Not logged in
Mon May 10 10:57:54 2021
Using ALS beatnote for calibration, test
We locked both arms and opened the shutter for Yend green laser.
After toggling the shutter on.off, we got a TEM00 mode of green laser locked to YARM.
We then cleared the phase Y history by clicking "CLEAR PHASE Y HISTROY" on C1LSC_ALS.adl (opened from sitemap > ALS > ALS).
We sent excitation signal at ITMY_LSC_EXC using awggui at 43Hz, 77Hz and 57Hz.
We measured the power spectrum and coherence of C1:ALS-BEATY_FINE_PHASE_OUT_HZ_DQ and C1:SUS-ITMY_LSC_OUT_DQ.
The BEATY_FINE_PHASE_OUT_HZ is already calibrated in Hz. This we assume is done by multip[lying the VCO slope in Hz/cts to the error signal of the digital PLL loop that tracks the phase of beatnote.
We calibrated C1:SUS-ITMY_LSC_OUT_DQ by multiplying with
where f is in Hz.
nm/cts is taken from
We added the calibration as Poles/zeros option in diaggui using gain=54.577e3 and poles as "0, 0".
We found that ITMY_LSC_OUT_DQ calibration matches well at 57Hz but overshoots (80 vs 40) at 43 Hz and undershoots (50 vs 80) at 77Hz.
If we had DRFPMI locked, we could have used the beatnote spectrum as independent measurement of arm lengths to calibrate the interferometer output.
We can also use the beatnote to confirm or correct the ITM actuator calibrations. Maybe shape is not exactly 1/f
unless we did something wrong here or the PLL bandwidth is too short.
Uploaded Mon May 10 12:13:41 2021
Uploaded Mon May 10 12:13:50 2021
Uploaded Mon May 10 12:14:01 2021