Optical Materials Express

Published by Optical Society of America
Online ISSN: 2159-3930
Publications
Article
A hybrid optical nanostructure of plasmon-coupled SQDs was developed for photonic applications. The coupling distances between the mono-layers of Au nanoparticles with a surface concentration of ~9.18 × 10-4 nm-2 and CdSe/ZnS SQDs with that of ~3.7 × 10-3 nm-2 were controlled by PMMA plasma etching. Time-resolved spectroscopy of plasmon-coupled SQDs revealed a strong shortening of the longest lifetime and ~9-fold PL enhancement. Polarization-resolved PL spectroscopy displayed linear polarization and depolarization at near- and far-field plasmon-coupling, respectively. The physical origin of PL enhancement could be attributable to both the large local field enhancement and the fast resonant energy transfer.
 
Conference Paper
The optimal design of liquid crystal infiltrated waveguide with distributed Bragger reflector is realized to confine the optical waves. The bandgap structure and propagation behavior of visible light is calculated to investigate propagation loss, polarization dependence transmission and wavelength tuning property.
 
Article
As alternatives to conventional metals, new plasmonic materials offer many advantages in the rapidly growing fields of plasmonics and metamaterials. These advantages include low intrinsic loss, semiconductor-based design, compatibility with standard nanofabrication processes, tunability, and others. Transparent conducting oxides such as Al:ZnO, Ga:ZnO and indium-tin-oxide (ITO) enable many high-performance metamaterial devices operating in the near-IR. Transition-metal nitrides such as TiN or ZrN can be substitutes for conventional metals in the visible frequencies. In this paper we provide the details of fabrication and characterization of these new materials and discuss their suitability for a number of metamaterial and plasmonic applications.
 
Summary of the experimental data for n I 2,Kerr-values from the literature corresponding to the c 11 nonlinear susceptibility coefficient (n I 2,Kerr = 3c 11 /4n 2 1 ε 0 c). The plotted values are the ones reported in Sec. 4.2, i.e. the data values do not necessarily correspond to the ones reported in the literature. References: Tan et al. 1993: [13]; Hache et al. 1995: [14]; DeSalvo et al. 1996 [16]; Li et al. 1997 [18]; Li et al. 2001 [19]; Ganeev et al. 2003 [20]; Moses et al. 2007 [15]. The theoretically predicted electronic nonlinearity is calculated with the 2-band model [24]. The average value curve was calculated through a weighted mean of the Miller's delta from all data, except the UV measurements below 400 nm, and the shaded areas denoted "σ " and "2σ " represent one and two standard deviations, respectively.
Article
We study the anisotropic nature of the Kerr nonlinear response in a beta-barium borate (\beta-BaB2O4, BBO) nonlinear crystal. The focus is on determining the relevant $\chi^{(3)}$ cubic tensor components that affect interaction of type I cascaded second-harmonic generation. Various experiments in the literature are analyzed and we correct the data from some of the experiments for contributions from cascading as well as for updated material parameters. We find that the Kerr nonlinear tensor component responsible for self-phase modulation in cascading is considerably larger than what has been used to date. We evaluate the impact of using such a cubic anisotropic response in ultrafast cascading experiments.
 
Article
Self-assembled monolayers (SAMs) of organic molecules are widely employed in surface chemistry and biology, and serve as ultra-fine lithographic resists. Due to their small thickness of only a few nanometers, the analysis of patterned monolayer surfaces using conventional methods requires thorough point-by-point scanning using complicated equipment. In the work reported herein, patterned monolayers are simply and directly observed using a bright-field optical microscope. The monolayers modify the spectral reflectivity pattern of a silica-on-silicon thin film, and introduce a contrast between bare and monolayer-coated regions of the substrate. The method can also distinguish between regions of single-layer and bi-layer coatings. The observations are supported by calculations, and by control experiments using atomic force microscopy, scanning Raman spectrometry and scanning reflection spectrometry. The results are useful for electro-optic devices, selective wafer-bonding protocols and lab-on-a-chip test systems. We show here that chemical reactions leading to the formation of a bi-layer of SAMs correspond to an optical contrast visible to the naked eye, enabling such detection to provide a simple, yet effective differentiation between monolayers and adsorbed analytes with possible applications for chemical and/or biological sensing.
 
Topography of the grating inscribed on the spin-coated negative photoresist layer (with a pulse energy of 15 mJ) and its corresponding cross section (b). 
Topography of the grating after the Ar ion etching process (a) and its corresponding cross section (b). 
Topography of the final grating inscribed on the Au surface (a) and its corresponding cross section (b). 
Article
Metallic gratings were fabricated using high energy laser interference lithography with a frequency tripled Nd:YAG nanosecond laser. The grating structures were first recorded in a photosensitive layer and afterwards transferred to an Au film. High quality Au gratings with a period of 770 nm and peak-to-valley heights of 20-60 nm exhibiting plasmonic resonance response were successfully designed, fabricated and characterized.
 
Article
First-principle study of bismuth-related oxygen-deficient centers ($=$Bi$\cdots$Ge$\equiv$, $=$Bi$\cdots$Si$\equiv$, and $=$Bi$\cdots$Bi$=$ oxygen vacancies) in Bi$_2$O$_3$-GeO$_2$, Bi$_2$O$_3$-SiO$_2$, Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$, and Bi$_2$O$_3$-Al$_2$O$_3$-SiO$_2$ hosts is performed. A comparison of calculated spectral properties of the centers with the experimental data on luminescence emission and excitation spectra suggests that luminescence in the 1.2-1.3 $\mu$m and 1.8-3.0 $\mu$m ranges in Bi$_2$O$_3$-GeO$_2$ glasses and crystals is likely caused by $=$Bi$\cdots$Ge$\equiv$ and $=$Bi$\cdots$Bi$=$ centers, respectively, and the luminescence near 1.1 $\mu$m in Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$ glasses and crystals may be caused by $=$Bi$\cdots$Ge$\equiv$ center with (AlO$_4$)$^-$ center in the second coordination shell of Ge atom.
 
Cross-section images of GOI material. (a) Cross-section TEM image of a representative GOI stack. (b) Cross-section high-resolution TEM image of Ge/SiO2 bonding interface (inset: selective area diffraction (SAD) pattern indicating high-quality, single-crystal Ge).  
Article
We present a method to fabricate tensile-strained germanium-on-insulator (GOI) substrates using heteroepitaxy and layer transfer techniques. The motivation is to obtain a high-quality wafer-scale GOI platform suitable for silicon-compatible optoelectronic device fabrication. Crystal quality is assessed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy. A biaxial tensile film strain of 0.16% is verified by XRD. Suitability for device manufacturing is demonstrated through fabrication and characterization of metal-semiconductor-metal photodetectors that exhibit photoresponse beyond 1.55 {\mu}m. The substrate fabrication process is compatible with complementary metal-oxide-semiconductor manufacturing and represents a potential route to wafer-scale integration of silicon-compatible optoelectronics.
 
