Publications by Year: 2013

2013
Mikhail A. Kats, Romain Blanchard, Patrice Genevet, and Federico Capasso. 2013. “Nanometre optical coatings based on strong interference effects in highly absorbing media.” NATURE MATERIALS, 12, 1, Pp. 20-24.Abstract
Optical coatings, which consist of one or more films of dielectric or metallic materials, are widely used in applications ranging from mirrors to eyeglasses and photography lenses(1,2). Many conventional dielectric coatings rely on Fabry-Perot-type interference, involving multiple optical passes through transparent layers with thicknesses of the order of the wavelength to achieve functionalities such as anti-reflection, high-reflection and dichroism. Highly absorbing dielectrics are typically not used because it is generally accepted that light propagation through such media destroys interference effects. We show that under appropriate conditions interference can instead persist in ultrathin, highly absorbing films of a few to tens of nanometres in thickness, and demonstrate a new type of optical coating comprising such a film on a metallic substrate, which selectively absorbs various frequency ranges of the incident light. These coatings have a low sensitivity to the angle of incidence and require minimal amounts of absorbing material that can be as thin as 5-20 nm for visible light. This technology has the potential for a variety of applications from ultrathin photodetectors and solar cells to optical filters, to labelling, and even the visual arts and jewellery.
nmat3443.pdf
Jiao Lin, Patrice Genevet, Mikhail A. Kats, Nicholas Antoniou, and Federico Capasso. 2013. “Nanostructured Holograms for Broadband Manipulation of Vector Beams.” NANO LETTERS, 13, 9, Pp. 4269-4274.Abstract
We report a new type of holographic interface, which is able to manipulate the three fundamental properties of light (phase, amplitude, and polarization) over a broad wavelength range. The design strategy relies on replacing the large openings of conventional holograms by arrays of subwavelength apertures, oriented to locally select a particular state of polarization. The resulting optical element can therefore be viewed as the superposition of two independent structures with very different length scales, that is, a hologram with each of its apertures filled with nanoscale openings to only transmit a desired state of polarization: As an implementation, we fabricated a nanostructured holographic plate that can generate radially polarized optical beams from circularly polarized incident light, and we demonstrated that it can broad range of wavelengths. The ability of a single holographic interface to simultaneously shape the amplitude, operate over a phase, and polarization of light can find widespread applications in photonics.
nl402039y.pdf
Pui-Chuen Hui, David Woolf, Eiji Iwase, Young-Ik Sohn, Daniel Ramos, Mughees Khan, Alejandro W. Rodriguez, Steven G. Johnson, Federico Capasso, and Marko Loncar. 2013. “Optical bistability with a repulsive optical force in coupled silicon photonic crystal membranes.” APPLIED PHYSICS LETTERS, 103, 2.Abstract
We demonstrate actuation of a silicon photonic crystal membrane with a repulsive optical gradient force. The extent of the static actuation is extracted by examining the optical bistability as a combination of the optomechanical, thermo-optic, and photo-thermo-mechanical effects using coupled-mode theory. Device behavior is dominated by a repulsive optical force which results in displacements of approximate to 1 nm/mW. By employing an extended guided resonance which effectively eliminates multi-photon thermal and electronic nonlinearities, our silicon-based device provides a simple, non-intrusive solution to extending the actuation range of micro-electromechanical devices. (C) 2013 AIP Publishing LLC.
1.4813121.pdf
David Woolf, Pui-Chuen Hui, Eiji Iwase, Mughees Khan, Alejandro W. Rodriguez, Parag Deotare, Irfan Bulu, Steven G. Johnson, Federico Capasso, and Marko Loncar. 2013. “Optomechanical and photothermal interactions in suspended photonic crystal membranes.” OPTICS EXPRESS, 21, 6, Pp. 7258-7275.Abstract
We present here an optomechanical system fabricated with novel stress management techniques that allow us to suspend an ultrathin defect-free silicon photonic-crystal membrane above a Silicon-on-Insulator (SOI) substrate with a gap that is tunable to below 200 nm. Our devices are able to generate strong attractive and repulsive optical forces over a large surface area with simple in-and out-coupling and feature the strongest repulsive optomechanical coupling in any geometry to date (g(OM)/2 pi approximate to -65 GHz/nm). The interplay between the optomechanical and photo-thermal-mechanical dynamics is explored, and the latter is used to achieve cooling and amplification of the mechanical mode, demonstrating that our platform is well-suited for potential applications in low-power mass, force, and refractive-index sensing as well as optomechanical accelerometry. (C) 2013 Optical Society of America
oe-21-6-7258.pdf
Konstantin E. Dorfman, Pankaj K. Jha, Dmitri V. Voronine, Patrice Genevet, Federico Capasso, and Marlan O. Scully. 2013. “Quantum-Coherence-Enhanced Surface Plasmon Amplification by Stimulated Emission of Radiation.” PHYSICAL REVIEW LETTERS, 111, 4.Abstract
We investigate surface plasmon amplification in a silver nanoparticle coupled to an externally driven three-level gain medium and show that quantum coherence significantly enhances the generation of surface plasmons. Surface plasmon amplification by stimulated emission of radiation is achieved in the absence of population inversion on the spasing transition, which reduces the pump requirements. The coherent drive allows us to control the dynamics and holds promise for quantum control of nanoplasmonic devices.
physrevlett.111.043601.pdf
Patrick Rauter, Stefan Menzel, B. Gokden, Anish K. Goyal, Christine A. Wang, Antonio Sanchez, George Turner, and Federico Capasso. 2013. “Single-mode tapered quantum cascade lasers.” APPLIED PHYSICS LETTERS, 102, 18.Abstract
We demonstrate tapered quantum cascade lasers monolithically integrated with a distributed Bragg reflector acting as both a wavelength-selective back mirror and a transverse mode filter. Each of the 14 devices operates at a different wavelength between 9.2 and 9.7 mu m, where nine devices feature single-mode operation at peak powers between 0.3 and 1.6W at room temperature. High output power and excellent beam quality with peak brightness values up to 1.6 MW cm(-2) sr(-1) render these two-terminal devices highly suitable for stand-off spectroscopy applications. (C) 2013 AIP Publishing LLC.
