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In the present study, pure and zinc (Zn) doped tin oxide (SnO2) thin films were grown by successive ionic layer adsorption and reaction method on the soda lime glass slides at 293 K. The prepared samples were examined to observe the impact of Zn doping on structural, morphological, electrical, and optical properties of SnO2 crystal lattice. The x-ray diffractometer (XRD), ultraviolet–visible spectrometer, energy dispersive x-ray analysis (EDAX), scanning electron microscope (SEM), Raman, x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectra measurements were conducted. And, two probe detection method was applied to find the shift in resistance values corresponding to varying temperatures. The XRD results depicted that the prepared thin films have the tetragonal rutile structure. The surface morphologies were observed to be affected by the changing concentrations of Zn doping. The EDAX evaluation exposed the existence of Zn ions in the prepared samples in addition to Sn and O. Resistivity vs temperature (r–t) measurements exhibited that all the samples possess the common 'r–t' characteristics of semiconductors. The XPS results uncovered the fact that the binding energy of SnO2 nanostructures was decreased by 0.9 eV due to the existence of Zn ions. It was also found out that the band gaps, calculated by using the absorption measurements, can be tuned from 2.02 eV to 2.50 eV by the different rates of Zn dopants in the SnO2 nanostructures. The Raman spectras of pure SnO2 and Zn doped SnO2 (Zn:SnO2) samples gave three peaks that were in the range of 490 cm−1, 580 cm−1 and 620 cm−1 for each peak separately. The PL spectra displayed that the emission intensity decreased with the introduction of impurities into the SnO2 lattice. [ABSTRACT FROM AUTHOR]

In this work, we continue our study of a new method for the detection of ionizing radiation with the potential for a dramatic improvement in coincidence time resolution (CTR) for time-of-flight positron emission tomography (ToF-PET) using the modulation of a material's optical properties instead of the scintillation mechanism. Our previous work has shown that for non-scintillation materials such as bismuth silicon oxide (BSO) and cadmium telluride (CdTe), their refractive index can be modulated by annihilation photon interactions. The ultrafast nature of this process however remains unexplored. The ionizing radiation-induced charge carriers alter the local band structure in these materials, thus changing the complex refractive index. This mechanism is routinely used at the linac coherent light source (LCLS) facility of the SLAC National Accelerator Laboratory to measure x-ray pulse arrival times with femtosecond scale resolution for photon energies between 0.5 and 10 keV. The method described here follows that example by using a frequency chirped visible continuum pulse to provide a monotonic wavelength-to-time mapping by which one can measure the time-dependent refractive index modulation. In addition, we describe an interference-based measurement setup that allows for significantly improved sensitivity while preserving a timing precision of approximately 10 fs (σ) when measuring the arrival time of below 10 keV x-ray pulses with yttrium aluminum garnet (YAG) crystal. The method is presented in the context of ToF-PET application with further discussions on the potential CTR achievable if a similar detection concept is adopted for detecting 511 keV photons. Semi-empirical analysis indicates that the predicted CTR achievable is on the order of 1 ps (FWHM). [ABSTRACT FROM AUTHOR]

The ability to cool quantum gases into the quantum degenerate realm has opened up possibilities for an extreme level of quantum-state control. In this paper, we investigate one such control protocol that demonstrates the resonant amplification of quasimomentum pairs from a Bose–Einstein condensate by the periodic modulation of the two-body s-wave scattering length. This shows a capability to selectively amplify quantum fluctuations with a predetermined momentum, where the momentum value can be spectroscopically tuned. A classical external field that excites pairs of particles with the same energy but opposite momenta is reminiscent of the coherently-driven nonlinearity in a parametric amplifier crystal in nonlinear optics. For this reason, it may be anticipated that the evolution will generate a 'squeezed' matter-wave state in the quasiparticle mode on resonance with the modulation frequency. Our model and analysis is motivated by a recent experiment by Clark et al that observed a time-of-flight pattern similar to an exploding firework (Clark et al 2017 Nature 551 356–9). Since the drive is a highly coherent process, we interpret the observed firework patterns as arising from a monotonic growth in the two-body correlation amplitude, so that the jets should contain correlated atom pairs with nearly equal and opposite momenta. We propose a potential future experiment based on applying Ramsey interferometry to experimentally probe these pair correlations. [ABSTRACT FROM AUTHOR]

