Range Of Pulse Parameters Research Articles

Pulse length effects in the nonresonant long-wave infrared nonlinear optical response of n-Ge, GaAs, and ZnSe

Nonlinear optical refraction and nonlinear absorption are characterized in important long-wave infrared optical materials with picosecond and femtosecond laser pulses. The effective nonlinear refractive indices are found to be constant across a range of pulse parameters. Nonlinear absorption far from resonance is observed at relatively low (∼1GW/cm2) intensities in these materials, and the onset intensity and fluence scale strongly with pulse length. A free carrier dominated nonlinear absorption mechanism is identified for picosecond pulses, whereas nonperturbative photoionization causes femtosecond absorption.

Study on the conversion mechanism of CO2 to O2 in pulse voltage dielectric barrier discharge at Martian pressure

CO2 constitutes around 95 % of the atmosphere on Mars, and its in-situ utilization is of great value. O2 is a significant target product transformed from CO2 that can support both human respiration and fuel combustion, its conversion mechanism remains unclear. In this study, using a dielectric barrier discharge (DBD) with parallel plate electrodes, simulation and experimental results are combined to discuss the discharge characteristics and CO2 conversion process, under Mars conditions. The DBD was driven by a repetitive frequency microsecond pulse voltage. According to the discharge current, the discharge process can be split into four stages, namely the positive (negative) discharge stage and the positive (negative) discharge extinguishing stage. With a contribution up to 98 % and primarily taking place in the positive discharge extinguishing stage, the recombination decomposition reaction of electron and CO+2 is the primary pathway of O2 synthesis. At the position near the edge of the cathode potential drop zone, electron impact ionization of CO2 ground state molecules dominates the formation of CO+2. Under the range of pulse parameters considered in this paper, increasing the pulse width can lengthen the time of recombination decomposition reaction of electron and CO+2 in positive discharge extinguishing stage, which is favorable for the formation of O2. Likewise, reducing the pulse's rising edge can increase the discharge intensity and CO+2 density, which is also favorable to O2 production.

Abstract 334: Acute Effects of Nonexcitatory Electrical Stimulation During Systole in Human-induced Pluripotent Stem Cell Derived Cardiomyocytes

Cardiac contractility modulation (CCM) is a cardiac therapy whereby non-excitatory electrical simulations are delivered during the absolute refractory period of the cardiac cycle. CCM is indicated for patients with heart failure (Class III/IV) and reduced ejection fraction. We previously evaluated the effects of CCM and found isolated adult rabbit cardiomyocytes (rabbit-CMs) display a transient increase in calcium and contractility. In the present study, we sought to extend these results to human cardiomyocytes using human stem-cell cardiomyocytes (hiPSC-CMs). hiPSC-CMs were studied in both monolayer and isolated cells and results compared to that of rabbit-CMs. Contractility, calcium handling and electrophysiology was evaluated by image and fluorescence analysis. CCM was applied with a custom device covering a range of pulse parameters including standard clinical parameters (Figure 1). Pacing threshold was determined and stimulation performed at twice the diastolic capture threshold. Robust contractile response was observed at 16 V/cm, 70 mA for pacing and 28 V/cm, 120 mA for CCM. Under these conditions hiPSC-CMs and rabbit-CMs displayed increased contraction amplitude of 30 % (1.79 a.u., CCM vs 1.38 a.u., Control) and 22 % (3.67 a.u., CCM vs 3.00 a.u., Control) respectively and faster kinetics that subsided when the CCM signal was eliminated. This study provides a comprehensive characterization of the effects of CCM on hiPSC-CMs and rabbit-CMs in parallel under identical experimental conditions. These data provide the first study of CCM in hiPSC-CMs and demonstrates the potential utility of hiPSC-CMs to evaluate safety and effectiveness of cardiac medical devices.

Programmable, Transform-Limited Pulses from a Terahertz Quantum Cascade Laser

We report programmable control of pulses from a quantum cascade laser. A programmable arbitrary waveform generator is used to control the emission of the lasers by gain-switching. Quantum cascade lasers with both multimode and single-mode emission are studied. Laser emission is coherently detected using a phase-resolved injection seeding technique based on time domain spectroscopy. For the single-mode laser, pulse widths of 500–4000 ps are demonstrated, with time–bandwidth products remaining close to, or below, unity for all pulse widths. Additionally, sequences of two pulses are demonstrated, where the pulse widths, delay, and amplitude of each of the pulses are programmed electronically. A range of pulse parameters are explored. This approach allows for the generation of arbitrary terahertz pulse sequences, which will enable coherent multidimensional spectroscopy and applications requiring optimized pulse shapes.

