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The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect.sup.1-3, tunable Mott insulators.sup.4,5 and unconventional superconductivity.sup.6. In addition, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors.sup.7-9, but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moiré potential in molybdenum diselenide (MoSe.sub.2)/tungsten diselenide (WSe.sub.2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, -15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle.sup.7. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moiré optics through variation of the twist angle. The trapping of interlayer valley excitons in a moiré potential formed by a molybdenum diselenide/tungsten diselenide heterobilayer with twist angle control is reported., Author(s): Kyle L. Seyler [sup.1] , Pasqual Rivera [sup.1] , Hongyi Yu [sup.2] , Nathan P. Wilson [sup.1] , Essance L. Ray [sup.1] , David G. Mandrus [sup.3] [sup.4] [sup.5] [...]

In this paper, an asymmetric photonic crystal waveguide is proposed for flat band slow light transmission. Two structural parameters of one cladding layer of the waveguide are carefully adjusted. They are the refractive index of the liquid infiltrated in the cladding on one side and the radius of the air holes in the infiltrated cladding. In such an asymmetric waveguide, we can achieve a very flat band corresponding to high group index such as 29.4 and low dispersion ([10.sup.4][ps.sup.2]/km) for [DELTA][omega]/[omega] = 1.46%. It is found that the value of [n.sub.g][DELTA][omega]/[omega] of the proposed waveguide can reach 0.429 and this waveguide can also yield a significant increase in the group index-bandwidth product [n.sub.g][DELTA][omega]/[omega] and improve the bandwidth. OCIS codes: 130.5296, 260.2030.

We propose a novel highly birefringent photonic crystal fiber (PCF) based on a double-hole unit. Because of the effect of the double-hole unit in which double airholes can be effectively viewed as elliptical airholes, the proposed PCF can achieve birefringence similar to that of an elliptical-hole PCF with high birefringence even up to the order of 0.01 and still avoid the inherent challenge to fabricate an elliptical-hole PCF. The proposed PCF also has a lower confinement loss than an elliptical-hole PCF with the same air-filling fraction. [c] 2010 Optical Society of America OCIS codes: 060.2310, 060.5295.

We have fabricated Fabry--Perot (FP) cavities in the THz region with a ZnTe crystal as a cavity layer by a simple stacking method. We observed more than a three times enhancement of the THz emission intensity in the FP cavities compared with the bare ZnTe crystal at the frequencies of the resonant modes and stopband edges. On the other hand, suppression of the THz emission occurs at frequencies in the stopband. The enhancement and suppression of the THz emission are caused by the modification of the optical density of state in the FP cavities compared to the vacuum. [c] 2009 Optical Society of America OCIS codes: 300.6495, 140.3948.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.12.015 Byline: A.A. Dakhel Keywords: Optical properties; Cadmium-dysprosium oxide; Dy-doped CdO; Mobility; Oxides; Rare earth oxides; TCO Abstract: Lightly Dy-doped CdO thin films (molar 0.5%, 1%, 2%, and 2.5%) have been prepared by a vacuum evaporation method on glass and Si wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-vis-NIR absorption spectroscopy, and dc-electrical measurements. Experimental data indicate that Dy.sup.3+ doping slightly stretchy-stresses the CdO crystalline structure and changes the optical and electrical properties. The bandgap of CdO was suddenly narrowed by about 20% due to a little doping with Dy.sup.3+ ions. Then, as the Dy doping level was increased, the energygap was also increased. This variation was explained by the effect of Burstein-Moss energy shift (or bandgap widening effect) together with a bandgap shrinkage effect. The electrical behaviour of the samples shows that they are degenerate semiconductors. However, the 2% Dy-doped CdO sample shows an increase in its mobility by about 3.5 times, conductivity by 35 times, and carrier concentration by 10 times relative to undoped CdO film. From transparent conducting oxide point of view, Dy is sufficiently effective for CdO doping. Author Affiliation: Department of Physics, College of Science, University of Bahrain, P.O. Box 32038, Bahrain Article History: Received 20 May 2008; Revised 6 November 2008; Accepted 18 December 2008 Article Note: (miscellaneous) Communicated by Associate Editor: Dr. Takhir Razykov

The properties of a wideband photonic crystal power splitter with different output power levels based on directional coupling are investigated numerically with the finite-difference time-domain method. The effects of changing the coupling length and radius of the coupling rods between parallel waveguides on output transmissions are investigated. By further splitting power in each branch a power splitter with four output branches is proposed. OCIS codes: 230.0230, 250.5300, 130.3130, 230.7390, 060.1810.