Accurate spectroscopy of highly-charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the 1s Lamb shift in hydrogen-like gold (Au+78) in a storage ring through spectroscopy of the Lyman x-rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higherorderQEDeffects. [ABSTRACT FROM AUTHOR]

Analyser-based imaging (ABI) is one of the several phase-contrast x-ray imaging techniques being pursued at synchrotron radiation facilities. With advancements in compact source technology, there is a possibility that ABI will become a clinical imaging modality. This paper presents the history of ABI as it has developed from its laboratory source to synchrotron imaging. The fundamental physics of phase-contrast imaging is presented both in a general sense and specifically for ABI. The technology is dependent on the use of perfect crystal monochromator optics. The theory of the x-ray optics is developed and presented in a way that will allow optimization of the imaging for specific biomedical systems. The advancement of analytical algorithms to produce separate images of the sample absorption, refraction angle map and small-angle x-ray scattering is detailed. Several detailed applications to biomedical imaging are presented to illustrate the broad range of systems and body sites studied preclinically to date: breast, cartilage and bone, soft tissue and organs. Ultimately, the application of ABI in clinical imaging will depend partly on the availability of compact sources with sufficient x-ray intensity comparable with that of the current synchrotron environment. [ABSTRACT FROM AUTHOR]

Single crystals of Gd3Ga3Al2O12 : Ce with different codopants were successfully grown using the Czochralski technique. Optical and scintillation properties of these codoped crystals were studied in detail including absorption, photoluminescence excitation and emission, decay time and thermoluminescence. This study revealed that while boron codoping improves the scintillation light output and energy resolution and decreases self-absorption in these crystals, calcium codoping affects their properties in the opposite manner. In addition to antisite defects, the effect of room temperature trap centres on the sensitivity of these crystals to light exposure is also reported for the first time. Light sensitivity was also found to be affected with the incorporation of codopants in the lattice. The effect of annealing in oxidizing and reducing atmospheres on the scintillation and optical properties of differently codoped crystals was also investigated in detail in order to better understand the defect structure of these crystals. All these measurements together are used to explain the effect of codoping on the crystal field and defect structure of these crystals. [ABSTRACT FROM AUTHOR]

By using a pulse laser at 532.36nm as the incident light, stimulated Raman scattering (SRS) of a series of a-cut and c-cut Nd:LuxY1−xVO4 (x = 0, 0.10, 0.26, 0.41, 0.61, 0.67, 0.80) crystals is investigated. For the π-polarization (E‖c), the gain coefficient reduced as x value increased. For the σ-polarization (E‖a), the Raman gain of all of the mixed crystals is larger than the pure Nd:YVO4, and the maximum value is obtained from the Nd:Lu0.1Y0.9VO4 crystal. Such results are also supported by the measurement of spontaneous Raman scattering spectra. [ABSTRACT FROM AUTHOR]

A detailed review of the properties of optically anisotropic materials (both uniaxial and biaxial) is presented. Attention is particularly focused on the biaxial case, and some little-known features of these media are highlighted. Since the optic axes can be defined in two different ways, there are strictly speaking four optic axes in a biaxial medium rather than just two. And whereas an optic axis is normally defined as a direction in which double refraction (birefringence) does not occur, this statement is certainly incorrect for two of the four optic axes, and arguably incorrect for the other two as well. Interesting 'avoided crossing' behaviour of the index surfaces is also demonstrated. The paper provides a valuable resource for anyone preparing a course on the optical properties of crystals or involved in the design of optical systems incorporating biaxial media. [ABSTRACT FROM AUTHOR]

Continuous-wave laser properties of Nd :GYSGG crystal based on the transition from 4F3/2 to 4I13/2 are investigated. With different output couplers, single or multiple wavelength lasers operating at 1321, 1336, 1404 and 1424 nm are obtained, which provide new options in these wavelength bands. In the 1.3μm region, the maximum output power is 2.5W, corresponding to the conversion efficiency of 18.5%. In the 1.4μm region, the maximum output power at 1424 nm is 707mW, corresponding to the conversion efficiency of 6.8%. The output power and conversion efficiency can be improved with better anti-reflection coatings for the laser crystal. [ABSTRACT FROM AUTHOR]

