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Message ID: 64     Entry time: Tue Jul 6 21:57:19 2010
Author: James Kunert 
Type: Misc 
Category: Hartmann sensor 
Subject: SURF Log -- SLED fiber output temporal analysis 

In the previous log, I describe the direct measurement of the fiber output beam using the Hartmann sensor with the plate removed. In order to analyze how these properties might change as a function of time, we left the camera running over the holiday weekend, Dr. Brooks having written a bash script which took images from the sensor every 500 seconds. This morning I wrote a MATLAB script to automatically analyze all of these images and plot the fit parameters as a function of time (weekendbeamtime.m, attached). Note that the formatiing of a few of the following graphs was edited manually after being outputted by the program (just to note why the plots look different than the code might imply).

The following plots were made:

Amplitude as a function of time:

Amplitude.png

Amplitude again, focused in with more analysis:

Amplitude2.png

 

Offset level:

Offset.png

 

Beam Size:

BeamSize.png

 

Centroid Displacement (note the axis values, it's fairly zoomed in):

CentroidDisplacement.png

Note that these values were converted into radians by approximating the fiber-output/CCD distance and dividing this from the displacement in mm (after converting from pixels). This distance was approximated by assuming a divergence angle of 0.085 and a beam size of ~5.1mm (being a value inbetween the horizontal and vertical beam sizes calculated). This gave a value of ~60mm, which was confirmed as plausible by a quick examination in the lab.

In the first three plots, there are obvious temporary effects which seem to cause the values to fluctuate much more rapidly than they do for the rest of the duration. It is suspected that this could be related to temperature changes within the sensor as the camera begins taking images. Further investigation (tomorrow) will investigate these effects further, while collecting temperature data.

Attachment 1: weekendbeamtime.m  2 kB  | Hide | Hide all
function [X Y wX wY]=weekendbeamtime(basename,guess,N)
%fits 1D gaussian curve to N images in sequence of basename basefile
thisfile=mfilename('fullpath');
thisdir=strrep(thisfile,mfilename(),'');

i=0;
X=[];
Y=[];
wX=[];
wY=[];
... 82 more lines ...
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