Photonic nanojet assisted enhancement of Raman signal: Effect of refractive index contrast

We discuss the enhancement of Raman signals using a photonic nanojet generated by dielectric microspheres. The highly confined field of the nanojet leads to an order of magnitude enhancement of the Raman signal from the substrate beneath. Enhancement is observed to depend strongly on the sizes of the microspheres as well as the contrast between their refractive index and that of the sample. Enhancement increases when the refractive index of the substrate increases relative to that of the microsphere, but decreases rapidly as the two become equivalent. Published by AIP Publishing.