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15 Jul 2006

Volume 100, Issue 2, Articles (02xxxx)

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Comparison of quantum well intermixing in GaAs structures using a low temperature grown epitaxial layer or a SiO2 cap

A. S. W. Lee, O. Hulko, D. A. Thompson, B. J. Robinson, and J. G. Simmons

J. Appl. Phys. 100, 023101 (2006); http://dx.doi.org/10.1063/1.2214360 (5 pages) | Cited 4 times

Online Publication Date: 17 July 2006

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Studies of quantum well intermixing (QWI) have been performed on Al-free GaAs based structures in which InGaAs quantum wells (QWs) have either GaAs barriers or InGaAsP quaternary barriers such that the barrier-QW compositional change consists solely of a group III change (GaAs barrier) or a group V change (quaternary barrier). These structures permit identification of the sublattice upon which intermixing occurs when the point defects responsible for the QWI are created by annealing in the presence of a (conventional) dielectric (SiO2) cap layer versus an InGaP cap layer grown at low temperature (LT-InGaP). QWI occurs on the group III sublattice via vacancy diffusion in both the LT-InGaP and SiO2 capped samples with identical group V compositions in the QW and barrier layers. For the samples with identical group III compositions for the QW and barriers, QWI is only observed with the LT-InGaP capping and occurs via group V interstitial diffusion and P–As exchange in the QW.
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68.65.Fg Quantum wells
61.72.J- Point defects and defect clusters
66.30.Lw Diffusion of other defects
61.72.Cc Kinetics of defect formation and annealing
77.55.-g Dielectric thin films

Optical properties and electric field enhancement in cholesteric liquid crystal containing different periodicities

Ryotaro Ozaki, Yuko Matsuhisa, Hiroyuki Yoshida, Katsumi Yoshino, and Masanori Ozaki

J. Appl. Phys. 100, 023102 (2006); http://dx.doi.org/10.1063/1.2215124 (4 pages) | Cited 5 times

Online Publication Date: 17 July 2006

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We study a defect mode in a one-dimensional photonic band gap of a cholesteric liquid crystal (CLC) consisting of two helicoidal periodicities. The optical properties of this CLC are analyzed using 4×4 transfer matrix and finite difference time domain (FDTD) methods. In calculated transmission spectra of this CLC, one of the defect modes always appears at the band edge wavelength of the inner CLC having a different helix to that of two sides of CLCs. Furthermore, the electric field analysis of this CLC has also been demonstrated by the FDTD method. At the defect mode wavelength, the electric field enhancement is found to be significant larger than a normal CLC.
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42.70.Df Liquid crystals
42.70.Qs Photonic bandgap materials
61.30.-v Liquid crystals

The ultrafast excitation processes in femtosecond laser-induced damage in dielectric omnidirectional reflectors

T. Q. Jia, H. Y. Sun, X. X. Li, D. H. Feng, C. B. Li, S. Z. Xu, R. X. Li, Z. Z. Xu, and H. Kuroda

J. Appl. Phys. 100, 023103 (2006); http://dx.doi.org/10.1063/1.2215217 (9 pages) | Cited 8 times

Online Publication Date: 17 July 2006

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A pump and probe system is developed, where the probe pulse duration τ is less than 60 fs while the pump pulse is stretched up to 150–670 fs. The time-resolved excitation processes and damage mechanisms in the omnidirectional reflectors SiO2/TiO2 and ZnS/MgF2 are studied. It is found that as the pump pulse energy is higher than the threshold value, the reflectivity of the probe pulse decreases rapidly during the former half, rather than around the peak of the pump pulse. A coupled dynamic model based on the avalanche ionization (AI) theory is used to study the excitation processes in the sample and its inverse influences on the pump pulse. The results indicate that as pulse duration is longer than 150 fs, photoionization (PI) and AI both play important roles in the generation of conduction band electrons (CBEs); the CBE density generated via AI is higher than that via PI by a factor of 102–104. The theory explains well the experimental results about the ultrafast excitation processes and the threshold fluences.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.79.Bh Lenses, prisms and mirrors

