Volume 92, Issue 2, 14 January 2008
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- interdisciplinary and general physics
Index of content:
The authors investigated the technological utility of counterclockwise (CCW) and clockwise (CW) circular-rotating fields ( and ) and spin-polarized currents with an angular frequency close to the vortex eigenfrequency , for the reliable, low-power, and selective switching of the bistate magnetization orientations of a vortex core (VC) in an array of soft magnetic nanoelements. CCW and CW circular gyrotropic motions in response to and , respectively, show remarkably contrasting resonant behaviors, (i.e., extremely large-amplitude resonance versus small-amplitude nonresonance), depending on the orientation of a given VC. Owing to this asymmetric resonance characteristics, the with can be used to effectively switch only the up (down) core to its downward (upward) orientation, selectively, by sufficiently low field and current density. This work provides a reliable, low power, effective means of information storage, information recording, and information readout in vortex-based random access memory, simply called VRAM.
- LASERS, OPTICS, AND OPTOELECTRONICS
92(2008); http://dx.doi.org/10.1063/1.2830696View Description Hide Description
is promising for yellow-amber-red light emitting diodes(LEDs). In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk LED structures are presented. Below , emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of , substantially lower than the Γ band gap of GaP. Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure.
92(2008); http://dx.doi.org/10.1063/1.2832666View Description Hide Description
Following the recent surge of interest in -doped strontium titanate as a possible blue light emitter, a time-resolvedphotoluminescenceanalysis was performed on nominally pure, Nb-doped and oxygen-deficient single-crystal samples. The doping effects on both the electronic states involved in the transition and the decay mechanism are respectively analyzed by comparing the spectral and dynamic features and the yields of the emission. Our time-resolvedanalysis, besides shedding some light on the basic recombination mechanisms acting in these materials, sets the intrinsic bandwidth limit of the proposed blue light emitting optoelectronic devices made of Ti-based perovskites heterostructures in the gigahertz range.
92(2008); http://dx.doi.org/10.1063/1.2830829View Description Hide Description
We propose a technique based on Fabry-Pérot fringes to analyze, in a broad wavelength range, the waveguideproperties of semiconductor lasers in the midinfrared spectrum. This technique has been applied to strain-balanced quantum cascade lasers, with a double phonon active region, in order to determine propagation losses and the effective index between 2.5 and wavelength. These results are in good agreement with the values obtained using another method.
92(2008); http://dx.doi.org/10.1063/1.2830998View Description Hide Description
Self-sustained pulsations in the output power of metal-organic chemical vapor deposition grown ridge-waveguide lasers with InGaAsquantum dot active region are reported. The characteristics of the output power pulsations (range, frequency, and modulation depth) are presented. The origin of the pulsations is explained in terms of the properties of the quantum dot active region.
A Sn-based metal substrate technology for the fabrication of vertical-structured GaN-based light-emitting diodes92(2008); http://dx.doi.org/10.1063/1.2834373View Description Hide Description
Through the use of tin (Sn) based solder balls and patterned laser lift-off technique, a metal substrate technology was proposed for the fabrication of vertical-structured metal substrate GaN-based light-emitting diodes (VM-LEDs). Advantages including reserving the merits of metallic substrate and simplifying the fabrication processes of vertical-structured GaN-based LEDs were demonstrated. As compared to conventional sapphire substrate GaN-based LEDs, the fabricated VM-LEDs with an emission area of show an increase in light output power about 145.36% at with a significant decrease in forward voltage from .
92(2008); http://dx.doi.org/10.1063/1.2830989View Description Hide Description
Photorefractive beam self-trapping is investigated in InP:Fe and is shown to occur within tens of microseconds after beam switch on. This fast response time is predicted by an analytical theoretical interpretation based on a simple photorefraction model which suggests buildups in a time range consistent with experiments.
92(2008); http://dx.doi.org/10.1063/1.2831910View Description Hide Description
Spectral distortions are commonly observed in terahertz transmission spectra of ground substances immersed in a transparent host medium. This effect originates from scattering due to the index contrast between the grains and diluent. A phenomenological expression quantitatively accounts for the scattering induced attenuation and the phase delay experienced by the electric field transmitted through the sample. Based on the knowledge of the refractive indices of the sample and the host material, we present a procedure to eliminate the scattering contribution from the absorption spectra.
Photonic crystal nanolaser monolithically integrated with passive waveguide for effective light extraction92(2008); http://dx.doi.org/10.1063/1.2831916View Description Hide Description
We recently reported room-temperature continuous-wave operation in a GaInAsP photonic crystal slab nanolaser. In this letter, we demonstrate effective light extraction from the nanolaser monolithically integrated with a passive waveguide by using a GaInAsP butt-joint regrowth technique. Theoretically, the extraction efficiency through the waveguide was calculated to be 80% for the optimum design of the coupling system of the nanolaser and the waveguide. In the experiment, we evaluated a differential quantum efficiency of 4%, which was degraded mainly due to the detection loss of the output light.
Very low transparency currents in double quantum well InGaAs semiconductor lasers with -doped resonant tunneling92(2008); http://dx.doi.org/10.1063/1.2825465View Description Hide Description
It is demonstrated that -type -doped resonant tunneling double quantum well (QW) lasers operated close to resonance exhibit an extremely low transparency current density of per QW. This suggests that the threshold current is almost identical to that of the best reported single QW device without doping and yet the modal gain is almost double. The low transparency current density is mainly due to the enhanced coupling between the QWs.
92(2008); http://dx.doi.org/10.1063/1.2832767View Description Hide Description
We report on active planar waveguides produced by carbonion implantation at dose of . The extraordinary refractive index of the sample surface experiences positive alternations after the implantation and subsequent thermal annealing treatment, constructing enhanced-well confined waveguide structures. The propagation loss of the waveguide is , which means acceptable quality for further guide-wave applications. The microluminescence spectra of the waveguide show fairly good potentials for laser action at 929 and .
