[Valera, Stefan, Kentaro, Yoichi, Masayuki, Yutaro]

We did the investigation around OMC. The OMC transmission is too small. We do not have a clear explanation for that yet.

We did the following things.
* put a gigE camera for OMC_REFL. Since the amount of the light was too much, we put 2'' mirror in front of the camera as an attenuator.
* found that what we believed is OMC trans, leakage light from OMC4, was actually some scattered light, which is not coming from OMC4. So we removed the OMC_trans set-up.
We also looked at the mirror, OMC4, itself by using a telephoto lens attached to a gigE camera, and then confirmed that seemingly no light is coming out from OMC4.
Probably the leakage light might be hitting the mount of OMC4.
* the power each OMC trans PD (GW channel) receives is too low. They are ~100 counts at maximum.
100 counts corresponds to ~0.9 mW, while the power of the incident beam to OMC should be ~ 30mW ( 4W(input) * 10%(PRM) * 25%(BS twice) * 30%(SRM)).
Two QPDs on OMC breadboard, which samples 0.25% of the incident power for each, received 0.09 mW. This indicates that the incident beam is really ~30 mW (actually 36mW from this number; QPDV1: 10000counts and TI of 100kOhm, QPDV2: 2500counts and TI of 20kOhm).

Next move
* measure the beam profile of the incident beam to OMC
* put a PD for OMC REFL to check if OMC is really critically-coupled or not.
* evacuate the chamber to see if ~ 700Hz huge peak disappears or not.