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Message ID: 1676     Entry time: Mon Jul 18 15:19:02 2016
Author: awade 
Type: Notes 
Category: Mode matching 
Subject: Remeasured beam profile after second EOM and after realignment 

I made some further alignment adjustments of the modulators and some changes to the polarization inputs and outputs. A lambda/2 wave plate was installed directly after the AEOM (for now) so that the PBS could be manually tuned to the 50% transmission point for s- polarisation into the AEOM.  For now we will ignore the circular polarization generated by the AEOM and the small amount introduced by the previous EOM.  

After checking the field after first EOM I determined that the residual polarization was 108 uW out of 83.4 mW or 0.13 %. Without the EOM installed the extinction was down to ~10 uW.  For now this level of circular polarization should be tolerable.  It is something we can optimize later.  

I also realigned (again) the AEOM and 2nd EOM using Antonio's methods.  This gave a satisfactory looking Gaussian beam. The profile was again remeasured. Its fitted values are:

Horz. beam waist = 259.6243 um
Horz. beam waist position = 1436.9167 mm
Vert. beam waist = 215.7146 um
Vert. beam waist position = 1319.3657 mm

Data and plots attached below.

 

Attachment 1: data20160718_south_AfterSecondEOMAgain_LowerPower.eps  134 kB  | Hide | Hide all
data20160718_south_AfterSecondEOMAgain_LowerPower.eps
Attachment 2: data20160718_south_AfterSecondEOMAgain_LowerPower.txt  146 Bytes  | Hide | Hide all
0.0254	0.0000005	0.0000005
1	560	848
3	703	1076
5	846	1213
7	986	1390
9	1079	1575
11	1157	1756
13	1309	1816
15	1406	1934
17	1503	2152
19	1601	2248
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