We have discussed some of the main issues regarding mirrors to be used in a high–optical-power
interferometer. These issues are thermal lensing, thermal aberration, thermal noise and thermoelastic noise.
These spurious effects do not act at the same level. Thermal issues arise directly from the laser power and
make necessary compensation systems more and more difficult as the power increases. Thermal noises
(standard and thermoelastic) are not related to the laser power, but dominate the shot noise in the central
spectral region, spoiling any gain of sensitivity expected from a higher laser power. An interesting approach
to reduce these effects is to change the readout beam from the fundamental currently used, to the
more widely spread (“exotic”) light power distributions, (either mesa, conical or high-order
Laguerre–Gauss). We have given the formulas for estimating the gains with respect to the above cited issues
for these different modes. Thus, we hope to contribute to the design of advanced instruments. It is already
possible to point out that exotic beams provide a high gain (up to a factor of five) in thermal
noise and thermoelastic noise and a huge gain in spurious thermal effects (up to two orders of
magnitude).
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