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.
Through the years many stable optical mounts have been designed, analyzed and tested at TNO. This paper gives an overview of the design principles used. Various examples are presented together with verification test results.
The use of adhesives in combination with an iso-static mount design allows mounting of optical components in a limited volume with limited deformation of the optical surfaces due to thermal and mechanical loads. Relatively large differences in thermal expansion over large temperature ranges can be overcome using a simple and predictable design at reasonable costs. Despite adhesives have limited dimensional stability and loadability, stable optical mounts can be realized when proper design principles are used.
Path length errors caused by beamwalk over the surface topography of optical components can have a detrimental influence on the accuracy of highly sensitive translational metrology, that is of particular relevance for In-Field Pointing payload concepts, investigated for the LISA space mission. This paper presents the results of our experimental and theoretical investigations in surface induced path length errors with a detailed characterisation of their magnitudes.
The LISA Optical Stability Characterization project is part of the LISA CTP activities to achieve the required Technology Readiness Level (TRL) for all of the LISA technologies used. This activity aims demonstration of the Telescope Assembly (TA), with a structure based on CFRP technology, that a CTE of 10-7 1/K can be achieved with measures to tune the CTE to this level. In addition the demonstration is required to prove that the structure exhibits highly predictable mechanical distortion characteristics when cooling down to - 90°C, during outgassing in space and when going from 1g environment to 0g.
This paper describes the test facilities as well as the first test results. A dedicated test setup is designed and realized to allow monitoring dimensional variations of the TA using three interferometers, while varying the temperature in a thermal vacuum chamber. Critical parameters of the verification setup are the length metrology accuracy in thermal vacuum and the thermal vacuum flexibility and stability. The test programme includes Telescope Assembly CTE measurements and thermal gradient characterization.
Detection and observation of gravitational waves requires extreme stability in the frequency range 0.03 mHz to 1 Hz. The Laser Interferometer Space Antenna (LISA) mission will attain this by creating a giant interferometer in space, based on free floating proof masses in three spacecrafts. Due to orbit evolution and time delay in the interferometer arms, the direction of transmitted light changes. To solve this problem, a picometer stable Point-Ahead Angle Mechanism (PAAM) was designed, realized and successfully tested. The PAAM concept is based on a rotatable mirror. The critical requirements are the contribution to the optical path length (less than 1.4 pm / rt Hz) and the angular jitter (less than 8 nrad / rt Hz). Extreme dimensional stability is achieved by manufacturing a monolithical Haberland hinge mechanism out of Ti6Al4V, through high precision wire erosion. Extreme thermal stability is realized by placing the thermal center on the surface of the mirror. Because of piezo actuator noise and leakage, the PAAM has to be controlled in closed-loop. To meet the requirements in the low frequencies, an active target capacitance-to-digital converter is used. Interferometric measurements with a triangular resonant cavity in vacuum proved that the PAAM meets the requirements.
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.
Detection and observation of gravitational waves requires extreme stability in the frequency range 3e-5 Hz to 1 Hz. NGO/LISA will attain this by creating a giant interferometer in space, based on free floating proof masses in three spacecrafts. To operate NGO/LISA, the following piezo mechanisms are developed:
1. A piezo stack mechanism (Point Angle Ahead Mechanism) Due to time delay in the interferometer arms, the beam angle needs to be corrected. A mechanism rotating a mirror with a piezo stack performs this task. The critical requirements are the contribution to the optical path difference (less than 1.4 pm/√Hz) and the angular jitter (less than 8 nrad/√Hz).
2. A piezo sliding mechanism (Fiber Switching Unit Actuator)
To switch from primary to the redundant laser source, a Fiber Switching Unit Actuator (FSUA) is developed. The critical requirements are the coalignment of outgoing beams of <+/-1 micro radian and <+/-1 micro meter. A redundant piezo sliding mechanism rotates a wave plate over 45 degrees.
3. A piezo stepping mechanism (In Field Pointing Mechanism)
Due to seasonal orbit evolution effects, beams have to be corrected over a stroke of +/-2.5 degrees. The critical requirements are the contribution to the optical path difference (less than 3.0 pm/√Hz) and the angular jitter (less than 1 nrad/√Hz). Due to the large stroke, a piezo stepping concept was selected. Dedicated control algorithms have been implemented to achieve these challenging requirements.
This paper gives description of the designs and the ongoing process of qualifying the mechanisms for space applications.
Detection and observation of gravitational waves requires extreme stability in the frequency range 3e-5 Hz to 1 Hz.
NGO/LISA will attain this by creating a giant interferometer in space, based on free floating proof masses in three
spacecrafts.
To operate NGO/LISA, the following piezo mechanisms are developed:
1. A piezo stack mechanism (Point Angle Ahead Mechanism)
Due to time delay in the interferometer arms, the beam angle needs to be corrected. A mechanism rotating a mirror with
a piezo stack performs this task. The critical requirements are the contribution to the optical path difference (less than 1.4
pm/√Hz) and the angular jitter (less than 8 nrad/√Hz).
2. A piezo sliding mechanism (Fiber Switching Unit Actuator)
To switch from primary to the redundant laser source, a Fiber Switching Unit Actuator (FSUA) is developed. The
critical requirements are the coalignment of outgoing beams of <+/-1 micro radian and <+/-1 micro meter. A redundant
piezo sliding mechanism rotates a wave plate over 45 degrees.
