Enhanced Dipole-Dipole Interaction in a Polymer Microcavity

We present experimental evidence for the enhancement of dipole-dipole interaction in a microcavity. We have studied the excitation energy transfer in poly(phenyl- p-phenylene vinylene) (PPPV) doped with 4-dicyanmethylene-2-methyl-6-( p-dimethylaminostyryl)- $4H$-pyran (DCM) molecules, placed within a Fabry-P\'erot resonator. As the spectral position of the cavity resonant mode is tuned across the DCM absorption profile, the transfer efficiency from PPPV to DCM changes significantly as revealed by photoluminescence studies. This behavior is clear evidence for the increase of the dipole-dipole interaction at spectral positions where the cavity modes are in resonance with the electromagnetic field emitted by the excited dipoles.