Interferometer Simulations and Lock Acquisition in LIGO 
Interferometer Simulations and Lock Acquisition in LIGO
by Caltech / Kip Thorne
Video Lecture 45 of 69
Copyright Information: This video is taken from a 2002 Caltech on-line course on "Gravitational Waves", organized and designed by Kip S. Thorne, Mihai Bondarescu and Yanbei Chen. The full course, including this and many other lecture videos, exercises, solutions to exercises, and lists of relevant reading, are available on the web at http://elmer.caltech.edu/ph237/
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Date Added: July 21, 2010

Lecture Description

Interferometer Simulations and Lock Acquisition in LIGO - Week 13, Lecture 24, Part 1  [by Matt Evans]

  1. Simulations of all or part of a LIGO interferometer
  1. What a simulation is
  2. Types of simulations:
  1. Frequency domain: fast, but limited to linear systems
  2. Time domain: slower, but necessary for nonlinearities

Example of a simulation:  Control system for a Fabry Perot cavity:

  1. Laser excites Fabry Perot cavity; returning light tapped off by Faraday isolator, detected to produce electronic signal which drives a magnetic actuator that adjusts a cavity mirror to lock the cavity to the laser.
  2. Simulation of the optics, the electronics, the mirror's mechanics, and the electromechanical transducers
  3. Linear parts of system treated via transfer functions

In complex system such as LIGO: subsystems (e.g. the above) treated as modules

Uses of simulations:

  1. Quantify things that can't be measured experimentally
  2. Selectively turn on and off noise sources

LIGO end-to-end (E2E) simulation system

  1. Used to develop and implement lock-acquisition method for LIGO-I
  2. Being prepared for detailed noise tracking in LIGO-I

Lock acquisition in LIGO-I

  1. What is lock acquisition?
  2. Locking a single Fabry Perot cavity
  1. Pound-Drever-Hall (PDH) error signal ("demod signal")
  2. lock acquisition contrasted with maintaining lock once acquired: nonlinear vs. linear
  3. Acquisition error signal = (demod signal)/(cavity power) - linear over length changes ~ wavelength
  4. Control (actuation) force to lock

        B. Locking a LIGO-I interferometer

  1. Four degrees of freedom must be locked using five error signals from three readout ports
  2. 5 x 4 dimensional sensing matrix (degrees of freedom -> error signals)
  1. Invertible in pieces (largest 2x2 piece, then 3x3, then 4x4) -> lock acquisition in stages

        c. 5 states of interferometer, from totally unlocked through partial locks to totally locked

        d. Examples of evolution through the 5 states: experimental data compared with simulations

