Aso, Ushiba, Hirose, Yano, Takahashi, Tanaka
### Abstract
We aligned the optical axis from IMC to X-arm and send the reflection beam to REFL PD. Now we succeeded to lock IR beam to X-arm. After the alignment, we centered the both POP forward QPD1 and QPD2.
### What we did
- First, we check where the IR beam hits on each mirror (IMMT2, PRM, PR2, PR3) after setting ALIGN state of IMMT1 and IMMT1. we found three beam at IMMT2, one is the coming from IMMT1, the second one is the reflect from IMMT2, the third one is not sure. we consider that the third one maybe the reflection beam. Ushiba-san said that the alignment of the X-arm was not so good judging from the amount of green transmitted light, so we decided to align the arm with green for a while.
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We misaligned ETMX and we sent green beam to Xend in a single pass. Then, we moved PR3 to maximize the GR power. Then, we aligned ETMX again, and the transmitted light camera showed the flash of TEM01 mixed with TEM00, so we decided to re-align ITMX or ETMX. we heard that EX had been measured yesterday, so we first took the alignment of EX. After the alignment of EX, the flash of TEM01 was gone and the GR power increased. However, we could not lock the GR beam to the X-arm. Looking at the green lock control signal, we found that it could not be locked because the oscillation at 1 Hz was too large. The eigen frequency of MC suspention in Length direction is around 1 Hz so WFS controls seems to oscilate IMC length. When the WFS control was turned off, The GR beam locked to the X-arm. In this state, we engaged ADS to ITMX and ETMX to make their alignment good.
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Now that the X-arm alignment was better, we checked the position of the IR beam on the PR3. Since the beam was slightly off the center of PR3, we adjusted the angle of IMMT2 so that the beam was at the center of PR3. Next, we checked the position of the reflected beam from the X-arm on POM2, and we adjusted the angle of PR2 so that the beam would be at the position of the beam on POM2 when POM1 was placed before. Finally, the reflected light from the x-arm was incident on the RFPD of the REFL.
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When we centering on PR3, the output of the IMMT2 coil went to the edge of the actuator range, so we offloaded it.
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At this time, the mirror did not move as desired, even with pico motors and coils. (If we kept moving it in the same direction, the direction of movement would reverse or move in the opposite direction than it should.) Later, I found out that this was due to the lack of light in the oplev. If you put light in the oplev
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Finally, we were able to lock the IR to the X arm by using XARM guardian (fig. 1, 2). we engaged ADS in PR2 and IMMT2 to maximize the amount of transmitted light. Then, in that state, we did centering almostly for two QPDs of the POP forword (fig. 3).
### Note
- When we go to the AOS_TMS_OVERVIEW screen from either the old or new ALS overview screen, the channel names are the old ones and do not reflect the new channel names looking at the amount of GR and IR transmitted power. So, it is necessary to reflect the current channel names.
- When we centered the QPD in POP forword, we noticed that the placement of each element of the QPD written on the medm screen of the QPD was different from the actual placement of the QPD. This needs to be corrected.
