Pulse Phenomena Research Articles

Transient of power pulse and its sequence in power electronics

Various failures and destructions occur in the applications of the power electronic converter. The real practice shows that these failures are connected with the concentration of the transient power pulse. In allusion to the physical characteristics of power electronic converters, this paper proposed that the power pulse and its sequence are the basis for power electronics in the perspective of electromagnetic energy. The authors analyzed the transient processes in the power semiconductors, electric conduction loops and controller system and illustrated the power pulse phenomena in high voltage and high power inverters. This investigation on the power pulse sequence is very meaningful for the failure analysis and device protection and has become an important topic in power electronics.

RECENT ADVANCES IN PULSED LASER ABLATED PLASMA PLUMES: A REVIEW

Pulsed laser ablation is a process in which an intense laser pulse interacts with the matter producing plasma. The present work describes the theoretical work being conducted in the past for the pulsed laser ablation phenomenon. It incorporates the theoretical models being proposed by various researchers around the globe for pulsed laser ablation. The main processes involved in the laser–matter interaction leading to plasma plume formation are the absorption and the reflection of the incident laser light by the condensed phase, ablation of the condensed phase, absorption of the laser light within the expanding plume, expansion of the vapor-plasma plume, and in the case of pulsed laser desorption, the interaction of the ablated species with the substrate surface. Thus the plasma, produced in the laser–matter interaction, plays an important role in the pulsed laser ablation (PLA) process.

Ultrashort Laser Pulse Phenomena: Fundamentals, Techniques, and Applications on a Femtosecond Time Scale, 2nd ed., by Jean-Claude Diels and Wolfgang RudolphUltrashort Laser Pulse Phenomena: Fundamentals, Techniques, and Applications on a Femtosecond Time Scale, 2nd ed. Jean-Claude Diels and Wolfgang Rudolph , Elsevier, New York, 2006, 652 pp.

Photomedicine and Laser SurgeryVol. 25, No. 1 Book ReviewUltrashort Laser Pulse Phenomena: Fundamentals, Techniques, and Applications on a Femtosecond Time Scale, 2nd ed., by Jean-Claude Diels and Wolfgang RudolphRaymond J. LanzafameRaymond J. LanzafameSearch for more papers by this authorPublished Online:12 Mar 2007https://doi.org/10.1089/pho.2007.9999AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail "Ultrashort Laser Pulse Phenomena: Fundamentals, Techniques, and Applications on a Femtosecond Time Scale, 2nd ed., by Jean-Claude Diels and Wolfgang Rudolph." , 25(1), p. 58FiguresReferencesRelatedDetailsCited byOptical spectroscopy, thermal analysis, and dynamic mechanical properties of graphene nano-platelets reinforced polyvinylchloride12 August 2021 | Journal of Materials Science: Materials in Electronics, Vol. 32, No. 17Robust, efficient, and broadband SHG of ultrashort pulses in composite crystals29 July 2019 | Optics Letters, Vol. 44, No. 15 Volume 25Issue 1Feb 2007 InformationCopyright 2007, Mary Ann Liebert, Inc.To cite this article:Raymond J. Lanzafame.Ultrashort Laser Pulse Phenomena: Fundamentals, Techniques, and Applications on a Femtosecond Time Scale, 2nd ed., by Jean-Claude Diels and Wolfgang Rudolph.Photomedicine and Laser Surgery.Feb 2007.58-58.http://doi.org/10.1089/pho.2007.9999Published in Volume: 25 Issue 1: March 12, 2007PDF download

Reply to comment by Y. Ben‐Zion on “Material contrast does not predict earthquake rupture propagation direction”

Reply to comment by Y. Ben‐Zion on “Material contrast does not predict earthquake rupture propagation direction”

Gravitational effects induced by high-power lasers

The gravitational field produced by a high-power laser is calculated according to the linearized Einstein field equation in weak field approximation. It is found that when a probe pulse propagates in the above gravitational field, the gravitational Faraday effect and defocusing phenomenon of the probe pulse are induced by the gradient of the energy density of the high-power laser pulse. The rotating angle of the polarization plane of the probe pulse and the variation of its light intensity are derived. The results are discussed and estimated under the conditions of our present experiment facility.

