[Haino and Inoue at X end, Izumi, Shoda, Arai, and Enomoto at Center area]
Today we tried to see whether or not the light we saw at X end is travelling through the duct without hitting somewhere.
To judge this, we did three things as follows:
- visual inspection at X end with an IR card and IR viewer; I think this results will be reported by someone else.
- we checked the direction of move of the beam spot at X end when we tilted PR3 in the known directions (for both of PIT and YAW) => the result says there are even-time bounces (including zero-time bounce).
- compared the measured and expected output of the PD at X end. => Consistent! The details are below.
-- Power entering the PD --
some numbers
the gain of the Thorlabs PDA100A: 50 dB --> V/W efficiency = 0.3 * 4.75*10^5 [V/W] (see p.8 of this manual, Hi-Z termination)
aperture of the PD: phi 9.8 mm (see here)
expected beam radius (w) at X end: 66 mm (see 3552) --> 1.1 % of the power of the beam enters the PD
the beam power that leaves Center area: 120 mW (at PSL; ) * 0.8 (IMC; rough number estimated from 691) * 0.94 (IFI; G1604999) * 0.10 (PRM) * 0.50 (BS) = 4.5 mW
V to cnt conversion factor: 2^14/10 [cnt/V]
Synthesising these numbers, we will have the expcted output of the PD in counts: 1.2 *10^4 [cnt].
On the other hand, the measured output of the PD was 1.0 *10^4 [cnt] at maximum (see the attached figure).
It can be said that these two numbers are consistent, considering there would be uncertainty in the A/W responsibility (0.3) of the PD and transmittance of IMC.
In conclusion, we could not find any evidence that shows the beam is hitting somewhere wrong.
