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1 Jun 2009

Volume 105, Issue 11, Articles (11xxxx)

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Tunable two-dimensional plasmon resonances in an InGaAs/InP high electron mobility transistor

H. Saxena, R. E. Peale, and W. R. Buchwald

J. Appl. Phys. 105, 113101 (2009); http://dx.doi.org/10.1063/1.3129319 (6 pages) | Cited 7 times

Online Publication Date: 1 June 2009

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Voltage-tunable plasmon resonances in the two-dimensional electron gas (2DEG) of a high electron mobility transistor (HEMT) fabricated from the InGaAs/InP materials system are reported. The device was fabricated from a commercial HEMT wafer by depositing source and drain contacts using standard photolithography and a semitransparent gate contact that consisted of a 0.5 μm period transmission grating formed by electron-beam lithography. Narrow-band resonant absorption of terahertz radiation was observed in transmission in the frequency range of 10–50 cm−1. The resonance frequency depends on the gate-tuned sheet charge density of the 2DEG. The observed separation of resonance fundamental from its harmonics and their shift with gate bias are compared with theory.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Influence of lattice parameters on the resonance frequencies of a cut-wire-pair medium

V. D. Lam, N. T. Tung, M. H. Cho, J. W. Park, J. Y. Rhee, and Y. P. Lee

J. Appl. Phys. 105, 113102 (2009); http://dx.doi.org/10.1063/1.3137198 (6 pages) | Cited 8 times

Online Publication Date: 1 June 2009

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We studied both theoretically and experimentally the influence of the lattice constant on the resonance frequencies of cut-wire-pair structures, which are essential components in assembling left-handed materials. These structures were designed and fabricated, and the transmission spectra were measured in the microwave-frequency regime. Numerical simulation was performed using the transfer-matrix method. All the numerical results were in good agreement with the experimental data. It was found that the lattice parameters of the cut-wire-pair structure provide sensitive effects on the electric resonance, especially, in the propagation k and the electric field E directions, while the magnetic resonance frequency is nearly unchanged, except for its bandwidth and depth. In addition, we also studied the effect of dielectric layer thickness on the resonance frequencies of the cut-wire-pair structure. These sensitive changes in the electric resonance might have remarkable effects on the effective plasma frequency and therefore on the left-handed behavior of combined structures consisting of cut-wire pairs and continuous wires.
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42.70.-a Optical materials
78.70.Gq Microwave and radio-frequency interactions
02.60.-x Numerical approximation and analysis
02.10.Yn Matrix theory
77.22.Ch Permittivity (dielectric function)

Monte Carlo simulation of terahertz quantum cascade laser structures based on wide-bandgap semiconductors

Enrico Bellotti, Kristina Driscoll, Theodore D. Moustakas, and Roberto Paiella

J. Appl. Phys. 105, 113103 (2009); http://dx.doi.org/10.1063/1.3137203 (9 pages) | Cited 18 times

Online Publication Date: 2 June 2009

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Wide-bandgap semiconductors such as GaN/AlGaN and ZnO/MgZnO quantum wells are promising for improving the spectral reach and high-temperature performance of terahertz quantum cascade lasers, due to their characteristically large optical phonon energies. Here, a particle-based Monte Carlo model is developed and used to quantify the potential of terahertz sources based on these materials relative to existing devices based on GaAs/AlGaAs quantum wells. Specifically, three otherwise identical quantum cascade structures based on GaN/AlGaN, ZnO/MgZnO, and GaAs/AlGaAs quantum wells are designed, and their steady-state carrier distributions are then computed as a function of temperature. The simulation results show that the larger the optical phonon energies (as in going from the AlGaAs to the MgZnO to the AlGaN materials system), the weaker the temperature dependence of the population inversion. In particular, as the temperature is increased from 10 to 300 K, the population inversions are found to decrease by factors of 4.48, 1.50, and 1.25 for the AlGaAs, MgZnO, and AlGaN structure, respectively. Based on these results, the AlGaN and MgZnO devices are then predicted to be in principle capable of laser action without cryogenic cooling.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors

