Mirror Elements Research Articles

Ultraprecision 5-Axis Control Machining of Fly-Eye Mirror in EUV Lithography

The study deals with the manufacture of so-called fly-eye mirror in EUV lithography by means of an ultraprecision 5-axis control milling. It is extremely difficult to manufacture a highly accurate fly-eye mirror by conventional methods such as photolithography, mechanical cutting by a lathe and so on since it consists of 500 circular arc mirror elements of 15 mm in length and 1 mm in width having a spherical surface of 660 mm in radius and there are minute steps among them. ln order to manufacture fly-eye mirror with high accuracy and efficiency, the study proposes two new machining methods to manufacture spherical surface by employing a rotational single-crystal diamond tool. 0ne is to use a sphere type tool with circular arc cutting edge of 660 mm in radius. The rotation of the cutting tool forms a convex spherical surface of 600 mm in radius within a circle of 1 mm in diameter. The movement of the cutting tool along the circular arc of a mirror elements makes it possible to machine fly-eye mirror elements. Though the method is theoretically efficient, it is found that it is not practical due to the difficulty of manufacturing the tool accurately. The other is to use a flat type tool with the cutting edge angle of 90 degree. The tool enables to manufacture spherical surfaces with any radius by feeding it along the mirror surface and bears practical use because the cutting method is independent of tool form accuracy. Machining experiment was conducted by use of the latter tool. The machined circular are mirror elements of oxgen-free copper show smooth spherical surface and required steps among them without any burrs. lt is found that the proposed method has the potential of producing the fly-eye mirror correctly.

Detecting exo-Earths with hypertelescopes in space: the Exo-Earth Discoverer concept

Densifled-pupil multi-aperture imaging interferometers also called hypertelescopes can provide direct images at their focal plane. Coronagraphic masking is applicable for nulling a star's image and searching associated planets. The scheme is applicable at the infra-red wavelengths where a planet has its best contrast, but also potentially at visible wavelengths where chlorophyll-like spectral features are to be searched. In the infra-red, where zodiacal and exo-zodiacal clouds tend to contaminate the image, the scheme provides a better rejection of this contamination than schemes using a beam-splitter and ∞at interference. For a typical Earth-like exo-planet the detection time is reduced 10 to 100 times. In the visible, planets are often resolved from their star by an interferometer's sub-aperture. Visible coronagraphy is then achievable in each sub-aperture before combining the beams and producing the high-resolution image. This relaxes the piston tolerances. Whether for sub-apertures or a densifled pupil, or even a con- ventional telescope, multiple stages of coronagraphy are of interest, if equipped with as many deformable mirrors or transmissive plates. Located in the successive image planes, such adaptive correctors can phase the residual stellar speckles without afiecting the planet peak. This generates a central peak of starlight, which can be masked without much obstructing the planet's wavefront. A design concept studied for an Exo-Earth Discoverer, a hyper- telescope variant proposed to NASA for its Terrestrial Planet Finder, involves 37 mirror elements of 1 meter, driven by small solar sails and arranged to form a 40-300 meter diluted spherical mirror. One or sev- eral focal combiners move along the focal surface. Optical solutions have been explored in preliminary detail.

Testing extreme ultraviolet optics with visible-light and extreme ultraviolet interferometry

Optics for extreme ultraviolet (EUV) lithography arguably have the most strict fabrication tolerances of any optical systems fabricated to date, and the development of EUV lithography pushes advanced optical fabrication techniques toward never before realized levels of figure accuracy and finish quality. As EUV lithography advances toward viability, the need for ultrahigh-accuracy wave front metrology tools has never been greater. To enable the development of diffraction-limited EUV optical systems, visible-light and EUV interferometries must work in close collaboration. We present a detailed comparison of EUV and visible-light wave front measurements performed across the field of view of a lithographic-quality projection optical system designed for use in the Engineering Test Stand developed by the Virtual National Laboratory and the EUV Limited Liability Company. The comparisons reveal that the present level of root mean square agreement lies in the 0.3–0.4 nm range, with an agreement of 0.15±0.03 nm, excluding astigmatism. Astigmatism is the most significant aberration component for the alignment of this optical system; it is also the dominant term in the discrepancy, and the aberration with the highest measurement uncertainty. With EUV optical systems requiring total wave front quality in the λEUV/50 (0.25 nm) range, and even higher surface-figure quality for the individual mirror elements (∼0.1 nm), improved accuracy through future comparisons, and additional studies, are required.

