Yesterday we worked on the tuning of the mode matching of the single bounce beam (NI+BS aligned) with the OMC.

At the beginning of the shift we performed a scan of the OMC to check the status of alignment and mode matching (scan started at 07:39:20 utc, duration 5min):

TEM00 peak at 0.68 mW, order 1 at 0.058 mW (8.5%), order 2 at 0.0094  mW (1.4%).

Given the rather large misalignment, we locked the OMC and improved its alignment.

New scan performed after the realignment, at 08:26:20 utc (5min):

TEM00 peak at 0.77 mW, order 1 at 0.0095 mW (1.2%), order 2 at 0.0091  mW (1.2%).

The mode matching is therefore already better than what was achieved during the previous shift on OMC mode matching on March 27th (51233) when the best mode mismatch was 1.5%. Moreover the image of the B1 camera clearly indicate that the mismatch is dominated by a difference of waist or difference of waist position between the tangiential and sagital axes (clover shape).

We locked again the OMC and displaced the MMT_M2_TX dof. During all this activity the SDB1 bench TY was controlled in high bandwidth and the drift control was engaged. At each step we slightly realigned the OMC and checked the effect of the MMT_M2_TX dof on the power transmitted by the OMC (B1_PD3_DC) and on the channel B1_PD3_DC_norm_B1s corresponding to the transmitted power normalized by the reflected power, which is our main figure of merit.

From the previous table its seems that the figure of merit constantly improves. With MMT_M2_TX rotated in TX by -650 steps, we performed another OMC scan at 09:41:40 utc:

TEM00 peak at 0.785 mW, order 1 at 0.0009 mW (0.11%), order 2 at 0.0091  mW (1.16%).

The main improvement concerns the alignment, while the mode matching did not change very significantly. We hold the new TX position of MMT_M2.

We then tried different angular positions of the MMT_M2_TY dof, which, according to Zeemax simulations performed by Matteo Tacca, is the degree of freedom that should be the most appropriate to compensate a motion of MMT_M1_Z. Note that in the past shifts on OMC mode matching (27/03 and 11/03) we have already changed the MMT_M2_TY by +1370 urad. Therefore we start from this position.

We have already noticed that when the SDB1 bench TY is controlled in high bandwidth, a motion of MMT_M2_TY excites a large resonance around 0.95 Hz that is difficult to dump. Thus we decide the put the SDB1 TY control in low bandwidth. In this case the resonance is no longer excited when moving MMT_M2_TY which enabled us to keep the OMC locked while changing the angular position of the mirror. Results are summarized in the table below.

From the previous table, it seems that the fom constantly improved from +1970 to +2770 steps and then remained constant from +2770 to +4170 steps.

We performed a OMC scan with MMT_M2_TX = +2770 steps at 12:36:00 utc:

TEM00 peak at 0.80 mW, order 1 at 0.0003 mW (0.04%), order 2 at 0.0087  mW (1.09%) > The mode matching seems to be slighty improved.

We performed a OMC scan with MMT_M2_TX = +3470 steps at 13:15:00 utc:

TEM00 peak at 0.80 mW, order 1 at 0.00065 mW (0.08%), order 2 at 0.0082  mW (1.03%) > The mode matching seems again slighty improved.

We performed a OMC scan with MMT_M2_TX = +4170 steps at 14:12:00 utc:

TEM00 peak at 0.785 mW, order 1 at 0.0004 mW (0.05%), order 2 at 0.0076  mW (0.97%) > The mode matching seems again slighty improved.

At this point we considered that a motion of +4170 steps on MMT_M2_TX was already quite large as it corresponded to a miscentering of the B1p beam on its camera of -800 um. We therefore decided to stop the rotation of MMT_M2 _TY at this level and we hold the new postion MMT_M2_TX = +4170 steps.

Then we tried to improve further the mode matching by rotating again the MMT_M2_TX, that we brought to TX = -1000 steps, with the bench TY controlled again in high bandwidth. This position was reached around 14:54:40 utc.

