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Photonic crystals

Francesco De Leonardis, Richard A Soref, Vittorio M N Passaro
In this paper we present a physical discussion of the indirect two-photon absorption (TPA) occuring in silicon carbide with either cubic or wurtzite structure. Phonon-electron interaction is analyzed by finding the phonon features involved in the process as depending upon the crystal symmetry. Consistent physical assumptions about the phonon-electron scattering mechanisms are proposed in order to give a mathematical formulation to predict the wavelength dispersion of TPA and the Kerr nonlinear refractive index n2...
January 18, 2017: Scientific Reports
Dongmei Liu, Dunzhao Wei, Yong Zhang, Zhenhua Chen, Rui Ni, Bo Yang, Xiaopeng Hu, Y Q Qin, S N Zhu, Min Xiao
Diffraction-free beams have attracted increasing research interests because of their unique performances and broad applications in various fields. Although many methods have been developed to produce such beams, it is still challenging to realize a tunable non-diffracting beam. Here, we report the generation of a tunable diffraction-free array through second-harmonic generation in a nonlinear photonic crystal, i.e., a 2D periodically-poled LiTaO3 crystal. In such a crystal, the second-harmonic wave is engineered by properly designing the domain structure based on the Huygens-Fresnel principle...
January 18, 2017: Scientific Reports
Shiva Abbaszadeh, Craig S Levin
The next generation of discoveries in molecular imaging requires positron emission tomography (PET) systems with high spatial resolution and high sensitivity to visualize and quantify low concentrations of molecular probes. The goal of this work is to assemble and explore such a system. We use cadmium zinc telluride (CZT) to achieve high spatial resolution, three-dimensional interaction positioning, and excellent energy resolution. The CZT crystals are arranged in an edge-on configuration with a minimum gap of [Formula: see text] in a four-sided panel geometry to achieve superior photon sensitivity...
January 2017: Journal of Medical Imaging
Iñigo Liberal, Nader Engheta
Vacuum fluctuations are one of the most distinctive aspects of quantum optics, being the trigger of multiple nonclassical phenomena. Thus, platforms like resonant cavities and photonic crystals that enable the inhibition and manipulation of vacuum fluctuations have been key to our ability to control light-matter interactions (e.g., the decay of quantum emitters). Here, we theoretically demonstrate that vacuum fluctuations may be naturally inhibited within bodies immersed in epsilon-and-mu-near-zero (EMNZ) media, while they can also be selectively excited via bound eigenmodes...
January 17, 2017: Proceedings of the National Academy of Sciences of the United States of America
Zhi-Guo Chen, R Y Chen, R D Zhong, John Schneeloch, C Zhang, Y Huang, Fanming Qu, Rui Yu, Q Li, G D Gu, N L Wang
Three-dimensional topological insulators (3D TIs) represent states of quantum matters in which surface states are protected by time-reversal symmetry and an inversion occurs between bulk conduction and valence bands. However, the bulk-band inversion, which is intimately tied to the topologically nontrivial nature of 3D Tis, has rarely been investigated by experiments. Besides, 3D massive Dirac fermions with nearly linear band dispersions were seldom observed in TIs. Recently, a van der Waals crystal, ZrTe5, was theoretically predicted to be a TI...
January 17, 2017: Proceedings of the National Academy of Sciences of the United States of America
Bahaa Ghammraoui, Lucretiu M Popescu
We investigate the use of energy dispersive x-ray coherent scatter computed tomography (ED-CSCT) as a non-invasive diagnostic method to differentiate between type I and type II breast calcifications. This approach is sensitive to the differences of composition and internal crystal structure of different types of microcalcifications. The study is carried out by simulating a CSCT system with a scanning pencil beam, considering a polychromatic x-ray source and an energy-resolving photon counting detector. In a first step, the multidimensional angle and energy distributed CSCT data is reduced to the projection-space distributions of only a few components, corresponding to the expected target composition: adipose, glandular tissue, weddellite (calcium oxalate) for type I calcifications, and hydroxyapatite for type II calcifications...
