K. Tanaka, Akutsu

Just measured the light power corresponding to the one into the IMC, in the PSL room.

• With the Tholabs' PD-type: 0.385 W just after IP2 (the final steering mirror (for input pointing) in the PSL room) when the shutter opened.
• With the water-cooling power meter/shutter (so it may not be precise for faint light): 0.28 W (but there seems minus 0.09W offset when no IR beam, so 0.28+0.09 ~ 0.37W, so consistent) Maybe I should do offset zero-ing if this power meter has such function. For the Thoorlabs' power meter I do the zero-ing always of course.
• MEDM as of today (and soo RTmode; so-called sum of IMC_REFL + IMC_TRANS): 0.317 W

So, the two off-the-shelf power meters seem consistent. Nice. But anyway, the calibration parameters in the corresponding RTmodel (and so MEDM) should be revisited. Maybe the viewport window would not absorb such amoun of loss power...

Note: repeat the same measurement with various power (control by the HWP) must make things more reliable.

Anyway, I confirmed there was a transmit beam behind the first steering mirro for the periscope just in front of the beam tube to the IMC. Maybe we can install a DCPD here for permant use.