[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?