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HIgh Frequency Oscillation

Dohyeon Kwon, Chan-Gi Jeon, Junho Shin, Myoung-Sun Heo, Sang Eon Park, Youjian Song, Jungwon Kim
Timing jitter is one of the most important properties of femtosecond mode-locked lasers and optical frequency combs. Accurate measurement of timing jitter power spectral density (PSD) is a critical prerequisite for optimizing overall noise performance and further advancing comb applications both in the time and frequency domains. Commonly used jitter measurement methods require a reference mode-locked laser with timing jitter similar to or lower than that of the laser-under-test, which is a demanding requirement for many laser laboratories, and/or have limited measurement resolution...
January 19, 2017: Scientific Reports
Seyed Amir Hossein Banuazizi, Sohrab R Sani, Anders Eklund, Maziar M Naiini, Seyed Majid Mohseni, Sunjae Chung, Philipp Dürrenfeld, B Gunnar Malm, Johan Åkerman
Spin torque nano-oscillators (STNO) represent a unique class of nano-scale microwave signal generators and offer a combination of intriguing properties, such as nano sized footprint, ultrafast modulation rates, and highly tunable microwave frequencies from 100 MHz to close to 100 GHz. However, their low output power and relatively high threshold current still limit their applicability and must be improved. In this study, we investigate the influence of the bottom Cu electrode thickness (tCu) in nano-contact STNOs based on Co/Cu/NiFe GMR stacks and with nano-contact diameters ranging from 60 to 500 nm...
January 17, 2017: Nanoscale
Enrico Amico, Olivier Bodart, Mario Rosanova, Olivia Gosseries, Lizette Heine, Pieter Van Mierlo, Charlotte Martial, Marcello Massimini, Daniele Marinazzo, Steven Laureys
Transcranial magnetic stimulation (TMS) in combination with neuroimaging techniques allows to measure the effects of a direct perturbation of the brain. When coupled to high density electroencephalography (TMS/hd-EEG), TMS pulses revealed electrophysiological signatures of different cortical modules in health and disease. However, the neural underpinnings of these signatures remain unclear. Here, by applying multimodal analyses of cortical response to TMS recordings and diffusion magnetic resonance imaging (dMRI) tractography, we investigated the relationship between functional and structural features of different cortical modules in a cohort of awake healthy volunteers...
January 16, 2017: Brain Connectivity
Tian Zhong, Jonathan M Kindem, Jake Rochman, Andrei Faraon
Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level-a technique to suppress ensemble decoherence due to inhomogeneous broadening...
January 16, 2017: Nature Communications
John Kealy, Sean Commins, John P Lowry
Non-competitive NMDA receptor antagonists are known to induce psychosis-like symptoms in rodents. Administration of such compounds cause behavioural effects such as memory impairment and hyperlocomotion. Additionally, drugs such as phencyclidine (PCP), ketamine and MK-801 all cause distinctive increases in striatal local field potential (LFP) in the high frequency oscillation (HFO) band in the power spectrum (140-180 Hz). Amperometric sensors provide a means to measure tissue oxygen (tO2; a BOLD-like signal) in the brains of freely-moving rats while simultaneously acquiring LFP using the same electrode...
January 10, 2017: Neuropharmacology
Émeric Mercier, Lionel Weicker, Delphine Wolfersberger, Deborah M Kane, Marc Sciamanna
We experimentally report the sequence of bifurcations destabilizing and restabilizing a laser diode with phase-conjugate feedback when the feedback rate is increased. Specifically, we successively observe the initial steady state, undamped relaxation oscillations, quasi-periodicity, chaos, and oscillating solutions at harmonics up to 13 times the external cavity frequency but also the restabilization to a steady state. The experimental results are qualitatively well reproduced by a model that accounts for the time the light takes to penetrate the phase-conjugate mirror...
January 15, 2017: Optics Letters
Tien-Tien Yeh, Hideto Shirai, Chien-Ming Tu, Takao Fuji, Takayoshi Kobayashi, Chih-Wei Luo
In this study, we carried out 800-nm pump and ultra-broadband mid-infrared (MIR) probe spectroscopy with high time-resolution (70 fs) in bulk Ge. By fitting the time-resolved difference reflection spectra [ΔR(ω)/R(ω)] with the Drude model in the 200-5000 cm(-1) region, the time-dependent plasma frequency and scattering rate have been obtained. Through the calculation, we can further get the time-dependent photoexcited carrier concentration and carrier mobility. The Auger recombination essentially dominates the fast relaxation of photoexcited carriers within 100 ps followed by slow relaxation due to diffusion...
