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 Wed Nov 25 16:40:32 2015, yutaro, Update, LSC, round trip loss of Y arm Wed Nov 25 23:34:52 2015, yutaro, Update, LSC, round trip loss of Y arm Fri Nov 27 03:38:23 2015, yutaro, Summary, LSC, round trip loss of Y arm Fri Nov 27 22:20:24 2015, yutaro, Update, LSC, round trip loss of Y arm Sat Nov 28 11:46:40 2015, yutaro, Update, LSC, possible error source of loss map measurement Mon Nov 30 10:41:45 2015, yutaro, Update, LSC, Does a baffle in front of ETMY have effect on loss map measurement? Mon Nov 30 17:17:30 2015, yutaro, Update, LSC, Does a baffle in front of ETMY have effect on loss map measurement? Mon Dec 7 11:11:25 2015, yutaro, Summary, LSC, round trip loss of X arm
Message ID: 11819     Entry time: Fri Nov 27 22:20:24 2015     In reply to: 11818
 Author: yutaro Type: Update Category: LSC Subject: round trip loss of Y arm

Here, I upload data I took last night, including the power of reflected power (locked/misaligned) and transmitted power for each point (attachement 1).

And I would like to write about possible reason why the loss I measured with POYDC and the loss I measured with ASDC are different by about 60 - 70 ppm (elog 11810 and 11818). The conclusion I have reached is:

It could be due to the strange bahavior of ASDC level.

This difference corresponds to the error of ~2% in the value of P_L/P_M. As reported in elog 11815, ASDC level changes when angle of the light reflected by ITMY changes, and 2% change of ASDC level corresponds to 10 urad change of the angle of the light according to my rough estimation with the figure shown in elog 11815 and attachment 2. This means that 2% error in P_L/P_M could occur if the angle of the light incident to YARM and that of resonant light in YARM differ by 10 urad. Since the waist width $w_0$ of the beam is ~3 mm, with the 10 urad difference, the ratio of the power of TEM10 mode is $(10\,\mu \mathrm{rad}/ \theta_0)^2\sim0.01$, where $\theta_0=\lambda/\pi w_0$. This value is reasonable; in elog 11743 Gautam reported that the ratio of the power of TEM10 was ~ 0.03, from the result of cavity scan. Therefore it is possible that the angle of the light incident to YARM and that of resonant light in YARM differ by 10 urad and this difference causes the error of ~2% in P_L/P_M, which could exlain the 60 - 70 ppm difference.

 Attachment 1: log.txt.zip  1 kB  Uploaded Fri Nov 27 20:45:15 2015
 Attachment 2: 17.png  43 kB
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