Volume 106, Issue 2, 15 July 2009
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic structure and transport
- 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
106(2009); http://dx.doi.org/10.1063/1.3172668View Description Hide Description
The Shockley–Read–Hall model (SRHM) and its simplified model (SSRHM) were used to describe the characteristics of a photoconductive semiconductor switch (PCSS) made from a semi-insulating (SI) gallium arsenide(GaAs) chip, biased at low voltage, and illuminated by a laser pulse. These characteristics include the free carrier densities, dynamic photoresistance, and time evolution of output pulses of the PCSS. The deep donor EL2 centers in SI GaAs play a dominant role in both the SRHM and SSRHM as electrons at EL2 unionized centers are strongly excited by the subband-gap photons at the wavelength of . Theoretical modeling on the evolution of the experimental measured output pulses led to a two-step micromechanism of electron excitation process within the GaAs chip. The minimum photoresistances predicted by the SSRHM are in good agreement with experimental measurements, which confirms the dominant role of EL2 in the generation of electric pulses from a SI GaAs photoconductivity switch on which the 1064 nm laser pulse is illuminated.
106(2009); http://dx.doi.org/10.1063/1.3153155View Description Hide Description
We considered a cholesteric slab whose axis is normal to their borders, when a uniform electric field is perpendicularly applied to the helix axis. We found the solution of the boundary value problem for the reflection and transmission of normally incident waves due to the slab. We showed that a left-circularly polarized thin reflection band is immersed in a wider right-circularly polarized band reflection, when the cholesteric is subjected to low amplitude fields. For larger field values, both reflection bands redshift simultaneously as the field increases. A device based on this phenomenon can be used as a electrically tunable universal filter.
106(2009); http://dx.doi.org/10.1063/1.3174444View Description Hide Description
This paper describes a rep-rated multibeam KrF laser driver design for the Inertial Fusion test Facility (FTF) recently proposed by NRL, then models its optical pulse shaping capabilities using the ORESTES laser kinetics code. It describes a stable and reliable iteration technique for calculating the required precompensated input pulse shape that will achieve the desired output shape, even when the amplifiers are heavily saturated. It also describes how this precompensation technique could be experimentally implemented in real time on a reprated laser system. The simulations show that this multibeam system can achieve a high fidelity pulse shaping capability, even for a high gain shock ignition pulse whose final spike requires output intensities much higher than the saturation levels associated with quasi-cw operation; i.e., they show that KrF can act as a storage medium even for pulsewidths of . For the chosen pulse, which gives a predicted fusion energy gain of , the simulations predict the FTF can deliver a total on-target energy of , a peak spike power of , and amplified spontaneous emission prepulse contrast ratios in intensity and in fluence. Finally, the paper proposes a front-end pulse shaping technique that combines an optical Kerr gate with cw light and a control beam shaped by advanced fiber optic technology, such as the one used in the National Ignition Facility (NIF) laser.
106(2009); http://dx.doi.org/10.1063/1.3176493View Description Hide Description
Nanoparticle-containing media can be used for efficient high-order harmonic generation of laser radiation. We present the results of studies of the harmonics generated in the laser-produced plasmas containing , Ag, Cu, and Au nanoparticles. These results are compared with the harmonics generated in the plasma produced on the surface of bulk targets at different delays between the subnanosecond heating prepulse and femtosecond pulse and different intensities of prepulse on the target surface. We discuss the harmonic enhancement, which was observed in the case of nanoparticle-containing plumes with regard to the monoparticle-containing plasmas. Morphological studies of plasma debris confirmed the presence and integrity of nanoparticles in the plumes.
106(2009); http://dx.doi.org/10.1063/1.3176499View Description Hide Description
A systematic investigation of the temperature characteristics of quantum dot lasers emitting at is reported. The temperature dependence of carrier lifetime, radiative efficiency, threshold current, differential efficiency, and gain is measured, and compared to the theoretical results based on a rate equation model. The model accurately reproduces all experimental laser characteristics above room temperature. The degradation of laser characteristics with increasing temperature is clearly shown to be associated to the thermal escape of holes from the confined energy levels of the dots toward the wetting layer and the nonradiative recombination therein.
