Distance dependence of fluorescence enhancement from photonic crystal surfaces

We experimentally verify the near-field nature of the fluorescence enhancement afforded by large area planar photonic crystal resonators. This is done by mapping the fluorescence enhancement factor for a fluorophore as a function of its distance above the device surface and comparing the results to numerical calculations. Experiments show that the decay of the enhancement factor is exponential as a function of distance from the device surface, and excellent agreement with the numerically calculated exponential decay length is obtained. In contrast to approaches involving surface plasmons on metal surfaces, we find that the maximum enhancement is obtained when the fluorophore is closest to the photonic crystal surface due to the absence of quenching at short distances. We also show that the decay length is largely controlled by the wavelength of light resonant in the device. (C) 2008 American Institute of Physics.