Folding Gravitational-Wave Interferometers
  The sensitivity of kilometer-scale terrestrial gravitational wave interferometers is limited by mirror coating thermal noise. We explore the effect of folding the arm cavities of such interferometers. While simple folding alone does not reduce the mirror coating thermal noise, it makes the folding mirror the critical mirror, opening up a variety of design and upgrade options. 
J.R. Sanders and Stefan W. Ballmer
gr-qc astro-ph.IM