Showing papers in "Optical Materials Express in 2012"
TL;DR: In this article, the excitation of surface-plasmon-polaritons on titanium nitride thin films was demonstrated and the performance of various plasmonic and metamaterial structures with the material as the plammonic component was discussed.
Abstract: The search for alternative plasmonic materials with improved optical properties, easier fabrication and integration capabilities over those of the traditional materials such as silver and gold could ultimately lead to real-life applications for plasmonics and metamaterials. In this work, we show that titanium nitride could perform as an alternative plasmonic material in the visible and near-infrared regions. We demonstrate the excitation of surface-plasmon-polaritons on titanium nitride thin films and discuss the performance of various plasmonic and metamaterial structures with titanium nitride as the plasmonic component. We also show that titanium nitride could provide performance that is comparable to that of gold for plasmonic applications and can significantly outperform gold and silver for transformation-optics and some metamaterial applications in the visible and near-infrared regions.
583 citations
TL;DR: In this article, the dispersion and absorption properties in the visible and near-infrared wavelength region have been determined for distilled water, heavy water, chloroform, carbon tetrachloride, toluene, ethanol, carbon disulfide, and nitrobenzene at a temperature of 20 °C.
Abstract: Liquid-filled photonic crystal fibers and optofluidic devices require infiltration with a variety of liquids whose linear optical properties are still not well known over a broad spectral range, particularly in the near infrared. Hence, dispersion and absorption properties in the visible and near-infrared wavelength region have been determined for distilled water, heavy water, chloroform, carbon tetrachloride, toluene, ethanol, carbon disulfide, and nitrobenzene at a temperature of 20 °C. For the refractive index measurement a standard Abbe refractometer in combination with a white light laser and a technique to calculate correction terms to compensate for the dispersion of the glass prism has been used. New refractive index data and derived dispersion formulas between a wavelength of 500 nm and 1600 nm are presented in good agreement with sparsely existing reference data in this wavelength range. The absorption coefficient has been deduced from the difference of the losses of several identically prepared liquid filled glass cells or tubes of different lengths. We present absorption data in the wavelength region between 500 nm and 1750 nm.
521 citations
TL;DR: In this paper, the authors discuss the advantages to be achieved by a further need as well as the pitfalls of the excessive use of imagination in the present era of persistent luminescence since the mid 1990s, the imagination played a more important role than the sparse solid experimental data and the chemical common sense and knowledge was largely ignored.
Abstract: The present status and future progress of the mechanisms of persistent luminescence are critically treated with the present knowledge. The advantages to be achieved by a further need as well as the pitfalls of the excessive use of imagination are shown. As usual, in the beginning of the present era of persistent luminescence since the mid 1990s, the imagination played a more important role than the sparse solid experimental data and the chemical common sense and knowledge was largely ignored. Since some five years, the mechanistic studies seem to have reached the maturity and – perhaps deceivingly – it seems that there are only details to be solved. However, the development of red emitting nanocrystalline materials poses a challenge also to the more fundamental studies and interpretation. The questions still luring in the darkness include the problems how the increased surface area affects the defect structure and how the “persistent energy transfer” really works. There is still some light to be thrown onto these matters starting with agreeing on the terminology: the term phosphorescence should be abandoned altogether. The long lifetime of persistent luminescence is due to trapping of excitation energy, not to the forbidden nature of the luminescent transition. However, the technically well-suited term “afterglow” should be retained for harmful, short persistent luminescence.
194 citations
TL;DR: Graphene saturable absorber mirror (SAM) was successfully fabricated by transferring large-size graphene flake on dielectric coating mirror as discussed by the authors, and the graphene transferred on the mirror was tested by Raman spectrum measurement and scanning electron microscope imaging.
Abstract: Graphene saturable absorber mirror (SAM) was successfully fabricated by transferring large-size graphene flake on dielectric coating mirror. The graphene transferred on the mirror was tested by Raman spectrum measurement and scanning electron microscope imaging. With the graphene SAM, passive Q-switching and continuous wave (CW) mode locking were experimentally demonstrated in a bulk laser at 2 μm wavelength.
144 citations
TL;DR: In this article, two different techniques for the preparation of nanoparticles from Ca2Si5N8:Eu2+,Tm3+ bulk powder were investigated for in vivo optical imaging.
