Volume 90, Issue 3, 15 January 2007
- 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
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Strain relaxation in patterned stripes grown on Si(001) by chemical vapour deposition was investigated after ion implantation and annealing. Ion channeling measurements indicate asymmetric strain relaxation with a significantly higher residual strain parallel to the stripes than perpendicular to the stripes. These results are confirmed by plan view transmission electron microscopy showing a much higher density of misfit dislocations running along the stripes than across the stripes. Estimates based on a piezoresistivity model indicate significant enhancements of electron and hole mobilities for asymmetrically strained Si cap layers on such SiGe stripes.
- LASERS, OPTICS, AND OPTOELECTRONICS
90(2007); http://dx.doi.org/10.1063/1.2431707View Description Hide Description
The authors demonstrate the selective postgrowth band gap engineering and the fabrication of band gap tuned laser in InAs–InAlGaAs quantum-dash lasers grown on InP substrate. The process utilizes nitrogen implantation to induce local defects and to enhance the group-III intermixing rate spatially upon the thermal annealing. Compared with the as-grown laser, intermixed laser with wavelength shifted by shows a 36% reduction in threshold current density and produces a comparable slope of efficiency. The integrity of the intermixed material is retained suggesting that intermixing process paves way to planar, monolithic integration of quantum-dash-based devices.
The effect of silicon doping in the selected barrier on the electroluminescence of multiquantum well light emitting diode90(2007); http://dx.doi.org/10.1063/1.2431717View Description Hide Description
The effect of silicon doping in the selected barrier on the electroluminescence of multiquantum well light emitting diode(LED) was studied using dual wavelength LEDs. The result verified that the hole carrier transport is easily blocked by the silicondoped barrier, and the dominant electron and hole recombination occurs at the wells between and the silicondoped barrier. The electroluminescence spectrum and the wavelength blueshift of the silicondopedLEDs were compared with undoped LEDs. The numerical simulation was done to clearly explain the hole blocking effect by the silicondoped barrier.
90(2007); http://dx.doi.org/10.1063/1.2431762View Description Hide Description
In the present letter the authors report on the realization of an all-fiber bismuth-doped laser with laser emission that can be chosen with corresponding fiber Bragg gratings between at least 1150 and . In their experiments they achieved a slope efficiency of about 24% at , which is the highest reported for this kind of laser.
90(2007); http://dx.doi.org/10.1063/1.2431448View Description Hide Description
The authors report far-infrared dielectric properties of powder form ferroelectric . Terahertz time-domain spectroscopy (TDS) measurement reveals that the low-frequency dielectric response of is a consequence of the lowest transverse optical (TO) soft mode TO1 at , which is directly verified by Raman spectroscopy. This result provides a better understanding of the relation of low-frequency dielectric function with the optical phonon soft mode for ferroelectric materials. Combining terahertz TDS with Raman spectra, the overall low-frequency optical phonon response of is presented in an extended spectral range from .
Second-harmonic generation in quantum cascade lasers with electric field and current dependent nonlinear susceptibility90(2007); http://dx.doi.org/10.1063/1.2431757View Description Hide Description
The authors demonstrate a quantum cascade laser design with an integrated resonant nonlinearity for second-harmonic generation. Its nonlinear power conversion efficiency is strongly dependent on the injected current density due to an electric field and current dependent nonlinear susceptibility. This dependence produces an observed tenfold increase of the conversion efficiency over the current density range of . Furthermore, bidirectional lasing at widely different wavelengths is a side effect for this active region design.
High-resolution mapping of the three-dimensional point spread function in the near-focus region of a confocal microscope90(2007); http://dx.doi.org/10.1063/1.2431764View Description Hide Description
Fluorescent nanobeads with a diameter of were used to map the three-dimensional point spread function in the near-focus region of a confocal microscope at high spatial resolution. Fluorescenceimages were taken in 109 equidistant planes ( apart) parallel to the focal plane; postacquisition stacking of these images allows the reconstruction of the point spread function in the axial plane. The experimental distribution is compared to theoretical calculations based on an integral representation for the light intensity in the focus region that takes into account stratified media, polarization, the Gaussian illumination profile, and the finite exit pinhole size.
