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3 Jan 2000

Volume 76, Issue 1, pp. 1-128

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Two-photon fluorescence imaging and spectroscopy of nanostructured organic materials using a photon scanning tunneling microscope

Yuzhen Shen, Daniel Jakubczyk, Faming Xu, Jacek Swiatkiewicz, Paras N. Prasad, and Bruce A. Reinhardt

Appl. Phys. Lett. 76, 1 (2000); http://dx.doi.org/10.1063/1.125637 (3 pages) | Cited 25 times

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Photon scanning tunneling microscopy and spectroscopy using femtosecond two-photon excitation are demonstrated. The measurement of both intensity dependence and spectral dependence is performed on a two-photon chromophore. A subdiffraction-limited resolution is obtained, and the domain-size dependence of spatial and spectral features is observed, which indicates the high degree of molecular order in the isolated nanoparticle. It is shown that the light confinement due to a quadratic dependence of the fluorescence intensity leads to an optical contrast enhancement with a coated probe. © 2000 American Institute of Physics.
Show PACS
07.60.Rd Visible and ultraviolet spectrometers
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.66.Vs Fine-particle systems
61.46.-w Structure of nanoscale materials
78.55.Kz Solid organic materials
07.79.Fc Near-field scanning optical microscopes

Efficient GaAs light-emitting diodes by photon recycling

E. Dupont, H. C. Liu, M. Buchanan, S. Chiu, and M. Gao

Appl. Phys. Lett. 76, 4 (2000); http://dx.doi.org/10.1063/1.125718 (3 pages) | Cited 13 times

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Heterostructure AlGaAs/GaAs light-emitting diodes (LEDs) with a thick active region have shown high external efficiencies, thanks to reabsorption in the active region. For high injection currents and low temperature, we report a 22% efficiency which corresponds to a 98% efficiency internally. We discuss the application of such LED when integrated with a quantum-well infrared photodetector for pixelless thermal imaging systems. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Thermal lensing effects in small oxide confined vertical-cavity surface-emitting lasers

M. Brunner, K. Gulden, R. Hövel, M. Moser, and M. Ilegems

Appl. Phys. Lett. 76, 7 (2000); http://dx.doi.org/10.1063/1.125638 (3 pages) | Cited 26 times

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The thickness and position of an oxide layer inside a vertical-cavity surface-emitting laser structure have been optimized for minimum optical scattering loss. In the resulting structure, the index guiding provided by the oxide aperture is very small. Consequently, for an oxide aperture radius <2 μm, the optical mode is only weakly confined. In devices using such small apertures, the formation of a thermal lens has a strong influence on optical guiding. The thermal lens leads to lower threshold currents and increased differential efficiency with continuous wave as compared to pulsed injection operation in devices with small apertures. © 2000 American Institute of Physics.
Show PACS
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

PbS quantum-dot-doped glasses for ultrashort-pulse generation

K. Wundke, S. Pötting, J. Auxier, A. Schülzgen, N. Peyghambarian, and N. F. Borrelli

Appl. Phys. Lett. 76, 10 (2000); http://dx.doi.org/10.1063/1.125639 (3 pages) | Cited 53 times

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We investigate the use of PbS quantum-dot-doped glasses as saturable absorbers for ultrashort-pulse lasers by means of absorption bleaching experiments and numerical analysis of the pulse shaping process using the Haus’ master equation. We explain the mode-locking mechanism and the limitations of these absorbers. The generation of transform-limited fs pulses is predicted by soliton mode locking initiated by the absorption saturation of higher excited states of the quantum-dot saturable absorber. © 2000 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
78.66.Li Other semiconductors
81.05.Hd Other semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
02.30.-f Function theory, analysis
06.60.Jn High-speed techniques (microsecond to femtosecond)
78.47.-p Spectroscopy of solid state dynamics
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Tg Optical solitons; nonlinear guided waves

Electroluminescence of a cubic GaN/GaAs (001) p–n junction

D. J. As, A. Richter, J. Busch, M. Lübbers, J. Mimkes, and K. Lischka

Appl. Phys. Lett. 76, 13 (2000); http://dx.doi.org/10.1063/1.125640 (3 pages) | Cited 26 times

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A cubic GaN p–n diode has been grown on n-type GaAs (001) substrates by plasma assisted molecular epitaxy. For p- and n-type doping, elemental Mg and Si beams have been used, respectively. The optical properties are characterized by photoluminescence at room temperature and 2 K. Current–voltage and capacitance–voltage measurements of the cubic GaN n+–p junction are performed at room temperature. The electroluminescence at 300 K is measured through a semitransparent Au contact. A peak emission at 3.2 eV with a full width at half maximum as narrow as 150 meV is observed, indicating that near-band edge transitions are the dominating recombination processes in our device. A linear increase of the electroluminescence intensity with increasing current density is measured. © 2000 American Institute of Physics.
Show PACS
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