Setup geometry. The liquid crystal (LC) fills the slab of thickness L , it is sandwiched between two silica layers of thickness d and it hosts silver nanoparticles (Ag) of radius r . The externally applied electric field E S , inclined at an angle φ with the z -axis, aligns the liquid crystal molecules in the direction of the unit vector n (parallel to the electric field). The vacuum electromagnetic plane wave is made to impinge orthogonally onto the device interface. 
(a) Plot of the transmissivity of the device reported in Fig.1 (evaluated using the effective medium model for the LC/nanoparticels mixture) as a function of the vacuum wavelength of the incident radiation and the angle φ . (b) Level plot of the transmissivity of panel (a) restricted to region II where the effective medium has indefinite permittivity. 
(a) Device transmissivity T as a function of the vacuum wavelength λ and the angle φ evaluated through full wave simulations. (b) Transmissivity T (φ) extracted from panel (a) at three different wavelengths where the mixture displays indefinite character.
Article
We predict that a liquid crystal/silver nanoparticles mixture can be designed so that, in a frequency range, its effective ordinary and extraordinary permittivities have real parts of different signs. We exploit this result to design a nano-photonic device obtained by sandwiching a few hundred nanometer thick slab of the proposed mixture between two silica layers. By resorting to full-wave simulations, we show that, by varying the direction of an externally applied electric field, the device can be used as an optical modulator since its transmissivity can be switched between 0.02 and 0.4 at a wavelength close to the frequency range where the medium is indefinite. The device functionality physically stems from the fact the orientation of the hyperbola characterizing extraordinary waves within the indefinite medium follows the applied electric field direction and therefore, if the hyperbola asymptote is nearly normal to the slab, full switch between evanescent and homogeneous propagating waves can be achieved within the medium.
 
Numerical simulation of soliton compression in a 15 mm long LiInS 2 bulk crystal. (a) Power spectral density at 0, 10 and 15 mm. (b) Temporal intensity at 0 and 10 mm. Input pulse: 50 fs FWHM and 50 GW/cm 2 centered at λ 1 = 3.0 µm. The simulation was done with a plane-wave SEWA model and the PSD was calculated assuming a ≃ 0.5 mm spot size, corresponding to an input pulse energy of around 6 µJ. 
Numerical simulation of supercontinuum generation in a 15 mm long LiInS 2 bulk crystal. (a) Power spectral density of the output pulses (thick lines) for input wavelengths ranging from 2.0-4.0 µm (thin lines). All input pulses have the same input intensity 300 GW/cm 2 and pulse duration 200 fs FWHM. The simulations were done with a plane-wave SEWA model and the PSD was calculated assuming a ≃ 0.5 mm spot size, corresponding to an input pulse energy of around 0.2 mJ. The input pulses were seeded with noise (one photon per mode) and the PSDs are averaged over 50 realizations. Each PSD displays the combined FW and SH spectral content. (b) Single realization at 2.8 µm showing the pulse evolution along the crystal for the FW and SH intensities in time and the PSDs in frequency domain. 
Article
We discuss a novel method for generating octave-spanning supercontinua and few-cycle pulses in the important mid-IR wavelength range. The technique relies on strongly phase-mismatched cascaded second-harmonic generation (SHG) in mid-IR nonlinear frequency conversion crystals. Importantly we here investigate the so-called noncritical SHG case, where no phase matching can be achieved but as a compensation the largest quadratic nonlinearities are exploited. A self-defocusing temporal soliton can be excited if the cascading nonlinearity is larger than the competing material self-focusing nonlinearity, and we define a suitable figure of merit to screen a wide range of mid-IR dielectric and semiconductor materials with large effective second-order nonlinearities $d_{\rm eff}$. The best candidates have simultaneously a large bandgap and a large $d_{\rm eff}$. We show selected realistic numerical examples using one of the promising crystals: in one case soliton pulse compression from 50 fs to 15 fs (1.5 cycles) at $3.0\mic$ is achieved, and at the same time a 3-cycle dispersive wave at $5.0\mic$ is formed that can be isolated using a long-pass filter. In another example we show that extremely broadband supercontinua can form spanning the near-IR to the end of the mid-IR (nearly 4 octaves).
 
Left: cross-section of WG structure with seven rings of tracks with different diameters. Right: ellipsoid of refractive indices of z -cut LiNbO 3 crystal. 
Left: track diameter versus cladding layer number for a seven-ring WG structure with different growth rate parameters p . Right: Cross-sections of seven-ring structures for (from top to bottom and left to right) p = 0 (uniform structure), 0 . 2 , 1 , 5. Other parameters are: pitch a = 2 . 5 μ m, D max = 2 . 4 μ m, D min = 1 μ m. 
Real parts of effective RIs as a function of wavelength for the PWM computed modes of a WG structure with seven rings of tracks. 
Article
We present a practical approach to the numerical optimisation of the guiding properties of buried microstructured waveguides, which can be fabricated in a z-cut lithium niobate (LiNbO3) crystal by the method of direct femtosecond laser inscription. We demonstrate the possibility to extend the spectral range of low-loss operation of the waveguide into the mid-infrared region beyond 3{\mu}m.
 
Article
Three-dimensional direct laser writing has become a well established, versatile, widespread, and even readily commercially available "workhorse" of nano- and micro-technology. However, its lateral and axial spatial resolution is inherently governed by Abbe's diffraction limitation - analogous to optical microscopy. In microscopy, stimulated-emission-depletion approaches have lately circumvented Abbe's barrier and lateral resolutions down to 5.6 nm using visible light have been achieved. In this paper, after very briefly reviewing our previous efforts with respect to translating this success in optical microscopy to optical lithography, we present our latest results regarding resolution improvement in the lateral as well as in the much more relevant axial direction. The structures presented in this paper set a new resolution-benchmark for next-generation direct-laser-writing optical lithography. In particular, we break the lateral and the axial Abbe criterion for the first time.
 
Article
Carrier dynamics in single-layer graphene grown by chemical vapor deposition (CVD) is studied using spatially and temporally resolved pump-probe spectroscopy by measuring both differential transmission and differential reflection. By studying the expansion of a Gaussian spatial profile of carriers excited by a 1500-nm pump pulse with a 1761-nm probe pulse, we observe a diffusion of hot carriers of 5500 square centimeter per second. We also observe that the expansion of the carrier density profile decreases to a slow rate within 1 ps, which is unexpected. Furthermore, by using an 810-nm probe pulse we observe that both the differential transmission and reflection change signs, but also that this sign change can be permanently removed by exposure of the graphene to femtosecond laser pulses of relatively high fluence. This indicates that the differential transmission and reflection at later times may not be directly caused by carriers, but may be from some residue material from the sample fabrication or transfer process.
 
