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Photonic crystals

K Iwano, Y Shimoi, T Miyamoto, D Hata, M Sotome, N Kida, S Horiuchi, H Okamoto
Croconic acid crystals show proton displacive-type ferroelectricity with a large spontaneous polarization reaching 20  μC/cm^{2}, which originates from the strong coupling of proton and π-electron degrees of freedom. Such a coupling makes us expect a large polarization change by photoirradiations. Optical-pump second-harmonic-generation-probe experiments reveal that a photoexcited croconic-acid crystal loses the ferroelectricity substantially with a maximum quantum efficiency of more than 30 molecules per one absorbed photon...
March 10, 2017: Physical Review Letters
C Braggio, G Carugno, M Guarise, A Ortolan, G Ruoso
We demonstrate an all-optical method for manipulating the magnetization in a 1-mm yttrium-iron-garnet (YIG) sphere placed in a ∼0.17  T uniform magnetic field. A harmonic of the frequency comb delivered by a multi-GHz infrared laser source is tuned to the Larmor frequency of the YIG sphere to drive magnetization oscillations, which in turn give rise to a radiation field used to thoroughly investigate the phenomenon. The radiation damping issue that occurs at high frequency and in the presence of highly magnetizated materials has been overcome by exploiting the magnon-photon strong coupling regime in microwave cavities...
March 10, 2017: Physical Review Letters
Pingping Qiu, Weibin Qiu, Zhili Lin, Houbo Chen, Yixin Tang, Jia-Xian Wang, Qiang Kan, Jiao-Qing Pan
In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC...
September 9, 2016: Nanomaterials
Zhengyu Yan, Chunqing Tian, Xincheng Qu, Weiyang Shen, Baofen Ye
A novel type of suspension array for multiplex detection of heavy metal ions with photonic crystal hydrogel microspheres was reported. The photonic crystal hydrogel microspheres have close-packed photonic crystal particles as their encoding units and ssDNA-functionalized hydrogel as the sensing units. The developed microspheres were successfully applied in multiplex detection of heavy metal ions.
March 8, 2017: Colloids and Surfaces. B, Biointerfaces
William Yao, Edward C Kuan, Nathan C Francis, Maie A St John, Warren S Grundfest, Zachary D Taylor
BACKGROUND AND OBJECTIVES: Bacterial biofilm formation within chronic wound beds, which provides an effective barrier against antibiotics, is a known cause of recalcitrant infections and a significant healthcare burden, often requiring repeated surgical debridements. Laser-generated shockwaves (LGS) is a novel, minimally invasive, and nonthermal modality for biofilm mechanical debridement which utilizes compressive stress waves, generated by photonic absorption in thin titanium films to mechanically disrupt the biofilm...
March 23, 2017: Lasers in Surgery and Medicine
Andrew E Sifain, Loza F Tadesse, Josiah A Bjorgaard, David E Chavez, Oleg V Prezhdo, R Jason Scharff, Sergei Tretiak
Conjugated energetic molecules (CEMs) are a class of explosives with high nitrogen content that posses both enhanced safety and energetic performance properties and are ideal for direct optical initiation. As isolated molecules, they absorb within the range of conventional lasers. Crystalline CEMs are used in practice, however, and their properties can differ due to intermolecular interaction. Herein, time-dependent density functional theory was used to investigate one-photon absorption (OPA) and two-photon absorption (TPA) of monomers and dimers obtained from experimentally determined crystal structures of CEMs...
March 21, 2017: Journal of Chemical Physics
Han-Bok Seo, Seung-Yop Lee
Structure-dependent colour is caused by the interaction of light with photonic crystal structures rather than pigments. The elytra of longhorn beetles Tmesisternus isabellae appear to be iridescent green in a dry state and turn to red when exposed to humidity. Based on the hygroscopic colouration of the longhorn beetle, we have developed centimeter-scale colorimetric opal films using a novel self-assembly method. The micro-channel assisted assembly technique adopts both natural evaporation and rotational forced drying, enhancing the surface binding of silica particles and the packing density by reducing the lattice constant and structural defects...
