Publications by Year: 2007

Nanfang Yu, Ertugrul Cubukcu, Laurent Diehl, David Bour, Scott Corzine, Jintian Zhu, Gloria Hoefler, Kenneth B. Crozier, and Federico Capasso. 2007. “Bowtie plasmonic quantum cascade laser antenna.” Optics Express, 15, 20, Pp. 13272-13281. Publisher's VersionAbstract
We report a bowtie plasmonic quantum cascade laser antenna that can confine coherent mid-infrared radiation well below the diffraction limit. The antenna is fabricated on the facet of a mid-infrared quantum cascade laser and consists of a pair of gold fan-like segments, whose narrow ends are separated by a nanometric gap. Compared with a nano-rod antenna composed of a pair of nano-rods, the bowtie antenna efficiently suppresses the field enhancement at the outer ends of the structure, making it more suitable for spatially-resolved high-resolution chemical and biological imaging and spectroscopy. The antenna near field is characterized by an apertureless near-field scanning optical microscope; field confinement as small as 130 nm is demonstrated at a wavelength of 7.0 mu m. (C) 2007 Optical Society of America.
Federico Capasso, Jeremy N. Munday, Davide Iannuzzi, and H. B. Chan. 2007. “Casimir forces and quantum electrodynamical torques: Physics and nanomechanics.” IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 13, 2, Pp. 400-414.Abstract
This paper discusses recent developments on quantum electrodynamical (QED) phenomena, such as the Casimir effect, and their use in nanomechanics and nanotechnology in general. Casimir forces and torques arise from quantum fluctuations of vacuum or, more generally, from the zero-point energy of materials and their dependence on the boundary conditions of the electromagnetic fields. Because the latter can be tailored, this raises the interesting possibility of designing QED forces for specific applications. After a concise review of the field in an historical perspective, high precision measurements of the Casimir force using microelectromechanical systems (MEMS) technology and applications of the, latter to nonlinear oscillators are presented, along with a discussion of its use in nanoscale position sensors. Then, experiments that have demonstrated the role of the skin-depth effect in reducing the Casimir force are presented. The, dielectric response of materials enters in a nonintuitive way in the modification of the Casimir-Lifshitz force between dielectrics through the dielectric function at imaginary frequencies epsilon(i xi). The latter is illustrated in a dramatic way by experiments on materials that can be switched between a reflective and a transparent state (hydrogen switchable mirrors). Repulsive Casimir forces between solids separated by a fluid with epsilon(i xi) intermediate between those of the solids over a large frequency range is discussed, including ongoing experiments aimed at its observation. Such repulsive forces can be used to achieve quantum floatation in a virtually frictionless environment, a phenomenon that could be exploited in innovative applications to nanomechanics. The last part of the paper deals with the elusive QED torque between birefringent materials and efforts to observe it. We conclude by highlighting future important directions.
Christine Y. Wang, L. Diehl, A. Gordon, C. Jirauschek, F. X. Kartner, A. Belyanin, D. Bour, S. Corzine, G. Hofler, M. TROCCOLI, J. Faist, and Federico Capasso. 2007. “Coherent instabilities in a semiconductor laser with fast gain recovery.” Physical Review A, 75, 3. Publisher's VersionAbstract
We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.
Alejandro Rodriguez, Mihai Ibanescu, Davide Iannuzzi, Federico Capasso, J.D. Joannopoulos, and Steven G. Johnson. 2007. “Computation and visualization of casimir forces in arbitrary geometries: Nonmonotonic lateral-wall forces and the failure of proximity-force approximations.” PHYSICAL REVIEW LETTERS, 99, 8. Publisher's VersionAbstract
We present a method of computing Casimir forces for arbitrary geometries, with any desired accuracy, that can directly exploit the efficiency of standard numerical-electromagnetism techniques. Using the simplest possible finite-difference implementation of this approach, we obtain both agreement with past results for cylinder-plate geometries, and also present results for new geometries. In particular, we examine a pistonlike problem involving two dielectric and metallic squares sliding between two metallic walls, in two and three dimensions, respectively, and demonstrate nonadditive and nonmonotonic changes in the force due to these lateral walls.
Jiming Bao, Nanfang Yu, Federico Capasso, Thomas Mates, Mariano Troccoli, and Alexey Belyanin. 2007. “Controlled modification of erbium lifetime in silicon dioxide with metallic overlayers.” APPLIED PHYSICS LETTERS, 91, 13. Publisher's VersionAbstract
The authors report systematic measurements of the lifetime of the 1.54 mu m transition of erbium implanted at different energies in SiO2 films coated with different metals (titanium and chromium). The lifetime shows a strong reduction (up to a factor of 20) with decreasing distance between the erbium and the metal overlay. Their experiments combined with rigorous theoretical modeling demonstrate that a high degree of control over the radiative properties of erbium can be achieved in erbium-implanted materials in a wide range of implantation energies. (C) 2007 American Institute of Physics.
