Two-finesse Fabry-Perot interferometer for probing intracavity lossy samples

This work proposes a Fabry-Perot (FP) resonator with two spatially separated eigenstates, called Jamin-Fabry-Perot. The sample is put only into one arm of the interferometer. One is then left with a dual asymmetric resonator with two different finesses: a low finesse associated with the arm containing the sample and a high one associated with the empty arm. We show theoretically and experimentally that the sensitivity of the interferometer depends only on the high finesse, therefore eliminating the effect of the intracavity losses.