Three crystals used in solid-state lasers, namely, yttrium aluminum garnet (YAG), yttrium orthovanadate (YV[O.sub.4]), and gadolinium calcium oxoborate (GdCOB), were investigated to determine the influence of dopants on their thermal diffusivity. The thermal diffusivity was measured by thermal wave method with a signal detection based on mirage effect. The YAG crystals were doped with Yb or V, the YV[O.sub.4] with Nd or Ca and Tm, and the GdCOB crystals contained Nd or Yb. In all cases, the doping caused a decrease in thermal diffusivity. The analysis of complementary measurements of ultrasound velocity changes caused by dopants leads to the conclusion that impurities create phonon scattering centers. This additional scattering reduces the phonon mean free path and accordingly results in the decrease of the thermal diffusivity of the crystal. The influence of doping on lattice parameters was investigated, additionally. OCIS codes: 160.0160, 160.1190, 160.3380, 160.5690.

The paper presents results on acousto-optic investigation of unusual acoustic phenomena taking place in crystals possessing strong anisotropy of elastic properties. Advantages of the applied method of analysis are demonstrated by the example of the commonly used acousto-optic material tellurium dioxide. The major goal of the research consists of experimental verification of theoretical conclusions related to peculiar cases of acoustic propagation and reflection recently observed in the crystalline material. In particular, the case of glancing incidence and the following reflection of elastic energy from a free boundary separating the paratellurite crystal and the vacuum is examined in the paper. It is shown in the acousto-optic experiment that, in the case of glancing incidence, energy flow of a reflected acoustic wave may propagate practically in a reverse direction with respect to an incident wave. It is also proved that strong elastic anisotropy of the crystal is responsible for the unusual propagation and reflection of the acoustic waves. The research confirms the conclusion that the examined acoustic effects may be useful in development of new acousto-optic devices. OCIS codes: 160.1050, 170.1065, 170.7180, 230.1040, 120.2440.

Sum-frequency generation (SFG) of > 16 W of 589 nm light has been achieved by a single pass through a 20 mm long, undoped, periodically poled, nearly stoichiometric lithium tantalate (PPSLT) crystal. This, to our knowledge, represents the highest reported average power in the visible produced by a single-pass SFG crystal and the highest visible average power produced by PPSLT. The stoichiometric lithium tantalate crystal was grown directly from the melt without magnesium doping. OCIS codes: 190.0190, 190.2620, 190.4400, 140.3580.

Recording of efficient reflection holograms is achieved in CdTe:Ge at [lambda] = 1.064[micro]m and [lambda] = 1.55 [micro]m. The gain factor measured at both wavelengths for counterpropagating two-beam coupling considerably exceeds the absorption constant and transcends all values previously reported for semiconductors with no external field. The dependences of the gain factor on intensity and grating spacing are studied. Some crystal characteristics are estimated in the frame of a single band, one mobile species approximation of space-charge formation. The homogeneity of photorefractive properties in the crystal volume is demonstrated. OCIS codes: 160.5320, 190.5330, 190.7070.

A nanosecond 1.3 [micro]m Nd:YAG laser-pumped external cavity eye-safe Raman laser based on [BaWO.sub.4] crystal is efficiently demonstrated. The average power of 1.5 [micro]m was 0.60W operating at a pulse repetition rate of 1.7 kHz and an incident pump power of 4.14W. Conversion efficiency of 14.5% and a high slope efficiency of 54.5% have been achieved. Pulse shortening was obviously observed. The pulse duration of the first Stokes was about 40ns, much shorter than the fundamental pulse with a duration of ~220 ns. OCIS codes: 140.3550, 140.3580, 190.5650, 230.5750.