We have investigated scattering of optical vortices via beam fanning as they propagate in photorefractive SBN crystal. The measurements show that the power decay of the vortex through the crystal depends on the order of the vortex. This decay for optical vortices is compared with that of the Gaussian laser beam and it is found to be faster than the vortices. The experimental results are explained using the dependence of the two-wave mixing or beam coupling in the photorefractive materials on the degree of coherence. Furthermore, the coherence dependence of the beam fanning has been verified with partially coherent light. [ABSTRACT FROM AUTHOR]

A resonant two-step quantum cutting process in a wavelength downconverter of Nd3+-Yb3+-codoped fluoroindogallate glasses is investigated by establishing and solving the simulated theoretical model of rate equations and power density propagation equations. Based on the optimized Nd3+ and Yb3+ concentration and the thickness of the wavelength downconverter, a total power efficiency of 128% and a total quantum efficiency of 176% have been obtained. A conversion efficiency of 18.69% for a c-Si solar cell under the modified spectrum relative to 16.46% under the normalized AM1.5G spectrum have been obtained through PC1D simulations, and the relative conversion efficiency reaches 1.14. Our results and techniques provide a framework for investigating and optimizing rare-earth-doped wavelength downconverters, potentially enabling a crystalline Si solar cell with an efficiency improvement. [ABSTRACT FROM AUTHOR]

We have investigated the correlation between the various plasma-enhanced chemical vapour deposition (PECVD) process parameters on the structural, compositional and optical properties of SiNx layers. The investigated process parameters are gas composition, radio frequency power and its frequency and deposition temperature. We also investigated SiON and ammonia-free SiNx layers. Refractive index, thickness, residual stress, structure and composition of the dielectric layers were determined using interferometry, wafer bowing, scanning electron microscopy, Fourier transform infra-red and secondary ion mass spectrometry measurements. SiNx films can be deposited to be almost stress-free with relatively low concentration of hydrogen (10 to 19% of atomic H). SiNx layers have the potential to cover a wide range of refractive indices (1.8-2.1) with possible extension down to 1.40 through various SiON layers. [ABSTRACT FROM AUTHOR]

Currently, optical cross-connects working on wavelength division multiplexing systems are based on optical fiber delay lines buffering. We designed and analyzed a novel photonic crystal optical memory, which replaces the fiber delay lines of the current optical cross-connect buffer. Optical buffering systems based on random photonic crystal optical memory have similar behavior to the electronic buffering systems based on electronic RAM memory. In this paper, we show that OXCs working with optical buffering based on random photonic crystal optical memories provides better performance than the current optical cross-connects. [ABSTRACT FROM AUTHOR]

The crystal structural parameters of Nd3+-doped rare earth orthotantalate GdxLu1-xTaO4 (x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction, and its emission and excitation spectra at 77 K are analysed. The relativistic model of ab initio self-consistent DV-Xα method, which is applied to the cluster NdO8 in GdxLu1-xTaO4, and the effective Hamiltonian model are used to investigate its spin-orbit and crystal-field parameters. The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm-1. According to the crystal-field calculations, 96 levels of Nd3+ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd3+:YAlO³. The results indicate that the free-ion parameters are similar to those of the Nd3+ in GdxLu1-xTaO4 and YAlO³ hosts, and the crystal-field interaction of Nd3+ in GdxLu1-xTaO4 is stronger than that in YAlO³. [ABSTRACT FROM AUTHOR]

We have designed and fabricated two types of two-port resonant tunneling filters with a triangular air-hole lattice in two-dimensional photonic crystal slabs. In order to improve the filtering efficiency, a feedback method is introduced by closing the waveguide. It is found that the relative position between the closed waveguide boundary and the resonator has an important impact on the dropping efficiency. Based on our analyses, two different types of filters are designed. The transmission spectra and scattering-light far-field patterns are measured, which agree well with theoretical prediction. In addition, the resonant filters are highly sensitive to the size of the resonant cavities, which are useful for practical applications. [ABSTRACT FROM AUTHOR]

A new method to enhance the output efficiency of the multi-frequency second harmonic generation process has been presented in the one-dimensional aperiodic optical superlattice by sandwiching linear layers between nonlinear media. The linear and nonlinear domain arrangements of aperiodic crystal are designed using the simulated annealing optimization method. The dependence of the output efficiency of second harmonic generation on the linear length has been investigated in detail; the most optimized structure being suggested. A comparison between pure nonlinear and linear-nonlinear layered structures is presented which shows an increasing amount of the output efficiency in the presence of linear layers for the nonlinear aperiodic crystals. [ABSTRACT FROM AUTHOR]