Free-carrier absorption and active layer heating in large optical cavity high-power diode lasers

B. S. Ryvkin and E. A. Avrutin

J. Appl. Phys. 100, 023104 (2006); http://dx.doi.org/10.1063/1.2212147 (8 pages) | Cited 4 times

Online Publication Date: 18 July 2006

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An analytical theory is developed for the thermal properties of a large optical cavity semiconductor laser high above threshold. The performance of symmetric and asymmetric waveguide structures is analyzed and compared. Narrow asymmetric waveguides are predicted to be advantageous from the thermal point of view.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Electromagnetism theory of waveguide array electro-optical scanner: Model and characteristics of optical field distribution in the waveguide array

Jiali Li, Shunxiang Shi, Jifang Liu, Yanling Sun, Hongzhou Dong, and Huawei Liang

J. Appl. Phys. 100, 023105 (2006); http://dx.doi.org/10.1063/1.2219152 (6 pages)

Online Publication Date: 19 July 2006

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Waveguide array electro-optical scanner (WAEOS) technology is presented. Based on the theory of the dielectric slab optical waveguide and the coupled wave equations of infinite waveguide array given by Yariv and Yeh [Optical Waves in Crystals (Wiley, New York, 1983)] , the coupled wave equations are modified for adapting the finite waveguide array of the WAEOS. A model of the optical field distribution in the waveguide array is derived, which determines the output field of the WAEOS. Some characteristics of the optical field distribution with uniform incidence and single waveguide incidence are given.
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42.79.Gn Optical waveguides and couplers
42.79.Ls Scanners, image intensifiers, and image converters

Photochromism and polaronic photocharge localization in diluted KTa1−xNbxO3

A. I. Gubaev, S. E. Kapphan, L. Jastrabik, V. A. Trepakov, and P. P. Syrnikov

J. Appl. Phys. 100, 023106 (2006); http://dx.doi.org/10.1063/1.2214302 (5 pages) | Cited 3 times

Online Publication Date: 19 July 2006

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Ultraviolet (UV)-light-induced optical absorption in the near infrared (NIR) region was observed in diluted KTa1−xNbxO3 single crystals (x = 0,0.004,0.007,0.012,0.07) at low temperatures. Illumination by wideband light (3.10–4.13 eV, 300–400 nm) is accompanied by the appearance of a broad NIR absorption band with the position of the maxima varying in the 0.69–0.8 eV (1.54–1.79μ, T = 1.3 K) region for different Nb concentrations. This UV-light-induced absorption is absent in nominally pure KTaO3, as well as in all Nb diluted specimens at elevated temperatures. The centers responsible for the photochromic NIR absorption bands are tied to interband optical transitions of pair Nb4+ electronic polarons. The photochromic experimental data, supplemented by luminescence studies in the visible range, evidence the strong localization of the photocharge carriers by pair Nb4+ polarons at low temperatures. It is suggested that namely the strong localization of the photocarriers plays a crucial role in photoinduced gigantic dielectric effects and possible phase transitions, which have been recognized recently in incipient ferroelectrics at low temperatures.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.38.-k Polarons and electron-phonon interactions
72.40.+w Photoconduction and photovoltaic effects
78.20.-e Optical properties of bulk materials and thin films
77.80.B- Phase transitions and Curie point
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Raman characteristics and nonlinear optical properties of tellurite and phosphotellurite glasses containing heavy metal oxides with ultrabroad Raman bands

