Miyakawa, Takano, Tanaka

This is a brief repor of the RFAM reduction trial done yesterday. The detail will be posted later.

We noticed that the our work done on Tuesday was totally wrong. Therefore, we first reduced the output power at PMC down to 1 W and set the polarization to s-pol, which we think is optimal for EOM to generate PM sideband. Next we directly measured RFAM with another RFPD after EOM1 without any polarizer before this PD, and observe that there are peaks at 13.7 MHz (f_imc) and 15 MHz (f_pmc). Around 45 MHz (f2) the peak seemd to be buried under the noise floor. When rotated the HWP so that the peak at f_imc is minimized, the peak height at f2 got higher. This implies that the best condition for f_imc and f2 is different.

After that, we recover the main beam path and tuned the wave plates so that RFAM measured by the RFAM was minimized and went out PSL room without increasing the output power. From the outside of PSL room, we rotated the HWP before two TFPs by ~ 280 deg, and checked the maximum and the minimum power. We confirmed that the minimum power was closed to zero, which means that the output power after EOM2 was close to pure linear polarization.

Finally we locked IMC and aligned PRM in order to check the offset of the demodulated signals from RFPDs on REFL table. We observed that the amplitude of these offset values were about one order smaller than the previous value.However, now the DC power at these PDs were almost half of the previous measurement because of lower power at PMC trans, so the actual reduction ratio is about ~ 5. Anyway, we are concident that the current RFAM level is improved by tuning the polariaztion in front of EOMs.