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  Coating Ring-down Measurement Lab elog  Not logged in ELOG logo
Message ID: 107     Entry time: Mon Sep 12 16:00:06 2016
Author: Gabriele 
Type: General 
Category: Daily Progress 
Subject: First fully automated measurements of ring down 

I finished the first version of the automation software to measure the ring down of the disk modes. I tested it with the new substrate that was installed yesterday. Here are some screenshots and a brief explanation of how it works.

It is based on a Python/Tk GUI, that can be launched on the workstation with the command ~/CRIME/crime.py

The main screen is similar to the following. Once a baseline spectrum is acquired, it is shown in the main panel:

The user should specify the folder and prefix of the result files, and other parameters related to the excitation. The when the "Excite and ring down..." button is pressed, here's what happens

  1. If a baseline spectrum (before excitation) is not available, one is acquired with the specified parameters
  2. A broadband white excitation is applied with the selected amplitude and duration

  1. Another spectrum is taken. This is then whitened by dividing it with the baseline. This could be used directly to select the modes that have been excited. However, some parts of the noise floor are non stationary, so a second whitening is performed: the noise background is estimated by removing all lines, and it is then again divided out from the spectrum.
  2. All lines above a SNR threshold are then selected and shown in the main window together with the whitened spectrum: 

At this point the amplitude of the peaks are continuosly monitored (every second) and thei amplitude shown in a new window. The user can select a subset of the modes for the plotting.

There are some wandering peaks in the spectrum, so some of the peaks aren't actually modes that get excited. This is easily fixed in the post processing of the results. 

All peak amplitudes are saved to files in real time, so if you stop the GUI you'll have some partial results.

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