G. Senthil Murugan, Takenobu Suzuki, and Yasutake Ohishi

J. Appl. Phys. 100, 023107 (2006); http://dx.doi.org/10.1063/1.2215218 (6 pages) | Cited 7 times

Online Publication Date: 19 July 2006

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A family of glasses suitable for ultrabroadband Raman amplifications was designed and fabricated. In addition to the bandwidth the gain characteristics of these glasses are expected to be much higher than those of the silica based materials. The thermal stabilities of these glasses in view of fiber fabrication were discussed. The various structural units which contribute to the overall Raman band were unraveled. Accordingly the various bands were tailored in such a way to get a wide continuous Raman band. The nonlinear optical properties which are vital for optical switching and other nonlinear processes were studied via third-harmonic generation measurements.
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42.70.Ce Glasses, quartz
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
78.35.+c Brillouin and Rayleigh scattering; other light scattering
42.15.Eq Optical system design

Nonlinear spectroscopy of PbS quantum-dot-doped glasses as saturable absorbers for the mode locking of solid-state lasers

A. M. Malyarevich, M. S. Gaponenko, K. V. Yumashev, A. A. Lagatsky, W. Sibbett, A. A. Zhilin, and A. A. Lipovskii

J. Appl. Phys. 100, 023108 (2006); http://dx.doi.org/10.1063/1.2215353 (5 pages) | Cited 5 times

Online Publication Date: 19 July 2006

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The bleaching relaxation characteristics of PbS quantum dots with diameters in the range of 3.8–4.3 nm synthesized in silicate and phosphate glasses have been studied under the conditions of femtosecond excitation. It has been observed that increase of pump fluence from 0.1 to 2.2 mJ/cm2 leads to the appearance of a second (slow) component in the bleaching relaxation kinetics and to the shortening of both the fast (from several tens of picoseconds to several picoseconds) and slow relaxation times. An absorption saturation fluence of ≈ 15 μJ/cm2 with a nonsaturable absorption coefficient of 2.5–3 cm−1 at 1.05 μm has been evaluated for the PbS quantum-dot-doped glasses studied. The nature of the nonsaturable absorption and the mechanism of the bleaching relaxation in PbS quantum dots have been discussed.
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78.30.Hv Other nonmetallic inorganics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Ce Glasses, quartz
42.60.Fc Modulation, tuning, and mode locking
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Exciton fine structure and biexciton binding energy in single self-assembled InAs/AlAs quantum dots

D. Sarkar, H. P. van der Meulen, J. M. Calleja, J. M. Becker, R. J. Haug, and K. Pierz

J. Appl. Phys. 100, 023109 (2006); http://dx.doi.org/10.1063/1.2209089 (4 pages) | Cited 6 times

Online Publication Date: 20 July 2006

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The exciton and biexciton emissions of a series of single quantum dots of InAs in an AlAs matrix have been studied. These emissions consist of linear cross polarized doublets showing large values of both the biexciton binding energy and the fine-structure splitting. At increasing exciton emission energy, corresponding to decreasing dot size, the biexciton binding energy of 9 meV decreases down to zero, reflecting a possible crossover to an antibinding regime. Simultaneously the fine-structure splitting diminishes from a value of 0.3 meV down to zero, at the same energy, suggesting a common origin for the two effects.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

Lasing mechanisms in organic photonic crystal lasers with two-dimensional distributed feedback

K. Forberich, A. Gombert, S. Pereira, J. Crewett, U. Lemmer, M. Diem, and K. Busch

J. Appl. Phys. 100, 023110 (2006); http://dx.doi.org/10.1063/1.2210589 (6 pages) | Cited 3 times

Online Publication Date: 21 July 2006

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We present a detailed experimental and theoretical investigation of the lasing characteristics of organic photonic crystal lasers. These lasers are based on strongly modulated two-dimensional polymer surface relief structures on which thin films of optically active organic materials have been deposited. We determine the in-plane photonic band structure of the corresponding quasiguided modes within an effective two-dimensional model. In addition, we calculate the total (three-dimensional) losses associated with these modes. This allows us to identify the lasing thresholds for square lattice geometries and to understand the emission pattern.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Qs Photonic bandgap materials
42.60.By Design of specific laser systems
42.70.Jk Polymers and organics

