Volume 85, Issue 2, 12 July 2004
- 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
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
85(2004); http://dx.doi.org/10.1063/1.1768309View Description Hide Description
We report a white beam x-raywaveguide (WG) experiment. A resonant beam coupler x-raywaveguide (RBC) is used simultaneously as a broad bandpass (or multibandpass) monochromator and as a beam compressor. We show that, depending on the geometrical properties of the WG, the exiting beam consists of a defined number of wavelengths which can be shifted by changing the angle of incidence of the white x-ray synchrotron beam. The characteristic far-field pattern is recorded as a function of exit angle and energy. This x-ray optical setup may be used to enhance the intensity of coherent x-ray WG beams since the full energetic acceptance of the WG mode is transmitted.
Generation and detection of ultrabroadband terahertz radiation using photoconductive emitters and receivers85(2004); http://dx.doi.org/10.1063/1.1768313View Description Hide Description
We report the coherent generation and detection of ultrabroadband terahertz (THz) radiation using low-temperature-grown photoconductive antennas as both emitters and receivers. THz radiation with frequency components over was obtained, the highest reported for a time-domain system based on photoconductive antennas. Such a system has a smooth spectral distribution between 0.3 and , ideal for spectroscopic applications. In addition, sharp spectral features at 8.0 and were observed, and explained in terms of optical phonon resonances in the photoconductive antennas.
85(2004); http://dx.doi.org/10.1063/1.1768306View Description Hide Description
The room temperature operation of quantum cascade lasers is reported. The structure, grown by molecular beam epitaxy on an substrate, is based on a vertical transition design and a low loss plasmon enhanced waveguide. The lasers emitting near operate in pulse regime up to . The threshold current density of -long lasers is at and at .
85(2004); http://dx.doi.org/10.1063/1.1771462View Description Hide Description
We demonstrate a simplified nonplanar wafer bonding technique for heterogeneous device integration. The improved technique can be used to laterally integrate dissimilar semiconductor devicestructures on a lattice-mismatched substrate. Using the technique, two different -based vertical-cavity surface-emitting laser active regions have been integrated onto without compromising the quality of the photoluminescence. Experimental and numerical simulation results are presented.
85(2004); http://dx.doi.org/10.1063/1.1769588View Description Hide Description
Electromagnetic radiation is emitted by the vibrational and collective modes of an opaque solid as the result of impulsive stimulated Raman scattering.Raman scattering of near-infrared femtosecond laser pulses produces coherent longitudinal optical phonon and plasmon oscillations in the semiconductor. These oscillations radiate into free space at frequencies and are directly detected. The spectra exhibit features consistent with Raman selection rules including interference of allowed and forbidden Raman scattering.
85(2004); http://dx.doi.org/10.1063/1.1771800View Description Hide Description
We report a recording medium in which a three-dimensional nanoscale structure can be photofabricated for multilayered optical memory using a two-photon process. By fabricating the structures in the medium, we can control the shape of recorded bits and, in effect, their spatial frequency distribution. We succeeded in recording bits with a interval in any particular plane and interval between successive layers. Thus, storage density of is achieved.
85(2004); http://dx.doi.org/10.1063/1.1771809View Description Hide Description
We report on amorphous organic thin films that exhibit efficient third-harmonic generation at telecommunication wavelengths. At , micrometer-thick samples generate up to of green light with input power of delivered by an optical parametric oscillator. This high conversion efficiency is achieved without phase matching or cascading of quadratic nonlinear effects. With these films, we demonstrate a low-cost, sensitive third-order autocorrelator that can be used in the time-frequency domain.
Coupled surface plasmon-polariton mediated photoluminescencefrom a top-emitting organic light-emitting structure85(2004); http://dx.doi.org/10.1063/1.1772516View Description Hide Description
We report strong photoluminescence from a top-emitting organic light-emitting structure where emission takes place through a thin silverfilm. We show that this emission is mediated via coupled surface plasmon-polariton modes. Our results show that the addition of a dielectric grating to otherwise planar structures, such as surface-emitting organic light-emitting diodes, may offer a way to increase the external efficiency of top-emitting organic light-emitting diodes.
85(2004); http://dx.doi.org/10.1063/1.1772524View Description Hide Description
We have demonstrated optical gain and laser emission in multimoded plastic waveguides containing a near-infrared-emitting compound, 2-(6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-methyl-benzothiazolium perchlorat. The poly(1-vinyl-2-pyrrolidone)-base planar waveguides, in length and in thickness, doped with of the compound have exhibited lasing at under transverse nanosecond photoexcitation at . Optical feedback is provided by the 4% reflective facets of the cleaved waveguide edges. The threshold for lasing is found to be . Gain spectroscopy has shown a moderate net modal gain of at for the pump fluence of . Our results will open the door to the study and development of compact plastic waveguide lasers and amplifiers operating in the near-infrared region.
Efficient generation of red light by frequency doubling in a periodically-poled nearly-stoichiometric crystal85(2004); http://dx.doi.org/10.1063/1.1772525View Description Hide Description
An efficient generation of red light in a periodically-poled nearly-stoichiometric (PPSLT) by extracavity single-pass frequency doubling of a diode-pumped, -switched Nd:YVO4 laser at was realized. An average power of of the red light is obtained at the fundamental power of with the conversion efficiency of 50%. The high conversion efficiency and steady output of red light indicate that the thick PPSLT is a competitive candidate for frequency conversion in order to construct a compact all-solid-state red laser.