Article
Tellurite glass fibers with embedded nanodiamond are attractive materials for quantum photonics applications. Reducing the loss of these fibers in the 600-800 nm wavelength range of nanodiamond fluorescence is essential to exploit the unique properties of nanodiamond in the new hybrid material. The first part of this study reported the origin of loss in nanodiamond-doped glass and impact of glass fabrication conditions. Here, we report the fabrication of nanodiamond-doped tellurite fibers with significantly reduced loss in the visible through further understanding of the impact of glass fabrication conditions on the interaction of the glass melt with the embedded nanodiamond. We fabricated tellurite fibers containing nanodiamond in concentrations up to 0.7 ppm-weight, while reducing the loss by more than an order of magnitude down to 10 dB/m at 600-800 nm.
 
Article
Tellurite glass fibers with embedded nanodiamond are attractive materials for quantum photonic applications. Reducing the loss of these fibers in the 600-800 nm wavelength range of nanodiamond fluorescence is essential to exploit the unique properties of nanodiamond in the new hybrid material. In the first part of this study, we report the effect of interaction of the tellurite glass melt with the embedded nanodiamond on the loss of the glasses. The glass fabrication conditions such as melting temperature and concentration of NDs added to the melt were found to have critical influence on the interaction. Based on this understanding, we identified promising fabrication conditions for decreasing the loss to levels required for practical applications.
 
Article
We propose new graphene-chitosan solution as a saturable absorber for a mode-locked Erbium-doped fiber laser. We demonstrate stable, mode-locked operation with pulse as short as 168 fs, which are the shortest pulses generated from an Er-doped fiber laser with the use of graphene so far. Graphene-chitosan solution was obtained in soluble forms by the addition of the acetic acid. The ring laser is able to generate optical solitons centered at 1554 nm wavelength with 15.2 nm bandwidth and 63 MHz repetition rate.
 
Schematics of die profiles in axial direction and of the glass flow direction for the two die designs used in this study. 
(a) Die constant calculated using the extrusion processing parameters and (b) cross- sectional area of the die welding chambers of the four extrusion trials considered here. 
Optical profiler images of 3D-printed Ti alloy die (a) media-blasted surface and (b) smoothed surface using conventional machining tool, and optical profiler image of (c) conventionally machined steel die surface. Details of die surface treatment are given in the text. The images have different vertical scale. The total range of the vertical scale is given as Δ z. The average S q values for the corresponding surfaces are also given. 
Optical profiler images of F2 glass preforms of extrusion trials A-E. The preforms were extruded through 3D-printed and conventionally machined dies. The images have different vertical scale. The total range of the vertical scale is given as Δ z. The average S q values for the 
Surface roughness S q of (a) dies with different surface finish, and (b) preforms of the four extrusion trials considered here. Note the different S q scale for the die and preform surfaces. 
Article
We report for the first time use of 3D-printed metal extrusion dies for the extrusion of an optical material into an extrudate at elevated temperatures. Using lead-silicate glass as the material to be extruded, the 3D-printed dies demonstrated the same glass flow behavior as conventionally machined metal dies. Evaluation of the extrusion force at set temperature and extrusion speed revealed that the metal-type of the dies used did not affect the glass flow behavior. Using 3D-printed dies as delivered, the high surface roughness of the 3D-printed dies resulted in high preform surface roughness. However, this effect was overcome by finishing the easily accessible internal die surfaces over 1-2mm length upstream from the die exit. The opportunity of using 3D-printed dies offers unprecedented flexibility in the die design for unlimited tailoring of fluid flow within the die, which paves the way towards extruded items of arbitrary shape.
 
Article
An ISO certified laser-induced damage threshold testing method was applied to characterize photopolymers widely used in 3D laser micro/nano-lithography. For the first time, commercial as well as custom made materials, including epoxy based photoresist (SU-8), hybrid organic-inorganic polymers (OrmoComp and SZ2080), thermopolymer (PDMS) and pure acrylate (PMMA), are investigated and directly compared. The presence of photoinitiator molecules within host matrix clearly indicating the relation between damage threshold and absorption of light is revealed. To simulate single- and multiphoton absorption processes optical resistance measurements were carried out at both fundamental (1064 and 1030 nm) and second harmonic (532 and 515 nm) wavelengths with laser pulse duration’s representing nanosecond and femtosecond regimes. Damage morphology differences from post mortal microscopic analysis were used to enrich the discussion about the possible breakdown mechanisms. The obtained characteristic values of damage threshold reveal potential of photopolymers and their possible applications in high power lasers.
 
Measured and calculated oscillator strengths in various Er 3+ doped glasses. 
Article
In this paper, mid-infrared emission properties and energy transfer mechanism were investigated in Er3+ doped germanate glass pumped by 980 nm diode laser. Spontaneous radiative transition probability and emission cross section at 2.7 μm were calculated to be as high as 36.45 s−1 and 1.61 × 10−20 cm2, respectively. Corresponding upconversion emission spectra and radiative lifetimes of 4I13/2 level were determined to elucidate the mid-infrared luminescent characteristics. Moreover, population behaviors of Er3+: 4I11/2 and 4I13/2 level were analyzed numerically via Inokuti-Hirayama model, rate equations and Dexter’s theory. In addition, DSC curves of developed samples were measured and thermal stabilities were studied to evaluate the ability of resisting thermal damage and crystallization. The results indicate that erbium activated germanate glass is a promising candidate for mid-infrared applications. This work may provide beneficial guide for investigation of population behaviors of Er3+ ions at 2.7 μm emissions.
 
Article
Amplification of 10-ns laser pulses to an energy of 500 mJ at a 10-Hz repetition rate in a cryogenic multi-pass multi-total-reflection-active-mirror (multi-TRAM) amplifier was achieved. By using a multi-TRAM, which is a YAG ceramic composite with three Yb:YAG active layers, a maximum single-pass gain of 12 and a total storage energy of 1.5 J were obtained.
 
Article
TiNxOy films with controllable optical properties have been fabricated by reactive mid-frequency magnetron sputtering from titanium nitride target. The optical and electrical properties were studied as a function of the reactive gas flow and were correlated with the film stoichiometry. The results showed that the behavior of TiNxOy films can be adjusted from metallic to dielectric by increasing oxygen content, which is of great significance to their extensive applications. Owing to the accurate control of optical properties, a TiNxOy based solar selective absorbing coating has been designed and prepared with the aid of TiO2/Si3N4/SiO2 antireflection layers. Its solar absorbance is as high as 97.5% and thermal emissivity is 4.3% with total thickness of 230 nm. The solar absorbance can maintain above 90% for a broad incident angle range from 0° to 65°.
 