Numerical Analysis of Electronic Transport Characteristics in Dielectrics Irradiated by Ultrashort Pulsed Laser Using the Nonlocal Fokker-Planck Equation

ABSTRACT The ultimate goal of this article lies in investigating theoretically the electronic transport characteristics in fused silica (SiO2) irradiated by ultrashort pulsed lasers. The nonlocal type of multivariate Fokker-Planck equation is modeled on the basis of the Boltzmann transport formalism to describe the ultrashort pulsed laser-induced damage phenomena in the energy-position space, together with avalanche ionization, three-body recombination, and multiphoton ionization. From the results, it is observed that the recombination becomes prominent and contributes to reduce substantially the rate of increase in electron number density when the electron density exceeds a certain threshold. With very intense laser irradiation, a strong absorption of laser energy takes place and an initially transparent solid is converted to a metallic state, a phenomenon well known as laser-induced breakdown. It is also found that full ionization is provided at intensities above threshold, and all further laser energy is deposited within a thin skin depth. The absorption length is of the order of a wavelength at very high laser fluence, and it becomes thinner as laser fluence is larger. This is because the absorbed energy is no longer consumed for multiphoton ionization, but rather leads to a drastic increase in the absorption coefficient because of Joule heating.

On the origin of giant pulses in radio pulsars

Induced Compton scattering of radio emission off the particles of the ultrarelativistic highly magnetized plasma of pulsar magnetosphere is considered. The scattering between the photon beams of substantially differing frequencies and orientations appears to result in photon transfer to the higher frequency. With the decreasing spectrum of pulsar radio emission, this may imply a significant amplification of the higher-frequency intensity. A detailed analysis shows that the rays of widely spaced frequencies can have different orientations, at least at certain locations in the pulsar magnetosphere. The numerical estimates confirm the possibility of an efficient beam-to-beam scattering in the pulsars known as giant pulse sources. Thus, the intensity amplification on account of induced scattering of the lower-frequency radiation is suggested to underlie the giant pulse phenomenon. A huge pulse-to-pulse scatter in the observed intensities of the giant pulse sources (over more than three orders of magnitude) testifies to significant variations of the efficiency of amplification. If this variability is attributed to the fluctuations of both the particle number density and the incident intensity and the latter are considered as the partially correlated Gaussian random quantities, one arrives at the power-law distribution of strong pulses in intensity. The formation of the giant pulse substructure, the broad-band spectral behaviour of the scattering efficiency and the link of giant pulses to the high-energy emission are discussed as well.

Giant Pulses — A Brief Review

We briefly review observational manifestations of pulsars with giant pulse emission and consider quasi-giant pulse phenomena in other pulsars. We argue that power-law statistics give the best definition of giant pulses. Finally, we speculate as to the origin of the giant pulses and a possible link with high energy emission.

Dynamics of pulse phenomena in helium dielectric-barrier atmospheric-pressure glow discharges

A study of pulse phenomena in conventional parallel-plate dielectric-barrier controlled atmospheric-pressure glow (DB-APG) discharges in helium is reported. Stable DB-APG discharges are found to occur at arbitrarily low frequencies as long as the gas voltage exceeds the Paschen breakdown voltage, i.e., no lower limit of ∼1 kHz exists for DB-APG operation. The interpulse preionization phenomenon is found to be an artifact of typical ∼10 kHz operation of DB-APG discharges and does not play a role in the formation of a stable pulse. Multiple pulses result from repeated temporally separated breakdown events in the discharge. A relatively simple zero-dimensional model that treats only the Paschen breakdown mechanism in the discharge and charge trapping phenomena at the dielectric surfaces can be used to simulate all important qualitative features of DB-APG phenomena. Finally, we show that control of the pulse intensity, number of pulses in a pulse train, and the time interval between pulse trains can be achieved using “ramp-plus-plateau” voltage input wave forms rather than typical sinusoidal wave forms.

Pulse phenomena of second-order impulsive differential equations with variable moments

This paper obtains sufficient conditions for presence or absence of pulse phenomena of second-order impulsive differential equations with variable times.

Characterization of ammonia emissions from soils in the upper coastal plain, North Carolina