Abstract: Ca2Si5N8:Eu2+,Tm3+ presents outstanding long lasting luminescence at about 610 nm. However, to be useful for in vivo optical imaging, persistent luminescence materials should possess high optical performance combined with sizes in the nanoscale. With this aim, we investigated two different techniques for the preparation of nanoparticles from Ca2Si5N8:Eu2+,Tm3+ bulk powder. First, nanoparticles were successfully prepared with the pulsed laser ablation method in liquid (abbreviated as PLAL). Secondly, nanoparticles obtained by selective sedimentation from the bulk compound resulted in satisfactory yield and allowed to perform the first real-time in vivo imaging with Ca2Si5N8:Eu2+,Tm3+ host. Finally the influence of surface functionalization on the biodistribution of the probe after systemic injection is discussed.
124 citations
TL;DR: In this article, a review on the preparation of quantum dots, structural design of electroluminescence devices using quantum dots and printing processes for full-color quantum dot display is discussed.
Abstract: Quantum dot-based light emitting diodes have extensively been investigated over the past two decades in order to utilize high color purity and photophysical stability of quantum dots. In this review, progresses on the preparation of quantum dots, structural design of electroluminescence devices using quantum dots, and printing processes for full-color quantum dot display will be discussed. The obstacles originating from the use of heavy metals, large hole injection barrier, and imperfect printing processes for pixilation have limited the practical applications of quantum dot-based devices. It is expected that recent complementary approaches on materials, device structures, and new printing processes would accelerate the realization of quantum dot displays.
121 citations
TL;DR: In this article, the suitability of three ternary tellurite glass families for use as optical fiber materials was investigated and the scalability of the glass volumes was assessed.
Abstract: We investigated the suitability of three ternary tellurite glass families for use as optical fibre materials. Systematically varied compositions were produced and the scalability of the glass volumes was assessed. Detailed thermal analysis was conducted to provide justification for the observed billet scaling results. Compositional trends in the linear and nonlinear refractive indices were measured and correlated to structural information gained from measured Raman spectra. Physical mechanisms are suggested to explain the observed trends. Finally we explore the suitability of these glasses for optical fibre fabrication.
107 citations
TL;DR: In this article, a photovoltaic infrared detector based on aligned single-walled carbon nanotubes (SWCNT) arrays is presented. But the method is not suitable for high-performance infrared sensors.
Abstract: The carbon nanotubes (CNTs) are an ideal material for infrared applications due to its excellent electronic and optoelectronic properties, suitable bandgap, mechanical and chemical stabilities. In this paper, we demonstrate a photovoltaic infrared detector which is based on aligned single-walled CNT (SWCNT) arrays. The device is fabricated by asymmetrically contacting the two ends of the SWCNT arrays with Pd and Sc of different work functions, which are known to form ohmic contacts with the valence and conduction bands of semiconducting SWCNTs respectively. The device is characterized at room temperature, exhibiting excellent diode characteristics, high responsivity of 9.87 × 10−5 A/W and infrared spectral detectivity of 1.09 × 107 cmHz1/2/W. The demonstration of the SWCNT arrays based infrared detector which is fabricated using a doping-free process paves the way to applications of CNT in such field as high-performance infrared sensors.
97 citations
TL;DR: In this article, a set of chalcogenide glass samples doped with different concentrations of rare earth ions was fabricated and the modeling results showed that an efficient mid-infrared laser action is possible if optical losses are kept at the level of 1dB/m or below.
Abstract: We present a study of chalcogenide glass fiber lasers doped with
Dy3+, Pr3+ or Tb3+ that would operate in the mid-infrared wavelength range.
A set of chalcogenide glass samples doped with different concentrations of
rare earth ions is fabricated. The modeling parameters are directly extracted
from FTIR absorption measurements of the fabricated bulk glass samples
using Judd-Ofelt, Fuchtbauer–Ladenburg theory and McCumber theory.
The modeling results show that, for all the dopants considered, an efficient
mid-infrared laser action is possible if optical losses are kept at the level of
1dB/m or below.
94 citations
TL;DR: In this paper, the authors compared the successful creation of sub-100 nm structures with two different few-cycle laser systems and chemically modified zirconium-based sol-gel composite material using crosslinker for resolution enhancement.
