Virgo Logbook

Injection system (General activities)

pillant, genin, gosselin, casanueva - 18:26 Tuesday 16 October 2018 (43103)

Master laser swap

This morning was swap the master laser.

The ML power at the input of the Slave laser is now 510 mW instead of 390mW previusly.

Was also reduced the BPC corrections but due to the cumulated drift last months the beam was clipped on

the last mirrors (EIB_M6 and EIB_M7). The beam was manually recentered on the optics of the EIB.

The AA matrix measurement is ongoing.

Comments to this report:

casanueva, genin, gosselin, pillant - 19:10 Tuesday 16 October 2018 (43104)

The AA sensing matrix has been remeasured and the loop in full bandwidth has been restored.

ACL_MATRIX_BEGIN   sensing_matrix   1   MCT_hNORM   FF_ACh   NF_ACh       MCT_vNORM   FF_ACv   NF_ACv
ACL_MATRIX_CH           MC_ty_err   ""       12.37       0.00   -2.28       0           0       0
ACL_MATRIX_CH           IB_ty_err   ""       19.67       0.00   -42.09       0           0       0
ACL_MATRIX_CH           MC_tx_err   ""       0           0       0           7.43       19.22   0.0
ACL_MATRIX_CH           IB_tx_err   ""       0           0       0           26.70          12.19   0.0
ACL_MATRIX_CH           IB_tz_err   ""       0           0       0           2.26       22.12   84.52
ACL_MATRIX_END       sensing_matrix

ACL_CONST_CH MC_ty_set   ""   0   LOOP_FREQ   1.4
ACL_CONST_CH IB_ty_set   ""   0   LOOP_FREQ   -2.1 #
ACL_CONST_CH MC_tx_set   ""   0   LOOP_FREQ   -1.5 #
ACL_CONST_CH IB_tx_set   ""   0   LOOP_FREQ   -0.2 #
ACL_CONST_CH IB_tz_set   ""   0   LOOP_FREQ   -14.5 #

gosselin, genin, pillant - 17:08 Wednesday 17 October 2018 (43117)

As foreseen in the maintenance plan, we have substituted the master laser (S/N:2059 bought in 2011) by the S/N 1222 (bought in 2002 and recently sent for servicing).

The settings of the new laser are the following:
I=1900mA
T_crystal=25.7C

We checked that we were roughly in the middle of a mode hop by scanning the temperature of the crystal and it was the case.

The losses through the faraday isolator at the output of the ML were about 20% and the coupling into the fiber was about 75%.

We noticed an excess of intensity noise in the high frequency region wrt to the previous ML. See first plot, where we compared the previous master laser during the night before the maintenance and the new installed one during the night after the maintenance.
However this power noise does not seem to affect the rest of the ISYS system (plot 2).
We investigated this problem and found that while opening the IMC loop, the two lasers have the same behavior (plot 3)

It seems that the actuator of the loop (piezo of the ML) has a different behavior than the previous one.
By manually changing the gain on the IMC loop we were indeed able to reduce this excess of power noise but the error signal started to oscillate. We came back to the initial value.

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