[Dan, Takano, Tanaka, Fujimoto]
Summary
From the previous SRC flash searches, it was found that a large yaw offset of the SRM is required to observe SRC flashes. Under such conditions, the SRM OPLEV beam went out of range of the QPD.
To address this issue, we performed centering of the OPLEV QPDs (TILT QPD and LEN QPD) for the aligned SRM.
Although the centering onto the QPDs were confirmed while we were in the mine, after returning to the control room we found that the beam was no longer incident on the TILT QPD. We plan to check the situation and recover the alignment tomorrow.
What we did
After obtaining a reasonable SRM alignment during the SRC flash search in the morning (klog #36876), we carried out the SRM OPLEV centering work in the mine in the afternoon.
Inspection around the QPD revealed that the beam was clipping on the holder of the first steering mirror. Therefore, we decided that rearrangement of all the optics, including the steering mirror, BS, TILT QPD, lens, folding mirror, and LEN QPD, was necessary.
First, we adjusted the position of the first steering mirror and aligned the beam onto the TILT QPD. After coarse alignment, fine adjustment was performed using the micrometer stage of the QPD while monitoring the QPD signals.
Next, alignment onto the LEN QPD was performed. For the LEN QPD, the distance relationships between the SRM and lens, and between the lens and LEN QPD, are important. Therefore, the downstream optics (BS, lens, folding mirror, and LEN QPD) were repositioned and aligned so that these distances matched the previous setup (klog #7952).
Fig. 1 shows a photograph of the final layout. The distances between optics are as follows:
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TM to upper viewport: 990 mm (assumed to be the same as the previous setup)
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Viewport to first steering mirror: 305 mm
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First steering mirror to BS: 40 mm
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BS to lens: 45 mm
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Lens to folding mirror: 110 mm
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Folding mirror to LEN QPD: 273 mm
After repositioning, final centering onto the QPD was performed using the micrometer stages of the QPD.
After the adjustment, the optical table was covered with aluminum foil, and we returned to the control room. At that point, we noticed that the beam was no longer incident on the TILT QPD. It is possible that the aluminum foil blocked the beam path or disturbed the alignment during covering. We plan to check the situation tomorrow and recover the alignment.