Abstract: Nanofabrication of structures with a feature size of sub-50 nm with ultrashort-laser based two-photon polymerization (2PP) technique is presented. The spatial resolution of the 2PP structures depends on the characteristics of the polymer material and the laser system used for fabrication. Here we compare the successful creation of sub-100 nm structures with two different few-cycle laser systems and chemically modified zirconium-based sol-gel composite material using cross-linker for resolution enhancement.
94 citations
TL;DR: In this paper, the authors present experimental results in synthesizing Au-Ag bimetallic nanoalloys with tunable localized surface plasmon resonance frequency through nanosecond laser-induced heating in the presence of polyvinyl alcohol as a reducing and capping agent via three different procedures: (i) Mixture of HAuCl4 and AgNO3 precursors.
Abstract: Here we present our experimental results in synthesizing Au-Ag bimetallic nanoalloys with tunable localized surface plasmon resonance frequency through nanosecond laser-induced heating in the presence of polyvinyl alcohol as a reducing and capping agent via three different procedures: (i) Mixture of HAuCl4 and AgNO3 precursors, (ii) Mixture of Au nanoparticles (NPs) and AgNO3 precursor and (iii) Mixture of both Au and Ag NPs. Presence of single absorption band and direct dependence of the Au/Ag molar ratio to the shift of the absorption peak and lack of core-shell structure in Transmission Electron Microscope images confirms that the formed NPs are homogeneous alloys.
TL;DR: The development of hollow core photonic crystal fibers with low losses over a broad spectral region in the near IR enabled the demonstration of a novel laser type - Hollow-core Optical Fiber Gas Laser (HOFGLAS) as discussed by the authors.
Abstract: The development of hollow core photonic crystal fibers with low losses over a broad spectral region in the near IR enabled the demonstration of a novel laser type - Hollow-core Optical Fiber Gas Laser (HOFGLAS). The laser combines attractive features of fiber lasers such as compactness and long interaction length of pump and laser radiation with those of gas lasers such as the potential for high output power and narrow line width. This paper summarizes recent developments and describes the demonstration of C2H2 and HCN prototype lasers. Avenues to extend laser emission further into the IR are discussed.
TL;DR: In this article, the first observation of transverse Anderson localization in a glass optical fiber is reported, where strong localization happens near the outer boundary of the fiber and no trace of localization is observed in the central regions.
Abstract: We report the first observation of transverse Anderson localization in a glass optical fiber. The strong localization happens near the outer boundary of the fiber and no trace of localization is observed in the central regions. However, these observations complement previous reports that the boundary of a disordered medium has a de-localizing effect. Our observations can be explained by considering the non-uniform distribution of disorder in the fiber, where the substantially larger disorder near the outer boundary of the fiber offsets the de-localizing effect of the boundary.
TL;DR: In this paper, a fluorinated phenyl-tolane based nematic mixture was developed and evaluated using terahertz time domain spectroscopy (THz-TDS).
Abstract: We develop a fluorinated phenyl-tolane based nematic mixture NJU-LDn-4 and evaluate its frequency-dependent birefringence utilizing terahertz time domain spectroscopy (THz-TDS). A large mean birefringence of 0.306 is obtained in a broad range from 0.4 to 1.6 THz, with a maximum of 0.314 at 1.6 THz. Furthermore, relation between molecular structures and birefringence property is discussed. This work reveals new insights for tailing liquid crystal molecules with desirable large birefringence in THz range, which is extremely meaningful for the design and fabrication of fast, compact and tunable terahertz devices.
TL;DR: In this article, pulsed laser ablation of silicon in aqueous solution is employed to generate Si-NPs in one step avoiding use of chemical precursors, which can be used for imaging applications.
Abstract: Heavy-metal-free semiconductor material like Silicon Nanoparticle (Si-NPs) is attracting scientists because of their diverse applications in biomedical field. In this work, pulsed laser ablation of silicon in aqueous solution is employed to generate Si-NPs in one step avoiding use of chemical precursors. Characterization by absorption, electron and photoluminescence analysis proves the generation of luminescent Si-NPs. The productivity rate of Si-NPs is investigated by Inductively Coupled Plasma Spectrometry. Furthermore, Si-NPs quantum yield and confocal microscopy studies corroborate the potential use of these biocompatible Si-NPs for imaging applications.
TL;DR: In this paper, the authors report the fabrication of silica microstructured optical fibers with the core exposed along the whole length, and characterize the stability of these new fibers when exposed to some typical sensing and storage environments.
Abstract: We report the fabrication of silica microstructured optical fibers with the core exposed along the whole length, and characterize the stability of these new fibers when exposed to some typical sensing and storage environments. We show the fiber loss to be the best achieved to date for exposed-core fibers, while the deterioration in the transmission properties is up to ∼2 orders of magnitude better than for the previously reported exposed-core fibers produced in soft glass. This opens up new opportunities for optical fiber sensors requiring long term and/or harsh environmental applications while providing real time analysis anywhere along the fibers length.
TL;DR: In this article, As2Se3 glass films using spin coating from ethylenediamine solutions are characterized as a function of annealing conditions, which partially recovers the As-Se3 pyramid structure and brings the film refractive indices close to the bulk value.
Abstract: Thin film selenide glasses have emerged as an important material for integrated photonics due to its high refractive index, mid-IR transparency and high non-linear optical indices. We prepared high-quality As2Se3 glass films using spin coating from ethylenediamine solutions. The physio-chemical properties of the films are characterized as a function of annealing conditions. Compared to bulk glasses, as-deposited films possess a distinctively different network structure due to presence of Se-Se homo-polar bonds and residual solvent. Annealing partially recovers the As-Se3 pyramid structure and brings the film refractive indices close to the bulk value. Optical loss in the films measured at 1550 nm wavelength is 9 dB/cm, which was attributed to N-H bond absorption from residual solvent.
TL;DR: In this paper, a parameterization of the dispersive conductivity of highly-doped graphene has been developed and used for use in finite-difference time-domain simulation of near infrared graphene-based photonic and plasmonic devices.
Abstract: A parameterization of the dispersive conductivity of highly-doped graphene has been developed and is presented for use in finite-difference time-domain simulation of near infrared graphene-based photonic and plasmonic devices. The parameterization is based on fitting a Pade approximant to the conductivity arising from interband electronic transitions. The resulting parameterization provides an accurate spectral representation of the conductivity in the wavelength range 1.3 – 2.3μm which is important for near infrared graphene plasmonics. Finite-difference time-domain simulations of straight graphene plasmonic waveguides of infinite and finite width are presented.
TL;DR: In this article, a new method is introduced to investigate localized volume variations resulting from laser exposure. But this method is based on the measurement of fused silica cantilevers deflection from which they calculate the effective stress and density variation in laser-affected zones.
Abstract: We introduce a new method to investigate localized volume variations resulting from laser exposure. Our method is based on the measurement of fused silica cantilevers deflection from which we calculate the effective stress and density variation in laser-affected zones. Specifically, we investigate density variations in fused silica exposed to femtosecond laser exposure in the regime where nanogratings are found. We demonstrate that a volume expansion is taking place in that particular regime.
TL;DR: Heike Ebendorff-Heidepriem, Kevin Kuan, Michael R. Oermann, Kenton Knight, and Tanya M. Monro as discussed by the authors.
Abstract: Heike Ebendorff-Heidepriem, Kevin Kuan, Michael R. Oermann, Kenton Knight, and Tanya M. Monro
TL;DR: In this paper, a model for temperature dependent emission cross sections of Nd-doped solid-state laser materials was presented for the conditions that the population inversion was induced into samples by a weak pumping field.
Abstract: Temperature dependencies of stimulated emission cross section for Nd:YAG, Nd:YVO4, and Nd:GdVO4 was carefully evaluated. Our spectral evaluations with fine spectral resolution were carried out under the condition that the population inversion was induced into samples by a weak pumping field. Within the temperature range from 15°C to 65°C, the variation of emission cross section at 1.06 μm in Nd:YAG was −0.20%/°C, while those in Nd:YVO4 and Nd:GdVO4 for π-polarization were −0.50%/°C and −0.48%/°C, respectively. Consideration of measured temperature dependence gave the numerical model for temperature dependent emission cross sections of Nd-doped solid-state laser materials. We have also presented numerical approximations of this model for our samples by a simple polynomial, which can be applicable within the temperature range from 15°C to 350°C.
