Person: Chaudhary, Kundan
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Chaudhary
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Kundan
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Chaudhary, Kundan
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Publication Ultra-confined mid-infrared resonant phonon polaritons in van der Waals nanostructures(American Association for the Advancement of Science, 2018) Tamagnone, Michele; Ambrosio, Antonio; Chaudhary, Kundan; Jauregui, Luis A.; Kim, Philip; Wilson, William; Capasso, FedericoHexagonal boron nitride has been proposed as an excellent candidate to achieve subwavelength infrared light manipulation owing to its polar lattice structure, enabling excitation of low-loss phonon polaritons with hyperbolic dispersion. We show that strongly subwavelength hexagonal boron nitride planar nanostructures can exhibit ultra-confined resonances and local field enhancement. We investigate strong light-matter interaction in these nanoscale structures via photo-induced force microscopy, scattering-type scanning near-field optical microscopy, and Fourier transform infrared spectroscopy, with excellent agreement with numerical simulations. We design optical nano-dipole antennas and directly image the fields when bright- or dark-mode resonances are excited. These modes are deep subwavelength, and strikingly, they can be supported by arbitrarily small structures. We believe that phonon polaritons in hexagonal boron nitride can play for infrared light a role similar to that of plasmons in noble metals at visible frequency, paving the way for a new class of efficient and highly miniaturized nanophotonic devices.Publication Using the discrete dipole approximation and holographic microscopy to measure rotational dynamics of non-spherical colloidal particles(Elsevier BV, 2014) Wang, Anna; Dimiduk, Thomas G.; Fung, Jerome; Razavi, Sepideh; Kretzschmar, Ilona; Chaudhary, Kundan; Manoharan, VinothanWe present a new, high-speed technique to track the three-dimensional translation and rotation of non-spherical colloidal particles. We capture digital holograms of micrometer-scale silica rods and sub-micrometer-scale Janus particles freely diffusing in water, and then fit numerical scattering models based on the discrete dipole approximation to the measured holograms. This inverse-scattering approach allows us to extract the position and orientation of the particles as a function of time, along with static parameters including the size, shape, and refractive index. The best-fit sizes and refractive indices of both particles agree well with expected values. The technique is able to track the center of mass of the rod to a precision of 35 nm and its orientation to a precision of 1.5°, comparable to or better than the precision of other 3D diffusion measurements on non-spherical particles. Furthermore, the measured translational and rotational diffusion coefficients for the silica rods agree with hydrodynamic predictions for a spherocylinder to within 0.3%. We also show that although the Janus particles have only weak optical asymmetry, the technique can track their 2D translation and azimuthal rotation over a depth of field of several micrometers, yielding independent measurements of the effective hydrodynamic radius that agree to within 0.2%. The internal and external consistency of these measurements validate the technique. Because the discrete dipole approximation can model scattering from arbitrarily shaped particles, our technique could be used in a range of applications, including particle tracking, microrheology, and fundamental studies of colloidal self-assembly or microbial motion.Publication Anisotropic Colloidal Templating of 3D Ceramic, Semiconducting, Metallic, and Polymeric Architectures(Wiley-Blackwell, 2013) Fu, Ming; Chaudhary, Kundan; Lange, Jonathan; Juarez, Jamie J.; Lewis, Jennifer; Braun, Paul V.