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Optics Express

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https://www.readbyqxmd.com/read/30469991/time-resolved-high-harmonic-spectroscopy-of-ultrafast-photoisomerization-dynamics
#1
Keisuke Kaneshima, Yuki Ninota, Taro Sekikawa
We report the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. We associated the harmonic yield variation with the changes in the molecule's electronic state and vibrational frequencies, which are caused by isomerization. This showed us that the electronic excited state of CHD created through two-photon absorption of 3...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469990/spectrally-interleaved-topologies-using-geometric-phase-metasurfaces
#2
Michael Yannai, Elhanan Maguid, Arkady Faerman, Qitong Li, Jung-Hwan Song, Vladimir Kleiner, Mark L Brongersma, Erez Hasman
Metasurfaces facilitate the interleaving of multiple topologies in an ultra-thin photonic system. Here, we report on the spectral interleaving of topological states of light using a geometric phase metasurface. We realize that a dielectric spectrally interleaved metasurface generates multiple interleaved vortex beams at different wavelengths. By harnessing the space-variant polarization manipulations that are enabled by the geometric phase mechanism, a vectorial vortex array is implemented. The presented interleaved topologies concept can greatly enhance the functionality of advanced microscopy and communication systems...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469989/random-laser-model-for-nd-3-doped-powders-and-its-application-to-stimulated-emission-cross-section-calculations
#3
I Iparraguirre, J Azkargorta, J Fernández, S García-Revilla, M Barredo-Zuriarrain, R Balda
A new theoretical approach for random lasing of Nd3+ doped powders is presented. The model's singularity lies in the fact that it proposes a probability distribution of the stimulated photon paths lengths in the sample, as well as a population inversion shared by different photon paths. The model's predictions satisfactorily compare with the results of laser threshold and absolute input/output energy slope of a real Random Laser. The main novel issue is that the best fit to the experimental results requires considering a high level of shared population inversion among different paths...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469988/three-dimensional-double-helical-dna-structure-directly-revealed-from-its-x-ray-fiber-diffraction-pattern-by-iterative-phase-retrieval
#4
Tatiana Latychevskaia, Hans-Werner Fink
Coherent diffraction imaging (CDI) allows the retrieval of an isolated object's structure, such as a macromolecule, from its diffraction pattern. CDI requires the fulfillment of two conditions: the imaging radiation must be coherent and the object must be isolated. We discuss that it is possible to directly retrieve the molecular structure from its diffraction pattern, which was acquired neither with coherent radiation nor from an individual molecule. This is provided that the molecule exhibits periodicity in one direction, as in the case of fiber diffraction...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469987/enhanced-flatness-of-20-ghz-channel-spacing-multiwavelength-brillouin-raman-fiber-laser-with-sub-millimeter-air-gap
#5
A W Al-Alimi, A R Sarmani, M H Al-Mansoori, A F Abas, M T Alresheedi, M A Mahdi
We discover the technique of controlling the flatness in signal amplitude of a multiwavelength Brillouin-Raman fiber laser by employing an air-gap outside of the cavity. The structure that is adjustable within sub-millimeter length behaves as flexible optical feedback that provides modifiable portions of multiple Fresnel reflectivities. This is the main benchmark that allows the efficient management of gain competition between self-lasing modes and Brillouin Stokes waves that is vital for self-flattening initiation...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469986/multi-dimensional-qam-equivalent-constellation-using-coherently-coupled-orbital-angular-momentum-oam-modes-in-optical-communication
#6
Yuan Li, Kaitlyn Morgan, Wenzhe Li, J Keith Miller, Richard Watkins, Eric G Johnson
In this work, a 1550 nm fiber-to-free-space optical communication link is successfully demonstrated employing the superposition of two coherently coupled orbital angular momentum (CCOAM) states. Information is encoded onto both the amplitude and phase of the CCOAM beams and is mapped to a three-dimensional (3D) constellation space using quadrature amplitude modulation (QAM) equivalent architecture. The 3D QAM constellation is based on a higher-order Poincare sphere equivalent for OAM states, and multiple spherical constellations are demonstrated for 64- and 128-QAM, providing a 6X and 7X increase in spectral efficiency by fully exploiting the available 3D space...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469985/structural-coloration-with-hourglass-shaped-vertical-silicon-nanopillar-arrays
#7
Brian M Gawlik, Gabriel Cossio, Hoyeong Kwon, Zulema Jurado, Briana Palacios, Shrawan Singhal, Andrea Alù, Edward T Yu, S V Sreenivasan
We demonstrate that arrays of hourglass-shaped nanopillars patterned into crystalline silicon substrates exhibit vibrant, highly controllable reflective structural coloration. Unlike structures with uniform sidewall profiles, the hourglass profile defines two separate regions on the pillar: a head and a body. The head acts as a suspended Mie resonator and is responsible for resonant reflectance, while the body acts to suppress broadband reflections from the surface. The combination of these effects gives rise to vibrant colors...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469984/dynamically-tunable-multi-lobe-laser-generation-via-multifocal-curved-beam
