Precision absolute positional measurement of laser beams

We describe an instrument which, coupled with a suitable coordinate measuring machine, facilitates the absolute measurement within the machine frame of the propagation direction of a millimeter-scale laser beam to an accuracy of around ±4  μm in position and ±20  μrad in angle

Automated precision alignment of optical components for hydroxide catalysis bonding

We describe an interferometric system that can measure the alignment and separation of a polished face of a optical component and an adjacent polished surface. Accuracies achieved are ∼ 1μrad for the relative angles in two orthogonal directions and ∼ 30μm in separation. We describe the use of this readout system to automate the process of hydroxide catalysis bonding of a fused-silica component to a fused-silica baseplate. The complete alignment and bonding sequence was typically achieved in a timescale of a few minutes, followed by an initial cure of 10 minutes. A series of bonds were performed using two fluids - a simple sodium hydroxide solution and a sodium hydroxide solution with some sodium silicate solution added. In each case we achieved final bonded component angular alignment within 10 μrad and position in the critical direction within 4 μm of the planned targets. The small movements of the component during the initial bonding and curing phases were monitored. The bonds made using the sodium silicate mixture achieved their final bonded alignment over a period of ∼ 15 hours. Bonds using the simple sodium hydroxide solution achieved their final alignment in a much shorter time of a few minutes. The automated system promises to speed the manufacture of precision-aligned assemblies using hydroxide catalysis bonding by more than an order of magnitude over the more manual approach used to build the optical interferometer at the heart of the recent ESA LISA Pathfinder technology demonstrator mission. This novel approach will be key to the time-efficient and low-risk manufacture of the complex optical systems needed for the forthcoming ESA spaceborne gravitational waves observatory mission, provisionally named LISA

Cyrille Rollet, La circulation culturelle d’un sitcom américain, Voyage au cœur de « Growing Pains », tome 2

Cyrille Rollet, docteur de l’École des hautes études en sciences sociales (ehess), consacre un ouvrage en deux volumes au sitcom américain Growing Pains. Si le premier tome de l’ouvrage, Physiologie d’un sitcom américain, Voyage au Cœur de « Growing Pains » (Paris, Éd. L’Harmattan, coll. Champs visuels, 2006), était consacré aux valeurs et discours développés par la série, le second s’attache à l’analyse de celle-ci dans une perspective intertextuelle. En s’intéressant à ce sitcom domestique ..

Cyrille Rollet, La circulation culturelle d’un sitcom américain, Voyage au cœur de « Growing Pains », tome 2.

Cyrille Rollet, docteur de l’École des hautes études en sciences sociales (ehess), consacre un ouvrage en deux volumes au sitcom américain Growing Pains. Si le premier tome de l’ouvrage, Physiologie d’un sitcom américain, Voyage au Cœur de « Growing Pains » (Paris, Éd. L’Harmattan, coll. Champs visuels, 2006), était consacré aux valeurs et discours développés par la série, le second s’attache à l’analyse de celle-ci dans une perspective intertextuelle. En s’intéressant à ce sitcom domestique ..

A la recherche de la centralité perdue

Les mutations majeures de l'organisation de l'espace économique semblent remettre en question le concept de centralité et ses applications tout particulièrement à l'échelle de la ville, des réseaux de villes et de l'économie globalisée. L'étalement urbain fait émerger une centralité diffuse, multiple. La globalisation recompose les flux matériels et immatériels, et redistribue le pouvoir économique au bénéfice des villes globales. Une analyse précise des termes « centre » et « centralité » et des phénomènes qu'ils recouvrent permet de montrer que les schémas classiques, convenablement adaptés, restent pertinents à l'échelle des villes, mais que de nouveaux schémas de centralité apparaissent bien au niveau mondial, essentiellement sur une base réticulaire. / The major changes of economic space organization seem to cast doubt over the concept of centrality and its applications, especially at the city, city network and global economy scales. Urban sprawl gives rise to a diffused or multiple centrality. Economic globalization reorganizes material and immaterial flows, and redistributes economic power to the advantage of global cities. A precise analysis of the terms center and centrality and of the phenomena they refer to permits to show that the classical patterns, if they are properly adapted, remain relevant at the urban scale, but that new centrality patterns are emerging at the world scale, on a reticular basis.VILLE;MONDIALISATION;RESEAU;CENTRALITE

