Volume 90, Issue 1, 01 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:
Single undoped Si nanowires were electrically characterized. The nanowires were grown by molecular-beam epitaxy on silicon substrates and were contacted by platinum/iridium tips. curves were measured and electron beam induced current investigations were performed on single nanowires. It was found that the nanowires have an apparent resistivity of , which is much smaller than expected for undoped Si nanowires. The conductance is explained by hoppingconductivity at the interface of the nanowiresurface.
- LASERS, OPTICS, AND OPTOELECTRONICS
Blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blueshift90(2007); http://dx.doi.org/10.1063/1.2424642View Description Hide Description
The authors present the design, growth, fabrication, experimental characterization, and theoretical analysis of blue quantum electroabsorption modulators that incorporate thick quantum structures for operation between 420 and . Growing on polar plane on sapphire, they obtain quantum structures with zigzag potential profile due to alternating polarization fields and demonstrate that their optical absorptionblueshifts with applied electric field, unlike the redshift of conventional quantum confined Stark effect. In quantum structures, they report the largest absorption change of for bias swing around , holding promise for blue optical clock generation and injection directly into silicon chips.
90(2007); http://dx.doi.org/10.1063/1.2424643View Description Hide Description
Here the authors demonstrate spectral optical chemical and biological sensors based on a nanoporous thin-film leaky waveguide that were fabricated by dip coating the gold-layer-covered glass substrate from the colloidal solution. The sensor operates by interrogating the resonance wavelengths for the leaky modes in a broad bandwidth using the Kretschmann configuration. Sensitivities of the sensor to refractive index of liquid and protein adsorption were investigated and compared with the spectral surface plasmon resonance sensors. The best fitting to the experimental data was carried out with the Fresnel equations, and thickness and porosity of the nanoporouswaveguiding layer were determined.
Near-infrared camera in polycrystalline germanium integrated on complementary-metal-oxide semiconductor electronics90(2007); http://dx.doi.org/10.1063/1.2425018View Description Hide Description
The authors demonstrate a two-dimensional array of Si-integrated photodetectors equipped with readout electronics and operating in the near infrared. The chip is realized in polycrystallineGe on a siliconcomplementary metal oxide semiconductor circuitry and includes , 64 analog to digital converters, dark current cancellation, and test/calibration facilities. They describe its design, fabrication, characterization, and operation as a near-infrared image sensor.
90(2007); http://dx.doi.org/10.1063/1.2425026View Description Hide Description
In this letter, volume Fresnel zone platesfabricated inside fused silica using femtosecond laser direct writing are demonstrated. A volume zone plate consists of a number of layers of Fresnel zone plates designed to focus light together. Results indicate that volume Fresnel zone plates increase the overall diffraction efficiency significantly. Phase zone plates yield considerably higher diffraction efficiency due to a number of reasons including negligible light absorption, robustness against fabrication phase errors, and minimum interference between different zone plates in a volume.
90(2007); http://dx.doi.org/10.1063/1.2426903View Description Hide Description
The authors report on the spectral properties of the modes in midinfrared whispering gallery lasers based on InAs. The behavior of the modes excited in cylindrical disk, pillbox, and mesa etched ridge resonators has been studied. The excitation of whispering gallery modes in these structures is found to depend strongly on the contact electrode and its location from the perimeter of the resonator. The authors also report on the threshold current and temperature sensitivity of different resonator and electrode combinations.
90(2007); http://dx.doi.org/10.1063/1.2426941View Description Hide Description
The authors use Fresnel diffraction from knife-edges to demonstrate the spatial coherence of a tabletop ultrafast x-raysource produced by laser-plasma interaction. Spatial coherence is achieved in the far field by producing micrometer-scale x-ray spot dimensions. The results show an x-raysource size of that leads to a transversal coherence length of at a distance of from the source. Moreover, they show that the source size is limited by the spatial spread of the absorbed laser energy.