#8
Enbo Xing, Hui Gao, Jiamin Rong, Si Ying Khew, Huagang Liu, Cunzhu Tong, Minghui Hong
Beams with curved properties, represented by Airy beam, have already shown potential applications in various fields. Here we propose a simple method to achieve a multifocal curved beam (MCB). The scheme is based on the ability of microspheres to control the distribution of the light field. Combined with the caustic effect, the dynamic control of the beam curvature and the foci can be realized. The simulation results confirm the mechanism behind this phenomenon. Furthermore, MCB is applied experimentally into the end-pumped microchip laser...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469983/reconfiguring-structured-light-beams-using-nonlinear-metasurfaces
#9
Yun Xu, Jingbo Sun, Jesse Frantz, Mikhail I Shalaev, Wiktor Walasik, Apra Pandey, Jason D Myers, Robel Y Bekele, Alexander Tsukernik, Jasbinder S Sanghera, Natalia M Litchinitser
Ultra-compact, low-loss, fast, and reconfigurable optical components, enabling manipulation of light by light, could open numerous opportunities for controlling light on the nanoscale. Nanostructured all-dielectric metasurfaces have been shown to enable extensive control of amplitude and phase of light in the linear optical regime. Among other functionalities, they offer unique opportunities for shaping the wave front of light to introduce the orbital angular momentum (OAM) to a beam. Such structured light beams bring a new degree of freedom for applications ranging from spectroscopy and micromanipulation to classical and quantum optical communications...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469982/light-scattering-control-in-transmission-and-reflection-with-neural-networks
#10
Alex Turpin, Ivan Vishniakou, Johannes D Seelig
Scattering often limits the controlled delivery of light in applications such as biomedical imaging, optogenetics, optical trapping, and fiber-optic communication or imaging. Such scattering can be controlled by appropriately shaping the light wavefront entering the material. Here, we develop a machine-learning approach for light control. Using pairs of binary intensity patterns and intensity measurements we train neural networks (NNs) to provide the wavefront corrections necessary to shape the beam after the scatterer...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469981/4-%C3%A3-128-gb-s-pdm-dmt-signal-transmission-over-1440-km-ssmf-with-high-phase-noise-tolerance
#11
Cai Li, Ming Luo, Xiang Li
In this paper, we propose an intensity modulation and coherent detection scheme with high phase noise tolerance for polarization division multiplexing (PDM) discrete multi-tone (DMT) signal transmission by employing Kramers-Kronig (KK) detection and digital carrier regeneration (DCR). At the transmitter side, DMT signal is modulated by a Mach-Zehnder modulator (MZM) setting bias around the null point and transmitted with the suppressed optical carrier. At the receiver side, a directly modulated lasers (DMLs) locating at the edge of DMT signal is used as the local oscillator (LO) for coherent detection...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469980/autonomous-illumination-control-for-localization-microscopy
#12
Marcel Štefko, Baptiste Ottino, Kyle M Douglass, Suliana Manley
Super-resolution fluorescence microscopy improves spatial resolution, but this comes at a loss of image throughput and presents unique challenges in identifying optimal acquisition parameters. Microscope automation routines can offset these drawbacks, but thus far have required user inputs that presume a priori knowledge about the sample. Here, we develop a flexible illumination control system for localization microscopy comprised of two interacting components that require no sample-specific inputs: a self-tuning controller and a deep learning-based molecule density estimator that is accurate over an extended range of densities...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469979/surface-enhanced-perfect-absorption-in-metamaterials-with-periodic-dielectric-nanostrips-on-silver-film
#13
Meng Qin, Shengxuan Xia, Xiang Zhai, Yu Huang, Lingling Wang, Lei Liao
Integrated dielectric metamaterials with plasmonic structures can cause drastic optical resonances and strengthen the capacity of light absorption. Here, we describe the optical properties of silicon nanoarrays on a thin silver film for extreme light confinement at subwavelength nanoscales. We attain the nearly total absorption in silicon nanostrips, which support magnetic quadruple Mie-type resonances in the visible regions. The Mie resonant field of the dielectric nanostrip engages the screening response of the silver film, resulting in plasmon resonance configuration and thus achieving perfect light absorption in the dielectric nanostrip...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469978/significantly-enhanced-infrared-absorption-of-graphene-photodetector-under-surface-plasmonic-coupling-and-polariton-interference
#14
Ye Zhang, Dejia Meng, Xiao Li, Honghao Yu, Jianjun Lai, Zhaoyang Fan, Changhong Chen
