Publications by Year: 2010

Zhihong Liu, Jiandong Huang, Pooran C. Joshi, Apostolos T. Voutsas, John Hartzell, Federico Capasso, and Jiming Bao. 2010. “Polarity-controlled visible/infrared electroluminescence in Si-nanocrystal/Si light-emitting devices.” APPLIED PHYSICS LETTERS, 97, 7.Abstract
We report the demonstration of a room-temperature visible/infrared color-switchable light-emitting device comprising a Si nanocrystal-embedded silicon oxide thin film on a p-type Si substrate. The device emits band-edge infrared light from the silicon substrate when the substrate is positively (forward) biased with respect to the Si-nanocrystal film. Under reverse bias, visible emission from the Si-nanocrystal film is observed. Compared to the photoluminescence of the Si-nanocrystal film, the visible electroluminescence is broader and blueshifted to shorter wavelength, and is ascribed to impact ionization in the Si-nanocrystal/SiO2 film. (C) 2010 American Institute of Physics. [doi:10.1063/1.3480403]
Fedenco Capasso. 2010. “Q & A Professor Federico Capasso Harvard University.” ELECTRONICS LETTERS, S, Pp. S51. 05692942.pdf
Robert F. Curl, Federico Capasso, Claire Gmachl, Anatoliy A. Kosterev, Barry McManus, Rafal Lewicki, Michael Pusharsky, Gerard Wysocki, and Frank K. Tittel. 2010. “Quantum cascade lasers in chemical physics.” CHEMICAL PHYSICS LETTERS, 487, 1-3, Pp. 1-18.Abstract
In the short space of 15 years since their first demonstration, quantum cascade lasers have become the most useful sources of tunable mid-infrared laser radiation. This Letter describes these developments in laser technology and the burgeoning applications of quantum cascade lasers to infrared spectroscopy. We foresee the potential application of quantum cascade lasers in other areas of chemical physics such as research on helium droplets, in population pumping, and in matrix isolation infrared photochemistry. (C) 2010 Elsevier B.V. All rights reserved.
By engineering the boundary conditions of electromagnetic fields between material interfaces, one can dramatically change the Casimir-Lifshitz force between surfaces as a result of the modified zero-point energy density of the system. Repulsive interactions between macroscopic bodies occur when their dielectric responses obey a particular inequality, as pointed out by Dzyaloshinskii, Lifshitz, and Pitaevskii. We discuss experimental verification of this behavior as well as a description of how this can be used to develop a scheme for quantum levitation. Based on these concepts, we discuss the possible development of a new class of devices based on ultra-low static friction and the ability to sort objects based on their dielectric functions.
K. J. Russell, F. Capasso, V. Narayanamurti, H. Lu, J. M. O. Zide, and A. C. Gossard. 2010. “Scattering-assisted tunneling: Energy dependence, magnetic field dependence, and use as an external probe of two-dimensional transport.” PHYSICAL REVIEW B, 82, 11.Abstract
For more than three decades, research on tunneling through planar barriers has focused principally on processes that conserve momentum parallel to the barrier. Here we investigate transport in which scattering destroys lateral momentum conservation and greatly enhances the tunneling probability. We have measured its energy dependence using capacitance spectroscopy, and we show that for electrons confined in a quantum well, the scattering enhancement can be quenched in an applied magnetic field, enabling this mechanism to function as an external probe of the origin of the quantum Hall effect.
Jonathan A. Fan, Chihhui Wu, Kui Bao, Jiming Bao, Rizia Bardhan, Naomi J. Halas, Vinothan N. Manoharan, Peter Nordlander, Gennady Shvets, and Federico Capasso. 2010. “Self-Assembled Plasmonic Nanoparticle Clusters.” SCIENCE, 328, 5982, Pp. 1135-1138.Abstract
The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials.
