Marc, Yuhang

Today we check the centering of the ir beam from M0 to M3 (see fig 1 of entry 2452) and added an iris just after M0.

It means that we now have several references to check the ir alignment injection inside the FC :

1) FI aperture after the OPO

2) new iris after M0

3) targets on PR window

We are still not sure about the reason of this misalignment (even though the ir injection inside the FC has not been checked during several weeks where 2 earthquakes & opening of the PR & BS chambers happened...).

But if it happens again, we can use these 3 references to try to find the reason.

We locked the p-pol PLL to 160 MHz to have ~7mW of ir power incident on PR chamber.

Then, we moved M2 and M3 to recover the ir beam on the PR window target. As explained in entry 2453, we used this time the weaker ir beam.

Then, we decided to move the dichroic mirror (SM2) picomotor.

We tried to use several references :

1)  camera looking at an ir sensor card on the ir reflection of the FC on the squeezing bench

2) camera looking at the 2 " mirror inside BS chamber.

3) 2 cameras looking at the FC targets

1) was useful to get back the beam on PR targets (even though we found out later on that the beam was not the reflection of FC)

2) was useful when moving SM2 picomotors.

After several motions using the Labview vi where we couldn't see changes on 2), we used the joystick.

We could see the beam hitting the edge of the 2" mirror.

After a rough centering (we also had to move slightly in yaw) we could get the beam on the FC 1st target.

We locked FC with green to insure a proper position of BS and unlocked it. We superposed green and ir on this target and then on the 2nd one by cutting alternatively green or ir.

We could finally locked back both green and ir (see fig 1).

As a reference, fig 2 and 3 shows the camera looking at the 2" mirror with green respectively on and off.