We performed a scan in the final configuration at 14:55:20 utc:

TEM00 peak at 0.787 mW, order 1 at 0.0026 mW (0.3%), order 2 at 0.0072  mW (0.91%) > The mode matching seems again slighty improved, however the alignment is a bit degraded, therefore the conclusion is not so clear.

In any case it seems that we have reached a mode matching of the order of 99%.

While rotating the MMT_M2_TX/TY, the bench was under drift control, therefore the TX/TY angular positions of SDB1 changed. This induced large positive correction on the marionetta TX correction, that was compensated by displacing the SDB1 motorized counter-weight by +18000 steps.

At the end of the shift we updated the values of the new sepoints in SDB1_LC configuration.

Since the beam position on the B1p camera have changed by -800 um, we decided to update the TY setpoint of SDB2 in order to recenter the beam on the camera. The SDB2 TY setpoint was changed from 1100 to 900 urad (Fig.1). With this new setpoint we recover a beam position which is only 300 um away from the initial position on the B1p camera, and it remains close to the center on B5 camera. This should be acceptable for the photodiode centering.

We also recentered the B1p on the quadrants with -800 steps on the B1p_M1_H picomotor and +700 steps on the B1p_M2_V picomotor. B5 quadrant centering was not checked due to an issue of communication with the ethernet bridge ethmt3 preventing the opening of the shutters.

Problems encountered during the shift:

• In the process SDB1_PDU, the values of Socket 1 and Socket 2 that are displayed are always 0, even when we switched on the picomotors. We are confident that the drivers were powered since we could successfully actuate the picomotors.
• We could not communicate with the SDB2 quadrants. The Ethernet bridge ethmt3 is unreachable with a ping command. A similar problem had been encountered earlier this year (https://logbook.virgo-gw.eu/virgo/?r=50426). Several attempts to switch on/off the power supplies PowerUnit11 and PowerUnit14 did not restore the communication with this Ethernet bridge. Until this problem is solved, this will prevent to use the B1p and B5 quadrants. Below we report the list of commands sent in an attempt to restore the communication.

2021-05-08-19h41m21-UTC    info gouaty       Disable power for device Switch using PowerUnit11
2021-05-08-19h41m39-UTC    info gouaty       Enable power for device Switch using PowerUnit11
2021-05-08-19h43m06-UTC    info gouaty       Disable power for device Switch using PowerUnit11
2021-05-08-19h43m07-UTC    info gouaty       Enable power for device Switch using PowerUnit11
2021-05-08-19h43m28-UTC    info gouaty       Disable power for device Switch using PowerUnit11
2021-05-08-19h43m43-UTC    info gouaty       Enable power for device Switch using PowerUnit11
2021-05-08-19h47m10-UTC    info gouaty       'B1p QD2:Open B1p QD2 galvo loop' sent to SDB2_Quadrants
2021-05-08-19h47m12-UTC    info gouaty       'B1p QD1:Open B1p QD1 galvo loop' sent to SDB2_Quadrants
2021-05-08-19h48m03-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-19h48m41-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-19h52m50-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-19h52m54-UTC    info gouaty       Disable output of PowerUnit14
2021-05-08-19h55m16-UTC    info gouaty       Enable output of PowerUnit14
2021-05-08-19h55m21-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-20h00m43-UTC    info gouaty       Disable output of PowerUnit14
2021-05-08-20h00m48-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-20h01m31-UTC    info gouaty       Enable output of PowerUnit14
2021-05-08-20h02m03-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-20h05m51-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-20h06m20-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-20h07m52-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-20h08m20-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-20h12m45-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-20h14m21-UTC    info gouaty       Enable output of PowerUnit11
2021-05-08-20h18m13-UTC    info gouaty       Disable output of PowerUnit11
2021-05-08-20h18m21-UTC    info gouaty       Enable output of PowerUnit11

2021-05-09 11h46m08 UTC    gouaty Disable output of PowerUnit11

2021-05-09 11h46m36 UTC    gouaty Enable output of PowerUnit11