KAGRA Logbook

IOO (IMC)

shogo.kambara - 13:43 Thursday 28 January 2016 (691)

Mode matching ratio of IMC

I calculated the Mode matching ratio of IMC.

That is 82.3%!!

How to calculate

I looked for the peaks of IMC transmission(Fig.1).

I calculated the positions[deg.] of peaks of high-order-modes by design values(Fig.2).

It is easy to calculate these positions by Gouy-phase.

I found out the peaks which located close by calculated positions[deg.](Fig.3).

I calculated the mode matching ratio of IMC by those peaks values(Fig.4).

I also upload the graph which was "mode scan for IMC in missalignment(pitch)" (Fig.5)

Images attached to this report

Comments to this report:

tomotada.akutsu - 14:01 Thursday 28 January 2016 (693)

Good job!

By the way, are these measurements done in the high finesse mode or low mode?

shogo.kambara - 18:09 Thursday 28 January 2016 (697)

These measurements are done in the high finesse!!

yuta.michimura - 11:40 Monday 01 February 2016 (711)

Very nice work!

From the fitting of the measured Gouy phase for each higher order modes, the round-trip Gouy phase of IMC is 64.6 +/- 0.2 deg (see attached figure).
This means that the cavity g-factor (rooted) is -0.428 +/- 0.004.
Using the measured round-trip length 53.30253(5) m (klog #616) and assuming MCi and MCo to be flat, the measured MCe RoC is 37.33 +/- 0.09 m.
This agree with the designed value 37.3 m, Hirose-san's measurement 37.3(1) m and Nakano-kun's previous measurement (see klog #637).

Images attached to this comment