Differences between revisions 33 and 36 (spanning 3 versions)

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

CTD.pdf

== 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

-  ⇤ ← Revision 33 as of 2013-09-25 00:47:48 → 
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  Editor: ManasadevithirugnanasambandamATligoDOTorg
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  Editor: ManasadevithirugnanasambandamATligoDOTorg
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== 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