Cao and coworkers studied the coupling between the surface plasmon modes of a metallic nanoparticle and the high-Q whispering gallery modes of a dielectric microdisk. The combination of these two resonant enhancement schemes leads to huge, multiplicative enhancement of the light field. The giant local field can greatly enhance various linear and nonlinear optical processes such as Raman or hyper-Raman scattering, and frequency conversion.
Using the near-field scanning optical microscope, Cao and coworkers observed the photonic nanojet generated by a dielectric microdisk under plane wave illumination. The nanojet propagates for a distance of several wavelengths without significant diffraction. Namely the width of nanojet stays subwavelength for propagation distance as long as several wavelength behind the microdisk. Thus the nanojet causes a large enhancement of thelocal field in the shadow region.
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