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

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

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

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

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

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

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

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

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