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.     

The Photography of Radioactive Materials

This paper discusses some or the many problems peculiar to the photography or radioactive materials. Specialized apparatus and techniques are described, such as telephotography via mirrors, illumination systems and macro techniques.     

Electroform replication used for multiple x-ray mirror production

Work done to produce x-ray mirrors via electroform replication is reported. Several advances have been made over previous work. We have produced lower grazing incidence angle (30 min) mirrors, obtained quantitative measurements up to higher energies (6.40 keV), produced about four times as many replicas from one mandrel, and obtained angular resolutions better than other work done with replicated metal mirrors.     

复杂曲面铝反射镜超精密制造现状

由于复杂曲面铝反射镜所具有的独特优势,其在光学系统中的应用越来越广泛。但是只采用超精密车削加工的光学反射镜精度受到超精密车削加工“误差复映”的限制,只能满足红外系统应用需求,其应用的进一步推广遭遇瓶颈。采用超精密车削、磁流变抛光、计算机控制表面成形(CCOS)的组合加工工艺,并结合复杂光学曲面的计算全息图法(CGH)面形检测技术,可以进一步提升铝反射镜的面形精度,满足可见光系统的应用需求,为复杂曲面铝合金反射镜的推广奠定了制造基础。

     

Designs and investigations of anti-glare blue-tint side-view car mirrors

Recent developments for luxury car industries have been in favor of anti-glare color-tint side-view exterior car mirrors. In this study, we explore the designs, the fabrications, and the investigations of anti-glare blue-tint samples suitable for the side-view car mirrors. With an aid of the thin film design software, the TiO₂-based backside-coated optical systems are prepared by the homemade and the retailed sputtering systems, and examined for the reflection spectra and the chromaticity diagrams. From four major designs of the anti-glare blue-tint mirrors, the ultra-thin metallic layer and the dielectric stack with the bottommost reflective layer offer the blue-tint at 85% highest reflection. Although the design requires only 40 min of the deposition time, the careful control of the ultra-thin metallic film thickness is crucial.     

Energy flow of electric dipole radiation in between parallel mirrors

We have studied the energy flow patterns of the radiation emitted by an electric dipole located in between parallel mirrors. It appears that the field lines of the Poynting vector (the flow lines of energy) can have very intricate structures, including many singularities and vortices. The flow line patterns depend on the distance between the mirrors, the distance of the dipole to one of the mirrors and the angle of oscillation of the dipole moment with respect to the normal of the mirror surfaces. Already for the simplest case of a dipole moment oscillating perpendicular to the mirrors, singularities appear at regular intervals along the direction of propagation (parallel to the mirrors). For a parallel dipole, vortices appear in the neighbourhood of the dipole. For a dipole oscillating under a finite angle with the surface normal, the radiating tends to swirl around the dipole before travelling off parallel to the mirrors. For relatively large mirror separations, vortices appear in the pattern. When the dipole is off-centred with respect to the midway point between the mirrors, the flow line structure becomes even more complicated, with numerous vortices in the pattern, and tiny loops near the dipole. We have also investigated the locations of the vortices and singularities, and these can be found without any specific knowledge about the flow lines. This provides an independent means of studying the propagation of dipole radiation between mirrors.     

Effect of energetic electron and proton bombardment on the reflectance of silicon-carbide mirrors in the extreme-ultraviolet region

Chemical-vapor-deposited silicon-carbide mirrors were exposed to bombardment by 95-keV electrons and 100-keV protons with accumulated fluxes comparable with those expected in low-altitude Earth orbit for simulated periods of as many as 5 years. The reflectances of four mirrors were measured at five wavelengths (58.4, 73.6, 104.8, 121.6, and 161 nm) and at 11 angles of incidence from 5° to 80°. The electron and proton exposure resulted in no significant change in the reflectances of the mirrors.     

Theory of reflectivity of an asymmetric mirror

By using the concept of transfer matrices and Bloch waves, we have derived a set of equations that provide insight into the operation of asymmetric Bragg reflectors that have been demonstrated to be useful in achieving high reflectivities in strained-material systems. These equations will be useful in the design of asymmetric mirrors and can be used to compare the trade-offs between the conventional, symmetric (quarter-wavelength), and asymmetric mirrors.     

