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AdV-COM (AdV commissioning (1st part) )

Allocca, Bersanetti, chiummo, Izumi, Swinkels - 0:11 Friday 16 December 2016 (35843)

Tuning central heating

We made a shift about differential lens tuning by using the CH on both CPs.

We explored full range of actuation for each arm independently and set a thermal lens on the WI CP. This was kind of unexpected, the lens should have been on the NI CP in order to compensate for an allegedely cold lens in the WI CP.

The configuration used to set this working point was both arms locked and mich in dark fringe and looked for a minimum in the B1p power, both for carrier and SBs. More details will be given after digesting data (and n-th pizzas :S). At the end of the shift the W-arm transmitted power became very noisy.

We leave the CH-CO2 shining on the WI CP at the chosen power, ITF with both arms locked and MICH in DF on B1p_6MHz..

Comments to this report:

rocchi - 14:50 Friday 16 December 2016 (35855)

I'm not that much surprised...

Allocca, Chiummo, Izumi - 19:47 Tuesday 20 December 2016 (35889)

In order to find the best TCS configuration, we applied a sinusoidal power variation to NI CH first and to WI CH later. This was in order to see for which CO2 power we got the best contrast defect.

Both the arms were locked and MICH was locked in DF.

During the measurement, we were monitoring the power circulating in the arm cavities, the power on B1p and the total power in the sidebads as extracted by the phase camera.

We first put a sinusoidal modulation on NI. However, we couldn't get a real decrease of the contrast defect. Therefore, we switched on the same sinusoidal actuation on WI CH, and in this case the minimum of B1p_DC dropped up to less than 5e-4 mW. Figure 1.

During the measurement we also acquired images with the phase camera. In figure 2 and 3 the power variation of the CO2 beam is shown for NI and WI, respectively. On the top, the images of the Lower sideband power at different times are added. A delay of ~ 700 seconds has been taken into account. The carrier power image was not as significant as the sidebands, since we were locked in dark fringe, and the upper sideband didn't look very different with respect the lower one.

A different beam shape is induced when the North or the West compensation is added. This has to be further investigated.

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