The mode matching of subcarrier laser on the OPA can be measured by observing the reflection on the SQZ_EQB1_IR_PD_MONI DC channel.  When the squeezer is in BAB mode, the measurement is affected by the transmission peaks of the BAB. On 15/04 the squeezer was switched to squeezing mode. When scanning the OPA with the SC beam on, the HOMs reflection peaks are visible with a sensitivity of better than 1% with respect to the fundamental mode peak, see Fig 1 and vertical zoom in Fig 2. The fast photodiode for SC AA was accidentally misaligned at the moment, and so the alignment was only roughly tuned, that's why misalignment modes are not well suppressed during the test.

Fig 3 shows a scan without the SC beam. The resonance peaks of subcarrier and CC beams contribute to much less than 1%.