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The potential fluence on the mirrors can be in excess of 1 J/cm^2.

The attenuator also needs to be failsafe. That means that damage to the optics should result in a lower transmission and make the system more safe as a result.

That means that transmissive attenuators, e.g. two compensating mirrors at 45 degrees, can not be used.

Instead a reflective attenuator design is employed which is harder to align.

Pre-2022 RP attenuator

Currently installed RP attenuator.

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That is in order to avoid that wedges compensate each other.

Update Jan 2022:

To avoid any kind of confusion, we now made sure that the thin part of the wedge is on the top, resulting in all back reflections being pointed downwards.

The thick side of the wedge is where the pencil markings are, although not perfectly centred.

Wavefront

Need to check this:

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