40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
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: 10650     Entry time: Wed Oct 29 11:45:11 2014     In reply to: 10640
Author: manasa 
Type: Update 
Category: General 
Subject: Y AUX laser - fiber coupled (52%) 



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)


modematching = 0.58632 

Optimized Path Component List:

    label    z (m)     type    parameters         

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

    L1       0.0923    lens    focalLength: 0.0750


I used the above configuration and was able to obtain ~52% coupling.

Input power = 250mW
Output power with absorptive ND 1.0 = 13 mW

I used the absorptive ND filter before the lens to keep the coupled output power within the range of fiber power meter and also avoid scattering of enormous amount of uncoupled light all over the table.

I have attached the screenshot of the out of loop ALS noise before opening the table (BLUE) and after closing down (MAGENTA). The beat note frequency and amplitude before and after were (14.4MHz/-9.3dBm) and (20.9MHz/-10 dBm).

Attachment 1: 31.png  63 kB  | Hide | Hide all
ELOG V3.1.3-