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The energy distribution of output electrons (EDOE) from a microchannel plate (MCP) is measured using electrons emitted by a vacuum photodiode excited by a 266 nm Ti-sapphire femtosecond laser. The photoelectrons emitted from the photocathode are focused on a specific location of the MCP by a magnetic lens. While exist an enough voltage difference between the two ends of MCP, the energy distribution curve of output electrons form MCP can be obtained by analyzing the data as function of the bias voltage applied to the charge collector. The result shows that the energy distribution curve obtained by this means consists of a sharp and a long tail when using pulse light source. The most probable electron energy (MPE) is 12.64 eV and the full width at half maximum (FWHM) of the energy distribution curve is about 29.23 eV while the applied voltage difference is 700 V in the experimental setup. The MPE is 10.63 eV and the FWHM of the energy distribution is 22.436 eV in simulation. The measured curve is consistent with the expectation from simulation.

In the two-dimensional Cartesian coordinate system, a transient electromagnetic forward algorithm of the magnetic moment in arbitrary direction is developed to simulate the electromagnetic response characteristics of the whole space geoelectric model. The magnetic moment ${\mathbf {M}}_{r}$ in arbitrary transmitting direction is decomposed into ${\mathbf {M}}_{x}$ and ${\mathbf {M}}_{y}$ . The transient electromagnetic fields excited by the magnetic moments ${\mathbf {M}}_{x}$ and ${\mathbf {M}}_{y}$ are forwarded separately, and then synthesized to obtain the electric field excited by the magnetic moment ${\mathbf {M}}_{r}$ . The time domain iteration’s results of the uniform whole space are compared with the analytical solutions to verify the correctness of algorithm. The comparison results show that the algorithm is reliable and can be used for whole space transient electromagnetic simulation in an arbitrary direction. The forward response of the magnetic moment in an arbitrary transmitting direction removes the shortcomings of the traditional two-dimensional whole space transient electromagnetic simulations where the magnetic moment can only be in the horizontal or vertical direction. The program code can be used for the forward response of other two-dimensional whole space geological mining models. It is of great significance to study the two-dimensional transient electromagnetic diffusion characteristics of different geological models by the sector sweeping method.

In this paper, a novel substrate integrated waveguide (SIW) filtenna with two controllable radiation nulls is proposed, which has the advantage of good radiation characteristics. Radiation nulls are generated by electric and magnetic mixed coupling structure and fundamental mode, respectively. And a quasi-elliptic characteristic can be obtained at the boresight gain direction. By changing the length of perturbation slot and the strength of electric coupling and magnetic coupling, the position of radiation nulls can be controlled independetly. Compared to conventional filtenna, the proposed SIW filtenna has no extra filtering circuit to increase the dimension and complexity. Two resonant modes in the passband can be excited through loading electric and magnetic mixed coupling structure in one SIW cavity. The measured results are in good agreement with simulated results. The good frequency selectivity and out-of–band rejection are achieved. The proposed antenna exhibits a maximum realized gain of 5.8 dBi at the operating bandwidth. The measured impedance bandwidth is from 9.44 GHz to 9.68 GHz and the cross-polarization levels are lower than -20 dB in both planes.

This paper proposed a novel hybrid-excited wound field synchronous machine (HE-WFSM) to efficiently use the field torque and reluctance torque. Meanwhile, an analytical method is utilized to achieve the torque-angle consistency principle, which allows the field torque and the reluctance torque to reach their maximum values at the same phase current angle. First, a novel HE-WFSM with two different rotor excitations is proposed. Second, the PMs and the field windings in the rotor are designed by an analytical method based on the magnetic equivalent circuit (MEC) to produce the same magnetic flux in the air gap to obtain the torque-angle consistency. Third, one practical HE-WFSM applied for a small power fan is designed by the analytical method as an example. Finally, all the performances of the proposed HE-WFSM are predicted by the finite element method (FEM), thereby verifying the improved torque characteristics.

