Increasing Pulse Width Research Articles

Nonlinear Thomson scattering radiation characteristics in tightly focused linearly polarized laser pulses with different pulse widths

In our work, the radiation characteristics of the pulse width for nonlinear Thomson scattering produced by the interaction of a linearly polarized tightly focused laser with a stationary electron are investigated. Theoretical derivation without approximation and numerical simulation results reveal that long pulses imply more complex electrodynamic processes. Radiation bifurcation and coupling phenomena caused by increasing pulse width are found. The radiation energy in the direction of maximum radiation also decreases with the increase of the pulse width. For the first time, the acceleration changes and γ value changes of electron motion caused by linearly polarized laser pulses are shown, and these changes are combined to explain the changes of radiation. At the same time, the full-spatial angular distribution of nonlinear Thomson scattering induced by linearly polarized light was plotted for the first time, and the existence and variation of the radiation angular width were found.

The pump and seed wavelength difference control of rogue wave generation under the group velocity matching condition

We numerically simulate the effects of the wavelength difference between the pump light and the seed light on the mid infrared supercontinuum and rogue wave under the condition of fiber group velocity matching. The results show that with the increase of the wavelength difference between the two pulses, the filling effect of the spectrum and the control of rogue wave first increase and then decrease. The appropriate wavelength difference can realize the effective control of rogue wave. In addition, the modulation depth and pulse width of seed light play an important role in the control of rogue wave. The control effect of rogue wave first increases and then decreases with the increase of modulation depth and pulse width.

Pulse width shortening combinations (PWSC) for ultra-dense WDM systems and calculation of PWSE

Abstract Optical communication systems introduced paradigm shift in the forte of data transmission at higher speeds and over longer distances where, on contrary electrical transmission systems failed due to higher amplitude degradation, interferences and lower bandwidths. However, pulse width increase (PWI) in the optical fiber limits the overall distance reach and also introduces more bit errors which needs to addressed. So far, pulse width shortening fibers (PFs) and fiber Bragg grating (FG) used individually in most of the reported studies, however pulse width shortening (PWS) took either high cost (in PFs) or lower PWS efficiency (PWSE) (in FG). Therefore, in this research manuscript, we made emphasis on the combined PWS effects of diverse techniques such as optical phase conjugation (OC), FG and PFs in ultra-dense wavelength division multiplexing (WDM) system. Total link length of 400 km has been covered in 128 channels ultra dense wavelength division multiplexing (UDWDM) system at 10 Gbps by incorporating diverse combined organized placements of FG, OC and PFs such as FG-PF, OC-PF and FG-PF-OC. Results revealed that economical and maximum PWSE arrangement for proposed system is FG-PF-OC.

Time periodic pulse electroosmotic flow of Jeffreys fluids through a parallel plate microchannel

AbstractThe purpose of this paper is to investigate the time periodic pulse electroosmotic flow (EOF) of Jeffreys fluids through a parallel plate microchannel. The driving mode of pulse EOF here is considered as a rectangle pulse. Using the method of Laplace transform, the analytical solution of velocity and volumetric flow rate of pulse EOF is derived. The effects of pertinent dimensionless parameters on the velocity and volumetric flow rate are discussed in detail. Results show that the pulse width is a valuable parameter for analyzing the influence of relaxation time and retardation time on magnitude of velocity and volumetric flow rate when the fluid flow reaches the steady state. Increasing the relaxation time reduces he magnitude of velocity and volumetric flow rate at low value pulse width , yet the trend is opposite for larger pulse width . The increase of retardation time will reduce the magnitude of velocity and volumetric flow rate no matter whether the value of pulse width is large or not. Furthermore, the frequency of velocity profile and volumetric flow rate is different because of the different pulse width . With the increase of pulse width , the different change frequency of velocity profile and volumetric flow rate slows down, which means a long cycle time. And as the relaxation time and pulse width grow, the time required for the fluid flow to reach a steady state will become longer. The conclusions have theoretical significance for biofluid based microfluidic transport systems driven by pulsed electric field.

