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1 Dec 2006

Volume 100, Issue 11, Articles (11xxxx)

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Space charge field and dynamics of the grating formation in a photorefractive polymer-dispersed liquid crystal based on a photoconducting polysiloxane

Lutz Paelke and Heinz-S. Kitzerow

J. Appl. Phys. 100, 113101 (2006); http://dx.doi.org/10.1063/1.2372434 (4 pages) | Cited 1 time

Online Publication Date: 1 December 2006

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A photorefractive system composed of liquid crystal droplets dispersed in a photoconducting polymer is characterized by means of two-beam coupling. The amplitudes and phases of the spatial variations of the refractive index and the absorption coefficient are measured using the moving grating technique. Dynamic measurements indicate that the phase of the refractive index modulation is nearly constant while the amplitude increases gradually. The maximum value of the internal space charge field can be estimated from the amplitude of the phase grating and is found to be of the order of one-hundredth of the external bias field.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Df Liquid crystals
42.70.Gi Light-sensitive materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Dj Gratings
72.40.+w Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Highly sensitive and ultrafast light modulation with a vanadyloxophthalocyanine-doped composite polymer guided wave mode device

Ryuji Matsumoto and Toshihiko Nagamura

J. Appl. Phys. 100, 113102 (2006); http://dx.doi.org/10.1063/1.2397291 (6 pages) | Cited 5 times

Online Publication Date: 4 December 2006

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We propose a guided wave mode (GWM) device with prism coupling, which is composed of a low-refractive-index polymer layer and a vanadyloxophthalocyanine-doped polymer layer. Reflectance dips due to the GWM were observed at specific incident angles depending on the wavelength and the thickness of each layer. The reflectance at the GWM can be controlled by the real part (n) and/or the imaginary part (k) of the complex refractive index of the waveguide layer. The k dependence of reflectance showing a minimum of almost zero at a certain value defined as kc was confirmed in the visible to near infrared region. The kc value varies linearly with the intensity of the evanescent wave. Highly sensitive and ultrafast control of reflection in the GWM geometry was demonstrated by the photoinduced complex refractive-index change upon femtosecond laser excitation of vanadyloxophthalocyanine.
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42.79.Hp Optical processors, correlators, and modulators
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Gn Optical waveguides and couplers

Energy transfer processes and heat generation in Yb3+-doped phosphate glasses

C. Jacinto, S. L. Oliveira, L. A. O. Nunes, T. Catunda, and M. J. V. Bell

J. Appl. Phys. 100, 113103 (2006); http://dx.doi.org/10.1063/1.2372409 (6 pages) | Cited 2 times

Online Publication Date: 5 December 2006

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In this work we present a study of energy transfer processes in Yb3+-doped phosphate glasses with different OH− contents and Yb3+ concentrations. Fluorescence and thermal lens (TL) techniques were used in order to analyze the Yb3+–OH− and Yb3+-other impurity interactions. The role of OH− groups is also presented and discussed. The results show that in the low concentration region up to ∼ 3×1020 Yb ions/cm3, the interaction between Yb3+ and OH radicals is the dominant process reducing the lifetime, increasing the TL dioptric power, and then endangering the performance of the system. For the high Yb3+ concentration limit, the Yb3+-other impurity interaction, which is favored by energy migration, is comparable to the Yb3+–OH− energy transfer, even for high OH− concentration. The nonradiative decay rate due to hydroxyl groups follows Förster-Dexter theory [ Ann. Phys. 2, 55 (1948); J. Chem. Phys. 21, 836 (1953) ] except at low Yb3+ concentration, being more active at low OH− levels, where quenching rate is probably due to several impurities.
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78.66.Jg Amorphous semiconductors; glasses
66.30.J- Diffusion of impurities

Two-state switching and dynamics in quantum dot two-section lasers

A. Markus, M. Rossetti, V. Calligari, D. Chek-Al-Kar, J. X. Chen, A. Fiore, and R. Scollo

J. Appl. Phys. 100, 113104 (2006); http://dx.doi.org/10.1063/1.2397293 (5 pages) | Cited 18 times

Online Publication Date: 5 December 2006

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The electrical control of the lasing wavelength in two-section quantum dot lasers is investigated. By changing the optical loss in the absorber section, the control of the ground-state (GS) and excited-state (ES) lasing thresholds and output powers is achieved. Additionally, a complex self-pulsation dynamics with simultaneous oscillations of the GS and ES intensities is observed. The experimental results are well explained in the framework of a rate equation model.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.55.Px Semiconductor lasers; laser diodes
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Electroluminescence efficiency of blue InGaN/GaN quantum-well diodes with and without an n‐InGaN electron reservoir layer

