LIGO Scientific Collaboration

Advanced Interferometer Configurations
Working group

Chair: Ken Strain

QND workshop

AEI, Hanover, December, 5th, 2005
Selected presentations:

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In its first stage the Laser Interferometric Gravitational wave Observatory (LIGO) uses power recycled cavity enhanced Michelson interferometer. Such an interferometer uses cavities in each arm to increase the signal. The sensitivity of these detectors is mainly limited by seismic, thermal and shot noise.
Seismic motion changes distances and has to be decoupled from the test masses. This is done with passively damped stacks with low resonance frequencies and low Q's. In addition, the mirrors are suspended with steel wires so that they act as pendulums with low resonance frequencies (around 1Hz) and high Q's. The motion at that resonance frequency is reduced with active feedback loops.
The thermal environment delivers 1/2 kT energy in each eigenmode of the system. Interesting eigenmodes are the eigenmodes of the pendulum and the eigenmodes of the substrate. A high Q in each eigenmode concentrates the thermal energy in a small frequency band around the eigenfrequency. Absorption of the laser fields in the optics creates hot spots which also changes the length of the interferometer arms.
Absorption also increases the temperature, causes thermal lensing and degradation of the spatial mode of the beam.Thermal lensing and beam degradation is one of the main technological challenges of Advanced LIGO.
The signal to shot noise limit is essentially caused by the photon counting error. The sensitivity of each interferometer can be enhanced by increasing the phase shift of the light in the interferometer using a more advanced configuration. Cavities in the arms are one example. The second way to increase the signal to shot noise limit is simply to increase the stored light power in the arms of the interferometer. But the finite abosrption of optical components and subsequent thermal lensing effects limit the power to probably 1MW in the arms in the foreseeable future.

The Lasers and Optics working group is developing brighter and better laser sources and studies optical components with higher internal Q and lower absorption.
The Suspensions and Seismic Isolation working group is developing better suspension systems for the optical components.
The goal of the advanced interferometer working group is to find and work on new optical configurations with the goal to increase the signal amplitude, detector bandwidth or to reduce the most fundamental noise: Quantum Noise.

None of these working groups can work isolated from the others because a change in one area affects usually all other areas. For example, a change in the optical configuration will change the light distribution in the interferometer and will also change the signal degradation through thermal lensing.

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The first LIGO detectors are build and are either taking data or people are working on fine tuning the interferometer. The sensitivity is closing in on the design sensitivity and first significant upper limits for gravitational radiation were already established.

Advanced LIGO will improve the sensitivity by another order of magnitude using more power, better optical components, better suspension systems, and a new optical configuration which is either called detuned signal recycling or detuned resonant sideband extraction.
In the past the AIC working group coordinated experiments performed by AIC members at the University of Florida, at the California Institute of Technology, and at the Australian National University. All three groups developed sensing and control schemes for this new optical configuration. The experimental and theoretical findings of all three experiments fed into the sensing and control scheme which is now the baseline for Advanced LIGO. The results were published in parallel in four papers which appeared on 1st March 2003 in Applied Optics Vol.42, No. 7.
Currently, the AIC is extending their sensing and control scheme to include wavefront sensing for spatial beam controls like angular alignment and active mode matching. It also continues to study thermal noise and its impact on the sensitivity as well as designs which potentially reduce the thermal noise. One of the leading approaches is to use larger beam sizes or non Gaussian beams (for example mexican hat beams). Members of the AIC also developed The AIC also oversees and coordinates the R&D program at the JIF interferometer at the University of Glasgow and the 40m-interferometer at the California Institute of Technology. Both prototypes are studying sensing and control effects for Advanced LIGO.

Beyond Advanced LIGO in AIC:
The direction for the Advanced LIGO research is more or less fixed and we have a very tight time scale. In contrast to this, the research beyond Advanced LIGO is very open for new ideas and has virtually no time scale. This is also the reason that it is much more difficult or impossible to summarize the actual and the expected activities. But we can try to define classes of possible improvements. One class of new designs depends heavily on the use of all reflective optics, e.g. phase gratings with low losses. White light cavities belong to this class. A Sagnac interferometer is another promising configuration which is mainly being examined by the Stanford group. Another class of new designs wants to tailor the interaction between the electromagnetic fields and atoms to increase the phase shift or the bandwidth of the detector. The length amplifier, Kerr media, and QND-systems belong to this class. These designs sometimes combine the white light cavity approach with active laser media inside the interferometer. Other QND based systems utilize squeezed light that is either generated inside the interferometer or enters the interferometer through the dark port. These systems are often based on additional 4km long cavities in the output beam that taylor the phase of the signal sidebands. In any case, the realization of an actual gravitational wave detector based on these technologies is not expected any time soon.

Software Tools for Advanced Interferometer Configurations is an irregularly held workshop implemented to present and exchange software tools for the modelling of optical interferometers. It also provides the community with a server for all programs made to simulate optical interferometers.

Progress Reports are available at
Look for groups with an attachment with letter D (ACIGA, Florida, GEO, and Stanford).

