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Entry  Mon Apr 8 17:44:20 2013, Evan, Notes, PMC, About PMCs 
    Reply  Tue Apr 9 15:39:16 2013, tara, Notes, PMC, About PMCs 
       Reply  Mon Apr 15 10:59:35 2013, tara, Notes, PMC, Debra matrix for PMC design laser_rin.jpglaser_rin.jpg
          Reply  Tue Apr 16 13:24:46 2013, Evan, Notes, PMC, Debra matrix for PMC design 
          Reply  Wed May 1 01:45:55 2013, tara, Notes, PMC, Debra matrix for PMC design 
             Reply  Wed May 1 11:57:02 2013, Zach, Notes, PMC, Debra matrix for PMC design 
                Reply  Wed May 1 15:28:06 2013, not Zach, Notes, PMC, Debra matrix for PMC design 
Message ID: 1145     Entry time: Mon Apr 8 17:44:20 2013     Reply to this: 1146
Author: Evan 
Type: Notes 
Category: PMC 
Subject: About PMCs 

[Rana, Tara, Evan, Eric, Nic] 

We are designing a PMC, to do that we should be able to answer some fundamental questions about a PMC.

Why do we want a PMC?

  • Intensity stabilization(is it?)
  • Filtering of beam profile
  • Alignment reference
  • Reference for waist size and position
  • Jitter suppression
  • Polarization filtering

What should we consider in the design of the cavity?

  • High finesse eventually causes the transmission to drop
  • Cavity g should be chosen so that higher-order PMC modes are well outside the bandwidth of the TEM00 mode
  • Finesse should be chosen so that laser intensity noise is suppressed below the shot noise limit at frequencies of interest
  • Number of mirrors - determines whether or not we get polarization filtering
    • In a 3-mirror cavity, when one polarization is resonant, the other will be antiresonant. In a 4-mirror cavity, both will resonate simultaneously (with small differences in transmission intensity and phase).

What should we consider in the design of the spacer?

  • Acoustic pickup (probably dominates over seismic pickup at frequencies we are interested in)
  • Steel or silica:
    • Longitudinal mode frequencies are comparable
    • Silica is harder to machine
  • Vacuum can?
  • Dimensions:
    • A shorter PMC will have higher vibrational modes
    • A longer PMC has more filtering
    • A spacer that is too thin will have easily excited bending modes

Other:

  • 15 MHz is too low for PDH modulation, because the bandwidth of the resulting loop is too low
  • For a resonant PD, we want a low Q (a few)
  • 3 mirror or 4 mirror design?

 

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