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Optical Simulation

Optical Simulation. Tools Goals Example: tuning of modulation frequency A few questions. François BONDU VIRGO. Optical Simulation: TOOLS. SIESTA Virgo Collaboration general mechanical and optical simulation time domain C, but « cards » for the user JAJY J.Y. Vinet

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Optical Simulation

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  1. Optical Simulation Tools Goals Example: tuning of modulation frequency A few questions • François BONDU • VIRGO 1

  2. 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 2

  3. 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 3

  4. 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 4

  5. 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 5

  6. 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) 6

  7. 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) 7

  8. 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 8

  9. 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 9

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