Construction of rugged, ultrastable optical assemblies with optical component alignment at the few microradian level

A method for constructing quasimonolithic, precision-aligned optical assemblies is presented. Hydroxide-catalysis bonding is used, adapted to allow optimization of component fine alignment prior to the bond setting. We demonstrate the technique by bonding a fused silica mirror substrate to a fused silica baseplate. In-plane component placement at the submicrometer level is achieved, resulting in angular control of a reflected laser beam at the sub-10-μrad level. Within the context of the LISA Pathfinder mission, the technique has been demonstrated as suitable for use in space-flight applications. It is expected that there will also be applications in a wide range of areas where accuracy, stability, and strength of optical assemblies are important

Construction of an optical test-bed for eLISA

In the planned eLISA mission a key part of the system is the optical bench that holds the interferometers for reading out the inter-spacecraft distance and the test mass position. We report on ongoing technology development for the eLISA optical system like the back-link between the optical benches and the science interferometer where the local beam is interfered with the received beam from the distant spacecraft. The focus will be on a setup to investigate the tilt-to-pathlength coupling in the science interferometer. To test the science interferometer in the lab a second bench providing a laser beam and a reference interferometer is needed. We present a setup with two ultra-stable low expansion glass benches and bonded optics. To suppress the tilt-to-pathlength coupling to the required level (few μm/rad) imaging optics are placed in front of the interferometer photo diodes

Mechanisation of Precision Placement and Catalysis Bonding of Optical Components

Precision-aligned, ultra-stable optical assemblies are needed for an increasing number of space applications, in areas such as science, metrology and geodesy

Sub-system mechanical design for an eLISA optical bench

We present the design and development status of the opto-mechanical sub-systems that will be used in an experimental demonstration of imaging systems for eLISA. An optical bench test bed design incorporates a Zerodur® baseplate with lenses, photodetectors, and other opto-mechanics that must be both adjustable - with an accuracy of a few micrometers - and stable over a 0 to 40°C temperature range. The alignment of a multi-lens imaging system and the characterisation of the system in multiple degrees of freedom is particularly challenging. We describe the mechanical design of the precision mechanisms, including thermally stable flexure-based optical mounts and complex multi-lens, multi-axis adjuster mechanisms, and update on the integration of the mechanisms on the optical bench

Design and construction of an optical test bed for LISA imaging systems and tilt-to-length coupling

The laser interferometer space antenna (LISA) is a future space-based interferometric gravitational-wave detector consisting of three spacecraft in a triangular configuration. The interferometric measurements of path length changes between satellites will be performed on optical benches in the satellites. Angular misalignments of the interfering beams couple into the length measurement and represent a significant noise source. Imaging systems will be used to reduce this tilt-to-length coupling. We designed and constructed an optical test bed to experimentally investigate tilt-to-length coupling. It consists of two separate structures, a minimal optical bench and a telescope simulator. The minimal optical bench comprises the science interferometer where the local laser is interfered with light from a remote spacecraft. In our experiment, a simulated version of this received beam is generated on the telescope simulator. The telescope simulator provides a tilting beam, a reference interferometer and an additional static beam as a phase reference. The tilting beam can either be a flat-top beam or a Gaussian beam. We avoid tilt-to-length coupling in the reference interferometer by using a small photo diode placed at an image of the beam rotation point. We show that the test bed is operational with an initial measurement of tilt-to-length coupling without imaging systems. Furthermore, we show the design of two different imaging systems whose performance will be investigated in future experiments