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Entry  Wed Oct 30 01:56:38 2013, tara, DailyProgress, optic, table work oldPBS.jpgnewPBS.jpg
    Reply  Thu Oct 31 00:02:17 2013, tara, DailyProgress, Electronics Equipment, TTFSS offset.pngD040105C.png
       Reply  Thu Oct 31 18:10:07 2013, Evan, DailyProgress, Electronics Equipment, TTFSS 
       Reply  Sun Nov 3 19:37:32 2013, rana, DailyProgress, Electronics Equipment, TTFSS 
          Reply  Tue Nov 5 01:11:15 2013, tara, DailyProgress, Electronics Equipment, TTFSS 
             Reply  Wed Nov 6 01:14:58 2013, tara, DailyProgress, Electronics Equipment, TTFSS beat_2013_11_05.pngbeat_2013_11_05.fig
                Reply  Thu Nov 7 05:08:13 2013, tara, DailyProgress, NoiseBudget, photothermal noise in SiO2/Ta2O5 beat_2013_11_07.pngbeat_2013_11_07.fig
                   Reply  Wed Nov 20 18:19:01 2013, tara, DailyProgress, NoiseBudget, photothermal noise in SiO2/Ta2O5 beat_compare.pngbeat_compare.fig
Message ID: 1388     Entry time: Wed Nov 20 18:19:01 2013     In reply to: 1384
Author: tara 
Type: DailyProgress 
Category: NoiseBudget 
Subject: photothermal noise in SiO2/Ta2O5 

I compared our beat measurement with results from Numata2003 and TNI. They agree well. I'm quite certain that we reach Brownian thermal noise from coatings.

 

 To make sure that what we measure is real Coating Brownian noise (It could be something else, i.e thermal noise in the support, spacer , or optical bond), we should compare our result to previous measurements to make sure that the numbers agree.

 Numata etal and TNI reported coating thermal noise measurement from suspended cavities (no spacer). They adjusted loss in the coatings to fit the measurement.  Phi coatings as reported in Numata is 4e-4 while TNI gives phi perp = phi_para = 2.7e-4.  Both agree with our result, see the plot below.  This means that our result is comparable with what they measured. It should be an evidence to support that we see real coating thermal noise, not contribution from something else (spacer, optical bond between the mirrors and the spacer).

beat_compare.png

Another evidence is from our previous measurement from 8" cavity.

  • The measurement also agrees with Numata's 2003 result, with phi coatings = 4e-4, see PSL:1018.
  • And the signal scales correctly with a factor of ~ 9 (from shorter cavity, and from smaller spotsize^2), seeT1200057. Had it been noise from optical bonding/ spacer (independent from spotsize), the scale factor would have been 8/1.45 ~ 5.5. The scale from substrate Brownian will also be different because of 1/w_spot dependent. Thermoelastic/ thermoopitc will have different slope.

So It is clear that our beat measurements from both 8" and 1.45" cavities are coating Brownian noise limited (around 50Hz-1kHz).

 

Attachment 2: beat_compare.fig  96 kB
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