Here, we present a graphene-based long-wavelength infrared photodetector, for enhancing the infrared absorption of which the design consists of magnetic- and electric-plasmon resonators of metasurface to excite the graphene surface-plasmonic polaritons (SPPs). Through tuning the graphene Fermi energy to achieve the distinct resonances in a matching frequency, peak graphene absorbance exceeding 67.2% is confirmed, even when a lossy dielectric is used, and the field angle of view is up to 90°. If the graphene is of a different carrier mobility, then the absorption frequency is lockable, and the device always can keep the system absorbance close to 100 percent...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469977/extreme-terahertz-electric-field-enhancement-in-high-q-photonic-crystal-slab-cavity-with-nanoholes
#15
Qijing Lu, Xiaogang Chen, Chang-Ling Zou, Shusen Xie
A one-dimensional photonic-crystal (PC) cavity with nanoholes is proposed for extreme enhancement of terahertz (THz) electric fields using the electromagnetic (EM) boundary conditions. Both slot (for the perpendicular component of the electric displacement field) and anti-slot (for the parallel component of the electric field) effects contribute to the considerable field enhancement. The EM energy density can be enhanced by a factor of (εh/εl)2 in the high-refractive-index material, where εh and εl are the permittivities of the high- and low-refractive-index materials, respectively...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469976/butterfly-neural-equalizer-applied-to-optical-communication-systems-with-two-dimensional-digital-modulation
#16
Tiago F B de Sousa, Marcelo A C Fernandes
This article aims to present, analyze and evaluate a new equalizer architecture, inspired by the butterfly equalizer used in optical communication, based on Artificial Neural Networks (ANN) of the Multi-Layer Perceptron (MLP) type for nonlinear systems with two-dimensional modulation named the Butterfly Neural Equalizer (NE-Butterfly). The NE-Butterfly is intended to equalize any channel that has real or complex taps, whether linear or nonlinear. Simulation results are presented for different types of nonlinear fiber optic channels with complex and real taps, also containing inter symbolic interference and additive noise...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469975/fs-laser-written-erbium-doped-double-tungstate-waveguide-laser
#17
Esrom Kifle, Pavel Loiko, Carolina Romero, Javier Rodríguez Vázquez de Aldana, Airán Ródenas, Venkatesan Jambunathan, Viktor Zakharov, Andrey Veniaminov, Antonio Lucianetti, Tomas Mocek, Magdalena Aguiló, Francesc Díaz, Uwe Griebner, Valentin Petrov, Xavier Mateos
We report on the first erbium (Er3+ ) doped double tungstate waveguide laser. As a gain material, we studied a monoclinic Er3+ :KLu(WO4 )2 crystal. A depressed-index buried channel waveguide formed by a 60 µm-diameter circular cladding was fabricated by 3D femtosecond direct laser writing. The waveguide was characterized by confocal laser microscopy, µ-Raman and µ-luminescence mapping, confirming that the crystallinity of the core is preserved. The waveguide laser, diode pumped at 981 nm, generated 8.9 mW at 1533...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469974/amplification-of-flat-laser-pulse-train
#18
A Hanuka, J K Santucci, D Edstrom, L Schachter, J Ruan
We present modeling and measurements of flattop amplification of a laser pulse train in a diode pumped Nd:YLF system. We establish a theoretical model, accounting for the transverse Gaussian shape of an amplified laser beam, in order to explain remaining slopes in the pulse train energy. The influence of the transverse Gaussian shape on the train's flatness has been experimentally verified. Based on the model we are able to increase the total amplification of a long train of infrared seed beam in the drive laser system at the Fermilab Accelerator Science and Technology facility...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469973/network-selection-method-based-on-madm-and-vh-based-multi-user-access-scheme-for-indoor-vlc-hybrid-networks
#19
Tao Shang, Zhi Peng Sun, Zan Yang Dong, Qian Li
Recently, the visible light communication (VLC) based on LEDs has attracted much attention. In this paper, in order to realize multi-user wireless communication for VLC-based indoor hybrid networks, a network selection method based on Multi Attribute Decision Making (MADM) is proposed, which effectively combines the subjective preference of the user with the objective performance of each network. And then, a VH-based (virtual handover) multi-user access scheme is proposed, which considers different MAC and channel information...
November 12, 2018: Optics Express
https://www.readbyqxmd.com/read/30469972/efficient-terahertz-generation-in-highly-nonlinear-organic-crystal-hmb-tms
#20
Jian Lu, Seung-Heon Lee, Xian Li, Seung-Chul Lee, Jae-Hyun Han, O-Pil Kown, Keith A Nelson
We report on generation of strong and broadband terahertz (THz) pulses via collinearly phase-matched optical rectification of near-infrared femtosecond pulses in the organic nonlinear optical HMB-TMS (2-(4-hydroxy-3-methoxystyryl)-3-methylbenzo[d]thiazol-3-ium 2,4,6-trimethylbenzenesulfonate) single crystals which exhibit optimal molecular orientation and large macroscopic optical nonlinearity for efficient THz wave generation. Single-cycle THz pulses with a peak electric field strength of 0.66 MV/cm and a bandwidth from 0...
November 12, 2018: Optics Express
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