This paper presents a recent progress in designing a nanometer-accurate inductive-type of edge sensor. A new
technology of Direct Deposit on Glass (DDG) has been developed. The DDG technology also has high rate of
reproducibility and is suitable for the mass production and still be a very cost-effective solution. The sensor designs are
fully optimized using mechanical and EM modeling for specific metrology needs. We discuss briefly on various
electronic architectures and their impacts on the maintainability of the system. We conclude the paper by showing the
In the framework of the Active Phasing Experiment (APE), four different phasing techniques are tested. The
ZErnike Unit for Segment phasing sensor (ZEUS) is integrated on the APE bench. APE has been tested in
the laboratory before it will be installed on one of the Nasmyth platform of a Very Large Telescope (VLT)
Unit Telescope to perform on sky tests. The ZEUS phasing sensor concept has its origins in the Mach-Zehnder
interferometer equipped with a spatial filter in its focal plane. In this paper, the ZEUS phasing sensor is
described together with its theoretical background and deployment within the APE experiment. The algorithms
and its elements used to reconstruct the wavefront are described. Finally, the preliminary results obtained in
the laboratory are presented.
The purpose of the Active Phasing Experiment, designed under the lead of ESO, is to study new phasing technologies
and to validate wavefront control concepts for Extremely Large Telescopes. The Active Phasing Experiment is currently
tested in the laboratory at the ESO headquarters and will be tested on sky at a Nasmyth focus of a VLT unit telescope at
the end of 2008. The test bench contains four different phasing sensors which are tested in parallel to compare them
under the same conditions. They have been developed by Istituto Nazionale di Astrofisica in Florenze, Instituto
Astrofisica Canarias in Tenerife, Laboratoire d'Astrophysique de Marseille and ESO. It includes also an Active
Segmented Mirror which simulates the segmentation of a primary mirror. A non-contact optical metrology has been
developed by Fogale Nanotech to control it. The VLT focus and the VLT atmospheric conditions are simulated in the
laboratory with a turbulence generator producing a seeing between 0.45 and 0.85 arcsec. Once installed on a VLT unit
telescope, the control system of the Active Phasing Experiment will be able to control the phasing of the ASM, but also
the guiding and the active optics of the VLT. This proceeding gives a brief summary of the opto-mechanical aspects of
the Active Phasing experiment, describes its control system and gives an analysis of the preliminary results obtained in
The largest telescopes (ELT) involve a highly segmented primary mirror. The monitoring of the mirror shape use
thousands of sensors, located on segment edges, which measure the relative piston, tip and tilt of all segments.
Today, telescopes with segmented primary mirrors use
capacitance-based edge sensors. Although this technology offers
excellent metrological performances, its practical use is limited by the intrinsic sensitivity to humidity, dust and
condensation, whose effect exceeds the requirements for future ELTs.
Being specialized in both capacitive and inductive metrology, Fogale nanotech has developed a novel concept of edge
sensors using the inductive technology, which does not suffer from humidity, condensation, and dust effects. Cost
effective sensor with specific layout, associated electronics, demonstrated metrological performance (sub-nanometer
resolution and nanometer stability) that outperforms the capacitive concept.
This paper presents a non-contact optical metrology measuring the pistons and tip/tilt angles of the 61 hexagonal
segments of a compact-sized segmented mirror. The instrument has been developed within the scope of a design
study for a European Extremely Large Telescope (E-ELT). It is used as reference sensor for cophasing of the
mirror segments in closed loop control. The mirror shape is also measured by different types of stellar light-based
phasing cameras whose performances will be evaluated with regard to a future E-ELT. Following a description
of the system architecture, the second part of the paper presents experimental results demonstrating the level of
precision: 0.48nm RMS in piston and 0.074 μrad RMS in tip and tilt.
The 10-m class Southern African Large Telescope (SALT) at Sutherland, South Africa, was inaugurated in November 2005, following completion of all its major sub-systems. It is the largest single optical telescope in the southern hemisphere. The SAMS (Segment Alignment Measurement System) is a unique capacitive edge sensing solution for the active alignment of the SALT primary mirror. Twelve thin film edge sensors are bonded directly onto the edges of each of the 91 segments, with heat-generating control electronics housed remotely in temperature-controlled enclosures. The SAMS is capable of measuring the tip/tilt and piston of each segment, as well as the change in global radius of curvature, a mode normally undetected by such a system. The primary objective was to build a system that offered an excellent cost-to-performance ratio without sacrificing measurement accuracy, a very necessary requirement because of the scale and number of sensors required for large segmented mirrors. This paper describes the results obtained during the commissioning and calibration of the completed system.
Nuclear magnetic resonance (NMR) measurements have become an important part of oilfield well-logging to identify and quantify oil and gas reservoirs. In this paper, some design aspects of NMR sensor for well-logging applications are discussed. The RF and static magnetic fields are computed using a 3D finite element method (FEM). A perturbation technique along with FEM is used to evaluate the power loss in conductors that avoids the need for small discretization steps along the conductor thickness. The magnet is built by stacking several magnet segments along the axial direction and the objective is to magnetize and shape these segments in such a way so as to produce a desired field profile in front of the magnet. An optimal control technique is used in conjunction with the FEM to speed up the design process with signal-to-noise ratio, frequency of operations, depth of investigation, and prepolarization time being the optimization constraints. Very good agreement between the measured and computed antenna efficiency and magnetic field is obtained thus validating the numerical model.