A dynamic flow-through chamber system was used to measure fluxes of ammonia-nitrogen (NH 3-N, where NH 3-N=(14/17)NH 3) from soil surfaces. The research site was located in eastern North Carolina (35.9°N latitude; 77.7°W longitude) and measurements were conducted during spring and winter 2000, in order to assess the NH 3 source strength of intensively managed agricultural soils and the physiochemical properties which control these emissions. Soil temperature ( T soil), soil pH, soil moisture, total Kjeldahl nitrogen (TKN=organic N+NH 3-N+NH 4 +-N) were monitored throughout both research periods. Soil temperature was found to explain the largest variability in soil NH 3 emissions (Log 10 NH 3-N Flux=0.054 T soil+0.66; R 2=0.71), suggesting that an approach similar in design to the biogenic emissions inventory system land use and temperature model for NO emissions, might be effective for modeling biogenic NH 3 emissions. Soil nitrogen was also significant in predicting NH 3 flux [NH 3 Flux=55.5(NH 3-N)−160, R 2=0.86; NH 3 Flux=0.6(TKN)−410, R 2=0.27], but only after the two days with the heaviest rainfall were removed from the regression, emphasizing the role of soil moisture in controlling the transfer of gases across the soil/air interface. Soil pH remained relatively constant throughout both research periods and therefore did not serve as a useful predictor of NH 3 flux. A rain event, followed by a drying period produced a characteristic pulse in ammonia emissions. This pulsing phenomenon has been observed for other trace gases by various researchers. This research location was the site of a commercial hog operation, which allowed for the comparison of soil and lagoon emissions (lagoon emissions were based on an algorithm developed by Aneja et al. (J. Geophys. Res. 105 (2000) 11,535). An analysis of the source strengths confirmed that lagoon emissions are a larger flux source (average lagoon flux ∼18,137 ng N m −2 s −1; average soil flux ∼54 ng N m −2 s −1); however soil surfaces make up a larger fraction of a commercial hog operation than the lagoon surfaces, and as a result they cannot be neglected when developing and apportioning NH 3 emissions. A yearly average of ammonia emissions at this site revealed that soil emissions represent approximately 28% of the lagoon emissions.

Giant Pulses from Two Pulsars

We present observational results from long term monitoring of giant pulses from two pulsars. One of the pulsars (PSR 0950+08) has been observed simultaneously at three different observatories, at different radio frequencies. There is evidence to suggest that the giant pulse phenomenon is intrinsic to the pulsar.

Numerical simulation of the propagation of a single laser pulse in a photorefractive medium

Abstract The paper presents a numerical study of the self-focusing time behaviour of a ns single laser pulse propagating in a biased photorefractive sillenite crystal. Assuming particular hypotheses in the case of short pulse illumination, a nonlinear partial differential equation linking the refraction index and the beam intensity has been derived from a mono-dimensional Kukhtarev band transport model. The numerical resolution of this equation has been coupled to the simulation of the propagation of a beam in a nonlinear medium using a Beam Propagation Method. We thus simulate the self-focusing phenomena of a single laser pulse on the nanosecond time-scale. These calculations let us describe the output beam profile evolution during the laser pulse and study theoretically the influence of different parameters on self-focusing such as the applied electric field, the beam intensity and waist. A successful comparison to previous experimental measurements is reported.

Giant Pulses from the Millisecond Pulsar B1821−24

We have carried out a survey for `giant pulses' in 5 millisecond pulsars. We detect individual pulses from the high Edot pulsar PSR B1821-24 with energies exceeding 50x the mean pulse energy. These giant pulses are concentrated in a narrow phase window coincident with the power-law non-thermal pulse seen in hard X-rays. This is the third example of the giant pulse phenomenon. It supports the idea that large B fields in the outer magnetosphere are critical to the formation of such pulses and further suggests a direct connection between giant pulses and high energy emission.

Laser-triggered electrical breakdown in liquid dielectrics. Imaging of the process by the shadowing technique

Electric breakdown in transformer oil subjected to a quasi-uniform dc electric field has been triggered by a focused laser pulse and prebreakdown discharge phenomena were imaged by the shadowing technique. Extensive data were recorded of the prebreakdown phenomena, such as streamers and gas bubble growth, from the initiation of the laser plasma to the disruptive discharge. The data was used to qualitatively and semi-quantitatively describe these phenomena. The image material also was used to improve and modify the qualitative description of the laser-triggered breakdown process previously presented by Sunesson et al. [1994].

Demographic Characteristics of 3 Artemisia tridentata Nutt. Subspecies

Previous research suggested that woody plant recruitment may occur in pulses in semi-arid areas. The overall objective of this study was to determine if this pulse phenomena was recorded in the demographic structures of big sagebrush (Artemisia tridentata Nutt.) stands in Wyoming. In 1997, approximately 75 stem cross sections were collected from 9 stands of each of 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth-rings were used to identify year of establishment and demographic characteristics were analyzed from age-class frequencies. Mean stand ages of the 3 subspecies were different (P = 0.002), and analyses revealed that Wyoming (A. tridentata ssp. wyomingensis) and mountain big sagebrush (A. tridentata ssp. vaseyana) stand ages (32 +/- 9 and 26 +/- 9 years, respectively) were significantly older than basin big sagebrush (A. tridentata ssp. tridentata) (17 +/- 3) stands (P < 0.05). Mean recruitment intervals (years) were shorter for basin (1.6) than for Wyoming (2.3) and mountain (2.2) sagebrush (P = 0.01). The number of cohorts did not differ among the subspecies (P = 0.11), but the percent of years with recruitment was significantly higher for basin (59%) compared to Wyoming (37%) and mountain (39%) subspecies (P < 0.0001). Age-class frequency distributions of each stand and regional stand combination were assessed for dispersion across each associated period of record. Chi-square goodness-of-fit tests were performed for the negative binomial distribution. All stands (with one exception) and all 3 regional stand combinations fit the negative binomial distribution. Age-class frequency patterns indicate that recruitment is clustered or aggregated across each period of record. Recruitment in big sagebrush stands occurs in pulses throughout Wyoming. DOI:10.2458/azu_jrm_v54i2_perryman

