Volume 95, Issue 4, 27 July 2009
- lasers, optics, and optoelectronics
- 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
- biophysics and bio-inspired systems
- interdisciplinary and general physics
Index of content:
Regular, almost quadratic pits were created in an island of molecules on a rutile (110) surface using noncontact atomic force microscopy at room temperature. Upon gradually approaching the scanning tip toward the surface, the interaction between the tip and the island was increased until manipulation was achieved. Analyzing the manipulation process unambiguously revealed that the manipulation was performed in the repulsive regime. Retracting the tip allowed for reproducible imaging the island after the manipulation process. Moreover, whole islands could be reshaped or even removed when scanning with appropriate scanning parameters.
- LASERS, OPTICS, AND OPTOELECTRONICS
95(2009); http://dx.doi.org/10.1063/1.3186081View Description Hide Description
We compare the performance of two quantum dot saturable absorber mirrors with one device operating at the quantum dotground state transition whereas the other operates at the first excited state transition. Time-resolved photoluminescence and heterodyne four-wave mixing experiments demonstrate faster recovery of the excited-state device compared to the ground-state device. Femtosecond pulses were achieved with both devices, with the ground-state device producing 91 fs pulses and the excited-state device producing 86 fs pulses in a Cr:forsterite laser. The fast absorption recovery dynamics indicates the potential of devices exploiting excited-state transitions for use in high repetition rate lasers.
95(2009); http://dx.doi.org/10.1063/1.3189703View Description Hide Description
We report on the observation of midinfrared intersubband (ISB) absorption in InGaAs/GaAsSb multiple quantum wells grown lattice-matched to InP substrates by molecular beam epitaxy. ISB absorption in a broad wavelength region is observed in quantum wells with well widths ranging between 4.5 and 12 nm. The conduction band offset at the InGaAs/GaAsSb heterointerface is measured to be 360 meV, giving an excellent agreement between the theoretically calculated ISB transition energies and the Fourier-transform infrared spectroscopy measurements over the whole range of well widths under investigation.
95(2009); http://dx.doi.org/10.1063/1.3189813View Description Hide Description
We report our observations of enhancement and suppression between two competing four-wave mixing(FWM) processes. The results show the evolution of the dressed effects (from pure enhancement into pure suppression) in the degenerate FWM processes. Moreover, due to induced atomic coherence in the system, there exist different interplays between these two FWM processes via different detuning parameters. In addition, the power dependences of enhancement and suppression are studied. Theoretical calculations are carried out, which are in good agreement with the experimental observations.
95(2009); http://dx.doi.org/10.1063/1.3189814View Description Hide Description
Single-mode laser diodes on GaSb substrates were developed using InGaAsSb/AlGaAsSb triple quantum well active regions grown by molecular beam epitaxy. The devices were fabricated using lateral Cr gratings, with a grating pitch designed to coincide with a strong absorption feature of HF gas, deposited adjacent to a dry-etched narrow ridge waveguide. High sidemode suppression was achieved, and in continuous-wave operation, devices with a long cavity provided 9 mW total output power at the 2396 nm target wavelength. High-resolution direct absorption measurements of HF gas agreed with HiTran calculations, yielding an absorption linewidth of 0.030 nm.
95(2009); http://dx.doi.org/10.1063/1.3190199View Description Hide Description
A concept of digital optical spectrometer-on-chip is proposed and results of their fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms which involves millions of lines specifically located and oriented in order to direct output light into designed focal points according to the wavelength. Spectrometers were fabricated on silicon dioxide and hafnium dioxide planar waveguides using electron beam lithography and dry etching. Optical performances of devices with up to 1000 channels for a central wavelength of 660 nm are reported.
95(2009); http://dx.doi.org/10.1063/1.3184594View Description Hide Description
We develop an approach to broad-band omnidirectional light absorption, based on light propagation in a metamaterial structure forming an effective “black hole.” The proposed system does not rely on magnetic response, is nonresonant, and can be fabricated from existing materials.
