Xiao-Dong Wang

Development and calibration of the Moon-based EUV Camera for Chang’e-3

The process of development and calibration for the first Moon-based extreme ultraviolet (EUV) camera to observe Earths plasmasphere is introduced and the design, test and calibration results are presented. The EUV camera is composed of a multilayer film mirror, a thin film filter, a photon-counting imaging detector, a mechanism that can adjust the direction in two dimensions, a protective cover, an electronic unit and a thermal control unit. The center wavelength of the EUV camera is 30.2 nm with a bandwidth of 4.6 nm. The field of view is 14.7 degrees with an angular resolution of 0.08 degrees, and the sensitivity of the camera is 0.11 count s(-1) Rayleigh(-1). The geometric calibration, the absolute photometric calibration and the relative photometric calibration are carried out under different temperatures before launch to obtain a matrix that can correct geometric distortion and a matrix for relative photometric correction, which are used for in-orbit correction of the images to ensure their accuracy.

A model for thickness effect on the band gap of amorphous germanium film

A Mott-Davis-Paracrystalline model was proposed to interpret thickness effect of the band gap for amorphous germanium (a-Ge). We believe that a-Ge has a semiconductor-alloy-like structure, it may contain medium-range order (MRO) and continuous random network (CRN) simultaneously and there is a dependence of MRO/CRN ratio on film thickness and preparation methods/parameters. For MRO is dominant, thickness effect can be described by one-dimensional quantum confinement (ODQC) effect of nanocrystals and strain-induced shrinkage of the band gap; For CRN is dominant, thickness dependence can be interpreted by changes in the quality of a CRN and ODQC effect of nanoamorphous phase.

Design and fabrication of far ultraviolet filters based on π-multilayer technology in high- k materials

Application of π-multilayer technology is extended to high extinction coefficient materials, which is introduced into metal-dielectric filter design. Metal materials often have high extinction coefficients in far ultraviolet (FUV) region, so optical thickness of metal materials should be smaller than that of the dielectric material. A broadband FUV filter of 9-layer non-periodic Al/MgF2 multilayer was successfully designed and fabricated and it shows high reflectance in 140–180 nm, suppressed reflectance in 120–137 nm and 181–220 nm.

Design and Fabrication of Far-Ultraviolet Reflective Broadband Filter Based on Dielectric Materials:

In the far-ultraviolet (UV) region, optical materials are dispersive and absorbing. The previous successful design method utilized in the visible band should be re-examined. We report on the design and fabrication of a far-UV reflective broadband filter based on dielectric materials lanthanum fluoride (LaF3) and magnesium fluoride (MgF2). Extended bandwidth technology is utilized in designing this filter. The obtained filter has a high reflectance in the working wavelength range of 140–180 nm, meanwhile, with good suppression in shorter and longer wavelength regions. In 2016, this filter was employed in a wide-angle aurora imager (WAAI) installed in the Feng Yun III satellite that will be launched in China.

Piezoelectric Actuated Phase Shifter Based on External Laser Interferometer: Design, Control and Experimental Validation

To improve the phase-shifting accuracy, this paper presents a novel integrated framework for design, control and experimental validation of the piezoelectric actuated phase shifter with a trade-off between accuracy and cost. The piezoelectric actuators with built-in sensors are adopted to drive the double parallel four-bar linkage flexure hinge-based mechanisms. Three mechanisms form the tripod structure of the assembled phase shifter. Then, a semi-closed loop controller with inner feedback and outer feedforward loops via the external laser interferometer is developed for accurate positioning of the phase shifter. Finally, experiments related with travel range, step response, linearity and repeatability are carried out. The linearity error is 0.21% and the repeatability error of 10 μm displacement is 3 nm. The results clearly demonstrate the good performance of the developed phase shifter and the feasibility of the proposed integrated framework.

Analysis and reduction of the TDI CCD charge transfer image shift

Based on the description of the charge transfer process of a time delay integration charge coupled device (TDI CCD), it is pointed out that the relative displacement of the target image and the transferred charge introduces the charge transfer image shift problem in a line transfer period, which leads to the decrease of the modulation transfer function (MTF) in the scanning direction. Based on the basic definition of MTF, the charge transfer image shift model of the TDI CCD is established. According to the quantitative calculation of this model, the MTF curves of the three-phase TDI CCD are obtained under the condition of different pulse widths of computer interface (CI) signals. The MTF changes with the pulse width of CI signals, and the maximum value at the spatial Nyquist frequency is obtained when the CI signals are equally spaced, which is difficult to achieve in the actual system because of the limitation of computed radiography readout signals. In this paper, we present the improved TDI CCD driving timing, which makes it possible to realize the equal interval distribution of CI signals by adjusting the technology compatibility kit signal. Finally, the experimental platform is built, and the MTF curves are calculated from the obtained target images. The result is consistent with the theoretical model.

Detection of an ordered-structure fraction in amorphous silicon

Amorphous silicon (a-Si) films were prepared by radio frequency magnetron sputtering. Spectroscopic ellipsometry (SE) was utilized to detect an ordered-structure fraction in a-Si. The SE analysis of a-Si films with different thicknesses (7.0–140.0 nm) demonstrates that no more than 2.81% of medium-range order exists in the samples, and interestingly, there is a thickness dependence of optical constants for a-Si in the range of 1.5–5.0 eV.

Selective visual attention based clutter metric with human visual system adaptability.

Most existing clutter metrics are proposed based on fixed structural features and experienced weight measures. In this paper, we identify the clutter as selective visual attention effects and propose a type of clutter metric. First, adaptive structural features are extracted from the blocks with an edge-structure similarity to the target. Next, the confusing blocks are selected by the similarity threshold based on the attention guidance map. The clutter is estimated by quantifying the effects of confusing blocks on target acquisition performance. The comparative field experiments, with a Search_2 dataset, show that the proposed metric is consistent with the adaptability of the human visual system (HVS) and outperforms other metrics.

In-situ and real time stress of 30.4 nm Mo/Si multilayer mirror for the moon-based EUV camera

Applications of Mo/Si multilayer mirrors for the moon-based extreme ultraviolet Camera (EUVC) require not only the minimal residual stress, but also little stress changes in the temperature environment on lunar surface. Hence, we deposit the 16.5 nm period Mo/Si multilayer mirror with a low as-deposited residual stress of -36 Mpa (compressive). The in-situ and real time stress tests are measured in the temperature cycling range from 20 °C to 130 °C. The results indicate that the stress gradually increases to the maximum of -100 MPa when heating up to 105 °C, then it gradually relaxes to 10 Mpa after thermal cycling to 130 °C. Such stress change has little influence on the performance of the Mo/Si multilayer mirror.