Demographic characteristics of 3 Artemisia tridentata Nutt. subspecies

Previous research suggested that woody plant recruitment may occur in pulses in semi-arid areas. The overall objective of this study was to determine if this pulse phenomena was recorded in the demographic structures of big sagebrush (Artemisia tridentata Nutt.) stands in Wyoming. In 1997, approximately 75 stem cross sections were collected from 9 stands of each of 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth-rings were used to identify year of establishment and demographic characteristics were analyzed from age-class frequencies. Mean stand ages of the 3 subspecies were different (P = 0.002), and analyses revealed that Wyoming (A. tridentata ssp. wyomingensis) and mountain big sagebrush (A. tridentata ssp. vaseyana) stand ages (32 +/- 9 and 26 +/- 9 years, respectively) were significantly older than basin big sagebrush (A. tridentata ssp. tridentata) (17 +/- 3) stands (P &lt; 0.05). Mean recruitment intervals (years) were shorter for basin (1.6) than for Wyoming (2.3) and mountain (2.2) sagebrush (P = &lt; 0.01). The number of cohorts did not differ among the subspecies (P = 0.11), but the percent of years with recruitment was significantly higher for basin (59%) compared to Wyoming (37%) and mountain (39%) subspecies (P 0.0001). Age-class frequency distributions of each stand and regional stand combination were assessed for dispersion across each associated period of record. Chi-square goodness-of-fit tests were performed for the negative binomial distribution. All stands (with one exception) and all 3 regional stand combinations fit the negative binomial distribution. Age-class frequency patterns indicate that recruitment is clustered or aggregated across each period of record. Recruitment in big sagebrush stands occurs in pulses throughout Wyoming.

Structure stability of ultraintense laser pulse in transverse homogeneous cold plasma

We study transverse structure symmetry of an ultraintense laser pulse through transverse homogeneous cold plasma. We derive a steady-structure equation of laser pulse and solve it under different on-axis conditions. We compare Hamiltonian values at solutions with different on-axis conditions to examine their relative stability. Numerical results show that for different ionic density, symmetric structure is not always stable relative to asymmetric one of same power. For a given ionic density, whether a symmetric structure is stable is determined by its power. This result agrees with the phenomenon of pulse "head bending", qualitatively. Our theory reveals that, in addition to the plasma's transverse inhomogeneity, there is another mechanism responsible for asymmetric structure.

A Brittle Failure Mode Plot Defining Conditions for High-Flux Flow

Stress and fluid-pressure conditions for the initial formation within intact rock of faults (shear fractures), extension fractures, and extensional shears, and for the reshear of existing faults, may all be represented on a generic failure plot of differential stress (σ1– σ3) versus least effective compressive stress, σ3' = (σ3– Pf), scaled to nominal tensile strength, T (~ half the cohesive strength). Plots of this kind may be used to define maximum sustainable overpressure in different tectonic environments and the structural conditions under which the flow of large fluid volumes may occur through fault-fracture meshes containing gaping extension and extensional shear fractures. They may also be adapted to different tectonic regimes and correlated to depth for particular fluid-pressure conditions. High-flux flow through distributed fault-fracture meshes requires the tensile overpressure condition, σ3' σ3), which can only be achieved in the absence of throughgoing cohesionless faults that are well oriented for frictional reactivation in the prevailing stress field. High-flux flow through distributed fault-fracture meshes, intrinsically a transient, pulsing phenomenon, may therefore occur as follows: (1) in effectively intact low-pemeability crust devoid of throughgoing favorably oriented faults, (2) where existing faults have become severely misoriented in the prevailing stress field, and (3) where existing faults have regained cohesive strength through hydrothermal cementation.

Nonequilibrium ultrashort laser pulse phenomena described by Fermion coherent states

Generating functionals for time-dependent many particle systems in a semiconductor are derived with Fermion coherent states. In the case of noninteracting electrons and holes the one particle correlation functions follow from the inverse of a matrix, containing the kinetic energy and the time-dependent driving electric field. It is important to reorder the Grassmann fields of the holes to obtain proper generating functionals. In the case of interacting electrons and holes a Hubbard Stratonovich transformation has to be performed with auxiliary commuting fields. A saddle point approximation is considered in terms of these new fields.