The imaging performance of active matrix flat-panel imagers designed for megavoltage imaging (MV AMFPIs) is severely constrained by relatively low x-ray detection efficiency, which leads to a detective quantum efficiency (DQE) of only ∼1%. Previous theoretical and empirical studies by our group have demonstrated the potential for addressing this constraint through the utilization of thick, two-dimensional, segmented scintillators with optically isolated crystals. However, this strategy is constrained by the degradation of high-frequency DQE resulting from spatial resolution loss at locations away from the central beam axis due to oblique incidence of radiation. To address this challenge, segmented scintillators constructed so that the crystals are individually focused toward the radiation source are proposed and theoretically investigated. The study was performed using Monte Carlo simulations of radiation transport to examine the modulation transfer function and DQE of focused segmented scintillators with thicknesses ranging from 5 to 60 mm. The results demonstrate that, independent of scintillator thickness, the introduction of focusing largely restores spatial resolution and DQE performance otherwise lost in thick, unfocused segmented scintillators. For the case of a 60 mm thick BGO scintillator and at a location 20 cm off the central beam axis, use of focusing improves DQE by up to a factor of ∼130 at non-zero spatial frequencies. The results also indicate relatively robust tolerance of such scintillators to positional displacements, of up to 10 cm in the source-to-detector direction and 2 cm in the lateral direction, from their optimal focusing position, which could potentially enhance practical clinical use of focused segmented scintillators in MV AMFPIs. [ABSTRACT FROM AUTHOR]

Using a photonic crystal fiber with a zero dispersion wavelength of the fundamental mode at 780 nm designed and fabricated in our lab, the ultraviolet and mid-infrared continua are generated by cross-phase modulation between red-shift solitons and blue-shift dispersive waves. The dependences of continuum on the pump power and wavelength are investigated. With the pump working at 820 nm, when the pump power increases from 300 to 500 mW, the bandwidths of ultraviolet and mid-infrared continua change from 80 to 140 nm and 100 to 200 nm, respectively. The wavelength of ultraviolet continuum is below 246 nm, and the wavelength of mid-infrared continuum exceeds 2500 nm. Moreover, the influences of pump power on wavelength and conversion efficiency of different parts of continua are also demonstrated. [ABSTRACT FROM AUTHOR]

We investigate the optical Kerr effect of SrTiO3 (STO) crystal, of which the nonlinear response time was measured to be less than 200 fs, while the nonlinear refractive index is estimated to be 2.16 × 10-15 cm2/W. Using the optical Kerr gate (OKG) technique with an STO crystal as the Kerr medium, we obtain narrow-bandwidth and symmetric gated spectra from a supercontinuum generated in distilled water by a femtosecond laser. The experimental results show superiority compared with the gated spectra obtained using OKG with CS2 as the Kerr medium, demonstrating that STO crystal is a promising OKG medium. [ABSTRACT FROM AUTHOR]

In this paper, the temperature dependence of birefringence in polarization maintaining photonic crystal fibres (PMPCFs) is investigated theoretically and experimentally. Utilizing the structural parameters of the PM-PCF samples in the experiment, two effects leading to the birefringence variation under different temperatures are analysed, which are the thermal expansion of silica material and the refractive index variation due to the temperature variation. The actual birefringence variation of the PM-PCF is the combination of the two effects, which is in the order of 10-9 K-1 for both fibre samples. Calculation results also show that the influence of refractive index variation is the dominant contribution, which determines the tendency of the fibre birefringence variation with varying temperature. Then, the birefringence beat lengths of the two fibre samples are measured under the temperature, which varies from -40 °C to 80 °C. A traditional PANDA-type polarization maintaining fibre (PMF) is also measured in the same way for comparison. The experimental results indicate that the birefringence variation of the PM-PCF due to temperature variation is far smaller than that of the traditional PMF, which agrees with the theoretical analysis. The ultra-low temperature dependence of the birefringence in the PM-PCF has great potential applications in temperature-insensitive fibre interferometers, fibre sensors, and fibre gyroscopes. [ABSTRACT FROM AUTHOR]

The electronic structures and the optical properties of N-doped β-Ga2O3 with different N-doping concentrations are studied using the first-principles method. We find that the N substituting O(1) atom is the most stable structure for the smallest formation energy. After N-doping, the charge density distribution significantly changes, and the acceptor impurity level is introduced above the valence band and intersects with the Fermi level. The impurity absorption edges appear to shift toward longer wavelengths with an increase in N-doping concentration. The complex refractive index shows metallic characteristics in the N-doped β-Ga2O3. [ABSTRACT FROM AUTHOR]

Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied. An improved plane expansion method combined with the supercell technique is used to calculate the band gaps and the pressure distribution at the defect position. The sonic pressure of defect modes shows that the waves are localized at or near the defect. As the fling fraction increases, more defect modes appear in the band gaps. [ABSTRACT FROM AUTHOR]

A novel optical beam splitter constructed on the basis of photonic crystal (PC) with hybrid lattices is proposed in this paper. The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams. Triangular-lattice graded-index PCs are combined for focusing each branch. Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design. The waveguide is unnecessary in the design. Thus the device has functions of both splitting and focusing beams. Size of the divided beam at site of full-width at half-maximum is of the order of λ/2. The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process. [ABSTRACT FROM AUTHOR]

A new nanolaser concept using silicon quantum dots (QDs) is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional (2D) photonic crystal can be used to select the model in the nanolaser. [ABSTRACT FROM AUTHOR]

The electronic structures and the optical properties of N-doped β-Ga2O3 with different N-doping concentrations are studied using the first-principles method. We find that the N substituting O(1) atom is the most stable structure for the smallest formation energy. After N-doping, the charge density distribution significantly changes, and the acceptor impurity level is introduced above the valence band and intersects with the Fermi level. The impurity absorption edges appear to shift toward longer wavelengths with an increase in N-doping concentration. The complex refractive index shows metallic characteristics in the N-doped β-Ga2O3. [ABSTRACT FROM AUTHOR]

The ab-plane optical conductivity of two single crystals belonging to the chalcogenide family, FeTe0.91 and FeTe0.7Se0.3, has been studied in the normal phase between 16 and 450 K. Several differences with respect to both conventional metals and other exotic superconductors, like the cuprates, have been found both in the undoped and in the doped material. In the former compound, the transition to an antiferromagnetic (AF) state at 67 K causes the opening of a pseudogap at &ohgr;0 =270 ± 25 cm1 and a decrease by 70% in the free carrier density, accompanied by a strong reduction in the carrier scattering rate. The multiband analysis of the low-energy optical conductivity requires at least two Drude components, in addition to a mid-infrared band. Above 350 K, a transfer of spectral weight between those terms produces a cusp anomaly in the spectral weight. This indicates a well-defined transition, rather than a crossover, to a less-metallic regime. Finally, in FeTe0.7Se0.3 the far-infrared conductivity decreases with T, in agreement with the semiconducting behavior of the resistivity, and precursor phenomena of superconductivity appear above Tc. [ABSTRACT FROM AUTHOR]

The ab-plane optical conductivity of two single crystals belonging to the chalcogenide family, FeTe0.91 and FeTe0.7Se0.3, has been studied in the normal phase between 16 and 450 K. Several differences with respect to both conventional metals and other exotic superconductors, like the cuprates, have been found both in the undoped and in the doped material. In the former compound, the transition to an antiferromagnetic (AF) state at 67 K causes the opening of a pseudogap at &ohgr;0 =270 ± 25 cm1 and a decrease by 70% in the free carrier density, accompanied by a strong reduction in the carrier scattering rate. The multiband analysis of the low-energy optical conductivity requires at least two Drude components, in addition to a mid-infrared band. Above 350 K, a transfer of spectral weight between those terms produces a cusp anomaly in the spectral weight. This indicates a well-defined transition, rather than a crossover, to a less-metallic regime. Finally, in FeTe0.7Se0.3 the far-infrared conductivity decreases with T, in agreement with the semiconducting behavior of the resistivity, and precursor phenomena of superconductivity appear above Tc. [ABSTRACT FROM AUTHOR]

A new pentagon polarization maintaining photonic crystal fibre with low nonlinearity is introduced. The full vector finite element method was used to investigate the distribution and the effective area of modal field, the nonlinear properties, the effective indices of two orthogonal polarization modes and the birefringence of the new PM-PCF effectively. It is found that the birefringence of the new polarization maintaining photonic crystal fibre can easily achieve the order of 10-4, and it can obtain higher birefringence, larger effectively mode-field area and lower nonlinearity than traditional hexagonal polarization maintaining photonic crystal fibre with the same hole pitch, same hole diameter, and same ring number. It is important for sensing and communication applications, especially has potential application for fibre optical gyroscope. [ABSTRACT FROM AUTHOR]

