Optical and structural elements made of silicon carbide are increasingly found in space instruments. Chemical vapor deposited silicon carbide (CVD-SiC) is used as a reflective coating on SiC optics in reason of its good behavior under polishing. The advantage of applying ion beam figuring (IBF) to CVD-SiC over other surface figure-improving techniques is discussed herein. The results of an IBF sequence performed at the Centre Spatial de Liège on a 100 mm CVD-SiC mirror are reported. The process allowed to reduce the mirror surface errors from 243 nm to 13 nm rms . Beside the surface figure, roughness is another critical feature to consider in order to preserve the optical quality of CVD-SiC . Thus, experiments focusing on the evolution of roughness were performed in various ion beam etching conditions. The roughness of samples etched at different depths down to 3 ≠m was determined with an optical profilometer. These measurements emphasize the importance of selecting the right combination of gas and beam energy to keep roughness at a low level. Kaufman-type ion sources are generally used to perform IBF but the performance of an end-Hall ion source in figuring CVD-SiC mirrors was also evaluated in this study. In order to do so, ion beam etching profiles obtained with the end-Hall source on CVD-SiC were measured and used as a basis for IBF simulations.
In this paper, we present an original concept of plasmonic-related instrumentation platform dedicated to diagnostic biosensing tests out of the laboratory. The developed instrumental platform includes both disposable one-use microfluidic affinity biochip and compact optical readout device for biochip monitoring involving mobile Internet devices for data processing and communication. The biochip includes both microfluidic and optical coupling structures formed into a single plastic slab. The microfluidic path of the biochip operates in passive capillary pumping mode. In the proof-of-concept prototype, we address specifically the sensing format involving Surface Plasmon Resonance phenomenon. The biochip is plugged in the readout device without the use of an index matching fluid. An essential advantage of the developed biochip is that its implementation involves conventional hot embossing and thin film deposition process, perfectly suited for mass production of low-cost microfluidic biochip for biochemical applications.
We present a thermoreflectance-based metrology concept applied to compound semiconductor thin films off-line
characterization in the solar cells scribing process. The presented thermoreflectance setup has been used to evaluate the
thermal diffusivity of thin CdTe films and to measure eventual changes in the thermal properties of 5 μm CdTe films
ablated by nano and picosecond laser pulses. The temperature response of the CdTe thin film to the nanosecond heating
pulse has been numerically investigated using the finite-difference time-domain (FDTD) method. The computational and
experimental results have been compared.
Aspherical optics are more and more exploited in optical set-up since they reduce the number of components and therefore the overall size and weight of the system. Their manufacturing has been made easier by ion beam etching for many years. Nevertheless, the ablation rate has to be known accurately for each material and the degradation of the surface roughness has to be taken under control. Some examples of achievements will be shown. The main key feature is the knowledge of the original absolute shape of the surface to be figured. In some cases, interferometric measurement is not well suited and heavy to set up for high aspherical surfaces with deep sag. To avoid the drawbacks of interferometry measurements, a low cost scanning measurement device has been designed and built whose performance allows defining the topology of any surface up to 150 * 90 mm<sup>2</sup> area with an accuracy better than 80 nm. Perspective of extension to larger surface will be presented.
Volume phase holographic gratings (VPHGs) possess unique properties that make them attractive for numerous applications. After reviewing major VPHG characteristics through theory, we discuss some aspects of the dichromated gelatin recording material and the holographic recording process. The large-scale VPHG research facility set up at the Center Spatial de Liège enables production of VPHGs up to 380 mm in diameter, with fringe frequencies from 315 to 3300 lp/mm. We describe the work that has been undertaken in our laboratory to remove the last limitations inherent in VPHGs.
To increase the size of the volume phase holographic gratings the Centre Spatial de Liege can produce, mosaic technic has been tested and characterized. This method consists of assembling VPH gratings recorded and processed independently into one larger grating. By this way, the final grating size becomes virtually unlimited and dispersive elements can accommodate the largest telescope beams.
The second research line about VPH gratings was the high line frequency domain: ν > 3000 lp/mm. Actually, for these frequencies, diffraction according to TE and TM modes is maximum for different wavelengths. However, it is possible to tune the index modulation to three times what is usually required to use the first diffraction TE peak. In this case, the second TE maximum matches the
first TM maximum and unpolarized light is so entirely diffracted. This article also summarizes our prospects in the field of very high index modulation gratings where Δ<i>n</i> as high as 0.14 has been reached; cryogenic temperature operation for which we have demonstrated our VPH gratings stand -180°C without any Blaze modification; and wavefront correction by post-polishing to minimize diffracted beam aberrations. With this latter technique, λ/6 wavefront over 10 cm diameter has been obtained in the first trial.
A new technique to improve the image quality of Ni replicated X-ray mirror is presented. During the manufacturing of XMM Mirror Module between 1994 to 1999, the classical manufacturing process showed its limits. In 1995, the XMM Mirror Module Qualification Model HEW was around 20 arcsec. In 1998, the fifth Flight Model Mirror Module reached 11 arcsec HEW, with a single mirror shell achieving 8 arcsec HEW. The performance of this technology is namely limited by the integration process of the shells.
The new technique is based on the following philosophy : Firstly, an accurate measurement of each mirror shell after integration. A dedicated metrology system has been built and allows a precise metrology of the actual surface. Secondly, a modification of the mirror shell and of the support to transfer the stress to a non optical active area. Finally, an ion figuring run to correct the residual shape error of the mirror. The control and evaluation of the process is assured by EUV PSF assessment achieved in the FOCAL X facility developed for XMM. The advantages of this new process are to shape the mirrors in their final hardware configuration and the versality of the process enabling improvement of other kinds of high accuracy mirrors.
An ion beam figuring facility is operational at the Centre Spatial de Liege since 1997. Its present capabilities are described. An extensive characterization program is running in order to determine the optimized parameters for various materials and operating conditions. In this frame, tests have been performed on a spherical gold-coated aluminum mirror plated in between the with nickel. The nickel plating was used to be super-polished to a BRDF of 1 10<SUP>-4</SUP> at 1 deg at 10 micrometers wavelength. Micro-roughness and etching rate measurements were realized and influence of ion bombardment on the coating has been established after removal of the gold coating. The gold coating removal of the gold coating. The gold coating removing was performed by using the ion beam flux. Finally, the mirror has been figure from the original sphere to a parabola. Surface characteristics evolution is also described in terms of micro-roughness and surface error. An overview of the research and development programs related to this facility is given. Results of this technique and potential impact on optics fabrication are then briefly exposed.
Ion beam figuring is a deterministic optical fabrication technique which efficiency has been mainly demonstrated on large optics these last years. One of the disadvantages of ion figuring is the high surface temperature of the workpiece. Temperature aspects have already ben mentioned by some authors but are weakly detailed. Therefore thermal effects on BK7 and Zerodur, mainly surface figure distortions and surface temperature measurements, have been investigated here in more detail.