January 11, 2017: Scientific Reports
Dong Zhu, Xin-He Wang, Wei-Cheng Kong, Guang-Wei Deng, Jiang-Tao Wang, Hai-Ou Li, Gang Cao, Ming Xiao, Kai-Li Jiang, Xing-Can Dai, Guang-Can Guo, Franco Nori, Guo-Ping Guo
Phonon-cavity electromechanics allows the manipulation of mechanical oscillations similar to photon-cavity systems. Many advances on this subject have been achieved in various materials. In addition, the coherent phonon transfer (phonon Rabi oscillations) between the phonon cavity mode and another oscillation mode has attracted many interest in nanoscience. Here, we demonstrate coherent phonon transfer in a carbon nanotube phonon-cavity system with two mechanical modes exhibiting strong dynamical coupling. The gate-tunable phonon oscillation modes are manipulated and detected by extending the red-detuned pump idea of photonic cavity electromechanics...
January 11, 2017: Nano Letters
Heewon Yang, Byungheon Han, Junho Shin, Dong Hou, Hayun Chung, In Hyung Baek, Young Uk Jeong, Jungwon Kim
Ultrafast electron-based coherent radiation sources, such as free-electron lasers (FELs), ultrafast electron diffraction (UED) and Thomson-scattering sources, are becoming more important sources in today's ultrafast science. Photocathode laser is an indispensable common subsystem in these sources that generates ultrafast electron pulses. To fully exploit the potentials of these sources, especially for pump-probe experiments, it is important to achieve high-precision synchronization between the photocathode laser and radio-frequency (RF) sources that manipulate electron pulses...
January 9, 2017: Scientific Reports
Cristian Donos, Ioana Mîndruţă, Mihai Dragoş Malîia, Alin Raşină, Jean Ciurea, Andrei Barborica
OBJECTIVE: To perform a side-by-side comparison of two epileptogenicity biomarkers, high frequency oscillations (HFOs) and delayed responses (DRs), as a result of single-pulse electrical stimulation. METHODS: We have recorded stimulation-evoked HFOs and DRs in 16 epileptic patients undergoing presurgical evaluation using the stereoelectroencephalographic method. To evaluate converging and complementary information provided by the biomarkers, we analyzed them individually and for logical "and"/"or" combinations between them...
December 18, 2016: Clinical Neurophysiology: Official Journal of the International Federation of Clinical Neurophysiology
J K Faulk, D T Edwards, M S Bull, T T Perkins
Atomic force microscopy (AFM) is widely used in biophysics, including force-spectroscopy studies of protein folding and protein-ligand interactions. The precision of such studies increases with improvements in the underlying quality of the data. Currently, data quality is limited by the mechanical properties of the cantilever when using a modern commercial AFM. The key tradeoff is force stability vs short-term force precision and temporal resolution. Here, we present a method that avoids this compromise: efficient focused-ion-beam (FIB) modification of commercially available cantilevers...
2017: Methods in Enzymology
Christos Papadelis, Eleonora Tamilia, Steven Stufflebeam, Patricia E Grant, Joseph R Madsen, Phillip L Pearl, Naoaki Tanaka
Crucial to the success of epilepsy surgery is the availability of a robust biomarker that identifies the Epileptogenic Zone (EZ). High Frequency Oscillations (HFOs) have emerged as potential presurgical biomarkers for the identification of the EZ in addition to Interictal Epileptiform Discharges (IEDs) and ictal activity. Although they are promising to localize the EZ, they are not yet suited for the diagnosis or monitoring of epilepsy in clinical practice. Primary barriers remain: the lack of a formal and global definition for HFOs; the consequent heterogeneity of methodological approaches used for their study; and the practical difficulties to detect and localize them noninvasively from scalp recordings...
December 6, 2016: Journal of Visualized Experiments: JoVE
Gar-Wing Truong, Eleanor M Waxman, Kevin C Cossel, Esther Baumann, Andrew Klose, Fabrizio R Giorgetta, William C Swann, Nathan R Newbury, Ian Coddington
We describe a dual-comb spectrometer that can operate independently of laboratory-based rf and optical frequency references but is nevertheless capable of ultra-high spectral resolution, high SNR, and frequency-accurate spectral measurements. The instrument is based on a "bootstrapped" frequency referencing scheme in which short-term optical phase coherence between combs is attained by referencing each to a free-running diode laser, whilst high frequency resolution and long-term accuracy is derived from a stable quartz oscillator...
December 26, 2016: Optics Express
Kentaro Ueda, Yosuke Orii, Yoshinori Takahashi, George Okada, Yusuke Mori, Masashi Yoshimura
We report third-harmonic generation (THG) at 355 nm in CsLiB<sub>6</sub>O<sub>10</sub> (CLBO) by using sum-frequency mixing process. As a fundamental laser source, we employ a hybrid master oscillator power amplifier (MOPA) system seeded by a gain-switched laser diode (GS-LD) at 1064 nm to produce narrow spectral picosecond pulses. Both CLBO and walk-off compensated prism-coupled CLBO device generate over 30-W output of 355-nm UV lights, which means walk-off effect in CLBO is negligible in the picosecond laser system...