Phase-correction of turbulent distortions of an optical wave propagating under conditions of strong intensity fluctuations.

Phase correction of a plane wave and a spatiolimited beam propagating through a turbulent layer of atmosphere were considered. The required adaptive corrector element size and the system bandwidth were found by numerical simulation. These requirements were determined to be the same as for a weak-intensity scintillation approximation. The size of the required segmented mirror element was found to be equal to Fried length r0, whereas the tolerable time lag was r0/V, where V is the wind velocity. However, the local slope sensors then became impractical, as did tip-tilt correction over the corrector subapertures.

Improved method for designing a cylindrical Zhang–Enke ion mirror

A series solution for the potential within a cylindrical, three-element Zhang–Enke ion mirror has been obtained. The only simplification is that the small gaps between mirror elements are ignored. Automated function minimization by the simplex method has been used to optimize the mirror region lengths and voltages. Flight times only along the central axis were used here for convenience, but the potential can be calculated fully in three dimensions. The mirror designed by this method has good focusing characteristics. Additional refinement could be obtained by optimization of three-dimensional ion trajectories starting from the one-dimensional parameters obtained here.

The EPSILON experimental pseudo-symmetric trap

Within the framework of the Adaptive Plasma Experiment (APEX) conceptual project, a trap with closed magnetic field lines, the Experimental Pseudo-Symmetric Closed Trap (EPSILON), is examined. The APEX project is aimed at theoretical and experimental development of the physical foundations for a steady state thermonuclear reactor designed on the basis of an alternative magnetic trap with tokamak-like large β plasma confinement. A discussion is given of thefundamental principle of pseudo-symmetry, which a magnetic configuration with tokamak-like plasma confinement should satisfy. Examples are given of calculations in the paraxial approximation of pseudo-symmetric curvilinear elements with a poloidal modulus B isoline. The EPSILON trap, consisting of two direct axisymmetric mirrors linked by two curvilinear pseudo-symmetric elements, is considered. To increase the equilibrium β, the plasma currents are short-circuited within curvilinear equilibrium elements. An untraditional scheme of MHD stabilization for a trap with closed field lines by use of axisymmetric mirrors with a divertor is analysed. The experimental installation EPSILON-One Mirror Element (OME), which is under construction for experimental investigation of stabilization by divertor, is discussed. The opportunity for applying the ECR method of plasma production in EPSILON-OME in conditions of high density and low magnetic field is examined.

Symmetry and antisymmetry in ferroelectric transducers

Many types of symmetry are utilized in crystal physics and engineering acoustics. In addition to the common mirror, rotation, inversion and translation symmetry elements encountered in single crystals and textured ceramics, transducer designers sometimes make use of the antisymmetry elements involved in color groups. We illustrate some potential applications of color symmetry in controlling the vibration modes in ferroelectric and ferromagnetic ceramics prepared as spheres, hemispheres, and rings conforming to black-and-white Curie groups.

224 複雑形状フライアイミラーの開発(OS5 電子部品・光学部品の超精密加工)

The fabrication of a fly-eye mirror used in an extreme ultraviolet lithography system was discussed. This mirror has a complex reflective surface consisting of many arc-shaped mirror elements. To realize the mirror, we focused on a process in which all elements were fabricated individually and then arranged side-by-side to form the mirror. As the first step in this process, the elements were fabricated as follows. Blocks of invar plated with electroless nickel were cut with a wire electric-discharge machine to produce the blanks of the elements. Then one side surface of each blank was polished to obtain a reflective surface. In this manner, the elements were fabricated with sufficient shape accuracy to satisfy the specifications of the fly-eye mirror.

Non-Scanning Rapid Prototyping System using a Digital Micromirror Device

A rapid prototyping system using a digital micromirror device (DMD) has been developed. A DMD is a micro mechanical light modulator with tilting mirror elements. In the developed system, the DMD and a mercury lamp are used as the pattern generator and the UV source, respectively. Since the developed rapid prototyping system does not require a mask or LASER, a simple, low-cost system can be realized. An exposure pattern modulated by the DMD is projected on the saface of the UV resin, and a hardened layer with the same shape as the exposure pattern projected on the resin surface is produced. The model can be constructed in any size by changing the optical magnification. By using illuminance compensation technique, both illumination non-uniformity and excess growth are improved. The model vibration system has been introduced in order to reduce leveling time of the resin. The rapid prototyping system using the DMD is highly cost-effective.

