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| == Designing and implementing a thermal compensation system for the 40m arm cavity == | = Tuning Fabry-Perot cavity modal frequencies using controlled thermoelastic deformations on mirror surface = |
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| The goal is to compensate for imperfections that arise due to optical inhomogeneities in the arm cavity mirrors by heating the ETM. The lessons learned from this exercise will help with designing/implementing a similar kind of system for the folding mirrors in the power recycling cavity. |
== Goal == To correct for the modal frequency shifts in the FP arm cavity that arise from the spatial inhomogeneities on the mirror surface. This will be done by imaging heat patterns on the ETM surface. The thermoelastic deformations created on the mirror surface introduces phase shifts to the cavity modes. The green ALS system will be used to mode scan the cavity continuously. A feedback control system will actively correct for the frequency shifts based on the cavity mode scan information. The lessons learned from this exercise will help in designing/implementing a similar kind of system for the folding mirrors in the signal recycling cavity. == System Overview == [[attachment:CTD.pdf]] {{attachment:CTD.jpg|alt text|width=600 height=200}} == Description == === PSL and Arm Green lasers === The PSL laser is locked to the arm cavity using the PDH error signal. The green laser is injected from the ETM side of the arm. The transmitted end-green from the arm interferes with the frequency-doubled PSL and produce a beatnote. The relative phase between the two lasers is kept constant using a phase-locked-loop (PLL) servo. Changing the frequency of the end-green laser will cause the green transmission == Fact-finding == 1. What are the ideal cavity parameters? (a reference to compare the different heating models) 2. Desired tuneable range and achievable range 3. Heaters and heating patterns 4. Practical/hardware limitations in implementing == Simulation/Modelling == 1. Find the ideal/real cavity parameters (higher order mode degeneracy) - SIS 2. Frequency tuning - SIS 3. Heating patterns - COMSOL 4. Thermally perturbed cavity analysis - SIS |
Tuning Fabry-Perot cavity modal frequencies using controlled thermoelastic deformations on mirror surface
Goal
To correct for the modal frequency shifts in the FP arm cavity that arise from the spatial inhomogeneities on the mirror surface. This will be done by imaging heat patterns on the ETM surface. The thermoelastic deformations created on the mirror surface introduces phase shifts to the cavity modes. The green ALS system will be used to mode scan the cavity continuously. A feedback control system will actively correct for the frequency shifts based on the cavity mode scan information.
The lessons learned from this exercise will help in designing/implementing a similar kind of system for the folding mirrors in the signal recycling cavity.
System Overview
== Description ==
PSL and Arm Green lasers
The PSL laser is locked to the arm cavity using the PDH error signal. The green laser is injected from the ETM side of the arm. The transmitted end-green from the arm interferes with the frequency-doubled PSL and produce a beatnote. The relative phase between the two lasers is kept constant using a phase-locked-loop (PLL) servo. Changing the frequency of the end-green laser will cause the green transmission
Fact-finding
- What are the ideal cavity parameters? (a reference to compare the different heating models)
- Desired tuneable range and achievable range
- Heaters and heating patterns
- Practical/hardware limitations in implementing
Simulation/Modelling
- Find the ideal/real cavity parameters (higher order mode degeneracy) - SIS
- Frequency tuning - SIS
- Heating patterns - COMSOL
- Thermally perturbed cavity analysis - SIS