Effect of evaporation on blinking properties of the glycerol microdrop Raman laser

R. Sharma, J. P. Mondia, J. Schäfer, Z. H. Lu, and L. J. Wang

J. Appl. Phys. 105, 113104 (2009); http://dx.doi.org/10.1063/1.3138082 (4 pages) | Cited 3 times

Online Publication Date: 2 June 2009

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We present long-term measurements of the blinking (on/off) behavior of the glycerol microdroplet Raman laser and demonstrate the dependency of the lasing bursts on the evaporation rate of the microdroplet. Electrodynamic levitation is used to study the glycerol microdroplets. Single and multimode lasing are achieved and shown here for droplets of 10.3 and 44.7 μm in diameter, respectively. Typical threshold fluences are measured to be between 200 and 390 mJ/cm2. Lasing occurs in temporally separated nearly symmetric bursts which increase in frequency and decrease in duration as the evaporation rate of the droplet is increased. Hence, we conclude that the Raman lasing blinking is caused by double resonances in the evaporating droplet and show that it can be manipulated by controlling the droplet’s evaporation rate.
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42.55.Ye Raman lasers

Luminescence enhancement and emission color adjustment of white organic light-emitting diodes with quantum-well-like structures

Su-Hua Yang, Bo-Cheng Hong, and Shih-Fong Huang

J. Appl. Phys. 105, 113105 (2009); http://dx.doi.org/10.1063/1.3138810 (7 pages) | Cited 4 times

Online Publication Date: 2 June 2009

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In recent years, white-light organic light-emitting diodes (OLEDs) have attracted considerable attention because of their potential applications in displays, backlight units, and general lighting. In this paper, we describe the fabrication of a high-luminance white-light OLED with dual-emission layers (EMLs). The 2,9-dimethyl-4,7-diphenyl-1,10-phenanhroline hole blocking layers (HBLs) were prepared to enhance the luminance and adjust the emission color of the device. For the device with a single-HBL structure, the excess holes were accumulated at the red EML (REML)/HBL1 interface. Consequently, most of the carriers were recombined in the REML, which led to a redshifted light emission. On the contrary, the device with a dual-HBL structure showed a blueshifted light emission. The device with a quantum-well-like structure increased the carrier trapping and recombination probabilities; as a result, a lower current density and a higher luminance intensity of the device were achieved. The maximum luminance intensity was 33 600 cd/m2 at 13 V, with CIE coordinates at (0.32, 0.32); the maximum current efficiency was 7.06 cd/A at 10 V; and the maximum power efficiency was 2.62 lm/W at 7 V and 294 cd/m2.
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85.60.Jb Light-emitting devices
68.65.Fg Quantum wells

Efficiency enhancement in seeded and self-amplified spontaneous emission free-electron lasers by means of a tapered wiggler

H. P. Freund and W. H. Miner, Jr.

J. Appl. Phys. 105, 113106 (2009); http://dx.doi.org/10.1063/1.3131630 (6 pages) | Cited 3 times

Online Publication Date: 3 June 2009

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The enhancement of the efficiency in free-electron lasers (FELs) through the use of a tapered wiggler is well known. The physics of the tapered wiggler interaction has been studied in theory and simulation, and large efficiency enhancements have been observed in the laboratory in oscillators and seeded amplifiers. In this paper, we study the differences in the tapered wiggler interaction between seeded amplifiers and in FELs that start up from noise and grow to saturation in a single pass through the wiggler. This configuration is commonly referred to as self-amplified spontaneous emission (SASE). In comparison with seeded amplifiers, SASE FELs exhibit shot-to-shot fluctuations due to random phase noise in the electron bunches, and our purpose in this paper is to determine the effect of this phase noise on the tapered wiggler interaction. To this end, we study the interaction numerically using the MEDUSA simulation code for seeded and SASE FELs operating in the infrared regime. The results of the simulations indicate that the overall efficiencies of the seeded and SASE FELs are comparable for a uniform wiggler but that the output spectrum for the SASE FEL is much broader than for the seeded case. For a tapered wiggler, the efficiency enhancement in the SASE FEL is less than that found in the seeded example due to the broader excited spectrum that detunes the tapered wiggler interaction.
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems

Out-of-plane thermal diffusivity measurement of transparent thin film by the acoustic grating excitation

E. V. Ivakin, M. U. Karelin, and A. V. Sukhadolau

J. Appl. Phys. 105, 113107 (2009); http://dx.doi.org/10.1063/1.3131662 (6 pages)

Online Publication Date: 3 June 2009

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The theory of pulsed photoacoustic phase method for out-of-plane thermal diffusivity measurement of thin dielectric film deposited on highly absorbing substrate is developed. The method is based on spatial modulation of the intensity of excitation. Optical detection of acoustic waves enables working with acoustic frequencies higher than 107 Hz and allows characterization of transparent films of submicron thickness. Pilot measurements have been carried out with SiO2 films on monocrystalline silicon wafer. Thermal diffusivity determined in the experiment agrees with the reference value for the bulk fused quartz.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films

Optical properties of aluminum-, gallium-, and indium-doped Bi4Ti3O12 thin films

Caihong Jia, Yonghai Chen, and W. F. Zhang

J. Appl. Phys. 105, 113108 (2009); http://dx.doi.org/10.1063/1.3138813 (4 pages) | Cited 7 times

Online Publication Date: 3 June 2009

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Undoped and Al-, Ga-, and In-doped Bi4Ti3O12 thin films were prepared on fused quartz substrates by chemical solution deposition. Their microstructures and optical properties were investigated by x-ray diffraction and UV-visible-NIR spectrophotometer, respectively. The optical band-gap energies, Urbach energies, and linear refractive indices of all the films are derived from the transmittance spectrum. Following the single oscillator model, the dispersion parameters such as the average oscillator energy (E0) and dispersion energy (Ed) are achieved. The energy band gap and refractive indices are found to decrease with introducing the dopants of Al, Ga, and In, which is useful for the band-gap engineering and optical waveguide devices. The refractive index dispersion parameter (E0/S0) increases and the chemical bonding quantity (β) decreases in all the films compared with those of bulk. It is supposed to be caused by the nanosize grains in films.
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78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Ps Other inorganic compounds
61.72.up Other materials

Blueshift of optical band gap in c-axis oriented and conducting Al-doped ZnO thin films

A. Di Trolio, E. M. Bauer, G. Scavia, and C. Veroli

J. Appl. Phys. 105, 113109 (2009); http://dx.doi.org/10.1063/1.3139275 (5 pages) | Cited 14 times

Online Publication Date: 3 June 2009

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We have investigated the structural, optical, and electrical properties of alumina-doped zinc oxide (AZO) thin films, grown by pulsed laser deposition. The optical transmittance of the films is over 80% in the visible region, and the absorption edge shifts from about 380 nm of the undoped sample to 320 nm of the AZO film. The calculated optical band gap (Eg) of 2 wt % AZO films shows a widening up to 3.82 eV with respect to the undoped film (3.28 eV). Higher doping concentration (6 wt %) leads to films with larger Eg (4.1 eV), but also epitaxial properties are affected. A further widening of the gap occurs when the AZO films are deposited by lowering the substrate temperature (Ts) from 450 to 250 °C. These blueshifts are respectively attributed to the increase in carrier concentration, induced by Al-donor doping, and also a lower degree of crystalline order. AZO films with doping concentration of 2 wt % show resistivity values of about 10−3 Ω cm and the local I-V curves, measured by scanning tunneling spectroscopy, show higher tunneling current than ZnO film. The Al-doping route proved to be effective in tailoring the optical and electrical properties without essentially affecting the crystalline structure of the films.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Spatially resolved determination of the dark saturation current of silicon solar cells from electroluminescence images