Thermal influence on passing of polarized light through the SnO2:In2O3 layers

N. A. Davidenko, V. A. Pavlov, N. G. Chuprina, I. I. Davidenko, and L. Baath

J. Appl. Phys. 100, 023111 (2006); http://dx.doi.org/10.1063/1.2210591 (3 pages) | Cited 2 times

Online Publication Date: 24 July 2006

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Thermal dependent changes of light depolarization degree were observed in the SnO2:In2O3 (ITO) layers deposited onto the flat glass substrates which are used usually as electrodes for optoelectronic devices. The observed effect is reversible. It can be attributed to the changes of nanostructure geometry in the bulk of the ITO layer as well as on its surface. Such geometric changes involve dispersion of polarized light. The investigated effect should be taken into consideration when developing optoelectronic devices because it can provoke distortion of the optical information field.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Using a quantum well heterostructure to study the longitudinal and transverse electric field components of a strongly focused laser beam

G. Kihara Rurimo, M. Schardt, S. Quabis, S. Malzer, Ch. Dotzler, A. Winkler, G. Leuchs, G. H. Döhler, D. Driscoll, M. Hanson, A. C. Gossard, and S. F. Pereira

J. Appl. Phys. 100, 023112 (2006); http://dx.doi.org/10.1063/1.2214207 (6 pages) | Cited 5 times

Online Publication Date: 25 July 2006

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We report a method to measure the electric energy density of longitudinal and transverse electric field components of strongly focused polarized laser beams. We used a quantum well photodetector and exploited the polarization dependent optical transitions of light holes and heavy holes to probe the electric field distribution in the focal region. A comparison of the measured photocurrent spectra for radially and azimuthally polarized beams at the light and heavy hole absorption peaks provides a measure of the amount of the longitudinal electric field component.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Lasing features in scattering gain media and amplified spontaneous emission systems

M. A. F. de Souza, A. Lencina, and P. Vaveliuk

J. Appl. Phys. 100, 023113 (2006); http://dx.doi.org/10.1063/1.2218030 (7 pages) | Cited 3 times

Online Publication Date: 25 July 2006

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An experimental study was made on lasing features in both scattering gain media and amplified spontaneous emission systems from a rhodamine-6G xanthene dye in ethanol solution. The emission intensity, spectral line-half-width, and lasing threshold are investigated in terms of dye concentration, cell thickness, and pump energy. The analysis shows that both systems behave quite different. It was found that the scattering gain media present best lasing properties which are enhanced to smaller cell thickness where the backscattering effect plays a significant role. In addition, its laserlike characteristics were found slightly dependent on dye concentration within the range in which the dimer species influence is absent. In return, the amplified spontaneous emission systems were observed strongly dependent on the product of cell thickness and dye concentration, namely, optical density. These systems present lasing properties only around an optimized value of optical density. Within this range, their emission intensity, spectral line-half-width, and threshold could overcome those obtained from scattering gain media.
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42.55.Mv Dye lasers

Experimental evaluation of curved polymer waveguides with air trenches and offsets

Brie Howley, Xiaolong Wang, Ray T. Chen, and Yihong Chen

J. Appl. Phys. 100, 023114 (2006); http://dx.doi.org/10.1063/1.2218038 (6 pages) | Cited 5 times

Online Publication Date: 25 July 2006

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Excess waveguide bend loss can be minimized through the use of offsets and air trenches. Offsets, used for reducing the junction loss between straight and curved waveguides, and air trenches, which prevent bend radiation loss, were simulated by a three-dimensional, semivectorial beam propagation method. Low loss polymer waveguide bend structures, employing both offsets and trenches, were fabricated. A reduction of the 180° bend insertion loss from 17.7 to 3.0 dB with a bending radius (BR) of 1.5 mm is experimentally confirmed at λ = 1.55 μm. BR ranging from 5 to 0.5 mm are evaluated with decent match when compared with simulation results. The polarization dependent loss is BR dependent with a maximum value of 0.4 dB when the BR is reduced to 0.5 mm. The experimental results confirm that the joint use of air trenches and junction offsets is effective in reducing the bend radii of low index contrast polymer waveguides in planar lightwave circuits.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Er coordination in Y2O3 thin films studied by extended x-ray absorption fine structure

