R. Colombelli, C. Gmachl, A. M. Sergent, D. L. Sivco, E. E. Narimanov, V. A. Podolskiy, A. Y. Cho, and F. Capasso. 2006. “Surface-plasmon quantum cascade microlasers with highly deformed resonators.” IEEE Journal of Selected Topics in Quantum Electronics, 12, 1, Pp. 66-70.Abstract
We report the demonstration of surface-plasmon microcylinder quantum cascade lasers with circular and deformed resonators. An improved self-alignment fabrication technique was developed that allows the use of wet etching, necessary to achieve smooth and clean surfaces, in combination with the deposition of the surface-plasmon-carrying metal layer up to the very edge of the resonator, where the optical mode is mostly located. The diameter of the microcylinders ranges from 75 to 180 /spl mu/m while their deformation coefficient /spl epsiv/ ranges from /spl epsiv/=0 to /spl epsiv/=0.32. Circular microcylinder lasers show a reduction of /spl sim/50% of the threshold current density with respect to devices with standard ridge-waveguide resonators. On the other hand, highly deformed microcylinder lasers exhibit a complex mode structure, suggesting the onset of chaotic behavior.
A Belyanin, F Xie, DB Liu, F. Capasso, and M Troccoli. 2005. “Coherent nonlinear optics with quantum cascade structures.” Journal of Modern Optics, 52, 16, Pp. 2293-2302.Abstract
We discuss several coherent nonlinear optical phenomena that occur in active quantum-cascade (QC) structures that support both laser action and, at the same time, nonlinear self-conversion of laser light into coherent radiation at other frequencies. In other words, the laser field serves as an intracavity optical pump for a desired nonlinear optical process. In such systems, resonant absorption of the pump field is overcome by laser gain, and giant resonant nonlinearities of the intersubband transitions can be fully exploited. The proposed approach holds promise to extend the operating wavelength of QC lasers to the spectral regions where they become less efficient, constrained by material limitations, or operate only at cryogenic temperatures. It may also lead to the development of new broadly tunable injection-pumped sources. We review recent development in this research direction including the demonstration of the Raman injection laser.
D Iannuzzi, M Lisanti, JN Munday, and F. Capasso. 2005. “The design of long range quantum electrodynamical forces and torques between macroscopic bodies.” Solid State Communications, 135, 9-10, Pp. 618-626.Abstract
The interaction between electrically neutral surfaces at sub-micron separation is dominated by the force arising from quantum fluctuations of the electromagnetic field, known as the Casimir force. This effect has been witnessing a renewed interest because of its potential impact in micro- and nanotechnology. Most recent literature has focused on the study of the attraction between bulk-like metallic surfaces in vacuum. Because electromagnetic fluctuations depend on the dielectric function of the surfaces, the use of different materials might reveal new aspects of the Casimir force and suggest novel solutions for the design of micro- and nanofabricated devices. Following this approach, we have measured the Casimir force using Hydrogen Switchable Mirrors-a metallic mirror that switches from highly reflective to transparent when exposed to hydrogen. The comparison of the results obtained in air and in hydrogen sheds light on the relative contribution of visible and infrared wavelengths to the Casimir interaction. We have also studied the dependence of the Casimir force on the metallic film thickness and have shown the effect of the skin-depth. The final section of the paper discusses the torque induced by quantum fluctuations on two birefringent plates and describes an experiment that should allow us to observe this phenomenon. (C) 2005 Elsevier Ltd. All rights reserved.
ML Povinelli, M. Loncar, M Ibanescu, EJ Smythe, SG Johnson, F. Capasso, and JD Joannopoulos. 2005. “Evanescent-wave bonding between optical waveguides.” Optics Letters, 30, 22, Pp. 3042-3044.Abstract
Forces arising from overlap between the guided waves of parallel, microphotonic waveguides are calculated. Both attractive and repulsive forces, determined by the choice of relative input phase, are found. Using realistic parameters for a silicon-on-insulator material system, we estimate that the forces are large enough to cause observable displacements. Our results illustrate the potential for a broader class of optically tunable microphotonic devices and microstructured artificial materials. (c) 2005 Optical Society of America.
