Reports until 16:35, Tuesday 29 November 2022
H1 SQZ
nutsinee.kijbunchoo@LIGO.ORG - posted 16:35, Tuesday 29 November 2022 - last comment - 15:12, Wednesday 15 March 2023(66093)
FC cavity length measured more precisely

Daniel, Naoki, Nutsinee

Using the original The way of the beast method we determined the FC cavilty length down to +-14um precision. We added 41.89 MHz sideband to the 40MHz EOM and added a 1kHz line from SR785 to this sideband. We locked the filter cavity on the 40MHz as usual. With the help of SR560 (3kHz double pole, 100 gain) we were able to see the injected 1 kHz clearly on the scope. While the cavity was locked, we tune the 41.89 MHz until the 1kHz line disapeared from the scope in both I and Q. We then fine tuned the frequency using SR785 (I-MON/1kHz excitation). We had about 2 Hz precision. In the end we settled with 41.781168 MHz as our FSR. 

 

Let

f_mea = 41.781168 MHz

n = 83 (number of FSR)

c = speed of light

FC cavity length is
(c*n)/(2*f_mea) = 297.774993 m +- 14um

 

The length given by the survey team (alog 65509 and  alog 62917) was 297773mm+-16.6mm

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Comments related to this report
victoriaa.xu@LIGO.ORG - 13:55, Friday 20 January 2023 (66920)

filter cavity FSR = 503.38757 kHz ± 0.02 Hz

victoriaa.xu@LIGO.ORG - 15:12, Wednesday 15 March 2023 (68015)

Dhruva, Vicky

In operation, the filter cavity length held at finite detuning, which changes FC length very slightly, within error of this. We can use the RLF frequency to estimate filter cavity length, when it is IR locked.

With FC-IR locked for sqz data taken 2/19/23, we calculate a filter cavity operating length of L_fc = 297.772(3) m.

  • FSR = c/(2*L_fc) = (CLF - RLF)/6.    -->  Lfc = c / (2*(clf-rlf)/6)
  • w/frequencies: CLF = 3.125 MHz, RLF = 104.645(30) kHz (corresponding to estimated 36 Hz FC carrier detuning),
    • FSR = 503,393(5) Hz
    • L_fc = 297.772(3) m