| Quote: |
|
* (JCD) Think about this box's purpose in life. What kind of gain do we need? Do we need more / less than we're currently getting? NPRO freq noise is 1/f and is 10kHz/rtHz at 1Hz (this is from a plot of an iLIGO NPRO from Rana's thesis, but it's probably similar). Talk to Kiwamu; the noise budget in the paper seems to indicate that we had some kind of boost on or something. Also, if we need much more gain than we already have, we'll definitely need a different box, maybe the PDH2 box that they have over in WBridge.
|
It's not so impressive yet, but here's a plot that shows (a) Rana's guess for laser frequency noise, (b) The inferred in-loop version of that noise, (c) The CARM linewidth FWHM, translated to Hz.
For (b), I take the loop that Rana and I measured last night, and I assumed that it continued on forever as 1/f toward low frequency. Then I do 1/(1+G) to get the closed loop version of the loop (which is a measurement with an artificial line tacked on the end), and multiply this with the laser freq noise, which is also totally artificial.
For (c), I do df/f = dL/L, with f = c/lambda_green, since the rest of the plot is meant to be in green frequency units.
This is my beginnings of trying to come up with a requirement for our green PDH boxes. We weren't very clear in the MultiColor paper about the nitty-gritty details (obviously), but then Kiwamu didn't expand on those details in his thesis either. He talks a lot more about the design considerations for the digital ALS loop, which isn't what I want today. I will send him an email to see if he had any notes that didn't make it into his thesis.
|