General requirement

RP requires attenuation to XX mJ.

Pre-2022 RP attenuator

Currently installed

4 mirrors and thin-film polarisers

p-pol as input

Attenuates to 0.5*0.8*0.5*0.1 = 0.02 (2%)

Issues:

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):