The power incident on the pre-modecleaner was increased from ~30W to ~138W. The power transmitted by the pre-modecleaner, as measured by a power meter located right after the pre-modecleaner, was ~123W. This is consistent with the visibility measurement conducted last week. The transfer function for the low and high power modes are similar. In the high power mode, the unity gain frequency was ~6 kHz with a phase margin of ~ 80 degrees. There is a problem with the transmission photodiode. Whilst the filter file for the photodiode appears to be okay, the output of the photodiode is not consistent with the amount of incident light. For the factor of ~4 increase in light power we observed an increase of less than 1 in the photodiode output. This problem does not show up in the low power mode. The photodiode was given a cursory inspection and appears to be okay. The signal cable was temporarily swapped but made no difference. This is a 2mm InGaAs photodiode (D1002929). I suspect one of the voltage regulators is sporadic. Perhaps the LM317S providing the bias voltage. This will be checked later today. Jason, Peter