G Gagliardi, S Borri, F Tamassia, F. Capasso, C. Gmachl, DL Sivco, JN Baillargeon, AL Hutchinson, and AY Cho. 2005. “A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers.” Isotopes in Environmental and Health Studies, 41, 4, Pp. 313-321.Abstract
We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 mu m, where strong fundamental absorption bands occur for the considered species and their isotopomers. The detection technique is based on audio-frequency and radio-frequency modulation of laser radiation. First experimental tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of C-13/C-12, O-18/O-16, O-17/O-16 and N-15/N-14 isotope ratios.
ML Povinelli, SG Johnson, M. Loncar, M Ibanescu, EJ Smythe, F. Capasso, and JD Joannopoulos. 2005. “High-Q enhancement of attractive and repulsive optical forces between coupled whispering-gallery-mode resonators.” Optics Express, 13, 20, Pp. 8286-8295.Abstract
We have calculated the optically-induced force between coupled high-Q whispering gallery modes of microsphere resonators. Attractive and repulsive forces are found, depending whether the bi-sphere mode is symmetric or antisymmetric. The magnitude of the force is linearly proportional to the total power in the spheres and consequently linearly enhanced by Q. Forces on the order of 100 nN are found for Q= 10(8), large enough to cause displacements in the range of 1 mu m when the sphere is attached to a fiber stem with spring constant 0.004 N/m. (c) 2005 Optical Society of America.
F. Capasso. 2005. “Light pulls waveguides together or pushes them apart.” Laser Focus World, 41, 12, Pp. 11.
M Lisanti, D Iannuzzi, and F. Capasso. 2005. “Observation of the skin-depth effect on the Casimir force between metallic surfaces.” Proceedings of the National Academy of Sciences, 102, 34, Pp. 11989-11992.Abstract
We have performed measurements of the Casimir force between a metallic plate and a transparent sphere coated with metallic films of different thicknesses. We have observed that, if the thickness of the coating is less than the skin-depth of the electromagnetic modes that mostly contribute to the interaction, the force is significantly smaller than that measured with a thick bulk-like film. Our results provide direct evidence of the skin-depth effect on the Casimir force between metallic surfaces.
M Troccoli, A Belyanin, F. Capasso, E Cubukcu, DL Sivco, and AY Cho. 2005. “Raman injection laser.” Nature, 433, 7028, Pp. 845-848.Abstract
Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials, enables the generation of optical gain at a frequency that is shifted from that of the incident radiation by an amount corresponding to the frequency of an internal oscillation of the material(1,2). This effect is the basis for a broad class of tunable sources known as Raman lasers(2,3). In general, these sources have only small gain (similar to10(-9) cm W(-1)) and therefore require external pumping with powerful lasers, which limits their applications. Here we report the realization of a semiconductor injection Raman laser designed to circumvent these limitations. The physics underlying our device differs in a fundamental way from existing Raman lasers(3-8): it is based on triply resonant stimulated Raman scattering between quantum-confined states within the active region of a quantum cascade laser that serves as an internal optical pump-the device is driven electrically and no external laser pump is required. This leads to an enhancement of orders of magnitude in the Raman gain, high conversion efficiency and low threshold. Our lasers combine the advantages of nonlinear optical devices and of semiconductor injection lasers, and could lead to a new class of compact and wavelength-agile mid- and far-infrared light sources.
JN Munday, D Iannuzzi, Y Barash, and F. Capasso. 2005. “Torque on birefringent plates induced by quantum fluctuations.” Physical Review A, 71, 4.Abstract
We present detailed numerical calculations of the mechanical torque induced by quantum fluctuations on two parallel birefringent plates with in-plane optical anisotropy, separated by either vacuum or a liquid (ethanol). The torque is found to vary as sin(2 theta), where theta represents the angle between the two optical axes, and its magnitude rapidly increases with decreasing plate separation d. For a 40 mu m diameter disk, made out of either quartz or calcite, kept parallel to a barium titanate plate at d similar or equal to 100 nm, the maximum torque (at theta=pi/4) is of the order of similar or equal to 10(-19) N m. We propose an experiment to observe this torque when the barium titanate plate is immersed in ethanol and the other birefringent disk is placed on top of it. In this case the retarded van der Waals (or Casimir-Lifshitz) force between the two birefringent slabs is repulsive. The disk would float parallel to the plate at a distance where its net weight is counterbalanced by the retarded van der Waals repulsion, free to rotate in response to very small driving torques.
