I placed the OSA (Optical Spectrum Analyzer) on the AP table and this OSA will monitor the REFL beam.
Tomorrow I will do fine alignment of the OSA.
(some notes)
- a new 90% BS in the REFL path for limiting the REFL beam power
I installed a 90 % beam splitter in the REFL path so that this BS limits the maximum power in the downstreams because we don't want to damage any more RFPDs.
The REFL beam has a power of about 610 mW and the BS has R = 94 % (the spec says 90 +/- 4 % ), resulting in a power of ~37 mW in the transmitted light.
Then the transmitted beam goes through the combination of a half-wave plate and PBS, which allows a fine adjustment of the power.
After passing through the lambda/2 + PBS, the beam is branched to four ways and each beam goes to the REFL RFPD, i.e. REFL11, 33, 55 and 165.
In the end each RFPD receives a laser power of 9 mW at maximum, which is reasonably lower than the power rate of the photo diodes (~17 mW ).
The new OSA uses the reflected light from the 90% BS.
- Squeezed the ABSL (ABSolute length Laser) path
I squeezed the path of the ABSL in order to accommodate the OSA.
I tried to keep the same optical distances for some lenses, but I guess their mode matching must be different from what they used to be.
So be aware of it.
- Modification of the AS OSA path
I have also modified the optical path of the AS OSA because there had been an extra zig-zag path which made the path more complex in unnecessary way.
Since I have squeezed the ABSL path, it allowed me to simplify the optical path. So I modified the path.
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I am installing an OSA on the AP table and it's ongoing.
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