Absorption spectra of meta-microwindmill absorber at different parameters errors. (a) With different gaps between the opposite subunits (t) (when r = 0 μm), (b) With different radius (r) at the vertex of the microfan (when t = 5 μm), (b1) Detailed view of absorption peak at around 2.43 THz in Fig. 7(b) and (b2) Detailed view of absorption peak at around 2.57 THz in Fig. 7(b). 
Article
We report a metamaterial based microwindmill array with a periodic arrangement that can be used in terahertz detector as an absorbing layer. It is found that this structure can absorb terahertz waves efficiently with an average absorptivity of 95% at multiple frequencies of 1.516, 2.205, 2.424 and 2.565 THz, which are absorption peaks of four kinds of drugs. The efficient absorbing property of meta-microwindmill on terahertz wave can be explained in terms of the synergetic effects of localized surface plasmon resonant effect and slow light mode. Moreover, the effect of the error of the structural parameters on the absorption efficiency is carefully analyzed in detail to guide the fabrication.
 
Article
A dispersion model describing two-phonon absorption is developed using several simplifications of the quasiparticle approach. The dielectric response is constructed from absorption bands corresponding to individual additive and subtractive combinations of phonon branches. The model also includes thermal effects, changes of the transition strength with temperature, originating in Bose-Einstein statistics, and the shift of phonon frequencies accompanying thermal expansion. The model is applied to the analysis of experimental data measured in the IR range on crystalline silicon. The modeled spectral dependencies of optical constants are capable of describing all features in the transmittance spectra 70–1000 cm−1 observable at 300 K for float-zone silicon. The phonon frequencies in the points of symmetry are obtained independently in good agreement with ab initio calculations. The model of thermal effects is verified using ellipsometric measurements 300–1000 cm−1 in the temperature range of 300–500 K. The agreement between the modeled and experimental data is good, except for the spectral range 750–850 cm−1, in which a better agreement at temperatures above 300 K would require including the three-phonon absorption. The analysis provides a reliable value of the thermal coefficient describing the phonon frequency shift and proves that changes of structure broadening with temperature are negligible within the temperature range of 300–500 K.
 
Article
We show that an elliptical nanohole array (ENA) penetrating through a metal/dielectric/metal (MDM) film produces multi-band circular dichroism (CD) in the near infrared (N-IR) region when the incident light is off-normal incidence. This extrinsic CD is a result of the elliptical symmetry of the nanohole, which gives rise to different polarization modes along its short and long axes. These two polarization modes introduce a net polar vector that forms a chiral triad with the off-normal incidence and the vector normal to the plane of the ENA. The proposed structure possesses four resonance peaks arising from the excitation of both internal- and external- surface plasmon polariton (SPP) modes with different diffraction orders to those wavelengths at which they couple to the incoming light. The formation of these resonance peaks is responsible for the multi-band CD.
 
Crystal structure of monoclinic Sr 6 Y 2 Al 4 O 15 .
XRD patterns of the Sr 6 (Y 1- x Ce x ) 2 Al 4 O 15 (0.005 ≤ x ≤ 0.20) phosphors. 
Excitation and emission spectra of the Sr 6 (Y 1- x Ce x ) 2 Al 4 O 15 (0.005 ≤ x ≤ 0.15) phosphors. The excitation and emission spectra were recorded at maximum peak wavelength for each samples. 
Excitation and emission spectra of the Sr 6 (Y 1- x Ce x ) 2 Al 4 O 15 (0.10 ≤ x ≤ 0.20) phosphors. The excitation spectra were obtained for emission at 600 nm and the emission spectra were obtained for excitation at 460 nm. 
Article
Novel Sr6(Y1-xCex)2Al4O15 (0.005 ≤ x ≤ 0.20) phosphors were synthesized in a single phase form by a conventional solid-state reaction method. These phosphors can be achieved the emission color tunable from blue to orange-red by controlling the Ce3+ doping site in the Sr6Y2Al4O15 lattice and exhibit orange-red emission centered on 600 nm by blue light irradiation as the Ce3+ concentration was increased. To the best of our knowledge, this is the first report of Ce3+ doping oxide phosphor exhibiting orange-red emission centered on 600 nm under blue light excitation.
 
Article
The dielectric/Ag structures were fabricated on glass substrates using various metal oxides as dielectrics and their optical properties were studied through transmittance and ellipsometry measurements. The structures with 10 nm Ag film deposited on various metal oxides (Al2O3, ZrO2, SrTiO3, TiO2, CaCu3Ti4O12, WO3 and HfO2) of 30 nm showed enhancement in transmittance compared to bare Ag film in the visible region. This enhancement in transmittance was explained through suppression of surface plasmon coupling at the dielectric/Ag interface. The surface plasmon wave-vector (kSP) was calculated using the measured dielectric constants for the dielectric and Ag through ellipsometry and employed to analyze the transmittance data. The kSP/k0 and δSP values were estimated and used to interpret the enhanced visible transmittance for different dielectric/Ag structures.
 
Article
Ultrafast demagnetization in magnetic nanoparticles has attracted considerable attention because of its potential applications such as spintronics. For such applications, it is important to develop materials in which ultrafast magnetization can be controlled by lower-power laser pulses. We developed a new method for fabricating Ag–Co hybrid nanoparticles in a TiO2 film using pulsed laser deposition, and elucidated ultrafast magnetization dynamics of these films by employing the pump–probe time-resolved Faraday rotation measurement. The measurements showed that localized surface plasmon resonance of the nanoparticles resulted in an enhancement of the ultrafast demagnetization of the films.
 
Article
2.0at.% Nd:YAG transparent ceramics were prepared by a solid-state reactive sintering method. The as-sintered specimens were annealed at different temperatures for different time. The ceramics with average grain size of 15μm are dense and homogeneous in structure. 1450°C is determined as the optimum annealing temperature and the annealing time longer than 5h is considered as the appropriate time by the optical spectra and laser performance. At this temperature and holding time, the concentration of color centers in the specimen is relatively low and the laser slope efficiency is the highest. It is concluded that less color centers and lower optical loss in Nd:YAG transparent ceramics are necessary to obtain the excellent laser performance.
 
Article
The electro-optical properties of vertically aligned in-plane switching (VA-IPS) liquid crystal (LC) cells are transformed by polymer networks. Three kinds of monomer materials are separately mixed with nematic E7 LC. The threshold voltage behavior reveals the strongest anchoring effect from the cross-linking TA-9164 polymer cell, which sustains good light transmittance at higher voltages and significantly improves the display responses. Without overdrive, the rising-time response of the TA-9164 polymer cell is comparable to that of the pure cell under overdrive. This paper demonstrates that a suitable monomer material applied to VA-IPS LC cells can boost their electro-optical performance.
 