We demonstrate graphene-on-diamond field effect transistor (FET) actions modulated by optically excited charge state of nitrogen-vacancy (NV) centers in diamond. Palladium (Pd) metal contacts on graphene serve as the source and the drain. Negative charge state NV- center in diamond serves as the gate with diamond being the gate dielectric and produces an electric field to enhance the hole concentration in the graphene channel. The conductivity of graphene varies with negative charge state NV- center, resulting in differential conductance. The negative gate bias is removed when a NV- center is converted to an NVo center. P-type graphene channel exhibits positive differential conductance under illumination by a blue (405 nm) laser beam while on the contrary negative differential conductance by a red (633 nm) laser beam. Furthermore, by simultaneous illumination of both blue and red laser beams, effects on differential conductance decrease according to the relative intensity of the two laser beams. Graphene FETs with wavelength dependent multiple optical inputs and one electrical output in response to the charge state of NV centers in diamond has been reported.

Resonant excitation analysis on asymmetrical lateral leakage of light in the finite zero-contrast grating (ZCG) mirror is demonstrated, and the size effect of the excited source is investigated. The dispersion equation of slab waveguide for the TM mode is proposed to evaluate the resonant condition of the ZCG mirror, and it is shown that the mirror effect of the infinite ZCG is resulted from the overlapping of order-mode resonance pairs. However, two leaky channels are excited in spectra of the finite ZCG mirror for the normal-incident Gaussian source, where bound states in the continuums (BICs) turn into quasi-BICs as the angular component is nonzero. The leaky channels are confined in the grating layer and the sublayer, and they are all transferred from the symmetrical mode to the asymmetrical mode along the lateral direction from the center of the ZCG. The asymmetrical loss of the lateral leakage of light relative to incidence direction, in principle, can break reflection reciprocity of the symmetrical system of the finite ZCG mirror. By changing the excited source from the grating side to the sublayer side, the lateral leakage of light of the finite ZCG mirror can be efficiently reduced.

In this paper, a slots-coupled omnidirectional circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) is proposed. The TM $_{01 \delta }$ and TE $_{\mathrm {011+\delta }}$ modes of the cylindrical DRA are simultaneously excited by four printed slots placed at 45 degrees to the radial direction. Omnidirectional CP fields are obtained when the fields of the two modes have the same amplitude and 90 degrees phase difference. Compared with the traditional probe-fed method, the structure of the proposed slots-coupled DRA is very simple, without introducing any groove, patch, choke or shorting pins. For the demonstration, a slots-coupled omnidirectional CP cylindrical glass DRA is designed for 5.8-GHz WLAN application. It is found that the proposed DRA can provide an AR bandwidth of ~8% (5.62-6.09 GHz) and a gain of ~5.6 dBic, with a height of $\sim 0.127\lambda _{0}$ . This performance is competitive with other reported omnidirectional CP DRAs.

An 8-port multiple-input multiple-output (MIMO) array operating in the long-term evolution (LTE) band 42 (3400-3600 MHz) based on the characteristic mode theory (CMT) is described. As designing a multi-antenna system with multiple significant modes is difficult for the CMT, a new method is, therefore, proposed to effectively provide useful physical insights and improve the envelope correlation coefficient (ECC). Although many of the same modes are excited by two antennas, the proposed method is still effective to improve the ECC of the two antennas. A detailed and reasonable framework adopting the CMT to analyze geometries with multi-significant modes is presented. The consideration of the mode number can be avoided by using this method. For an arbitrary structure, it is verified that the modal weighting coefficient (MWC) phases of the same modes excited by two ports are in phase or out of phase. Therefore, for the design of a multi-port MIMO array, the same modes excited by different ports can be divided into two types: equiphase modes and antiphase modes in the proposed method, and the tradeoff of the equiphase modes and the antiphase modes is first proposed and analyzed as an efficient way to improve the ECC. Furthermore, the proposed method can also be applied to asymmetric structures. In order to prove the effectiveness of the proposed method in the design of MIMO antennas with desirable ECC, an 8-port MIMO array for 5G mobile applications is implemented and measured.