Marko Loncar, Benjamin G. Lee, Laurent Diehl, Mikhail Belkin, Federico Capasso, Marcella Giovannini, Jerome Faist, and Emilio Gini. 2007. “Design and fabrication of photonic crystal quantum cascade lasers for optofluidics.” OPTICS EXPRESS, 15, 8, Pp. 4499-4514. Publisher's VersionAbstract
We present novel designs and demonstrate a fabrication platform for electrically driven lasers based on high quality-factor photonic crystal cavities realized in mid-infrared quantum cascade laser material. The structures are based on deep-etched ridges with their sides perforated with photonic crystal lattice, using focused ion beam milling. In this way, a photonic gap is opened for the emitted TM polarized light. Detailed modeling and optimization of the optical properties of the lasers are presented, and their application in optofluidics is investigated. Porous photonic crystal quantum cascade lasers have potential for on-chip, intracavity chemical and biological sensing in fluids using mid infrared spectroscopy. These lasers can also be frequency tuned over a large spectral range by introducing transparent liquid in the photonic crystal holes. (c) 2007 Optical Society of America
Aydogan Ozcan, Ertugrul Cubukcu, Alberto Bilenca, Brett E. Bouma, Federico Capasso, and Guillermo J. Tearney. 2007. “Differential near-field scanning optical microscopy using sensor arrays.” IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 13, 6, Pp. 1721-1729.Abstract
In this paper, we introduce a new aperture-type near-field scanning optical microscopy (NSOM) imaging concept that relies on specially designed large-area (e.g., >200 nm x 200 nm) aperture geometries having sharp corners. Unlike in conventional NSOM, the spatial resolution of this near-field imaging modality is not determined by the size of the aperture, but rather by the sharpness of the corners of the large aperture. This approach significantly improves the light throughput of the near-field probe and, hence, increases the SNR. Here, we discuss the basic concepts of this near-field microscopy approach and illustrate both theoretically and experimentally how an array of detectors can be utilized to further improve the SNR of the near-field image. The results of this work are particularly relevant for imaging of biological samples at a spatial resolution of <50 nm with significantly improved image quality.
J. A. Fan, M. A. Belkin, M. TROCCOLI, S. Corzine, D. Bour, G. Hoefler, and F. Capasso. 2007. “Double-metal waveguide lambda similar or equal to 19 mu m quantum cascade lasers grown by metal organic vapour phase epitaxy.” ELECTRONICS LETTERS, 43, 23, Pp. 1284-1285. Publisher's VersionAbstract
Quantum cascade lasers designed to emit at lambda similar or equal to 19 mu m grown by metal organic vapour phase epitaxy are demonstrated to operate in pulsed mode up to 170 K The structures are processed into a double-metal waveguide that enhances mode confinement while minimising waveguide losses. The performance of the material grown at rates of 6 and 1 angstrom/s is compared. The devices constitute the longest-wavelength quantum cascade lasers grown by metal organic vapour phase epitaxy to date.
Mariano A. Zimmler, Jiming Bao, Ilan Shalish, Wei Yi, Joonah Yoon, Venkatesh Narayanamurti, and Federico Capasso. 2007. “Electroluminescence from single nanowires by tunnel injection: an experimental study.” NANOTECHNOLOGY, 18, 23. Publisher's VersionAbstract
We present a hybrid light-emitting diode structure composed of an n-type gallium nitride nanowire on a p-type silicon substrate in which current is injected along the length of the nanowire. The device emits ultraviolet light under both bias polarities. Tunnel injection of holes from the p-type substrate ( under forward bias) and from the metal ( under reverse bias) through thin native oxide barriers consistently explains the observed electroluminescence behaviour. This work shows that the standard p-n junction model is generally not applicable to this kind of device structure.
