Search

Third order optical limiting utilizes nonlinear absorption or scatter to preferentially reduce the optical throughput of intense light through a medium. While these processes are dependent on intensity, it is often the transmitted energy or power that needs to be limited to avoid eye, sensor or detector damage. This is problematic when the input is a vortex mode or other higher order Gaussian distributions such as Bessel-Gaussian modes where the relationship between optical power and the on axis intensity is more complicated than for the TEM00 Gaussian mode. Here we show that for higher order Bessel-Gaussian modes that beam power transmission is not equivalent to peak intensity transmission through intensity dependent absorption or scatter based optical limiters. We present a theoretical model and experimental data that demonstrates that the power throughput in these media, increases by 4 and 7 times for n = 1 and 2 Bessel Gaussian modes, respectively, over that observed when a TEM00 mode is used.

Binders have an important function in the performance of Li-ion batteries even though they are only used in small quantities. In addition to poor adhesion properties, the traditional polyvinylidene difluoride binder raises many environmental and health concerns because of their processing that involves hazardous organic solvents. In this study, we introduced a water-soluble, environmentally friendly tapioca starch binder modified with polyethylene glycol (PEG) groups as a novel binder for Si anode electrodes in Li-ion batteries. The experiments and density functional theory simulations indicate that abundant hydroxyl groups in the starch improve the binding strength with Si nanoparticles, and the integrated PEG groups facilitate Li-ion transfer in the Si electrode. The mechanical behavior of the electrode is significantly improved, as confirmed by nanoindentation and scratch tests. Excellent electrochemical performance is observed, with an initial lithiation capacity of 3486 mA h g-1 and a noteworthy second cycle capacity retention of 98%, demonstrating its potential as a cheap and sustainable binder for Li-ion batteries.

It is now well established that the nonlinear optical properties of ZnO nanoparticles can be significantly enhanced by coupling them to metallic nanoparticles. While the nonlinear absorption properties are well reported, there is large variation in the coefficients of nonlinear refraction reported in literature, largely due to simplifications made during the analysis of experimental z-scan data used to determine the coefficients. This work presents closed aperture z-scan theory which incorporates the effects of nonlinear absorption, thus providing a more accurate measure of the coefficient of nonlinear refraction. With this theory, it is shown that the coefficient of nonlinear refraction increases by an order of magnitude when ZnO is coupled to Au nanoparticles.

ZBLAN glass tends to undergo heavy devitrification, forming crystallites that act as scattering centers and results in a large attenuation loss. In this study, attenuation loss values were obtained for ZBLAN glass test samples that were melted and then cooled rapidly at a rate of 4000 °C/min, which yielded amorphous samples that were free of micro/nano-crystalline inclusions. Using an approach by Forouhi and Bloomer, which incorporates Kramers–Kronig relations, in conjunction with measured optical data using ellipsometry, an attenuation loss of 0.092 dB/Km at 1800 nm wavelength was estimated for amorphous ZBLAN test samples.

ZBLAN glass is a heavy metal fluoride glass that tends to undergo heavy devitrification, resulting in a crystalline material. It has many applications, including its use as an optical waveguide for fiber‐optic technology. However, when the glass is processed with traditional casting techniques, crystallites form readily that act as scattering centers, which results in large attenuation losses. In this study, it has been experimentally demonstrated that processing ZBLAN rapidly with a heating rate of 25 000 K/min and cooling rate of 4000 K/min yields test samples that are fully amorphous and retain a disordered molecular arrangement characteristic of its molten state. This novel method was developed using a specifically designed equipment named a Rapid Electro‐thermal Processing Device, or “REPD.” The REPD applies ohmic heating and thermal conduction to a heat sink to rapidly process the ZBLAN material. The absence of crystallites in the rapidly processed ZBLAN test samples were verified using transmission electron microscopy (TEM) analysis. Applying a theoretical algorithm, the critical cooling rate for yielding fully amorphous ZBLAN glass was determined to be 1081 K/min for a sample volume of 9.4 × 10−8m3.

ZBLAN glass is a heavy metal fluoride glass that shows great potential in the application of long-haul telecommunication cables. However, during processing in the fiber-drawing temperature region, the material tends to undergo heavy devitrification, resulting in a crystalline fiber that is not usable as an optical waveguide. In this study, ZBLAN glass was processed with different cooling rates to discern how the rate of cooling affects the process of crystallization. Rapidly cooled ZBLAN glass test samples were then analysed with a wide range of spectroscopy and imaging techniques including EDS, SEM, TEM and XRD. These techniques revealed there are two predominant crystal phases, one rich in zirconium and barium, the other in zirconium and sodium. Ultimately, a critical cooling rate was established to be somewhere between 900 °C/min and 4000 °C/min, with a theoretically predicted value of 1081 °C/min for a test sample volume size of 9.4 × 10−8 m3. Cooling above this critical cooling rate yielded fully amorphous ZBLAN test samples that were completely free of nano-crystalline inclusions. Using Kramers-Kronig relations, an attenuation loss for the fully amorphous ZBLAN test samples was estimated to be 0.09 dB/Km at a wavelength of 1800 nm.

