[Shalika, Mitsuhashi-san]

In continuation to the ongoing ringdown measurement, this elog covers tests of the photodiode to be used at the transmitted beam path. We suspect that the ringdown measurement is not accurate because of absence of RF switch and an unsuitable PD. 

We tested the decay time of two PDs after shutting down the AOM. 

1. PDA20CS-EC --(this is the one that was initially installed. We suspect we should change this with PD in 2)

a. The decay time for the 20dB gain setting is 0.4 µs (Fig. 1)

b. The decay time for the 30dB gain setting is 0.4 µs (Fig. 2)

2. PDA05CF2

a. The decay time (oscilloscope time scale as 1µs) is 0.8 µs (Fig. 3)

a. The decay time (oscilloscope time scale as 500 ns) is 0.8 µs (Fig. 4)

It seems this is very close to the previous ringdown time estimated by us (0.9 µs) and the above-measured time is not accurate for both PDs. We realize it might be happening because we don't have an RF switch installed yet.

Next Step:

We will install the RF switch between the RF driver and AOM, and observe the PD responses again. 

Notes:

1. We brought RF switch from ATC clean room to ATC cryogenic room, today. 

2. I have brought a mulitmeter from electrical shop to ATC.