Efficiency enhancement of free electron Maser oscillator by mode selection with a prebunched electron beam

A. Abramovich, H. Kleinman, A. Eichenbaum, Y. M. Yakover, A. Gover, and Y. Pinhasi

Appl. Phys. Lett. 76, 16 (2000); http://dx.doi.org/10.1063/1.125641 (3 pages) | Cited 3 times

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We present a method for enhancing the efficiency of a Free Electron Laser Maser oscillator by locking it to a preferred resonator mode. This is done by prebunching of the e beam before injection into the wiggler. In a free running oscillator, the longitudinal mode that dominates the mode competition process during the oscillation buildup period is usually the highest gain mode. However, this mode does not extract the highest energy from the e beam. Lower eigenfrequency modes would provide a higher efficiency if they could dominate the mode competition process. By prebunching the e beam at a frequency near any one of the longitudinal eigenfrequencies of the resonator (having a gain>1), we can make that mode dominant at saturation. The eigenfrequency for which the maximum efficiency is obtained is the lowest eigenfrequency of the resonator for which the net small signal gain is greater than 1. Employing an experimental setup of a prebunched beam Free Electron Maser, we demonstrated efficiency enhancement of 30% for this lowest eigenfrequency mode (as compared to the highest gain mode). Simulation results predict an efficiency enhancement of up to 50%. © 2000 American Institute of Physics.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
41.60.Cr Free-electron lasers
42.60.Fc Modulation, tuning, and mode locking
41.85.Ct Particle beam shaping, beam splitting
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Magnetic-field-enhanced quantum-cascade emission

J. Ulrich, R. Zobl, K. Unterrainer, G. Strasser, and E. Gornik

Appl. Phys. Lett. 76, 19 (2000); http://dx.doi.org/10.1063/1.125642 (3 pages) | Cited 42 times

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We have observed an enhancement of terahertz intersubband electroluminescence in a quantum cascade structure in the presence of a magnetic field applied normal to the epitaxial layers. At a field of B = 7.2 T the emission efficiency doubles. This effect is attributed to the suppression of nonradiative Auger–intersubband transitions caused by Landau-quantization of the in-plane electron motion. The magnetic field dependence of the luminescence intensity shows strong oscillations. These magnetointersubband oscillations are caused by the modulation of the transition rate via resonant inter-Landau-level transfer. © 2000 American Institute of Physics.
Show PACS
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
73.23.-b Electronic transport in mesoscopic systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.70.Di Landau levels
42.55.Px Semiconductor lasers; laser diodes

Blue InGaN-based laser diodes with an emission wavelength of 450 nm

Shuji Nakamura, Masayuki Senoh, Shin-ichi Nagahama, Naruhito Iwasa, Toshio Matsushita, and Takashi Mukai

Appl. Phys. Lett. 76, 22 (2000); http://dx.doi.org/10.1063/1.125643 (3 pages) | Cited 114 times

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Blue InGaN single-quantum-well-structure laser diodes (LDs) with an emission wavelength of 450 nm were grown on an epitaxially laterally overgrown GaN substrate by a metalorganic chemical vapor deposition method. The threshold current density and voltage were 4.6kA cm−2 and 6.1 V, respectively. The estimated lifetime was approximately 200 h under room-temperature continuous-wave operation at an output power of 5 mW. When the number of InGaN well layers of the LDs with emission wavelengths longer than 435 nm varied from one to three, the lowest threshold current density was obtained when the number of well layers was one. © 2000 American Institute of Physics.
Show PACS
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Second-harmonic imaging of poled silica waveguides

Jesper Arentoft, Kjeld Pedersen, Sergey I. Bozhevolnyi, Martin Kristensen, Ping Yu, and Christian B. Nielsen

Appl. Phys. Lett. 76, 25 (2000); http://dx.doi.org/10.1063/1.125644 (3 pages) | Cited 10 times

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Electric-field poled silica-based waveguides are characterized by measurements of second-harmonic generation (SHG) and of the linear electro-optic effect (LEO). A SHG scanning technique allowing for high-resolution imaging of poled devices is demonstrated. Scans along the direction of the poling field show that the second-order optical nonlinearity is located near the interface between differently doped glass layers. Both SHG and LEO measurements indicate that the ratio between the main elements of the second-order nonlinear optical susceptibility tensor, χ33(2) and χ31(2), is significantly smaller than three. © 2000 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Jq Electro-optical effects
42.65.An Optical susceptibility, hyperpolarizability
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