Recycling Cavity Degeneracy

• 'Frontal modulation' scheme depends on efficient coupling

  • Local oscillator field generated at laser, coupled into recycling cavity (not co-resonant in arm cavities)
  • Recycling cavity is nearly degenerate (ROC[cold] ~ 15 km, length ~ 9 m)
  • Original design depends on specific, balanced thermal lensing

• RF sideband efficiency found to be very low

  • H1 efficiency: ~6% (anti-symmetric port relative to input)
  • incorrect/insufficient ITM thermal lens makes g1·g2 > 1 (unstable resonator)

Notes: