Today we performed the measurements of the Mode Matching of the input beam to the arm cavities.

First, we noticed that the picomotors which are used to move the meniscus lens on SIB1 were disconnected. Therefore, we plugged it on the rack of central building, as shown in the Fig. 1. Then, we started the process PicoAppOL in Acl and it worked as expected.

In the first measure, we explore the lock of the cavities with the green beam and with the IR unlocked. The steps followed are summarized below:

• INJ locked;
• PR and SR misaligned;
• Go to automation and bring the ITF state to LOCKED_BEATING_BOOST_ON
• unlock IR and lock ALS
• Make scan of the cavities running the script "LSC_init.py" located in /olusers/virgorun/ISC/LSC
• change value of CARM to make one FSR;
• The data is observed looking at the channels LSC_B7_DC and LSC_B8_DC.

We did a first rough test, by measuring the ratio between the 00 and 02 TM modes for the north and west cavities, which were around ......, respectively.

Then, we proceeded to make the improvement of the matching by moving the Meniscus Lens located in SIB1. We first, did the matching measure exploring the mirrors free swinging by giving a "kick" to the input/output mirrors of the cavities, and checking the height of the order 2 mode in the FSR relatively to the fundamental mode (#34307).

The procedure followed is described below:

• Align the arm cavities
• measure the mismatch with the Matlab script available in /users/optics/Commissioning/180323_matching
• with the picomotors (PicoOLEI) L1z in the forward direction;
• when necessary, move the counter-weight on SIB1 to compensate for the corrections on IB_TZ_CORR;
• open dampers F7_TX_ON, F7_TZ_ON and MIR_Z_ON;
• give a "kick" on the Input/End Mirrors (put a value from 0 to 10 on the variable zCorMir of the cards of the desired mirror, that will cause a free swinging movement, as shown in Fig. 2)
• realign arms and repeat the procedure until the matching desired is achieved.

In our measurements we took as reference the North End Mirror (used 5 as reference number for zCorMirr locate in the DPS card ScNECDMirLN, page 4). We couldn't make the measurements in this way for the West Arm, because the "kicks" in the Input or End Mirrors didn't cause the effect necessary to measure the mismatch. Anyway, we verified the power in trasmitted in the arms in the locked condition every time we changed the position of the Meniscus Lens, and the power improved for both arms (proving that the mismatch was improved for West and North cavities). The table below summarizes the measurements performed (see Fig. 3):

Fig. 4 shows the measurement with the best mismatch achieved for the North cavity.

We finally unplugged the power suppy of the picomotors actuator in the central building.