Qiaobing Xu, Jiming Bao, Robert M. Rioux, Raquel Perez-Castillejos, Federico Capasso, and George M. Whitesides. 2007. “Fabrication of large-area patterned nanostructures for optical applications by nanoskiving.” NANO LETTERS, 7, 9, Pp. 2800-2805. Publisher's VersionAbstract
Cost-effective and convenient methods for fabrication of patterned metallic nanostructures over the large (mm(2)) areas required for applications in photonics are much needed. In this paper, we demonstrate the fabrication of arrays of closed and open, loop-shaped nanostructures by a technique (nanoskiving) that combines thin-film deposition by metal evaporation with thin-film sectioning. These arrays of metallic structures serve as frequency-selective surfaces at mid-infrared wavelengths. Experiments with structures prepared using this technique demonstrate that a closed-looped structure has a single dominant resonance regardless of the polarization of the incident light, while open structures have resonances that are anisotropic with respect to the polarization of the electric field. Finite-difference time-domain (FDTD) simulations reproduce the scattering spectra of these frequency-selective surfaces, provide an explanation of the wavelength of the experimentally observed resonances, and rationalize their polarization dependence based on the patterns of current induced in the nanostructures.
Mikhail A. Belkin, Marko Loncar, Benjamin G. Lee, Christian Pfluegl, Ross Audet, Laurent Diehl, Federico Capasso, David Bour, Scott Corzine, and Gloria Hoefler. 2007. “Intra-cavity absorption spectroscopy with narrow-ridge microfluidic quantum cascade lasers.” OPTICS EXPRESS, 15, 18, Pp. 11262-11271. Publisher's VersionAbstract
We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximate to 9 mu m quantum cascade lasers. A deep-etched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge. The absorption lines of the liquid modify the laser waveguide loss, resulting in significant changes in the laser emission spectrum and the threshold current. A volume of liquid as small as similar to 10pL may, in principle, be sufficient for sensing using the proposed technique. This method, similar to the related gas-phase technique, shows promise as a sensitive means of detecting chemicals in small volumes of solutions. (c) 2007 Optical Society of America.
Nanfang Yu, Laurent Diehl, Ertugrul Cubukcu, Christian Pfluegl, Bour David, Corzine Scott, Jintian Zhu, Gloria Hoefler, Kenneth B. Crozier, and Federico Capasso. 2007. “Near-field imaging of quantum cascade laser transverse modes.” OPTICS EXPRESS, 15, 20, Pp. 13227-13235. Publisher's VersionAbstract
We report near field imaging of the transverse lasing modes of quantum cascade lasers. A mid-infrared apertureless near-field scanning optical microscope was used to characterize the modes on the laser facet. A very stable mode pattern corresponding to a TM00 mode was observed as function of increasing driving current for a narrow active region quantum cascade laser. Higher order modes were observed for devices with a larger active region width-to-wavelength ratio operated in pulsed mode close to threshold. A theoretical model is proposed to explain why specific transverse modes are preferred close to threshold. The model is in good agreement with the experimental results. (C) 2007 Optical Society of America.
F. Xie, V. R. Chaganti, D. Smith, A. Belyanin, F. Capasso, and C. Gmachl. 2007. “Nonlinear optics with quantum cascade lasers.” LASER PHYSICS, 17, 5, Pp. 672-679. Publisher's VersionAbstract
We discuss new approaches to monolithic integration of quantum cascade lasers with resonant intersubband nonlinearities. We show that the proposed approaches can greatly enhance the performance of quantum cascade lasers and give rise to new functionalities. Examples considered include extreme frequency up- or down-conversion and wide-range electric tuning.
Elizabeth J. Smythe, Ertugrul Cubukcu, and Federico Capasso. 2007. “Optical properties of surface plasmon resonances of coupled metallic nanorods.” OPTICS EXPRESS, 15, 12, Pp. 7439-7447. Publisher's VersionAbstract
We present a systematic study of optical antenna arrays, in which the effects of coupling between the antennas, as well as of the antenna length, on the reflection spectra are investigated and compared. Such arrays can be fabricated on the facet of a fiber, and we propose a photonic device, a plasmonic optical antenna fiber probe, that can potentially be used for in-situ chemical and biological detection and surface-enhanced Raman scattering. (c) 2007 Optical Society of America.
Yaroslav A. Urzhumov, Gennady Shvets, Jonathan Fan, Federico Capasso, Daniel Brandl, and Peter Nordlander. 2007. “Plasmonic nanoclusters: a path towards negative-index metafluids.” OPTICS EXPRESS, 15, 21, Pp. 14129-14145. Publisher's VersionAbstract
We introduce the concept of metafluids - liquid metamaterials based on clusters of metallic nanoparticles which we will term Artificial Plasmonic Molecules (APMs). APMs comprising four nanoparticles in a tetrahedral arrangement have isotropic electric and magnetic responses and are analyzed using the plasmon hybridization (PH) method, an electrostatic eigenvalue equation, and vectorial finite element frequency domain (FEFD) electromagnetic simulations. With the aid of group theory, we identify the resonances that provide the strongest electric and magnetic response and study them as a function of separation between spherical nanoparticles. It is demonstrated that a colloidal solution of plasmonic tetrahedral nanoclusters can act as an optical medium with very large, small, or even negative effective permittivity, epsilon(eff), and substantial effective magnetic susceptibility, chi(eff) = mu(eff) - 1, in the visible or near infrared bands. We suggest paths for increasing the magnetic response, decreasing the damping, and developing a metafluid with simultaneously negative epsilon(eff) and mu(eff). (c) 2007 Optical Society of America.