Study of polarization properties of light emitted from -plane InGaN/GaN quantum well-based light emitting diodes106(2009); http://dx.doi.org/10.1063/1.3176964View Description Hide Description
This paper discusses the optical characteristics of a nonpolar -plane InGaN/GaN quantum well with different indium compositions, quantum well widths, and injection carrier densities. The self-consistent Poisson and Schrödinger solver has been applied to study the band structures in nonpolar -plane InGaN-based quantum welllight emitting diodes(LEDs). We find that the larger indium composition and smaller well width make the energy separation of -like state to -like state larger, and as a result enhance the polarization ratio of light. However, the polarization ratio decreases as the carrier injection increases, which might be a drawback for high power applications. We have studied the optimization condition for designing the -plane InGaNquantum wellLED for applications, such as liquid crystal display backlight modules and lasers, which would be useful information for device designs.
106(2009); http://dx.doi.org/10.1063/1.3176965View Description Hide Description
In this paper we experimentally investigated the birefringence and absorption coefficients of alpha barium borate (-BBO) crystal in the range of 0.3–10 THz by using a broadband air photonic terahertz time-domain spectrometer in both transmission and reflection modes. Several phonon modes were observed for and beams. The highest phonon mode at 6.8 THz has absorption coefficient of . The comparison between the optical properties of the -BBO and beta barium borate crystals showed that their phonon frequencies are different and -BBO crystal has smaller refractive index,birefringence, and absorption coefficients in low frequency region. The blueshift behavior of the lowest phonon of the -BBO crystal over the temperature range of 10–293 K has also been characterized.
106(2009); http://dx.doi.org/10.1063/1.3177341View Description Hide Description
Integrated photonics require optical isolators that achieve low insertion loss and large optical isolation. Here we describe a surface plasmon enhanced optical isolator based on nonreciprocal coupling from a dielectric waveguide coupled to a surface plasmon waveguide. The surface plasmon core consists of a magnetic metal which results in a large nonreciprocity, allowing for device lengths on the order of . The analysis and modeling presented here indicate that greater than 30 dB isolation and less than 3 dB insertion loss are possible.
106(2009); http://dx.doi.org/10.1063/1.3177344View Description Hide Description
Porous silicon based one-dimensional photonic crystals, such as Bragg mirror and optical microcavity, has been modified by infiltration of a new biocompatible polymer, an amino functionalized poly(-caprolactone) , and characterized as optical biochemical sensors. The entrapped polymer adds strong chemical stability to the nanocrystalline matrix on exposure to alkaline solutions preserving the device sensing abilities in monitoring volatile substances and chemical compounds. On the basis of these results, these hybrid structures can be proposed as a high performance platform for biochemical applications.
106(2009); http://dx.doi.org/10.1063/1.3176976View Description Hide Description
A new approach to diffractiveimaging using polychromatic diffraction data is described. The method is tested using simulated and experimental data and is shown to yield high-quality reconstructions.Diffraction data produced using a high-harmonic generation source are considered explicitly here. The formalism can be readily adapted, however, to any short-wavelength source producing a discrete spectrum and possessing sufficient spatialcoherence.
Spectral properties and luminescence lifetime of blue light of solid state cathodoluminescence based on poly[(2-methoxy-5-(-ethyl-hexyloxy)phenylene vinylene]106(2009); http://dx.doi.org/10.1063/1.3176980View Description Hide Description
The heterojunction of poly[(2-methoxy-5-(-ethyl-hexyloxy)phenylene vinylene] was prepared based on a layered optimization scheme. In three different voltage ranges, the emission spectra of the device changed. The red light was obtained at low applied voltages. With increasing the applied voltages, a blue light was observed. In the medium of the voltage range, one can see both of these two emissions. These two types of the emission resulted from the bombardment of the luminescent material of the MEH-PPV by the hot electron that accelerated in the layer , which was named solid state cathodoluminescence. In this paper we investigated the spectral properties, frequency response, and luminescence lifetime of blue light in solid state cathodoluminescence.