December 26, 2016: Optics Express
Abel Lorences-Riesgo, Mikael Mazur, Tobias A Eriksson, Peter A Andrekson, Magnus Karlsson
We demonstrate and characterize an all-optical self-homodyne (SH) frequency superchannel enabled by comb regeneration at the receiver. In order to generate the superchannel, we use a frequency comb with 26 carriers spaced by 25 GHz at the transmitter, from which 24 carriers are modulated with polarization-multiplexed 32 quadrature amplitude modulation (PM 32-QAM) data. To enable comb regeneration at the receiver side, the two central carriers remain unmodulated. High fidelity comb regeneration is achieved by filtering the two unmodulated carriers with an approximately 25 MHz wide optical filter based on Brillouin amplification before a parametric mixer...
December 26, 2016: Optics Express
Lin Wang, Yuan Cao, Minggui Wan, Xudong Wang, Xinhuan Feng, Bai-Ou Guan, Jianping Yao
A wavelength-tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier (NL-SOA) is proposed and experimentally demonstrated. The single-frequency operation is achieved based on the spectral narrowing effect resulted from the inverse four-wave mixing in a NL-SOA. By incorporating the NL-SOA in the fiber laser cavity, single-frequency lasing is achieved. The lasing frequency can be tuned by tuning the center wavelength of a tunable filter (TF) incorporated in the laser cavity...
December 26, 2016: Optics Express
Mu-Han Yang, Maxim Abashin, Payam A Saisan, Peifang Tian, Christopher G L Ferri, Anna Devor, Yeshaiahu Fainman
Non-degenerate 2-photon excitation (ND-2PE) of a fluorophore with two laser beams of different photon energies offers an independent degree of freedom in tuning of the photon flux for each beam. This feature takes advantage of the infrared wavelengths used in degenerate 3-photon excitation (D-3PE) microscopy to achieve increased penetration depths, while preserving a relatively high 2-photon excitation cross section in comparison to that of D-3PE. Here, using spatially and temporally aligned Ti:Sapphire laser and optical parametric oscillator beams operating at near infrared (NIR) and short-wavelength infrared (SWIR) optical frequencies, we employ ND-2PE and provide a practical demonstration that a constant fluorophore emission intensity is achievable deeper into a scattering medium using ND-2PE as compared to the commonly used degenerate 2-photon excitation (D-2PE)...
December 26, 2016: Optics Express
Long Huang, Hanshuo Wu, Ruixian Li, Lei Li, Pengfei Ma, Xiaolin Wang, Jinyong Leng, Pu Zhou
A high-power 1064 nm single-frequency polarization-maintained fiber amplifier based on an all-fiber master oscillator power amplifier configuration is demonstrated. To mitigate the stimulated Brillouin scattering (SBS) and the mode instability (MI) effect, a polarization-maintained Yb-doped fiber with a high dopant concentration and a 25 μm core diameter is adopted in the main amplifier stage; in addition, step-distributed longitudinal strain is imposed on the active fiber to broaden its effective SBS gain spectrum and further increase the SBS threshold...
January 1, 2017: Optics Letters
Animesh Nayak, Jaehong Park, Kurt De Mey, Xiangqian Hu, Timothy V Duncan, David N Beratan, Koen Clays, Michael J Therien
Octopolar D2-symmetric chromophores, based on the MPZnM supermolecular motif in which (porphinato)zinc(II) (PZn) and ruthenium(II) polypyridyl (M) structural units are connected via ethyne linkages, were synthesized. These structures take advantage of electron-rich meso-arylporphyrin or electron-poor meso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted terpyridyl and 4'-pyrrolidinyl-2,2';6',2″-terpyridyl ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc connectivity, to probe how electronic and geometric factors impact the measured hyperpolarizability...
December 28, 2016: ACS Central Science
Kenneth E Strawhecker, Emil J Sandoz-Rosado, Taylor A Stockdale, Eric D Laird
The data included here provides a basis for understanding "Interior morphology of high-performance polyethylene fibers revealed by modulus mapping" (K.E. Strawhecker, E.J. Sandoz-Rosado, T.A. Stockdale, E.D. Laird, 2016) [1], in specific: the multi-frequency (AMFM) atomic force microscopy technique and its application to ultra-high-molecular-weight Polyethylene (UHMWPE) fibers. Furthermore, the data suggests why the Hertzian contact mechanics model can be used within the framework of AMFM theory, simple harmonic oscillator theory, and contact mechanics...
February 2017: Data in Brief
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