[miyoki, uchiyama, hasegawa]

We proposed a new challenging idea to make a beam line along 3km arm by using a strong collimated LED torch.
At present, the Y arm is evacuated and has two optical windows in GVs near BS and EYA tanks. If we inject a very strong and collimated light from the BS side window, we can expect that a faint portion of light reaches the other window and illuminates the ETM because the rest portion of light will be damped by many baffles in the arm. If we find the faint light at the ETM and put a slit in front of the ETM, we can find rough alignment of the ETM by adjusting the reflected light also to go through the same slit. If we inject it from the EYA tank and find a faint light at the BS, we can find rough alignment of BS by adjusting the reflected light at the BS to illuminate PR3 mirror.

Firstly, we tried to illuminate the ETM from BS side. The bright spot at the BS side was visible from EYA tank. However, it was hard to find faint light on the slit plate that was set in front of ETM in EYA tank even if we turned off all other light around ETM area. We may have to use digital camera whose exposure time around 10 seconds or more to find the faint light(, but we did not.). Actually, the torch illumination power was around 800 lm. So, Michimurra-kun bought 15000 lm torch to try again.