Nanfang Yu, Ertugrul Cubukcu, Laurent Diehl, Mikhail A. Belkin, Kenneth B. Crozier, Federico Capasso, David Bour, Scott Corzine, and Gloria Hofler. 2007. “Plasmonic quantum cascade laser antenna.” APPLIED PHYSICS LETTERS, 91, 17. Publisher's VersionAbstract
We report a plasmonic quantum cascade laser antenna that confines coherent midinfrared radiation well below the diffraction limit. The antenna was fabricated on the facet of a midinfrared quantum cascade laser and consists of a pair of gold nanorods separated by a gap. The antenna near field was characterized by an apertureless near-field scanning optical microscope; field confinement of about 100 and 70 nm, limited by the gap size, was demonstrated at wavelengths of 7.0 and 5.3 mu m, respectively. This device may find important applications in midinfrared subwavelength chemical and biological imaging and spectroscopy. (C) 2007 American Institute of Physics.
Jiming Bao, Malek Tabbal, Taegon Kim, Supakit Charnvanichborikarn, James S. Williams, Michael. J. Aziz, and Federico Capasso. 2007. “Point defect engineered Si sub-bandgap light-emitting diode.” OPTICS EXPRESS, 15, 11, Pp. 6727-6733. Publisher's VersionAbstract
We present a novel approach to enhance light emission in Si and demonstrate a sub-bandgap light emitting diode based on the introduction of point defects that enhance the radiative recombination rate. Ion implantation, pulsed laser melting and rapid thermal annealing were used to create a diode containing a self-interstitial-rich optically active region from which the zero-phonon emission line at 1218 nm originates. (C) 2007 Optical Society of America.
J. N. Munday and Federico Capasso. 2007. “Precision measurement of the Casimir-Lifshitz force in a fluid.” PHYSICAL REVIEW A, 75, 6. Publisher's VersionAbstract
The Casimir force, which results from the confinement of the quantum-mechanical zero-point fluctuations of electromagnetic fields, has received significant attention in recent years for its effect on micro- and nanoscale mechanical systems. With few exceptions, experimental observations have been limited to interacting conductive bodies separated by vacuum or air. However, interesting phenomena, including repulsive forces, are expected to exist in certain circumstances between metals and dielectrics when the intervening medium is not vacuum. In order to better understand the effect of the Casimir force in such situations and to test the robustness of the generalized Casimir-Lifshitz theory, we have performed precision measurements of the Casimir force between two metals immersed in a fluid. For this situation, the measured force is attractive and is approximately 80% smaller than the force predicted by Casimir for ideal metals in vacuum. We present experimental results and find them to be consistent with Lifshitz's theory.
C. Pfluegl, L. Diehl, A. Tsekoun, R. Go, C. K. N. Patel, X. WANG, J. Fan, I. Tanbun-Ek, and F. Capasso. 2007. “Room-temperature continuous-wave operation of long wavelength (lambda=9.5 mu m) MOVIPE-grown quantum cascade lasers.” ELECTRONICS LETTERS, 43, 19, Pp. 1026-1028. Publisher's Version pflugl_el_43_20072162_2007.pdf
Ross Audet, Mikhail A. Belkin, Jonathan A. Fan, Benjamin G. Lee, Kai Lin, and Federico Capasso. 2007. “Single-mode laser action in quantum cascade lasers with spiral-shaped chaotic resonators.” APPLIED PHYSICS LETTERS, 91, 13. Publisher's VersionAbstract
The authors have fabricated and characterized quantum cascade lasers with spiral-shaped microresonators. The lasers operate in pulsed mode at room temperature with peak optical power greater than 20 mW and in continuous wave at temperatures up to 125 K. They exhibit single-mode emission in both pulsed mode and continuous wave operation, with a 30 dB side-mode suppression ratio at injection currents well above threshold. Subthreshold spectral measurements indicate that the spiral cavities support whispering-gallery-like modes. Single-mode lasing occurs on one of these modes. Far-field profiles reveal enhanced directionality compared to microdisk lasers. (C) 2007 American Institute of Physics.