N. Otsuji, K. Fujiwara, and J. K. Sheu

J. Appl. Phys. 100, 113105 (2006); http://dx.doi.org/10.1063/1.2398690 (7 pages) | Cited 7 times

Online Publication Date: 5 December 2006

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The temperature dependence of the electroluminescence (EL) spectral intensity has been investigated in detail between T = 20 and 300 K at various injection current levels for a set of two blue InGaN/GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with and without an additional n-doped In0.18Ga0.82N electron reservoir layer (ERL). The radiative recombination efficiency of the main blue emission band ( ∼ 480 nm) is found to be significantly improved at all temperature regions and current levels when the additional ERL is introduced. For high injection currents If, i.e., large forward bias voltages Vf, a quenching of the EL intensity is observed for T<100 K for both LED structures, accompanying appearance of short-wavelength satellite emissions around 380–430 nm. Furthermore, the low-temperature intensity reduction of the main EL band is stronger for the LED without the ERL than with the ERL. For low If, i.e., small Vf, however, no quenching of the EL intensity is observed for both LEDs even below 100 K and the short-wavelength satellite emissions are significantly reduced. These results of the main blue emission and the short-wavelength satellite bands imply that the unusual evolution of the EL intensity with temperature and current is caused by variations of the actual potential field distribution due to both internal and external fields. They significantly influence the carrier capture efficiency by radiative recombination centers within the active MQW layer and the carrier escape out of the active regions into high-energy recombination centers responsible for the short-wavelength satellite emissions.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Structure and photoluminescence properties of evaporated GeOx/SiO2 multilayers

M. Ardyanian, H. Rinnert, and M. Vergnat

J. Appl. Phys. 100, 113106 (2006); http://dx.doi.org/10.1063/1.2400090 (4 pages) | Cited 4 times

Online Publication Date: 5 December 2006

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Amorphous GeOx/SiO2 multilayers were prepared by successive evaporations of GeO2 and SiO2 powders onto substrates maintained at 100 °C. The evolution of the structure was investigated by x-ray reflectometry, transmission electron microscopy, infrared-absorption spectrometry and Raman spectrometry for annealing temperatures less than 800 °C. These experiments allowed us to follow the phase decomposition of the GeOx alloy and to observe the appearance of amorphous and crystallized germanium aggregates. The evolution of the photoluminescence in the range of 0.8–2.2 eV was correlated to the structure of the films.
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68.65.Ac Multilayers
78.55.Qr Amorphous materials; glasses and other disordered solids
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.40.Gh Other heat and thermomechanical treatments

Highly transparent cathodes comprised of rare earth and Au stacked layers for top-emission organic light emitting diodes

G. Z. Ran, W. Q. Zhao, L. Dai, and G. G. Qin

J. Appl. Phys. 100, 113107 (2006); http://dx.doi.org/10.1063/1.2388875 (4 pages) | Cited 2 times

Online Publication Date: 6 December 2006

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We report the transparent cathodes comprised of a low work function rare earth element (RE) and a Au capping layer for top-emission organic light emitting diodes (TOLEDs). The Sm/Au, Yb/Au, Gd/Au, and Dy/Au cathodes possess a transmittance up to ∼ 60% when the RE/Au thickness is 5/10 nm. The light extraction efficiencies for the TOLEDs with a silicon anode and a RE/Au cathode are computed to be 9%–13%, markedly higher than that for a similar device but with an Al/Au cathode. The surface plasmon polaritons at the Yb(or Sm)/Au cathode are found to be much weaker than those at the Al/Au cathode.
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85.60.Jb Light-emitting devices

Analysis of the linewidth enhancement factor (α-factor) in compressively strained InGaAsP quantum wire lasers

