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Photostrictive Actuators Based on Piezoelectrics
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
The photovoltage generated in some piezoelectric materials can be significantly greater than the band-gap energy. This “bulk” or “anomalous” photovoltaic effect (APV) is observed primarily in the direction of the spontaneous polarization (PS) in the ferroelectric material (Chu et al. 1994a; Uchino 1996) and the generated photovoltage is proportional to the specimen length along the direction of PS. Several important features of the bulk photovoltaic effect can be identified. The APV effect is observed in both a uniform single crystal and polycrystalline ceramic having non-centro-symmetry crystallographically. Furthermore, the effect produces a steady photovoltage and photocurrent under uniform illumination that is largely independent of any photothermal effects. Finally, the magnitude of the induced voltage is greater than the band gap of the crystal (e.g., perovskite oxide has a band-gap ~3.3 eV).
Fractional effects on solitons in a 1D array of rectangular ferroelectric nanoparticles
Published in Waves in Random and Complex Media, 2020
Yaouba Amadou, Mibaile Justin, Malwe B. Hubert, Gambo Betchewe, Serge Y. Doka, Kofane T. Crepin
The physics of nanostructures is the interdisciplinary field of research which use theoretical and experimental methods to determine the physical properties of materials in the nanoscale size range. Those properties encompass the structural electronic, optical and thermal behavior of nanomaterials [11–16]. There are a wide variety of functionalities of ferroelectric materials such as electronic conductivity, anomalous photovoltaic effect, and so on. These functionalities are potentially applicable to new nanoelectric devices. Extensive studies toward ferroelectric materials have been carried out to demonstrate their memory performance and their applications are shown in more domains [17,18]. Since ferroelectric materials are materials governed with non-volatile memory effect, fractional derivatives are more suitable for modeling memory phenomena within them.
Geometric-phase metalens to be used for tunable optical tweezers in microfluidics
Published in Liquid Crystals, 2023
René Geromel, Roman Rennerich, Thomas Zentgraf, Heinz Kitzerow
In summary, dielectric meta-lenses made of silicon with high numerical aperture and short focal lengths based on the design rules of the Pancharatnam-Berry phase were fabricated and characterised. It is confirmed that the same meta-lens acts as a converging and a diverging lens, depending on the handedness of circularly polarised light that is transmitted through these meta-surfaces. Circularly polarised diffraction experiments indicate reasonable conversion efficiencies of 50% and higher. Experimental measurement and visualisation of the beam propagation prove focussing of the light at the distance from the meta-lens that is expected. In previous experiments, it was shown that meta-lenses of this type can be used as optical tweezers to manipulate LC droplets [39]. Here, we demonstrated that changing the handedness of circularly polarised light transmitted through the meta-lens placed on a microfluidic channel can be used to trap and release polymer beads, respectively. Changing the state of polarisation that is necessary for this purpose can not only be achieved by mechanically rotating a QWP but also by electro-optic addressing of a suitable polarisation converter composed of an addressable LC layer and a passive LC layer. In our first attempts presented here, the electro-optic LC switch had slightly lower performance than mechanical rotation of commercial optical components, yet reasonable contrast ratios could be achieved. This observation may help to pave the way towards supplying microfluidic devices with integrated optical tweezers that can be controlled by electrical signals. In addition, all-optical switching using the colossal nonlinear optical effect of LCs [32] or the anomalous photovoltaic effect acting on an LC [43,44] may be envisaged.