Development of latent images due to transient free carrier electrons by femtosecond laser pulses and its application to grating shape trimming90(2007); http://dx.doi.org/10.1063/1.2426963View Description Hide Description
The effects of prepulse exposure on the threshold energy to encode a micrograting structure on a glass surface by a prepulse-postpulse exposure technique using femtosecond ( pulse duration) laser pulse irradiation were examined by measuring the laser intensity diffracted by the microgratings. It was revealed that prepulse exposure reduces the threshold energy of the postpulse from , which enables to develop a latent image of the free carriers generated by the prepulse with the postpulse. This technique was applied to trim the shape of the micrograting pattern with the prepulse pattern. The role of the prepulse was investigated by comparing the dynamics of the photoexcited carriers in two dielectrics ( glass and MgO single crystal) that have largely different lifetimes of photoexcited carriers. It was determined that the ultrashort relaxation time of the photoexcited carriers in glass limits the time delay of the postpulse to develop a latent image.
Doping effect of multiwall carbon nanotubes on the microwave electromagnetic properties of NiCoZn spinel ferrites90(2007); http://dx.doi.org/10.1063/1.2429020View Description Hide Description
NiCoZn ferrites have been found exhibiting two well separated resonance peaks. One is due to domain wall movement at . One is due to spin rotation at . With increasing the content of multiwall carbon nanotubes(MWCNTs) in the NiCoZn ferrite/MWCNT/wax hybrid composites, both resonance peaks are maintained, but their peak positions are found dependent on the MWCNT content. The damping factor for spin rotation is found decreasing as the content of MWCNT in composites increases. The dielectric loss of hybrid composites is also found significantly increased by increasing the content of MWCNT. The doping effects of MWCNT are thought due to the interaction between the ferrite and MWCNT. The microwave permeability of pure MWCNT has also been investigated, and it is believed due to the residual nanosized Ni particles.
Effect of liquid crystal concentration on the lasing properties of dye-doped holographic polymer-dispersed liquid crystal transmission gratings90(2007); http://dx.doi.org/10.1063/1.2426885View Description Hide Description
Optically pumped single-mode lasing was achieved from a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)--pyran dye-doped holographicpolymer-dispersed liquid crystal transmission grating with various liquid crystal concentrations, which played an important role in the lasing generation and wavelength selection. With the decrease of the liquid crystal concentration, under the excitation of a frequency-doubled Nd:yttrium aluminum garnet laser operating at , the lasing wavelength was blueshifted, and the full width at half maximum of the lasing peak became narrower. The lowest threshold pumping energy was found to be about ∕pulse at a liquid crystal concentration of . The lasing emission was thermally switchable due to the change of the refractive index modulation.
90(2007); http://dx.doi.org/10.1063/1.2430404View Description Hide Description
The feasibility of chalcogenide rib waveguides working at has been demonstrated. The waveguides comprised a several micron thick filmdeposited by thermal evaporation on a polished glass substrate and further etched by physical etching in Ar or atmosphere. Output images at and some propagation losses roughly estimated at proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realization of components able to work in the mid- and thermal infrared up to and even more.
Increase in midwave infrared light emitting diode light output due to substrate thinning and texturing90(2007); http://dx.doi.org/10.1063/1.2430484View Description Hide Description
Midwave infrared (MWIR) light sources with high optical power are required for many applications. The authors report here the MWIR ( peak) light emission from an interband cascade light emitting diode (LED) structure with 18 cascaded active/injection regions grown on GaSb substrate. The light emission is observed from the substrate side of the device. An increase of six times of light output power is observed due to substrate thinning and another 50% increase is observed due to texturing the emission surface. The authors observed emission power for room temperature operation with LED injection current. Experiments were carried out with different grating patterns and etch depths. The device with a square grating and a etch depth has the highest optical emission power.
90(2007); http://dx.doi.org/10.1063/1.2430485View Description Hide Description
An electrically tunable negative permeability metamaterial consisting of a periodic array of split ring resonators infiltrated with nematic liquid crystals is demonstrated. It shows that the transmitted resonance dip of the metamaterial can be continuously and reversibly adjusted by an applied electric field, and the maximum shift is about with respect to the resonance frequency around . Numerical simulation shows that the permeability is negative near the resonance frequency, and the frequency range with negative permeability can be dynamically adjusted and widened by about by the electric field. It provides a convenient means to design adaptive metamaterials.