M. Abul Khayer and A. Haque

J. Appl. Phys. 100, 113108 (2006); http://dx.doi.org/10.1063/1.2388850 (6 pages) | Cited 1 time

Online Publication Date: 6 December 2006

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The linewidth enhancement factor (α-factor) of compressively strained (CS) InGaAsP/InP quantum wire (QWire) lasers is theoretically studied using an eight-band k⋅p formalism. It is found that tensile strained (TS) barriers lower the value of the α-factor by suppressing elastic strain relaxation. When multiple QWire layers are stacked vertically, the α-factor decreases owing to the increase in the modal gain. However, the decrease is lower than expected, because enhanced strain relaxation in multiple-layer stack tends to increase the α-factor. Comparison of the α-factors of QWires and QWells at the lasing frequency shows that the peak value of the α-factor decreases monotonically with increasing confinement, but an improvement in the α-factor of QWires at threshold condition relative to the α-factor of QWell lasers is not achieved unless the QWire width is reduced below a critical value. These results provide useful guidelines for designing CS QWire lasers with reduced values of the α-factor.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Light-polarization characteristics of electroluminescence from InGaN/GaN light-emitting diodes prepared on (11math2)-plane GaN

Hisashi Masui, Troy J. Baker, Michael Iza, Hong Zhong, Shuji Nakamura, and Steven P. DenBaars

J. Appl. Phys. 100, 113109 (2006); http://dx.doi.org/10.1063/1.2382667 (5 pages) | Cited 33 times

Online Publication Date: 7 December 2006

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Light polarization and emission spectra from InGaN/GaN quantum-well light-emitting diodes (LEDs) were investigated. The LEDs were prepared on the (11math2) plane of wurtzite GaN. Polarization and spectrum measurement was performed at different observation angles with respect to the LED surface. Partially polarized electroluminescence was confirmed at any angle of observation, where the emission intensity tended to be greater when a polarizer was aligned along the c axis of the InGaN/GaN LED structure. The results clearly indicated the inclination of the c axis relative to the LED surface. As a result, two light polarizations were identified and they were assigned to two different electronic transitions in relation to emission peak energies. Possible alteration of the valence-band structure was suggested due to the induced strain.
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85.60.Jb Light-emitting devices

Ultraviolet emission in Tm3+-doped fluoride fiber pumped with two infrared wavelengths

E. B. Mejía

J. Appl. Phys. 100, 113110 (2006); http://dx.doi.org/10.1063/1.2396671 (4 pages) | Cited 6 times

Online Publication Date: 7 December 2006

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An infrared, two-wavelength pumping scheme for generating UV in Tm3+-doped fibers is investigated and proposed as an alternative because the pump wavelengths are accessible from laser diodes. Spectral characterizations of fiber samples with different concentrations revealed that moderate concentrations are best suitable to produce UV (348–362 nm) emission when single—or double-line pumping with 1117 and 725 nm. Detailed spectroscopic measurements realized to the fiber with the best performance, the 2000 ppm wt, allowed to obtain the copumping wavelengths (in the ∼ 725 nm region) that enhanced the UV emission. For example, when applying tens of milliwatts at 725 nm, which represented a 28% increase of total pump power, the UV emission increased in an avalanchelike fashion up to three orders of magnitude. Then, a high-power 1117 nm source that currently exists in the market and a moderate power 725 nm source under development are possible to be used as pumps for this scheme.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.72.Bj Visible and ultraviolet sources
42.70.Ce Glasses, quartz

Enhanced Zn–Cd interdiffusion and biexciton formation in self-assembled CdZnSe quantum dots in thermally annealed small mesas

E. Margapoti, L. Worschech, A. Forchel, T. Slobodskyy, and L. W. Molenkamp

J. Appl. Phys. 100, 113111 (2006); http://dx.doi.org/10.1063/1.2390547 (4 pages) | Cited 3 times

Online Publication Date: 7 December 2006

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By controlled annealing of small ZnSe mesas with embedded CdZnSe quantum dots (QDs) at considerably low temperatures, significant changes of the QD luminescence have been observed. To investigate the spectral evolution of single exciton lines several thermal annealing steps were performed successively, and large energy shifts of single exciton (X) lines due to annealing were traced. In annealed QDs the biexciton (XX) emission is drastically enhanced. Biexciton binding energies less than 10 meV were recorded for the thermally annealed CdZnSe QDs, indicating a considerable change in the QD confinement. The pronounced energy shifts of the QD luminescence is attributed to the Cd–Zn interdiffusion between the CdZnSe QDs and the surrounding ZnSe matrix. In small mesas interdiffusion activation energy (EA) of less than 1 eV was determined. This value of EA is half of that recorded for the Cd–Zn interdiffusion in large QD ensembles, indicating that the sidewalls of the etched mesas play an important role in the observed diffusion process.
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68.35.Fx Diffusion; interface formation
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
61.72.Cc Kinetics of defect formation and annealing