An undoped YVO4 crystal is employed to achieve efficient stimulated Raman scattering conversion in a diode-pumped actively Q-switched Nd:YAG laser. With an incident pump power of 16.2 W, an 1176 nm first Stokes average output power of 3.0 W was generated at a pulse repetition rate of 50 kHz, corresponding to an optical-to-optical conversion efficiency of 18.3%. Moreover, the maximum optical-to-optical conversion efficiency of 21.3% was found at 20 kHz. The maximum pulse energy is higher than 83 [micro]J at both 20 and 30kHz. With an incident pump power of 7.6W, the underestimated peak power of 43.5 kW was demonstrated at 20 kHz with mode-locked modulation. OCIS codes: 140.3480, 140.3540, 140.3550, 290.5910.

A scintillating crystal's surface reflectance has to be well understood in order to accurately predict and optimize the crystal's light collection through Monte Carlo simulations. In this paper, we measure the inner surface reflectance properties for BGO. The measurements include BGO crystals with a mechanically polished surface, rough-cut surface, and chemically etched surface, and with various reflectors attached, both air-coupled and with coupling compound. The measurements are performed with a laser aimed at the center of a hemispherical shaped BGO crystal. The hemispherical shape eliminates any non-perpendicular angles for light entering and exiting the crystal. The reflected light is collected with an array of photodiodes. The laser can be set at an arbitrary angle, and the photodiode array is rotated to fully cover 2[pi] of solid angle. The current produced in the photodiodes is readout with a digital multimeter connected through a multiplexer. The two rows of photodiodes achieve 5-degree by 4-degree resolution, and the current measurement has a dynamic range of [10.sup.5] : 1. The acquired data was not described by the commonly assumed linear combination of specular and diffuse (Lambertian) distributions, except for a very few surfaces. Surface roughness proved to be the most important parameter when choosing crystal setup. The reflector choice was of less importance and of almost no consequence for rough-cut surfaces. Pure specular reflection distribution for all incidence angles was measured for polished surfaces with VM2000 film, while the most Lambertian distribution for any surface finish was measured for titanium dioxide paint. The distributions acquired in this paper will be used to create more accurate Monte Carlo models for light reflection distribution within BGO crystals. Index Terms--Lambertian reflection, light collection, Monte Carlo methods, scintillation crystal.

Experimental studies and analysis of acousto-optic diffraction in [alpha]Ba[B.sub.2][0.sub.4] and [Li.sub.2][B.sub.4][0.sub.7] crystals are given. Ultrasonic wave velocity, elastic compliance and stiffness coefficients, and piezo-optic and photoelastic coefficients of [alpha]-Ba[B.sub.2][0.sub.4] and [Li.sub.2][B.sub.4][0.sub.7] crystals are determined. The acousto-optic figure of merit has been estimated for different possible geometries of acousto-optic interaction. It is shown that the acousto-optic figures of merit for [alpha]-Ba[B.sub.2][O.sub.4] crystals reach the value [M.sub.2]= (270 [+ or -] 70) x [10.sup.-15] [s.sup.3]/kg for the case of interaction with the slowest ultrasonic wave. The directions of propagation and polarization of those acoustic waves are obtained on the basis of construction of acoustic slowness surfaces. The acousto-optic diffraction is experimentally studied for [alpha]-Ba[B.sub.2][0.sub.4] and [Li.sub.2][B.sub.4][0.sub.7] crystals. OCIS codes: 160.4670, 260.1180, 050.1940, 070.1060, 230.1040.

The luminescence excitation spectra, luminescence spectra and the nanosecond-scale decay kinetics were studied. The ZnO and ZnO:Al nanopowders were prepared by vaporization-condensation in a solar furnace using different raw powders: commercial, hydrothermal and those obtained by plasma synthesis. Exciton-phonon as well as exciton-exciton interaction processes in nanopowders, a bulk crystal and ZnO ceramics were studied and compared. The fast decay and low afterglow intensity of ZnO nanopowders and ceramics support these materials for scintillators. Index Terms--Ceramic, fast luminescence, nanopowders, ZnO.