Two-dimensional photonic crystal membrane lasers operating in the visible regime at room temperature90(2007); http://dx.doi.org/10.1063/1.2430488View Description Hide Description
The authors report on the fabrication and characterization of visible two-dimensional photonic crystal(PhC) band-edge lasers with multiple-quantum-well active layers. High-quality PhC air-bridge membranes are produced by optimizing the inductively coupled plasmaetching process for AlGaInPmaterials. Room-temperature lasing operation at the wavelengths ranging from is obtained by tuning the PhClattice parameters. The lasing action originates from high-symmetry band-edge modes, which is verified by three-dimensional finite difference time domain computation.
Observation of low optical overlap mode propagation in nanoscale indium phosphide membrane waveguides90(2007); http://dx.doi.org/10.1063/1.2430624View Description Hide Description
The authors have developed a nanoscale, rib-loaded waveguide that propagates a low optical overlap mode (LOOM) in which less than 1% of the modal field energy resides in the semiconductor material. Because of the small modal fill factor, the potential for extremely low waveguide propagation loss, on the order of or less, is predicted. Elevated membrane waveguides, thick with a thick rib, have been fabricated in InP using a multistep microelectromechanical release process. Both transverse electric and transverse magnetic LOOM propagations have been observed and measurements are compared to theoretical predictions.
90(2007); http://dx.doi.org/10.1063/1.2430625View Description Hide Description
The authors report on the fabrication and optical characterizations of two-dimensional photonic crystals fabricated by nanoimprint lithography in a nanocompositepolymer incorporating highly luminescent and red emitting (CdSe)ZnS core-shell colloidal nanocrystals.Photonic crystal structures enhance the light emitted from the quantum sized nanoparticles in the composite layer by slowing the propagation speed of the photons, thus increasing the coupling to the out-of-plane radiative modes. A 200% enhancement of the light collection is achieved compared to an unpatterned sample.
90(2007); http://dx.doi.org/10.1063/1.2429025View Description Hide Description
The authors present an efficient source of high purity polarization-entangled photon pairs in the standard telecommunication band using a type-II degenerate parametric downconversion process. They first measured the spatial intensity distributions of the downconverted light to verify the beamlike, collinear, and noncollinear generations at the wavelength. All four Bell states could easily be generated by selecting the intersection of two downconverted light cones in the noncollinear phase matching. They observed two-photon fringe visibilities of up to and violations of Bell’s inequality by up to nine standard deviations when the accidental coincidences were subtracted.
90(2007); http://dx.doi.org/10.1063/1.2429908View Description Hide Description
A buried grating structure with a selectively grown absorptive InGaAsP layer was fabricated and characterized by scanning electron microscopy and photoluminescence. The InP corrugation was etched by introducing a mask that was more stable than a conventional photoresist mask during the etching process. Moreover, the corrugation was efficaciously preserved during the selective growth of the absorptive layer with the mask. Though this absorptive layer was only selectively grown on the concave region of the corrugation, it has a high intensity around the peak wavelength in comparison with that of InGaAlAs multiple quantum well, which was grown on the buried grating structure.
90(2007); http://dx.doi.org/10.1063/1.2430685View Description Hide Description
The authors report here a complete experimental realization of one-way decoy pulse quantum key distribution, demonstrating an unconditionally secure key rate of for a fiber length. This is two orders of magnitudes higher than the value that can be obtained with a nondecoy system. They also introduce a simple test for detecting the photon number splitting attack and highlight that it is essential for the security of the technique to fully characterize the source and detectors used.
High power heavily strained type-I quantum well GaSb-based diode lasers with more than of continuous wave output power and a maximum power-conversion efficiency of 17.5%90(2007); http://dx.doi.org/10.1063/1.2430012View Description Hide Description
The authors demonstrate a double quantum well GaSb-based diode laser operating at with a room-temperature cw output power of and a maximum power-conversion efficiency of 17.5%. Laser differential gain with respect to current increases by a factor of 2 and laser threshold current is nearly halved when the compressive strain in the quantum wells is increased from 1.2% to 1.6%. This improvement is due to substantially improved hole confinement in the heavily compressively strained active region.