jennifer.wright@LIGO.ORG - posted 16:33, Monday 04 August 2025 - last comment - 09:43, Wednesday 15 April 2026(86184)
Calculating curvature of SR3 when heated up by 2W.
Jennie W, Camilla C
A while ago we heated up then cooled down the SR3 heater (alog #84749).
As part of measurements using this data I calculated the curvature change, following the approach at LLO by Aidan given iin alog #27262. Matlab code is below.
%calculate SR3 spherical lensPin = 2;%Wdouble_pass = 2;SR3_t = (3*3600) + (11*60); % Time for cooldown in s.delta_ITMY = -2.67e-5;% decrease in defocus of ITMY according to Hartmann sensor.D_ITMY = delta_ITMY./double_pass;% defocus change in DioptresD_ITMY_error = 5e-6;% error on defocus in Dioptres.R_SR3 = 36.013;% cold radius of curvature in mdelta_R = (2./((2/R_SR3)+D_ITMY))-R_SR3; % change in curvature during cooldown in m/delta_delta_R = D_ITMY_error.*(2./((2./R_SR3)+D_ITMY)); % error on curvature change.
This means the rate of defocus change is 6.6750uD per Watt.
The final curvature change is + 0.0087 m +/- 0.0002 m as the mirror becomes less curved due to cooldown.
In 84749Camilla had a look at the HWS images from these times, and I think her conclusion is that we shouldn't trust the reported spherical powers that Jennie is using above to estimate the curvature change. Matt later redid a HWS measurement using the SR3 heater heater, in 88413, we can use the value from that alog for uD/W instead and scale that to the power used here.\
In the time that Jennie is using above, the SR3 heater is set to 2W requested power, but the power readback reports 1.9W.