92(2008); http://dx.doi.org/10.1063/1.2824846View Description Hide Description
Europiumdopedgallium oxide thin film electroluminescent devices with bright, red emission and relatively low threshold voltages of were produced using pulsed laser deposition. The use of transparent conducting electrodes of amorphous InGaZnO on transparent aluminumtitanium oxide/indium tin oxide/7059 Corning glass substrates resulted in a device that is transparent throughout the visible spectrum. At , with excitation, the luminance was . The Sawyer-Tower circuit analysis and time dependent emission measurements suggest that the charge trapping at the aluminumtitanium oxide/ interface plays an important role in producing efficient emission.
92(2008); http://dx.doi.org/10.1063/1.2829885View Description Hide Description
Single-mode optical fibers for the middle infrared are needed for many applications such as infrared fiber lasers, spatial filtering, and interferometry. Index guiding photonic crystal fibers offer many advantages over regular step-index fibers such as a wide spectral range and large core area. In this paper, we report the design and fabrication of single-mode octagonal photonic crystal fibers. These fibers were fabricated from silver halide polycrystalline materials which have high transmission in the middle infrared. The fibers showed a single-mode behavior at with low losses and a large mode diameter .
92(2008); http://dx.doi.org/10.1063/1.2835051View Description Hide Description
Si ring resonators on silicon on insulator show at least 50 times stronger photoluminescence(PL) with sharp peaks than the surrounding Si slab region at room temperature. The frequencies of the PL peaks are well explained by the resonant frequencies of the rings and the intensities are by the ratio of the quality factors of the PL peaks and the modal volumes of resonances. This suggests that the Purcell effect should be responsible for the enhancement.
The use of combination of nonlinear optical materials to control terahertz pulse generation and detection92(2008); http://dx.doi.org/10.1063/1.2831658View Description Hide Description
We suggest composite nonlinear optical media based on the pair of ZnTe and GaP crystals for terahertz pulse detection or generation. The influence of laser wavelength, pulse duration, and media thickness on the terahertz pulse conversion are studied. The optimization of the compositestructure performed numerically allowed for essential improvement of the phase-matching condition observed in the experiment.
92(2008); http://dx.doi.org/10.1063/1.2834898View Description Hide Description
We passively generate picosecond optical pulses directly from a single-stage oscillator using carbon nanotube mode locker. The mode locker immunized to the high optical power induced damage employs the evanescent field interaction of propagating light with the nanotubes. The mode locker endures the intracavity power of up to . For the enhanced interaction, vertically aligned nanotubes are synthesized and applied. The output pulses are monitored for to find that there is no significant degradation of average power and spectral width.
92(2008); http://dx.doi.org/10.1063/1.2834899View Description Hide Description
We propose elliptic deformation of apertures for shaping focusing patterns of tightly focused linearly polarized beams. Numerical integration of the vectorial Rayleigh-Sommerfeld diffraction formula predicts the formation of symmetric focusing patterns by shrinking the aperture shape in the direction perpendicular to the polarization of the beams. The elliptic deformation is also applied to a focused linearly polarized beam through an annular aperture to demonstrate the formation of smaller symmetric focal spot than that through a simple oval aperture.
92(2008); http://dx.doi.org/10.1063/1.2834903View Description Hide Description
We have demonstrated thermal emission of linearly polarized and narrow-band midinfrared waves from subwavelength gratings of narrow and deep rectangular cavities engraved on a Ausurface.-wide and -deep, high-aspect trenches were accurately manufactured by inversion from master molds. Organ pipe resonance of surface plasmons in the cavities exhibits a Lorentzian emission peak centered at . The maximum emittance reaches 0.90 and the peak width is as narrow as 0.13–0.23. This simple emitter is expected to play a key role in the infrared sensing technologies for analyzing our environment.
92(2008); http://dx.doi.org/10.1063/1.2819614View Description Hide Description
Stimulated emission and laser action with well developed longitudinal optical modes from an double heterostructure with a GaNactive layergrown on a silicon substrate by metal-organic chemical vapor deposition is demonstrated. Lasing was observed from cleaved platelets at room temperature with well resolved Fabry-Pérot modes at a wavelength as short as at room temperature. A clear threshold was observed in the plot of the emission intensity versus the pumping power at both and room temperature. The effective index of refraction during laser operation was measured to be 2.65.
92(2008); http://dx.doi.org/10.1063/1.2830838View Description Hide Description
In this letter, a frequency-selective circulator via mode coupling between a circular photonic crystal(CPC)surfacewaveguide and resonator systems is developed. The curve surfacewaveguide is formed by reducing the outermost rods radii. It has a transmission efficiency of 95% when the surface concentric distance is reduced by half. The resonator system, which consists of rod(s) are placed at each of the CPC perpendicular axis. Using optimized resonator physical parameters, selected frequencies are dropped at different locations with efficiency of 97%. It is suggested that several circulators can be cascaded to build a large scale frequency-selective multiplexing system.
Long-term stabilized two-beam combination laser amplifier with stimulated Brillouin scattering mirrors92(2008); http://dx.doi.org/10.1063/1.2831659View Description Hide Description
The beam combination method is the promising technique for constructing a very high energy laser with a high repetition rate over such as a real fusion driver. In our previous works, the phase control technique essential for realizing this system was proposed and demonstrated experimentally. However, these previous works were done without amplifiers. In this work, we employed amplifiers to test the real beam combination system and obtained a well stabilized phase controlling with fluctuation by standard deviation during 5000 laser shots at total output energy.