Pulse Coupling Research Articles

Output coupling from a trapped Bose-Einstein condensate in a vortex state

We consider the properties of an atom laser produced by the output coupling of a trapped vortex state with a Raman scattering process. We find a linearized analytic solution from which a generalized resonance condition for Raman output coupling is developed. Using numerical simulations of a two-component Gross-Pitaevskii equation in two and three dimensions, the output beam from a trapped central vortex state is analyzed for cases of pulsed and continuous coupling where the vortex core is either transverse or parallel to the direction of propagation. We show how the parameters of the Raman light fields control the spatial phase of the output beam.

“Pulsed field losses and coupling current loop in a large‐current superconductor”, Electrical Engineering in Japan Volume 142, Number 4, 2003, pages 27–33

AbstractThe original article to which this Erratum refers was published in Electrical Engineering in Japan, Volume 142, Number 4, 2003, pages 27–33An error appeared in the above article. The affiliations are correct as here. We apologize for any inconvenience this error may have caused.

Pulsed field losses and coupling current loop in a large‐current superconductor

AbstractPulsed field losses in a short sample (445 mm length) of 46‐kA Nb3Sn cable‐in‐conduit conductor of superconducting magnet for the fusion experimental reactor “ITER” are measured by a calorimetric method. The coupling time constant between strands is obtained as 30 ms through pulsed loss. Based on this time constant and interstrand conductance measurement, it is expected that there is a coupling current loop length of about 400 mm, which is longer than half the fabrication twist pitch in the fourth cabling stage. A geometrical calculation on several‐stage cabling shows this value to be reasonable. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 27–33, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10088

Ultrashort-pulse investigation of the propagation properties of the LP_11 mode in 155-μm communication fibers

The coupling of an ultrashort laser pulse into a single-mode optical communication fiber gives rise to two propagating pulses as a result of the excitation of two guided modes, the fundamental, LP(01) , and the leaky, LP(11) . Such a phenomenon provides a new approach to the study of the propagation properties of the LP(11) mode. An experiment with tunable 110-fs pulses at a wavelength near 1550 nm is described. Information about the group velocity, the polarization-rotation length, the attenuation coefficient, and the cutoff wavelength of the LP(11) mode is obtained in a simple and direct way for various fibers.

Studies on nonconventional high-gain target design for ICF

This paper reports some of the studies on nonconventional ICF approaches performed at the ICF Physics and Technology Laboratory of the AEEF in Frascati, Italy. Having as reference potential difficulties associated to the conventional central spark ignition (fuel mixing) and to the usual approach to fast ignition by laser (transfer and coupling of the energy pulse, fast electrons energy tuning), we have made explorative work on possible alternatives. The performances of targets ignited near stagnation by pulses of heavy ion beams (HIB) or by macroparticle impact were previously studied. The needed driver energy, the power, and the beam quality requirements, as well as the level of synchronization the implosion and the igniting pulse have been found. More recently, to relax some requirements on the HIB beam parameters set by the previous approach, the injected entropy approach (IE) has been introduced. In this method, the conditions for spark formation are set in the final stages of the implosion, when the spark fuel size is a few times the final size at stagnation (volume a few tens of the final). Energy is injected at this time to set the spark fuel on a high adiabat. In this paper, for illustration and comparison purposes, some relevant results we previously obtained for near-stagnation ignition are first introduced and critically reviewed. The new IE method, after a short analytical introduction, is presented and illustrated by the results of extensive 2-D numerical simulations. The considered cases refer to imploding cylinders of finite length. As required by this approach, one or two opposing beams axially injected additional energy, whereas the acceleration stage of the cylindrical low-entropy implosion was assumed driven by a different driver. Heavy ion beams, soft X-rays (SXR), and laser generated light ion beams were considered as vectors for the entropy injection. Issues related to the feasibility of these generators are discussed. The study was made for various initial conditions leading to different ignition modes and burn propagation. The most recent results on the injected entropy method to the ignition of high gain targets are included.

New simplified coupling scheme for the delivery of 20 MW Nd:YAG laser pulses by large core optical fibers

The feasibility of transmitting 20 MW, 5 ns laser pulses from a frequency doubled Nd:YAG laser through a standard 1500 μm multi mode optical fiber is demonstrated. A new coupling scheme employing an optical homogenizer prevents breakdown in air without the use of a vacuum chamber. At the same time a very homogeneous flat top beam profile on the fiber surface is achieved. The new scheme therefore clearly simplifies fiber coupling of high power laser pulses. Experiments on the delivery of more than 20000 pulses with 110 mJ mean energy without fiber damage have been performed.

