Volume 93, Issue 10, 08 September 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
- applied biophysics
- interdisciplinary and general physics
Index of content:
and its implications for , , , , and " title="Origin of hardness in and its implications for , , , , and " />
First-principles calculations were performed on the superhard material, (Vicker hardness exceeding ), to reveal the origin of its high hardness. Our simulated lattice parameters, bulk modulus, and hardness are in excellent agreement with the experimental data. A three-dimensional B network with a peculiar dimer along the -axis and a planar honeycomb B sublattice is uncovered to be mainly responsible for the high hardness. We further predicted that five other transition metal B compounds (, , Mo,Ta, Os, and Tc) within the structure are potential superhard materials.
- LASERS, OPTICS, AND OPTOELECTRONICS
93(2008); http://dx.doi.org/10.1063/1.2966153View Description Hide Description
We studied the performance of an evanescent wave magnetometer with a coated cell of adjustable length. The cell length varies from a few millimeters to less than . Two kinds of antirelaxation coatings are used: octadecyltrichlorosilane (OTS) and dichlorooctamethyltetrasiloxane (Surfasil). Sub-kilohertz linewidth can be achieved for a thick OTS-coated cell. Magnetometers with coated ultrathin cells have superior performance in inhomogeneous magnetic fields, and can achieve a spatial resolution of better than .
93(2008); http://dx.doi.org/10.1063/1.2978398View Description Hide Description
A large-area interdigitated terahertz emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAsheterostructure is investigated as a terahertz source for excitation wavelengths between 1.1 and . The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of and have a resistivity of . Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below . Furthermore the emission properties for several excitation powers are investigated, showing a linear increase in terahertz emission.
93(2008); http://dx.doi.org/10.1063/1.2978399View Description Hide Description
We report on the detailed analysis of femtosecondsurface plasmon polariton (SPP) pulse generation under resonant excitation. Using prism coupling technique we excite femtosecond SPP pulses at a gold/air interface with ultrafast laser pulses. We show that the photon-SPP coupling is a resonant process with a finite spectral bandwidth that causes a spectral phase shift and a narrowing of the SPP pulse spectrum. Both effects result in a temporal pulse broadening and, therefore, set a lower limit on the duration of ultrafast SPP pulses with consequences for ultrafast SPP applications.
High-intensity nanosecond-pulsed laser-induced plasma in air, water, and vacuum: A comparative study of the early-stage evolution using a physics-based predictive model93(2008); http://dx.doi.org/10.1063/1.2979704View Description Hide Description
A comparative study has been performed for properties(temperature, density, and electron Coulomb coupling constant) of plasma induced by high-intensity nanosecond laser-metal interactions in air, water, and vacuum. The study is for early-stage plasma evolution, where the above plasma properties are very difficult to measure experimentally and hence a comparative property study has been rarely reported in literature. In this paper a physics-based predictive model is used as the investigation tool. The model was verified based on experimental measurements for the early-stage plasma pressure and front propagation and the late-stage plasma temperature and electron number density, which are relatively easy to measure. Therefore, the experimentally verified model can provide reasonably accurate information on the difficult-to-measure plasma temperature and density in the early-stage at least in the semiquantitative sense, and the information will be very useful for the fundamental laser plasma study and relevant laser applications. It has been found that plasma with very different temperatures and densities can be created in different media.
93(2008); http://dx.doi.org/10.1063/1.2980423View Description Hide Description
Crystalline-orientation and pump dependent polarization states of microchip lasers were observed experimentally. Linear polarization was observed at six crystalline orientations in the (111) plane relative to the beam propagation direction along the  crystalline axis of crystal. The extinction ratio of the linear polarization decreases and the laser tends to oscillate at random polarization state at high pump power levels. Linear polarization states of microchip laser was selected by the anisotropic spectroscopic properties of the -ion in cubic crystal. The random polarization oscillation at high pump power was caused by the strong thermal-induced birefringence and depolarization.