90(2007); http://dx.doi.org/10.1063/1.2431768View Description Hide Description
The authors present a power-efficient large-scale lensless optical traps on a chip (OTOCs) as an optofluidic element for optical sorting of microparticles. Based on the well-known Talbot self-imaging effect in the Fresnel region, the OTOC makes use of a two-dimensional microfabricated chessboardlike structure to create an optical lattice near its emergent plane. Simultaneous trapping of hundreds of microparticles in a regular array is proved experimentally without adopting an external optical projection lens configuration. Furthermore, the authors demonstrate experimental results for large-scale sorting of microparticles by sizes using the OTOC.
90(2007); http://dx.doi.org/10.1063/1.2432280View Description Hide Description
Vanadiumdopedgalliumlanthanum sulphide glass (V:GLS) displays three absorption bands at 580, 730, and identified by photoluminescence excitation measurements. Broad photoluminescence, with a full width at half maximum of , is observed peaking at when exciting at 514, 808, and . The fluorescence lifetime and quantum efficiency at were measured to be and 4%, respectively. From the available spectroscopic data, the authors propose the vanadium ions’ valence to be and be in tetrahedral coordination. The results indicate a potential for the development of a laser or optical amplifier based on V:GLS.
90(2007); http://dx.doi.org/10.1063/1.2420781View Description Hide Description
By introducing a defect layer into the periodic cladding of Bragg fiber, the core mode and the defect mode may anticross near their cutoff inside band gap. The defect location suppresses and flattens dramatically the group velocity of coupled core mode and the defect thickness changes gradually its dispersion.Theoretical investigation reveals zero dispersion and zero dispersion slope at various low ’s can be achieved simultaneously at arbitrary wavelengths. Specially, the proper defect in the sixth bilayer leads to the lowest of 0.074 of light speed in vacuum at . The optical energy is confined well in the core and the leakage loss is sufficiently low.
90(2007); http://dx.doi.org/10.1063/1.2431718View Description Hide Description
The method of decoy-state quantum key distribution requests different intensities of light pulses. Existing theory has assumed exact control of intensities. Here the authors propose a simple protocol which is secure and efficient even there are errors in intensity control. In their protocol, decoy pulses and signal pulses are generated from the same father pulses with a two-value attenuation. Given the upper bound of fluctuation of the father pulses, their protocol is secure provided that the two-value attenuation is done exactly. They propose to use unbalanced beam splitters for a stable attenuation.
90(2007); http://dx.doi.org/10.1063/1.2430913View Description Hide Description
Gallium nitride based microcavitylight emitting diodes less than thick emitting at a peak wavelength of have been fabricated. The epitaxial structure was grown by metal organic chemical vapor deposition, and the device was fabricated using a laser lift-off process. Cavity thinning was carried out using inductively coupled plasmaetching until a cavity length of roughly (, corresponding to a cavity order of 4 for in GaN) was achieved. Devices are presented that show perfectly detuned angular emission and perfectly resonant emission between the cavity length and emission wavelength.
90(2007); http://dx.doi.org/10.1063/1.2432295View Description Hide Description
Tunable emission in the near infrared is demonstrated on a silicon platform. The building blocks for the tunable light sources consist of porous siliconmicrocavities infiltrated with erbiumdoped nematic liquid crystals. Erbium ions are the luminescence source, porous siliconmicrocavities narrow the emission band, and liquid crystals enable tuning of the peak wavelength. Greater than attenuation is achievable by thermal actuation with microcavities having a factor of 200. The bandwidth of the tunable emission is limited by the liquid crystal birefringence.
Fabrication of implanted channel waveguides in single crystal buried epitaxial layers for infrared to blue upconversion laser systems90(2007); http://dx.doi.org/10.1063/1.2422891View Description Hide Description
Fabrication and intense infrared to blue upconversion emission of proton-implanted , (YAG) channel waveguides are reported for the first time to authors’ knowledge. The single or multiple implanted channels are buried by positive induced index change in stacked planar layers grown by liquid-phase epitaxy on pure YAG substrates. The codoping considerably enhances the IR to blue upconversion emission of ions after excitation in resonance with either or absorption transition around .