A Novel Non-Linear Ion Mirror with Only Three Elements

A novel tubular ion mirror has been designed for reflectron time-of-flight mass spectrometry (TOF-MS). This design consists of only three cylindrical elements. With this mirror, an electric field is achieved that is non-linear along the mirror axis and has improved off-axis homogeneity compared with conventional simple geometry ion mirrors. The practical operation of this mirror is simpler than that of conventional diaphragm ion mirrors. Design parameters, including the relative lengths and voltages of the three elements, can be determined empirically. Once the mirror depth dimensions have been implemented, the voltages of the middle and rear elements are the only adjustable parameters. The electric field achieved by the mirror deviates only slightly from a linear mirror with constant field strength. The second-order deviation curve reveals two regions of curvature; all ions are turned around in the second curvature region. A plot of arrival time vs ion kinetic energy has a flattened “S” shape. The aspects of this shape are affected by the voltages of the middle and rear elements. SIMION 7 simulation demonstrates that this new non-linear ion mirror can perform second-order kinetic energy correction for large kinetic energy variation (33%) and substantial beam dimensions. Both the ion kinetic energy variation and the mirror element voltages affect the mass resolution obtained with the mirror. Ion trajectory simulations with a 10 mm diameter beam from a standard, two-field source predict that baseline resolution can be 16,000, 7600 and 1200 for 15%, 26% and 33% kinetic energy variations, respectively.

A New Approach to Obtain Alternative Active Building Blocks Realizations based on their Ideal Representations

Abstract This paper describes a systematic approach to obtain alternative realizations for a particular active building block based on its simple ideal representation. The proposed approach relies on the properties of two categories of ideal elements; the well-known nullor elements and the mirror elements, which are basically used to model the active devices featuring voltage or current inverting properties. These ideal elements are used to obtain ideally equivalent nullor-mirror representations for a particular active device. The described approach results in alternative representations which give the designer a choice of circuits that may be used to build the active device with the possibility of enhancing its characteristics. As an example, the proposed approach is used to generate alternative realizations for the negative type of the second-generation current conveyor (CCII-). Most of the CCIIrealizations result in high performance in terms of impedance level, accuracy and frequency response. PSpice simulations that demonstrate the performance of the different realizations are also given.

Satellite-Earth remote sensor scatter effects on Earth scene radiometric accuracy

A general modelling formalism is used to extend near-field point spread function (PSF) measurements over a wide-field off-axis angular range, covering a dynamic range of 5 to 6 orders of magnitude, using bidirectional reflectance distribution function (BRDF) measurements of the scan mirror and other key optical elements. Line spread function (LSF) model results were compared with measured near-field LSF measurements for the Moderate Resolution Imaging Spectroradiometer (MODIS) of the Earth Observing System (EOS), demonstrating excellent agreement between model and measurements. When realistic effects of sensor scattered light are taken into account, significant radiometric bias errors are produced near high-contrast structured scenes (e.g. bright clouds over dark oceans and land; broken snow and ice scenes). Image restoration using an asymptotically exact PSF is shown to produce results significantly different from those produced by traditional near-field 5 × 5, 7 × 7, ..., PSF kernel matrix inversion techniques. The results reported have implications for future remote-sensor specifications and testing, in-flight and surface-based calibration comparisons, and the assessment of radiometric bias errors in the presence of moderate- to high-contrast Earth scenes.

Liquid crystal flow control using microfabrication techniques

One of the more critical parts of the fabrication of high quality liquid crystal over silicon (LCOS) devices is a controlled means of introducing the liquid crystal (LC) into the gap formed between the silicon backplane and the coverglass. Existing backplane fabrication techniques leave the mirror elements standing proud of the silicon die, causing a disruption to the LC flow-front due to capillary pinning. If the LC flow is not uniform in its spatial extent and the filling speed not tightly controlled, LC alignment defects are generated which affect the optical performance of the device in a detrimental way. To gain better control over the LC filling, a process has been developed in which the inter-mirror trenches are filled with a dielectric material. The self-aligning insulator filled trench (SIFT) process is a novel variation on the lift-off process. It has been developed to fill the interpixel trenches, thus producing a smooth planar surface. Different surface preparation processes are compared and it is demonstrated that this new SIFT process leads to even LC spreading, uniform LC alignment and a complete elimination of capillary pinning. The process also provides some insight into the nature of LC surface interactions.

Monte Carlo studies of the COMPASS RICH 1 optical properties

A dedicated Monte Carlo has been built to study the optical properties of the RICH 1 detector presently under construction for the COMPASS experiment at CERN. In this paper we focus on the optimization of the position of the photon detector with respect to the RICH mirror and on the alignment of the mirror elements forming the mirror surface.