A Soibel, F. Capasso, C. Gmachl, ML Peabody, AM Sergent, R Paiella, HY Hwang, DL Sivco, AY Cho, HC Liu, C Jirauschek, and FX Kartner. 2004. “Active mode locking of broadband quantum cascade lasers.” IEEE JOURNAL OF QUANTUM ELECTRONICS, 40, 7, Pp. 844-851. Publisher's VersionAbstract
Active mode locking in broadband quantum cascade (QC) lasers with a repetition rate of about 14.3 GHz has been achieved through the modulation of the laser bias current. At low driving currents, the active mode locking in broadband QC lasers resembles the active mode locking in single-wavelength QC lasers, while at high driving currents, the mode locking properties are governed by the broad spectral gain of these lasers. At high bias currents, the active modulation excites Fabry-Perot modes across the entire gain spectrum from 6.7 to 7.4 mum, with clear evidence of mode locking. The spectral width of the optical gain in the broadband QC lasers exceeds 2 THz and indicates the potential for generating subpicosecond pulses.
KJ Russell, I Appelbaum, W. Yi, DJ Monsma, F. Capasso, CM Marcus, V. Narayanamurti, MP Hanson, and A. C. Gossard. 2004. “Avalanche spin-valve transistor.” APPLIED PHYSICS LETTERS, 85, 19, Pp. 4502-4504.Abstract
A spin-valve transistor with a GaAs/AlGaAs avalanche-multiplying collector is demonstrated with >1000% magnetocurrent variation and approximate to35x amplification of the collector current. The intrinsic amplification of the magnetic-field sensitive collector current should allow fabrication of spin-valve transistors with high gain in a variety of materials. (C) 2004 American Institute of Physics.
D Iannuzzi, M Lisanti, and F. Capasso. 2004. “Effect of hydrogen-switchable mirrors on the Casimir force.” PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 101, 12, Pp. 4019-4023.Abstract
We present systematic measurements of the Casimir force between a gold-coated plate and a sphere coated with a hydrogen-switchable mirror. Hydrogen-switchable mirrors are shiny metals that can become transparent upon hydrogenation. Despite such a dramatic change of the optical properties of the sphere, we did not observe any significant decrease of the Casimir force after filling the experimental apparatus with hydrogen. This counterintuitive result can be explained by the Lifshitz theory that describes the Casimir attraction between metallic and dielectric materials.
R Colombelli, K Srinivasan, M Troccoli, O Painter, C. Gmachl, DM Tennant, AM Sergent, DL Sivco, AY Cho, and F. Capasso. 2004. “Fabrication technologies for quantum cascade photonic-crystal microlasers.” NANOTECHNOLOGY, 15, 5, Pp. 675-681.Abstract
In this paper we describe the technological and fabrication methods necessary to incorporate both photonic and electronic-band engineering in order to create novel surface-emitting quantum cascade microcavity laser sources. This technology offers the promise of several innovative applications such as the miniaturization of QC lasers, and multi-wavelength two-dimensional laser arrays for spectroscopy, gas-sensing and imaging. This approach is not limited to light-emitting devices, and may be efficiently applied to the development of mid- and far-infrared normal-incidence detectors.
K Srinivasan, O Painter, R Colombelli, C. Gmachl, DM Tennant, AM Sergent, DL Sivco, AY Cho, M Troccoli, and F. Capasso. 2004. “Lasing mode pattern of a quantum cascade photonic crystal surface-emitting microcavity laser.” APPLIED PHYSICS LETTERS, 84, 21, Pp. 4164-4166.Abstract
The identification of the lasing mode within a quantum cascade photonic crystal microcavity laser emitting at lambdasimilar to8 mum is presented. The symmetry of the lasing mode is determined by the position of nodal lines within micro-bolometer camera measurements of its polarized spatial distribution. Full three-dimensional finite-difference time-domain simulations are also performed, and the resulting vertically emitted radiation field pattern is seen to follow the experimental results closely. (C) 2004 American Institute of Physics.
M Troccoli, D Bour, S Corzine, G Hofler, A Tandon, D Mars, DJ Smith, L Diehl, and F. Capasso. 2004. “Low-threshold continuous-wave operation of quantum-cascade lasers grown by metalorganic vapor phase epitaxy.” APPLIED PHYSICS LETTERS, 85, 24, Pp. 5842-5844.Abstract
We report on the realization of InGaAs/InAlAs quantum-cascade lasers grown by metalorganic vapor phase epitaxy operating in continuous wave with low-threshold current densities at temperatures as high as 188 K. Threshold current densities of 950 A/cm(2) and output powers of 125 mW are measured at 80 K, while 3 mW of continuous output power are measured at 180 K, with a threshold of 2.5 kA/cm(2). In pulsed mode, peak output powers of more than 0.4 W were obtained at 80 K and of 160 mW at 300 K with thresholds of 700 A/cm(2) and 2.75 kA/cm(2), respectively. (C) 2004 American Institute of Physics.