We experimentally study the generation and storage of double slow light pulses in a Pr3+:Y2SiO5 crystal. Under electromagnetically induced transparency, a single signal pulse is stored in the spin coherence of the crystal. By simultaneously switching on two control fields to recall the stored information, the spin coherence is converted into two slow light pulses with distinct frequencies. Furthermore, the storage and controlled retrieval of double slow light pulses are obtained by manipulating the control fields. This study of double slow light pulses may have practical applications in information processing and all-optical networks. [ABSTRACT FROM AUTHOR]

A polarization beam splitter based on a self-collimation Michelson interferometer (SMI) in a hole-type silicon photonic crystal is proposed and numerically demonstrated. Utilizing the polarization dependence of the transmission spectra of the SMI and polarization peak matching method, the SMI can work as a polarization beam splitter (PBS) by selecting an appropriate path length difference in the structure. Based on its novel polarization beam splitting mechanics, the polarization extinction ratios (PERs) for TM and TE modes are as high as 18.4 dB and 24.3 dB, respectively. Since its dimensions are only several operating wavelengths, the PBS may have practical applications in photonic integrated circuits. [ABSTRACT FROM AUTHOR]

The extreme versatility of the internal conical refraction in biaxial crystals in the transformation of Gaussian laser beams is demonstrated and discussed. By means of simple variations in the focusing and polarization of the input beam, various beam configurations like Bessel-Gauss, Hermite-Gauss, Laguerre-Gauss, and others are shown to be produced from a lowest-order Gaussian beam passed through a biaxial crystal along one of its optical axes. Further transformations of the beam profile and formation of more complex light patterns were obtained in a cascaded scheme, when the beam was passed consecutively through two crystals. These observations, together with the known ability of conical refraction to form a variety of other complex light structures, demonstrate the unique properties of the effect in manipulations with the amplitude, phase, and polarization of light beams. [ABSTRACT FROM AUTHOR]

UV radiation in the spectral region beyond ∼320 nm is strongly absorbed by lithium niobate single crystals. The strong absorption and the consequent localized heating of the crystal triggers physical processes which can affect the state of the material not only by changing the refractive index, as shown in the past, but also by changing its ferroelectric disposition. UV laser irradiation of the polar surfaces in particular can induce or inhibit the inversion of ferroelectric domains. A summary of these UV light induced effects and their utility in the microstructuring of this very important optical ferroelectric crystal will be presented here. [ABSTRACT FROM AUTHOR]

The nonlinear properties of quasi-periodic photonic crystals based on the Thue-Morse sequence are investigated. The intrinsic spatial asymmetry of these one-dimensional structures for odd generation numbers results in bistability thresholds, which are sensitive to the propagation direction. Along with resonances of perfect transmission, this feature allows us to achieve strongly non-reciprocal propagation and to create an all-optical diode. The salient qualitative features of such optical diode action are readily explained through a simple coupled resonator model. The efficiency of a passive scheme that does not necessitate an additional short pump signal is compared to an active scheme where such a signal is required. [ABSTRACT FROM AUTHOR]

Nanocomposites of poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene]-zinc selenide (MOPPV-ZnSe) are synthesized by mixing the polymerization of 1,4-bis (chloromethyl)-2-methoxy-5-octoxy-benzene in the presence of ZnSe quantum dots. The resulting MOPPV-ZnSe nanocomposites possess a well-defined interfacial contact, thus significantly promoting the dispersion of ZnSe within the MOPPV matrix and facilitating the electronic interaction between these two components. Raman and UV-visible absorption spectra are influenced by the incorporation of ZnSe nanocrystals. High-resolution transmission electron microscopic and tapping-mode atomic force microscopic results show clearly the evidence for phase-segregated networks of ZnSe nanocrystals, which provide a large area of interface for charge separation to occur. Steady-state spectra of MOPPV-ZnSe nanocomposites are markedly quenched by the introduction of intimate polymer/ZnSe junctions. Time-resolved photoluminescence measurements show that the lifetime decays quickly, which further confirms the occurrence of charge transfer in MOPPV-ZnSe nanocomposites. [ABSTRACT FROM AUTHOR]

