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Entry  Tue Aug 28 16:27:22 2012, ericq, Update, PSL, PBS and Half Wave plates introduced 
    Reply  Tue Aug 28 17:16:54 2012, ericq, Update, PSL, Power reduced! 
       Reply  Tue Aug 28 17:43:04 2012, Jenne, Update, PSL, Power reduced! 
       Reply  Wed Aug 29 17:02:41 2012, ericq, Update, PSL, Power reduced! 
          Reply  Wed Aug 29 17:35:34 2012, Koji, Update, PSL, Power reduced! 
    Reply  Tue Aug 28 17:51:39 2012, Jenne, Update, PSL, PBS and Half Wave plates introduced 
Message ID: 7299     Entry time: Tue Aug 28 17:51:39 2012     In reply to: 7295
Author: Jenne 
Type: Update 
Category: PSL 
Subject: PBS and Half Wave plates introduced 

Quote:

[Jenne, Eric]

We installed a Half Wave Plate -> Polarized Beam Splitter -> Half Wave Plate in the PSL beam line, immediately after the EOM, to be used for attenuating the beam when we vent, as in Entry 6892.

It was illuminating to discover that the optics labeled QWP0-1064-10-2 are indeed half wave plates, instead of quarter wave plates as QWP suggests. 

The PBS transmits "P"/Horizontal polarization, but the beam coming from the EOM is "S"/Vertically polarized, and we want to keep that, since we do not want the beam attenuated quite yet. 

So, we use the HWP to rotate the P from the EOM to S, so that the majority of the power passes through the PBS. The second HWP then rotates the transmitted S back into P, which continues to the mode cleaner. When we want to attenuate, we will simply rotate the first HWP to change the proportion of S polarized light that will pass straight through the PBS and towards the mode cleaner. 

After setting the proper HWP angles, we aligned the PBS via minimizing the MC reflection.

Since we have not yet attenuated the power, we have not yet changed the BS for the MC reflection, since this would damage the PD. The beam splitter will be changed out for a 100% reflectivity mirror to increase the power to the PD when we do.

 

 Before we did this, I centered PSL POS and ANG, which gives us a reference of where the PSL beam was good when the MC spots were ~centered.  There had been a beam dump blocking them, possibly from the last time we put in the power attenuator optics.  This beam dump was moved a little to be out of the way of the PSL QPDs, and the PBS placed closer to the lens after the EOM, so that the PBS reflected beam is dumped.  However, we should not remove that razor dump when we remove the attenuation optics, since it is also dumping a stray IR beam from the PSL QPD pickoff windowd.

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