Optical fiber taper coupling and high-resolution wavelength tuning of microdisk resonators at cryogenic temperatures90(2007); http://dx.doi.org/10.1063/1.2431719View Description Hide Description
A system for studying microcavityresonators at cryogenic temperatures through evanescent coupling via optical fiber taper waveguides is reported, and efficient fiber coupling to AlGaAs microdisk cavities with embedded quantum dots is demonstrated. As an immediate application of this tool, the authors study high-resolution tuning of microdisk cavities through nitrogen gas adsorption, as first discussed by Mosor et al. [Appl. Phys. Lett.87, 141105 (2005)]. By proper regulation of the nitrogen gas flow and delivery of the gas to the sample surface, continuous tuning can be achieved with modest gas flows, and overall wavelength shifts as large as are achieved.
90(2007); http://dx.doi.org/10.1063/1.2431767View Description Hide Description
On-chip all-optical switching based on the carrier plasma dispersion in an argon ion implantedphotonic crystal(PhC) nanocavity that is connected to input/output waveguides is described. A high dose of is introduced, and annealing is used to recrystallize the silicon and thus create dislocation loops at the center of the PhC slab. Dislocation loops enable the fast recombination of the carriers, which allows a fast switching recovery time for PhC switches. The switching window is three times smaller than that without ion implantation, while the required operating energy remains almost the same .
Hybrid inorganic/organic microstructured light-emitting diodes produced using photocurable polymer blends90(2007); http://dx.doi.org/10.1063/1.2431772View Description Hide Description
Light-emitting diodes(LEDs) in the form of a one-dimensional array of microstripes emitting at were fabricated from AlInGaN inorganic semiconductor. These microlight sources were then used to “directly write” microstructures in photocurable blends of organic light-emitting polymers (LEPs) spin coated onto the LED surface. In this way, thin microstripes of LEP as narrow as have been fabricated and integrated with the micro-LEDs. These “self-aligned” polymer microstripes serve as wavelength downconverters under further excitation by the UV micro-LEDs, producing hybrid inorganic/organic microstructured LEDs.
Role of external cavity reflectivity for achieving polarization control and stabilization of vertical cavity surface emitting laser90(2007); http://dx.doi.org/10.1063/1.2431790View Description Hide Description
The authors present the experimental results showing how the external mirrorreflectivity affects the polarizationproperties of a vertical cavity surface emitting laser subject to optical feedback from an extremely short external cavity. The amplitude of modulation of the polarization switching current with the external cavity length is found to be proportional to the external mirrorreflectivity, confirming its key role in achieving polarization control and stabilization of such lasers using optical feedback. Numerical simulations presented here show good agreement with experiments.
- PLASMAS AND ELECTRICAL DISCHARGES
90(2007); http://dx.doi.org/10.1063/1.2431791View Description Hide Description
The authors report experimental results showing that high yields of singlet oxygen can be generated in a three-electrode microcathode sustained discharge (MCSD) configuration. This configuration consists of a microhollow cathodedischarge (MHCD) acting as a plasmacathode to sustain a stable glow discharge between the MHCD and a third, planar electrode placed at a distance of . Experiments were performed in pure oxygen and in mixtures of oxygen with rare gases (He or Ar) at pressures up to . relative yields of 7.6% were measured downstream in the afterglow of the MCSD discharge.
Superradiant terahertz Smith-Purcell radiation from surface plasmon excited by counterstreaming electron beams90(2007); http://dx.doi.org/10.1063/1.2432270View Description Hide Description
The authors show that evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about two orders of magnitude as well as lower its transition threshold from a spontaneous emission to a stimulated one. An emission mechanism of the superradiant SPR is theoreticallyanalyzed by the dielectric conversion of the structured metal surface and the boundary matching condition of Maxwell’sequations in comparison with numerical simulations.
Influence of a large oblique incident angle on energetic protons accelerated from solid-density plasmas by ultraintense laser pulses90(2007); http://dx.doi.org/10.1063/1.2432242View Description Hide Description
The acceleration of energetic electron, proton, and heavy ion beams produced by ultrahigh-intensity laser pulses through thin plastic targets is studied using two-dimensional hybridparticle-in-cell simulation. When the laser is incident at a large angle, the proton beams accelerated from the front and rear surfaces of the target deviate from the normal direction because of the formation of non-Gaussian asymmetric sheath field at the target surfaces. In particular, the simulations clearly show that the proton beam in the backward direction can have higher Bragg peak energy than that of the forward direction if the incident angle is sufficiently large.