V Tamosiunas, R Zobl, G Fasching, J Ulrich, G Strasser, K Unterrainer, R Colombelli, C. Gmachl, K West, L Pfeiffer, and F. Capasso. 2004. “Magnetic field effects in terahertz quantum-cascade lasers.” SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 19, 4, SI, Pp. S348-S350.Abstract
We have measured the emission intensity and spectra of terahertz quantum-cascade lasers in an external magnetic field applied normal to the epilayers. We have observed a reduction of the threshold current, an enhancement of laser emission intensity and shifts of the emission line. A wider operating range was predicted for the selected waveguide design according to our finite-difference time-domain simulation results. The intensity enhancement and the threshold current reduction are attributed to the suppression of nonradiative Auger-intersubband transitions by Landau quantization of the in-plane electron motion, to the modulation of the injection rate via resonant inter-Landau-level transfer, and to the modulation of waveguide properties.
D Bour, M Troccoli, F. Capasso, S Corzine, A Tandon, D Mars, and G Hofler. 2004. “Metalorganic vapor-phase epitaxy of room-temperature, low-threshold InGaAs/AlInAs quantum cascade lasers.” JOURNAL OF CRYSTAL GROWTH, 272, 1-4, Pp. 526-530.Abstract
We have grown 30-stage AtInAs-GaInAs quantum cascade laser structures by low-pressure metalorganic vaporphase epitaxy (MOVPE). The growth rate for the active region was set very low (0.1 nm/s), and growth stops were employed at all interfaces. The devices were operated pulsed at room temperature, with a threshold current density of 2.8 kA/cm(2), a lasing wavelength of 7.6mum, and a peak power of 150mW. CW operation was achieved up to a temperature of 180 K. These characteristics compare favorably with MBE-grown QC lasers of similar structure. (C) 2004 Elsevier B.V. All rights reserved.
A Soibel, F. Capasso, C. Gmachl, ML Peabody, AM Sergent, R Paiella, DL Sivco, AY Cho, and HC Liu. 2004. “Stability of pulse emission and enhancement of intracavity second-harmonic generation in self-mode-locked quantum cascade lasers.” IEEE JOURNAL OF QUANTUM ELECTRONICS, 40, 3, Pp. 197-204.Abstract
We report the observation of stable pulse emission and enhancement of intracavity second-harmonic generation (SHG) in self-mode-locked quantum cascade (QC) lasers. Down-conversion of the detector signal by heterodyning with an RF signal allows the direct observation of the pulsed laser emission in the time domain and reveals a stable train of pulses characteristic of mode-locked lasers. The onset of self-mode locking in QC lasers with built-in optical nonlinearity results in a significant increase of the SHG signal. A pulse duration of similar to12 ps is estimated from the measured increase of the SHG signal in pulsed emission compared to the power expected for the SHG signal in CW emission. This value is in good agreement with the pulse duration deduced from the optical spectral width.
C. Gmachl, N Owschimikow, A Belyanin, AM Sergent, DL Sivco, ML Peabody, AY Cho, and F. Capasso. 2004. “Temperature dependence and single-mode tuning behavior of second-harmonic generation in quantum cascade lasers.” APPLIED PHYSICS LETTERS, 84, 15, Pp. 2751-2753.Abstract
Second-harmonic generation (SHG) is reported in quantum cascade (QC) lasers with active regions that also support nonlinear cascades with large second order nonlinear susceptibility. SHG has been measured from 10 up to 250 K heat sink temperature, with about 1 muW of nonlinear power at 10 K and about 50 nW at 250 K. Single-mode and tunable SHG at 3.5 mum wavelength has been measured from single-mode QC distributed feedback lasers operating at the fundamental pump wavelength of 7.0 mum. Thermal tuning results in a tuning rate for the SHG emission of similar to0.2 nm/K for temperatures above similar to100 K. (C) 2004 American Institute of Physics.