mm lightweight C/SiC composite mirror mounted on a C/SiC optical bench

We tested the optical performance at cryogenic temperatures of an 800 mm diameter lightweight mirror, consisting of carbon-fiber reinforced silicon carbide and with a mass of 11.2 kg. The ceramic composite of the mirror was HB-Cesic, developed by ECM, Germany, and Mitsubishi Electric Corporation, Japan. The test was carried out while the mirror was mounted, via Invar stress relief supports, on a lightweight optical bench also made of HB-Cesic. During the test, both the mirror and the optical bench were cooled to 18 K in a liquid-helium chamber. The test consisted of measuring the mirror's change of surface figure with an interferometer installed outside the cryo-chamber. The cryogenic deformation of the mirror was 110 nm RMS with no significant residual deformation after cooling, which is very promising for the applicability of the HB-Cesic composite to large lightweight cryogenic space optics.

Composite mirror surface deformation due to lay-up sequences within quasi-isotropic laminates

We address surface accuracy issues associated with the thermal stability of continuous-fiber-reinforced quasi-isotropic composite mirrors. Thermally induced surface deformations in /n quasi-isotropic laminates, where n=3, 4, and 6, are numerically and experimentally investigated for the effects of stacking sequence and surface resin layers. Symmetric laminates and asymmetric laminates caused by the presence of surface resin layers for fiber print-through (FPT) mitigation are considered in numerical models to evaluate the surface characteristics due to thermal variance of T=16.6 °C (30 °F). Numerical results from finite element analyses reveal that the presence of an out-of-plane sinusoidal surface deformation pattern is inevitable in quasi-isotropic laminates, and the surface patterns are associated with stacking sequences within the laminates. Analyses assuming the thermal variance reveal that none of the /n laminates meet the diffraction-limited surface deformation requirement (</20) for precision composite optics, with the mean average magnitude of surface deformation in /n symmetric laminates due to the thermal variance being 250 nm. Projections of this data further reveal that temperature variations must be maintained within ±2 °C to expect diffraction-limited performance. Similarly, tight control over moisture content will be required. Adding surface resin layers in quasi-isotropic laminates for FPT alleviation produces larger out-of-plane deformations than high-frequency surface variations due to FPT.

Cryogenic optical measurements of 12-segment-bonded carbon-fiber-reinforced silicon carbide composite mirror with support mechanism

A 720 mm diameter 12-segment-bonded carbon-fiber-reinforced silicon carbide (C/SiC) composite mirror has been fabricated and tested at cryogenic temperatures. Interferometric measurements show significant cryogenic deformation of the C/SiC composite mirror, which is well reproduced by a model analysis with measured properties of the bonded segments. It is concluded that the deformation is due mostly to variation in coefficients of thermal expansion among segments. In parallel, a 4-degree-of-freedom ball-bearing support mechanism has been developed for cryogenic applications. The C/SiC composite mirror was mounted on an aluminum base plate with the support mechanism and tested again. Cryogenic deformation of the mirror attributed to thermal contraction of the aluminum base plate via the support mechanism is highly reduced by the support, confirming that the newly developed support mechanism is promising for its future application to large-aperture cooled space telescopes.

A nickel-carbon-fibre composite for large adaptive mirrors: fabrication methods and properties

We present results from our recent research into carbon-fibre composite (CFC) mirror fabrication for optical and infra-red applications. In particular this research is aimed towards the next generation of extremely large telescopes to offer an alternative to thin glass shell adaptive secondary mirrors. We address the issues involved with CFC mirror production, in particular the accuracy of the form replication process, a suitable surface for polishing to optical quality, no fibre print-through, environmental stability (shape change due to thermal and moisture variations), material uniformity and lifetime. We have performed experiments into the effectiveness of cold electroplating thick nickel coatings to totally encapsulate the CFC base substrate; the manufacturing procedure and properties of the Ni-CFC mirror are described here.

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing. These structures are considered to be caused by the different hardness of those materials. The roughness obtained for the bare mirrors is 20 nm rms for flat surfaces and 100 nm rms for curved surfaces. It was confirmed that a SiSiC slurry coating is effective in reducing the roughness to 2 nm rms. The scattering properties of the mirrors were measured at room temperature and also at 95 K. No significant change was found in the scattering properties through cooling, which suggests that the microscopic surface structure is stable with changes in temperature down to cryogenic values. The C/SiC mirror with the SiSiC slurry coating is a promising candidate for the SPICA telescope.

The optical system of an adaptive 25-m telescope with a composite primary mirror composed of spherical segments

This paper presents the results of a calculation of the four-mirror two-stage optical system of a large optical telescope with a composite primary mirror (CPM), whose aspheric reflecting surface is approximated by hexagonal segments of spherical shape. Our analysis of the image quality showed that, when a definite size is chosen for the elements of the CPM, the proposed approximation makes it possible in principle to achieve an equivalent angular resolution of the optical system of the telescope better than 0.1″. Elements of the CPM about 1 m across can be used for the 25-m telescope. It is expedient to put such a technical solution into practice both in the processing aspect and from the viewpoint of applying adaptive control of the shape of the reflective surface of the CPM.

Axially symmetric composite electromagnetic mirror for perfect axial-aberration correction

A new element of charged-particle optics is proposed and examined: an axially symmetric composite electromagnetic mirror employing a focusing magnetic field as well as an electrostatic one, the two fields overlapping. It is shown that the chromatic and spherical aberration coefficients of the mirror are opposite in sign to those found in conventional axially symmetric optics; their magnitude is twice the length of the paraxial particle trajectory as projected on the mirror axis of symmetry. As a result, the negative axial aberration coefficients can be varied over the wide range from a few millimeters to one meter with the mirror focal length and the particle energy being fixed. This property offers a way to fully compensate for the axial aberration of optimized ion or electron objective lenses in current use. A correction system incorporating the mirror is proposed. As compared with the sole correction arrangement used in electron optics, the system considered has about 1/5 times as many alignment degrees of freedom (mechanical and electrical) and should therefore display far greater stability; furthermore, it can work with ions as well as electrons.