In this paper, we experimentally demonstrate that molecules with maximum absorption wavelength corresponding to the first excitation energy of base liquid molecules are able to significantly improve the electrical performances of natural ester oils. The positive lightning impulse breakdown and acceleration characteristics, ac breakdown characteristics, and streamer structure of the natural ester oils, as well as the electronic properties of the molecules, are presented. The molecules with different absorptions in ultraviolet lights were doped into the natural ester oil. The positive lightning impulse breakdown characteristics of natural ester oil with different doped molecules indicated that the doped molecule with great absorption in the medium wavelength ultraviolet irradiation was able to significantly enhance the positive lightning impulse breakdown and acceleration voltages of natural ester oil by 15% and 60%, respectively. In addition, it also enhanced the ac breakdown voltage by 17%. The base liquid molecules exhibited first excitation energy of 4 eV, which corresponds to the maximum absorption wavelength of such molecules, indicating that the improved electric breakdown strength was a result of the reduced the number of excited molecules and weakened ionization of molecules during the streamer propagation.

Metal particles and bubbles are two typical impurities in transformer oil that can cause partial discharge (PD) and even electric breakdown. The PD characteristics are closely related to the motions of these impurities in flowing transformer oil. In this paper, the motions of impurities were obtained by a camera and a simulation model at first. Then, we employed three methods, namely, antennas, a non-inductive resistor, and the method recommended by IEC 60270, to measure the PD signals simultaneously. The breakdown experiments of transformer oil containing the metal particles and bubbles were also performed. In terms of these, single PD waveforms, statistical characteristics, and breakdown voltage were obtained. The results showed that the metal particles could excite ultrahigh frequency (300 MHz-3 GHz) PD signals, whereas bubbles only excited signals in the very high-frequency band (30-300 MHz). Moreover, the PDs induced by the metal particles had a higher repetition rate and a smaller amplitude than the PDs induced by bubbles. In addition, the metal particles easily caused PD, whereas bubbles easily led to the breakdown. Possible reasons for different discharge characteristics between the two impurities were discussed on the basis of the motions of impurities and the distortions of electric field.

The formula for analyzing the response characteristics of the induced current on a transmission line (TL) excited by high-frequency electromagnetic (EM) waves is a mixed integral-differential equation. The integral part is the Fredholm integral equation of the first kind with serious ill-posedness, which causes difficulty in solving it stably. The regularization technique is a useful method for the analysis of the ill-posed problems. Therefore, in this paper, a method based on the Tikhonov regularization technique is proposed to analyze the high-frequency electromagnetic response of a finite length TL illuminated by external EM waves. The integral operator is discretized by the Simpson formula. The validity and correctness of the proposed method have been verified by numerical examples and the applicability of the proposed method at different errors has been analyzed via the TL with different height.

The design and development of a high-performance, dual-polarization, hybrid aperture-coupled microstrip patch antenna are presented. In the presented design, the horizontal and vertical polarizations are excited using the aperture coupling method. The isolation level of better than 51 dB and cross-polarization level of less than −30 dB are achieved from the measurement results of the designed single element. To achieve better cross-polarization levels, the $2 \times 2$ element subarrays of the proposed unit cell, while the horizontal polarization ports are mirrored, are designed and fabricated, and a lower than −39-dB cross-polarization level is achieved in the measurement results. Finally, to characterize the scan performance of the unit cell and subarray, a $4 \times 10$ element array of the proposed single element is fabricated and a better than −45-dB cross-polarization level is observed while scanning up to 45°.

