  We propose a solution for increasing the axial resolution of confocal
microscopes. In the experimental set-up described in this paper an interference
phenomenon between two counterpropagating beams is used to determine the axial
position of a luminophore. The optical path difference between the two waves,
which is related to the position of the luminophore, is recovered thanks to a
second interferometer by using partial coherence interferometry demodulation
technique. The proposed solution can find applications in biology for
localizing with nanometric resolution a small number of tagged species.