TL;DR: In this article, five different chiral metamaterials in the terahertz (THz) regime, fabricated on fully flexible polyimide substrates, are comparatively studied via numerical calculations and experimental measurements.
Abstract: Five different chiral metamaterials in the terahertz (THz) regime, fabricated on fully flexible polyimide substrates, are comparatively studied via numerical calculations and experimental measurements. The chiral properties of these metamaterials, which are discussed based on their optical activity, circular dichroism, and the retrieved effective parameters, show pronounced pure optical activity (larger than 300°/wavelength), as well as important circular polarization generation and filtering capabilities. Negative refractive index is also obtained for all the considered designs.
TL;DR: In this paper, the spectral properties of antenna-enhanced hydrogen sensing geometries are investigated through extensive finite element (FEM) simulations, and it is shown that the hydrogen-induced spectral behavior of the system is governed by two competing effects: a small blueshift caused by dielectric function changes in the palladium and a much stronger redshift due to an expansion of the lattice.
Abstract: In this work, we numerically investigate the nature of spectral shifts in antenna-enhanced hydrogen sensing geometries consisting of a gold bowtie antenna next to a palladium nanodisk. We find through extensive finite element (FEM) simulations that the hydrogen-induced spectral behavior of the system is governed by two competing effects: a small blueshift caused by dielectric function changes in the palladium and a much stronger redshift due to an expansion of the palladium lattice. Our findings enable the accurate numerical characterization and especially the optimization of sensitive antenna-enhanced hydrogen sensors. As a first application, we calculate the performance improvement of gap antennas compared to single cut-wire antenna elements.
TL;DR: In this article, the authors presented a technique in which small solute nonlinearities may be extracted from large solvent signals by performing simultaneous Z-scans on two samples (solvent and solution).
Abstract: We present a technique in which small solute nonlinearities may be extracted from large solvent signals by performing simultaneous Z-scans on two samples (solvent and solution). By using a dual-arm Z-scan apparatus with identical arms, fitting error in determining the solute nonlinearity is reduced because the irradiance fluctuations are correlated for both the solvent and solution measurements. To verify the sensitivity of this technique, the dispersion of nonlinear refraction of a squaraine molecule is measured. Utilizing this technique allows for the effects of the solvent n2 to be effectively eliminated, thus overcoming a longstanding problem in nonlinear optical characterization of organic dyes.
TL;DR: In this paper, the properties of localized surface plasmon resonance (LSPR) in Au/Ag alloy were investigated experimentally and numerically, and it was found that LSPR spectra of nanostructures at near-infrared wavelengths changed drastically at the 50% Au /Ag mole fraction.
Abstract: Optical properties of localized surface plasmon resonance (LSPR) in Au/Ag alloy were investigated experimentally and numerically. It was found that LSPR spectra of nanostructures at near-infrared wavelengths changed drastically at the 50% Au/Ag mole fraction. Both the experimental results and the finite-difference time-domain simulations using experimentally obtained n, k values showed a similar tendency. At 50% molar fraction, electromagnetic field enhancement reached almost the same value as in pure Au.
TL;DR: Although the persistent luminescence can be induced by ultraviolet light in all three phosphors, only for BaSi2O2N2:Eu low energy radiation allows filling of the traps responsible for the afterglow.
Abstract: In this work we study the persistent luminescence properties of europium-doped alkaline earth silicon oxynitrides (CaSi2O2N2, SrSi2O2N2 and BaSi2O2N2). All compounds show afterglow emission, with an emission spectrum which is similar to the steady state photoluminescence. The afterglow decay time for BaSi2O2N2:Eu and SrSi2O2N2:Eu is about 50 and 100 minutes respectively, while for CaSi2O2N2:Eu the afterglow intensity is very low. Although the persistent luminescence can be induced by ultraviolet light (250-300 nm) in all three phosphors, only for BaSi2O2N2:Eu low energy radiation (350-500 nm) allows filling of the traps responsible for the afterglow.
TL;DR: In this article, the authors demonstrate a simple way to make materials that display angle-independent structural color by packing core-shell colloidal particles consisting of high-refractive-index cores and soft, transparent shells.