Markus Glatthaar, Johannes Giesecke, Martin Kasemann, Jonas Haunschild, Manuel The, Wilhem Warta, and Stefan Rein

J. Appl. Phys. 105, 113110 (2009); http://dx.doi.org/10.1063/1.3132827 (5 pages) | Cited 9 times

Online Publication Date: 4 June 2009

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We present a novel method to determine spatially resolved the dark saturation current of standard silicon solar cells. For this two electroluminescence images are taken at two different voltages. From these two images, first the spatial voltage distribution can be calculated. Second by applying the Laplacian to the voltage image from Ohm’s law and the continuity equation, the current through the device at a certain position can be determined. Knowing the local current through the device, the local voltage, and the emitter sheet resistance allows to determine the local dark saturation current. The clue of this method is to cope with the noise by using an appropriate noise reduction algorithm. By simulating electroluminescence images with realistic noise and known dark saturation current we demonstrate the applicability of the method with our noise reduction algorithm. Experimentally we compare our method with spectral response light beam induced current on multicrystalline solar cell.
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84.60.Jt Photoelectric conversion
85.30.De Semiconductor-device characterization, design, and modeling
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Achromatic reflectron compressor design for bright pulses in femtosecond electron diffraction

G. H. Kassier, K. Haupt, N. Erasmus, E. G. Rohwer, and H. Schwoerer

J. Appl. Phys. 105, 113111 (2009); http://dx.doi.org/10.1063/1.3132834 (10 pages) | Cited 7 times

Online Publication Date: 4 June 2009

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We have designed a femtosecond electron gun suitable for ultrafast electron diffraction experiments, operating in the 30–100 kV regime. The concept is based on recompression of chirped expanding electron pulses emitted from a direct current photogun using a novel dispersion-corrected reflectron concept. We show, using detailed numerical simulations, that our design is capable of producing electron pulses containing 200 000 electrons with a full width at half maximum pulse duration of 130 fs, a root mean squared (rms) pulse radius of 140 μm, and transverse coherence length of 1.5 nm at 100 kV. Our analysis includes the bunch properties at the sample, as well as interactions of the main pulse of high charge density with diffracted electrons. Since our design employs only static electron optics, we believe that it will be easier to implement than concepts based on radio frequency compression.
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61.05.J- Electron diffraction and scattering
02.60.-x Numerical approximation and analysis
85.60.Ha Photomultipliers; phototubes and photocathodes
06.60.Jn High-speed techniques (microsecond to femtosecond)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Refraction-enhanced x-ray radiography for inertial confinement fusion and laser-produced plasma applications

Jeffrey A. Koch, Otto L. Landen, Bernard J. Kozioziemski, Nobuhiko Izumi, Eduard L. Dewald, Jay D. Salmonson, and Bruce A. Hammel

J. Appl. Phys. 105, 113112 (2009); http://dx.doi.org/10.1063/1.3133092 (8 pages) | Cited 6 times

Online Publication Date: 4 June 2009

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We explore various laser-produced plasma and inertial confinement fusion applications of phase-contrast x-ray radiography, and we show how the main features of these enhancements can be considered from a geometrical optics perspective as refraction enhancements. This perspective simplifies the analysis and often permits simple analytical formulas to be derived that predict the enhancements. We explore a raytrace approach to various material interface applications, and we explore a more general example of refractive bending of x rays by an implosion plasma. We find that refraction-enhanced x-ray radiography of implosions may provide a means to quantify density differences across shock fronts as well as density variations caused by local heating due to high-Z dopants. We also point out that refractive bending by implosions plasmas can blur fine radiograph features and can also provide misleading contrast information on area-backlit pinhole imaging experiments unless its effects are taken into consideration.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.57.-z Laser inertial confinement
52.70.La X-ray and γ-ray measurements
52.80.Qj Explosions; exploding wires