106(2009); http://dx.doi.org/10.1063/1.3177251View Description Hide Description
The laser wavelength of a band-edge liquid crystal laser is known to vary in a stepwise fashion with temperature. This report describes a method for removing the discontinuous shifts in the laser wavelength by doping a nematic sample with two different chiraldopants which exhibit opposing dependences of the natural pitch on temperature. On cooling from the isotropic phase to room temperature the total shift of the laser wavelength is 15 nm with no discontinuities. This is in contrast to that observed for samples consisting of only one chiraldopant whereby the wavelength shift was as large as 75 nm for the same temperature range.
106(2009); http://dx.doi.org/10.1063/1.3176897View Description Hide Description
Highly (100)-oriented (PZT)films of up to are deposited on the (PLT)-coated amorphous substrate by one cycle of sputtering and annealing. The films possess fibrous columnar nanostructures and vertically grow on the PLT/glass substrate. Microstructure analysis and property characterization indicate that the films possess very promising optical, waveguiding, and electro-optic (EO) properties, as well as low propagation loss. The transparency of in the range of and the linear EO coefficient of 341.4 pm/V have been measured in the films. Due to the large EO coefficient and the micrometric thickness, a giant phase retardation of 2.93 rad has been measured under an electric field of 50 kV/mm.
106(2009); http://dx.doi.org/10.1063/1.3183957View Description Hide Description
The photoelectric effects in (LNO) single crystal have been systematically studied with the two kinds of LNO wafers of tilt of 10° and untilted at the ambient temperature. The ultrafast response photoelectric effect of 120 ps rise time was observed in 10° tilted LNO single crystal with a 266 nm laser pulse of 25 ps duration. The photocurrent responsivity of untilted LNO with an interdigitated electrode of finger width and interspacing is 17.1 mA/W under the irradiation of 300 nm wavelength UV light at 10 V bias. The noise current under sunlight is only 73 pA at 10 V bias. The experimental results suggest that the LNO single crystal is one of the promising materials for photodetectors working in UV region.
Contribution of positive and negative ions to the electrohydrodynamic force in a dielectric barrier discharge plasma actuator operating in air106(2009); http://dx.doi.org/10.1063/1.3183960View Description Hide Description
We present a parametric study of the electrohydrodynamic force generated by surfacedielectric barrier discharge plasma actuators in air for sinusoidal voltage waveforms. The simulation results confirm that momentum is transferred from the charged particles to the neutral species in the same direction during both positive and negative parts of the cycle. The momentum transfer is due to positive ions during the positive part of the cycle (electrode above the dielectric layer is the anode), and to negative ions during the negative part of the cycle. The relative contribution of the positive and negative parts of the cycle depends on the voltage amplitude and frequency. The model predicts that the contribution of negative ions tends to be dominant at low voltage frequencies and high voltage amplitudes.
- PLASMAS AND ELECTRICAL DISCHARGES
Characterizations of strip-line microwave micro atmospheric plasma and its application to neutralization106(2009); http://dx.doi.org/10.1063/1.3153972View Description Hide Description
In this work, we estimate the plasma parameters of strip-line microwave micro atmospheric plasma (SMMAP) such as rotational temperature both from OH and rotational transitions (610–770 and 770–980 K in Ar, respectively), electron density from Stark broadening (about in mixture of Ar and ), and the distribution of electric field before ignition of SMMAP ( at maximum, and applied voltage less than 5 V). Since the lower applied voltage of SMMAP might enable us to conduct efficient processing without electrostatic damage (ESD), we applied jet-type SMMAP to neutralization. The result of neutralization showed that it can reduce surface charge from ±1000 to ±100 V for 0.2 s at 10 W with Ar gas flow within 4 V offset voltage, which provides efficient plasma processing without ESD.