We grew a Gd-doped lead chloride single crystal by the Bridgman method and investigated scintillation properties of the crystals at low temperature. We measured the relative light yield, energy resolution, fluorescence decay time, and proportionality of the crystals for the [gamma]-ray at low temperature. The energy resolution is measured to be 25.6% for the [sup.137] Cs 662 keV [gamma]-ray, and the fluorescence decay time of the crystal is composed of two components with decay times of 1.35 and 6.20/[micro]s at 173 K. Index Terms--Crystal growth, gadolinium, lead compound, scintillation detector.

Intrinsic emission of undoped and [Ce.sup.3+] doped single crystal (SC) and single crystalline films (SCF) of YAl[O.sub.3] (YAP) was studied using the time-resolved luminescence spectroscopy under excitation by pulsed X-ray and synchrotron radiation. In contrast to YAP SCF, the YAP bulk SC are characterized by the presence of Y-in-Al-positions antisite defects (AD) and large concentration of vacancy-type defects (VD) of different types, which contribute to the intrinsic emission of YAP SC. Such type defects are centers of the luminescence in the UV (6.0-4.75 eV) and near UV (4.75-2.2 eV) ranges, overlapping with the Ce absorption and emission bands. Furthermore, they can give rise to shallow trapping centers as well. For this reason the AD and VD can strongly influence the scintillation properties of YAP:Ce SC. Specifically, the decay kinetics of the Ce emission in YAP:Ce SC, besides the fast component (23.3 [+ or -] 3.5 ns) related to radiative 5d-4f transition of Ce ions, contains also two slow components in the hundred ns and [mu]s ranges, which are due to the AD and VD-related traps. The advantages of scintillators based on YAP:Ce SCF, namely faster scintillation decay and lower contribution of slow components in the total light yield, can be achieved due to the absence of above mentioned bulk crystal defects. Index Terms--Antisite and vacancy type defects, intrinsic luminescence, scintillators, YAP single crystals and single crystalline films.

Intrinsic and Ce-related luminescence of LuAP:Ce single crystalline films (SCF) in comparison with their bulk single crystal (SC) analogs were analyzed for the first time using the time-resolved luminescence spectroscopy under synchrotron radiation excitation. Difference in luminescent properties of SCF and SC are due to the absence of the Lu-at-Al-site antisite defects (AD) and extremely low concentration of vacancy-type defects (VD) in SCF. SCF contamination by Pb ions from flux is noted, which gives rise to an additional emission band in UV range. In SCF, the absence of emission and trapping centers formed by the mentioned AD and VD can explain their favorable timing characteristics with respect to SC. The role of [Pb.sup.2+] trace impurities in LuAP-based SCF scintillators is considered as well. Index Terms--Antisite and vacancy type defects; intrinsic and Ce-related luminescence; LuAP:Ce single crystal and single crystalline films, scintillators.

Luminescence of new irregular [Ce.sup.3+]-related centers: the unperturbed and perturbed [Ce.sup.3+] ions located in [Al.sup.3+] sites and the [Ce.sup.3+.sub.LU] ions perturbed by [Lu.sup.3+.sub.Al] ions was found. The systematic study of these centers by means of the ESR and luminescence methods and their influence on scintillation characteristics was performed. The structure and symmetry of the irregular [Ce.sup.3+] centers was established and their spectral characteristics were explained. Index Terms--Antisite defects, ESR, luminescence, scintillators.