March 21, 2017: Scientific Reports
David Freese, David Hsu, Derek Innes, Craig Levin
Positron Emission Tomography (PET) relies on accurate timing information to pair two 511 keV photons into a coincidence event. Calibration of time delays between detectors becomes increasingly important as the timing resolution of detector technology improves, as calibration error can quickly become a dominant source of error. Previous work has shown the maximum likelihood estimate of these delays can be calculated by least squares estimation, but that approach is not tractable for complex systems and degrades in the presence of randoms...
March 13, 2017: IEEE Transactions on Medical Imaging
Mingxuan Cao, Siwei Yang, Yating Zhang, Xiaoxian Song, Yongli Che, Haiting Zhang, Yu Yu, Gu Ding, Guizhong Zhang, Jianquan Yao
Graphene quantum dots (GQDs) have received great attention owing to their unique structure and novel phenomena of optical absorption/emission. In this letter, we observed the tunable amplified spontaneous emission (ASE) in GQDs doped cholesteric liquid crystals (CLC) for the first time. The GQDs are dispersed in CLC homogeneously with the weight ratio of 0.5 wt%. Under optical excitation, a typical ASE is triggered in the system above a 1.25 mJ/cm2 threshold. In addition, the emission peak at the long wavelength edge of the photonic bandgap shifts from 662 nm to 669 nm with the change of working temperature...
March 20, 2017: Nanotechnology
Xiaolong Xu, Qingjun Song, Haifeng Wang, Pan Li, Kun Zhang, Yilun Wang, Kai Yuan, Zichen Yang, Yu Ye, Lun Dai
The group IV-VI compound tin selenide (SnSe) has recently attracted particular interest due to its unexpectedly low thermal conductivity and high power factor, showing great promise for thermoelectric applications. With an orthorhombic lattice structure, SnSe displays intriguing anisotropic properties due to the low symmetry of the puckered in-plane lattice structure. When thermoelectric materials, like SnSe, have decreased dimensionality, their thermoelectric conversion efficiency may be improved due to increased power factor and decreased thermal conductivity...
March 20, 2017: ACS Applied Materials & Interfaces
Nikita Kostylev, Maxim Goryachev, Andrey D Bulanov, Vladimir A Gavva, Michael E Tobar
The low dielectric losses of an isotopically pure single crystal (28)Si sample were determined at a temperature of 20 mK and at powers equivalent to that of a single photon. Whispering Gallery Mode (WGM) analysis revealed large Quality Factors of order 2 × 10(6) (dielectric loss ~5 × 10(-7)) at high powers, degrading to 7 × 10(-5) (dielectric loss ~1.4 × 10(-6) at single photon energy. A very low-loss narrow line width paramagnetic spin flip transition was detected with extreme sensitivity in (28)Si, with very small concentration below 10(10) cm(-3) (less than 10 parts per trillion) and g-factor of 1...
March 20, 2017: Scientific Reports
Nathaniel J L K Davis, Francisco J de la Peña, Maxim Tabachnyk, Johannes M Richter, Robin D Lamboll, Edward P Booker, Florencia Wisnivesky Rocca Rivarola, James T Griffiths, Caterina Ducati, S Matthew Menke, Felix Deschler, Neil C Greenham
Cesium lead halide nanocrystals, CsPbX3 (X = Cl, Br, I), exhibit photoluminescence quantum efficiencies approaching 100% without the core-shell structures usually used in conventional semiconductor nanocrystals. These high photoluminescence efficiencies make these crystals ideal candidates for light-emitting diodes (LEDs). However, because of the large surface area to volume ratio, halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, which is one of the limiting factors for white-light applications requiring a mixture of different crystal compositions to achieve a broad emission spectrum...
February 23, 2017: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
S Nappini, A Matruglio, D Naumenko, S Dal Zilio, F Bondino, M Lazzarino, E Magnano
X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption Spectroscopy (XAS) provide unique knowledge on the electronic structure and chemical properties of materials. Unfortunately this information is scarce when investigating solid/liquid interfaces and chemical or photochemical reactions under ambient conditions because of the short electron inelastic mean free path (IMFP) that requires a vacuum environment, which poses serious limitation on the application of XPS and XAS to samples present in the atmosphere or in the presence of a solvent...