Analysis of imaging properties of a vibrating thin flat mirror

Thin flat mirrors are often used in designing various optical measurement systems. Such mirrors are generally deformed by environmental conditions during measurements. A detailed theory of deformation of a thin flat mirror that oscillates harmonically in the direction of the normal to its surface is introduced in our work. The mirror is treated as a vibrating membrane, and the time-dependent effect of the mirror deformation on the properties of reflected light is studied. A relation is derived for a dynamic wave aberration. On the basis of this relation, calculation of the Strehl definition of the deformed mirror is performed both by exact integration and by approximation. The results obtained can be used for analysis of the influence of mechanical vibrations on the accuracy of optical measurement systems in various practical applications where thin flat mirrors are used.     

高速倾斜反射镜机械谐振频率的改善

高速倾斜反射镜（以下简称倾斜镜）是自适应光学,跟踪瞄准等系统中的重要器件。随着系统对宽带和精度等指标要求的提高,倾斜镜的结构固有愈来愈成为系统性能的重要限制因素。本文从机械振动理论出发提出了一种通过降低模态耦合人而改善倾斜镜机械谐振频率的方法。     

Self-supported subwavelength gratings with a broad band of high reflectance analysed by the rigorous coupled-wave method

Based on rigorous electromagnetic theory and the coupled-wave method, the reflectance performance of the self-supported subwavelength grating (SSG) with different geometrical and physical parameters, such as the incident wavelength, the grating period, the grating thickness, the filling ratio of the grating, the incident angle, and the refractive index of the outer space, is systematically investigated. For TE polarization, numerical results reveal that a very broad band (Δλ/λ=26.13%) of high reflectance (R>99%) is achieved in the near-infrared region. Motivated by the micro-electromechanical systems actuator, the SSG is expected to have extensive potential applications in many optoelectronic devices including tunable optical mirrors or filters.     

Closed-loop stable control of two deformable mirrors for compensation of amplitude and phase fluctuations

A method for closed-loop stable control of two deformable mirrors for compensation of both amplitude and phase fluctuations is described. A generic implementation is described as well as an implementation that integrates the concept behind a point diffraction interferometer with a two-deformable-mirror system. The relationship of the closed-loop control algorithm to previously developed open-loop iterative algorithms is described. Simulation results are presented that indicate that the system is stable and provides superior performance over that of a single-deformable-mirror system. The impact of finite servo bandwidth on control of two deformable mirrors is evaluated by means of wave optical simulation, and it is found that to achieve a performance improvement attributable to compensation of amplitude fluctuations, the bandwidth of the two-deformable-mirror system must be at least twice the Greenwood frequency.     

Frequency Stabilization of the He-Ne Maser

A bright and monochromatic radiation from an optical maser can be used as a stable standard of wavelength, when plane mirrors in the maser are automatically controlled so that the oscillation frequency can be kept very close to the center of the atomic line. The separation of mirrors is modulated at a low frequency with a small amplitude. The fundamental-, the second-harmonic, and the third-harmonic components of the modulation frequency in the light output give correction signals for the tilt of mirrors, the power level of excitation, and the separation of mirrors. The photobeat between two independently-stabilized masers of 1.15 microns filled with Ne20 and Ne22, respectively, has been observed. The observed fluctuation of beat frequencies shows a Gaussian distribution, and no systematic frequency drift has been found. It is found that the frequency of each maser stays within several parts in 1010 and the resettability is just as good. Some difficulties with stray magnetic field from magnetostriction coils and with earth magnetic field are found. Preliminary experiments on pressure shift and its effect on the stabilized maser are discussed. The theory has been developed, and the frequency deviations as functions of the gas pressure and of the amplitude of modulation have been calculated.     