This paper presents both investigations of high-energy luminescence with maximum at 7.5 eV in Ba[F.sub.2]:[Y.sup.3+] and Ba[F.sub.2]:[Yb.sup.3+] crystals and theoretical calculations of cross-luminescence spectrum in crystals of barium fluoride with interstitial ions of fluorine. The dependencies of the 7.5 eV emission intensity as function of different impurities mol. concentration are presented. The intensity of this emission increases with concentration of rare-earth impurity, but in the case of doping by [Yb.sup.3+] and [Y.sup.3+] this intensity is less than that in the case of [La.sup.3+] doping. This feature (as well as the nonlinear dependence) can be due to the creation of clusters, i.e., aggregation of impurity ions and [F.sup.-]--interstitials. The intensity of the 7.5 eV luminescence in Ba[F.sub.2]:[Y.sup.3+] crystal after annealing at 1000 K increased by three times but it remained less than in the case of [La.sup.3+] doping. Theoretical calculations of the core hole electronic and spatial structure and cross-luminescence spectrum were performed in the [[Ba.sub.6][F.sub.12]] cluster. This cluster contains interstitial ion of fluorine, which is surrounded by six ions of [Ba.sup.2+]. In the case of using Hartree-Fock method the calculated luminescence spectrum of Ba[F.sub.2] crystal with interstitial fluorine shows cross-luminescence band with main maximum at 5.2 eV and high-energy band at 11.7 eV. In the case of using TD DFT method the energies of both cross-luminescence transitions and of transition between interstitial ion and core levels are in satisfactory agreement with experimental data, being all overestimated by approximately the average value of 0.8 eV. Index Terms--Clustering method, impurity, luminescence.

In this paper, we present a long path-length axial absorption detection method in photonic crystal fibers (PCFs). A PCF, also called a holey fiber or microstructured fiber, is an optical fiber which consists of a periodic array of very tiny and closely spaced air holes on the scale of [micro]m running through the whole length of the fiber. Here, a PCF with porous microstructures was used as a sample container for absorption detection. Light was guided by total internal reflection and propagated axially in the air holes of PCFs that were filled with the solution of the absorbing species by vacuum pumping. Excellent linearity was obtained for different sample concentrations, and high sensitivity was achieved due to the long optical path length. In addition, as the dimension of the PCF is small, the sample volume is greatly reduced. Moreover, due to its robustness, the PCF can be coiled up to keep the footprint small, making it suitable for microchip absorption detection. It can be widely used for both off-chip and on-chip detection of absorbing species, such as ions, alkaloids, and biomolecules.

A novel intrinsic fiber optic pressure sensor realized with a polarization-maintaining photonic crystal fiber (PM-PCF) based Sagnac interferometer is proposed and demonstrated experimentally. A large wavelength-pressure coefficient of 3.42 nm/MPa was measured using a 58.4 cm long PM-PCF as the sensing element. Owing to the inherently low bending loss and thermal dependence of the PM-PCF, the proposed pressure sensor is very compact and exhibits low temperature sensitivity. OCIS codes: 060.2370, 060.2420, 060.5295.

Uniaxial crystals may become biaxial in an external field. The general and exact law of double refraction on the boundary of an isotropic medium and a biaxial crystal lead to an unwieldy set of involved formulas. Rotations of the principal axes of the optical permittivity tensor in the crystal subjected to the field lead to further difficulties in ray and wave tracing. Therefore, we propose a calculus in which the directions of refracted rays and waves in an unperturbed uniaxial crystal are taken as the first approximation, and then small perturbations of rays and waves due to the applied field are considered. Our approach is based on Huygens's principle and a generalized form of Fresners ray equation. As an example, the method is applied to the electro-optic modulation of ray and wave directions in a BaTi[O.sub.3] crystal of 4mm symmetry. OCIS codes: 080.2720, 120.5710, 160.1190, 160.2100, 260.1180.

Knowledge about the temperature distribution inside solid-state laser crystals is essential for calculation of thermal phase shift, thermal lensing, thermally induced birefringence, and heat-induced crystal bending. Solutions for the temperature distribution for the case of steady-state heat loading have appeared in the literature only for simple cylindrical crystal shapes and are usually based on numerical techniques. For the first time, to out knowledge, a full analytical solution of the heat equation for an anisotropic cubic cross-section solid-state crystal is presented. The crystal is assumed to be longitudinally pumped by a Gaussian pump profile. The pump power attenuation along the crystal and the real cooling mechanisms, such as convection, are considered in detail. A comparison between our analytical solutions and its numerical counterparts shows excellent agreement when just a few terms are employed in the series solutions. OCIS codes: 120.6780, 120.6810, 140.3580, 140.3480.

