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Entry  Mon Mar 6 12:34:30 2017, johannes, Summary, ASS, ASS light injection scenarios 
    Reply  Mon Aug 21 20:11:25 2017, johannes, Summary, General, Loss measurements plan 
       Reply  Mon Aug 21 21:26:41 2017, gautam, Summary, General, Loss measurements plan 
          Reply  Tue Aug 22 16:56:54 2017, johannes, Summary, General, AS laser existing components inventory 
             Reply  Mon Aug 28 23:22:56 2017, johannes, Update, PSL, PSL table auxiliary NPRO aom_switching_zoomin.pngaom_switching_zoomout.pngaom_switching_mini_zoomin.pngaom_switching_mini_zoomout.png
                Reply  Tue Aug 29 20:04:09 2017, rana, Update, PSL, PSL table auxiliary NPRO 
                   Reply  Tue Aug 29 21:36:59 2017, johannes, Update, PSL, PSL table auxiliary NPRO isomet_mini_1st_zoomout.pngisomet_mini_0th_zoomout.png
                      Reply  Tue Sep 5 23:13:44 2017, johannes, Update, PSL, PSL table auxiliary NPRO PSL_IR.pdfpsl_aux_laser.pdf
                         Reply  Thu Sep 7 23:09:00 2017, johannes, Update, PSL, PSL table auxiliary NPRO 3200-1113_200_switching_PD10A_zoomin.png3200-1113_200_switching_PD10A_zoomout.png
                            Reply  Mon Sep 11 12:40:32 2017, johannes, Update, PSL, PSL table auxiliary NPRO psl_aux_laser2.svg.pngPSL_IR2.png
Message ID: 13301     Entry time: Thu Sep 7 23:09:00 2017     In reply to: 13298     Reply to this: 13306
Author: johannes 
Type: Update 
Category: PSL 
Subject: PSL table auxiliary NPRO 

I brought the DEI Pulser unit and a suitable Pockels cell over from Bridge today (I also found an identical Pockels cell already at the 40m on the SP table, now that I knew what to look for).

I also brought the 200MHz AOM (Crystal Technology 3200-1113) along which can achieve rise times of 10 ns(!). Before I start setting up the Pockels cell I wanted to try this different AOM and look at its switching behavior. It asks for a much smaller beam (<65 um diam.) than what's currently in the path to the fiber (500 um diam.), although it's clear aperture is technically big enough (~1mm diam.). So I still tried, and the result was a somewhat elliptical deflected beam, and the slower decay was again visible after switching the RF input.

I was using the big Fluke function generator for the 200MHz seed signal, a Mini Circuits ZASWA-2-50 switch and a Mini Circuits ZHL-5W-1 amplifier. For the last two I moved two power supplies (+/-5V for the switch and +24V for the amplifier) into the PSL enclosure. I started at low seed power on the Fluke, routing the amplified signal into a 20dB attenuator before measuring it with an RF power meter. The AOM saturates at 2.5W (34 dBm), which I determined is achieved with a power setting on the Fluke of -4 dBm. As expected, this AOM performed faster (~80ns fall time) but I again observed the slower decay.

This struck me as weird and I started swapping components other than the AOM, which I probably should have done before. It turned out that it was the PD I was using (the same PDA10CF Gautam had used for his MC ringdown investigations). When I changed it to a PDA10A (Si diode, 150MHz bandwidth) the slow decay vanished! One last round of crappy screenshots:

   

Rather than proceeding with the Pockels cell, tomorrow I will make the beam in the AOM smaller and hope that that takes care of the ellipticity. If it does: the AOM can theoretically switch on ~10ns timescale, same for the switch (5-15ns typical), and the amplifier is non-resonant and works up to 500MHz, so it shouldn't be a limiting factor either. If this doesn't work out, we can still have ~100ns switching times with the other AOMs.

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