Mode-locked operation characteristics of a monolithic integrated two-section InGaAs/GaAs double quantum wells laser with asymmetric waveguide

We report on subpicosecond pulse generation using passively mode locked lasers (MLL) based on asymmetric waveguide with InGaAs/GaAs double quantum wells (DQW) passively mode-locked lasers (MLLs) grown in one epitaxial step. With systematic measurement of the performances of two-section MLLs, we found that the gain region current, absorber reverse bias voltage and operating temperature all have obvious modulation effects on the mode-locked frequency, line width, pulse width, emitting wavelength, and signal intensity of the MLL. Especially, the prepared device emitting at 1065.4 µm exhibited ∼396 fs of a pulse width at 12.155 GHz repetition rate, peak power of ∼1.25 W under an ideal time bandwidth product (TBWP) at 20 °C. To our knowledge, it is the best value ever reported for DQW MLLs. And we obtained that the pulse width increase caused by the temperature rise should be in the range of 6.5–11.4 fs/°C, also found that the heat accumulation or thermal effect in the reverse bias section has a key influence on MLL. This is of great significance for us to improve the performance of MLL.

Characteristics of a dielectric barrier discharge plasma actuator driven by pulsed-DC high voltage

Dielectric barrier discharge using pulsed-DC high voltage (pulsed-DC DBD) have been proven to be capable of effectively reducing skin friction drag in turbulent boundary layers with limited power consumption, thus producing significant net power savings. In this work, the characteristics of pulsed-DC DBD, including power consumption, induced flow structure, thermal effect, and body force, are investigated sequentially. Both the power consumption and pressure waves produced by pulsed-DC DBD are similar to that of DBD using nanosecond pulses (ns-DBD), whereas the wall-bounded jet structure resembles that of DBD using sinusoidal high voltage (ac-DBD). A curved wall jet is induced at a small pulse width, which turns into a straight one due to the combined effect of momentum and thermal addition when the pulse width increases. With increasing pulse width, the induced body force goes up while the thermal effect weakens. Although pulse frequency has no impact on the wall-bounded jet topology, the body force increases with pulse frequency because of the enhanced energy entrainment. With these results, four parameters that affect the performance of pulsed-DC DBD are extracted, including the pulse leading edge, pulse width, frequency, and amplitude, which lays the foundation for the optimization of pulsed-DC DBD.

Numerical simulation of dynamic characteristics of droplet in oil under a CPPM electric field

The size of droplets in oil are dynamically changes during demulsification, thereby changing the optimum demulsification electric field frequency. Thus, the constant pulsed electric field cannot meet the requirement of optimum frequency. The variable frequency pulsed electric field can cater to the change in optimum demulsification frequency, and has high demulsification ability. However, the dynamic characteristics of the droplet in oil at the variable frequency pulsed electric field are unclear. Therefore, a chaotic pulse position modulation (CPPM) electric field is considered a type of variable frequency pulsed electric field, where the pulse frequency is chaotic but pulse width and field intensity are constant. The droplet deformation dynamic model under the CPPM electric field is established by applying finite element method. The dynamic and chaotic characteristics of the droplet deformation in oil in this electric field are investigated, and the influence of pulse width and electric field intensity on droplet deformation is discussed. Results show that the deformation of droplet in oil is nonstationary vibration with the action of the CPPM electric field, and its deformation is chaotic vibration. The chaos of droplet deformation decreases with the increase in pulse width, and an optimum pulse width can be found to make the droplet have large deformation ratio and high vibration times. The deformation ratio of droplet can be increased by increasing the electric field intensity, but the droplet are easy to split and the deformation is no longer chaotic at high electric field intensity, and an optimum electric field intensity can be found to make the droplet have large deformation ratio and deformation stability.

Effects of Varying Pulse Width and Frequency of Wireless Stimulation in Rat Sciatic Nerve.

Peripheral nerve stimulation is a commonly used method for assisting movements after spinal cord injury, stroke, traumatic brain injury, and other types of neurological damage or dysfunction. There are many different patterns of electrical stimulation used to accomplish movement. And so, our study investigated stimulation with a wireless floating microelectrode array (WFMA) in comparison to previously reported data on functional electrical stimulation. To determine the effect on hindlimb movement, we tested a range of frequencies and pulse widths using WFMAs that were implanted in the rat sciatic nerve for 38 weeks. Frequencies between 1 and 50 Hz did not change the minimum current amplitude required to elicit movement in the hindlimb. Increasing pulse width from 57.2 to 400.4 µs decreased the minimum current required but had an associated increase in total charge applied per pulse. Overall, the WFMA provides a stable wireless peripheral nerve interface suitable for functional electrical stimulation.Clinical Relevance- This work establishes the efficacy of various stimulation parameters for controlling movement with a wireless peripheral nerve stimulator.