Thermally synthesized ruby microstructures and luminescence centers

A R. Zanatta, C T. M. Ribeiro, U. Jahn, S. B. Aldabergenova, and H P. Strunk

J. Appl. Phys. 100, 113112 (2006); http://dx.doi.org/10.1063/1.2393009 (7 pages) | Cited 2 times

Online Publication Date: 7 December 2006

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This work reports on the synthesis and the optical-structural investigation of light-emitting microstructures obtained from amorphous aluminum nitride (AlN) thin films doped with chromium. The samples were prepared by radio frequency sputtering an Al target, with approximately 0.8 ppm of chromium, in an atmosphere of pure nitrogen. After deposition, the samples were thermally annealed up to 1050 °C under a flow of dry oxygen. The experimental investigation included photoluminescence, cathodoluminescence, energy dispersive x-ray spectroscopy, and scanning and transmission electron microscopy techniques. According to the experimental data, films annealed at 1050 °C for 15 min exhibit relatively strong luminescence at ∼ 685 nm. Further thermal annealing at this temperature induces the development of microscopic features onto the surface of the films that emit red light at approximately 693 nm. In view of their distinctive luminescence characteristics and spatial dimensions, the observed features have been designated by ruby microstructures (RbMS’s). For the present AlN films, the occurrence of these RbMS’s is associated with Cr3+ ions in oxygen-rich environments (α-alumina) that arise in consequence of the thermal treatments and of the presence of microimperfections (pores, voids, etc.) in the samples.
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78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth

Mechanism of the persistent phosphorescence in Sr4Al14O25:Eu and SrAl2O4:Eu codoped with rare earth ions

Eiichiro Nakazawa, Yoshinori Murazaki, and Susumu Saito

J. Appl. Phys. 100, 113113 (2006); http://dx.doi.org/10.1063/1.2397284 (7 pages) | Cited 10 times

Online Publication Date: 7 December 2006

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Luminescence and phosphorescence properties are investigated in two series of strontium aluminates, Sr4Al14O25:Eu2+ and SrAl2O4:Eu2+, codoped with rare earth (lanthanoid, Ln) ions. Persistent phosphorescence is observed for the phosphors codoped with Pr, Nd, Dy, Ho, and Er. In the phosphorescence process of these phosphors, the excited electron in the Eu2+ ion is transferred between the Eu and the codopant Ln ions through the 5d states of these ions. When the trivalent codopant ion Ln3+ captures the excited electron in the 4f shell, the ion is reduced to the divalent state and, therefore, the energy necessary to thermally relieve the electron from the ion is determined by the energy difference between the 4fn and the 4fn−15d configurations of the divalent Ln ion. The trapping depths (activation energies) of the Ln ions, estimated theoretically on the basis of this mechanism, coincide with the observed depths (0.8±0.2 eV) for the persistently phosphorescent phosphors, and those of the nonpersistent Ln ions are larger or smaller by 0.7 eV than the former. It is also elucidated that the retrapping of the electron released from a trap plays an important role in the persistent phosphorescence process.
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78.55.Hx Other solid inorganic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Phase transition induced gain depression in Nd3+:SBN lasers

E. Martín Rodríguez, D. Jaque, J. A. Sanz García, J. García Solé, and A. A. Kaminskii

J. Appl. Phys. 100, 113114 (2006); http://dx.doi.org/10.1063/1.2372445 (8 pages)

Online Publication Date: 8 December 2006

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In this work the origin of the phase transition induced gain depression in diode pumped Nd3+ doped Sr0.6Ba0.4(NbO3)2 lasers has been systematically investigated. The mechanisms capable of intracavity beam distortions are discussed and their relative contribution to the gain depression is investigated. We also provide evidence of two effects: a phase transition induced polarization switching and an enhancement in the laser performance when phase transition is overcome.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Fc Modulation, tuning, and mode locking
42.65.Pc Optical bistability, multistability, and switching, including local field effects

GeS2/metal thin film bilayered structures as write-once-type optical recording materials

Naohiko Kato, Tatsuo Fukano, Yasuhiko Takeda, Akihiro Takeichi, Tomoyoshi Motohiro, and Shoichi Kawai