Based on dual transverse Pockels effect, complete polarization conversion can be achieved by using only one electro-optic crystal and its two externally applied voltages. The electro-optic phase retardation and the azimuth angle of the field-induced principal dielectric axes of the crystal can be independently and linearly controlled by the amplitude and direction of the applied electric field, and the formulas for this correlation are deduced for arbitrary input and output polarization states. The candidate crystals mainly include the uniaxial crystals of 3 m, [bar.6]2 m, and 32 symmetry groups, and the cubic crystals of [bar.4]3 m and 23 symmetry groups. Theoretical analysis demonstrates that one crystal exhibiting both dual transverse Pockels effect and optical activity can also be used for complete polarization converter. The continuous polarization rotation of a linearly polarized light from 0[degrees] to 180[degrees] has been performed experimentally by use of single lithium niobate crystal with four lateral electrodes. In addition the light beam position-dependent polarization conversion by using a bulk electro-optic crystal is also measured in the experiment. This new type of polarization converter will have potential applications in many fields due to its simple configuration, explicit control logic of polarization conversion, and lower power consumption. OCIS codes: 060.1660, 060.4510, 120.2130, 230.2090, 260.1180, 260.5430.

A filling-factor-graded wavelike two-dimensional photonic crystal (2DPC) possessing a light-path bending effect that is polarization dependent is theoretically studied by using a qualitative analysis of the isofrequency curves. The numerical simulation results obtained by using the finite-difference time-domain method demonstrate that such a graded 2DPC has potential applications in a polarization splitter and a parallel-plane resonant cavity. A new kind of waveguide structure that combines a filling-factor-graded wavelike 2DPC and one-dimensional multilayer thin films is also discussed. OCIS codes: 310.5445, 260.5430.

Based on the theory of photonic crystals and the framework of a single-channel reflection filter that we presented before, structures of reflection filters with multiple channels are proposed. These structures can overcome some drawbacks of conventional multichannel transmission filters and are much easier to fabricate. We have practically fabricated the reflection filters with two and three channels, and the tested results show approximate agreement with theoretical simulation. Moreover, the superprism effect is also simulated in the single-channel reflection filter, the superiorities to transmission filters are discussed, and these analyses may shed some light on new applications of reflection filters in optical communication and other systems. OCIS codes: 230.0230, 310.0310, 230.4170, 350.2460.

Under the approximation of small birefringence, the properties of radially and azimuthally polarized vortex beams tightly focused through a uniaxial birefringent crystal are investigated. The contour plots of intensity distribution near the focus and in the real focal plane are illustrated by performing numerical calculations. The dependence of the focal shift on numerical aperture and birefringence are analyzed. Moreover, the Strehl ratio in the real focal plane as a function of birefringence is also analyzed. It is revealed that the variation of birefringence has no influence on the focal shift and the Strehl ratio of azimuthally polarized vortex beams. OCIS codes: 260.1440, 050.1960.

Two types of vertical surface emitting photonic crystal cavities based on beaming mechanism and coupled surface modes are studied. It is shown that vertical emission with a zero divergence angle and a high quality factor can be easily achieved by the back-to-back cavity design. The periodic modulation to the cavity surface alters nonradiative surface modes into radiative surface modes, and the constructive interference of the radiative waves gives rise to vertical emission and improves the quality of the output beam. A high quality factor can be attributed to the nonradiative surface mode on the cavity back whose small part of energy can be transferred into the cavity surface by coupling. The resonant property and the coupling efficiency of the cavities are investigated and optimal cavity configurations are obtained. These open coupled-cavities are good candidates of highly directional light sources. America OCIS codes: 140.3945, 240.6690, 230.5298.

We present a photonic crystal cloaking device at optical wavelengths based on the association of two lattices working in different regimes, namely, stop band and negative refraction. The idea is to reconstruct in phase an incident cut Gaussian modulated plane wave by using the photonic crystal dispersion properties to ensure that no light penetrates in the core of the device. It is believed that such a cloaking device could become a building block for future generations of 3D integrated optical circuits. OCIS codes: 220.2740, 230.5298, 080.2710.

