William Brzozowski, David Robertson, Ewan Fitzsimons, Henry Ward, Jennifer Keogh, Alasdair Taylor, Maria Milanova, Michael Perreur-Lloyd, Zeshan Ali, Andrew Earle, Daniel Clarkson, Robyn Sharman, Martyn Wells, Phil Parr-Burman
This paper will present an overview of the LISA (Laser Interferometer Space Antenna) optical bench and discuss the innovative methods developed to analyse and mitigate significant engineering challenges. There are two optical benches for each of the three LISA spacecraft. The optical bench consists of numerous components which form the paths of the interferometers used to measure the displacement changes caused by gravitational waves. Given each spacecraft is separated by 2.5 million Km, a laser beam sent from one to another arrives with a significantly lower irradiance than on departure. It is in part because of this that various engineering challenges are faced by the LISA OB. This is alongside the extremely demanding nature of measuring gravitational waves at a sensitivity of pico-meters per root-Hertz.
L. d'Arcio, J. Bogenstahl, M. Dehne, C. Diekmann, E. Fitzsimons, R. Fleddermann, E. Granova, G. Heinzel, H. Hogenhuis, C. Killow, M. Perreur-Lloyd, J. Pijnenburg, D. Robertson, A. Shoda, A. Sohmer, A. Taylor, M. Tröbs, G. Wanner, H. Ward, D. Weise
For observation of gravitational waves at frequencies between 30 μHz and 1 Hz, the LISA mission will be implemented in a triangular constellation of three identical spacecraft, which are mutually linked by laser interferometry in an active transponder scheme over a 5 million kilometer arm length. On the end point of each laser link, remote and local beam metrology with respect to inertial proof masses inside the spacecraft is realized by the LISA Optical Bench. It implements further- more various ancillary functions such as point-ahead correction, acquisition sensing, transmit beam conditioning, and laser redundancy switching.
A comprehensive design of the Optical Bench has been developed, which includes all of the above mentioned functions and at the same time ensures manufacturability on the basis of hydroxide catalysis bonding, an ultrastable integration technology already perfected in the context of LISA's technology demonstrator mission LISA Pathfinder. Essential elements of this design have been validated by dedicated pre-investigations. These include the demonstration of polarizing heterodyne interferometry at the required Picometer and Nanoradian performance levels, the investigation of potential non-reciprocal noise sources in the so-called backlink fiber, as well as the development of a laser redundancy switch breadboard.
The Laser Interferometer Space Antenna, as well as its reformulated European-only evolution, the New Gravitational-Wave Observatory, both employ heterodyne laser interferometry on million kilometer scale arm lengths in a triangular spacecraft formation, to observe gravitational waves at frequencies between 3 × 10−5 Hz and 1 Hz. The Optical Bench as central payload element realizes both the inter-spacecraft as well as local laser metrology with respect to inertial proof masses, and provides further functions, such as point-ahead accommodation, acquisition sensing, transmit beam conditioning, optical power monitoring, and laser redundancy switching.
These functions have been combined in a detailed design of an Optical Bench Elegant Breadboard, which is currently under assembly and integration. We present an overview of the realization and current performances of the Optical Bench subsystems, which employ ultraprecise piezo mechanism, ultrastable assembly techniques, and shot noise limited RF detection to achieve translation and tilt metrology at Picometer and Nanoradian noise levels.
J. Bogenstahl, M. Tröbs, L. d’Arcio, C. Diekmann, E. Fitzsimons, J. Hennig, F. Hey, C. Killow, M. Lieser, S. Lucarelli, M. Perreur-Lloyd, J. Pijnenburg, D. Robertson, A. Taylor, H. Ward, D. Weise, G. Heinzel, K. Danzmann
LISA (Laser Interferometer Space Antenna) is a proposed space-based instrument for astrophysical observations via the measurement of gravitational waves at mHz frequencies. The triangular constellation of the three LISA satellites will allow interferometric measurement of the changes in distance along the arms. On board each LISA satellite there will be two optical benches, one for each testmass, that measure the distance to the local test mass and to the remote optical bench on the distant satellite. For technology development, an Optical Bench Elegant Bread Board (OB EBB) is currently under construction. To verify the performance of the EBB, another optical bench - the so-called telescope simulator bench - will be constructed to simulate the beam coming from the far spacecraft. The optical beam from the telescope simulator will be superimposed with the light on the LISA OB, in order to simulate the link between two LISA satellites. Similarly in reverse, the optical beam from the LISA OB will be picked up and measured on the telescope simulator bench. Furthermore, the telescope simulator houses a test mass simulator. A gold coated mirror which can be manipulated by an actuator simulates the test mass movements. This paper presents the layout and design of the bench for the telescope simulator and test mass simulator.
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