J. Appl. Phys. 100, 113115 (2006); http://dx.doi.org/10.1063/1.2398556 (7 pages)

Online Publication Date: 8 December 2006

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GeS2/metals thin film bilayered structures were examined for write-once-type optical recording materials. Decreases in the reflectance of GeS2/Ag and GeS2/Cu structures at a certain elevated temperature were observed. The phenomena were attributed to the formation of metal sulfides with high optical absorption coefficients by the interface reaction between transparent GeS2 and highly reflective metals. In contrast to GeS2/Ag or GeS2/Cu, an increase in the reflectance was observed in GeS2/Au, which was presumably due to the change of optical interference conditions caused by the decrease in the GeS2 film thickness and the improvements of the crystallinity of Au caused by the decrease of the lattice defects along the grain boundaries of Au. Examination of the GeS2/metals bilayered structures as optical disc memories revealed that the reactions occurred within submicrosecond during the recording laser irradiations. The recording sensitivities of GeS2/Ag or GeS2/Cu which corresponded to the reaction temperatures was able to be controlled by Al doping to Ag or Cu. The reflectance of the GeS2/metals samples except the GeS2/Cu kept enough value to be optically readable in the wider range from 500 to 800 nm than the recording layer containing organic dye of the conventional compact disc recordable. The spectra after the heat treatments showed the smaller wavelength dependence than that before the heat treatment. These features indicate the promising properties of these structures in application to optical recording media that can be used in the wide wavelength range.
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42.79.Vb Optical storage systems, optical disks

Band gap engineering for laser cooling of semiconductors

Jacob B. Khurgin

J. Appl. Phys. 100, 113116 (2006); http://dx.doi.org/10.1063/1.2395599 (6 pages) | Cited 9 times

Online Publication Date: 8 December 2006

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A number of methods for improvement of the efficiency of laser cooling in semiconductors are suggested and analyzed theoretically. It is shown that by combining band gap engineering in the electronic domain and photonic band gap engineering in the optical domain, one can attain an enhancement in refrigeration efficiency provided the nonradiative efficiency is not drastically affected.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
71.20.Nr Semiconductor compounds
42.70.Qs Photonic bandgap materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Spectroscopic properties of Pr3+ ions in NaGd(WO4)2 crystal

Hongyan Wang, Guohua Jia, Fugui Yang, Yanping Wei, Chaoyang Tu, Zhenyu You, Yan Wang, Zhaojie Zhu, and Jianfu Li

J. Appl. Phys. 100, 113117 (2006); http://dx.doi.org/10.1063/1.2399887 (7 pages) | Cited 2 times

Online Publication Date: 8 December 2006

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A Pr3+-doped NaGd(WO4)2 single crystal has been grown by the Czochralski technique along the (0 0 1) orientation. The refractive indices were measured precisely as a function of wavelength. A Raman spectrum, polarized absorption spectra, fluorescence spectra, and fluorescence decay curve have been recorded at room temperature. The standard and modified Judd-Ofelt theories have been performed to analyze the absorption spectra to determine the spectroscopic parameters, including the Judd-Ofelt intensity parameters Ωt (t = 2,4,6), radiative transition probabilities, radiative lifetimes, and branching ratios. The stimulated emission cross sections and fluorescence lifetime of the promising laser level were obtained.
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42.70.Hj Laser materials
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.45.+h Stimulated emission
81.10.Fq Growth from melts; zone melting and refining

Photonic band gaps in non-close-packed inverse opals

D. P. Gaillot and C. J. Summers

J. Appl. Phys. 100, 113118 (2006); http://dx.doi.org/10.1063/1.2396670 (10 pages) | Cited 5 times

Online Publication Date: 11 December 2006

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An advanced dielectric function has been designed to compute the photonic band structures of non-close-packed inverse opals fabricated using conformal infiltration and by a recently described sacrificial-layer technique. A model is proposed to correctly simulate complex dielectric structures resulting from conformal backfilled infiltrations. While large photonic band gaps (PBGs) and a reduced refractive index requirement (RIR) are predicted to occur in these inverse structures, the results also indicate a high degree of sensitivity to the dielectric/air network topology enabling fine PBG tailoring. Optimized structurally modified non-close-packed inverse opals with lower refractive indices offer enhanced optical properties compared to narrow PBGs observed in conventional inverse shell opals using high index materials such as silicon or germanium. Three-dimensional finite-difference time-domain computations predict that many experimentally achievable non-close-packed inverse structures exhibit significantly enhanced PBG properties: a RIR as low as 2.65 and PBG width of ∼ 10%. Additionally, a PBG width of 14.2% is predicted for an optimized high index non-close-packed inverse structure in which the interstitial air void is smaller than in structures fabricated by conformal means. The robustness and simplicity of this technique combined with predicted adjustable PBG properties is therefore demonstrated to provide alternative fabrication routes to the synthesis of photonic crystal devices operating in the visible with lower refractive indices.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Wavelength dependence of electro-optic effect in tetragonal lead magnesium niobate lead titanate single crystals

