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Entry  Tue Jun 28 16:59:35 2022, Paco, Summary, ALS, ALS beat allan deviation (XARM) xbeat_1340469968.pdffrac_avar_xbeat.pdf
    Reply  Tue Jun 28 18:53:16 2022, rana, Summary, ALS, ALS beat allan deviation (XARM) 
       Reply  Wed Jun 29 14:28:06 2022, Paco, Summary, ALS, ALS beat allan deviation (XARM) frac_adev_xbeat.pdf
Message ID: 16962     Entry time: Wed Jun 29 14:28:06 2022     In reply to: 16959
Author: Paco 
Type: Summary 
Category: ALS 
Subject: ALS beat allan deviation (XARM) 

I guess it didn't make sense since f_beat can be arbitrarily moved, but the beat is taken around the PSL freq ~ 281.73 THz. Attachment #1 shows the overlapping tau allan deviation for the exact same dataset but using the python package allantools, where this time I used the PSL freq as the base frequency. This time, I can see the minimum fractional deviation of 1.33e-13 happening at ~ 20 seconds.

Quote:

what's the reasoning behind using df/f_beat instead of df/f_laser ?


Another, more familiar interpretation

The allan variance is related to the beatnote spectral density as a mean-square integral (the deviation is then like the rms) with a sinc window.

\sigma^2_\nu = 2 \int_0^{\infty} S_\nu(f) \lvert \frac{\sin({\pi f \tau})}{\pi f \tau} \lvert ^2 df

Attachment 1: frac_adev_xbeat.pdf  20 kB  Uploaded Thu Jun 30 11:12:41 2022  | Show | Show all
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