Design of the wide dual-band rectangular souvenir dielectric resonator antenna (DRA) is discussed. The proposed wide dual-band rectangular DRA was excited by using a U-slot. The $TE_{111}{^{\mathrm {y}}}$ mode of the rectangular DRA and the slot resonator were employed to design the lower band, while the higher-order $TE_{113}{^{\mathrm {y}}}$ and $TE_{311}{^{\mathrm {y}}}$ modes were utilized to design the upper band. By merging two pairs of modes in each band, the impedance bandwidth of the lower and upper bands were enhanced simultaneously. New design formulas that determine the dimensions of the wide dual-band rectangular DRA were obtained. Design guideline was also given to facilitate the design. To demonstrate the usefulness of the formulas, a wide dual-band rectangular DRA fabricated using K-9 glass was designed for 2.4/5.2-GHz WLAN applications. To upgrade the antenna as the souvenir-DRA, the word “LOVE” was carved on the sidewall of the glass DRA by using the sandblasting machine, and it was found that the content and position of the word has little effect on the antenna performance. The impedance bandwidths of the proposed wide dual-band DRA can be achieved as ~25% for the lower band and ~13% for the upper band.

We propose a tunable terahertz (THz) absorber design that utilizes a bulk Dirac semimetal (BDS)-based metasurface. The absorber consists of a BDS film with a periodic ring slot, dielectric layer, and fully reflective gold mirror. Simulations indicate that localized surface plasmon resonance is excited within certain regions close to the ring slot, leading to dipolar plasmon resonance of periodic arrays along the polarization direction, thereby producing resonant absorption. The BDS conductivity scales linearly with the Fermi level that can be tuned by bias application, enhancing the electromagnetic-field concentration and shrinking the effective current path, thereby blue-shifting the operating frequency within an ultrawideband. The thickness of the proposed design is significantly less than the resonant wavelength; therefore, the design yields an ultrathin metasurface absorber. This paper may lead to the investigations of the tunable metasurface device based on the BDS.

An excessively tilted LPFG-assisted surface plasmon polaritons sensor (Ex-TLPFG assisted SPP sensor) with ultrahigh sensitivity is proposed and numerically investigated using the finite-element-method-based full-vector complex coupled mode theory. We show that the SPP mode is transited (or excited) gradually from both the p-polarized TM $_{0,j}$ and EH $_{v,j}$ ( $v\geq 1$ ) modes, and hence, the proposed SPP sensor can be tuned to achieve strong resonance of either the degenerate TM $_{0,j}$ and EH $_{2,j}$ modes or EH $_{1,j}$ mode to optimize the sensitivity for analyte refractive index sensing. The results confirm that a transition point corresponding to the phase matching curve of the SPP mode is obtained, which can be used to predict the optimized grating period. By this approach, ultrasensitive SPP refractometric sensor can be obtained and the sensitivity can be further improved through a simple method: reducing the fiber cladding combined with an optimized grating period. We demonstrate that a giant sensitivity as high as $10100\,\text{nm}/\text{RIU}$ is achieved for the degenerate TM $_{0,32}$ and EH $_{2,32}$ modes (or $7400\,\text{nm/RIU}$ for the EH $_{1,32}$ mode). These appealing characteristics make the proposed Ex-TLPFG-assisted SPP sensor ideal for biochemical analyte sensing applications.

A dual-polarized antenna with omnidirectional radiation and high isolation performance is proposed in this paper. The proposed antenna consists of courtyard-shaped metal frame, feeding network, and metal background. Working mechanism of the proposed antenna is analyzed by the theory of characteristic modes. Two orthogonal polarizations can be achieved by utilizing the orthogonal current distributions on the courtyard-shaped metal frame. In order to obtain the horizontal-polarized mode, eight slots etched on the walls of the courtyard-shaped metal frame are excited. A feeding network is placed at the inner part of courtyard-shaped metal frame for a compact design. Measured results show that the proposed antenna can cover the impedance bandwidth of 1.80–2.81 GHz for both polarizations with their corresponding isolations better than 35 dB. A peak gain of 7 dBi and a gain ripple less than 3 dB in the horizontal radiation plane are achieved. The proposed antenna can be applied in the indoor wireless communication.