Dipolar energy states in clusters of perpendicular magnetic nanoislands

E. Mengotti, L. J. Heyderman, A. Bisig, A. Fraile Rodríguez, L. Le Guyader, F. Nolting, and H. B. Braun

J. Appl. Phys. 105, 113113 (2009); http://dx.doi.org/10.1063/1.3133202 (4 pages) | Cited 6 times

Online Publication Date: 4 June 2009

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We investigated the energy states in compact clusters of ferromagnetic islands with perpendicular anisotropy arranged on a triangular lattice. Due to their finite nature, we were able to determine the energies of all possible cluster states using dipolar energy calculations. We employed photoemission electron microscopy to observe the magnetic states in arrays of clusters of monodomain Co/Pt multilayer islands and following demagnetization, we observed a shift in the energy distribution to lower energies as the dipolar coupling increased. These multistate island clusters not only provide model arrangements of frustrated Ising-type nanomagnets but are also interesting for data storage applications.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ch Domain walls and domain structure
75.75.-c Magnetic properties of nanostructures
75.10.Hk Classical spin models
75.60.-d Domain effects, magnetization curves, and hysteresis

Microscopic design of GaInNAs quantum well laser diodes on ternary substrates for high-speed and high-temperature operations

Takeshi Fujisawa, Masakazu Arai, Takayuki Yamanaka, Yasuhiro Kondo, and Fumiyoshi Kano

J. Appl. Phys. 105, 113114 (2009); http://dx.doi.org/10.1063/1.3126522 (8 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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Material properties of highly strained GaInNAs quantum wells grown on GaInAs or quasi-GaInAs substrates are investigated by using microscopic theory together with a band structure calculation based on ten-band k⋅p theory specially formulated for highly strained materials. It is shown that the material gain of GaInNAs quantum wells is reduced by incorporating N into a well layer although the strain in the well layer becomes small. The reduction can be compensated by properly choosing barrier materials. The performance of laser diodes, such as characteristic temperatures T0 and differential gains, is also investigated, and the present results show that very high T0( ≃ 140 K) and differential gain with moderate strain ( ≃ 1.6%) can be achieved by carefully designing quantum well structures, indicating the applicability of these lasers for high-temperature and high-speed operation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Experiments with an 834 m2 ring laser interferometer

R. B. Hurst, G. E. Stedman, K. U. Schreiber, R. J. Thirkettle, R. D. Graham, N. Rabeendran, and J.-P. R. Wells

J. Appl. Phys. 105, 113115 (2009); http://dx.doi.org/10.1063/1.3133245 (10 pages) | Cited 6 times

Online Publication Date: 5 June 2009

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An ultralarge ring He–Ne ring laser gyroscope, UG-2, with area 834 m2 and dimensions 39.7×21 m2, has been built underground at Cashmere Cavern, Christchurch, New Zealand (latitude −43.575°). Earth rotation is sufficient to unlock it, giving a Sagnac frequency of 2.18 kHz. Supermirrors are used with transmission ∼ 0.18 parts per million (ppm) and optical loss unexpectedly high at ∼ 200 ppm per reflection. The cavity Q is 1.5×1012. Residual Sagnac frequency error caused by backscatter coupling is measured as <2 parts in 108. Its best stability is achieved for an averaging time of ∼ 2000 s, for which the Allan Deviation of the Sagnac frequency is 0.08 mHz, or four parts in 108 of Earth rotation rate. The dominant processes generating the residual rotational noise are, for times <10 s, microseismic ground movements, and for times >1000 s, mechanical movement of the mirror assemblies, which act to change the geometrical dimensions and tilt. At all averaging times the residual rotational noise is well above the limit imposed by quantum phase fluctuations. It is concluded from comparisons among many large ring lasers that the excess mirror losses arise from high order aberrations, and UG-2 may be larger than the optimum size.
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42.55.Wd Fiber lasers
07.60.Ly Interferometers

