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Entry  Fri Oct 29 05:40:51 2010, kiwamu, Update, PSL, wideband EOM aligned : AM decreased by 24dB EOMalign.png
    Reply  Fri Oct 29 16:03:35 2010, kiwamu, Update, PSL, wideband EOM : installed the triple resonant box small_DSC_2654.jpg
Message ID: 3819     Entry time: Fri Oct 29 05:40:51 2010     Reply to this: 3825
Author: kiwamu 
Type: Update 
Category: PSL 
Subject: wideband EOM aligned : AM decreased by 24dB 

At the PSL table I aligned the wideband EOM more carefully.

Amplitude modulation (AM) components in the main beam at 29.5MHz were successfully diminished by 24 dB. 

Last night when we were locking the MC, we noticed that the reflected light had AM which somewhat disturbes the Pound-Drever-Hall locking of the MC.

So I aligned the wideband EOM to reduce the AM components.

 


(method)

  In order to observe AMs I put a photodiode PDA255 whose bandwidth is 50MHz after the wideband EOM.

Before the PD I also put a convex lens together with a stack of ND filters and put a steering mirror to control the beam spot on the PD.

 EOMalign.png

First I aligned the EOM such that the DC voltage from the PD was maximized. This process corresponds to a coarse alignment.

And then I tried reducing a peak at 29.5MHz seen in the spectrum analyzer. 

 

(results)

At the beginning the AM peak in the spectrum analyzer was at about -48 dBm.

After the alignment of the EOM it went down below the PD's dark noise floor of -72 dBm.

I checked the alignment also with an IR viewer, it looks quite good.

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