During the week end, we investigated the IMC loop behavior in order to improve it:
- Measurement of the IMC loop: UGF 80 kHz, phase margin 19° (22dB of attenuation); UGF 100 kHz, phase margin 17° (19dB of attenuation)
- Effect of the SL electronic loop: the gain of SL electronic loop was increased then decreased by 4dB, no effect observed on the possibility to improve the IMC loop
- Measurement of the pEOM transfer function: the IMC was locked in 1/f regime and a perturbation signal was injected into (i) the pEOM preamplifer (ii) directly the pEOM. Their behavior was normal.
- Measurement of the IMC_ref photodiode response : The IMC was unlocked and the its end mirror tilted. The pahse-pEOM was swapped by an amplitude-pEOM. The response of the pEOM was measured by using calibrated photodiode on the laser bench ; then the response of several photodiode on the LB and EIB (to measure the TF of SL and PMC) including the IMC_ref were measured -> Normal behavior.
- Measurement of the SL optical injection frequency band : 1.9MHz. After increasing the power injected into the SL (20% recovered from the fiber amplifier pick-off beam) the injection frequency band was increased by 10% as expected. This allowed to improve the IMC loop : UGF 115 kHz, phase margin 19° (18dB attenuation). This effect needs to be investigated.

Once the data fully analyzed, plots and more accurate numbers will be provided in a separate logbook entry.