Trinh Tu Van, John R. Bargar, and Jane P. Chang

J. Appl. Phys. 100, 023115 (2006); http://dx.doi.org/10.1063/1.2214299 (8 pages) | Cited 8 times

Online Publication Date: 25 July 2006

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Extended x-ray absorption fine structure (EXAFS) spectroscopy was employed to study the Er coordination in polycrystalline Y2O3 thin films, which was found to dictate their photoluminescence (PL) properties. Incorporation of Er with concentrations varying from 6 to 14 at. % was achieved by radical-enhanced atomic layer deposition at 350 °C. In all samples, Er was found to be in the optically active trivalent state, confirmed by their x-ray absorption near-edge spectroscopy spectra. Modeling of the EXAFS data revealed that the local structure of Er3+ is similar to that of Er3+ in Er2O3. Specifically, Er3+ is coordinated with six O at 2.24 and 2.32 Å. Excellent fits to the EXAFS for samples with Er3+ concentration less than 8 at. % were achieved when the second coordination shell was modeled as a mixture of Y3+ and Er3+, indicating a complete miscibility of Er3+ in the Y2O3 matrix under these experimental conditions. This behavior is attributed to the almost perfect ionic size match between Y3+ and Er3+, having identical valence state and coordination characteristics. For thin films with higher Er concentrations, the EXAFS analysis revealed an exsolution with Er2O3 domain. Since there is no indication of Er clustering, it is concluded that the PL quenching observed in samples with the Er doping level exceeding 8 at. % is likely due to Er ion-ion interaction but not Er immiscibility in Y2O3. Specifically, an increase in the Er3+ concentration implied an increase in the average number of Er3+ in the second coordination shell, thus making ion-ion interaction possible. The critical interionic distance between two Er3+ was determined to be ∼ 4 Å, thus setting an upper limit on the Er3+ concentration in Y2O3 at ∼ 6×1021 cm−3, at least three orders of magnitude higher than the Er3+ solubility limit in the conventional SiO2 host (<1018 cm−3).
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78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
78.66.Nk Insulators
61.72.S- Impurities in crystals
64.75.-g Phase equilibria

Plasma modeling for ultrashort pulse laser ablation of dielectrics

L. Jiang and H. L. Tsai

J. Appl. Phys. 100, 023116 (2006); http://dx.doi.org/10.1063/1.2216882 (7 pages) | Cited 13 times

Online Publication Date: 26 July 2006

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In ultrashort pulse (<10 ps) laser ablation of dielectrics, affected materials are first transformed into absorbing plasma with metallic properties and, then, the subsequent laser-plasma interaction causes material removals. For ultrashort-pulse laser ablation of dielectrics, this study proposes a model using the Fokker-Planck equation for electron density distribution, a plasma model for the optical properties of ionized dielectrics, and quantum treatments for electron heating and relaxation time. The free electron density distribution of the plasma within the pulse duration is then used to determine the ablation crater shape. The predicted threshold fluences and ablation depths for barium aluminum borosilicate and fused silica are in agreement with published experimental data. It is found that the significantly varying optical properties in time and space are the key factors determining the ablation crater shape. The effects of fluence and pulse duration are also studied.
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52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.Ff Fokker-Planck and Vlasov equation
52.25.-b Plasma properties

Mixing effects in postdischarge modeling of electric discharge oxygen-iodine laser experiments