Chongjun He, Wenwei Ge, Xiangyong Zhao, Haiqing Xu, Haosu Luo, and Zhongxiang Zhou

J. Appl. Phys. 100, 113119 (2006); http://dx.doi.org/10.1063/1.2384813 (4 pages) | Cited 1 time

Online Publication Date: 11 December 2006

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The refractive indices, birefringence, and linear electro-optic (EO) effect of 0.62Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 single crystals have been characterized as a function of wavelength. The dispersions of refractive indices for both ordinary and extraordinary rays were accurately described by a two-term Sellmeier dispersion equation, in which the parameters connected to the energy band structure were determined. A strong dispersion was found for birefringence and EO coefficient γc = γ33−(no/ne)3γ13. With the increasing wavelengths, both of them decrease fast. The two-term Sellmeier dispersion model, in which one oscillator frequency is polarization dependent, was shown to represent closely all the results. The polarization potential, which specifies the magnitude of the oscillator frequency shift, was 0.40 eV m4 C−2.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity

CO2 laser induced temperature profiles in n-GaAs: An analytical model probed with the Seebeck effect

J. Stiens, W. Vandermeiren, C. De Tandt, R. Vounckx, G. Shkerdin, and V. Kotov

J. Appl. Phys. 100, 113120 (2006); http://dx.doi.org/10.1063/1.2399896 (11 pages) | Cited 2 times

Online Publication Date: 12 December 2006

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An analytic model describing the distribution of the electron temperature created by absorption of an optical beam with a cylindrical symmetry in a layered structure was developed. Main attention was paid to the contribution of the lattice heating in the stationary and nonstationary regimes. It was shown that both the spatial distribution of the incident stationary beam and the temporal distribution of the incident pulses can be retrieved from the spatial and temporal electron temperature dependences near the illuminated surface. Electron temperature distributions can be measured using the thermoelectric effect. Experimental results of the spatial and temporal measurements of the thermoelectric voltage were compared with the theoretical calculations and a satisfactory agreement between experimental and theoretical results was found near the incident beam center for the quasistationary regime. The experimentally derived Seebeck detector’s responsivity equals 17.5 μV/W cm−2.
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72.20.Pa Thermoelectric and thermomagnetic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Micromachining of ridge optical waveguides on top of He+-implanted β-BaB2O4 crystals by femtosecond laser ablation

R. Degl'Innocenti, S. Reidt, A. Guarino, D. Rezzonico, G. Poberaj, and P. Günter

J. Appl. Phys. 100, 113121 (2006); http://dx.doi.org/10.1063/1.2396716 (5 pages) | Cited 4 times

Online Publication Date: 13 December 2006

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We report on a technique for the fabrication of ridge optical waveguides on top of β-BaB2O4 (BBO) crystals. The BBO crystals were first implanted by He+ ions to form planar optical waveguides. In the second step, the femtosecond laser ablation technique was employed for micromachining of ridge-type optical waveguides. A thorough study of material-specific ablation parameters for BBO has been performed in order to achieve ablated structures with smooth sidewalls. A further process of Ar+ ion smoothing in a plasma chamber was used to reduce the sidewall roughness of the ablated ridges from 75 to 35 nm root mean square. We demonstrated optical waveguiding in these femtosecond-ablated plasma-treated waveguides and measured total propagation losses of less than 10 dB/cm at 532 nm, making them suitable for nonlinear- and electro-optical applications.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
79.20.Ds Laser-beam impact phenomena
61.80.Jh Ion radiation effects
42.70.Mp Nonlinear optical crystals
42.65.-k Nonlinear optics

Strain-induced in-plane optical anisotropy in (001) GaAs/AlGaAs superlattice studied by reflectance difference spectroscopy