Amplified spontaneous emission (ASE) characteristics of a green fluorescent dye (10-(2-benzothiazolyl)-1,1,7,7- tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1] benzo- pyrano [6,7,8-ij]quinolizin-11-one) (C545T) encapsulated in a highly ordered three-dimensional (3D) inverted-opal titania (Ti[O.sub.2]) photonic crystal (PC) microcavity were studied. Due to the utilization of a Ti[O.sub.2] PC, the emission spectrum was greatly narrowed and the ASE threshold, gain, and loss were significantly improved. The threshold, gain, and loss reached 1.25 mJ [pulse.sup.-1] [cm.sup.-2], 34.69 [cm.sup.-1], and 16.9 [cm.sup.-1], respectively. The possible reason for the improvement in the ASE performance by the PC is attributed to the 3D photon localization by the microcavity effect of the PC. OCIS codes: 140.2050, 140.3280, 160.3380, 140.3380.

We have studied the acousto-optic (AO) diffraction in [Sn.sub.2] [P.sub.2][S.sub.6] crystals and found that they manifest high values of an AO figure of merit. The above crystals may therefore be used as highly efficient materials in different AO applications. OCIS codes: 160.4670, 260.1180, 050.1940, 070.1060, 230.1040.

The nonvolatile holographic storage of a near-stoichiometric LiNb[O.sub.3]:Cu:Ce crystal with green light was investigated. With an increase in composition, improved nonvolatile holographic performance was obtained. The sensitivity S' of the near-stoichiometric [LN.sub.49.57]:Cu:Ce crystal is 1 order of magnitude larger than the congruent crystal. And according to our research, Ce ions should be the deep centers of the LiNb[O.sub.3]:Cu:Ce crystal. OCIS codes: 160.3730, 190.5330, 210.2860, 090.7330.

Dispersion of the principal refractive indices of pure and [Yb.sup.3+] (20 at.%)-doped KY[(W[O.sub.4]).sub.2] crystal is obtained in the visible range of the spectrum. A comparatively strong increase of the refractive indices (0.005-0.007) was observed for the doped crystal. Temperature dependence of the principal refractive indices is measured in the temperature region of 290-690 K. Thermo-optical coefficients (TOCs) of the first dn/dt and the second (1/2)([d.sup.2]n/[dT.sup.2]) order are determined. It is found that TOCs are negative for [n.sub.p] and [n.sub.g] and positive for [n.sub.m] in both crystals. Doping increases [dn.sub.p]/dT almost two times more in comparison to that of the pure crystal, while for the other two indices TOC changes are insignificant. OCIS codes: 140.3380, 140.3580, 140.5680, 140.6810, 160.4760.

A method is described that allows for deterministic coupling of charge-tunable quantum dots to high-Q photonic crystal cavity modes. Flexible cavity design and gate-voltage-tunable trion transitions in quantum dot molecules can be used to overcome the limitations of large fluctuations and also to achieve conditional quantum dynamics of two confined spins.

The study presents a theoretical, as well as an experimental analysis of the water-steel phononic crystals with triangular and honeycomb lattices, which consist of various complete band gaps and deaf bands in them. The results of the analysis demonstrate that the symmetry reduction leads to the opening of the first complete band gaps for the honeycomb lattices, which is not found in the triangular ones.

The determination of optical constants from spectra of low-symmetry single crystals or from spectra stemming from unfavorable crystal faces by dispersion analysis is a difficult task. Besides oscillator frequencies, band positions can additionally depend on oscillator strength as well as on the relative orientation of the transition moment. Therefore the results of the analysis are highly prone to errors. We present an easy method to validate the oscillator data resulting from dispersion analysis by the comparison of measured and simulated spectra of randomly oriented polycrystalline materials. Depending on the crystallite size, either average reflectance and transmittance theory (ARTT) or average refractive index theory (ARIT) can be applied to model the spectra of polycrystalline compounds. As an alternative to ARIT, effective medium theory (EMA) can also be employed. However, since principal dielectric functions do not exist in the general triclinic case, which are needed for the application of EMA, we suggest using the eigenvalues of the dielectric tensor function instead. Our method for the verification of optical constants of single crystals is validated using monoclinic CuO as an example. OCIS codes: 260.1180, 260.3060, 300.6250.

