The implications of Mexican-hat mirrors: calculations of thermoelastic   noise and interferometer sensitivity to perturbation for the   Mexican-hat-mirror proposal for advanced LIGO
  Thermoelastic noise will be the most significant noise source in advanced-LIGO interferometers with sapphire test masses. The standard plan for advanced-LIGO has optimized the optics, within the framework of conventional mirrors, to reduce thermoelastic noise. Recently, we and our collaborators have proposed going beyond the bounds of traditional optics to increase the effective beam spot size and thus lower thermoelastic noise. One particular proposal for mirror shapes (``Mexican-hat mirrors'') yields the class of ``mesa'' beams.   In this paper, we outline a general procedure for analyzing light propagating in individual arm cavities, and the associated thermoelastic noise, in the presence of arbitrary optics. We apply these procedures to study the Mexican-hat proposal. Results obtained by the techniques of this paper were presented elsewhere, to demonstrate that the Mexican-hat proposal for advanced-LIGO both significantly lowers thermoelastic noise and does not significantly complicate the function of the interferometer. 
R. O'Shaughnessy, S. Strigin, S. Vyatchanin