A symmetrical hybrid driving waveform (SHDW) is proposed in this paper, which includes a symmetrical saw-tooth driving waveform and a sinusoidal friction regulation waveform, and the sinusoidal friction regulation waveform is applied to the shrinkage period of the symmetrical saw-tooth driving waveform. In other words, the proposed SHDW can be achieved when the waveform symmetry of the hybrid driving method is 50%. The SHDW can effectively drive the designed symmetrical linear piezoelectric stick-slip actuator, and the motion direction is also easily regulated. The excitation principle of the actuator excited by the SHDW is explained in detail. A prototype is fabricated and the experimental investigations of the actuator characteristics are carried on. The higher velocity and the larger driving capacity are realized using by the SHDW relative to the asymmetrical hybrid driving waveform. Testing results show that the prototype excited by the SHDW can obtain the peak no-load speeds of 0.41 and 0.39 mm/s in the forward and reverse directions when the saw-tooth driving waveform voltage is 10 $\text{V}_{\text {p-p}}$ for 800 Hz and the sinusoidal friction regulation waveform voltage is 2 $\text{V}_{\text {p-p}}$ for 39 kHz. The step efficiencies can reach 92% and 90%. The driving capacities can reach 10.52 and 9.85 [(mm/s)g/mW] with the load of 70 g under the locking force of 0.1 N. The actuator excited by the SHDW will make it ideal for miniature information technology devices.

Mode-evolutional multi/demultiplexer for few-mode fibers was demonstrated using stacked polymer waveguides. Owing to the stacked structure, $\mbox{TE}_{00}$ , $\mbox{TE}_{10}$ , and $\mbox{TE}_{01}$ modes, which correspond to $\mbox{LP}_{01}$ , $\mbox{LP}_{11}^{ {\mathrm{even}}}$ , and $\mbox{LP}_{11}^{\mathrm{odd}}$ modes, respectively, were selectively excited by the fabricated multiplexer. The mode excitation ratio was evaluated from the near-field patterns of excited modes using a mode analysis method called the averaged interference component method that we have developed. The evaluated mode excitation ratio was ranging from 6.4 to 9.7 dB for both transverse electric (TE) and transverse magnetic (TM) polarizations of first-order TE modes within the center and long wavelength (CL)-band.

A broadband linear polarization converter based on a reflecting metasurface is presented. The polarization converter is composed by a periodic arrangement of metallic particles, positioned in a square lattice with a periodicity T equal to 4.6mm. The metallic elements are printed on a metal-backed Rohacell HF31 layer with a thickness of 3mm. The unit cell topology is optimized by using a genetic algorithm. The polarization converter works from 7.3 GHz to 29.01 GHz. Since the genetic algorithm provides arbitrary cell geometries where surface currents are not excited, a refinement procedure is proposed for removing unnecessary pixels. The highest working frequency polarization converter obtained at the end of the refinement process is extended up to 32.88 GHz thus obtaining a relative bandwidth of 129.54%.

We present a metallic helical nanocone, which is a combination of a helical structure and a conic structure. Surface plasmon poloritons are excited at the boundary of the bottom of the helical nanocone, then guided and rotated by the groove provide by the helical structure on the nanocone, and finally, squeezed to the apex of the tip to form a highly localized strong electromagnetic field. The intensity distributions and polarization of the electric fields generated by the metallic helical nanocone are simulated with 3-D finite-difference time-domain method, which indicate that highly confined and hybridly polarized optical fields can be produced at the apex of the metallic helical nanocone.

In this paper, the two-photon-excited emission spectra of polymer optical fibers doped with the conjugated polymer Poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) have been measured pumping the fibers transversely to their symmetry axis. Measurements include evolutions of the emission spectra with excitation wavelength and with propagation distance, together with an analysis of emission photostability. Comparisons with results for one-photon-excited emission are also presented and discussed.

Infrared photoluminescence properties are investigated for Pr3+ containing fluoroindate glasses with formula (mol% compositions) (99-x)[ 40InF(3)-20SrF(2)-20BaF(2)-20ZnF(2)]:xPrF(3) (x= 0.1, 0.2, 0.5, 1.0 and 2.0 mol%). Different mechanisms of population and quenching for Pr3+ D-1(2) and (1)G(4) levels are shown from photoluminescence (PL), photoluminescence excitation (PLE) and decay time values. Cross relaxation processes are put in evidence in different ways for the population of excited levels as a function of the Pr3+ concentration, depending on the excitation wavelength. Different dependences on Pr3+ concentrations are observed for D-1(2) and (1)G(4) levels.