We design three kinds of photonic crystal fibres (PCF) with two zero-dispersion wavelengths (ZDWs) using the improved full vector index method (FVIM) and finite-difference frequency domain (FDFD) techniques. Based on these designed fibres, the effect of fibre structure, pump power and wavelength on the modulation instability (MI) gain in the anomalous dispersion region close to the second ZDW of the PCFs is comprehensively analysed in this paper. The analytical results show that an optimal MI gain can be obtained when the optimal pump wavelength (1530 nm) is slightly shorter than the second ZDW (1538 nm) and the optimal pump power is 250 W. Importantly, the total MI gain bandwidth has been increased to 260 nm for the first time, so far as we know, for an optimally-designed fibre with L = 1.4 nm and d/L = 0.676, and the gain profile became much smoother. The optimal pump wavelength relies on the second ZDW of the PCF whereas the optimal pump power depends on the corporate operation of the optimal fibre structure and optimal pump wavelength, which is important in designing the most appropriate PCF to attain higher broadband and gain amplification. [ABSTRACT FROM AUTHOR]

By means of the theory of electromagnetic wave propagation and transfer matrix method, this paper investigates the band rules for the frequency spectra of three kinds of one-dimensional (1D) aperiodic photonic crystals (PCs), generalized Fibonacci GF(p, 1), GF(1,2), and Thue-Morse (TM) PCs, with negative refractive index (NRI) materials. It is found that all of these PCs can open a broad zero-n gap, TM PC possesses the largest zero-n gap, and with the increase of p, the width of the zero-n gap for GF(p, 1) PC becomes smaller. This characteristic is caused by the symmetry of the system and the open position of the zero-n gap. It is found that for GF(p, 1) PCs, the possible limit zero-n gaps open at lower frequencies with the increase of p, but for GF(1,2) and TM PCs, their limit zero-n gaps open at the same frequency. Additionally, for the three bottom-bands, we find the interesting perfect self-similarities of the evolution structures with the increase of generation, and obtain the corresponding subband-number formulae. Based on 11 types of evolving manners Qi (i = 1, 2, ..., 11) one can plot out the detailed evolution structures of the three kinds of aperiodic PCs for any generation. [ABSTRACT FROM AUTHOR]

This paper reports on a comparative study of the spatial distributions of the electrical, optical, and structural properties in an AlGaN/GaN heterostructure. Edge dislocation density in the GaN template layer is shown to decrease in the regions of the wafer where the heterostructure sheet resistance increases and the GaN photoluminescence band-edge energy peak shifts to a high wavelength. This phenomenon is found to be attributed to the local compressive strain surrounding edge dislocation, which will generate a local piezoelectric polarization field in the GaN layer in the opposite direction to the piezoelectric polarization field in the AlGaN layer and thus help to increase the two-dimensional electron gas concentration. [ABSTRACT FROM AUTHOR]

Three-dimensional photonic crystal (PC) heterostructures with high quality are fabricated by using a pressure controlled isothermal heating vertical deposition technique. The formed heterostructures have higher quality, such as deeper band gaps and sharper band edges, than the heterostructures reported so far. Such a significant improvement in quality is due to the introduction of a thin TiO2 buffer layer between the two constitutional PCs. It is revealed that the disorder caused by lattice mismatch is successfully removed if the buffer layer is used once. As a result, the formed heterostructures possess the main features in the band gap of constitutional PCs. The crucial role of the thin buffer layer is also verified by numerical simulations based on the finite-difference time-domain technique. [ABSTRACT FROM AUTHOR]

The luminescence properties of orange-yellow-emitting Eu[sup2+]-activated Sr[sub3]SiO[sub5] were optimized for application to blue/near ultraviolet (n-UV) light-emitting diodes (LEDs). Sr[sub2.97]SiO[sub5]:Eu[sup2+][sub0.03] showed strong orange-yellow emission peaking at -580 nm under blue and n-UV light of 450 and 405 nm, respectively, and the effects of Ca and Ba substitutions into Sr[sup2+] sites on the emission band change were investigated. For the substitution of Ca, Ca[sub3]SiO[sub5]:Eu[sup2+] showed no orange-yellow emission under blue light due to the different crystal structures of Ca[sub3]SiO[sub5] (monoclinic) and Sr[sub3]SiO[sub5] (tetragonal). The redshift and blueshift of the emission band of (Sr[sub1-x]Ba[subx])[sub3]SiO[sub5]:Eu[sup2+] were explained by the competition between crystal field effect and Nephelauxetic effect. The 460 nm-emitting blue LED-pumped white LED with Sr[sub3]SiO[sub5]:Eu[sup2+] or a mixture of Sr[sub3]SiO[sub5]:Eu[sup2+] and green phosphor (Ba[sub2]SiO[sub4]:Eu[sup2+]) were fabricated and they showed color coordinates of (0.343, 0.281) and (0.349, 0.339), respectively. [ABSTRACT FROM AUTHOR]

Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied. [ABSTRACT FROM AUTHOR]

We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as [?]-negative materials (ENMs) with [?] 0, or m-negative materials (MNMs) with [?] > 0 and m < 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material (ENM or MNM) under some restrictions. [ABSTRACT FROM AUTHOR]

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric (TE) guided mode and transverse-magnetic (TM) guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguides is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.5mm. A finite-difference time-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB. [ABSTRACT FROM AUTHOR]

We identify a newly found Z(4430) with the first radial excitation of the tetraquark basic supermultiplet to which X(3872) and X(3876) belong. Experimental predictions following from this hypothesis are spelled out. [ABSTRACT FROM AUTHOR]

We present a continuous-wave dual-crystal optical parametric oscillator that generates signal waves of about 1.4μm wavelength with a tunable difference frequency Δv between 0.64 and 5.3 THz. A model of the parametric gain in such a system indicates that the lowest reachable value for Δv depends on the refractive index dispersion of the nonlinear material used. As a proof of principle, we demonstrate the generation of terahertz radiation by photomixing the signal waves. Frequencies between 0.64 and 0.85 THz are created and detected coherently with ion-irradiated InGaAs interdigitated photomixers. [ABSTRACT FROM AUTHOR]

Cadmium dizinc diborate (CdZn2B2O6) single crystals have been grown for the first time. The crystal structure of CdZn2B2O6 is the same as that of the Cd3Zn3B4O12. The x-ray diffraction, infrared and Raman spectra, differential scanning calorimetry analysis and density indicate that the physical and chemical properties of both crystals are very similar. Especially, the nonlinear optical coefficients of CdZn2B2O6 and Cd3Zn3B4O12 crystals are 2.6 and 2.4 times as large as that of KH2PO4 crystal respectively. Chemical etching experiments indicated that these crystals are very stable in neutral solution and not hygroscopic in air at room temperature. [ABSTRACT FROM AUTHOR]

Single-crystalline layered SnO2 microrods were synthesized by a simple tin-water reaction at 900 degC. The structural and optical properties of the sample were characterized by x-ray powder diffraction, energy-dispersive x-ray spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, Raman scattering and photoluminescence (PL) spectroscopy. High resolution transmission electron microscopy studies and selected area electron diffraction patterns revealed that the layered SnO2 microrods are single crystalline and their growth direction is along [1 1 0]. The growth mechanism of the microrods was proposed based on SEM, TEM characterization and thermodynamic analysis. It is deduced that the layered microrods grow by the stacking of SnO2 sheets with a (1 1 0) surface in a vapour-liquid-solid process. Three emission peaks at 523, 569 and 626 nm were detected in room-temperature PL measurements. [ABSTRACT FROM AUTHOR]

This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. [ABSTRACT FROM AUTHOR]

Double waveguides were produced in potassium titanyl phosphate (KTiOPO4or KTP) by ion exchange in pure RbNO3at 340?°C for 45?min, and subsequently ion implantation with 500?keV O ions at a dose of 1 × 1015ions?cm?2. By the prism-coupling method the guided mode spectra as well as the refractive index profiles of the ion-exchanged sample were determined. The relative value of the refractive index distribution of the ion implanted KTP sample in the zdirection was simulated, which indicates the formation of double waveguides. The field pattern of the propagation light in the waveguide was collected and studied by the end-coupling method. The near-field pattern of two planar operating waveguides was observed, one upon the other. The irradiation damage as well as the Rb distribution was analysed by means of the Rutherford backscattering spectrometry technique. [ABSTRACT FROM AUTHOR]

We report a temperature tuned mid-IR generating system ranging from 5 to 12μm by difference frequency mixing of output waves from two optical parametric oscillators (OPOs) in a silver gallium sulfide (AgGaS2) crystal. One of the OPOs generate signal wave of 1.6μm, while the other produced tunable radiation from 1.846 to 2.353μm. The AgGaS2 crystal is temperature tuned to allow phasematching for tunable output from 5 to 12μm. [ABSTRACT FROM AUTHOR]