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Entry  Sat Jan 7 00:45:47 2012, Frank, DailyProgress, NoiseBudget, current TTFSS noise budget TTFSS_enoise.pngTTFSS_fnoise.png
    Reply  Wed Jan 11 20:50:08 2012, tara, DailyProgress, NoiseBudget, current TTFSS noise budget 14_75MHz.png21_5MHz.png
       Reply  Tue Apr 23 18:43:39 2013, tara, DailyProgress, RefCav, HOM for new sideband frequencies HOM35.5MHz0.5m.pngHOM35.5MHz1m.pngHOM38MHz0.5m.pngHOM38MHz1m.pngshot_vs_beta.png
          Reply  Thu Jan 9 09:09:44 2014, Evan, DailyProgress, RefCav, Sideband frequencies for refcavs pdh_choice_close.pdfpdh_choice_close.pdf
Message ID: 1157     Entry time: Tue Apr 23 18:43:39 2013     In reply to: 782     Reply to this: 1394
Author: tara 
Type: DailyProgress 
Category: RefCav 
Subject: HOM for new sideband frequencies 

35.5 MHz and 38MHz sideband frequencies are chosen for  1.45 " refcav. These frequencies will be suitable for cavities formed by 0.5/0.5m RoC mirrors and 1.0/1.0m RoC mirrors.

 

HOM35.5MHz0.5m.png                           HOM38MHz0.5m.png

  a) For0.5m/0.5m RoC mirrors 1.45" cavity, f1 = 35.5MHz.           b) For0.5m/0.5m RoC mirrors 1.45" cavity, f2 = 38MHz

HOM35.5MHz1m.png                                HOM38MHz1m.png

 c) For 1m/1m RoC mirrors 1.45" cavity, f1 = 35.5MHz                d) For 1m/1m RoC mirrors 1.45" cavity, f2 = 38MHz

 

Since we will use a crystal oscillator to drive the EOMs, I have to check how much power we need for the sideband.

If the crystal oscillator can provide us with enough power, we can use the crystal to drive a broadband EOM directly. Otherwise we will need an EOM driver, or a resonant EOM.

 

==shot noise level vs mod index(Beta)==

shot_vs_beta.png

To see how much should the mod index be, I plot shot noise level vs Beta, with Power intpu = 1mW and 2 mW, and Finesse = 1e5 (for  T=300 ppm mirrors)and 2e5 (For AlAs/GaAs coatings), with mode match = 80%. It seems that for the lowest shot noise level, we need beta = 0.8.

For resonant EOM, mod depth = 0.2 rad/V, for BB EOM, mode depth = 15mrad/V , see psl:745.  These correspond to 4V (25dBm) and 53 V (47dBm) for the resonant and BB EOMs, respectively.

 

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