Generation of strong-field spectrally tunable terahertz pulses

The ideal laser source for nonlinear terahertz spectroscopy offers large versatility delivering both ultra-intense broadband single-cycle pulses and user-selectable multi-cycle pulses at narrow linewidths. Here we show a highly versatile terahertz laser platform providing single-cycle transients with tens of MV/cm peak field as well as spectrally narrow pulses, tunable in bandwidth and central frequency across 5 octaves at several MV/cm field strengths. The compact scheme is based on optical rectification in organic crystals of a temporally modulated laser beam. It allows up to 50 cycles and central frequency tunable from 0.5 to 7 terahertz, with a minimum width of 30 GHz, corresponding to the photon-energy width of ΔE=0.13 meV and the spectroscopic-wavenumber width of Δ(λ-1)=1.1 cm-1. The experimental results are excellently predicted by theoretical modelling. Our table-top source shows similar performances to that of large-scale terahertz facilities but offering in addition more versatility, multi-colour femtosecond pump-probe opportunities and ultralow timing jitter

Electro-optically tunable microring resonators in lithium niobate

Optical microresonators have recently attracted a growing attention in the photonics community. Their applications range from quantum electro-dynamics to sensors and filtering devices for optical telecommunication systems, where they are likely to become an essential building block. The integration of nonlinear and electro-optical properties in the resonators represents a very stimulating challenge, as it would incorporate new and more advanced functionality. Lithium niobate is an excellent candidate material, being an established choice for electro-optic and nonlinear optical applications. Here we report on the first realization of optical microring resonators in submicrometric thin films of lithium niobate. The high index contrast films are produced by an improved crystal ion slicing and bonding technique using benzocyclobutene. The rings have radius R=100 um and their transmission spectrum has been tuned using the electro-optic effect. These results open new perspectives for the use of lithium niobate in chip-scale integrated optical devices and nonlinear optical microcavities.Comment: 15 pages, 8 figure

Magnetic detection of a single action potential in Chara corallina internodal cells.

The electrical activity that occurs in plants has not yet been detected magnetically. Magnetic detection of electrical activity in some animal as well as in human cells and organs, on the other hand, is an established research method. Our experiments demonstrate the propagation of a single action potential in the internodal cell of the green algae Chara corallina, measured magnetically. The propagation velocity and the intracellular current were determined

Running electric field gratings for detection of coherent radiation

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Magnetic detection of injury-induced ionic currents in bean plants.

A superconducting quantum interference device (SQUID) multichannel magnetometer was used to measure the temporal and spatial evolution of the magnetic field accompanying stimulation by burning and/or cutting of Vicia faba plants. These magnetic fields are caused by ionic currents that appear after injury in different parts of the plant. All measured V. faba plants responded to the burning stimulation with detectable quasi-d.c. magnetic signals. In order to measure these signals, a suitable modulation had to be used. The covariance method was applied to analyse the measured data. The results demonstrate a dipolar-like magnetic signal, exponentially decreasing in time, above the cutting type of injury. After the burning stimulation, the magnetically detected activity was concentrated predominantly above the leaves/petioles and less above the stem. Possible mechanisms for this behaviour are suggested. A comparison with previously known electrical measurements of plant injury is given

Spatial and temporal distribution of magnetic field due to injury currents in Vicia faba plants

Introduction Different types of wounds on plants cause measureable changes in the biochemical and biophysical behaviour of plants. Among them are also electrophysiological changes. Studies using extracellular and intracellular electrodes have revealed that wounding of tissue causes in a variety of plants changes in the electrical membrane voltage e.g. [1, 2, 3, 4]. Typically, the electrical response consists of a rapid action potential-like depolarization followed by a slower long lasting depolarization usually termed the variation potential. The elementary basis of these transient voltage changes is not yet known. It has been speculated, that the fast transient depolarization is an action potential and is therefore propagated - just as in nerve cells - as a true long distance electrical signal [2]. The slow voltage transient on the other hand might be the consequence of chemical signals which are distributed via the xylem [5]. Wounding induced voltage changes are transmitted from th

Localization of Septal Accessory Pathways Using

Introduction Radiofrequency (RF) catheter ablation has become a method of choice in curative treatment of pharmacologically refractory paroxysmal supraventricular tachycardias involving an accessory atrioventricular connection. Prerequisite for successful ablative treatment is the precise identification of an aberrant pathway. Although magnetic field mapping has shown promise in facilitating the localization of preexcitation sites prior to RF intervention (see, e.g., [1]), its ability in discriminating among different septal accessory pathways has yet to be confirmed. The aim of this study is to develop criteria for such discrimination using computer simulations. 2 Methods Our simulation study followed methodology that was presented in detail elsewhere [2,3]. First, we positioned an anatomical model of the human ventricles [3] in the boundary element torso model at the heart's anatomical location documented by radiographic images [3]. Second, we used an anatomical model of the huma