The ultimate goal of characterizing the temperature actuator turned to be fruitful in obtaining the calibration values for ETMX and ETMY (Calibration of ITMs were done previously here but not for ETM). In this process, I measured the PZT response by displacing one of the test masses in the frequency range of 20 Hz and 900 Hz and measured the transfer functions in counts/counts.
ETMX = [12.27 x 10 -9/ f2 ] m/count
ETMY = [14.17 x 10 -9/ f2] m/count
I calculated these calibration values from the measurements that we have taken( in detail : elog) and did the following calculations:
The measurements I made were :PZT count/ Actuator Count separately for all the test masses.
PZT count/ Actuator count = [PZT count/ arm cavity displacement(m) ]*[ displacement of a test mass(m) / Actuator Count]
For a same laser and assuming flat response of the PZT, the term [PZT count/ arm cavity displacement(m) ] remains for all the test masses.
The fitting was done on the gain plots of the PZT Response vs Test mass displacement and a function G * f ^-2 was fitted. The resulting G values were:
ETMX: 8.007* f ^-2
ITMX: 3.067* f ^-2
ETMY :11.389* f ^-2
ITMY : 3.745* f ^-2
To calculate the calibration of ETMX:
[PZT count/ Actuator count : ETMX ] / [ displacement of a test mass(m) / Actuator Count :ETMX] = [PZT count/ Actuator count : ITMX ] / [ displacement of a test mass(m) / Actuator Count :ITMX]
putting the values from the above fitting and Kiwamu's elog,
the calibrated value was calculated to be [12.27 * 10^-9 /f^-2 ]m/count.
A similar calculation was done for ETMY.
The attached are the fitting plots for the measurements taken.
Now using these and the previously measured calibrations, I will get the complete calibrated TF of the thermal actuator.