Nonlinear Thomson scattering of a relativistic elliptically polarized laser with varied incident pulse widths

Within the frame of classical electrodynamics, nonlinear Thomson scattering by a stationary electron of an elliptically polarized tightly focused laser has been investigated. The electron’s trajectory, energy gain, spatial radiation distribution and temporal characteristics are studied. Due to the properties of the elliptically polarized laser pulse, the energy curve is jagged and the trajectory of electrons is in an elliptical spiral shape. It is demonstrated that the net energy gain of the electron is nearly zero in the few-cycle domain, whereas the net energy gain increases as the laser has a larger pulse width. We describe a mechanism of electron energy gain variation during an elliptical polarized laser pulse. Furthermore, with pulse width increases, the spatial radiation distribution has more sets of local maxima and each set has four local maximums. Additionally, the results show that the electron has the potential to generate a single attosecond pulse when the laser has a few-cycle width pulse. The larger the pulse width is, the weaker the maximal radiation power will be.

Sub-10 MeV proton-induced single-event transients in 65 nm CMOS inverter chains

Sub-10 MeV proton-induced single-event transients (SETs) were firstly reported in this work. Sub-10 MeV proton experiment demonstrates that sub-10 MeV proton-induced SET pulse can be wider than 200 ps and the average SET pulse-width increases with proton energy. The analysis indicates that the observed SETs are attributed to recoil ions and SETs induced by oxygen recoils can be much wider than those induced by silicon recoils. The average deposited charge of the recoil ions increases with proton energy, which is the reason for the increased average SET pulse-width as proton energy increases.

A Study of the Characteristics of Plasma Generated by Infrared Pulse Laser-Induced Fused Silica

When high energy infrared laser pulses are incident on fused silica, the surface of the fused silica is damaged and a laser-induced plasma is produced. Based on the theory of fluid mechanics and gas dynamics, a two-dimensional axisymmetric gas dynamic model was established to simulate the plasma generation process of fused silica induced by a millisecond pulse laser. The results show that the temperature of the central region irradiated by the laser is the highest, and the plasma is first produced in this region. When the laser energy density is 1.0 × 104 J/cm2 and the pulse width is 0.2 ms, the maximum expansion velocity of the laser-induced plasma is 17.7 m/s. Under the same experimental conditions, the results of the simulation and experiment are in good agreement. With an increase in pulse width, the plasma expansion rate gradually decreases.

Dependence of Temperature and Back-Gate Bias on Single-Event Upset Induced by Heavy Ion in 0.2-μm DSOI CMOS Technology

The dependence of temperature and back-gate bias on single-event upset (SEU) sensitivity is investigated based on a 0.2-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> double silicon-on-insulator (DSOI) technology. At room temperature, an obvious decrease in SEU cross section with the negative back-gate bias is experimentally observed for a DSOI static random access memory (SRAM). The physical mechanism of single-event effect (SEE) is explained through technology computer-aided design (TCAD) simulations. TCAD simulations were also performed to explain the impact of back-gate bias on charge collection and full width at half maximum (FWHM) of the pulsewidth at various temperatures. Both charge collection and FWHM of the pulsewidth increase significantly with temperature rising from 240 to 400 K. It is demonstrated that the SEU threshold linear energy transfer (LET) for a DSOI 6T SRAM cell decreases with an increase in temperature. Compared with a fully depleted SOI (FDSOI) technology, the unique independent back-gate bias scheme for a DSOI SRAM cell exhibits higher tolerance to SEU. At 400 K, it is found that the SEU threshold LET (LET_th) for a DSOI 6T SRAM cell increases by 12.5&#x0025; with back-gate bias of nMOS reduced from 0 to &#x2212;15 V.

