Sachin Arvind Kasture

Enhanced magneto-optical effects in magnetoplasmonic crystals

Plasmonics allows light to be localized on length scales much shorter than its wavelength, which makes it possible to integrate photonics and electronics on the nanoscale. Magneto-optical materials are appealing for applications in plasmonics because they open up the possibility of using external magnetic fields in plasmonic devices. Here, we fabricate a new magneto-optical material, a magnetoplasmonic crystal, that consists of a nanostructured noble-metal film on top of a ferromagnetic dielectric, and we demonstrate an enhanced Kerr effect with this material. Such magnetoplasmonic crystals could have applications in telecommunications, magnetic field sensing and all-optical magnetic data storage.

Plasmon-mediated magneto-optical transparency

Magnetic field control of light is among the most intriguing methods for modulation of light intensity and polarization on sub-nanosecond timescales. The implementation in nanostructured hybrid materials provides a remarkable increase of magneto-optical effects. However, so far only the enhancement of already known effects has been demonstrated in such materials. Here we postulate a novel magneto-optical phenomenon that originates solely from suitably designed nanostructured metal-dielectric material, the so-called magneto-plasmonic crystal. In this material, an incident light excites coupled plasmonic oscillations and a waveguide mode. An in-plane magnetic field allows excitation of an orthogonally polarized waveguide mode that modifies optical spectrum of the magneto-plasmonic crystal and increases its transparency. The experimentally achieved light intensity modulation reaches 24%. As the effect can potentially exceed 100%, it may have great importance for applied nanophotonics. Further, the effect allows manipulating and exciting waveguide modes by a magnetic field and light of proper polarization.

Interfacing Spins in an InGaAs Quantum Dot to a Semiconductor Waveguide Circuit Using Emitted Photons

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Plasmonic crystals for ultrafast nanophotonics: Optical switching of surface plasmon polaritons

We demonstrate that the dispersion of surface plasmon polaritons in a periodically perforated gold film can be efficiently manipulated by femtosecond laser pulses in spectral regions far from the intrinsic gold resonances. Using a time- and frequency-resolved pump-probe technique we observe shifting of the plasmon polariton resonances with response times from 200 to 800 fs depending on the probe photon energy, by which we obtain comprehensive insight into the electron dynamics in gold. We show that Wood anomalies in the optical spectra provide pronounced resonances indifferential transmissionand reflection with magnitudes upto 3%for moderate pump fluences of 0.5 mJ/cm 2 .

Plasmonic quasicrystals with broadband transmission enhancement

Plasmonic quasicrystals (PlQCs), by integrating the properties of quasicrystals (rotational symmetry and long range ordering but lack translational symmetry) and surface plasmon polariton mediated effects, offer several advantages over plasmonic crystals (PlCs). For example, in PlQCs one could have broadband, polarization independent response. However, large area patterning by electron beam lithography requires precise lattice coordinates as well as a practical way to design the structures for specific spectral response. We demonstrate design and fabrication of large area quasicrystal air hole patterns of π/5 symmetry in metal film in which broadband, polarization and launch angle independent transmission enhancement is observed. We demonstrate bi-grating quasicrystals to show that designable transmission response is possible over visible to near infrared wavelength regions with about 15 times enhancement. These would be useful in many applications like energy harvesting, nonlinear optics and quantum plasmonics.

Modulation of a surface plasmon-polariton resonance by subterahertz diffracted coherent phonons

Coherent sub-THz phonons incident on a gold grating that is deposited on a dielectric substrate undergo diffraction and thereby induce an alteration of the surface plasmon-polariton resonance. This results in efficient high-frequency modulation (up to 110 GHz) of the structures reflectivity for visible light in the vicinity of the plasmon-polariton resonance. High modulation efficiency is achieved by designing a periodic nanostructure which provides both plasmon-polariton and phonon resonances. Our theoretical analysis shows that the dynamical alteration of the plasmon-polariton resonance is governed by modulation of the slit widths within the grating at the frequencies of higher-order phonon resonances.

Near dispersion-less surface plasmon polariton resonances at a metal-dielectric interface with patterned dielectric on top

We report possibility of surface plasmon polariton modes that can be excited by incident light of a fixed frequency coming at wide angles. We experimentally show such modes in structures with smooth dielectric-metal-dielectric interfaces having 2-D dielectric patterns on top. Calculated field profile establishes the field localization at the metal-dielectric interfaces. We show that the position and dispersion of the excited modes can be controlled by the excitation geometry and the 2-D pattern.

Studying periodic nanostructures by probing the in-sample optical far-field using coherent phonons

Optical femtosecond laser pulses diffracted into a crystalline substrate by a goldgrating on top interact with gigahertz coherent phonons propagating towards the grating from the opposite side. As a result, Brillouin oscillations are detected for diffracted light. The experiment and theoretical analysis show that the amplitude of the oscillations for the first order diffracted light exceeds that of the zero order signal by more than ten times. The results provide a method for internal probing of the optical far-field inside materials containing periodic nanostructures.

Intensity magnetooptical effect in magnetoplasmonic crystals

Significant increase of the intensity magnetooptical effect (transversal Kerr effect) is observed in transmission for a magnetoplasmonic crystal consisting of the perforated noble-metal film attached to a smooth magnetic dielectric layer. It is largely due to the magnetic field induced shift of the Fano resonances in transmission associated with the surface plasmon polaritons excited at the metal/magnetic-dielectric interface. It is shown that the quasi-guided modes of the magnetic layer also lead to the enhancement of the intensity magnetooptical effect. The considered magnetoplasmonic structures are of great importance for applications in telecommunication and molecular sensing as they also drastically enhance other magnetooptical effects.

Proximity error correction method for continuous moving stage electron beam writing

Fabrication of high density waveguide-like structures using electron-beam lithography is challenging due to concerns such as stitching errors and proximity issues, which lead to irregularities in the fabricated structure. Continuous moving stage writing method is used to avoid the stitching errors for the long waveguide-like structures, but conventional proximity error correction methods cannot be applied in such cases. The authors propose a simple theoretical method to proximity correct such structures and experimentally demonstrate it in the case of high density millimeter long waveguide-like or grating structures. This method is ideal for high aspect ratio writing, which involves structures that have elements that are much longer than the separation between them. Also, in this method, every element can be assigned a single dose and thus does not need fracturing of individual elements. Experimental results agree well with the theoretically obtained corrections.