Abstract: Making materials that display angle-independent structural color requires control over both scattering and short-range correlations in the refractive index. We demonstrate a simple way to make such materials by packing core-shell colloidal particles consisting of high-refractive-index cores and soft, transparent shells. The core-shell structure allows us to control the scattering cross-section of the particles independently of the interparticle distance, which sets the resonance condition. At the same time, the softness of the shells makes it easy to assemble disordered structures through centrifugation. We show that packings of these particles display angle-independent structural colors that can be tuned by changing the shell diameter, either by using different particles or simply by varying the concentration of the suspension. The transparency of the suspensions can be tuned independently of the color by changing the core diameter. These materials might be useful for electronic displays, cosmetics, or long-lasting dyes.
TL;DR: In this article, the authors proposed and demonstrated passive harmonic mode locking of an erbium doped fiber laser with soliton pulse shaping using carbon nanotubes polyvinyl alcohol film.
Abstract: We have proposed and demonstrated passive harmonic mode locking of an erbium doped fiber laser with soliton pulse shaping using carbon nanotubes polyvinyl alcohol film. Two types of samples prepared by using filtration and centrifugation were studied. The demonstrated fiber laser can support 10th harmonic order corresponding to 245 MHz repetition rate with an output power of ~12 mW. More importantly, all stable harmonic orders show timing jitter below 10 ps. The output pulses energies are between 25 to 56 pJ. Both samples result in the same central wavelength of output optical spectrum with similar pulse duration of ~1 ps for all harmonic orders. By using the same laser configuration, centrifugated sample exhibits slightly lower pulse chirp.
TL;DR: In this article, a direct switching between a transparent (or reflecting) planar (P) state to an opaque (or transparent) focal conic (FC) state and vice-versa of a polymer free bistable cholesteric light shutter without any homogeneous polyimide (PI) layer was demonstrated based on the sign inversion of dielectric anisotropy of dual frequency liquid crystal (DFLC).
Abstract: In this paper, a direct switching between a transparent (or reflecting) planar (P) state to an opaque (or transparent) focal conic (FC) state and vice-versa of a polymer free bistable cholesteric light shutter without any homogeneous polyimide (PI) layer, is demonstrated based on the sign inversion of dielectric anisotropy of dual frequency liquid crystal (DFLC). The direct switching was achieved by applying square wave field at low (1 kHz) and high (50 kHz) frequency. As a result, the DFLC light shutter sustains bistable bright and dark states in electric field off state and exhibits excellent electro-optic performance. The direct switching from the FC to P states not only supports more uniform P state but also significantly reduces switching voltage by eliminating the high field homeotropic (H) state required for the switching in the conventional polymer stabilized cholesteric texture (PSCT) light shutter. The driving voltage applied to make a transition from the P to FC one is relatively low (3Vp-p/µm). Further, switching time from FC to P state was reduced drastically with homeotropic PI layer. Results show that dual frequency cholesteric liquid crystal (DFCLC) light shutter holds a great promise for use in energy efficient display devices and switchable windows.
TL;DR: In this paper, a bottom-up approach to fabricate by self assembly a metamaterial from metallic nanoparticles in a two-step process was introduced, where the material dispersion with increasing nanoparticle densities, from dispersed to randomly packed nanoparticles, was measured by spectroscopic ellipsometry, demonstrating high permittivity values in the visible.
Abstract: We introduce a novel bottom-up approach to fabricate by self assembly a metamaterial from metallic nanoparticles in a two-step process. In the first step, a metamaterial made of densely packed silver nanoparticles is required. The material dispersion with increasing nanoparticle densities, from dispersed to randomly packed nanoparticles, was measured by spectroscopic ellipsometry, demonstrating high permittivity values in the visible. In the second step, this material was used to prepare spherical clusters by a method based on oil-in-water emulsion. The optical properties of these clusters were equally investigated by spectroscopic means. Comparisons with rigorous numerical simulations clearly indicate that, depending on the cluster size, their spectral response can be unambiguously associated with the excitation of a magnetic dipole resonance. As a consequence, such spherical clusters are promising building blocks for future metamaterials possessing a magnetic response in the visible range.