Experimental investigation on DBD plasma reforming hydrocarbon blends

To improve the ‘detonation-supporting’ performance of fuel-rich catalytic combustion products, DBD plasma, stimulated by adjustable nanosecond pulse power supply, was used to further regulate the components and concentrations of the hydrocarbon blends. In this paper, the parameters including load voltage, frequency, rising (falling) edge, pulse width and feeding flow rate were changed respectively, and the corresponding concentration and proportion change of the components in blend gas were investigated. According to the experiment result, it was found that when the discharge frequency is low, the plasma mainly promotes the transformation of light gaseous substances, while it mainly promotes the conversion to heavy hydrocarbons when the frequency is larger. Increasing load voltage will strengthen this trend. The controlling and reforming effect of plasma on the blend gas will decrease with the increase of voltage rising (falling) edge and the feeding flow rate. The regulation effect will be strengthened with the increase of pulse width under 200 ns. With the increase of discharge intensity, the ‘carbon’ settles on the walls of the reactor, which will change the dielectric constant, leading to the loss of control of the discharge.

Research on Dilution of Laser Cladding Assisted by Pulsed Current Based on Orthogonal Experiment

With characteristics of high cladding efficiency, small grain size and low porosity, follow-up feeding pulse current assisted laser cladding can realize online self-healing of cracks on the cladding layer and get a crack-free cladding layer. It is a very promising new laser cladding technology. In this study, effects of cladding parameters (laser power, scanning speed, powder feed rate, pulse current, pulse frequency and pulse width) on dilution rate of coating were discussed through a six-factor three-level orthogonal experimental design method. Results demonstrated that laser power, scanning speed and powder feed rate can influence dilution ratio greatly, while pulse current, pulse frequency and pulse width influence the dilution ratio slightly. Among the top three major factors, laser power can influence the dilution ratio mostly, followed by powder feed rate and scanning speed. The dilution ratio increases with the increase of laser power, scanning speed and pulse width, but it decreases with the increase of powder feed rate and pulse frequency. With the increase of pulse current, the dilution ratio decreases firstly and then increases.

Effect of Pulse Current on Mechanical Behavior of High Temperature Titanium Alloy Ti55

The effects of pulse current on the tensile properties of high temperature titanium alloy Ti55 were investigated by pulse current assisted uniaxial tensile test under different electrical parameters. It was found that with the increase of peak current and pulse width, the tensile properties of Ti55 are significantly improved. At the same time, the pulsation effect of current on the mechanical properties of Ti55 was investigated. The results show that the tensile displacement of low pulsation group was higher, while the elongation of high pulsation group was higher. In order to explore the mechanism of pulsation effect of current, EBSD was adopted. The results indicated that high pulse current can significantly promote the dislocation movement and recrystallization. In addition, some macrozones was found in low pulsation group, which indicated that high pulsation current was more suitable for material forming than low pulsation current.

Evolution of melt convection in a liquid metal driven by a pulsed electric current* *Project supported by the National Natural Science Foundation of China (Grant Nos. U1760204, 51974183, 52071194, and 52074180).

Gain refinement in metal alloy can be achieved by applying an electric current pulse (ECP) in solidification process. Forced flow inside the melt has been proved to be a key role in grain refinement. In this paper, the fluid flow inside Ga 20 wt%–In 12 wt%–Sn alloy induced by a damping sinusoidal ECP flowing through two parallel electrodes into the cylindrical melt was investigated by both experimental measurements and numerical simulations. Experimental results showed that a strong descending jet was induced beneath the bottom of electrodes under the application of ECP. Besides, it was found that flow intensity increases with the increase of amplitude, frequency, and pulse width, respectively. In order to unlock the formation mechanism of flow pattern and the relevance of flow intensity varied with electrical parameters, a three-dimensional numerical model under the application of ECP was established. Meanwhile, a comparative study was conducted by numerical simulations to reveal the distributions of electromagnetic fields and forced flow. Numerical results showed that the downward Lorentz force induced by ECP was concentrated beneath the bottom of electrodes. This downward Lorentz force induces a descending jet and provokes a global forced flow. According to numerical simulations, the evolution of flow intensity with electrical parameters under the application of ECP can be understood by the time averaged impulse of Lorentz force.

Effect of pulse width on the characteristics of a dielectric barrier discharge plasma actuator driven by high-voltage pulses

In this study, high-voltage pulses are used to drive dielectric barrier discharge plasma actuators (DBDAs) for flow control purposes. The rising/falling edges of the pulse are kept nearly constant in nanosecond timescale, while the pulse width is varied from nanosecond to microsecond timescale. The impact of pulse width on the characteristics of the DBDA is investigated experimentally with a high-speed schlieren system and a high-fidelity force balance. In the case of small pulse width, a pressure wave propagating at the local speed of sound is produced each time at discharge ignition, and a vertical jet plume is induced after multiple discharge pulses due to heat accumulation (buoyancy effect). As a comparison, for cases with large pulse widths, two pressure waves are created sequentially with a time lag close to the pulse width, and a starting vortex followed by a near-wall jet is produced, demonstrating that significant momentum similar to that of DBD driven by sinusoidal high voltage has been imparted to the near-wall flow. A proportional increase of the induced body force with the cube root of the pulse width is demonstrated, while the pulse energy decreases nonlinearly as the pulse width increases. The maximum body force of 2.49 mN m−1 is reached at a pulse width of 380 μs.

