Following a discussion we had with Matteo and Simon I switch the position of the power meter and the birefringence readout with respect to the flipping mirror.
Meaning that the power meter is now in reflection and birefringence readout is now in transmission. The reason being to avoid possible polarizations issue at this reflection.
Because there is not enough space on the imaging unit, I added a small optical board that hosts all the birefringence readout part.
Just before it, I placed a 1" IR reflective mirror that sends the ir power to the power meter. This mirror is installed on a flipping mount (which was before holding a lens).
On the birefringence board I placed a optical density 3 and its reflection is sent to a vantablack beam-dump (not sure but seems so).
A 100 mm focal length lens coated for green and IR (it is coming from FC experiment) is mounted on a black tube linked to the PBS.
Then, 2 Thorlabs photodiode are looking at its reflection and transmission.
The trouble is that now there is only 1 power supply so we might have to switch one for a PSD.
Also, I tried to connect one photodiode to the lockin amplifier but it was saturating so I will have to add optical densities.
Thanks a lot for the report.
I have some questions. What is the input power of the beam and wouldn't it be possible to further reduce that power by using the HWP right after the fiber-output?
In any case, I remember that we had to use several ND filters as well...
Regarding the power supply of the PD, Can't you use the one from the absorption-PD? I think they are both from TL and the power supply should be the same.
By the way, was there a reason to reject the PSDs which we used in the past?
You're welcome.
The input power is 30 mW and can indeed be tweaked with the HWP.
Also, the lockin amplifier settings have not been changed yet.
For the photodiode powersupply we will take the one used for the 1310 nm beam I think.
For the PSDs, one is now used in FC experiment so only one is available.
It seems that with the 100 mm focal length lens, the beam is small enough for the photodiode. And we can also tune their gain.