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Entry  Tue Oct 21 18:40:46 2014, manasa, Update, General, End laser fiber setup 
    Reply  Fri Oct 24 10:08:24 2014, manasa, Update, General, Y AUX laser - fiber coupled 
       Reply  Fri Oct 24 18:53:23 2014, rana, Update, General, Y AUX laser - fiber coupled 
       Reply  Mon Oct 27 12:17:46 2014, manasa, Update, General, Y AUX laser coupling telescope design AUXmode.zipAUXmode.png
          Reply  Wed Oct 29 11:45:11 2014, manasa, Update, General, Y AUX laser - fiber coupled (52%) 31.png
Message ID: 10640     Entry time: Mon Oct 27 12:17:46 2014     In reply to: 10638     Reply to this: 10650
Author: manasa 
Type: Update 
Category: General 
Subject: Y AUX laser coupling telescope design 

Since I obtained a poor coupling efficiency from the earlier setup, I went back to calculate the coupling efficiency of the current setup.

For the current setup, I took the average of the x and y waist of the input beam and calculated the distance at which the input beam diameter would match the (fiber +collimator) beam diameter.

Average waist = 40.2um @-3.3mm from face of doubling crystal

(Fiber PM980 + Collimator f=2.0mm) beam waist = 205um

Distance(z) at which the input beam waist is 205um = 11.9cm

The closest available lens was f = 12.5cm. So I used it to couple the input beam by placing it at z ~12.5cm on a micrometer stage.

Since this gave only 10% coupling, I went back to calculate (using 'a la mode') the best possible coupling that can be obtained taking into consideration the ellipticity of the beam.

The maximum obtainable coupling (mode overlap) is 14.5%  which is still poor.

 

Redesign

Taking into account the ellipticity of the input beam, the available lenses and the space restrictions (lens can be placed only between z= 8 to 28cm), I calculated the best possible coupling efficiency (using 'a la mode').

The maximum possible mode overlap that can be obtained is 58.6% (matlab code and plot attached)

>>auxmode

modematching = 0.58632 

Optimized Path Component List:

    label    z (m)     type    parameters         

    -----    -----     ----    ----------         

    L1       0.0923    lens    focalLength: 0.0750

 

Attachment 1: AUXmode.zip  14 kB
Attachment 2: AUXmode.png  13 kB  | Hide | Hide all
AUXmode.png
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