Ion beam machining error control and correction for small scale optics

Ion beam figuring (IBF) technology for small scale optical components is discussed. Since the small removal function can be obtained in IBF, it makes computer-controlled optical surfacing technology possible to machine precision centimeter- or millimeter-scale optical components deterministically. Using a small ion beam to machine small optical components, there are some key problems, such as small ion beam positioning on the optical surface, material removal rate, ion beam scanning pitch control on the optical surface, and so on, that must be seriously considered. The main reasons for the problems are that it is more sensitive to the above problems than a big ion beam because of its small beam diameter and lower material ratio. In this paper, we discuss these problems and their influences in machining small optical components in detail. Based on the identification-compensation principle, an iterative machining compensation method is deduced for correcting the positioning error of an ion beam with the material removal rate estimated by a selected optimal scanning pitch. Experiments on ?10?mm Zerodur planar and spherical samples are made, and the final surface errors are both smaller than λ/100 measured by a Zygo GPI interferometer.     

Including outer scale effects in zonal adaptive optics calculations

Mellin transform techniques are applied to evaluate the covariance of the integrated turbulence-induced phase distortions along a pair of ray paths through the atmosphere from two points in a telescope aperture to a pair of sources at finite or infinite range. The derivation is for the case of a finite outer scale and a von Karman turbulence spectrum. The Taylor hypothesis is assumed if the two phase distortions are evaluated at two different times and amplitude scintillation effects are neglected. The resulting formula for the covariance is a power series in one variable for the case of a fixed atmospheric wind velocity profile and a power series in two variables for a fixed wind-speed profile with a random and uniformly distributed wind direction. These formulas are computationally efficient and can be easily integrated into computer codes for the numerical evaluation of adaptive optics system performance. Sample numerical results are presented to illustrate the effect of a finite outer scale on the performance of natural and laser guide star adaptive optics systems for an 8-m astronomical telescope. A hypothetical outer scale of 10 m significantly reduces the magnitude of tilt anisoplanatism, thereby improving the performance of a laser guide star adaptive optics system if the auxiliary natural star used for full-aperture tip/tilt sensing is offset from the science field. The reduction in higher-order anisoplanatism that is due to a 10-m outer scale is smaller, and the off-axis performance of a natural guide star adaptive optics system is not significantly improved.     

Fabrication of small complex-shaped optics by plasma chemical vaporization machining with a microelectrode

We have developed plasma chemical vaporization machining by using a microelectrode for the fabrication of small complex-shaped optical surfaces. In this method, a 0.5 mm diameter pipe microelectrode, from which processing gas is drawn in, generates a small localized plasma that is scanned over a workpiece under numerical computer control to shape a desired surface. A 12 mm x 12 mm nonaxisymmetric mirror with a maximum depth of approximately 3 microm was successfully fabricated with a peak-to-valley shape accuracy of 0.04 microm in an area excluding the edges of the mirror. The average surface roughness was 0.58 nm, which is smooth enough for optical use.     

Ion-beam damage in hollandite

The phenomenon of ion-beam damage in hollandite, first reported by Headley [1], has been investigated in the hollandite phase in Synroc, and a related electron-beam damage phenomenon has been investigated in a synthetic barium aluminium hollandite. An explanation of the beam damage phenomena is proposed in terms of twinning in the monoclinic form of hollandite.     

Fabrication of optics by use of plasma chemical vaporization machining with a pipe electrode

We figure optical surfaces by plasma chemical vaporization machining (CVM) with a pipe electrode, in which an rf plasma generated at the electrode tip under approximately atmospheric pressure moves over the surfaces. We propose a shaping method in which the movement of plasma on the surfaces can be determined. Flat and aspheric surfaces are successfully figured with the desired peak-to-valley shape accuracy of 0.1 microm. The root-mean-square roughness of the resultant surfaces is at the subnanometer level. These results confirm that the plasma CVM and the shaping method have the capability to fabricate optics with high accuracy.     

Medium-precision null-screen testing of off-axis parabolic mirrors for segmented primary telescope optics: the large millimeter telescope

The feasibility of using null screens for testing the segments of a parabolic segmented telescope mirror for the Large Millimeter Telescope (LMT) is analyzed. An algorithm for designing the null screen for testing the off-axis segments of conic surfaces is described. Actual screen designs for the different classes of segments of the LMT are presented. The sensitivity of the test and the required accuracies for the fabrication and positioning of the screen are analyzed. A measuring accuracy of approximately 12 microm in surface sagitta is within the reach of the technique.     

