With K.Tanaka
I have been measuring the spectrum, TF and phasing of the RFQPD for WFS on the REFL surface plate since yesterday.
We will do it again tomorrow.
I referred to klog#16774.
RFQPD for WFS at REFL is for demodulation at 17 MHz, 45 M Hz.
What I need to measure is QPD{1,2}_{17Hz,45Hz}.
TF measurement of RFQPD
TF measurement of RFQPD
We measured the transfer function of each segment of RFQPD.
Two methods were used to measure it.
I applied an excitation signal from Moku Lab to the TEST of RFQPD and measured the transfer function of each segment.
The excitation signal was applied from Moku Lab to the AM laser and then from the AM laser to the RFQPD, and the transfer function of each segment was measured.
The figure shows the transfer function of the test and AM laser at 17 MHz and 45 MHz for QPD1 and the
power spectrum when differenced at 17Hz.
Figure 1 (transfer function results at 17Hz) shows that at frequency 17Hz it is not peaky, and at frequency 45Hz magnitude lower than 17Hz but does not appear to be abyss.
Ideally, the waveform would be peak at 17Hz and abyss at 45Hz. I need to check if QPD1 is frequency tuned.
I measured the transfer function of QPD1 and the power spectrum.
QPD2 measurements are on the way. I will summarize the method and results later.