The domain inversion in RuO2:LiNbO3 crystal wafer by the digital holographic interferometry is quantitatively studied. The crystal wafer is placed into one arm of a Mach-Zehnder-type interferometer to record a series of holograms. An unexpected phase contrast adjacent to the domain wall is measured and the influence of the external voltage on it is studied.

A simple optical method for determination of crystallographic orientations [+ or -]x, [+ or -]y, and [+ or -]z in photorefractive crystals based on light amplification via backward two-wave mixing (TWM) is presented. We consider a photorefractive Fe-doped lithium niobate crystal (LiNb[O.sub.3]:Fe) with a standard x-y-z cut as an example to illustrate the principle, manipulation, and experimental results of this method in detail. Also we see that the direction of the light amplification, namely, the direction of the nonreciprocal steady-state energy transfer, strongly depends on the direction of the grating vector with respect to the corresponding crystallographic axes mainly under the diffusion mechanism. Finally, a way of determining the sign of the charge carriers in photorefractive materials is proposed. OCIS codes: 190.7070, 190.5330, 160.5320, 120.4820.

An analysis is presented of the optical properties of photonic woodpile structures. Large superprism phenomena inside polymeric woodpile structures having a refractive index of less than n=1.6 is demonstrated.

A set of simple equations that can be used to predict the separation between the primary and secondary Laue spots as a function of sample dimensions, beam position on the sample, and incident-beam energy assuming a pseudoparallel incident beam is presented. These equations can be used to identify the peaks from the back-surface of the sample.

Extinction data sets for four centimeter-sized anisotropic crystals were collected in air with standard spindle-stage methods and submitted to a new Windows-based version of EXCALIBR, termed EXCALIBRW. EXCALIBRW solved these data sets with varying degrees of accuracy related to the external shape of the crystal: the more rounded the crystal, the more precise the results. For an olivine crystal ground into a sphere, the results were similar to those obtained for a crystal immersed in an index-matching fluid. However, even for samples bounded with growth or cleavage faces, the program determined the orientation of the optical indicatrix and 2V with an error of only 1-2[degrees]. Thus, this logical extension of spindle-stage methods is helpful: (1) to orient centimeter-size single crystals for various types of mineralogical measurements (e.g., spectroscopy or diffusion studies in which it might be undesirable to place the sample in a liquid); (2) as a non-destructive means of identifying gemstones based upon a determination of their optical class (i.e., isotropic vs. uniaxial vs. biaxial); and (3) for optical characterization by determination of 2V. In addition, the newest version of EXCALIBR is easier to use, mathematically more robust in its solution algorithms, and provides solutions for crystals in less favorable orientations than the earlier versions of EXCALIBR.

A variety of different types of light scattering, which might contribute to the transmission losses in the bulk of high-quality CaF2 monocrystals are investigated experimentally and theoretically. Scattering measured in high-quality samples are comparable with the scattering calculated from thermodynamic fluctuations, indicating that the transmission of these samples is approaching the theoretical limit.

The alternating current photoconductivity (ac-PC) of TiGaS2 layered single crystals and the spectral distribution of the photocurrent is studied at different values of light intensity, applied voltage, and temperature. A continuous distribution of traps in the energy gap is presented by the values of the photoconductivity response time, which are reported from the light intensity dependence of ac-PC.

Bidimensional photonic crystals fabrication process has been developed by using an optimized process. As a result of the high aspect ratio and of the almost cylindrical hole shape, very low radiation losses have been obtained.

Optical properties of epitaxial ZnO layers are studied in the spectral region from 1.5 to 5.4 eV using four-zone null spectroscopic ellipsometry. The experimental data is analyzed by using the model dielectric function (MDF) of ZnO based on the excitonic state and the three-dimensional M(sub 0).

The temperature dependencies of light yield found for stilbene, p-terphenyl, and anthracene single crystals provide information necessary to assess their possible use as scintillation materials in advanced applications for high and low temperatures. Index Terms--Charge traps, crystals, fast neutrons, organic scintillators.