Abstract
A new surface-enhanced coherent anti-Stokes Raman scattering (CARS) diagnostic of chiral molecules using one-dimensional arrays of metallic nanocylinders is reported. It is found that such structures can be made biresonant, with one resonance arising from guided resonance (GR) of the periodic structure and the another--from the surface plasmon resonance (SPR). Enormous enhancements of the CARS signal can be expected when the pump laser beam is tuned to GR and the emitted anti-Stokes signal is tuned to SPR. Peak field enhancement corresponding to GR is systematically studied for metallic and dielectric nanorods as a function of the incidence angle, material losses, and nanorod diameter. Using coupled dipole approximation (CDA), we provide analytic estimates of the maximum local field enhancements and resonance widths, and find optimum parameters for the field amplification in our essentially two-dimensional geometry. It is shown that the maximum field enhancement at GR is always limited by resistive losses, which can never be completely cancelled by the far-field dipolar interaction. Full electromagnetic simulations supplement CDA-based calculations and qualitatively confirm their findings. Two types of CARS applications are envisioned: one is based on simultaneous enhancement of both two pump waves and of the emission of the anti-Stokes signal, and another one is designed specifically for detection of chiral molecules in crossed fields with very low background noise.
Published Version
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