Course Index

  1. The Nature of Gravitational Waves
  2. Gravitational Waves Data Analysis
  3. Gravitational Wave Sources in Neutron Stars
  4. Introduction to General Relativity: Tidal Gravity
  5. Mathematics of General Relativity: Tensor Algebra
  6. Mathematics of General Relativity: Tensor Differentiation
  7. Introduction to General Relativity (4/5)
  8. Introduction to General Relativity (5/5)
  9. Weak Gravitational Waves in Flat Spacetime (1/6)
  10. Weak Gravitational Waves in Flat Spacetime (2/6)
  11. Weak Gravitational Waves in Flat Spacetime (3/6)
  12. Weak Gravitational Waves in Flat Spacetime (4/6)
  13. Weak Gravitational Waves in Flat Spacetime (5/6)
  14. Weak Gravitational Waves in Flat Spacetime (6/6); Propagation of Gravitational Waves Through Curved Spacetime (1/5)
  15. Propagation of Gravitational Waves Through Curved Spacetime (2/5)
  16. Propagation of Gravitational Waves Through Curved Spacetime (3/5)
  17. Propagation of Gravitational Waves Through Curved Spacetime (4/5)
  18. Propagation of Gravitational Waves Through Curved Spacetime (5/5)
  19. Generation of Gravitational Waves by Slow-Motion Sources in Curved Spacetime (1/2)
  20. Generation of Gravitational Waves by Slow-Motion Sources in Curved Spacetime (2/2)
  21. Astrophysical Phenomenology of Binary-Star GW Sources (1/5)
  22. Astrophysical Phenomenology of Binary-Star GW Sources (2/5)
  23. Astrophysical Phenomenology of Binary-Star GW Sources (3/5)
  24. Astrophysical Phenomenology of Binary-Star GW Sources (4/5)
  25. Astrophysical Phenomenology of Binary-Star GW Sources (5/5); Post-Newtonian G-Waveforms for LIGO & Its Partners (1/2
  26. Post-Newtonian Gravitational Waveforms for LIGO & Its Partners (2/2)
  27. Supermassive Black Holes and their Gravitational Waves (1/3)
  28. Supermassive Black Holes and their Gravitational Waves (2/3)
  29. Supermassive Black Holes and their Gravitational Waves (3/3); Gravitational Waves from Inflation (1/2)
  30. Gravitational Waves from Inflation (2/2)
  31. Gravitational Waves from Neutron-Star Rotation and Pulsation (1/2)
  32. Gravitational Waves from Neutron-Star Rotation and Pulsation (2/2)
  33. Numerical Relativity as a Tool for Computing GW Generation (1/2)
  34. Numerical Relativity as a Tool for Computing GW Generation (2/2)
  35. The Physics Underlying Earth-Based Gravitational Wave Interferometers (1/4)
  36. The Physics Underlying Earth-Based Gravitational Wave Interferometers (2/4)
  37. The Physics Underlying Earth-Based Gravitational Wave Interferometers (3/4)
  38. The Physics Underlying Earth-Based Gravitational Wave Interferometers (4/4)
  39. Overview of Real LIGO Interferometers (1/2)
  40. Overview of Real LIGO Interferometers (2/2)
  41. Thermal Noise in LIGO Interferometers and its Control (1/2)
  42. Thermal Noise in LIGO Interferometers and its Control (2/2)
  43. Control Systems and Laser Frequency Stabilization (1/2)
  44. Control Systems and Laser Frequency Stabilization (2/2)
  45. Interferometer Simulations and Lock Acquisition in LIGO
  46. Seismic Isolation in Earth-Based Interferometers
  47. Quantum Optical noise in GW Interferometers (1/2)
  48. Quantum Optical noise in GW Interferometers (2/2)
  49. LIGO data analysis (1/2)
  50. LIGO data analysis (2/2)
  51. The Long-Term Future of LIGO: Facility Limits
  52. The Long-Term Future of LIGO: Techniques for Improving on LIGO-II
  53. Large Experimental Science and LIGO as an Example (1/2)
  54. Large Experimental Science and LIGO as an Example (2/2)
  55. Resonant-Mass GW Detectors for the HF Band (1/2)
  56. Resonant-Mass GW Detectors for the HF Band (2/2)
  57. CAJAGWR talk by W.O. Hamilton on Resonant-Mass GW Detectors
  58. Doppler tracking of spacecraft for GW detection in the low frequency band
  59. Pulsar timing for GW detection in the very low frequency band
  60. LISA (Laser Interferometer Space Antenna) for GW Detection in LF Band: Conceptual Design (1/2)
  61. LISA (Laser Interferometer Space Antenna) for GW Detection in LF Band: Conceptual Design (2/2)
  62. LISA's Lasers and Optics (1/2)
  63. LISA's Lasers and Optics (2/2)
  64. Time-Delay Interferometry [TDI] for LISA (1/2)
  65. Time-Delay Interferometry [TDI] for LISA (2/2)
  66. LISA's Distrubance Reduction System (DRS) [Drag-Free System] (1/2)
  67. LISA's Distrubance Reduction System (DRS) [Drag-Free System] (2/2)
  68. The Big-Bang Observatory [BBO]: A Possible Follow-On Mission to LISA
  69. GW's from Inflation and GW Detection in ELF Band via Anisotropy of CMB Polarization

Course Description

Caltech's Physics 237-2002: Gravitational Waves
A Web-Based Course organized and Designed by Kip S. Thorne, Mihai Bondarescu and Yanbei Chen.

This course contains all the materials from a graduate-student-level course on Gravitational Waves taught at the California Institute of Technology, January through May of 2002. The materials include Quicktime videos of the lectures, lists of suggested and supplementary reading, copies of some of the readings, many exercises, and solutions to all exercises. The video files are so large that it may not be possible to stream them from most sites, but they can be downloaded. Alternatively, the course materials on DVD's can be borrowed via Interlibrary Loan from the Caltech Library (click on CLAS, then on Call Number, then enter QC179.T56 2002 ).

Questions and issues about this course and website can be directed to Mihai Bondarescu or Yanbei Chen.

Resources:

Credits:
Lectures by Thorne and Guest Lecturers*
Video of lectures by Bondarescu and Chen
Homework problems by Thorne and Guest Lecturers
Homework solutions by Bondarescu and Chen

*John Armstrong (JPL), Barry Barish, Erik Black, Alessandra Buonanno, Yanbei Chen, Riccardo De Salvo, Ronald Drever, Matt Evans, William Folkner (JPL), William Hamilton (LSU), Mark Kamionkowski, Albert Lazzarini, Lee Lindblom, Sterl Phinney, Mark Scheel, Bonny Schumaker (JPL), Robert Spero (JPL), Alan Weinstein, Phil Willems.

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