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40m Log |
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Tue Apr 24 11:31:59 2018, gautam, Configuration, ALS, Proposed changes to EX fiber coupling 
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Tue Apr 24 18:54:15 2018, gautam, Configuration, ALS, Proposed changes to EX fiber coupling
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Wed Apr 25 19:09:37 2018, gautam, Configuration, ALS, New look EX Fiber coupling    
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Thu Apr 26 11:24:50 2018, gautam, Configuration, ALS, New look EX Fiber coupling - pol stability
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Thu Apr 26 18:58:21 2018, Bruce, Configuration, ALS, New look EX Fiber coupling - pol stability
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Fri Apr 27 01:36:02 2018, gautam, Configuration, ALS, IR ALS noise performance    
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Wed May 2 21:39:33 2018, gautam, Configuration, ALS, IR ALS for EY
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Fri May 4 21:17:57 2018, gautam, Configuration, ALS, BeathMouth pulled out of PSL table
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Tue May 8 00:40:51 2018, gautam, Configuration, ALS, BeathMouth pulled out of PSL table 
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Thu May 24 19:41:28 2018, gautam, Configuration, ALS, BeathMouth reinstalled on PSL table
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Thu May 24 13:06:17 2018, gautam, Configuration, ALS, DFD noises 
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Thu May 24 20:31:03 2018, gautam, Configuration, ALS, DFD noises 
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Message ID: 13817
Entry time: Fri May 4 21:17:57 2018
In reply to: 13807
Reply to this: 13824
13886
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Author: |
gautam |
Type: |
Configuration |
Category: |
ALS |
Subject: |
BeathMouth pulled out of PSL table |
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I have been puzzled about the beat note level we get out of the BeatMouth for some time.
- The beat PD used is the Menlo FPD310.
- But the version we have is an obsolete version of the product, for which a manual is hard to find.
- Hence, I don't know the transimpedance/electrical characteristics of this PD.
- The optical damage threshold of the PD is quoted as 2mW, which is a number I have been careful not to exceed.
- But I've felt that the beat amplitude level we get out of this PD is far too low considering the amount of DC optical power (as measured with a fiber power meter) incident on the PD.
- After some emailing and online hunting, I've gathered some numbers for the PD which are now on the wiki.
- The fiber beam splitters we use inside the BeatMouth don't have PM fibers. There are 3 such splitters inside the BeatMouth. So the overlap efficiency on the PD is unknown.
- But even so, the beat levels I was seeing were too low.
I have pulled the box out in order to re-characterize the DC power levels incident on the PD, and also to change the gain setting on the PD to the lower gain which is more compatible with the level of optical power we have going into the BeatMouth. The modern catalog for the FPD310 (see wiki) suggests that the maximum output voltage swing of the PD is 1Vpp driving a 50ohm load. With 50% overlapping efficiency between the PSL and AUX beams, and 400 uW of optical power from each beam, I expect an output of 0.5Vpp. Even with perfect overlap, I expect 0.8Vpp. So these numbers seem reasonable.
I also plan to check the scaling of electrical beat amplitude to optical power for a couple of levels to see that these scale as expected... |