Linewidth-broadened Fabry–Perot cavities within future gravitational wave detectors

The bandwidth of LIGO-like terrestrial interferometric gravitational wave detectors is set by the pole of the Fabry–Perot cavities within the arms of the Michelson interferometer. This constraint arises because the gain of gravitational wave-induced signal sidebands is limited to frequencies within the linewidth of the cavities. The nature of standard Fabry–Perot cavities is such that one cannot independently adjust for increased gain without suffering a loss of bandwidth. If these quantities could be decoupled, the resulting improvement in bandwidth may lead to viable high frequency detectors. A pair of anti-parallel diffraction gratings within a Fabry–Perot cavity can increase the bandwidth of a LIGO-scale detector by a factor of ≈1000.