1.4804261.pdf
Nicholas B. Schade, Miranda C. Holmes-Cerfon, Elizabeth R. Chen, Dina Aronzon, Jesse W. Collins, Jonathan A. Fan, Federico Capasso, and Vinothan N. Manoharan. 2013. “Tetrahedral Colloidal Clusters from Random Parking of Bidisperse Spheres.” PHYSICAL REVIEW LETTERS, 110, 14.Abstract
Using experiments and simulations, we investigate the clusters that form when colloidal spheres stick irreversibly to-or ``park'' on-smaller spheres. We use either oppositely charged particles or particles labeled with complementary DNA sequences, and we vary the ratio alpha of large to small sphere radii. Once bound, the large spheres cannot rearrange, and thus the clusters do not form dense or symmetric packings. Nevertheless, this stochastic aggregation process yields a remarkably narrow distribution of clusters with nearly 90% tetrahedra at alpha = 2.45. The high yield of tetrahedra, which reaches 100% in simulations at alpha = 2.41, arises not simply because of packing constraints, but also because of the existence of a long-time lower bound that we call the ``minimum parking'' number. We derive this lower bound from solutions to the classic mathematical problem of spherical covering, and we show that there is a critical size ratio alpha(c) = (1 + root 2) approximate to 2.41, close to the observed point of maximum yield, where the lower bound equals the upper bound set by packing constraints. The emergence of a critical value in a random aggregation process offers a robust method to assemble uniform clusters for a variety of applications, including metamaterials. DOI:10.1103/PhysRevLett.110.148303
physrevlett.110.148303.pdf
Mikhail A. Kats, Romain Blanchard, Patrice Genevet, Zheng Yang, M. Mumtaz Qazilbash, D. N. Basov, Shriram Ramanathan, and Federico Capasso. 2013. “Thermal tuning of mid-infrared plasmonic antenna arrays using a phase change material.” OPTICS LETTERS, 38, 3, Pp. 368-370.Abstract
We demonstrate that the resonances of infrared plasmonic antennas can be tuned or switched on/off by taking advantage of the thermally driven insulator-to-metal phase transition in vanadium dioxide (VO2). Y-shaped antennas were fabricated on a 180 nm film of VO2 deposited on a sapphire substrate, and their resonances were shown to depend on the temperature of the VO2 film in proximity of its phase transition, in good agreement with full-wave simulations. We achieved tunability of the resonance wavelength of approximately 10% (> 1 mu m at lambda similar to 10 mu m). (C) 2013 Optical Society of America
ol-38-3-368.pdf
You-Jin Lee, Nicholas B. Schade, Li Sun, Jonathan A. Fan, Doo Ri Bae, Marcelo M. Mariscal, Gaehang Lee, Federico Capasso, Stefano Sacanna, Vinothan N. Manoharan, and Gi-Ra Yi. 2013. “Ultrasmooth, Highly Spherical Monocrystalline Gold Particles for Precision Plasmonics.” ACS NANO, 7, 12, Pp. 11064-11070.Abstract
Ultrasmooth, highly spherical monocrystalline gold particles were prepared by a cyclic process of slow growth followed by slow chemical etching, which selectively removes edges and vertices. The etching process effectively makes the surface tension isotropic, so that spheres are favored under quasi-static conditions. It is scalable up to particle sizes of 200 nm or more. The resulting spherical crystals display uniform scattering spectra and consistent optical coupling at small separations, even showing Fano-like resonances in small clusters. The high monodispersity of the particles we demonstrate should facilitate the self-assembly of nanoparticle clusters with uniform optical resonances, which could in turn be used to fabricate optical metafluids. Narrow size distributions are required to control not only the spectral features but also the morphology and yield of clusters in certain assembly schemes.
nn404765w.pdf
Mikhail A. Kats, Romain Blanchard, Shuyan Zhang, Patrice Genevet, Changhyun Ko, Shriram Ramanathan, and Federico Capasso. 2013. “Vanadium Dioxide as a Natural Disordered Metamaterial: Perfect Thermal Emission and Large Broadband Negative Differential Thermal Emittance.” PHYSICAL REVIEW X, 3, 4.Abstract
We experimentally demonstrate that a thin (approximately 150-nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises because of the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT). Within the IMT region, the VO2 film comprises nanoscale islands of the metal and dielectric phases and can thus be viewed as a natural, disordered metamaterial. This structure displays ``perfect'' blackbodylike thermal emissivity over a narrow wavelength range (approximately 40 cm(-1)), surpassing the emissivity of our black-soot reference. We observe large broadband negative differential thermal emittance over a >10 degrees C range: Upon heating, the VO2-sapphire structure emits less thermal radiation and appears colder on an infrared camera. Our experimental approach allows for a direct measurement and extraction of wavelength-and temperature-dependent thermal emittance. We anticipate that emissivity engineering with thin-film geometries comprising VO2 and other thermochromic materials will find applications in infrared camouflage, thermal regulation, and infrared tagging and labeling.
physrevx.3.041004.pdf

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