• S Anantha Ramakrishna

      Articles written in Pramana – Journal of Physics

    • On the dual symmetry between absorbing and amplifying random media

      S Anantha Ramakrishna

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      We re-examine the dual symmetry between absorbing and amplifying random media. By analysing the physically allowed choice of the sign of the square root to determine the complex wave vector in a medium, we draw a broad set of conclusions that enables us to resolve the apparent paradox of the dual symmetry and also to anticipate the large local electromagnetic field enhancements in amplifying random media.

    • Magnetic response of split-ring resonator metamaterials: From effective medium dispersion to photonic band gaps

      Sangeeta Chakrabarti S Anantha Ramakrishna

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      On systematically investigating the electromagnetic response of periodic split-ring resonator (SRR) metamaterials as a function of the size-to-wavelength ($a/\lambda$) ratio, we find that the stop bands due to the geometric resonances of the SRR weaken with increasing ($a/\lambda$) ratio, and are eventually replaced by stop bands due to Bragg scattering. Our study traces the behaviour of SRR-based metamaterials as the resonance frequency increases and the wavelength of the radiation finally becomes comparable to the size of the unit cell of the metamaterial. In the intermediate stages, the dispersion of the SRR metamaterial can still be described as due to a localized magnetic resonances while Bragg scattering finally becomes the dominant phenomenon as $a/\lambda \sim 1/2$.

    • Plasmonic properties of gold-coated nanoporous anodic alumina with linearly organized pores

      Dheeraj Pratap P Mandal S Anantha Ramakrishna

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      Anodization of aluminium surfaces containing linearly oriented scratches leads to the formation of nanoporous anodic alumina (NAA) with the nanopores arranged preferentially along the scratch marks. NAA, when coated with a thin gold film, support plasmonic resonances. Dark-field spectroscopy revealed that gold-coated NAA with such linearly arranged pores shows a polarization-dependent scattering, that is larger when the incident light is polarized parallel to the scratch direction than when polarized perpendicular to the scratch direction. Fluorescence studies from rhodamine-6G (R6G) molecules dissolved in polymethylmethacrylate (PMMA) and deposited on these NAA templates showed that fluorescence can be strongly enhanced with the bare NAA due to multiple light scattering in the NAA, while fluorescence from the molecules deposited on gold-coated NAA is strongly quenched due to the strong plasmonic coupling.

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