This morning we performed a couple of tests in order to better understand the behaviour of the IMC locking loop when the ML/SL locking loop is changed.

We first measured the power of the master laser transmitted by the optical fiber on the laser bench and check the alignment of the ML on the optical fiber which was ok.

With 1.58A pumping current, we had 273mW on the laser bench.

With 1.75mA pumping current, we had 400mW on the laser bench.

Then we made 2 tests:

- SL loop att increased by 4dB from 10dB att to 14 dB att. P_Master laser=273mW, IMC loop att=16dB

- SL loop att increased by 4dB from 10dB att to 14 dB att. P_Master laser=400mW, IMC loop att=16dB

In both cases, the IMC cavity can be locked with attenuation comprised between 11dB and 23dB.

For comparison, in the plot you can find the previous measurements.

As one can see the OLTF has imporved but is not yet back to the nominal situation. The UGF has been increased form 60 kHz to 110 kHz.

In order to further improve the situation, we could replace the master laser by the spare one as foreseen in the maintenance plan.

On the long term, we can think to move the high frequency actuation (Electrooptic path) physically after the PMC cavity in order to avoid behing anoyed by the slave laser loop/injection locking loop.