[Jennie, Jason, Rahul, Keita, Masayuki]
We have observed the light coming out from the HAM2 after the MC1 reflection.
This is the summary report for the optics alignment in HAM1 after the JAC.
JAC_L1
An iris was placed and centered on the output beam from the JAC before installing the L1 lens. The lens was then installed such that the beam remained centered on the iris.
JM2
This optic will need to be repositioned after the EOM is installed. Therefore, we placed it without fine adjustment for now. The angular alignment was done using an iris located at the position where the HR surface of JM3 will be. Notes for final installation:
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The barrel must be cleaned before final installation.
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A beam dump must be installed behind the mirror.
JM3
Although JM3 also needs to be swapped to tip-tilt, the beam reflected from JM3 serves as the alignment reference after the EOM. Therefore, we performed careful alignment. An iris was placed at the planned location of JAC_M3, and the beam was centered on it by adjusting JM3.
JAC_L2, JAC_L3
The two lenses were then installed. They were centered using the same iris that had been used for the JM3 alignment.
JAC_M3
The angle of the reflected beam from JAC_M3 is critical, as it determines the polarization mismatch caused by the periscope’s rotation. An iris was placed at the output beam hole, and the beam was aligned parallel to the hole line. Previous measurements confirm that the input beam axis to the IMC in HAM1 is parallel to the hole within ~1 mrad ([link]). Therefore, this alignment ensures that the polarization mismatch remains within acceptable limits.
Periscope (initial alignment attempts)
Initial alignment of the periscope was performed using the first iris (IR1) placed prior to installation.
Since the incoming beam was horizontal and parallel to the hole line, we expected the output beam to be rotated by exactly 90° and remain horizontal through the hole. After centering the beam on the iris by eye, we checked from the HAM2 viewport but did not observe the beam.
We attempted minor adjustments to the periscope, JM2, and JAC_M3. Some scattered light was eventually seen at the output periscope of the HAM2 IMC reflection path. However, IR camera footage from Keita showed that the focus did not match, and the light was deemed irrelevant. The detail can be found in Keita's alog.
Periscope (refined alignment)
On the following day, a second iris (IR2) was introduced to further constrain the horizontal alignment. This iris was placed approximately at the same height as IR1 and roughly aligned parallel to the hole line. The periscope was then re-aligned to pass through both irises.
From the POP septum window, we confirmed that the HAM2 periscope was visible and used it for alignment. Using an IR viewer, the beam was observed to hit the upper-left (10 o’clock) corner of the periscope structure. We switched to aligning JM2 and JAC_M3 using the top periscope mirror and IR1 as references (IR2 was removed at this point).
To identify the beam spot, we intentionally misaligned the pitch to make the beam hit the upper part of the periscope structure. To avoid blocking the beam, the iris was temporarily removed (its location was marked with three dog clamps; one clamp was slightly loose but the offset was minor, ~1 mm).
While keeping the pitch misaligned, yaw centering was performed using JAC_M3. Once centered visually, the iris was replaced, and JM2 was used to center the beam through it.
Fortunately, JM2 and the periscope top mirror are located at similar opical position, so the beam position remained nearly unchanged on the periscope mirror. This beam walking converged in two iterations.
The iris was removed again, and the beam was swept from top to bottom of the top periscope mirror using JAC_M3. The mirror was then centered using the midpoint of this motion. The iris was replaced, and pitch alignment was re-checked using JM2, again requiring just two iterations.
At this stage, some faint beam was observed using the viewer through the viewport. Although it wasn’t visible on a card, adjusting JAC_M3 slightly allowed us to confirm beam output from HAM2.
Final Checks
Finally, the IR1 centering was confirmed, and IR2 was placed near the periscope to act as a reference.
When checking the beam on JAC_L3, we found that it was offset by about 5 mm in the yaw direction. Further alignment is likely needed.
The beam spot on the periscope mirror is not perfectly centered, but it is close enough that no adjustment to the top mirror is deemed necessary.