[Ushiba, Tanaka, Komori]

Abstract:

We started adjusting the IY height to reduce the pitch thermal noise of IX.
Although moving the GAS filters induces large excitations at 22 Hz, we successfully changed the setpoint in the IY GAS control filters during DC readout.
The next step is to continue the adjustment using a fishing rod to further lower the IY height.

Detail:

We are now able to directly control the beam spot position on IY and have started adjusting its height.
By lowering the IY height, the entire input beam axis shifts to follow a specific spot on IY, which leads to better centering of the beam spot on IX.
We expect that this centering will reduce the pitch thermal noise of IX.

As a first trial, we adjusted the setpoint of the IY GAS control filters during the DC readout.
The changing speed was several hundred counts in 100 seconds.
Although this rate of change caused significant excitation at 22 Hz, it did not lead to IFO lock loss.
We modified the setpoints of F1, F2, F3, and BF until the COILOUT value reached approximately 25,000 counts, which is close to saturation.

So far, we have not found a better setting than the original configuration.
The sensitivity in the 60–90 Hz range improved slightly, but jitter coupling increased (see Fig. 1), resulting in a degraded BNS range.

The next step is to offload the COILOUT using a fishing rod and further lower the IY height.