1. Optical simulation – March 04 1 Optical Simulation François BONDU VIRGO Tools Goals Example: tuning of modulation frequency A few questions

2. Optical simulation – March 04 2 Optical Simulation: TOOLS SIESTAVirgo Collaboration o general mechanical and optical simulationtime domain C, but « cards » for the user JAJYJ.Y. Vinet o Computes TF of optical cavities for GW, frequency noise, mirror motionsfrequency domain Fortran (STF) F. Bondu o Same as JAJY, but only frequency noise. Cavity sweeping is possible ( obsolete since JAJY gives calibrated answers ) Matlab

3. Optical simulation – March 04 3 Optical Simulation: TOOLS NVV. Loriette o Computes the properties of the interferometer cavities (reflection, transmission, gain) using the measured mirror maps o Includes the thermal effectsstatic response Matlab FINESSEA. Freise o Interferometer response, including high order modes o intensive maintenance and upgrade o used by LIGOfrequency domain « cards » from the user point of view; graphical interface Analytical formulae

4. Optical simulation – March 04 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 o Modulation frequency o Cavity lengths o Match the beam parameters (waist size, waist position) 4) Estimate the impact of the thermal effects on the sensitivity 5) Laser power understanding / tuning

5. Optical simulation – March 04 5 Optical Simulation: Example (1/3) Tuning of the modulation frequency with Input Mode Cleaner FSR laser EO ~ x+ ~ ~ 22 MHz6,24.. MHz 1 kHz x Spectrum analyzer 6,24.. MHz mod. frequency 1 kHz line amplitude 1: setup

6. Optical simulation – March 04 6 Optical Simulation: Example (2/3) 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) Tuning of the modulation frequency with Input Mode Cleaner FSR

7. Optical simulation – March 04 7 Optical Simulation: Example (2/3) 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) Tuning of the modulation frequency with Input Mode Cleaner FSR

8. Optical simulation – March 04 8 Optical Simulation: Open questions Evaluate the impact of not-so-often considered asymmetries o asymmetry of the modes of the long cavities radius of curvature, high order mode content… o asymmetry of the lower and upper sidebands o … (birefringence, polarization, …) o get analytical expressions when possible Questions o How much is it possible to increase the finesse of the arms? the recycling gain? o Effect of misalignment/ mismatching on the stability of high unity gain loops? (ex. second stage of frequency stabilization). o Effect of losses (contamination, high order modes) on TF for frequency noise? o Models with different mirror properties for carrier and sidebands

9. Optical simulation – March 04 9 Optical Simulation: Open questions Questions (continued) o Use information from beam shape at various points of the interferometer o Learn about DC control o Simulation of astigmatism o tuning of the matching of the IMC: understand the requirements