Advanced LIGO subsystems
are the organizational units of the overall project. Follow the links below to view the mission and progress of each subsystem.

Auxiliary Optics Core Optics
Data Acquisition Data and
Input Optics

LIGO Technology Development and Migration

Explore the menu of case study links (left) to view impacts of LIGO technology across the broader science and engineering community.

Technology Type:  Sensor Technology

EUCLID Displacement Sensor

** Institution:  University of Birmingham
** Contact:  Clive Speake  
0121 414 4679
** Funding Agency:  PPARC Innovative Technology Fund
** Technology Source:  LIGO Scientific Collaboration (LSC) members
      outside of LIGO Laboratory

 Patent Thumbnail

[cs eds]Interferometers are excellent instruments for measuring displacements. In fact interferometric gravitational-wave detectors provide the best displacement sensitivity of any scientific instruments. However, there are three challenges to using simple interferometers as displacement sensors. First, they require that the mirror whose displacement is to be sensed must be aligned in pitch and yaw with respect to the light beam. Second, interferometers are often limited in their dynamic range. And third, the sensor must have very good internal mechanical and thermal stability consistent with the required displacement sensitivity. The Advanced LIGO suspension alignment sensors use shadow sensors. These are simple and sensitive at the nm level. The interferometric displacement sensor was developed at Birmingham University as part of the United Kingdom contribution to Advanced LIGO risk reduction. This work resulted in a patented invention (US2010/0238456 A1) that uses homodyne interferometry to overcome the dynamic range problem, a compact and very stiff mechanical design using low CTE material to achieve stability, and a clever optical design to achieve a tolerance against mirror pitch and yaw misalignment of more than 1 degree. In addition to providing risk reduction for Advanced LIGO the EUCLID sensor also provides a possible upgrade path to an improved suspension system beyond Advanced LIGO.[cs eds]


1.  An Interferometer-based Optical Readout Scheme for the LISA Proof-Mass  Stuart Aston and Clive Speake  AIP Conference Proceeding Nov. 26, 2006 Vol. 873, pp. 326-333
2.  Optical Readout Techniques for the Control of Test-Masses in Gravitational Wave Observatories   Stuart Aston,  LIGO DCC Number G1100826-v1
3.  Mirror Tilt Immunity Interferometry with a Cat's Eye Retroreflector   Peña-Arellano et al.   Applied Optics   Volume: 50   Issue: 7   Pages: 981-991   2011