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General requirement

RP requires attenuation to 14 mJ, so 1.75% at 800 mJ input.

Pre-2022 RP attenuator

Currently installed

4 mirrors, wave plate and thin-film polariser

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
  • Loads of different optics (splitting ratio and 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):

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