C. G. Tang, Y. H. Chen, X. L. Ye, Z. G. Wang, and W. F. Zhang

J. Appl. Phys. 100, 113122 (2006); http://dx.doi.org/10.1063/1.2399308 (5 pages) | Cited 6 times

Online Publication Date: 14 December 2006

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In-plane optical anisotropy (IPOA) in (001) GaAs/AlGaAs superlattice induced by uniaxial strain has been investigated by reflectance difference spectroscopy (RDS). Uniaxial strain on the order of 10−4 was introduced by bending a strip sample with a stress apparatus. The IPOA of all interband transitions shows a linear dependence on strain. The birefringence and dichroism spectra induced by strain are obtained by RDS on the basis of a three-phase model, which is in good agreement with the reported results.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Fm Birefringence

Optical susceptibilities of supported indium tin oxide thin films

Jonathan L. Humphrey and Darius Kuciauskas

J. Appl. Phys. 100, 113123 (2006); http://dx.doi.org/10.1063/1.2392995 (6 pages) | Cited 1 time

Online Publication Date: 15 December 2006

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The third-order nonlinear optical susceptibility of indium tin oxide (ITO) thin films on glass substrates, χ(3)ITO, was determined in the near-IR spectral region using degenerate four wave mixing (DFWM) spectroscopy with 100 fs laser pulses. A DFWM method for measuring thin films on thick substrates was refined for the characterization of films less than 100 nm thick and applied to ∼ 25 nm thick ITO films. It was found that χ(3)ITO is purely electronic at 900–1300 nm (11 000–7700 cm−1) and has a value of (2.16±0.18)×10−18 m2 V−2. The χ(3)ITO value reaches (3.36±0.28)×10−18 m2 V−2 at 1500 nm (6700 cm−1) due to two-photon absorption by free carriers (electrons). Ultrafast electron relaxation was also observed. The ∼ 100 fs lifetime of this process could reflect electron scattering in the conduction band.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Wc Optical coatings
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.66.Nk Insulators
78.47.-p Spectroscopy of solid state dynamics

Characterization of an external electro-optic sampling probe: Influence of probe height on distortion of measured voltage pulses

S. Seitz, M. Bieler, G. Hein, K. Pierz, U. Siegner, F. J. Schmückle, and W. Heinrich

J. Appl. Phys. 100, 113124 (2006); http://dx.doi.org/10.1063/1.2396798 (7 pages) | Cited 6 times

Online Publication Date: 15 December 2006

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We experimentally and theoretically investigate the distortion that an external electro-optic sampling tip imprints on a measured voltage pulse that propagates along a coplanar stripline. By using the electro-optic effect of the GaAs substrate on which the stripline is fabricated we obtain the undisturbed voltage pulse, which serves as a reference pulse. This allows us to quantitatively compare the voltage pulse measured with the external electro-optic sampling tip to the undisturbed voltage pulse. The sensitivity of the sampling measurement and the distortion of the voltage pulse are determined for different heights of the tip which is lifted off the stripline. The experimental data agree very well with numerical finite difference calculations. We find that small changes of the tip height already influence the measurements strongly. From the experiments we infer an optimum working height of the sampling tip of only 0.5 μm. Our investigations help to improve the accuracy of electro-optic sampling measurements.
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85.60.Bt Optoelectronic device characterization, design, and modeling
84.40.Az Waveguides, transmission lines, striplines
02.50.-r Probability theory, stochastic processes, and statistics

Long persistent light emitting diode

D. Jia and D. N. Hunter

J. Appl. Phys. 100, 113125 (2006); http://dx.doi.org/10.1063/1.2400091 (6 pages) | Cited 6 times

Online Publication Date: 15 December 2006

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Light emitting diodes (LEDs) coated with Sr2MgSi2O7:Eu2+,Nd3+ (blue), SrAl2O4:Eu2+,Dy3+ (green), SrS:Eu2+,Y3+,Ce3+ (orange), and CaS:Eu2+,Tm3+,Ce3+ (red) long persistent phosphors were prepared. LEDs which have a 450 nm blue emission were used as an excitation source for the coated phosphors. Blue (475 nm), green (520 nm), orange (606 nm), and red (650 nm) emissions of the phosphors were found for each coated LED. Long persistent afterglow emissions from the phosphors excited by using LEDs were obtained. The persistence time of the phosphors’ afterglow emissions coated on LEDs is found in the same order of magnitude as the phosphorescence persistence time of the long persistent phosphors.
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85.60.Jb Light-emitting devices
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