KAGRA Logbook

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IOO (General)

taiki.tanaka - 22:33 Friday 02 November 2018 (6830)

modulation index

Kohei Yamamoto, Taiki Tanaka

We measured modulation indices of EOM1 and EOM2a and EOM2b(see the plot) .

These measurements follow 6798.

While sweeping the modulation frequencies, basically at 0.1[MHz] at one time, the modulation index repeatedly go down and up. It's strange... And also we found the asymmetry b/w upper and lower sideband, which might suggest that we have unexpected AM.Â

While sweeping the modulation frequencies, basically at 0.1[MHz] at one time, the modulation index repeatedly go down and up. It's strange... And also we found the asymmetry b/w upper and lower sideband, which might suggest that we have unexpected AM.

Next week, we will check how much such AM we have with the RAM monitor and tune the polarization angle with EOM.

While sweeping the modulation frequencies, basically at 0.1[MHz] at one time, the modulation index repeatedly go down and up. It's strange... And also we found the asymmetry b/w upper and lower sideband, which might suggest that we have unexpected AM.Â

Next week, we will check how much such AM we have with the RAM monitor and tune the polarization angle with EOM.

Images attached to this report

Comments to this report:

tomoyuki.uehara - 23:07 Friday 02 November 2018 (6841)

Thank you for the measurement. This (also http://klog.icrr.u-tokyo.ac.jp/osl/?r=6798) is a important measurement for checking the EOMs health condition. The resonant frequency looks like frequency-shifted from my measurement in UF (https://gwdoc.icrr.u-tokyo.ac.jp/DocDB/0056/T1605611/003/mod-index-in27dBminput.png).

	Resonant frequency@this measurement / MHz	Resonant frequency@UF / MHz	Difference / MHz
f1a	16.8(3)	17.2(1)	0.4(3)
f1b	16.8(3)	16.9(1)	0.1(3)
f2	45.0(3)	45.1(1)	0.1(3)
f3a	56.6(3)	56.0(1)	0.6(3)
f3b	56.8(3)	56.5(1)	0.3(3)
fIMC	--	14.3(1)	--

*I assume the measurment uncertainty is 0.3 MHz in this measument.

Small correction:

- The unit is dBm (not V). (http://klog.icrr.u-tokyo.ac.jp/osl/?r=6798)

- Horizontal axis is MHz. (graphs)