40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  Cryo Lab eLog  Not logged in ELOG logo
This is a draft message, edit and submit it to make it permanent  
Message ID: 2803     Entry time: Thu Aug 26 19:40:06 2021
Author: rana 
Type: Noise Hunting 
Category: Laser 
Subject: high frequency frequency noise measurement w/ DFD and new low pass 

I modified Aaron's DFD box: I replaced the SLP-1.9 (1.9 MHz low pass filter) with a 44 MHz low pass that we conveniently had in the lab.

The purpose of this is to measure the high frequency noise of some of our lasers to figure out if there's any difference between the RIO Planex and Teraxion NLL.

I did the hookup and everything looks good so far. So far I have measured the RIO E/W beat and the RIO E vs Terax beat.

Need to do some more data processing to get plots.

Some notes along the way:

  • For monitoring the output of the RF amp, we want to use the CPL IN port of the bi-directional coupler that goes between the amp and the DFD. The CPL IN measures a coupled version of the input, whereas the CPL OUT measures the reflection that comes back from the DFD box. At 175.5 MHz, with the 44 MHz low pass on the mixer IF port, the reflected signal ~ -40 dBm when the CPL IN was at ~ -10 dBm.
  • I have made a shared folder in ligo.wbridge dropbox called PSOMA_data. Now that Moku is logged in to dropbox, and dropbox installed on the gaston workstation, the files are automatically synced to the workstations. We can also share the folder with our personal dropbox accounts so that there's seamless data availability.
  • Also attaching the times series plot used to calibrate the discriminant. I used the Marconi knob to scan the frequency and find the min & max of the DFD box at

Attaching beat note noise spectra showing the noise of the DFD (with no pre-amp, so probably Moku input noise), the RIO Planex (E & W lasers from the Cryocav table), and the Teraxion NLL. Looks like they're similar in HF noise.

Attachment 1: TeraRIOEast_beat_Screenshot.png  1.026 MB  Uploaded Thu Aug 26 21:01:46 2021  | Hide | Hide all
Attachment 2: Planex-Beatnote-ASD.pdf  44 kB  Uploaded Fri Aug 27 18:07:27 2021  | Hide | Hide all
Attachment 3: DFD-Discriminant-Cal.pdf  32 kB  Uploaded Fri Aug 27 18:08:43 2021  | Hide | Hide all
ELOG V3.1.3-