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University of Florida:
Guido Mueller
Volker Quetschke
David Reitze
David Tanner
Hsin-Jung Lin

Trinity University
Dennis Ugolini

Northwestern University
Max Kelner
Subramanian Krishnamurthy
Mary Salit
Selim Shahriar
Yanbei Chen
Dennis Coyne
Erika D'Ambrosio
Riccardo DeSalvo
Ron Drever
Jay Heefner
Bill Kells
Luca Matone
Miyakawa Osamu
Kip Thorne
Rob Ward
Alan Weinstein
Phil Willems
Stan Whitcomb
Hiro Yamamoto
Bryan Barr
Simon Chelkowski
Stefan Danilishin
Andreas Freise
Jan Harms
Martin Hewitson
Stefan Hild
Sabina Huttner
Harald Lueck
Roman Schnabel
Ken Strain
Benno Willke
Australian National University:
Jong Chow
Benedict Cusack
Glen De Vine
Malcolm Gray
David McClelland
Stanford University:
Dan DeBra
Ray Beausoleil
Peter Beyersdorf
Robert Byer
Marty Fejer
Ke-Xun Sun

Columbia University
Szabolcs Marka
Keiko Kokeyama
Sato Shuichi
Masa-katsu Fujimoto
Seiji Kawamura
Fumiko Kawazoe
Volker Leonhardt
Atsushi Nishizawa
Shihori Sakata
Kentaro Somiya
Syracuse University:
Peter Saulson

Moscow University:
Vladimir Braginski
Farid Khalili
Sergey Vyachanin
LIGO-Lab., Hanford, WA:
Daniel Sigg

University of Rochester
Adrian Melissinos
Peter Fritschel
Gregg Harry
Nergis Mavalvala
David Shoemaker
Thomas Corbitt

Email to all the members listed above.

(If you want to be included as a member and listed here, please send your address to Guido Mueller.)

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Memoranda of Understanding are available at:

Design studies and white papers about advanced interferometer configurations:
Interferometer Configuration Issues for LIGO II
White Paper
LIGO II Configuration options

Informal reports and notes:
Spring 2001-reports
Spring 2000-reports
Modecleaner Noise (first draft)
DRreport.pdf Summary of the DR-Experiment in Florida
July2000-updates with NEW parameters

More informations about LIGO II can be found at:

A collection of notes/papers about Advanced LIGO:

Signal Sensing

Sensing and Control in Dual-Recycling Laser Interferometer Gravitational-Wave Detectors, Kenneth Strain et al., Appl. Optics, 42(7), pg. 1244 (2003)
Dual-recycled cavity-enhanced Michelson interferometer for gravitational-wave detection, Guido Mueller et al., Appl. Opt. 42(7), pg. 1257 (2003)
Signal extraction and optical design for an advanced gravitational-wave interferometer, James Mason, Phil Willems, Appl. Opt. 42(7), pg. 1269 (2003)
Power-recycled Michelson interferometer with resonant sideband extraction, D.A. Shaddock et al., Appl. Opt. 42(7), pg 1283 (2003)
Kentaro New Photodetection Method using Unbalanced Sideband for Squeezed Quantum Noise in Gravitational Wave Interferometer, Kentaro Somiya
P010042-01 Advanced LIGO Optical Configuration and Prototyping Effort, Alan Weinstein
P010042-00 Advanced LIGO Optical Configuration, Prototyping, and Modeling (long version), Alan Weinstein
G010322-00 Development of an RSE Interferometer using the Third Harming Demodulation, Osamu Miyakawa
T010064-00.pdf A Study of Gravitational Waves and The Responde of Advanced LIGO as Tep-Level Parameters are varied, Lisa Goggin, Alan Weinstein
T-020021-00-D.pdf Sideband Requirements in Advanced LIGO, Guido Mueller
T020023-00-D.pdf Signal Sensing in Advanced LIGO, Guido Mueller

Pointing Requirements and Wavefront Sensing

T020022-01.pdf Pointing Requirements in Advanced LIGO, Guido Mueller
G030111-00 Wavefront Sensing for Advanced LIGO, Alan Weinstein, Marcus Benna
T020144-00.pdf Wavefront Sensing in Dual-Recycled Interferometers, Alan Weinstein, Marcus Benna, T020144-00


G020429-00 40 Meter Lab program for AdvLIGO R&D, Alan Weinstein
G030033-00 40m Laboratory Upgrade Progress Report, Osamu Miyakawa
T010115-00.pdf Conceptual Design of the 40 meter Laboratory Upgrade for Prototyping an Advanced LIGO Interferometer, Alan Weinstein
T000121-00.pdf Determining Lengths and Optical Parameters for Dual Recycling at the 40m LIGO Prototype, Ted Jou, Alan Weinstein

Garching Prototype

Keita.pdf Dynamical bandwidth control of the dual-recycled interferometer was demonstrated using Garching 12m prototype, Keita Kawabe


T010160-00.pdf Simulations of Advanced LIGO: comparisons between Twiddle and E2E, Richard George, Alan Weinstein

Spatial Profiles, Thermal lensing

T030009-00-R.pdf Status Report on Maxican-Hat Flat-Topped Beams for Advanced LIGO, Erika D'Ambrosio, Richard O'Shaughnessy, Sergey Strigin, Kip S. Thorne, Sergey P. Vyatchanin
P000001-00.pdf Determination and optimization of mode matching into optical cavities by heterodyne detection, Guido Mueller, Qi-ze Shu, Rana Adhikari, D.B. Tanner, David Reitze, Daniel Sigg, Nergis Mavalvala, Jordan Camp, Opt. Lett. 25(4), p 266 (2000)

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Beyond Advanced LIGO

G030090-00 White Light Cavities, Guido Mueller, Stacy Wise, David Reitze, D.B. Tanner

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Web page (occasionally) maintained by Guido Mueller .
Last updated July 10, 2003.