Damping of the tunneling mechanism in high-order harmonic generation processes induced by femtosecond visible laser pulses95(2009); http://dx.doi.org/10.1063/1.3186358View Description Hide Description
The high-order harmonic generation (HHG) of coherent light pulses in gases is strictly dependent on the ionization dynamics that delocalizes the electron wave function in the laser field continuum. Here we report on the investigation of such dynamics by varying the energy of a 400 nm, 60 fs driving laser pulse. The experimental data provide the unambiguous evidence of a hybrid dynamical region, not described by the full-tunneling approximation models, where the HHG photon number exponentially decays when the Keldysh parameter is varied from 1 to 3. Finally, a phenomenological model, suitable to account for this hybrid regime, is reported.
95(2009); http://dx.doi.org/10.1063/1.3189812View Description Hide Description
We show that quantum dot intersublevel transitions can be coupled to midinfrared photonic crystal modes. The coupling is observed under optical pumping with intersublevel transitions of InGaAsself-assembledquantum dotsresonant around wavelength. An enhancement in the intersublevel absorption and a spectral tuning are evidenced when the optical modes of two-dimensional photonic crystals enter in resonance with the photoinduced intersublevel absorption. This effect is illustrated in the case of GaAs two-dimensional photonic crystal membranes with lattice periodicities of 10.5, 9.5, and containing multilayers of self-assembledquantum dots.
95(2009); http://dx.doi.org/10.1063/1.3190504View Description Hide Description
We report the fabrication and study of high efficiency ultraviolet light emitting diodes with inverted micropyramid structures at GaN-sapphire interface. The micropyramid structures were created by anisotropic chemical wet etching. The pyramid structures have significantly enhanced the light output efficiency and at the same time also improved the crystal quality by partially relieving the strain and reducing the dislocation defects in GaN. The electroluminescent output power at normal direction was enhanced by 120% at 20 mA injection current and the output power integrated over all directions was enhanced by 85% compared to a reference sample.
95(2009); http://dx.doi.org/10.1063/1.3193537View Description Hide Description
We study the effect of laser wavelength (400 and 800 nm) on the near-field processing of crystalline silicon (Si) in the femtosecond pulse duration regime through subwavelength apertures. Distinct differences in the obtained nanostructures are found in each case both in terms of their physical sizes as well as their structure, which can be tuned between craters and protrusions. A single or a few femtosecond pulses can deliver enough energy on the substrate to induce subdiffraction limited surface modification, which is among the smallest ever reported in subwavelength apertured near-field scanning optical microscope schemes.
95(2009); http://dx.doi.org/10.1063/1.3186062View Description Hide Description
The photoluminescence and decay time of Er-doped amorphous silicon nitride films with different Si concentrations are studied in the temperature range of 4 to 320 K. The temperature quenching of the Er emission lifetime demonstrates the presence of nonradiative trap centers due to excess Si in the films. The temperature dependence and the dynamics of the energy coupling between amorphous silicon nitride and Er ions are investigated at different temperatures using two independent methods, which demonstrate phonon-mediated energy coupling. These results can lead to the engineering of more efficient Er-doped, Si-based light sources for on-chip nanophotonics applications.
95(2009); http://dx.doi.org/10.1063/1.3189702View Description Hide Description
In this work a photoconductive probe tip applicable for near- and far-field measurements in the terahertz frequency regime is demonstrated as a powerful alternative to existing terahertz scanning near-field optical microscopy approaches. The probe tip is based on a triangular-shaped patch of freestanding low-temperature-grown GaAs of only thickness with a pair of tapered metallic wires on top. Using nonresonant electric field enhancement at the tip of the probing device, wide metallic structures are spatially resolved and a bandwidth of 2 THz is demonstrated.
95(2009); http://dx.doi.org/10.1063/1.3193532View Description Hide Description
We report on the photoluminescenceproperties of erbium (Er) doped epilayers synthesized by metal organic chemical vapor deposition. The crystalline quality and surface morphology of Er doped were nearly identical to those of Er dopedGaN. The photoluminescence intensity of the emission in Er doped was an order of magnitude lower than in Er dopedGaN and decreased with the increase of the In content. The reduction in emission intensity was accompanied by enhanced emission intensities of deep level impurity transition lines.
