Forward-propagating surface-enhanced Raman scattering and intensity distribution in photonic crystal fiber with immobilized Ag nanoparticles.

A 30 cm long solid-core photonic crystal fiber (PCF) with immobilized and discrete Ag nanoparticles was used to obtain forward-propagating surface-enhanced Raman scattering (SERS) of 2 microM Rhodamine 6G (R6G) aqueous solution filled in the cladding air channels. The intensity distributions of characteristic Raman vibrational bands of silica and R6G in PCF were mapped for the first time to our knowledge by hyperspectral Raman imaging. We show that the measured SERS intensity arises exclusively from the forward-propagating core mode as a result of evanescent-field interaction with R6G in the innermost ring of the cladding air channels.