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Message ID: 1680     Entry time: Fri Jul 22 23:28:52 2016
Author: awade 
Type: DailyProgress 
Category: Mode matching 
Subject: South path: EOM3 Placement and beam profile (also note on D4σ fit) 

Measured beam for third EOM south path

I measured the beam as it would enter the third and final EOM after the PMC (note that the PMC was removed from the path for now).  The first PLCX-25.4-64.4-UV-1064 (f = 143.23 mm) was placed at 2769.5 mm from the laser head (see attached updated map of south path). The beam profile measurements are attached as txt file along with plot. The z = 0 reference point is the first bolt on the second table or 2815 mm referenced from the laser head.

The fit of the data was:

Horz. beam waist = 112.7457 um
Horz. beam waist position = 2908.1548 mm
Vert. beam waist = 115.3321 um
Vert. beam waist position = 2940.4081 mm
Mean beam waist = 114.0389 um
Mean beam waist position = 2924.2815 mm

It appears that the actual beam waist is 150 um and 166 um in horizontal and vertical respectively for the data. (At least if we trust the D4σ fit).



It seems that the CCD measurements close to the waist don't fit well with the data at a large distance.   I am using the D4σ definition of beam width.  This should be the same as 1/e^2 clip method when dealing with Gaussian beams. However, it is possible that small beams have biased results from dark noise + offsets in pixels well outside the beam that weight the integral of the beam profile. This may be a deficiency in this method. At some stage I should check how to get the best possible pre calibration for the CCD baseline. 





Attachment 1: plot20160722_south_BeamProfileIntoThirdEOM.eps  132 kB  | Hide | Hide all
Attachment 2: data20160722_south_BeamProfileIntoThirdEOM.txt  108 Bytes  | Hide | Hide all
0.0254	0.0000005	0.0000005
1	456	584
2	402	557
3	328	350
4	332	300
5	391	357
6	504	421
8	768	615
10	1064	835
Attachment 3: North_South_layout_progress_dist_final_v8.pdf  113 kB  | Hide | Hide all
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