93(2008); http://dx.doi.org/10.1063/1.2980401View Description Hide Description
For lossy metamaterials, there exist the negative index of refraction regimes that may originate from double negative or single negative of the real parts of complex permittivity and permeability. To represent the regimes of negative index, a material quality factor space is proposed. Within the space the different negative index regimes are found located in the different regions. The contour map of the complex index of refraction in the space show that the negative index can be always possible to realize in three ways, and the loss of single negative metamaterials is greater than that of double negative metamaterials.
93(2008); http://dx.doi.org/10.1063/1.2980517View Description Hide Description
We report on the study of a single-photon-emitting diode at . The device is composed of quantum dots embedded in the -region of a diode structure. The high signal to noise ratio of the electroluminescence, as well as the small second order correlation function at zero-delay , implies that the device has a low multiphoton emission probability. By comparing the device performances under different excitation conditions, we have, in detail, discussed the basic parameters, such as signal to noise ratio and , and provided some useful information for the future application.
93(2008); http://dx.doi.org/10.1063/1.2975845View Description Hide Description
We report on the properties of GaNAsP/GaP lasers which offer a potential route to producing lasers monolithically on silicon. Lasing has been observed over a wide temperature range with pulsed threshold current density of at 80 K . Temperature dependence measurements show that the radiative component of the threshold is relatively temperature stable while the overall threshold current is temperature sensitive. A sublinear variation of spontaneous emission versus current coupled with a decrease in external quantum efficiency with increasing temperature and an increase in threshold current with hydrostatic pressure implies that a carrier leakage path is the dominant carrier recombination mechanism.
93(2008); http://dx.doi.org/10.1063/1.2978203View Description Hide Description
A ZnO/MgZnO-based one-dimensional photonic crystal multiquantum well laser operating at an emission wavelength of 360.7 nm is demonstrated. The photonic crystal providing optical feedback was fabricated in the form of parallel grooves with a period of 277.3 nm and a depth of 100 nm in a layer deposited directly on the epitaxial material. At a temperature of 11 K, 16 mW peak power is emitted from the laser surface, and the threshold intensity amounts to . From temperature-dependent output power versus pump intensity curves, we deduced a of 60 K and a maximal operating temperature of 135 K.
93(2008); http://dx.doi.org/10.1063/1.2981212View Description Hide Description
The response of a compact photonic immunoassaybiosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscopemeasurements indicate and top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.
Evanescent coupling in arrays of type II femtosecond laser-written waveguides in bulk -cut lithium niobate93(2008); http://dx.doi.org/10.1063/1.2981801View Description Hide Description
We report on the first fabrication of evanescently coupled planar arrays of type II waveguides in -cut lithium niobate by femtosecond laser inscription. A particular choice of writing parameters allows the evanescent field of the individual waveguide modes to extend significantly beyond the damage lines into the neighboring guides, thus realizing a coupling constant of at a wavelength of 633 nm.
The effect of the last quantum barrier on the internal quantum efficiency of InGaN-light emitting diode93(2008); http://dx.doi.org/10.1063/1.2981640View Description Hide Description
The effect of the last quantum barrier (LQB) on the internal quantum efficiency of GaN-light emitting diode(LED) was systematically investigated using a dual-wavelength GaN-LED design. Compared with a conventional GaN-LQB, a high indium contained -LQB efficiently reduced the unintentional Mg impurity in the last quantum well and improved its photoluminescence and electroluminescence intensity up to 72% and 15%, respectively.
93(2008); http://dx.doi.org/10.1063/1.2977488View Description Hide Description
We report the observation of enhanced optical transmission through the metal subwavelength hole arrays with nanoparticle inside the hole, and demonstrate the transmission enhancement and the suppression due to the excitation of the localized surface plasmon (LSP). We interpret this phenomenon with the Fano theory considering the real and imaginary parts of the polarizability of the LSP.