Andrew D. Palla, David L. Carroll, Joseph T. Verdeyen, and Wayne C. Solomon

J. Appl. Phys. 100, 023117 (2006); http://dx.doi.org/10.1063/1.2215355 (11 pages) | Cited 6 times

Online Publication Date: 26 July 2006

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In an electric discharge oxygen-iodine laser, laser action at 1315 nm on the I(math)→I(math) transition of atomic iodine is obtained by a near resonant energy transfer from O2(a math) which is produced using a low-pressure electric discharge. The discharge production of atomic oxygen, ozone, and other excited species adds higher levels of complexity to the postdischarge kinetics which are not encountered in a classic purely chemical O2(a math) generation system. Mixing effects are also present. In this paper we present postdischarge modeling results obtained using a modified version of the BLAZE-II gas laser code. A 28 species, 105 reaction chemical kinetic reaction set for the postdischarge kinetics is presented. Calculations were performed to ascertain the impact of a two stream mixing mechanism on the numerical model and to study gain as a function of reactant mass flow rates. The calculations were compared with experimental data. Agreement with experimental data was improved with the addition of new kinetics and the mixing mechanism.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
52.80.-s Electric discharges

Ultraviolet pulse laser induced modifications of native silicon/silica interfaces analyzed by optical second harmonic generation

T. Scheidt, E. G. Rohwer, H. M. von Bergmann, and H. Stafast

J. Appl. Phys. 100, 023118 (2006); http://dx.doi.org/10.1063/1.2216873 (6 pages)

Online Publication Date: 27 July 2006

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Native silicon/silica (Si/SiO2) interfaces are investigated by electric field induced second harmonic (EFISH) generation employing near infrared femtosecond laser pulses (782.8 nm, 80 fs, 10 nJ, 80 MHz repetition rate). Here, the temporal EFISH evolution induced by the femtosecond laser irradiation is recorded with a time resolution of 0.2 s. Comparative EFISH studies are performed with Si/SiO2 interfaces, preexposed to ultraviolet (UV) laser pulses (308 nm, 16 ns, 0.45–2.8 J/cm2) as well as virgin Si/SiO2. After UV irradiation the femtosecond laser induced electron injection and trapping in the ultrathin oxide is found to be drastically accelerated in contrast to the essentially unaffected interfacial hole dynamics. This result is explained by an enhanced interfacial electron trap density caused in most cases by the UV laser induced melting and recrystallization of the near-interface silicon. Furthermore, three-dimensional second harmonic imaging reveals a saturation effect of the UV induced sample modification due to the melting of the near-interface silicon, for which a threshold fluence of 0.47 J/cm2 is extracted for xenon chloride (XeCl) laser irradiation. Below this threshold an accumulative behavior of the UV induced modification is observed for repeated exposure to several UV laser pulses. This is pointing to a dose dependent modification process presumably due to thermally driven interface chemistry and/or microscopic structural and electronic changes of the Si/SiO2 interface.
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78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Transmission properties of perturbed optical Cantor multilayers

Francesco Chiadini, Antonio Scaglione, and Vincenzo Fiumara

J. Appl. Phys. 100, 023119 (2006); http://dx.doi.org/10.1063/1.2216878 (5 pages) | Cited 3 times

Online Publication Date: 27 July 2006

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Fractal multilayers of two distinct dielectric materials are structures exhibiting stop bands and transmission peaks in their electromagnetic response. In this work we analyze how the transmission spectrum of a Cantor fractal multilayer changes when a defect, consisting of a dielectric layer different from those constituting the multilayer, is inserted midway through its thickness. Unlike a periodic multilayer structure, no transmission peaks (defect modes) appear in the stop band by inserting a defect in a Cantor multilayer. We show that a defect in the fractal structure results in a frequency shift of its transmission spectrum and in a change of the width of both stop bands and transmission peaks. The extent of such spectrum modifications depends on either the thickness and the refractive index of the defect layer. By suitably modulating these parameters a tunable narrow band filter can be realized to cover a desired range of frequency. This feature may hold attraction for certain applications such as dense wavelength division multiplexing systems and sensors.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
42.70.-a Optical materials