Double-layer imprint lithography on wafers and foils from the submicrometer to the millimeter scale

In this paper, a thermal imprint technique, double-layer nanoimprint lithography (dlNIL), is introduced, allowing complete filling of features in the dimensional range of submicrometer to millimeter. The imprinting and filling quality of dlNIL was studied on Si substrates as a model system and compared to results obtained with regular NIL (NIL) and reverse NIL (rNIL). Wavy foils were imprinted with NIL, rNIL and dlNIL and the patterning results compared and discussed. With dlNIL, a new application possibility was introduced in which two different resists having, for example, a different etch resistance to a certain plasma were combined within one imprint step. dlNIL allows extension to many resist combinations for tailored nanostructure fabrication.     

Ion-beam sputtering and nanostructures of noble metals

Using the technique of ion-beam sputtering on gold (Au) and silver (Ag) metal films, metal nanoclusters vis-à-vis nanostructure materials are synthesized on silica glass substrates. Analyses of Rutherford backscattering spectra of Ar⁺-ion irradiated films confirm the ion-beam sputtering of metal films. Exponential decrease of experimentally measured areal density of Au atoms with the increase of ion doses has been elucidated. Optical absorption spectroscopy results reveal the formation of metal nanoclusters on the glass substrates. Red shift of the surface-plasmon resonance position due to the sputtering induced size reduction of Au nanoclusters on the silica substrates has been explained. Size reduction in this case is further corroborated with the scanning electron microscopy results.     

Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics

Cr/Sc and Ni/V multilayers, intended as normal incidence soft x-ray mirrors and Brewster angle polarizers, have been synthesized by employing a novel modulated low-energy and high-flux ion assistance as a means of engineering the interfaces between the subnanometer layers on an atomic scale during magnetron sputter deposition. To reduce both roughness and intermixing, the ion energy was modulated within each layer. The flat and abrupt interfaces yielded soft x-ray mirrors with near-normal incidence reflectances of R = 20.7% at the Sc 2p absorption edge and R = 2.7% at the V 2p absorption edge. Multilayers optimized for the Brewster angle showed a reflectance of R = 26.7% and an extinction ratio of R(s)/R(p)=5450 for Cr/Sc and R = 10% and R(s)/R(p)=4190 for Ni/V. Transmission electron microscopy investigations showed an amorphous Cr/Sc structure with an accumulating high spatial frequency roughness. For Ni/V the initial growth mode is amorphous and then turns crystalline after approximately 1/3 of the total thickness, with an accumulating low spatial frequency roughness as a consequence. Elastic recoil detection analyses showed that N was the major impurity in both Cr/Sc and Ni/V with concentrations of 15 at. % and 9 at. %, respectively, but also O (3 at. % and 1.3 at. %) and C (0.5 at. % and 1.9 at. %) were present. Simulations of the possible normal incidence reflective properties in the soft x-ray range of 100-600 eV are given, predicting that reflectivities of more than 31% for Cr/Sc and 5.8% for Ni/V can be achieved if better control of the impurities and the deposition process is employed. The simulations also show that Cr/Sc is a good candidate for mirrors for the photon energies between the absorption edges of B (E = 188 eV) and Sc (E = 398.8 eV).     

Ion-beam engineering of Co/TiO2 multilayer nanostructures

Multilayer structures consisting of Co/TiO₂ bilayers with partial layer thicknesses varied within several nanometers and a total thickness of up to 100 nm were obtained using the ion-beam sputter deposition method and studied using a combination of analytical techniques. It is shown that, in [Co(2 nm)/TiO₂(2 nm)]₁₅, [Co(2 nm)/TiO₂(4 nm)]₁₅, and [Co(4 nm)/TiO₂(4 nm)]₁₂ structures, the mean-square surface roughness does not exceed 0.9 nm, all partial layers are continuous, all interfaces are plane-parallel and sharp, and the characteristics of each layer are close to those of the corresponding bulk material. The [Co(2 nm)/TiO₂(4 nm)]₁₅ structure is characterized by the maximum transparency (exceeding 7% in he visible spectral range. The properties of these multilayer films are promising for applications in magnetooptics and spintronics. The surfaces of [Co(4 nm)/TiO₂(2 nm)]₁₅ and [Co(6 nm)/TiO₂(2 nm)]₁₂ structures have mean-square roughnesses above 1 nm and exhibit percolations with a surface density of up to 5 × 10⁷ cm^?2. A decrease in the partial layer thickness below 2 nm leads to the mixing of layers, while an increase in the thickness of individual TiO₂ layers above 6 nm leads to significant differences of the optical transmission spectrum from that of the anatase form of TiO₂ and to a decrease in the transparency.     

