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Message ID: 5436     Entry time: Fri Sep 16 16:34:54 2011
Author: Paul 
Type: Update 
Category: SUS 
Subject: ITMY SRM oplev telescope plan 

I've calculated a suitable collimating telescope for the ITMY/SRM oplev laser, based on the specs for the soon-to-arrive 2mW laser (model 1122/P) available here: http://www.jdsu.com/ProductLiterature/hnlh1100_ds_cl_ae.pdf

Based on the fact that the 'beam size' value and 'divergence angle' value quoted don't match up, I am assuming that the beam radius value of 315um is _not_ the waist size value, but rather the beam size at the output coupler. From the divergence angle I calculated a 155um waist, (zR = 12cm). This gives the quoted beam size of about 316um at a distance of 8.5" away from the waist. This makes me think that the output coupler is curved and the waist is at the back of the laser, or at least 8.5" from the output coupler.

The collimating telescope gives a waist of size 1142um (zR=6.47m) at a distance of 1.427m away from the original laser waist, using the following lens combo:

 

L1 f=-0.15 @ 0.301m

L2 f=0.3 @ 0.409m

 

This should be fine to get a small enough spot size (1-2mm) on the QPDs.

 

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