Inverting second generation current conveyors: the missing building blocks, CMOS realizations and applications

The concept of voltage mirror is introduced and used, together with the current mirror, to ideally represent the current and voltage inverting properties of some analogue building blocks. The properties of the nullor and mirror elements are used to relate the different devices in the ideal case as well as to define the adjoint network for each building block. Two new types of second generation current conveyor (CCII) are introduced. One is the adjoint of the CCII+ and is named the inverting second generation current conveyor ‘negative’ (ICCII–); the other is the ICCII+. CMOS realizations of the ICCII– are presented and new ICCII– based current mode circuits are obtained by applying a voltage-to-current-mode transformation to the CCII+ based circuits.

Surface micromachined segmented mirrors for adaptive optics

This paper presents recent results for aberration correction and beam steering experiments using polysilicon surface micromachined piston micromirror arrays. Microfabricated deformable mirrors offer a substantial cost reduction for adaptive optic systems. In addition to the reduced mirror cost, microfabricated mirrors typically require low control voltages (less than 30 V), thus eliminating high-voltage amplifiers. The greatly reduced cost per channel of adaptive optic systems employing microfabricated deformable mirrors promise high-order aberration correction at low cost. Arrays of piston micromirrors with 128 active elements were tested. Mirror elements are on a 203-/spl mu/m 12/spl times/12 square grid (with 16 inactive elements, four in each corner of the array). The overall array size is 2.4 mm square. The arrays were fabricated in a commercially available surface micromachining process. The cost per mirror array in this prototyping process is less than $200. Experimental results are presented for a hybrid correcting element comprised of a lenslet array and piston micromirror array, and for a piston micromirror array only. Also presented is a novel digital deflection micromirror that requires no digital to analog converters, further reducing the cost of adaptive optics systems.

Modeling, design, fabrication and measurement of a single layer polysilicon micromirror with initial curvature compensation

A micromirror array for optical phase modulation is designed, fabricated and tested in this paper. It consists of 5×5 single layer polysilicon-based, electrostatically driven actuators. The micromirror array is made by using only two masks and can be driven independently by 25 channel circuits. About 6 π phase modulation can be obtained in He–Ne laser ( λ=633 nm) with 67% fill-factor. The deflection characteristics of the actuators with residual stresses and initial curvature are modeled and confirmed by experiments. The initial curvatures of mirror and spring element are also predicted by an appropriate modeling and compensated by using the gold metallization. The modeling results agree well with the experimental results. The detailed modeling of the deflection characteristics and pull-in behavior and the compensation method of obtaining a flat surface give us more exact prediction and better performance of the optical micromirror.

Self-consistent spatial mode analysis of self-adaptive laser oscillators

A theoretical analysis involving ABCD ray transfer matrices is used to find the self-consistent fundamental spatial mode solutions of self-adaptive laser resonators. The resonators investigated consist of a nonlinear medium in a self-intersecting loop geometry together with a feedback output coupler mirror and additional intracavity elements. A simplified system without intracavity elements is analyzed initially, and an analytic expression for the mode solution is deduced. Addition of an intracavity lens is shown to permit enhancement of the quality of the phase-conjugation process as well as control of the mode size. The theoretical analysis is extended to model an experimental self-adaptive laser oscillator utilizing gain-grating formation in a solid-state Nd:YAG laser amplifier. Good agreement is found between the theory and the experimental results.

Polarization-induced noise in a fiber-optic Michelson interferometer with Faraday rotator mirror elements

Faraday rotator mirror elements have been used in a number of applications as compensators for induced birefringence in retracing paths. In interferometric systems, such as the fiber-optic Michelson interferometer, this approach proved to be useful in providing maximum fringe visibility and insensitivity to the polarization state of light injected into the interferometer. However, it is found that, when the characteristics of the fiber coupler depend on the polarization state of the input beam, the efficiency of the Faraday mirror elements is limited. Theoretical analysis and experimental results in support of this statement are presented.

Time-division multiplexing of polarization-insensitive fiber-optic Michelson interferometric sensors

A system of time-division multiplexing of polarization-insensitive fiber-optic Michelson interferometric sensors that uses Faraday rotator mirror elements is demonstrated. This system is constructed with conventional low-birefringence single-mode fiber and is able to solve the polarization-fading problem by a combination of Faraday rotator mirrors with unbalanced Michelson interferometers. The system is lead-fiber insensitive and has potentials for practical field applications.