3. A piezo stepping mechanism (In Field Pointing Mechanism)
Due to seasonal orbit evolution effects, beams have to be corrected over a stroke of +/-2.5 degrees. The critical
requirements are the contribution to the optical path difference (less than 3.0 pm/√Hz) and the angular jitter (less than 1
nrad/√Hz). Due to the large stroke, a piezo stepping concept was selected. Dedicated control algorithms have been
implemented to achieve these challenging requirements.
This paper gives description of the designs and the ongoing process of qualifying the mechanisms for space applications.
Adhesives are widely used in optomechanical structures for bonding optical components to their mounts. The main
advantage of using adhesives is the excellent strength to weight ratio. Adhesive bonding is seen as a desirable joining
technique as it allows for greater flexibility in design. A disadvantage of adhesives however is the limited dimensional
stability and loadability. To design stable optical mounts, accurate prediction of stresses and deformation is therefore
needed.
Adhesives show strong temperature and loading history dependent behavior. Viscoelastic material models are needed for
accurate prediction of stresses and strains in bonded joints. However, representative material data for adhesives is
difficult to find.
In this research, an experimental framework is build up to determine relevant mechanical properties of adhesives for
improving stress and deformation prediction. This paper shows the results of the characterization experiments and
modeling techniques. Also the implementation of material models in finite element code is briefly discussed. The
obtained models are used in the mount design in the EUCLID and TROPOMI programs as described in “Ultra stable isostatic
bonded optical mount design for harsh environments, J.A.C.M Pijnenburg et al” (this conference).
Through the years many stable optical mounts have been designed, analyzed and tested at TNO. This paper gives an
overview of the design principles used. Various examples are presented together with verification test results.
The use of adhesives in combination with an iso-static mount design allows mounting of optical components in a limited
volume with limited deformation of the optical surfaces due to thermal and mechanical loads. Relatively large
differences in thermal expansion over large temperature ranges can be overcome using a simple and predictable design at
reasonable costs. Despite adhesives have limited dimensional stability and loadability, stable optical mounts can be
realized when proper design principles are used.
The LISA Optical Stability Characterization project is part of the LISA CTP activities to achieve the required
Technonlogy Readiness Level (TRL) for all of the LISA technologies used. This activity aims demonstration of the
Telescope Assembly (TA), with a structure based on CFRP technology, that a CTE of 10-7 1/K can be achieved with
measures to tune the CTE to this level. In addition the demonstration is required to prove that the structure exhibits
highly predictable mechanical distortion characteristics when cooling down to -90°C, during outgassing in space and
when going from 1g environment to 0g.
This paper describes the test facilities as well as the first test results. A dedicated test setup is designed and realized to
allow monitoring dimensional variations of the TA using three interferometers, while varying the temperature in a
thermal vacuum chamber. Critical parameters of the verification setup are the length metrology accuracy in thermal
vacuum and the thermal vacuum flexibility and stability. The test programme includes Telescope Assembly CTE
measurements and thermal gradient characterization.
Detection and observation of gravitational waves requires extremely accurate displacement measurement in the
frequency range 0.03 mHz to 1 Hz. The Laser Interferometer Space Antenna (LISA) mission will attain this by creating a
giant interferometer in space, based on free floating proof masses in three spacecrafts. Due to orbit evolution and time
delay in the interferometer arms, the direction of transmitted light changes. To solve this problem, a picometer stable
Point-Ahead Angle Mechanism (PAAM) was designed, realized and successfully tested. The PAAM concept is based on
a rotatable mirror. The critical requirements are the contribution to the optical path length (less than 1.4 pm / rt Hz) and
the angular jitter (less than 8 nrad / rt Hz). Extreme dimensional stability is achieved by manufacturing a monolithical
Haberland hinge mechanism out of Ti6Al4V, through high precision wire erosion. Extreme thermal stability is realized by placing the thermal center on the surface of the mirror. Because of piezo actuator noise and leakage, the PAAM has to be
controlled in closed-loop. To meet the requirements in the low frequencies, an active target capacitance-to-digital
converter is used. Interferometric measurements with a triangular resonant cavity in vacuum proved that the PAAM meets the requirements.
The LISA Technology Package (LTP) aboard of LISA pathfinder mission is dedicated to demonstrate and verify key technologies for LISA, in particular drag free control, ultra-precise laser interferometry and gravitational sensor. Two inertial sensor, the optical interferometry in between combined with the dimensional stable Glass ceramic Zerodur structure are setting up the LTP. The validation of drag free operation of the spacecraft is planned by measuring laser interferometrically the relative displacement and tilt between two test masses (and the optical bench) with a noise levels of 10pm/√Hz and 10 nrad/√Hz between 3mHz and 30mHz. This performance and additionally overall environmental tests was currently verified on EM level. The OB structure is able to support two inertial sensors (≈17kg each) and to withstand 25 g design loads as well as 0...40°C temperature range. Optical functionality was verified successfully after environmental tests. The engineering model development and manufacturing of the optical bench and interferometry hardware and their verification tests will be presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.