The 4.5 hour heating test last night on ITMX was successful. The initial thermal lens transient is shown in the attached plot.
The thermal lens forms relatively rapidly in response to the CO2 heating. Then it decays at the same rate when the heating is turned off. Once again, Physics works.
When the offset in the spherical power at t = 0s is accounted for, the thermal lens magnitude is approximately 80 micro-diopters (double-passed) for 680mW of applied CO2 laser power.
Further analysis on the shape and centering of the lens is pending ...
(The noise in the HWS measurement in the last half hour is coming from SUS injections into ITMX).
Further analysis of the HWS measurements of the thermal lens show:
- the (double-passed) change in spherical power was 78.7 micro-diopters after 4.5 hours (close to steady-state).
- the applied power was 631 mW
Therefore, the single-passed ITMX steady-state thermal lens coefficient is 62.3 micro-diopters per Watt
Additionally, I reviewed the thermal lens location over time. The attached plot shows the location of the thermal lens in the ITMX coordinates. The HWS data is correctly positioned in this coordinate system.
The thermal lens center drifted left by 15 mm or so after the first hour or so. I've plotted the center of the lens at earlier time.
The thermal lens center is measured at [-53.5, 4.7] mm. To center this lens we need to move the upper periscope pico (PICO_F_3) by [-8900, +800] counts.
I moved the mirror from [-16012, -16006] to [-24909, -15190].
The CO2X central heating should be centered now.