Joerg Heber and Federico Capasso. 2010. “The staircase to flexibility.” NATURE MATERIALS, 9, 5, Pp. 374-375. nmat2758.pdf
N. YU, Q. J. Wang, M. A. Kats, J. A. Fan, F. Capasso, S. P. Khanna, L. Li, A.G. Davies, and E. H. Linfield. 2010. “Terahertz plasmonics.” ELECTRONICS LETTERS, 46, 26, S, Pp. S52-S57.Abstract
Semiconductor microstructures can be used to tailor the dispersion properties of surface plasmon polaritons in the terahertz (THz) frequency range, and therefore can be used as important building blocks for terahertz optical devices. The physical principles of three structures are discussed: plasmonic second-order gratings, designer (spoof) surface plasmon polariton structures, and channel polariton structures. The effectiveness of these structures is demonstrated by utilising them to improve power throughput and to reduce the beam divergence of edge-emitting THz quantum cascade lasers. Plasmonics promises compact and low-loss solutions for manipulating light at THz wavelengths, and will have a large impact on applications such as imaging, light detection and ranging (LIDAR), and the heterodyne detection of chemicals.
Hyunyong Choi, Vasileios-Marios Gkortsas, Laurent Diehl, David Bour, Scott Corzine, Jintian Zhu, Gloria Hoefler, Federico Capasso, Franz X. Kaertner, and Theodore B. Norris. 2010. “Ultrafast Rabi flopping and coherent pulse propagation in a quantum cascade laser.” NATURE PHOTONICS, 4, 10, Pp. 706-710.Abstract
Pulse propagation phenomena are central to ultrashort pulse generation and amplification in lasers(1-5). In the coherent regime, the phase relationship between the pulse and the material transition is preserved, allowing both optical fields and material states to be controlled(6). The most prominent form of coherent manipulation is Rabi flopping(7), a phenomenon well established in few-level absorbers, including atoms and single quantum dots(8-19). However, Rabi flopping is generally much weaker in semiconductors because of strong dephasing in the electronic bands, in contrast to discrete-level systems. Although low-density induced coherent oscillations have been observed in semiconductor absorbers(11,13-20), coherent pulse propagation phenomena in active semiconductor devices have not been observed. In this Letter, we explore coherent pulse propagation in an operating quantum cascade laser and directly observe Rabi flopping and coherent pulse reshaping. This work demonstrates the applicability of few-level models for quantum cascade lasers and may stimulate novel approaches to short pulse generation(21,22).
Nanfang Yu and Federico Capasso. 2010. “Wavefront engineering for mid-infrared and terahertz quantum cascade lasers.” JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 27, 11, Pp. B18-B35.Abstract
We review our recent work on beam shaping of mid-infrared (mid-IR) and terahertz (THz) quantum cascade lasers (QCLs) using plasmonics. Essentials of QCLs are discussed; these include key developments, the operating principle based on quantum design, and beam quality problems associated with laser waveguide design. The bulk of the present paper is focused on the use of surface plasmons (SPs) to engineer the wavefront of QCLs. This is achieved by tailoring the SP dispersion using properly designed plasmonic structures, in particular, plasmonic Bragg gratings, designer (spoof) surface plasmon structures, and channel polariton structures. Using mid-IR and THz QCLs as a model system, various functionalities have been demonstrated, ranging from beam collimation, polarization control, to multibeam emission and spatial wavelength demultiplexing. Plasmonics offers a monolithic, compact, and low-loss solution to the problem of poor beam quality of QCLs and may have a large impact on applications such as sensing, light detection and ranging (LIDAR), free-space optical communication, and heterodyne detection of chemicals. The plasmonic designs are scalable and applicable to near-infrared active or passive optical devices. (C) 2010 Optical Society of America
Qijie Wang, Changling Yan, Nanfang Yu, Julia Unterhinninghofen, Jan Wiersig, Christian Pfluegl, Laurent Diehl, Tadataka Edamura, Masamichi Yamanishi, Hirofumi Kan, and Federico Capasso. 2010. “Whispering-gallery mode resonators for highly unidirectional laser action.” PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 107, 52, Pp. 22407-22412.Abstract
Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (lambda similar to 10 mu m) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of similar to 5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers.