Photoinduced motions in azo-containing polymers.

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

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Piezoelectric and ferroelectric materials and structures for energy harvesting applications

A series of amorphous azobenzene-containing polymers were cast as thin films and shown to produce both reversible volume diffraction gratings and high-efficiency surface gratings by laser irradiation at an absorbing wavelength. The latter process involves localized mass transport of the polymer chains to a high degree, as atomic force microscopy reveals surface profile depths near that of the original film thickness. A mechanism for this phenomenon is proposed which involves pressure gradients as a driving force, present due to different photochemical behaviors of the azo chromophores at different regions of the interference pattern. The phase addition of the two beams in the interference pattern leads to regions of high trans-cis-trans isomerization by the absorbing azo groups, bordered by regions of low isomerization. As the geometrical isomerization requires free volume in excess of that available in the cast films, the photochemical reaction in these areas produces a laser-induced internal pressure ab...

Mechanism of Optically Inscribed High-Efficiency Diffraction Gratings in Azo Polymer Films

Light scattering by small particles has a long and interesting history in physics. Nonetheless, it continues to surprise with new insights and applications. This includes new discoveries, such as novel plasmonic effects, as well as exciting theoretical and experimental developments such as optical trapping, anomalous light scattering, optical tweezers, nanospasers, and novel aspects and realizations of Fano resonances. These have led to important new applications, including several ones in the biomedical area and in sensing techniques at the single-molecule level. There are additionally many potential future applications in optical devices and solar energy technologies. Here we review the fundamental aspects of light scattering by small spherical particles, emphasizing the phenomenological treatments and new developments in this field. The interaction of light with small spherical particles has long been a topic of interest to researchers. Indeed, understanding many natural phenomena, including rainbows and the solar corona, requires knowledge of how light behaves in such circumstances. Xiaofeng Fan and co-workers from Jilin University in China and Oak Ridge National Laboratory in the USA have now reviewed the physics and applications that arise during the interaction of light with small spherical particles. The researchers describe how Mie theory can be used to describe optical scattering by small dielectric particles, and, in the case of metallic particles, how light excites surface plasmons to generate an optical response featuring asymmetric Fano resonances. In the special case when metallic particles are surrounded by an optical gain medium, plasmons can be amplified; the resulting device is known as a ‘spaser’.

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Light scattering and surface plasmons on small spherical particles

Light scattering by small particles has a long and interesting history in physics. Nonetheless, it continues to surprise with new insights and applications. This includes new discoveries, such as novel plasmonic effects, as well as exciting theoretical and experimental developments such as optical trapping, anomalous light scattering, optical tweezers, nano-spasers, and novel aspects and realizations of Fano resonances. These have led to important new applications, including several ones in the biomedical area and in sensing techniques at the single-molecule level. There are additionally many potential future applications in optical devices and solar energy technologies. Here we review the fundamental aspects of light scattering by small spherical particles, emphasizing the phenomenological treatments and new developments in this field.

/pdf/light-scattering-and-surface-plasmons-on-small-spherical-4pdzxflt35.pdf

In this paper, an asymmetric plasmonic structure composed of a MIM (metal-insulator-metal) waveguide and a rectangular cavity is reported, which can support double Fano resonances originating from two different mechanisms. One of Fano resonance originates from the interference between a horizontal and a vertical resonance in the rectangular cavity. And the other is induced by the asymmetry of the plasmonic structure. Just because the double Fano resonances originate from two different mechanisms, each Fano resonance can be well tuned independently by changing the parameters of the rectangular cavity. And during the tuning process, the FOMs (figure of merit) of both the Fano resonances can keep unchanged almost with large values, both larger than 650. Such, the transmission spectra of the plasmonic structure can be well modulated to form transmission window with the position and the full width at half maximum (FWHM) can be tuned freely, which is useful for the applications in sensors, nonlinear and slow-light devices.