Strong enhancement of terahertz radiation from semiconductor surfaces using hemispherical lens coupler85(2004); http://dx.doi.org/10.1063/1.1772861View Description Hide Description
We report an enhancement of terahertz radiation power from surfaces excited by ultrashort laser pulses using an hemispherical lens coupler. The power of the terahertz radiation from the surface with the lens coupler is 50 times larger than that from the surface without the lens coupler. The enhancement is explained mainly by the increase of the transmission efficiency of the wave from to free space.
85(2004); http://dx.doi.org/10.1063/1.1771467View Description Hide Description
A nanoscale metal–semiconductor grating is proposed for efficient and ultrafast photodetection. Theoretical and experimental results of efficient absorption in nanoscopic semiconductorwires are presented. The strong confinement of light in subwavelength metal–semiconductor gratings is achieved by Fabry–Pérot resonances involving vertical transverse magnetic surface-plasmon waves and transverse electric guided waves. Photodetectors have been fabricated with cross sections of Ag and GaAswires. The reflectivity and photocurrent mesurements are in good agreement with theoretical estimates.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
85(2004); http://dx.doi.org/10.1063/1.1769587View Description Hide Description
We propose an evaluation method for macroscopic elastic constants of composites, which is called the effective-mean-field method. The method is based on Mori–Tanaka’s mean-field (MTMF), and the effective-medium approximation methods, in which complex elastic fields disturbed by many inclusions are replaced by the average fields of a virtually homogenized composite, and the MTMF formulae are utilized in the entire fraction range of inclusion. It is demonstrated for porous samples that the proposed method can reproduce power-law behavior with regard to porosity.
85(2004); http://dx.doi.org/10.1063/1.1768307View Description Hide Description
Epitaxially stabilized iron monosilicide films with the structure have been investigated by conversion electron Mössbauer spectroscopy and x-ray diffraction. A detailed investigation of the elastic strain in these metastable layers is presented. Using hyperfine interaction information the tetragonal distortion of the silicide lattice could be quantified for layers as thin as . A general tendency for strain relaxation with increasing layer thickness is observed.
85(2004); http://dx.doi.org/10.1063/1.1771452View Description Hide Description
Monte Carlo simulations of stress buildup and relief shed light onto the physical origin of trench formation in islands. By monitoring the stress evolution as the island grows layer by layer, we find that a trench is most likely being formed halfway during growth. The primary driving force for this phenomenon is the reduction of the concentrated stress below the edges of the island, but not the need to provide Si into it, as is widely believed. However, once the trench is formed, subsequent intermixing through it is enhanced, and nearly compensates for the stress in the island.
85(2004); http://dx.doi.org/10.1063/1.1771804View Description Hide Description
The photoluminescence(PL) of AlGaNquantum wells with AlN barrier layers deposited on substrates fabricated of AlNsingle crystals is studied in the temperature range from under pulsed band-to-band excitation of the well material. The abnormal temperature dependence of the PL peak position and differences in the character of the peak shift with increasing excitation power density observed at low and elevated temperatures are interpreted in terms of carrier/exciton localization and screening of the built-in electric field. The formation of these localized states with narrow energy distribution and high density is favorable for efficient light emission.
85(2004); http://dx.doi.org/10.1063/1.1769593View Description Hide Description
To quantify the effect of hydrogen on the kinetics of interdiffusion in olivine, diffusion couples composed of crystals with ratios of and were annealed under water-saturated conditions at and . With buffered at the phase boundary, . The resulting interdiffusivity, , is approximately one order of magnitude larger than that measured under anhydrous conditions. The enhancement in diffusivity in the presence of water results from an increase in the concentration of cation vacancies associated with the introduction of high concentrations of protons as point defects into the olivine structure.
Real-time evolution of the indium tin oxide film properties and structure during annealing in vacuum85(2004); http://dx.doi.org/10.1063/1.1771456View Description Hide Description
Indium tin oxide films produced by reactive middle frequency magnetron sputtering were annealed in a vacuum. The electrical and optical properties of the film have been studied in situ along with direct characterization of the crystalline structure. Even in the amorphous state, the filmresistivity significantly decreases with increasing temperature due to a free-electron density enhancement, likely by the generation of oxygen vacancies. A rapid crystallization within the temperature range of leads to a further decrease of the resistivity due to donor activation. The resistivity and the optical properties depend nonlinearly on the crystalline fraction.
85(2004); http://dx.doi.org/10.1063/1.1771457View Description Hide Description
Interfacial chemistry of , , and is investigated by x-ray photoelectron spectroscopy in order to understand the interfacial layer formation mechanism. Deposition of and films was carried out on wafers by electron-beam evaporation with oxygen backfill. We show that the interfacial layer formation takes place predominantly at the initial stage of the film deposition. Temporary direct bonding between metal and is proposed to be the source of the catalytic reaction resuting in formation of interfacial layer. Formation of interfacial layer was suppressed by chemically grown thin oxide blocking the direct bonding. We also demonstrate reduced interfacial layer after modified Shiraki surface etch, compared to the Radio Corporation of America clean. This indicates that a more complete hydrogen termination and atomically smoother surface can delay the onset of interfacial layer formation.
85(2004); http://dx.doi.org/10.1063/1.1771810View Description Hide Description
thin films were deposited on (0001) sapphire substrates by pulsed-laser deposition.Structural and optical properties of films were strongly correlated to the processing conditions. The composition of the films varied nonmonotonically as a function of deposition temperatures due to the difference of vapor pressure between Cd and Zn species. The optical energy bandgap of thin films, measured by photoluminescence and transmittance, changed from . The change of the optical properties was mainly attributed to the change of the stoichiometry of , as determined by Rutherford backscattering spectroscopy.