Coupling of arterial pulse and 10-Hz rhythm in sympathetic nerve discharge

We used time series analysis to characterize the relationships among the arterial pulse (AP) and the cardiac-related and 10-Hz rhythms in sympathetic nerve discharge (SND) of urethane-anesthetized cats. We found that 10-Hz activity was more tightly coupled to the AP than to the cardiac-related rhythm. These data support the view that the dynamic coupling of AP and the 10-Hz rhythm in SND involves a direct influence of baroreceptor activity on the 10-Hz oscillator.

Highly Ionized Carbon Plasma Generation by Dual-Laser Ablation for Diamond-Like Carbon Film Growth

AbstractCarbon plasmas produced by excimer laser ablation show a low ionization yield of about 8-10%. The coupling of a second CO2laser pulse into the plasma in the dual-laser ablation process significantly increases the plasma temperature and the ionization. The resulting rapid expansion of the plasma gives rise to high ion kinetic energies and broader ion expansion profiles [1]. Optical emission spectroscopy and an ion probe have been used to investigate the dynamics of the carbon plasma. Single and dual-laser ablated carbon plumes have been deposited on DC-biased silicon substrates to form amorphous carbon films. The diamond-like behavior of these films was studied by Raman spectroscopy. The Raman spectra were deconvolved to gauge the effect of the density and the energy of ions on the formation of diamond-like sp3 -bonded carbon (DLC) films. The advantage offered by the dual-laser process for the growth of DLC films is discussed.

1H decoupling for in vivo (19)F MRS studies using the time-share modulation method on a clinical 1.5 T NMR system.

Time-share modulation has been implemented successfully on a clinical 1.5 T nuclear magnetic resonance (NMR) system to perform in vivo (19)F[-(1)H] decoupling. It uses commercially available radiofrequency (RF) filters, a transistor-transistor logic (TTL)-controlled attenuator, and a double-resonant RF surface coil suitable for (19)F magnetic resonance spectroscopy (MRS) studies in vivo. This decoupling scheme gives a threefold improvement in signal-to-noise ratio performance compared with the conventional WALTZ-4 decoupling scheme, when significant interaction exists between the decoupler and the receiver. It can also eliminate receiver saturation (i.e., saturation due to coupling of the strong proton decoupling pulse to the (19)F coil) without the need for a high-isolation coil system, thus allowing flexibility in coil geometry. This method has been demonstrated in vivo in patients receiving 5-fluorouracil chemotherapy. Magn Reson Med 44:5-9, 2000.

2D measurement and spatio-temporal coupling of few-cycle THz pulses

The propagation of few-cycle THz pulses are measured by the improved CCD based 2D THz imaging system. There exists strong spatio-temporal shaping effect, leading to dramatically time dependent beam diameter and wave front. Theoretical simulation is given.

A well-collimated quasi-continuous atom laser

Extraction of sodium atoms from a trapped Bose-Einstein condensate (BEC) by a coherent, stimulated Raman process is demonstrated. Optical Raman pulses drive transitions between trapped and untrapped magnetic sublevels, giving the output-coupled BEC fraction a well-defined momentum. The pulsed output coupling can be run at such a rate that the extracted atomic wave packets strongly overlap, forming a highly directional, quasi-continuous matter wave.

Analyzing electromagnetic pulse coupling by combining TLT, MoM, and GTD/UTD

An important problem in electromagnetic compatibility (EMC) analysis is to determine the coupling of an electromagnetic field into a shielded cable. Using the transmission line theory (TLT), the disturbance voltage induced inside the cable is easily calculated from the current distribution on its shield. This current distribution depends on the incident electromagnetic field and is efficiently determined by the method of moments (MoM). Extending the MoM with the geometrical and uniform theory of diffraction (GTD/UTD) makes it possible to solve scattering problems that are too large and too complex for the plain MoM. The combination of the three approaches-TLT, MoM, and GTD/UTD-allows calculation of the disturbance voltage inside a shielded cable, which is part of a complex scattering structure. The fundamentals of each method and the way of putting them together are shown in this paper. The application of the proposed method is demonstrated by an example: the pulse coupling between a monopole antenna and a shielded cable is analyzed, taking into account a large conducting structure in the vicinity.

Intersubband laser coupled three-level asymmetric quantum wells: new dynamics of quantum interference

The improved density-functional theory is employed to obtain the eigenstates of electrons in an asymmetric quantum well. On the basis of calculated eigenstates, the semiconductor Bloch equations are used to calculate the transient density matrix when a pulsed intersubband laser coupling is applied to the system. The new dynamics of the individual absorption peaks is analyzed for the first time by use of a self-consistent-field theory. Based on this, the time-averaged optical spectrum is calculated to show the coherent-transition-induced quantum interference in the system. The new phenomena of probe-field amplification is observed, and the threshold laser intensity for observing it is given.