March 17, 2017: Nanoscale
Yan Chen, Yang Zhang, Daniil Karnaushenko, Li Chen, Jianhua Hao, Fei Ding, Oliver G Schmidt
Piezophotonic light-emitting devices have great potential for future microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) due to the added functionality provided by the electromechanical transduction coupled with the ability of light emission. Piezophotonic light-emitting source based on Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 (PMN-PT) bulk is severely restricted by many challenges, such as high voltage burden, low integration density, and micromanufacturing complexity. Developing chip-integrated devices or incorporating such photonic components onto a Si platform is highly sought after in this field...
March 15, 2017: Advanced Materials
Chenhui Peng, Yubing Guo, Taras Turiv, Miao Jiang, Qi-Huo Wei, Oleg D Lavrentovich
Controlling supramolecular self-assembly in water-based solutions is an important problem of interdisciplinary character that impacts the development of many functional materials and systems. Significant progress in aqueous self-assembly and templating has been demonstrated by using lyotropic chromonic liquid crystals (LCLCs) as these materials show spontaneous orientational order caused by unidirectional stacking of plank-like molecules into elongated aggregates. In this work, it is demonstrated that the alignment direction of chromonic assemblies can be patterned into complex spatially-varying structures with very high micrometer-scale precision...
March 15, 2017: Advanced Materials
Kutan Gürel, Valentin J Wittwer, Sargis Hakobyan, Stéphane Schilt, Thomas Südmeyer
We demonstrate the first diode-pumped Ti:sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard f-to-2f interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes with a feedback bandwidth of 55 kHz limited by the pump diode driver used in this experiment...
March 15, 2017: Optics Letters
Andrey M Vyunishev, Anatoly S Chirkin
We study the frequency doubling in a quadratic nonlinear photonic crystal consisting of periodically poled structures mediated by uniform layers with random lengths. These structures can be formed by new local impact methods for ferroelectric crystal structuring. The statistical frequency doubling theory is developed for such structures. The effect of the number of random layers and variation in their thicknesses on the second-harmonic conversion efficiency is clarified. It is demonstrated that a proper choice of the intermediate layer thickness can enhance or suppress the conversion efficiency...
March 15, 2017: Optics Letters
Esrom Kifle, Xavier Mateos, Javier Rodríguez Vázquez de Aldana, Airan Ródenas, Pavel Loiko, Sun Yung Choi, Fabian Rotermund, Uwe Griebner, Valentin Petrov, Magdalena Aguiló, Francesc Díaz
Depressed-index channel waveguides with a circular and photonic crystal cladding structures are prepared in a bulk monoclinic Tm:KLu(WO<sub>4</sub>)<sub>2</sub> crystal by 3D direct femtosecond laser writing. The channel waveguide structures are characterized and laser operation is achieved using external mirrors. In the continuous-wave mode, the maximum output power of 46 mW is achieved at 1912 nm corresponding to a slope efficiency of 15.2% and a laser threshold of only 21 mW. Passive Q-switching of a waveguide with a circular cladding is realized using single-walled carbon nanotubes...
March 15, 2017: Optics Letters
Changxu Lin, Yin Jiang, Cheng-An Tao, Xianpeng Yin, Yue Lan, Chen Wang, Shiqiang Wang, Xiangyang Liu, Guangtao Li
In this article, the fabrication of an active organic-inorganic one-dimensional photonic crystal structure to offer electrothermal fluorescence switching is described. The film is obtained by spin-coating of liquid crystal elastomers (LCEs) and TiO2 nanoparticles alternatively. By utilizing the property of LCEs that can change their size and shape reversibly under external thermal stimulations, the λmax of the photonic band gap of these films is tuned by voltage through electrothermal conversion. The shifted photonic band gap further changes the matching degree between the photonic band gap of the film and the emission spectrum of organic dye mounting on the film...
March 22, 2017: ACS Applied Materials & Interfaces
Kali Prasanna Nayak, Jameesh Keloth, Kohzo Hakuta
We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm...
February 25, 2017: Journal of Visualized Experiments: JoVE
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