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ayumu.toriyama - 19:09 Tuesday 09 August 2022 (21742) Print this report
First development of identifying IR center position by TCam photo

[Kenta Tanaka, Yuzurihara, Shiota (Aogaku), S. J. Tanaka (Aogaku), Toriyama (Aogaku)]

Because ITMX and ITMY has birefringence, in order to apply ASC, the relative position between mirror center snd IR position shold be known by TCam.

Aogaku member stayed at KAGRA site from Aug. 3 to Aug. 10.

We developed 1st version code to estimate the IR center position by TCam photo.

I attached the example of IX and EX. 

After further code test the code will be included in TCam system.


Images attached to this report
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takafumi.ushiba - 21:52 Wednesday 10 August 2022 (21752) Print this report

Thank you for your great efforts on the beam position confirmation.
I would like to ask you to apply this analysis to X arm Green beam and Y arm IR beam because current alignment is performed by checking GRX beam position on ETMX and IRY beam position on ETMY.

hirotaka.yuzurihara - 22:40 Friday 19 August 2022 (21838) Print this report

Sorry for late reply.

We will try to apply the IR beam position on ETMY, when Kenta-san takes the TCam photo.

But, I'm not sure this tool works for GRX beam position on ETMX, because it was designed for identifying IR beam position. I hope it works.

Anyway, we will check it later.

hirotaka.yuzurihara - 20:48 Wednesday 24 August 2022 (21887) Print this report

Further report.


  • Kenta-san took the TCam photo for ETMY which was illuminated by IR. For other photos, see the web archive.
  • I attach one example. In the private chat with Ushiba-san, he gave me the comment : the brightest point in the photo might not bethe IR center, but just a scattering light. We need to check that.

ETMX by Green

  • I attach one example when IR was not locked and Green was locked. By using our code, we can identify the center of Green laser. In this case, the exposure time is very short (100 ms). We will try more longer exposure time.
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hirotaka.yuzurihara - 22:36 Wednesday 24 August 2022 (21889) Print this report

[Kenta, Yuzu]

Tonight from 21:00~22:30 , we took the TCam photo of ETMX and ETMY.

For ETMX which was illuminated only by GreenX,

  • we confirmed that by using the developped code, we can idenfity the beam center by GreenX! I attach two examples [1] [2]. For other examples, see here.
  • Accordingly, the script name was changed from `~/bin/` to `~/bin/`.
  • Currently, we reccomend to use the exposure time 1s and gain 470 for ETMX which was illuminated only by GreenX.
    • This reccomented exposure time is not suitable for fittin of mirror center by GreenX. So, I set the required exposure time as 10 s for launching the fitting of mirror center.

For ETMY which was illuminated by IR,

  • we took many TCam photos and the movies by changing the exposure times. (see here) The scattered light on ETMY is a noise and it blocks for finding the beam center.
  • We need to propose another way fot finding the beam center. For example, cut the noise reagion and analyze the left reagion.
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