February 7, 2017: Physics in Medicine and Biology
Asaf Dahan, Assaf Levanon, Mordechai Katz, Haim Suchowski
We introduce a generalization of the adiabatic frequency conversion method for an efficient conversion of ultrashort pulses in the full nonlinear regime. Our analysis takes into account dispersion as well as two-photon processes and Kerr effect, allowing complete analysis of any three waves with arbitrary phase mismatched design and any nonlinear optical process. We use this analysis to design an efficient and robust second harmonic generation, the most widely used nonlinear process for both fundamental and applied research...
January 16, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Yuqi Zhang, Qianqian Fu, Jianping Ge
A test-paper-like photonic crystal (PC) viscometer is fabricated based on the positive correlation between viscosity and the infiltration time for viscous liquid to entirely soak the PC film. It can be broadly used in different occasions to quickly determine the viscosity for many liquids, considering its portable and disposable characteristics and the requirement of little samples.
January 16, 2017: Small
Stefanie Herbst, Bartolome Soberats, Pawaret Leowanawat, Matthias Lehmann, Frank Würthner
A new perylene bisimide (PBI) dye self-assembles through hydrogen bonds and π-π interactions into J-aggregates that in turn self-organize into liquid-crystalline (LC) columnar hexagonal domains. The PBI cores are organized with the transition dipole moments parallel to the columnar axis, which is an unprecedented structural organization in π-conjugated columnar liquid crystals. Middle and wide-angle X-ray analyses reveal a helical structure consisting of three self-assembled hydrogen-bonded PBI strands that constitute a single column of the columnar hexagonal phase...
January 16, 2017: Angewandte Chemie
Luca Nucara, Vincenzo Piazza, Francesco Greco, Valentina Robbiano, Valentina Cappello, Mauro Gemmi, Franco Cacialli, Virgilio Mattoli
Stimuli-responsive photonic crystals (PCs) represent an intriguing class of smart materials very promising for sensing applications. Here, selective ionic strength responsive polymeric PCs are reported. They are easily fabricated by partial sulfonation of polystyrene opals, without using toxic or expensive monomers and etching steps. The color of the resulting hydrogel-like ordered structures can be continuously shifted over the entire visible range (405-760 nm) by changing the content of ions over an extremely wide range of concentration (from about 70 M to 4 M)...
January 12, 2017: ACS Applied Materials & Interfaces
Marian Chapran, Enrico Angioni, Neil John Findlay, Benjamin Breig, Vladyslav Cherpak, Pavlo Stakhira, Tell Tuttle, Dmytro Volyniuk, Juozas Vidas Grazulevicius, Yuriy A Nastishin, Oleg D Lavrentovich, Peter John Skabara
A new interface engineering method is demonstrated for the preparation of an efficient white organic light emitting diode (WOLED) by embedding an ultra-thin layer of the novel ambipolar red emissive compound 4,4-di-fluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10-4 cm2 V-1 s-1 and 2 × 10-4 cm2 V-1 s-1, respectively at electric fields higher than 5.3 × 105 V cm-1...
January 12, 2017: ACS Applied Materials & Interfaces
Haiyun Dong, Chunhuan Zhang, Xianqing Lin, Zhonghao Zhou, Jiannian Yao, Yong Sheng Zhao
Wavelength switchable micro/nanoscale laser is essential to construct various ultracompact photonic devices. However, traditional semiconductors as the gain media generally provide only monochromatic laser output due to their continuous energy band structures. For luminescent conjugated molecules, the broad emission band usually contains a series of vibronic peaks, which is very helpful for extending the lasing spectrum to several different wavelengths. Here we propose a novel strategy to realize wavelength switchable lasers based on the controlled competition of dual-wavelength vibronic lasing in single-component organic microcrystals...
January 11, 2017: Nano Letters
Antonio Consoli, Cefe López
Two major elements are required in a laser device: light confinement and light amplification. Light confinement is obtained in optical cavities by employing a pair of mirrors or by periodic spatial modulation of the refractive index as in photonic crystals and Bragg gratings. In random lasers, randomly placed nanoparticles embedded in the active material provide distributed optical feedback for lasing action. Recently, we demonstrated a novel architecture in which scattering nanoparticles and active element are spatially separated and random lasing is observed...