A method that characterizes two-mode waveguides whose modes cannot be selectively excited (such as buried waveguides) is presented and demonstrated. The theoretical results are presented for $N$ modes, although for the sake of simplicity, only the two-mode case is developed. The values of the optical mode fields are recovered from several images of the waveguide exit face, where both modes interfere with different relative intensity in each image. From these mode fields, both the squared index distribution, except in an additive constant, and the effective index difference can be obtained by inverting the Helmholtz equation. As in the case of the standard monomode intensity method, the relative values of effective indices and index distributions become absolute if the modes are retrieved in a point of known index, for instance, in the substrate. The method can also be applied to multimode guides if only two modes are excited. In fact, an inexpensive setup is proposed to excite the first two modes of a multimode buried waveguide. This waveguide was fabricated by ion exchange in glass and buried by electromigration. The shape of the squared refractive index recovered by the proposed method agrees with that reported in the literature.

The hollow metallic rectangular parallelepiped with roof is excited by a dipole antenna located near it. The induced current distribution on the surface of parallelepiped and the neighboring electric field are numerically investigated by using the electromagnetic simulator WIPL-D based on the method of moment. The calculation frequency is 945 MHz., Microwave Conference, 2007. KJMW 2007. Korea-Japan, 15-16 Nov.2007 Okinawa Gender Equality Center "Tiruru", Naha, Okinawa, Japan, Korea-Japan Microwave Conference 2007, pp.29-32

Method of moments (MoM) simulation of fringe waves generated by a line source that excites a perfectly reflecting wedge is introduced and compared with the exact physical theory of diffraction (PTD) fringe waves. IEEE Antennas and Propagation Society

Numerical computation was performed to derive particle compositions of high-pressure SF/sub 6/ plasmas in which the electron temperature T/sub e/ is greater than the gas temperature T/sub g/. The effective excitation temperature T/sup ex/ for each of particles was proposed to express the distribution of particles in excited states. Furthermore, the relation equations for chemical equilibrium in a two-temperature plasma were developed on the basis of the second law of thermodynamics. At fixed T/sub g/ in the range of 6000-9000 K, the increasing T/sub e/ from 9000-20 000 K encourages the dissociation and ionization of particles, causing the composition of SF/sub 6/ plasma at 0.1 MPa to differ markedly from the composition under the condition of thermal equilibrium.

Ultrawide bandwidth light-emitting diodes (LEDs) using eight layers of InAs/GaAs quantum dots (QDs) of equally tuned heights are reported. Tilted and tapered waveguides of various dimensions are tested under continuous-wave operation conditions. An emission spectrum with 3-dB bandwidth up to 173 nm at a peak wavelength of 1064.5 nm is achieved. The measured emission spectra of the QDs-LEDs as a function of the injection current indicated that the obtained large bandwidth is related to the contribution of the excited states (p, d) from the ensemble of the dots to the recombination mechanism. Continuous-wave output power of 0.6 mW is measured in the corresponding device that is made of a 1-mm-long waveguide and with tilted and tapered angles of 6° and 2°, respectively.

"A new application of a metamaterial-inspired inclusion, i.e. the Split-Ring Resonator (SRR), combined with a commercial Ground Penetrating Radar (GPR) is presented. An SRR is embedded within a soil sample and excited by the GPR antenna. Exploiting the resonant properties of the inclusion, the dielectric permittivity of a typical soil is estimated by observing the GPR data. The proposed method turns out to be very quick and the results are in agreement with many findings in the open technical literature. The point of strength of this approach is the combination of GPR technology and metamaterial concepts that leads to a quick and accurate in-situ estimation, i.e. not-destructive, of the dielectric properties of the underground."

