A half-wave plate (HWP) and a photodetector (PD) were installed to adjust the laser polarization and measure the power drift, respectively (Figure1).
The HWP was installed between M1 and M2 (Photo1); the PD was temporarily installed behind M20 (Photo2; M20 transmitted).
The current polarization was set to S at the HWP output (at A in fig1) by the HWP. Before we set to the S polarization, the polarization was about 10 degrees rotated compared to S polarization at A.
(memo: When polarization was set to S at the HWP (at A in fig1), the polarization at B (in front of PMC), C (PMC output), D (EOM1 output), or E (EOM2 output)
was also S (linear polarization). (The polarization was checked by polarizing beam splitter.))
Transmitted optical power of M20 is measured by the PD to check the polarization drift mainly.
(Uehara, Miyakawa)
The power at the end of PSL room was monitored for almost a day (Fig 1).
After the adjustment of polarization about 10degree, successfully we did not see any drop which had been seen before, even we worked in the PSL room (-17hour) and the temperature was disturbed. Small oscillation of 20 min can be seen. We are not sure the exact reason, but probably because of the air cotroller.
So we can work in the PSL room without any concern about power drop from now!
