Two-photon-excited fluorescence enhanced by a surface plasmon.

We demonstrate a technique that utilizes surface-plasmon resonance to intensify the fluorescence produced by multiphoton excitation. By enhancing the electric field initially generated by the excitation laser light, the presence of plasmon resonance introduces a gain 90 times higher in the experimentally observed fluorescence intensity than that produced from total internal reflection fluorescence. We also analyze the enhancement efficacy of surface-plasmon resonance as a function of the excitation wavelength.