Non-equilibrium modeling of the Fe XVII 3C/3D ratio for an intense X-ray free electron laser

We present a review of two methods used to model recent LCLS experimental results for the 3C/3D line intensity ratio of Fe XVII (S. Bernitt, et al. Nature, 492, 225 (2012)), the time-dependent collisional-radiative method and the density matrix approach. These are described and applied to a two-level atomic system excited by an X-ray free electron laser. A range of pulse parameters is explored and the effects on the predicted Fe XVII 3C and 3D line intensity ratio are calculated. To investigate the behavior of the predicted line intensity ratio, a particular pair of A-values for the 3C and 3D transitions was chosen (2.22 × 1013 s−1 and 6.02 × 1012 s−1 for 3C and 3D, respectively), but our conclusions are independent of the precise values. We also reaffirm the conclusions from Oreshkina et al. (N.S. Oreshkina, et al. Phys. Rev. Lett. 113, 143001 (2014); Ibid. J. Phys. B, 49, 094003 (2015)): the nonlinear effects in the density matrix are important and the reduction in the Fe XVII 3C/3D line intensity ratio is sensitive to the laser pulse parameters, namely, pulse duration, pulse intensity, and laser bandwidth. It is also shown that for both models the lowering of the 3C/3D line intensity ratio below the expected time-independent oscillator strength ratio has a significant contribution due to its emission from the plasma after the laser pulse has left the plasma volume. Laser intensities above ∼1 × 1012 W/cm2 are required for a reduction in the 3C/3D line intensity ratio below the expected time-independent oscillator strength ratio.

Population transfer to theE Σ1gexcited electronic state ofLi2by femtosecond laser pulses with all possible interstate radiative couplings

Population transfer to the excited electronic state $E\text{ }{^{1}\ensuremath{\Sigma}}_{\text{g}}$ of ${\text{Li}}_{2}$ by transform limited delayed femtosecond pulses has been investigated. The validity of the usual neglect of some field-molecule coupling terms in such transfers, accomplished using counterintuitively ordered pulses through ``adiabatic passage on light-induced potentials,'' has been reexamined. It has been found that such an approximation cannot be justified in the case of the ladder system $X\text{ }^{1}\ensuremath{\Sigma}^{+}_{\text{g}}\text{\ensuremath{-}}A\text{ }^{1}\ensuremath{\Sigma}^{+}_{\text{u}}\text{\ensuremath{-}}E\text{ }^{1}\ensuremath{\Sigma}^{+}_{\text{g}}$ of ${\text{Li}}_{2}$. However, the transfer can be successfully accomplished over a range of pulse parameters, which is more restricted than those obtained with the usual approximation. In this scheme, when two pulses with a small frequency difference between them are used, the lower-frequency pulse must precede the higher-frequency pulse for a successful transfer. We introduce an adiabatic representation, appropriate to this full coupling case, for examining the mechanism of transfer. In our representation the initial wave packet may be prepared on more than one adiabatic state, and at an early stage it is transferred to a single adiabatic surface after which the evolution mostly proceeds adiabatically. The vibrational analysis of the final wave packet shows that for short pulses high vibrational states are generally excited, while for pulses with larger width low-lying vibrational states are preferred in cases where successful transfer occurs. These results can be understood in terms of the motion of the wave packet on the time-dependent adiabatic potentials.

Crystallographic texture and microstructure of pulsed diode laser-deposited Waspaloy

The role of both laser pulse length and duty cycle in controlling the grain size and crystallographic texture of diode laser-deposited Waspaloy powder is investigated. Thin-walled test structures of Waspaloy have been produced using a range of pulse parameters and analyzed by means of scanning electron microscopy and electron backscatter diffraction. Results have been correlated with a simple analytical model of the effect of the laser pulse on the substrate temperature and melt-pool geometry in order to help explain the trends observed. Findings show that pulse parameters have a marked effect on the resulting grain morphology and crystallographic orientation. Modelling has indicated that this arises because the microstructure is highly dependent on the melt-pool geometry, particularly the inclination angle of the melt-pool boundary.