Article
In this work, flip-chip ultraviolet light-emitting diodes (FCUV-LEDs) on patterned sapphire substrate (PSS) at 375 nm were grown by an atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). A specialized reactive plasma deposited (RPD) AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high-resolution X-ray diffraction, the full-width at half-maximum of the rocking curve shows that the FCUV-LEDs with RPD AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. From the transmission electron microscopy (TEM) image, it can be observed that the tip and incline portion of the pattern was smooth using the RPD AlN nucleation layer. The threading dislocation densities (TDDs) are reduced from 7 × 107 cm−2 to 2.5 × 107 cm−2 at the interface between the u-GaN layers for conventional and AlN PSS devices, respectively. As a result, a much higher light output power was achieved. The improvement of light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence measurement and numerical simulation confirm such increase of output power can be attributed to the improvement of material quality and light extraction.
 
Article
Electron beam evaporation (without and with plasma assistance) as well as ion beam sputtering are used to prepare optical mixture coatings for applications in the ultraviolet spectral range. It is demonstrated that intermixing aluminum oxide/ aluminum fluoride materials by these physical vapor deposition techniques results in optical coatings with flexible refractive indices varying between 1.40 and 1.75 in the deep ultraviolet spectral region. At the same time, extinction coefficients vary between less than 1x10−4 and 2x10−3. For evaporated layers, at certain mixture ratios, mechanical stress appears to be close to zero.
 
Experimental arrangement of the confirming of laser grade quality. This setup included a 880-nm laser diode as a pump source, a delivering fiber, collimating and focusing lens, Nd:YVO 4 microchip, flat output coupler, and a Yb:FAP ceramic sample. 
X-ray diffraction pattern of FAP powder as a raw material for Yb:FAP ceramics and Yb:FAP ceramics. Diffraction from Yb:FAP ceramics were from the surface of 3 mm × 3mm. 
Dependence of the output power on the incident pump power for Nd:YVO4 microchip laser with the insertion of Yb:FAP ceramics. 
Slope efficiency of Nd:YVO4 laser as a function of output coupling. 2at.% Yb:FAP ceramics with the thickness of 0.6 mm was placed in the resonator. 
Article
We have realized highly transparent Yb:fluorapatite (FAP) ceramics by use of slip casting under rotational magnetic field, even though the main crystal axis become a hard magnetization axis due to the enhancement of magnetic anisotropy by the total angular momentum of 4f electrons in doped rare-earth ions. We confirmed that our Yb:FAP ceramics reached to have a laser-grade quality: it did not interrupt laser oscillation when it was inserted into a lasing cavity. We also evaluate the absorption and the round-trip loss including Fresnel loss of our Yb:FAP ceramics, which were 3.7 cm−1 at 902 nm and 0.26 (11.5% by a single pass) at 1064 nm, respectively.
 
Article
Studies on transparent laser ceramics continues to rapidly progress, this holds true for non-cubic ceramics as well. Cubic transparent ceramics have been demonstrated to be superior to their single crystal counterparts for laser applications. However, fabrication of anisotropic laser ceramics through ceramic processing is still a challenging problem in material science due to the birefringence inherent to these materials. Currently, there are two possible methods used to reduce the effects of birefringence in anisotropic laser ceramics: by achieving an orientated texture through the application of a high magnetic field, or by generating nanostructured grains through a fast sintering consolidation process. This research work presents an alternative method to process anisotropic Yb:S-FAP optical ceramics through a fast consolidation process. The methodology can be used as a versatile and practical way to develop nanostructured transparent ceramics with an anisotropic structure for laser and optical applications.
 
A parallel plate uniaxial anisotropic chirowaveguide. 
Characteristics curves for mode 1 Ω (thick solid line) and mode 2 Ω (thick dotted line) in (a) type-i material, (b) type-ii material, and (c) type-iii material.
The energy flux density in (a) type-i and type-ii and (b) type-iii materials for different values of chirality parameter.
Article
Theoretical analysis of electromagnetic wave propagation in planar waveguides filled with uniaxial chiral anisotropic media is presented. The guide parallel plates are assumed to be perfect electric conductors. The material filling the waveguide is a generalized medium that incorporates chiral and metamaterials. The behavior of the field intensities, the dispersion curves, and the energy flux for three varieties of uniaxial chiral media are examined numerically. The results demonstrate the phenomena of backward waves in uniaxial anisotropic chiral media. The comparisons of the computed results of the presented general formulations with published results for some material cases confirm the accuracy of the presented analysis.
 
Article
Optical, spectroscopic and thermo-mechanical properties of monoclinic Li6Eu1-xGdx(BO3)3 (x = 0,0.25,0.35) bulk single crystals, grown to be used in the design of heat-scintillation cryogenic bolometers (HSCBs), were investigated. The linear thermal expansion was determined along the a, b, c and c* directions over the temperature range 303–873 K, and its tensor principal coefficients were calculated for both x = 0.25 and x = 0. In addition, the anisotropic thermal conductivity was measured over the temperature range 20-400 K in Li6Eu0.75Gd0.25(BO3)3 (LGEB7, x = 0.25), and the principal components of its tensor at 300 K were established. Spectroscopic properties such as polarized absorption, polarized emission, Raman spectroscopy and optical refractive indices are also reported for the first time. Based on the polarized emission spectra, the line and oscillator strengths, the radiative lifetimes and fluorescent branching ratios were obtained. The intensity parameters Ωλ (λ = 2,4) were obtained and then predicted via the Judd–Ofelt theory. The crystal field parameters and the 7F1 level splitting were discussed using the simple overlap model (SOM) and the method of equivalent nearest neighbours (MENN). The 613 nm emission originates from the 5D0→7F2 transition and the associated stimulated emission peak cross section reaches its maximum value in π-polarization, ≈1.07 × 10−20 cm2 in LGEB7. The thermo-mechanical characterizations and spectroscopic analysis in LGEB7 suggest that this crystal has better optical properties than the Eu3+-doped Li6Y(BO3)3 crystals. However, its potential for solid-state laser applications is still quite speculative, unless a clever thermo-mechanical management of the crystal under laser operation is designed.
 
The measured NLO coefficients of ReCOB crystals Crystal d 11 d 12 d 13 d 31 d 32 d 33 d eff * Reference 
SHG conversion efficiency of TmCOB crystals at 1064 nm (crystal cuts out of principal planes).  
Article
New nonlinear optical (NLO) crystals TmCa4O(BO3)3 (TmCOB) were grown by the Czochralski pulling method, and the anisotropy of second-harmonic-generation (SHG) properties were characterized. Based on the ratio of the peaks of the 2ω signals produced by TmCOB and that of KTP crystal samples at the low fundamental energy, the NLO tensor coefficients d12, d32, d31 and d13 were determined and found to be 0.24, 1.70, −0.55 and −0.32 pm/V, respectively. At 1064 nm, the phase-matching (PM) curves and the effective NLO coefficients (deff) in spatial distribution were evaluated. Efficient SHG was realized on a (32.5°, 180°)-cut TmCOB sample (4 × 4 × 11.8 mm3) in principal plane, by using a 1064 nm Nd:YAG pico-second laser, where the highest conversion efficiency of the single-pass light reached up to 51%, while for a (112.5°, 35.9°)-cut TmCOB sample (4 × 4 × 8 mm3) in spatial PM direction, the single-pass light reached 58%. Meanwhile, the angular noncritical phase matching (A-NCPM) wavelengths along the Y and Z principal axes were calculated and measured, and the limit of type-I PM wavelength of TmCOB was found to be 716 nm.
 