Effect of spin-polarized electrons on terahertz emission from photoexcited GaAs

James M. Schleicher, Shayne M. Harrel, and Charles A. Schmuttenmaer

J. Appl. Phys. 105, 113116 (2009); http://dx.doi.org/10.1063/1.3133093 (7 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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The influence of elliptically and circularly polarized excitation on terahertz emission from unbiased bulk GaAs at normal incidence and room temperature is reported. Illumination of GaAs above the bandgap produces both spin-polarized electrons and shift currents. The induced currents are monitored via terahertz emission spectroscopy. The terahertz emission amplitude is compared to theoretical calculations as a function of excitation beam ellipticity. Exciting slightly above the bandgap (800 nm at room temperature) with elliptical polarization generates shift currents that deviate substantially from theoretical predictions. On the other hand, exciting either below the bandgap (835 nm at 77 K) to produce optical rectification or far above the bandgap (400 nm at room temperature) to produce shift currents generates emission in agreement with theoretical calculations. Spin-polarized electrons created by elliptically polarized excitation are the source of the observed discrepancy.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces

A study of background signals in terahertz apertureless near-field microscopy and their use for scattering-probe imaging

Victoria Astley, Hui Zhan, Rajind Mendis, and Daniel M. Mittleman

J. Appl. Phys. 105, 113117 (2009); http://dx.doi.org/10.1063/1.3141727 (7 pages) | Cited 8 times

Online Publication Date: 8 June 2009

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Apertureless near-field microscopy is an imaging technique in which a small metal tip is held close to a surface, converting evanescent waves to propagating waves and permitting extreme subwavelength spatial resolution. This technique has recently been adapted for use in the terahertz region of the spectrum. Here, the interpretation of the measured signals and the suppression of background scattering can be complicated by the extremely broad bandwidth of the terahertz source and by the coherent (i.e., phase-sensitive) detection of the scattered radiation. We have analyzed the use of tip-sample distance modulation for the removal of background signals. We find that significant background signals, originating from scattering off the probe tip, can be observed even after modulation. These background signals result from path-length difference modulation, and thus are relevant when phase-sensitive detection is used. We use a dipole antenna model to explain the spatial variation in the scattered signal. Since this signal originates from the tip only, it can be used to characterize free-space terahertz wave fronts with subwavelength resolution.
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07.79.Fc Near-field scanning optical microscopes
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Microscopic origins of the induced χ(2) in thermally poled phosphate glasses

P. Thamboon and D. M. Krol

J. Appl. Phys. 105, 113118 (2009); http://dx.doi.org/10.1063/1.3125445 (11 pages) | Cited 1 time

Online Publication Date: 9 June 2009

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We have investigated the microscopic origins of the induced χ(2) in two phosphate glasses: a self-prepared lanthanum phosphate glass with molar composition 0.2La2O3 0.8P2O5 and a commercial sodium alumino phosphate glass (IOG-1, Schott Glass Technologies, Inc.) with molar composition 0.6P2O5 0.24Na2O 0.13Al2O3 0.03Ce2O3. The drastic difference in alkali content in these two phosphate glass systems results in different origins of their induced χ(2). For the poled lanthanum phosphate glass, the origin of the induced χ(2), which is directly proportional to the dc field established inside the glass, is the result of charge migration. A model that uses a single-positive-charge carrier with a nonblocking cathode describes the anodic surface χ(2) of 30 μm thickness. For the poled sodium alumino phosphate glass, two mechanisms—dipole reorientation via the applied field and charge migration—are responsible for the origin of the bulk and the surface χ(2). Dipole reorientation via the applied field is suggested for the bulk contribution, while a charge migration model that involves multiple-charge carriers with nonblocking electrodes is appropriate for the surface χ(2).
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77.22.Ej Polarization and depolarization
42.70.Ce Glasses, quartz

Shadowgraphic studies of triazene assisted laser-induced forward transfer of ceramic thin films

