Optical Simulation

1

• Optical Simulation

Tools Goals Example tuning of modulation
frequency A few questions

• François BONDU
• VIRGO

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Optical Simulation TOOLS

• SIESTA Virgo Collaboration
• general mechanical and optical simulation time
  domain
• C, but  cards  for the user
• JAJY J.Y. Vinet
• Computes TF of optical cavities
• for GW, frequency noise, mirror
  motions frequency domain
• Fortran
• (STF) F. Bondu
• Same as JAJY, but only frequency noise. Cavity
  sweeping is possible
• ( obsolete since JAJY gives calibrated answers
  )
• Matlab

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Optical Simulation TOOLS

• NV V. Loriette
• Computes the properties of the interferometer
  cavities
• (reflection, transmission, gain) using the
  measured mirror maps
• Includes the thermal effects static response
• Matlab
• FINESSE A. Freise
• Interferometer response, including high order
  modes
• intensive maintenance and upgrade
• used by LIGO frequency domain
•  cards  from the user point of view graphical
  interface
• Analytical formulae

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Optical Simulation GOALS

• 1) Understand and tune the contrast defect
• shot noise level and modulation index
• 2) Understand and tune the interferometer
  asymmetry
• frequency noise rejection ratio / optical TF for
  stabilization
• 3) Tune the instrument
• Modulation frequency
• Cavity lengths
• Match the beam parameters (waist size, waist
  position)
• 4) Estimate the impact of the thermal effects on
  the sensitivity
• 5) Laser power understanding / tuning

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Optical Simulation Example (1/3)
Tuning of the modulation frequency with Input
Mode Cleaner FSR
1 setup
laser
EO
EO
1 kHz line amplitude

22 MHz
6,24.. MHz

x

6,24.. MHz mod. frequency
x

1 kHz
Spectrum analyzer
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Optical Simulation Example (2/3)
Tuning of the modulation frequency with Input
Mode Cleaner FSR
2 results
FINESSE prediction A  bump  appears if
demodulation phase is not correct. The  good 
frequency point is the one that does not change
of place for various demodulation phases (various
cable lengths)
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Optical Simulation Example (2/3)
Tuning of the modulation frequency with Input
Mode Cleaner FSR
3 results
FINESSE prediction A  bump  appears if
demodulation phase is not correct. The  good 
frequency point is the one that does not change
of place for various demodulation phases (various
cable lengths)
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Optical Simulation Open questions

• Evaluate the impact of not-so-often considered
  asymmetries
• asymmetry of the modes of the long cavities
• radius of curvature, high order mode content
• asymmetry of the lower and upper sidebands
• (birefringence, polarization, )
• get analytical expressions when possible
• Questions
• How much is it possible to increase the finesse
  of the arms? the recycling gain?
• Effect of misalignment/ mismatching on the
  stability of high unity gain loops? (ex. second
  stage of frequency stabilization).
• Effect of losses (contamination, high order
  modes) on TF for frequency noise?
• Models with different mirror properties for
  carrier and sidebands

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Optical Simulation Open questions

• Questions (continued)
• Use information from beam shape at various
  points of the interferometer
• Learn about DC control
• Simulation of astigmatism
• tuning of the matching of the IMC understand
  the requirements