In this work we describe an effective strategy for the avoidance of common-mode resonances excited in a printed array of loaded dipoles with inherent filtering properties (filtenna). Previous works demonstrated that, for E-plane scanning, such resonances occur due to the unbalanced excitation of the dipoles. The present approach is based on the use of an X-band hybrid-ring connected to the filtenna structure. A design with operational bandwidth spanning from 8.5 to 10.5 GHz is presented and validated with simulations.

Date of Conference: 8-13 July 2001 Conference name: IEEE Antennas and Propagation Society International Symposium. 2001 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting A space-domain represention for the surface fields excited by an elementary current source was discussed. Green's function was used and an approximation was made using Fourier series (FS), where FS coefficients were calculated using numerical integration. The integrals were evaluated numerically along the real axis using a Gausian quadrature algorithm. However, the developed scheme yielded field expressions that remain valid along the paraxial region for arbitraily small and large separation between observation and source points.

Two-dimensional modeling of positive streamer in the air between a point anode and a plane cathode is performed. A number of radicals (excited molecules and atoms) produced by a streamer is calculated. The streamers near sharp and dull anodes are simulated. The sharp anode has five times smaller radius of tip curvature, and three times higher Laplacian field at the tip than the dull one. The results show that near the sharp anode, the streamer produces radicals ten times faster and at lower energy cost than near the dull anode. The mean energy cost of one radical is 10 eV.

Summary form only given. Conjugated polymers find rapidly growing application in electroluminescent displays and are extensively studied for use in photovoltaics and laser diodes. For a wide range of conjugated materials ultrafast pump-probe experiments have revealed the excited state dynamics of singlet and triplet excitons as well as positively and negatively charged polarons. Charge carriers play a key role in all the above mentioned applications. However, there is yet no clear picture of the mechanisms which lead to their generation.Photocurrent excitation cross-correlation measurement. on methyl-substituted ladder-type poly(para)phenyl (m-LPPP), a prototypical conjugated polymer with very appealing properties for the above mentioned applications, have suggested that charge carrier generation occurs preferentially from higher lying states during energy migration. Our approach to examining this mechanism consists of an innovative modification of the ultrafast time-resolved pump-probe technique.

Polydiacetylenes are a well-known class of one-dimensional /spl pi/-conjugated semiconducting polymers. They display optical transitions with high oscillator strength and low photoluminescence efficiency (typically 10/sup -4/). This is consistent with ultrafast relaxation of the primary photoexcited state 1/sup 1/B/sub u/ into one or more dark states, i.e. states which are energetically below the 1/sup 1/B/sub u/ state and not optically coupled to the ground state. The recent availability of sub-10-fs pulses in the visible range enables direct monitoring of this process. In this work we study solutions of polycarbazolyldiacetylene in benzene, which show a steep onset of ground state absorption. The differential transmission signal is shown as a function of pump-probe delay at the probe wavelength of 590 nm. Because of the negligible ground state absorption at this wavelength, the increased transmission is assigned to stimulated emission from the photoexcited 1/sup 1/B/sub u/ state. The decay of the emission corresponds to the quick internal conversion to the lower energy, optically dark 2/sup 1/A/sub g/ state. The same dynamics are observed over the whole stimulated emission region. Superimposed on the transient signal we observe coherent molecular oscillations. The lack of oscillations different from those identified in the Raman spectrum suggests that ground state vibrations are probed. The absence of excited state modes can be explained by the short lifetime of the excited 1/sup 1/B/sub u/ state, which is rapidly depopulated towards the dark state.

The transient analysis of non-linearly loaded power lines is carried out. The line is excited by indirect lightning and the analysis is performed in the time domain, where the line is represented as an equivalent dynamic m-port and the effects of the lightning excitation are taken into account through equivalent independent sources. The analysis has been carried our taking into account the effects of the finite ground conductivity. Furthermore, an accurate model has been used for the non-linear surge-arresters, to take into account dynamic effects.

An efficient procedure based on the three-dimensional finite-difference time-domain approach is developed for the electromagnetic simulation of lightning interaction to structures of composite materials, realized by thin panels protected by conductive paint. The procedure is applied to the analysis of the electromagnetic field inside a cubic box with inner wiring, excited by a transient low current injection.