Article
This paper demonstrates that we can further eliminate the remaining micro pores by hot isostatic press (HIP) approach. The porosity of Nd:LuAG laser ceramics sharply declined from 7 × 10−6 to 5.60 × 10−7 after additional HIP. Annealing is one of the key steps to optimize the quality of vacuum sintered ceramics, such as make the transmittance rise from 79.98% to 81.02% at 1200nm. However, the trend is in the opposite direction for the HIPed Nd:LuAG: fallen from 82.65% to 25.50% at 1200nm. The microstructure of Nd:LuAG studied by microscope, SEM and TEM shows that a large number of pores and a few second phases like Lu2SiO5 appeared along grain boundaries in post-annealed HIPed Nd:LuAG. The gas composition was confirmed as argon by GCMS analysis. By further optimizing the annealing process of HIPed ceramics we found that vacuum annealed at 1600 °C for 10h and oxygen re-annealed at 1200 °C for 30h can reduce pores and make the ceramic quality better, the transmittance can reach 83.05% at 1200nm, and the porosity dropped to 3.2 × 10−7.
 
Typical XRD patterns of CdS thin films as-deposited and annealed at 250 @BULLET C.  
Relevant structural parameters for as-deposited and annealed CdS films. 
Chemical composition of CdS films determined by XPS. 
Plot of (αhν) 2 versus hν of CdS films as-deposited and annealed at different tem- peratures.  
Article
In the current work, the effect of an annealing process on structural, morphological, and optical behaviors of cadmium sulfide thin films is presented. A chemical bath deposition method for cadmium sulfide deposition is based on the use of glycine as a complexing agent. Cadmium sulfide thin films were grown by chemical bath deposition and annealed in a nitrogen atmosphere at 0, 100, 150, 200, and 250 °C for 30 minutes. Crystallographic and morphological studies of CdS thin films were performed by scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray diffraction. The optical behavior of CdS thin films was evaluated by UV-Visible spectroscopy and band gap values were calculated by approximation using a Tauc plot. After annealing, densified CdS films formed by nanostructured crystallites exhibit suitable band gap values and present relatively high transmittance in the visible region, allowing their application as a window material for solar cells.
 
Article
We report demonstration of efficient continuous-wave lasing from chromium-doped zinc selenide using anti-reflection microstructures (ARMs) in place of thin-film AR coatings or Brewster angle cavity geometries. ARM textures are more resistant to laser-induced damage than coatings, exhibit low-loss, wide angular acceptance, broad wavelength effectiveness, and are not susceptible to water absorption. Slope-efficiencies of 68% were achieved, which compares favorably to the thin-film control samples at 58% for the same cavity. ARMs hold promise for near-term power scaling and wavelength agility of transition-metal-ion doped II-VI lasers.
 
Article
Many techniques have been suggested and investigated for the microlens array fabrication in three dimensional structures. We present the fabrication of a fused silica based mold for the microlenticular lens array using a femtosecond laser and a CO2 laser. The three dimensional microlenticular array mold is surface-machined on a fused silica plate by a femtosecond laser and polished with a CO2 laser. The CO2 laser treatment process can be customized to obtain a smooth surface. To evaluate the performance of the fabricated glass mold, we replicated a PDMS microlenticular lens arrays from the fabricated glass micro lenticular array mold.
 
Dependences of blue and near infrared integrated UC emission intensities on the excitation power density for the samples doped with 1 mol% Tm 3+ (a) and 3 mol% Tm 3+ (b).  
Dependence of Er 3+ fluorescence intensity ratio on the sample temperature (squared dots); numerical fitting curve by using the theoretical formula exp( ) R C E kT = −Δ  
(a) UC emission spectra for the mixture doped with various Tm 3+ concentrations under 980 nm excitation; (b) normalized UC spectra plotted by using the data in Fig. 6(a).  
Time scanning spectra for blue UC emission of NaY(WO 4 ) 2 microstructures doped with 3 mol%Tm 3+ /10 mol%Yb 3+ (a) and 0.3 mol%Tm 3+ /10 mol%Yb 3+ (b) measured at excitation power density under excitation of 980 nm laser.  
Article
Tm3+/Yb3+ codoped NaY(WO4)2 microstructures with various Tm3+ concentrations and 10 mol% Yb3+ concentration and 1 mol% Er3+/10 mol% Yb3+ codoped NaY(WO4)2 microstructure were prepared via a microwave-assisted hydrothermal reaction. The crystal structure and microscopic morphology of the products were characterized by means of XRD and FM-SEM. Er3+/Yb3+ doped NaY(WO4)2 microstructure was used as temperature sensing probe for studying on the laser heating behavior in Tm3+/Yb3+ doped NaY(WO4)2 microstructures. It was found that higher laser excitation density resulted in higher sample temperature, and the sample with higher Tm3+ doping concentration exhibited more obvious heating effect when excited by 980 nm laser. Moreover, the time scanning upconversion spectra displayed that the upconversion luminescence intensities for both the samples with low and high Tm3+ concentrations almost unchanged with 980 nm laser irradiation time when the excitation power density was lower, but decreased greatly when the excitation power density was higher, and the sample with low Tm3+ concentration displayed larger luminescence intensity change rate. This phenomenon was explained by Arrhenius’s model for the thermal quenching process.
 
