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Instead a reflective attenuator design is employed which is harder to align.
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2022 RP attenuator
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Currently installed RP attenuator.
Consists of 4 mirrors, a wave plate and thin-film polariser
Requires p-pol as input. A wave plate before the RP attenuator (not shown) changes s- to p-pol for this.
Attenuates to 0.5*0.8*0.5*0.1 = 0.02 (2%)
Maybe a bit more attenuation due to the polariser, as this technically is not enough for a 800 mJ beam.
Issues:
- Appears to introduce astigmatism
- Ghosts when changing polarisation
- Loads of different optics (splitting ratio and polarisation)
Fig 1: Currently installed RP-attenuator. Red arrows indicate the beam path.
Fig 2: Photo of old RP attenuator before decommissioning. Note that a different hole pair was used by now.
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(currently installed)
4 mirrors and s-pol as input (one wave plate needs to be removed).
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Pre-2022 RP attenuator
Currently installed RP attenuator.
Consists of 4 mirrors, a wave plate and thin-film polariser
Requires p-pol as input. A wave plate before the RP attenuator (not shown) changes s- to p-pol for this.
Attenuates to 0.5*0.8*0.5*0.1 = 0.02 (2%)
Maybe a bit more attenuation due to the polariser, as this technically is not enough for a 800 mJ beam.
Issues:
- Appears to introduce astigmatism
- Ghosts when changing polarisation
- Loads of different optics (splitting ratio and polarisation)
Fig 1: Currently installed RP-attenuator. Red arrows indicate the beam path.
Fig 2: Photo of old RP attenuator before decommissioning. Note that a different hole pair was used by now.