January 10, 2017: Scientific Reports
P St J Russell, R Beravat, G K L Wong
Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM)...
February 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Yun Long, Jinsong Xia, Yong Zhang, Jianji Dong, Jian Wang
Driven by the increasing demand on handing microwave signals with compact device, low power consumption, high efficiency and high reliability, it is highly desired to generate, distribute, and process microwave signals using photonic integrated circuits. Silicon photonics offers a promising platform facilitating ultracompact microwave photonic signal processing assisted by silicon nanophotonic devices. In this paper, we propose, theoretically analyze and experimentally demonstrate a simple scheme to realize ultracompact rejection ratio tunable notch microwave photonic filter (MPF) based on a silicon photonic crystal (PhC) nanocavity with fixed extinction ratio...
January 9, 2017: Scientific Reports
Xiaoxia Liu, Xingda Song, Zhiyong Dong, Xiaoting Meng, Yiping Chen, Li Yang
We have developed a sensitive photonic crystal fiber (PCF)-based immunosensor for detection of alpha fetoprotein (AFP). The unique PCF possesses a morphology characterized by numerous pore structures and a large surface area-to-volume ratio, which can be used as an immune-reaction carrier to improve the sensitivity and reaction speed of AFP detection. The PCF-based immunosensor possesses a low limit of detection of 0.1ng/mL, which is five times lower than that of the capillary-based sensor and 35 times lower than that of the traditional enzyme-linked immunosorbent assay...
December 30, 2016: Biosensors & Bioelectronics
Yanyan Zhi, Xiao-Chong Yu, Qihuang Gong, Lan Yang, Yun-Feng Xiao
Detection of nanoscale objects is highly desirable in various fields such as early-stage disease diagnosis, environmental monitoring and homeland security. Optical microcavity sensors are renowned for ultrahigh sensitivities due to strongly enhanced light-matter interaction. This review focuses on single nanoparticle detection using optical whispering gallery microcavities and photonic crystal microcavities, both of which have been developing rapidly over the past few years. The reactive and dissipative sensing methods, characterized by light-analyte interactions, are explained explicitly...
January 6, 2017: Advanced Materials
Margarita Franco-Ortiz, Adalberto Corella-Madueño, Rodrigo Rosas-Burgos, J Adrian Reyes, Carlos Avendaño
We consider a one dimensional photonic crystal made by an infinite set of nonlinear nematic films immersed in a linear dilectric medium. The thickness of each equidistant film is negligible and its refraction index depends continuously on the electric field intensity, giving rise to all the involved nonlinear terms which joints from a starting linear index for negligible amplitudes to a final saturation index for extremely large fiel intensities. We show that the nonlinear exact solutions of this system form an intensity dependent band structure which we calculate and analyze...
January 6, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Yu Guo, Shanhui Fan
We numerically demonstrate narrowband thermal emission with unity emissivity peak in the near-infrared range by critically coupling a flat tungsten surface with guided resonances of a dielectric photonic crystal slab. The tungsten surface is separated from the photonic crystal slab by a vacuum gap. The structure possesses significant tunability for both the center frequency and the linewidth of the thermal emission band. Moreover, the tungsten surface, being un-structured, should exhibit enhanced thermal stability at elevated temperature as compared to tungsten nanostructures...
December 26, 2016: Optics Express
Mariusz Klimczak, Bartłomiej Siwicki, Binbin Zhou, Morten Bache, Dariusz Pysz, Ole Bang, Ryszard Buczyński
Two all-solid glass photonic crystal fibers with all-normal dispersion profiles are evaluated for coherent supercontinuum generation under pumping in the 2.0 μm range. In-house boron-silicate and commercial lead-silicate glasses were used to fabricate fibers optimized for either flat dispersion, albeit with lower nonlinearity, or with larger dispersion profile curvature but with much higher nonlinearity. Recorded spectra at the redshifted edge reached 2500-2800 nm depending on fiber type. Possible factors behind these differences are discussed with numerical simulations...
December 26, 2016: Optics Express
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