Broadband quasi-phase-matched second-harmonic generation in a nonlinear photonic crystal

Isao Tomita, Masaki Asobe, Hiroyuki Suzuki, Junji Yumoto, and Yuzo Yoshikuni

J. Appl. Phys. 100, 023120 (2006); http://dx.doi.org/10.1063/1.2213150 (8 pages) | Cited 3 times

Online Publication Date: 27 July 2006

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We analyze the properties of quasi-phase-matched second-harmonic generation (SHG) from a defect waveguide in photonic-crystal (PhC) slabs embedded in a periodically χ(2) inverted material with a collinear beam configuration. We show that by controlling the material dispersion with the structural dispersion of a defect waveguide in PhC slabs of infinite height, it is possible to realize a much wider frequency range for quasi-phase-matched SHG than without the PhC structure. Also, taking the fabrication of actual devices into consideration, we examine the case for PhC slabs of finite height and show that, although guided modes are index confined in the vertical direction (while they are confined by the PhC structure in the horizontal direction), the effect that the PhC structure has on the broadening of the frequency range remains and that the broadened range can be comparable to that for the PhC slabs of infinite height if appropriate structural parameters are taken.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Comparison between four-level model and six-temperature model on the description of a simple mechanical Q-switched CO2 laser

Tie-Jun Wang, Qiong-Yi He, Jin-Yue Gao, Han Sun, Zhi-Hui Kang, Yun Jiang, and Ying-Fei Zhang

J. Appl. Phys. 100, 023121 (2006); http://dx.doi.org/10.1063/1.2218271 (6 pages)

Online Publication Date: 28 July 2006

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We investigate both the four-level model and the six-temperature model to describe the dynamical processes of a simple mechanical Q-switched CO2 laser that is realized by a fast chopper. The Q-switched process and the effect of the dynamic parameters on the output intensity of the Q-switched CO2 laser are reported using the two models. Theoretical comparisons between the two models on the effect of dynamical parameters, and the experimental results are presented. Both the models are well consistent with the experimental one for the main output laser pulse.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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Simulation of a direct current microplasma discharge in helium at atmospheric pressure

Qiang Wang, Demetre J. Economou, and Vincent M. Donnelly

J. Appl. Phys. 100, 023301 (2006); http://dx.doi.org/10.1063/1.2214591 (10 pages) | Cited 43 times

Online Publication Date: 20 July 2006

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A numerical simulation of a dc microplasma discharge in helium at atmospheric pressure was performed based on a one-dimensional fluid model. The microdischarge was found to resemble a macroscopic low pressure dc glow discharge in many respects. The simulation predicted the existence of electric field reversals in the negative glow under operating conditions that favor a high electron diffusion flux emanating from the cathode sheath. The electric field adjusts to satisfy continuity of the total current. Also, the electric field in the anode layer is self adjusted to be positive or negative to satisfy the “global” particle balance in the plasma. Gas heating was found to play an important role in shaping the electric field profiles both in the negative glow and the anode layer. Basic plasma properties such as electron temperature, electron density, gas temperature, and electric field were studied. Simulation results were in good agreement with experimental observations.
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52.80.Hc Glow; corona
52.50.Dg Plasma sources
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs

Computational modeling of process induced damage during plasma clean

S. Rauf, A. Haggag, M. Moosa, and P. L. G. Ventzek

J. Appl. Phys. 100, 023302 (2006); http://dx.doi.org/10.1063/1.2216253 (9 pages) | Cited 6 times

Online Publication Date: 20 July 2006

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When partially completed circuits come in contact with plasmas during integrated circuit fabrication, current from the plasma can potentially damage active devices on the wafer. A suite of computational models is used in this article to investigate damage to ultrathin (1.0–5.5 nm) transistor gate dielectric (SiO2) during Ar/O2 based plasma cleaning in a capacitively coupled plasma reactor. This modeling infrastructure includes a two-dimensional plasma equipment model for relating process control parameters to ion and electron currents, a three-dimensional model for flux density calculation within a circular via, an electrostatic model for computing potential across the gate dielectric, and a percolation model to investigate dielectric damage characteristics. Computational results show that when the plasma current comes in contact with the gate dielectric, the gate dielectric rapidly charges up and the potential difference across the dielectric saturates at the level necessary to support the plasma induced current. The steady-state voltage across the dielectric determines the propensity of irreversible damage that can occur under this electrical stress. Gate dielectric damage was found to be most sensitively linked to dielectric thickness. As thin dielectrics (<2.0 nm) are leaky, direct tunneling current flow ensures that the potential drop across the gate dielectric remains small. As a consequence, the dielectric is able to withstand the plasma current and the probability of damage is small. However, for thicker dielectrics where Fowler-Nordheim tunneling is dominant, a large voltage builds up across the gate dielectric due to the plasma induced current. The probability of thicker dielectrics getting damaged during the plasma process is therefore high. For given plasma conditions and gate dielectric thickness, current collection area (i.e., antenna size) determines the voltage buildup across the gate dielectric. Damage probability increases with the size of the antenna connected to the transistor gate electrode. Via aspect ratio and plasma process condition variations (around a given set of process conditions) have a relatively smaller effect on plasma induced device damage.
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85.30.De Semiconductor-device characterization, design, and modeling
52.77.Bn Etching and cleaning
85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.30.Tv Field effect devices

Nonlinear transformation of electromagnetic wave in time-varying plasma medium: Longitudinal propagation

Zoran M. Trifkovic and Bozidar V. Stanic

J. Appl. Phys. 100, 023303 (2006); http://dx.doi.org/10.1063/1.2218035 (6 pages) | Cited 4 times

Online Publication Date: 24 July 2006

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The nonlinear transformation of a linearly polarized source plane electromagnetic wave, propagating along an external static magnetic field in free space for t<0, due to the sudden creation of homogeneous plasma at t = 0 and sudden switching off the external magnetic field after an elapsed time interval τ, is studied. This transformation has been analyzed by using the second order perturbation theory in radio approximation. For t>τ, the stationary (rectification and space-varying) modes, the electron and electromagnetic plasma oscillations and traveling electron and electromagnetic plasma waves have been created. Among the large variety of nonlinear longitudinal electric modes the appearance of rectification mode was observed. The efficiency of excitation of the longitudinal electric rectification mode has been studied for different values of source wave angular frequency, electron cyclotron angular frequency, and duration time τ of external static magnetic field.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

A two-dimensional hybrid model of the Hall thruster discharge

F. I. Parra, E. Ahedo, J. M. Fife, and M. Martínez-Sánchez

J. Appl. Phys. 100, 023304 (2006); http://dx.doi.org/10.1063/1.2219165 (11 pages) | Cited 20 times

Online Publication Date: 26 July 2006

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Particle-in-cell methods are used for ions and neutrals. Probabilistic methods are implemented for ionization, charge-exchange collisions, gas injection, and particle-wall interaction. A diffusive macroscopic model is proposed for the strongly magnetized electron population. Cross-field electron transport includes wall collisionality and Bohm-type diffusion, the last one dominating in most of the discharge. Plasma quasineutrality applies except for space-charge sheaths, which are modeled taking into consideration secondary-electron-emission and space-charge saturation. Specific weighting algorithms are developed in order to fulfil the Bohm condition on the ion flow at the boundaries of the quasineutral domain. The consequence is the full development of the radial plasma structure and correct values for ion losses at lateral walls. The model gains in insight and physical consistency over a previous version, but thrust efficiency is lower than in experiments, indicating that further model refinement of some phenomena is necessary.
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52.75.Di Ion and plasma propulsion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Rr Particle-in-cell method
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
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