K. S. Kaur, R. Fardel, T. C. May-Smith, M. Nagel, D. P. Banks, C. Grivas, T. Lippert, and R. W. Eason

J. Appl. Phys. 105, 113119 (2009); http://dx.doi.org/10.1063/1.3132822 (8 pages) | Cited 9 times

Online Publication Date: 9 June 2009

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The laser-induced forward transfer process of solid ceramic donor materials (gadolinium gallium oxide and ytterbium doped yttrium aluminium oxide) was studied using triazene polymer as a sacrificial layer by means of a time-resolved nanosecond-shadowgraphy technique. The dependence of the ablation dynamics and quality of the ejected donor material on the laser fluence and thickness of the sacrificial and donor layers were investigated and discussed.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.D- Time resolved spectroscopy (>1 psec)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Manipulating emission of CdTeSe nanocrystals embedded in three-dimensional photonic crystals

Céline Vion, Carlos Barthou, Paul Bénalloul, Catherine Schwob, Laurent Coolen, Alex Gruzintev, Gennadii Emel’chenko, Vladimir Masalov, Jean-Marc Frigerio, and Agnès Maître

J. Appl. Phys. 105, 113120 (2009); http://dx.doi.org/10.1063/1.3129311 (7 pages) | Cited 3 times

Online Publication Date: 10 June 2009

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We report experimental and theoretical results on the photoluminescence of CdTeSe nanocrystals, embedded in a silica opaline structure by infiltration of a highly diluted solution. Strong modification of emission diagrams of embedded nanocrystals have been observed in good agreement with theoretical models. At macroscopic scale, we measured the difference of nanocrystals emission lifetime embedded either in an opal for which the emission is in the gap, or in an opal of smaller balls diameter for which the emission is outside the gap. The photonic bandgap effect leads to a lifetime increase of the order of 10%. These lifetime variations are shown to be in good agreement with the calculated local density of states modification due to the pseudogap.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
42.70.Qs Photonic bandgap materials
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

A generalized equivalent circuit theory for the electric and magnetic resonances of metallic wire networks

Weiyi Zhang and S. T. Chui

J. Appl. Phys. 105, 113121 (2009); http://dx.doi.org/10.1063/1.3143037 (11 pages) | Cited 1 time

Online Publication Date: 10 June 2009

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We generalize Kirchoff’s law for multiply connected wire networks to finite frequencies. We focus on the boundary conditions not present in the conventional Kirchoff’s law at joints when more than three wires come together, which is absent in our previous “circuit theory” for the finite frequency properties of metallic wire networks for singly connected structures. These boundary conditions at the joints involve introducing localized boundary electric fields, in addition to the electric fields of inductive and capacitive origins. The boundary fields act as natural “Lagrange multipliers” for imposing the boundary conditions on the circuit currents. In this way the number of equations is the same as the number of unknowns. The eigenmodes determine not only the circuit current and charge profiles, but also the boundary electric fields which supplement such profiles. The application to T- and H-shape metallic wire networks suggests that the basic types of resonances are mainly controlled by the symmetry and the wire dimensions of the networks. The low frequency modes form along the longest connected paths of the wire network while the high frequency modes can be generated via succeedingly adding more nodes along these various wire paths. The characteristic behavior of the electric and magnetic responses can be inferred from the circuit current profile of a given mode, which offers a simple physical picture on circuit design with particular electromagnetic parameters.
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84.30.Bv Circuit theory
84.32.Hh Inductors and coils; wiring
76.90.+d Other topics in magnetic resonances and relaxations (restricted to new topics in section 76)