A Detection Performance Analysis of Sanya Incoherent Scatter Radar Tristatic System

AbstractIncoherent scatter radars (ISR) are among the most powerful ground‐based instruments for solar‐terrestrial physics, measuring multiple plasma parameters over almost the entire vertical extent of the ionosphere. In Sanya, on Hainan Island, China, an advanced high‐power phased array ISR, known as the Sanya incoherent scatter radar (SYISR), is under construction. A tristatic system is planned, with a transmitter at Sanya (SY) Station (109.6°E, 18.3°N), together with receivers at SY, Fuke (FK) (109.1°E, 19.5°N), and Qiongshan (QS) (110.2°E, 19.7°N) on Hainan Island. With the pulse width increasing, the SNR increases for a phased array monostatic ISR, while the SNR initially increases and then remains unchanged for a phased array bistatic ISR. SNR first increases and then decreases as the detection height increases from 100 km to 1,000 km for both the monostatic and bistatic ISR for typical ionospheric conditions. The relative error decreases fast with increasing pulse width when the pulse width is lower than 130 μs for both monostatic and bistatic ISR. When the pulse width is over 130 μs, the relative error decreases very slowly for a monostatic ISR, while it decreases very slowly and then stays unchanged with increasing pulse width for a bistatic ISR. Relative error increases slowly below 500 km, but increases fast for heights over 500 km for both the monostatic ISR and bistatic ISR. It is shown that a tilt angle of 20°–30° and a clockwise‐rotation angle of 157° are reasonable choices for the FK receiving array in the SYISR tristatic system.

Charge transfer in plasma assisted dry reforming of methane using a nanosecond pulsed packed-bed reactor discharge

This paper is aimed to investigate the effect of packing material on plasma characteristic from the viewpoint of charge transfer process. Both the charge accumulation and release processes in the dielectric barrier discharge reactor and packed-bed reactor were investigated by measuring voltage and current waveforms and taking ICCD images. The packing material was ZrO2 pellets and the reactors were driven by a parameterized nanosecond pulse source. The quantity of transferred charges in the dielectric barrier discharge reactor was enhanced when decreasing pulse rise time or increasing pulse width (within 150 ns), but reduced when the gas gap was packed with pellets. The quantity of accumulated charges in the primary discharge was larger than the quantity of released charges in the secondary discharges in the dielectric barrier discharge reactor, but they were almost equal in the packed-bed reactor. It indicates that the discharge behavior has been changed from the view of charge transfer process once the gas gap was packed with pellets, and the ICCD images confirmed it.

Parametric Analysis of Laser Beam Percussion Drilling for Thin Titanium Alloy Sheet Using Yb: Yag Fiber Laser

Laser beam percussion drilling (LBPD) can create high density holes in aerospace materials with the repeated application of laser pulses at a single spot. In this study, one-parameter-at-a-time approach has been used to investigate the individual effect of peak power, pulse width and pulse frequency on geometrical accuracy and metallurgical distortion during LBPD of 0.85[Formula: see text]mm thick Ti–6Al–4V sheet using 200[Formula: see text]W Yb:YAG fiber laser. It has been found that the output parameters behave differently at the higher and lower values of a particular input process. The increase of pulse width from 1 to 1.50[Formula: see text]ms increases hole taper by 20% whereas the same corresponding change from 1.50 to 2.00[Formula: see text]ms reduces the taper by 20%. The increase of pulse frequency from 10 to 50[Formula: see text]Hz reduces hole circularity by 40% but the same proportionate change from 50 to 90[Formula: see text]Hz reduces circularity by 79%. Increase of peak power from 1.70 to 2.0[Formula: see text]kW increases hole taper by 8% but the corresponding increase from 2 to 2.30[Formula: see text]kW is 143%.