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eleonora.capocasa - 0:20 Saturday 15 June 2019 (9246) Print this report
Round-trip Gouy phase of PRC and SRC

Yutaro, Stefan,  Eleonora

The round-trip Gouy phase of PRC and SRC have been measured with a cavity scan using the tecnique reported by Stefan in entry #9241.

Since the scan has been done applying a constant force on the PRM/SRM, we fitted the costant acceleration of the mirrors and used it to convert the time axis into cavity length. In such way the FSRs are equally spaced.

The round trip Gouy phase is found as the distance between the fundamental mode and the 1st HOM peak.

The measured round-trip Gouy phase is 30 +/-2 deg for PRC and 48 +/-2 deg for SRC.  (See Fig.1, 2 for PRC and Fig. 3, 4 for SRC.)

The nominal values are respectively 33 deg for PRC and 35 deg for SRC.

Such a large deviation of the SRC Gouy phase is compatible with a change in the distance between SR2 and SR3 of ~1 cm with respect to the nominal one  (See entry #9245  by Yutaro)

Note that since MICH offset varies during the scan it does not allow to measure the cavity finesse.

Images attached to this report
Comments to this report:
eleonora.capocasa - 13:53 Saturday 15 June 2019 (9248) Print this report

According to the simulation reported in  about the HOM density expected in the PRC as a function of the Gouy phase of SRC and PRC, it seems that the error of few degrees that we might have in PRC is more critical than the much larger error we measured for SRC. See attached picure.

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