Influence of sputter rate and crystal orientation on the distribution of carbon in polycrystalline copper surfaces treated by plasma immersion ion implantation106(2009); http://dx.doi.org/10.1063/1.3176488View Description Hide Description
The sputter rate influences the resulting thickness of the carbon containing layer within a surface that was treated by plasma immersion ion implantation. Choosing a polycrystalline substrate with rather large crystals and a material with an inherent high sputter rate, inhomogeneous distributions of carbon over the substrate area due to different thicknesses of the incorporated carbon can be detected. A correlation of three factors namely the carbon x-ray intensity in electron probe microanalysis, the thickness of the carbon layer, and the sputter rate in depth profiling measurements via secondary ion mass spectrometry can be shown. Essential for these factors is the crystal orientation that is visualized by mapping via electron backscatter diffraction. The differences in carbon content due to the orientation are most likely one of the reasons that the adhesion of diamond-like carbon films on copper does not improve with an interlayer of implantedcarbon.
106(2009); http://dx.doi.org/10.1063/1.3176496View Description Hide Description
The influence of controlled phase shift between very high frequency voltages applied to the powered electrodes on the plasma uniformity and etch rate was studied in a capacitive triode-type reactor. Radial profiles of plasma optical emission were measured as a function of the phase shift in process plasma with the low frequency bias power both turned off and on. Radial profiles of KrF photoresistetch rate over a wafer were obtained in the same conditions (with the bias power turned on). Besides, plasma density at the wafer center and edge was measured versus the phase shift in pure Ar plasma. It occurred that all measuredcharacteristics strongly depend on the phase shift and correlate with each other. It has been shown that the phase-shift control can considerably improve both the plasma and etch-rate uniformity in very high-frequency capacitive reactors.
106(2009); http://dx.doi.org/10.1063/1.3176904View Description Hide Description
The characteristics of advanced discharge modes were investigated through measurements of spatiotemporal infrared emission, discharge current, infrared intensity, and luminous efficacy in an acplasma display panel with an auxiliary electrode located between scan and common electrodes. Pulse waveforms that included auxiliary pulses applied to the auxiliary electrode after every sustain pulse were used. The proposed advanced discharge modes are as follows: In mode 1, strong discharges are generated by the sustain pulses only, whereas strong discharges are generated by the sustain pulses and a weak discharge is generated by the auxiliary pulse applied after the scan pulse in mode 2. In mode 3-1, strong discharges are generated by the sustain pulses and weak discharges are generated by the auxiliary pulses applied after the scan and common pulses, while all sustain and auxiliary pulses generate discharges having similar intensities in mode 3-2. Mode 1 and mode 2 are efficient modes; the luminous efficacy was improved in mode 1 owing to more homogeneous discharge due to the auxiliary electrode and a priming effect due to the auxiliary pulse. The luminous efficacy was also improved in mode 2, because of decreased power consumption induced by a decrease in wall charges and sustained or increased luminance due to priming particles. Mode 3-1 and mode 3-2 are inefficient modes; the luminous efficacy was reduced in mode 3-1 as a result of a decrease in the luminance due to insufficiently generated priming particles. The luminous efficacy was also reduced in mode 3-2, because of short-coplanar-gap discharges of the sustain pulses. It was found that advanced discharge modes were changed successively from mode 1 to mode 3-2 when sustain or auxiliary pulses of higher voltage were applied. The maximum luminous efficacy can be obtained in mode 1 at a low sustain pulse voltage and in mode 2 at mid and high sustain pulse voltages.
106(2009); http://dx.doi.org/10.1063/1.3160329View Description Hide Description
We recently reported on the direct measurements of the energy distribution of energetic neutrals incident onto the cathode of an argon dc glow discharge [T. Ito and M. A. Cappelli, Appl. Phys. Lett.90, 101503 (2007)]. In this paper, we provide a more extensive report of the experimental data, as well as direct comparisons to Monte Carlo simulations in which neutral-neutral and ion-neutral collision processes are modeled with differential scattering cross sections. The experimental results, which are limited to relatively small forward angle sampling in our present configuration, are found to be in excellent agreement with Monte Carlo simulations. The simulations reveal that high energy neutrals are striking the cathode with a wide range of angles, while ions are more anisotropic. Therefore, it is difficult to predict the neutral energy distribution with commonly used simple analytical models that do not consider scattering of neutrals within the sheath. We propose the use of an extended analytical model in this paper, which seems to provide reasonable energy distributions over the range of discharge voltage studied.