By investigating the action spectra (the relationship between the irradiation wavelength and apparent quantum efficiency of reactions under constant irradiance) of a number of reactions catalyzed by nanoparticles including plasmonic metals, nonplasmonic metals, and their alloys at near-ambient temperatures, we found that a photon energy threshold exists in each photocatalytic reaction; only photons with sufficient energy (e.g., higher than the energy level of the lowest unoccupied molecular orbitals) can initiate the reactions. This energy alignment (and the photon energy threshold) is determined by various factors, including the wavelength and intensity of irradiation, molecule structure, reaction temperature, and so forth. Hence, distinct action spectra were observed in the same type of reaction catalyzed by the same catalyst due to a different substituent group, a slightly changed reaction temperature. These results indicate that photon–electron excitations, instead of the photothermal effect, play a dominant role in direct photocatalysis of metal nanoparticles for many reactions.

Many organic synthesis systems use thermal catalysis to achieve higher product efficiency, and it is of interest to drive reactions by light irradiation at moderate reaction conditions. Other than semiconductors, recent reports have shown that metal nanostructures can be used as direct photocatalysts to drive chemical reactions. In this review, we summarize recent progress in direct photocatalysis in organic synthesis using plasmonic and non-plasmonic metal nanostructures. It starts with a comprehensive introduction to surface plasmons and the role of interband transitions in non-plasmonic metal nanostructures. The application of metal nanostructures in organic synthesis is systematically reviewed, followed by the reaction mechanisms; the role of light-excited energetic electrons, enhanced electromagnetic fields and the photothermal effect are detailed. The influence of light intensity and wavelength is discussed, as well as the critical parameters of photocatalyst design. Finally, the outlook and future opportunities of this new exciting field will be discussed.

The nonlinear response of zinc oxide and zinc oxide-gold hybrid colloidal nanostructures to 532 nm nanosecond pulses was investigated. The z-scan technique was used to measure the nonlinear absorption of zinc oxide, zinc-oxide: gold hybrids and mixed colloids of zinc-oxide and gold. Despite similar zinc oxide concentrations, the colloids containing gold nanoparticles displayed stronger intensity dependent nonlinear absorption with optical limiting thresholds for the three samples of 35 J/cm2, 6.1 J/cm2 and 4.1 J/cm2, respectively. Therefore, by combining gold with zinc-oxide to form hybrid nanostructures or by simply mixing gold and zinc-oxide nanostructures together, the optical limiting threshold is reduced which is advantageous for optical limiting applications.

This paper investigates whether coupling gold nanoparticles to nanostructured zinc oxide enhances fluorescence emission, to produce efficient nanoscale UV emitters that radiate through nonlinear optical absorption processes. The z-scan technique is used to measure nonlinear absorption simultaneously with measurements of nonlinear-absorption-induced fluorescence in zinc oxide nanostructures and hybrid zinc oxide–gold nanostructures. This allows for better determination of the nonlinear excitation and energy dissipation pathways. The measurements show that the nonlinear absorption of the hybrid structures is enhanced by up to two orders of magnitude compared to the pure zinc oxide nanostructures. However, it is found that the increase in nonlinear absorption does not correspond to an equivalent increase in fluorescence due to the competition between two-photon absorption and excited state absorption.

In this paper we report the design and experimental realisation of a novel refractive index sensor based on coupling between three nanoscale stripe waveguides. The sensor is highly compact and designed to operate at a single wavelength. We demonstrate that the sensor exhibits linear response with a resolution of 6 × 10^−4 RIU (refractive index unit) for a change in relative output intensity of 1%. Authors expect that the outcome of this paper will prove beneficial in highly compact, label-free and highly sensitive refractive index analysis.

A thorough analysis of the resonance light scattering (RLS) technique for quantitative scattering measurements of subwavelength nanoparticles is reported. The systematic error associated with using a measurement at a single angle to represent all of the scattered light is investigated. In-depth analysis of the reference material was performed to identify and minimize the error associated with the reference material. Semiconductor ZnO nanobullets and spherical Au nanoparticles of various sizes were used to verify the approach. A simple and inexpensive modification to standard fluorometers is demonstrated using a glass prism allowing scattering measurements in the slightly forward and backwards directions. This allows quantification of the systematic error associated with RLS which is consistently overlooked.