93(2008); http://dx.doi.org/10.1063/1.2977864View Description Hide Description
We report on a two-photon detector based on resonantly enhanced nonlinear absorption between subbands in InGaAs/InAlAs quantum wells and demonstrate its use as a quadratic autocorrelator for midinfrared pulses. Modified device design allows for device operation at room temperature, which is crucial for applications in practical systems.
Investigation of spectral gain narrowing in quantum cascade lasers using terahertz time domain spectroscopy93(2008); http://dx.doi.org/10.1063/1.2979682View Description Hide Description
The spectral gain of bound-to-continuum terahertz quantum cascade lasers(QCLs) is measured as a function of current density using terahertz time-domain spectroscopy. During lasing action the full width at half maximum (FWHM) of the gain is found to monotonically decrease with increasing current density until lasing action stops at which point the FWHM reaches a minimum (0.22 THz for a laser operating at 2.1 THz). Band structure calculations show that the spectral gain narrowing is due to the alignment and misalignment of the injector with the active region as a function of the applied bias field.
Spatial modulation instability driven by light-enhanced nonlinearities in semiconductor CdZnTe:V crystals93(2008); http://dx.doi.org/10.1063/1.2982084View Description Hide Description
We present the experimental observation of spatial modulation instability in photorefractive semiconductor crystals (CdZnTe:V), where the optical nonlinear effects are enhanced by light. We find that the total refractive index change can be expressed as sum of a uniform index change, which can exceed the value of 0.003, and a local index change which is limited to . However, only the later, arising from the intensity-enhanced photorefractive effect, contributes to the formation of the modulation instability. Finally, we find that the refractive index change experiences large temporal fluctuations induced by the combination of uniform cw illumination and applied electric field.
93(2008); http://dx.doi.org/10.1063/1.2982097View Description Hide Description
A monolithic white light emitting diode using a (Ga,In)N/GaN multiple quantum well(MQW) light converter is demonstrated. Blue photons emitted under electrical injection by (Ga,In)N/GaN QWs located inside a GaN junction are partly absorbed by another (Ga,In)N/GaN MQW situated outside the junction which emits yellow-green light. The combination of the blue and yellow-green components results in white light emission.
- PLASMAS AND ELECTRICAL DISCHARGES
Order of magnitude enhancement in neutron emission with deuterium-krypton admixture operation in miniature plasma focus device93(2008); http://dx.doi.org/10.1063/1.2979683View Description Hide Description
The effect of varied concentrations of deuterium-krypton admixture on the neutron emission of a fast miniature plasma focusdevice was investigated. It was found that a judicious concentration of Kr in can significantly enhance the neutron yield. The maximum average neutron yield of for pure filling at 3 mbars was enhanced to with admixture operation, which represents a -fold increase. More than an order of magnitude enhancement in the average neutron yield was observed over the broader operating range of 1–4 mbars for and admixtures.
93(2008); http://dx.doi.org/10.1063/1.2979700View Description Hide Description
An alternative concept for accelerating thin foils to high velocity has been proposed and tested. The thin Al foil has been accelerated by the ablative plasma generated by means of the third harmonic (, ) of the iodine laser pulse of the energies of 75 and 190 J irradiating a massive Cu target. Two separation distances of the foil from the massive target of 100 and were used. It has been shown that this method of an indirect, two-step acceleration, named as the reversed acceleration scheme, can be more effective than the classic, direct-drive approach. The Al flyer foil has reached a velocity of , i.e., significantly higher than that in the comparable “classic” ablative accelerationexperiment.
93(2008); http://dx.doi.org/10.1063/1.2980436View Description Hide Description
Plasma with a gas temperature below room temperature is not yet fully understood although it is expected to be an attractive tool for applications to material processing. In the present work, gas-temperature-dependent generation of a cryoplasma jet was studied. So far, we have generated a helium cryoplasma jet under atmospheric pressure. At gas temperatures below , the helium excimer, , was observed clearly from by optical emission spectroscopy.