Enhanced photoluminescence in [Er2O3/TiO2]m photonic crystals

A. M. Grishin, S. I. Khartsev, and D. O. Dzibrou

J. Appl. Phys. 105, 113122 (2009); http://dx.doi.org/10.1063/1.3143082 (9 pages) | Cited 2 times

Online Publication Date: 11 June 2009

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We survey optical properties of [Er2O3/TiO2]6/Er2O32/[TiO2/Er2O3]6 photonic crystals (PCs) pulsed laser deposited on to the glass substrates. The dispersion relations of refractive indexes and extinction coefficients of the constituent materials were obtained from the comparison of experimental and simulated transmission spectra of single layer Er2O3 and TiO2 reference films. Based on these data several PCs have been designed and grown to match stop band and cavity mode resonance at wavelengths close to the 523 nm Er3+-ion Fraunhofer 4S3/2 absorption line. Precise control of chemical composition and uniform multilayer thickness enable achievement of superior optical performance of sintered PCs. Obtained dispersion relations were combined with the 2×2 transfer matrix formalism to compute PC transmittance that appeared to be in a good agreement with the experimental spectra. Pumping PCs with 514 nm light source we observed a strong photoluminescence (PL) at 1535 nm. In PC specially designed for the resonance wavelength λres = 514 nm, C-band PL intensity experiences fivefold enhancement compared to a single layer Er2O3 film of equivalent thickness.
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78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials
82.80.-d Chemical analysis and related physical methods of analysis
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

The effects of oxygen concentration and light intensity on the photostability of zwitterionic chromophores

S. G. Raymond, G. V. M. Williams, B. Lochocki, M. D. H. Bhuiyan, A. J. Kay, and J. W. Quilty

J. Appl. Phys. 105, 113123 (2009); http://dx.doi.org/10.1063/1.3143865 (7 pages) | Cited 2 times

Online Publication Date: 11 June 2009

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Photostability measurements at different oxygen partial pressures and light intensities have been made on host-guest films containing amorphous polycarbonate and an organic chromophore with a high second order nonlinear optical figure of merit. We find that the photodegradation quantum efficiency dramatically increases with increasing oxygen partial pressure. At very low oxygen partial pressures (8×10−6 bar) the average number of photons required to photodegrade a chromophore is as high as 2×108 at 655 nm. The photodegradation quantum efficiency in air is observed to decrease with increasing optical intensity. We show that this is due to a reduced oxygen content in the film caused by chromophore photodegradation rather than ground state bleaching. There is an anomalous increase and then decrease in the photoluminescence intensity that cannot easily be explained.
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82.50.-m Photochemistry
78.55.Kz Solid organic materials
78.66.Nk Insulators
42.65.-k Nonlinear optics
42.70.Jk Polymers and organics

Directional light emission through a metallic nanostructure

Yongliang Zhang, Deyin Zhao, Chuanhong Zhou, and Xunya Jiang

J. Appl. Phys. 105, 113124 (2009); http://dx.doi.org/10.1063/1.3139295 (6 pages) | Cited 7 times

Online Publication Date: 15 June 2009

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In this paper, we numerically investigate the highly directional beaming effect when a transverse magnetic plane wave passes through a metallic slit-bumps nanostructure by using the finite difference time domain method. We find that the narrow bump with width w ∼ 0.1λspp can serve as a good light emitter and two arrays of narrow bumps with suitable separation can diffract the surface plasmons into highly directional collimated beams. The number and the direction of the beams can be controlled by adjusting the geometry parameters of the nanostructure. The structure with optimized parameters has practical applications as directional surface plasmon polaritons couplers in integrated photonic devices.
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81.07.Bc Nanocrystalline materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Ag Apertures, collimators
42.79.Gn Optical waveguides and couplers
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Tungsten and barium transport in the internal plasma of hollow cathodes

James E. Polk, Ioannis G. Mikellides, Ira Katz, and Angela M. Capece

J. Appl. Phys. 105, 113301 (2009); http://dx.doi.org/10.1063/1.3111970 (13 pages) | Cited 1 time

Online Publication Date: 1 June 2009

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The effect of tungsten erosion, transport, and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from 8200 h and 30 352 h ion engine wear tests. Erosion and subsequent redeposition of tungsten in the electron emission zone at the downstream end of the insert reduce the porosity of the tungsten matrix, preventing the flow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushed back to the emitter surface by the electric field and drag from the xenon ion flow. This barium ion flux is sufficient to maintain a barium surface coverage at the downstream end greater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length, so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollow cathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.
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82.45.Fk Electrodes
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
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