Transverse intensity patterns imaged at the input or output surfaces, demonstrating the giant and isotropic self-defocusing effect in the m-cresol/nylon solution. (a) The focused Gaussian beam (12 μ m FWHM) at the input of the sample. (b) The output (33 μ m FWHM) due to normal diffraction after propagating 2mm in our sample at a power less than 1mW. (c) The output (219 μ m FWHM) due to strong defocusing nonlinearity at a power of 30mW. (d) The input dark cross (38 μ m stripe width) created by using an amplitude mask of two thin wires. (e) Linear diffraction output after 5mm propagation in the sample at a power less than 1mW. (f) At a power of 100mW, the output profile shows that Y-junctions of diverging solitons are created with little variation between the horizontal and vertical directions. 
Quantifying the defocusing nonlinearity of the m-cresol/nylon solutions with different concentrations. (a) The output beam diameter (after 2mm propagation) as a function of input power for different concentrations of nylon. (b) The measured | n 2 |, absolute values of the Kerr coefficient, as a function of nylon concentrations using the z-scan method. As seen from these figures, the strength of the nonlinearity in our thermal media can be easily turned across a large range, simply by varying the nylon concentration. 
Transverse intensity patterns imaged at the input or output surfaces demonstrating formation of a dark soliton observed in m-cresol/nylon solution. (a) Input: a dark stripe with a width of 39 ± 2 μ m created using a π -phase mask. (b) Linear output beam profile after 10 mm of propagation at power less than 1 mW. The dark stripe diffracts to a width of 100 ± 3 μ m. (c) Nonlinear output beam profile after 10 mm of propagation at 50mW power. The stripe width decreases to 41 ± 2 μ m. 
Demonstration of dark soliton attraction. Transverse intensity patterns imaged at the input or output surfaces showing: (a) Interference indicating the two separate π -phase-jumps; (b) The two dark stripes at the input, separated by a distance of 100 μ m; (c) Linear output at power less than 1mW after 5mm of propagation. (d)-(f) Output patterns taken at different powers of 1.0, 2.0 and 3.0 W respectively. The stripe separation decreases to 64 μ m in (f). (g) Plot of the stripe separation as a function of input power. 
Article
We report a new type of thermal nonlinear media (m-cresol/nylon solutions) that exhibits a giant tunable self-defocusing nonlinearity. The measured Kerr coefficient in such thermal nonlinear solutions is orders of magnitude higher than that of most previously known thermal materials. In addition, we demonstrate the generation of dark spatial solitons in these isotropic nonlocal nonlinear media, and observe to our knowledge the strongest effect of dark-soliton attraction ever reported in thermal defocusing media.
 
θ-2θ Synchrotron grazing incidence X-ray diffraction (GIXD) patterns obtained from SA (a) and SB (b). Powder patterns from pure Er/Tm mono-and di-silicates (c,e) and pure Er/Tm oxides (d). (f) SIMS depth profiles of Er, Tm, Si and O from the Tm 2 O 3 (75 nm)/Er 2 O 3 (75 nm) layers formed on Si by rf sputtering and thermal annealing at 950 °C for 1 h.
(a) PL spectra of the samples with excitation wavelength of 532 nm. The peaks are categorized into three bands (1300, 1470, and 1530 nm). The positions of main PL peaks from Er 3+ ions are 1529.7 and 1535.6 nm for SA and SB, respectively. (b) Stark energy levels of Er 3+ ions in Er 2 O 3 and of Tm 3+ ions in Y 2 O 3 [19], [28] and the transitions corresponding to the PL peaks from the SB. 
Wavelength excitation dependence of PL spectra from the SA sample. The spectra are obtained at room temperature.
Model of energy transfer between Er 3+ and Tm 3+ ions in SA (Er 2x Tm 2-2x SiO 5 and Er 2x Tm 2-2x Si 2 O 7 ) and SB (Er 2x Tm 2-2x O 3 ) with the two-excitation wavelengths. ET1, ET2 and ET3 indicate energy transfers between Tm 3+ and Er 3+ ions. CR1 and CR2 indicate crossrelaxations between Tm 3+ and Tm 3+ ions and Tm 3+ and Er 3+ ions, respectively.
Article
We demonstrate simultaneous light emissions in O (1260-1360 nm), S (1460-1530 nm), and C (1530-1565 nm) telecommunications bands from films composed of mixtures of polycrystalline Er2xTm2-2xSiO5 and Er2xTm2-2xSi2O7 and of polycrystalline Er2xTm2-2xO3 grown by radio frequency (rf) magnetron sputtering using polycrystalline Tm2O3, Er2O3 and SiO2 targets on Si(100) substrates. Photons are emitted in the O and S + C bands when the samples are optically excited at 532 nm and in the S and C bands when excited at 785 nm. The simultaneous dual-wavelength light emissions are discussed in terms of energy transfers between Er3+ and Tm3+ ions in the polycrystalline Er-Tm compounds.
 
(a) Low-magnification FESEM image (b) High-magnification FESEM image of Sb 2 Te 3 nanosheets. (c) TEM image of a single perfect hexagonal nanosheet. To further confirm the thickness and the width of as-prepared Sb 2 Te 3 nanosheets, the atomic force microscope (AFM) topography images of Sb 2 Te 3 nanosheets are investigated. We carry out AFM measurements in a Multimode 8 system. As shown in Fig. 2, the Sb 2 Te 3 nanosheet has very clean and flat surface with a uniform thickness about 120 nm across the lateral dimensions. The height profiles corresponding to the line-cut in Fig. 2(a) is shown in Fig. 2(b). The two dotted lines in Fig. 2(b) correspond to the two blue points of the line-cut in 
Experimental scheme for the generation of ring-shaped beams. M1, silver-coated plane mirror; A1 and A2, attenuators; BS1 and BS2, beam splitters; NM, nonlinear material. Inset maps (a) and (b) show the initial spatial intensity distributions of pump and probe beams, respectively. Inset map (c) displays four kinds of nonlinear samples, from left to right in the order: IPA solution, Sb 2 Te 3 dispersion solutions in IPA with a concentration of 156, 312, and 625 ug/ml. 
The DSS of RSBs generated in four types of medium when P fs is tuned. Spatial intensity profiles of the probe beam after passed through four dispersion solutions at concentration of (a) 625 ug/ml (b) 1.25 mg/ml (c) 2.5 mg/ml, and (d) 5 mg/ml. 
Intensity distribution of RSBs in free space propagation at different propagation distances of (a)20, (b) 25, (c) 30, (d) 35, (e) 40, (f) 45 cm, and (g) 450 cm when P fs is 8 mW. 
Article
Hexagonal nanosheets of Sb2Te3 single crystals with uniform morphology are successfully synthesized through a solvothermal method. We experimentally demonstrate that topological insulator Sb2Te3 as an optical media can be used for the generation of ring-shaped beams based on a giant optical nonlinearity and the effect of graded-index plasma lens. Good propagation properties in free space are exhibited by the generated ring-shaped beam and the dark spot size of ring-shaped beams can be conveniently controlled by adjusting the power of the pump beam. We also find that it is more easily to generate a ring-shaped beam in the high concentration Sb2Te3 dispersion solution and the divergence angle of the ring-shaped beam increases as the concentration of dispersion solution increase.
 
Article
The color-tunable upconversion (UC) emission and optical temperature sensing behaviour was observed from the Er-Yb-Mo codoped Bi7Ti4NbO21 (BTN) ferroelectric oxide. By control of the Mo concentration, the ceramics are capable of generating color tunability from green to yellow, then to red. The optical temperature sensing behaviour of green and red UC emission was studied using the temperature fluorescence intensity ratio (FIR) technique at temperature region from 133 to 450K, showing a relatively high sensitivity. The experimental data fitted a linear function very well, which suggests that the oxides could be used for optical temperature sensing applications. The polarization-electric field (P-E) hysteresis loops have been investigated, indicating it maintained ferroelectric properties with doping. Based on the profiles of XRD, Rietveld refinement and the XPS analysis, the structure variety by Er-Yb-Mo codoping and mechanism responsible in color-tunable UC emission were discussed in detail.
 