Pulsed gas metal arc welding of Al–Cu–Li alloy

An experimental Al–Cu–Li–Mg–Ag–Zr type alloy in the form of 13.7 mm thick plates was studied for its fusion characteristics using gas metal arc welding (GMAW) and pulsed gas metal arc welding (P-GMAW). High copper 2319 filler of 1.6 mm diameter was used. The burn-off characteristics of 2319 filler wire in GMAW and P-GMAW were experimentally determined, including the relation between pulse current and pulse duration for the desired one-drop detachment per pulse (ODPP) condition and feasible range of pulse parameters. The effect of welding parameters on bead geometry and shape relationships was investigated through beadon-plate experiments in the welding current range above the spray transition current. Reasonably good weld beads were obtained in P-GMAW at currents as low as 194 A and welding speeds of 45 cm min–1. P-GMAW yielded significantly higher weld penetration compared to GMAW.

Coherent manipulation of superconducting quantum interference devices with adiabatic passage

The method of stimulated Raman adiabatic passage is applied in order to coherently manipulate a three-level superconducting quantum interference device quantum bit with two microwave pulses. Simulations indicate that this method has the potential to allow for efficient control of the system for a wide range of pulse parameters.

Coherent manipulation of superconducting quantum interference devices with adiabatic passage

The method of stimulated Raman adiabatic passage is applied in order to coherently manipulate a three-level superconducting quantum interference device quantum bit with two microwave pulses. Simulations indicate that this method has the potential to allow for efficient control of the system for a wide range of pulse parameters.

Measurement and calculation of arc power and heat transfer efficiency in pulsed gas metal arc welding

This study investigates the heat transfer efficiency of the pulsed gas metal arc welding (GMAW-P) process. The arc power and heat input were calculated from arc current and voltage measurements and the heat input was also measured with a liquid nitrogen calorimeter. The measured heat transfer efficiency for GMAW-P varied slightly over a wide range of pulse parameters, with an average value of 70%, a maximum of 72% and a minimum of 68%. Welding heat transfer efficiency based on arc power calculated as the product of average current and voltage was too high (averaging 82%), while that calculated using the product of the root mean square (RMS) of the average current and voltage was too low (averaging 61%). Both also varied significantly with pulsing parameters. Mathematical analysis shows that average instantaneous power values must be used when current and voltage vary significantly with time. The experimental differences between the average instantaneous power and the other calculated values are explained by the relative phases of the pulsed current, voltage and arc resistance waveforms.

Different types of calcium channels and secretion from bovine chromaffin cells.

Bovine chromaffin cells possess several types of Ca2+ channels, and influx of Ca2+ is known to trigger secretion. However, discrepant information about the relative importance of the individual subtypes in secretion has been reported. We used whole-cell patch-clamp measurements in isolated cells in culture combined with fura-2 microfluorimetry and pharmacological manipulation to determine the dependence of secretion on different types of Ca2+ channels. We stimulated cells with relatively long depolarizing voltage-clamp pulses in a medium containing 60 mM CaCl2. We found that, within a certain range of pulse parameters, secretion as measured by membrane capacitance changes was mainly determined by the total cumulative charge of Ca2+ inflow and the basal [Ca2+] level preceding a stimulus. Blocking or reducing the contribution of specific types of Ca2+ channels using either 20 microM nifedipine plus 10 microM nimodipine or 1 microM omegaCTxGVIA (omega-conotoxin GVIA) or 2 microM omegaCTxMVIIC (omega-conotoxin MVIIC) reduced secretion in proportion to Ca2+ charge, irrespective of the toxin used. We conclude that for long-duration stimuli, which release a large fraction of the readily releasable pool of vesicles, it is not so important through which type of channels Ca2+ enters the cell. Release is determined by the total amount of Ca2+ entering and by the filling state of the readily releasable pool, which depends on basal [Ca2+] before the stimulus. This result does not preclude that other stimulation patterns may lead to responses in which subtype specificity of Ca2+ channels matters.