Independently tunable double Fano resonances in asymmetric MIM waveguide structure

We investigate UV photorefraction in Mg-doped LiNbO3 crystals. Strong UV photorefraction is achieved in highly Mg-doped LiNbO3 crystals with high two-wave mixing gain, fast response, and low noise. It is also demonstrated experimentally that so-called damage-resistant dopants such as Mg are damage resistant only in the visible and that they will enhance photorefraction in the UV.

Enhancement of ultraviolet photorefraction in highly magnesium-doped lithium niobate crystals

Based on the two-center model and the multi-three-wave mixing model, we theoretically study the possible origins of the threshold effect of the incident light intensity for the photorefractive light-induced scattering in LiNbO3:Fe,M, (M=Mg2+, Zn2+, In3+) crystals. Our results show that the value of the threshold intensity of incident light is strongly dependent on the dark conductivity of the crystal, and the maximum total fanning noise is dependent on the concentration of Fe ion on the Li site. These two factors together determine the threshold behavior of incident light intensity for the photorefractive light-induced scattering in LiNbO3:Fe,M crystals when the incident light intensity is in moderate range.

The threshold effect of incident light intensity for the photorefractive light-induced scattering in LiNbO3:Fe,M (M=Mg2+, Zn2+, In3+) crystals

In this work we studied photorefractive effect of lithium niobate $({\mathrm{LiNbO}}_{3})$ doped with $\mathrm{Zn}$, $\mathrm{In}$, and $\mathrm{Na}$ at ultraviolet $(\mathrm{UV})$ wavelength down to $351\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. It is found that the $\mathrm{UV}$ photorefraction of ${\mathrm{LiNbO}}_{3}$ doped with $\mathrm{Zn}$, $\mathrm{In}$, or $\mathrm{Na}$ was enhanced significantly as compared to that of the nominally pure ${\mathrm{LiNbO}}_{3}$. Our results show that the statement that the property of resistance against photorefraction in highly $\mathrm{Zn}$ and $\mathrm{In}$ doped ${\mathrm{LiNbO}}_{3}$ is correct only in visible light range. By contrary, these crystals exhibit as excellent photorefractive characteristics in $\mathrm{UV}$. We also find that there are doping concentration threshold values of $\mathrm{Zn}$ and $\mathrm{In}$ for the disappearance of the light-induced lens-like effect both in visible and in $\mathrm{UV}$, but such concentration threshold values are not found for $\mathrm{UV}$ photorefraction within the highest doping concentrations we used. In highly $\mathrm{Zn}$ or $\mathrm{In}$ doped ${\mathrm{LiNbO}}_{3}$ crystals, diffusion dominates over photovoltaic effect and electrons are determined to be the dominant charge carriers in $\mathrm{UV}$ photorefraction. The results are of interest to the study on the defect structure of ${\mathrm{LiNbO}}_{3}$. Further investigation on this field is greatly urgent.

Ultraviolet photorefractivity features in doped lithium niobate crystals

A simple method to trap and manipulate metallic micro/nano-particles on the surface of photorefractive crystals is proposed. After inducing inhomogeneous charge density and space-charge fields in photorefractive crystals by non-uniform illumination, both uncharged and charged metallic particles can be trapped on the illuminated surface due to dielectrophoretic force and electrophoretic force, respectively. A transition from dielectrophoresis to electrophoresis is observed when manipulating nano-silver particles with high surface space-charge field. Our results show that this method is simple and effective to form surface microstructures of metallic particles.

Qian Sun

Papers

Independently tunable double Fano resonances in asymmetric MIM waveguide structure

Enhancement of ultraviolet photorefraction in highly magnesium-doped lithium niobate crystals

The threshold effect of incident light intensity for the photorefractive light-induced scattering in LiNbO3:Fe,M (M=Mg2+, Zn2+, In3+) crystals

Ultraviolet photorefractivity features in doped lithium niobate crystals

Optical trapping and manipulation of metallic micro/nanoparticles via photorefractive crystals