Effects of curved mirrors in waveguide resonators

Waveguide gas lasers (CO(2) ones especially) continue to be widely used. We have previously studied simple resonator designs with plane mirrors close to each end of the waveguide. Here we examine theoretical predictions concerning hybrid waveguide/free-space resonators with square-bore guides and curved mirrors. We show how resonator mode losses vary as functions of guide length and width, guide-to-mirror distance, mirror radius of curvature, and mirror tilt. We have tested a 7-W cw rf-excited CO(2) laser with unusually good near-TEM(00) transverse-mode quality; it is one of many promising resonator geometries not covered by earlier published research. The common case 3 reflector, sometimes viewed as guaranteeing near-TEM(00) mode performance, is shown to be alarmingly sensitive to small misalignments for certain guide geometries.     

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.     

刀具对中误差对离轴抛物面镜慢刀伺服车削加工的影响

离轴抛物面镜单件高效加工是离轴三反消像散(TMA)结构光学系统的技术难点之一.单点金刚石慢刀伺服车削加工技术可用于离轴非球面加工,加工尺寸范围较大,加工精度较高.此工艺制造的离轴抛物面面型精度可达到亚微米级,粗糙度达到纳米级.因此,可直接用于红外光学应用,若经后续抛光则可用于空间望远镜等更高精度需求的场合.介绍了慢刀伺服车削加工离轴抛物面镜的在轴加工方法,理论推导了刀具对中误差所带来的面形误差的极值分布规律.仿真研究进一步揭示了工件中心区域面形误差的详细分布.实验数据与理论结果和仿真计算结果均吻合.     

Methodology for third-order astigmatism compensation in off-axis spherical reflective systems

The main constraint of classical off-axis reflecting systems is the primary astigmatism that has long been a research topic of interest. This astigmatism in off-axis spherical reflective imaging systems can be eliminated by using the proper configuration. These configurations could be derived from the marginal ray fans equation, and they are valid for small angles of incidence. The conditions for the astigmatism compensation in configurations with two and three off-axis mirrors have been derived and analyzed, which have not been reported previously. The expression that defines the conditions for primary astigmatism compensation in a four-mirror system is presented. This shows that the marginal ray fan equation can be used to obtain the condition for astigmatism compensation of a reflective system with any number of mirrors. The developed methodology is verified by ray-tracing analysis of some examples.     

中国古代青铜器表面鎏镀技术（二）

3鎏镀与鎏焊 3．1鎏镀工艺 鎏镀富锡铜时鎏镀件置于炉中不免相互紧靠,甚至上下叠放。若镀件之间不放置范板相隔,加热去汞时不免会有镀液流淌而导致上下两鎏镀件焊在一起。如果说商代早中期就有了鎏镀富锡铜的青铜器,则最晚在商代晚期已有少数鎏焊件。考古学者认为,两周时期青铜器已采用铜焊工艺。     

The electrostatic systems used for the multipassage magnetic mass spectrometers

Improvement in the power of resolution is desirable in the multiplication of passages in magnetic fields; our guiding principle is to carry out the operation using a single magnetic prism. In the multipassage process the ions must first turn back after leaving the prism. This turnback is obtained by an electrostatic mirror. We obtain a large enough number of passages by placing two mirrors and two systems with time-varying roles at right angles. These systems are referred to as lens-mirror 1. When they act as mirrors, they enable the particles to circulate in a closed circuit; when they act as lenses, they enable the particles to enter the circuit or leave it. The coupling of two multipassage spectrometers is momentarily possible thanks to lens-mirror 2. The function change results from a change in electrode potential. The requirements for these electrostatic systems and their construction are studied.     

Radiation pressure and stability of interferometric gravitational-wave detectors

The effect of radiation pressure on the stability of Fabry-Perot cavities with hanging mirrors is investigated. Such cavities will form an integral part of the laser interferometric gravitational-wave detectors that are being constructed around the globe. The mirrors are hung by means of a pendulum suspension and are locked by servo controls. We assume a realistic servo-control transfer function that satisfies the standard stability criteria. We find that for positive offsets from the resonance of the cavity the system is stable. However, we show that for negative offsets instabilities can occur, although the servo system has the effect of increasing the instability threshold, compared with the nonservoed case. Conditions for stability are finally given, involving the finesse of the cavity, the input power, the mass of the mirrors, the servo gain, and the phase detuning from perfect resonance. Gravitational-wave detectors with arm cavities having a finesse as low as approximately 200 could exhibit instabilities. Some implications for the locking of these detectors are finally given.