95(2009); http://dx.doi.org/10.1063/1.3191668View Description Hide Description
Ferroelectricthin films with high optical quantity were deposited on quartz substrates by radio frequency magnetron sputtering at . The interplay between third- and fifth-order optical nonlinearities is observed by performing -scans under femtosecond laser excitation with 1.60 eV photon energy. The measured third-order nonlinearities mainly originate from electronic Kerr effect and two-photon absorption (2PA), while the population redistribution assisted by 2PA leading to an equivalent stepwise process is the main mechanism of the fifth-order effect.
95(2009); http://dx.doi.org/10.1063/1.3193550View Description Hide Description
We demonstrate experimentally an enhancement in Raman scattering in Rb atomic vapor due to the atomic coherence initially prepared by a weak write laser. We find that the enhanced Raman scattering depends on the spatial distribution of the atomic spin coherence and can be explained with a simple picture of three-wave mixing. This effect can in principle be used to have a light conversion efficiency near unity in Raman process. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
Role of edge dislocation and Si impurity in linking the blue luminescence and yellow luminescence in -type GaN films95(2009); http://dx.doi.org/10.1063/1.3187540View Description Hide Description
A close relationship is found between the blue and yellow luminescence bands in -type GaNfilms, which are grown without intentional acceptor doping. The intensity ratio of blue luminescence to yellow luminescence decreases with the increase in edge dislocation densities as demonstrated by the (102) full width at half maximum of x-ray diffraction. In addition, the ratio decreases with the increase in Si doping. It is suggested that the edge dislocation and Si impurity play important roles in linking the blue and yellow luminescence.
95(2009); http://dx.doi.org/10.1063/1.3186041View Description Hide Description
We study the properties of electromagnetic Bloch waves in semi-infinite periodic structures created by alternating metamaterial and dielectric layers. We derive and analyze the dispersion relations in the long-wavelength limit for both TE- and TM-polarized surface Bloch modes for magnetic metamaterials with negative refraction and metal-dielectric plasmonic superlattices. We reveal that in the subwavelength regime, the bulk modes are characterized by three different refractive indices (“trirefringence”), while the surface modes can propagate parallel to the Bloch wavevector and along the interface between superlattice and semi-infinite dielectric.
95(2009); http://dx.doi.org/10.1063/1.3191675View Description Hide Description
Room temperature photoluminescence(PL) spectra have been measured for alloys with Bi concentrations in the 0.2%–10.6% range. The decrease in the PL peak energy with increasing Bi concentration follows the reduction in bandgap computed from density functional theory. The PL peak energy is found to increase with PL pump intensity, which we attribute to the presence of shallow localized states associated with Bi clusters near the top of the valence band. The PL intensity is found to increase with Bi concentration at low Bi concentrations, peaking at 4.5% Bi.
95(2009); http://dx.doi.org/10.1063/1.3192357View Description Hide Description
The growth mechanism of thin films is studied starting from highly textured ZnS precursor films. These precursors were converted to by subsequent deposition of Cu, Sn, and S at high temperatures. Orientation measurements revealed that the texture of the ZnS precursor is inherited by the layer. On the basis of texture and transmission electron microscopy measurements, a growth model is proposed. According to this model, the initial formation of nuclei is controlled by a topotactic or epitactic mechanism with respect to the ZnS precursor. The further growth of the grains appears to be independent of the precursor lattice.
95(2009); http://dx.doi.org/10.1063/1.3176408View Description Hide Description
Phase resonances are observed in the microwave response of metal transmission gratings comprised of identical but alternately orientated tapered slits. Despite each slit having identical dimensions, and being equally spaced from its neighbors, these high-Q mode are nonetheless supported even at normal incidence. The excitation of these modes is attributed to the interference between Fabry–Perot-like modes and diffractively coupled surface waves.