On-site partial discharge measurements on premoulded cross-bonding joints of 170 kV XLPE and EPR cables

A total number of 15 premoulded joints of three 170 kV cable circuits (XLPE and EPR) were equipped with partial discharge (PD) sensors. The developed sensors are based on inductive high frequency coupling of partial discharge pulses occurring in the joints. The PD activity of each joint was monitored during an after laying AC acceptance test. The test voltage of 190 kV was generated by means of a frequency-tuned series-resonance test set. The signals of the PD sensors were assessed with a spectrum analyser in a frequency range from 15 to 50 MHz, allowing a good separation of noise from PD signals under high interference levels. The investigation demonstrated the feasibility of on-site PD measurements on joints during after laying tests.

Numerical studies on resonant and enhancement effects for coupling of microwave pulses into narrow slots

In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling process of microwave pulse into a slot is studied by using the modified FD-TD method, and the dependence of microwave coupling on slot sizes, the carrier frequencies and the polarization directions of the incident waves is analysed. Resonant and enhancement effects which occur in this process are observed. The condition at which the resonant effect takes place is also presented.

Laser-induced distortion for increased input coupling of light to droplet-cavity modes

Localized laser-induced electrostrictive distortion to liquid droplets is shown to increase the input coupling of mode-locked laser pulses to optical microcavity resonances. The increase in input coupling for a given pulse is dependent on the number of preceding laser pulses, as well as on their intensities. The electrostrictive distortion locally increases the leakage rate of light from the droplet-cavity modes. For lower input intensities, the localized distortion does not significantly degrade the quality factors of those cavity modes that spatially overlap the distortion. The increased input coupling is demonstrated by a decrease in the input intensity required to generate stimulated Raman scattering in the double-resonance condition with a train of mode-locked laser pulses. The cumulative effect of too many input pulses of too great an intensity ruins the quality factors of the resonances such that there is not sufficient feedback to support the stimulated Raman scattering.

Partial synchronization in populations of pulse-coupled oscillators.

I study the long-term behavior of populations of nonlinear oscillators with all-to-all, noninstantaneous, pulse coupling. With fast enough excitatory coupling both the fully synchronized and the asynchronous state are unstable. In this case individual units fire quasiperiodically even though the network as a whole shows a periodic firing pattern. The behavior of networks with three or more units is different in this regard from that of two-unit networks. With inhibitory coupling the network can break up into a variable number of fully synchronized clusters. For fast inhibition the number of clusters tends to be large, while the number of clusters is smaller for slow inhibition. \textcopyright{} 1996 The American Physical Society.

The optical coupling of analog signals

An optocoupling circuit based on the Siemens IL300 linear optocoupler and the methods to assess its static and dynamic performances are presented. It is shown that IL300, due to its built-in linearizing feedback photodiode, makes it possible to build coupling schemes that associate good linearity with the inherent properties of optical devices, as true galvanic isolation, high isolation voltage and transmission down to dc. The integral linearity, 0.029%, obtained on the coupling of typical nuclear spectroscopy pulses makes us believe that traditional capacitive coupling used in nuclear spectroscopy circuits can be replaced by optical coupling in the near future.

Numerical studies on nonlinear coupling of high-power microwave pulses into a cylindrical cavity

In this paper, we use Maxwell's equations and a set of electron-fluid equations to study the nonlinear coupling processes, which occur when high-power microwave pulses are incident on a cylindrical cavity with a cylindrical aperture. We use Einstein's theory of relativity to revise the electron equations of momentum conservation. Making use of the finite-difference time-domain method, we simulate nonlinear microwave couplings under different atmospheric conditions. Compared with linear coupling results, some new nonlinear coupling phenomena are observed and explained.

Some numerical methods for dosimetry: Extremely low frequencies to microwave frequencies

This paper describes some of the numerical methods that have been developed for calculations of induced electric fields, current densities, and specific absorption rates for anatomically based heterogeneous models of the human body with increasingly finer resolutions. These methods, namely, the impedance method and the finite difference time domain (FDTD) method, have been used for dosimetric calculations for a number of bioelectromagnetic problems for whole‐body or partial‐body exposures, for far‐field or near‐field sources, and for CW or transient fields. The paper gives detailed calculations for some recent applications such as currents induced in the user's body by the electromagnetic fields (emfs) of electric blankets using the impedance method, coupling of an ultrawideband pulse using the frequency‐dependent FDTD method incorporating dispersive properties of the various tissues, and specific absorption rate distributions in the head for emfs of cellular telephones. Because of accurate modeling of tissue heterogeneities and shapes, these methods are likely to play an increasing role in emerging technologies with bioelectromagnetic concerns.