[Izumi, Sugimoto, Yokogawa]

The noise of PLLX

Yesterday, Izumi-san found that the noise of the PLLX control signal are higher than before. Since, these noise had coherence with the microphone in the PSL room, we assumed that the couse of noise increse was acoustic noise. We confirmed the folloing two points.

• The alignmet of the beatnote
  • It was suspected that the alignment of the beatnote got worse, so we aligned the beam path using the steering mirrors for taking the beatnote. However, it turned out that the alignment was not getting worse.
• The influence of the wind from the KOACH in the PSL room
  • It was supected that the noise increased due to the wind from the KOACH, so we turned off the KOACH and measured the noise. By doing so, the noise decresed. (I forgot saving the noise plot in my tablet.)

Since it was found that the noise increased due to the wind from the KOACH, we confirmed the noise when we knocked the optics for IR beam path in order to see if the wind was shaking the optics. However, even if we knocked the optics, there was no change in the noise. Also, even when the KOACH is on, the noise sometimes became peliodically smaller. That was strange.

The amplitude of the beatnote

Since the power of the main IR beam was raised about 3 times by Nakano-san, we adjusted the beam power before the RFPD for detecting the beatnote. The folloing table shows the beam power of the main laser (MEPHISTO) side and the AUX laser (PROMETHEUS) side before the RFPD and the amplitude of the beatnote before and after adjusting the power.