Dual-rotating compensator ellipsometer configuration and orientation of external in-plane magnetization components are shown schematically. 
Optical function of Bi:GIG layer. The real part ℜ{ε 11 } and the imaginary part ℑ{ε 11 } of the function is plotted using solid and dashed lines, respectively. 
Fitted spectral dependence of off-diagonal tensor component from ellipsometric measurement of Bi:GIG in transverse and longitudinal MO configuration. 
Photon energy [eV]
Article
A ferromagnetic garnet, used as a magneto-optical (MO) material in magneto-photonic and magneto-plasmonic structures, is characterized. We present a general procedure to determine optical and magneto-optical functions of the magneto-optic garnet by using Mueller matrix ellipsometry. In the first step, the optical functions (the refractive index spectra) of the (CaMgZr)-doped gallium-gadolinium garnet (sGGG) substrate and the Bi-substituted gadolinium iron garnet Gd1.24Pr0.48Bi1.01Lu0.27Fe4.38Al0.6O12 (Bi:GIG) are obtained in the spectral range from 0.73 eV to 6.42 eV (wavelength range 193 nm – 1.7 μm). Subsequently, the spectra of the magneto-optical tensor components are obtained by applying an external in-plane magnetic field in longitudinal and transverse geometry. The obtained functions are then used to fit the Mueller matrix spectra of a magneto-plasmonic structure with a gold grating on the magneto-optic garnet layer. This structure has recently been demonstrated to have strongly enhanced transverse magneto-optic Kerr response at visible and near-infrared frequencies. By taking possible fabrication imperfections (surface roughness, residual photo-resist layer, thickness deviation) into account, the measured strongly enhanced MO response fits very well to the numerical model predicting these exaltations.
 
Article
We report the laser irradiation-induced oxidation of bismuth metal investigated in situ by micro-Raman spectroscopy as a function of irradiation power and time. The purely optical synthesis and characterization of β-Bi2O3 oxide microislands on metallic Bi surfaces is shown to be stable over time, even at room-temperature. By closely examining possible reactions on simple Bi morphologies it is revealed for the first time that the ensuing oxide phase is critically dependent on the final oxide volume and follows a fixed kinetic transformation sequence: 3 2 O 2 ( g ) + 2 Bi ( l ) → β – Bi 2 O 3 ( s ) → α – Bi 2 O 3 ( s ) . These findings are unusual within the framework of traditional Bi2O3 thermal transformation relations. An electrostatic mechanism involving a changing Bi2O3 surface-to-volume ratio is proposed to explain the room-temperature metastability of small β-Bi2O3 volumes and the subsequent transformation sequence, as well as unifying the results of previous studies.
 
a) presents the XRD θ-2θ scan of the PLD-processed BSCO thin film on LAO substrate. Besides the peaks of LAO substrate, only BSCO (00l) peaks can be detected, indicating that the film is c-axis oriented without any second phase. The rocking curve of BSCO (0 0 12) peak has a full width at half maximum (FWHM) of 0.11°, suggesting good crystallinity of the film. The epitaxial nature of the BSCO film on LAO substrate was confirmed by the φ scan measurement, as shown in Fig. 1(b). The presence of four peaks of the BSCO film reveals that the four-fold symmetry of BSCO and the film is epitaxial grown on LAO substrate. The epitaxial relationship between the BSCO film and the LAO substrate was determined to be (001) BSCO||(001) LAO and [100] BSCO||[100] LAO. 
(a) TEM and (b) high resolution TEM of BSCO/LAO interface. The inset of Fig. 2 (a) is the SEAD pattern taken from the film part. 
(a) low and (b) high magnification surface SEM images of the PLD-processed BSCO film. 
(a) Temperature dependence of resistivity of the PLD-processed BSCO thin film, the inset is the Seebeck coefficient of the film; (b) photograph of the BSCO thin film on a labeled paper; (c) transmittance spectra of the BSCO thin film after abstracting the substrate contribution. The inset shows the transmittance spectra of bare LAO substrate as well as BSCO thin film on the LAO substrate; (d) (αhν) 2 versus hν plot of BSCO thin film. 
Article
Transparent conductive p-type Bi2Sr2Co2Oy thin films were epitaxial grown on LaAlO3 substrate by pulsed laser deposition. Film with thickness of 50 nm showed a room temperature resistivity of about 5.5 mΩ cm and an average optical transmittance of about 51% in the visible region, resulting in a significant high figure of merit of 1350 MΩ−1. This is one of the highest values reported for the p-type transparent conducting oxides, demonstrating that epitaxial Bi2Sr2Co2Oy thin films have great potential applications in optoelectronic devices.
 
Article
Broadband circular and linear polarization conversions have been proposed in the paper by using thin birefringent reflective metasurfaces, which are composed of two orthogonal I-shaped structures placed on the top of a printed circuit broad with grounded plane on the bottom. We show that the metasurface manipulates the reflective phases of two orthogonal linearly-polarized waves independently by changing the dimensions of I-shaped structure. Hence, the polarization states of a linearly-polarized incident wave with normal incidence can be manipulated as desired after reflected by the anisotropic metasurface. Two polarization conversions have been presented by using such thin birefringent reflective metasurfaces: from linearly-polarized wave to circularly-polarized wave, and from linearly-polarized wave to cross-polarized wave. The metasurfaces work at microwave frequency, and the axial ratio better than 1dB is achieved within fractional bandwidth of 15% for circular polarization. Numerical and experiment results demonstrate good polarization conversions in a broad frequency band, which have excellent agreements with the theoretical calculations.
 
Article
Red fluorescence lamellae in prismatic layers of Pinctada vulgaris shell were investigated. SEM-EDS, XRD, and TG-DTA were utilized to characterize prismatic layers. We found that prismatic layers are calcitic prismatic (CP) layers with rich organic substances. Excitation spectrum for red fluorescence determined by a spectrophotometer indicates that the fluorescent matter in the organic substances is porphyrin compound derivatives. By using a fluorescence microspectroscope, the cross section of CP layers shows red fluorescence forming lamellar pattern. The lamellar pattern consists of red and black parallel zones with a modulation of emission intensity. Elemental mapping show a correlation of the fluorescence intensity decay with sulphur-rich zones occupying the CP layers in the black zones.
 
Top-cited authors
Alexander V Kildishev
  • Purdue University
Gururaj Naik
  • Rice University
Heike Ebendorff-Heidepriem
  • University of Adelaide
Tanya M. Monro
  • University of Adelaide
Jongbum Kim
  • University of Maryland, College Park