Ion-beam etching for the precise manufacture of optical coatings

We propose using ion-beam etching as an additional tool for the accurate control of the thickness of thin films during the manufacture of sensitive optical multilayer coatings. We use a dual ion-beam sputtering system in the deposition and etch modes. In the deposition mode both the assist and sputtering ion beams are used to produce dense films at deposition rates in the range of 0.1-0.3 nm/s. In the etch mode, only the assist ion beam is used to remove material at a rate of less than 0.1 nm/s. A very high precision in the layer thicknesses can be obtained by alternating between deposition and etch modes. We observed that etching did not significantly affect the surface quality and the uniformity of the coatings. We introduced etching into our current manufacturing process and demonstrated its potential for the fabrication of several optical multilayer systems with performances that are very sensitive to the thickness of their layers.     

Ion-beam processing of single crystal diamond using SOG mask

Various ion-beam etching characteristics of diamond and selectivity between diamond and spin-on-glass (SOG) were examined. The maximum selectivity of diamond and SOG was 12.7 in oxygen reactive ion-beam etching process at 100 V acceleration voltage. Using this etching condition and dot-shaped SOG mask, conical diamond field electron emitter arrays with 30 nm curvature radius, 2.58 μm base radius and 5.86 μm height were fabricated.     

离子束溅射沉积Co膜光学特性的尺寸效应研究

本文采用离子束溅射沉积了不同厚度的Co膜,利用Lambda-900分光光度计,对不同厚度的Co膜从波长为310nm到1300nm范围测量了薄膜的反射率和透射率.选定波长为310、350、400、430、550、632、800、1200nm时对薄膜的反射率、透射率和吸收率随薄膜厚度变化的关系进行讨论.实验结果显示,Co膜的光学特性都有明显的尺寸效应.对在可见光范围内同一波长时的反射率和透射率随薄膜厚度变化关系的实验结果作于同一图上,发现反射率曲线与透射率曲线都有一个处在网状膜阶段的交点,这个交点对应的厚度作为特征厚度,该厚度可认为是金属薄膜生长从不连续膜进入连续膜的特征判据.     

Applied optics of optics and opticists. Physics and street lighting

Sodium lamps for street lighting have been produced by Philips for several decades. Continuing research has improved the quality of these lamps and modified them to meet the demands of professional users.     

离子束溅射Si薄膜的纵向结晶性分析

研究了离子束溅射制备微晶硅薄膜的生长纵向结晶演化过程.纵向分布Raman光谱分析显示,当硅薄膜厚度减薄时,表面硅层的结晶峰强度明显减弱,峰位有微弱的蓝移.最薄的样品显示为非晶态结构.当Raman激光聚焦斑点向64.5nm厚的薄膜样品深层面聚焦取样时,微晶硅薄膜的结晶性先由表层向下逐渐变好,最大晶粒尺寸达3.318nm,最高晶化率达47.6%.最后,当激光聚焦斑点到达薄膜与玻璃衬底的界面孵化层时,硅薄膜显非晶态.     

反应离子束溅射沉积和还原退火工艺制备VO_x多晶薄膜

通过反应离子溅射沉积和后退火工艺制备出优质微测辐射热计用的氧化钒薄膜。对薄膜退火前后进行了扫描电子显微镜分析,结果表明,制备的VOx多晶薄膜致密均匀,退火后晶粒尺寸变大。电学测试表明,在室温时薄膜的方块电阻约为50kΩ,电阻温度系数为-0.022/K,满足制作高性能微测辐射热计的要求。     

Scattering optics of snow

Permanent snow and ice cover great portions of the Arctic and the Antarctic. It appears in winter months in northern parts of America, Asia, and Europe. Therefore snow is an important component of the hydrological cycle. Also, it is a main regulator of the seasonal variation of the planetary albedo. This seasonal change in albedo is determined largely by the snow cover. However, the presence of pollutants and the microstructure of snow (e.g., the size and shape of grains, which depend also on temperature and on the age of the snow) are also of importance in the variation of the snow's spectral albedo. The snow's spectral albedo and its bidirectional reflectance are studied theoretically. The albedo also determines the spectral absorptance of snow, which is of importance, e.g., in studies of the heating regime in snow. We investigate the influence of the nonspherical shape of grains and of close-packed effects on snow's reflectance in the visible and the near-infrared regions of the electromagnetic spectrum. The rate of the spectral transition from highly reflective snow in the visible to almost totally absorbing black snow in the infrared is governed largely by the snow's grain sizes and by the load of pollutants. Therefore both the characteristics of snow and its concentration of impurities can be monitored on a global scale by use of spectrometers and radiometers placed on orbiting satellites.