Power supply of master IR laser has been connected to UPS. Power supply of power amp is connected to power line directly without UPS.
As a resut, both power supplies of this UPS and the power amp are connected to an independent power line.
This modification makes more secure laser operation. Existence of UPS survives the master laser longer, that can avoid breaking the power amp.
After this replacement, we measured the spectra of some signals related to PMC (error signal, feedback signal, trans/reflect power, etc,. ) in order to check if there is any change before and after the power supply is replaced. Fig. 1 shows the results. The black line is the spectrum before the replacement (2021/01/07 00:35 UTC), the blue one is the spectrum after the replacement (02:38 UTC). As you can see, the blue one has a spike at 6 kHz.
We found that the overall gain (K1:PSL-PMC_COMMON_GAIN) gets larger when PMC locks again. (14 dB -> 22 dB, fig. 2). So we considered that the control is about to oscillate due to the gain increase, I reduced the gain 22dB to 14 dB. then the spikes are disappeared in red lines.
What we are wondering is why the gain was so large this time..
