General requirement
RP requires attenuation to XX mJ.
Pre-2022 RP attenuator
Currently installed
4 mirrors and thin-film polarisersÂ
p-pol as input
Attenuates to 0.5*0.8*0.5*0.1 = 0.02 (2%)
Issues:
- Appears to introduce astigmatism
- Ghosts when changing polarisation
2022 RP attenuator
4 mirrors and s-pol as input (one wave plate needs to be removed).
Mirrors are 35%R from MPO, AR coating on back and 2 degree wedge.
Attenuation should be down to 0.35^4 = 0.015 (1.5%) or 800 mJ * 0.35^4 = 12 mJ
Reflectivity was tested:
Wedge orientation:
We determined that the thick side of the wedge needs to alternate sides when looking from the back of the mirror mounts.
That is in order to avoid that wedges compensate each other.
Quote for mirrors (arrived first week Dec):