Longer Pulse Duration Research Articles

MP79-19 COMPARISON OF DUSTING AND FRAGMENTING USING THE NEW SUPER PULSE THULIUM FIBER LASER TO A 120W HOLMIUM:YAG LASER

INTRODUCTION AND OBJECTIVES:Holmium:YAG laser is the current lithotrite of choice. Although improvements such as higher pulse frequency, longer pulse duration, and multi-pulse technology have advan...

Pattern of bubble evolution in liquids under repetitive pulsed power

Pulsed electric fields (PEFs) are employed in a newly developed food sterilization technology via repetitive electric pulses. The evolution of bubbles and the consequent electrical breakdown of the liquid treatment chamber are the main technical hurdles for industrial applications of this technology. The evolution pattern of the bubbles and the effect of pulse parameters on the bubbles under repetitive pulses are studied. Repetitive bipolar rectangular pulses (6–10 kV, 20–80 μs in duration, with a 50–200 Hz repetition rate) are applied to a gap (1 cm) containing sodium chloride solution (with a conductivity of 30 μS/cm). A high-precision bubble monitoring system is developed to recognize and count microbubbles with diameters greater than 50 μm. The pattern of the bubble evolution can be divided into 4 stages: the initial stage, developing stage, converging stage and discharging stage. The saturated time, number, area and average diameter of the bubbles are introduced as feature parameters to better characterize the bubble evolution, and the relevant time-varying curves for different pulse parameters are obtained based on experimental images. The experimental results show that a stronger electric field, a longer pulse duration and a higher repetition rate speed up the evolution of the bubbles. The growth of the bubbles depends more on the effect of continuous long pulses, and the electric field might be a deciding factor concerning the initiation of microbubbles, while the increase in bubble volume is mainly a result of the thermal effect of current.

Determination of Radar Features During Simulator Space Sensing with Radio Pulses of Short Duration

In this paper, we analyzed the features of obtaining radar information, and also determined the advantages of using short pulses in comparison with pulses of long duration. In the course of the study it was determined that the range is limited by the characteristics of the pulse and the propagation loss. Long pulses can be superimposed and interpreted as a single reflected echo or object. Short pulses improve the radar’s resolution by returning individual echoes, but they require a system with a wider bandwidth.

Keyhole cutting of carbon fiber reinforced polymer using a long-duration nanosecond pulse laser

The machining performance of a high-energy nanosecond pulse laser with a near-infrared wavelength is investigated for carbon fiber-reinforced polymer (CFRP) with two different fiber arrangements. This research work demonstrates for the first time that a keyhole mode cutting can be achieved for CFRP materials using a high-energy nanosecond pulse laser of a Long Pulse mode (120 ns). Specifically, it is shown that the short-duration Q-Switch mode (8 ns) results in ineffective material removal for CFRP, despite much higher peak laser power intensity than the Long Pulse mode. In Long Pulse mode, multi-pass straight line and contour cutting experiments are further performed to investigate the effect of laser processing parameters and resultant machined surface integrity. Plasma absorption effects using both pulse modes are discussed. The results show that a 2.2 mm thick cross-ply CFRP panel can be cut through using as few as 6 laser passes, and a high-quality machined surface can be produced with a limited heat-affected zone and minimal fiber pull-out using Argon assist gas. The successful outcomes from this work provide the key to enable efficient CFRP laser machining using high-energy nanosecond pulse lasers, and offer insight into the unique energy absorption mechanisms for CFRP laser machining.

Tunable and switchable harmonic h-shaped pulse generation in a 303 km ultralong mode-locked thulium-doped fiber laser

We experimentally demonstrated a type of tunable and switchable harmonic h-shaped pulse generation in a thulium-doped fiber (TDF) laser passively mode locked by using an ultralong nonlinear optical loop mirror. The total cavity length was ∼3.03 km, the longest ever built for a TDF laser to our best knowledge, which resulted in an ultralarge anomalous dispersion over −200 ps2 around the emission wavelength. The produced h-shaped pulse can operate either in a fundamental or in a high-order harmonic mode-locking (HML) state depending on pump power and intra-cavity polarization state (PS). The pulse duration, no matter of the operation state, was tunable with pump power. However, pulse breaking and self-organizing occurred, resulting in high-order HML, when the pump power increased above a threshold. At a fixed pump power, the order of HML was switchable from one to another by manipulating the PS. Switching from the 8th up to the 48th order of HML was achieved with a fixed pump power of ∼4.15 W. Our results revealed the detailed evolution and switching characteristics of the HML and individual pulse envelope with respect to both the pump power and PS. We have also discussed in detail the mechanisms of both the h-shaped pulse generation and the switching of its HML. This contribution would be helpful for further in-depth study on the underlying dynamics of long-duration particular-envelope pulses with ultralarge anomalous dispersion and ultralong roundtrip time.

Deformation twinning in a mild steel: Loading dependence and strengthening

Deformation twinning in a mild steel is investigated under quasi-isentropic compression (IC) and shock compression (SC) to about 12 GPa, as regards the effects of pulse duration (plateau width) and strain rate (rising edge slope), and associated twin strengthening. The pulse duration ranges from 80 ns to 790 ns; and two rise times are explored, approximately 30 ns for SC and 300 ns for IC. Free-surface velocity histories are measured to obtain strain and strain rate. The postmortem samples are characterized with electron backscatter diffraction, and the yield strengths of the samples pre-deformed by impact are examined with a materials testing system. For SC, twin density and size increase with pulse duration up to 580 ns. At longer pulse durations, the increase in twin density is stagnated as a result of deviatoric stress relaxation, while twin size continues growing. For IC (410 ns), twin density and size are much larger than the SC counterpart, as a result of shallower rising edge. Increased deformation time can compensate the effects of reduced strain rate or applied stress for deformation twinning. Twin strengthening effect is strong in postmortem samples, depends on twin density instead of area fraction, and follows the empirical Hall–Petch relationship.

Isolated attosecond pulse generation from polarizationgating pulse with 10 fs duration

Isolated attosecond pulses make it possible to study and control the ultrafast electron processes in atoms and molecules. High order harmonic generation (HHG) is the most promising way to generate such pulses, which is benefited from the broad plateau structure of the typical HHG spectrum. In previous HHG studies on the polarization gating pulse with longer pulse duration, one needs to dramatically increase the separation in time between the two counter-rotating circularly-polarized pulses to generate the nearly-linear half-cycle " polarization gate”. This leads to a low harmonic conversion efficiency because the field outside the polarization gate is much stronger than inside the polarization gate. In this paper, by using Lewenstein model, we theoretically simulate the high-order harmonic generation from helium atom subjected to the polarization gating pulse with 10 fs pulse duration. It is found that high-order harmonic spectra each with a higher efficiency and regular structure can still be obtained by reasonably adjusting the delay time ratio and the amplitude ratio of electric fields between the two counter-rotating pulses. Further, a single 175 as pulse in the time domain is obtained by Fourier transforming the 80th order harmonics into the 172nd order harmonic without compensating for the harmonic chirp. This scheme has two main advantages. First, the adjustment of the polarization gate width from half optical cycle into nearly one cycle ensures higher intensity of the synthesized electric field inside the polarization gate. Second, the suitable adjustment of the amplitude ratio between two electric fields ensures the low ionization probability before the polarization gate, and thus further fulfills the harmonic phase matching condition in the process of the propagation.

Rabbit lung hemorrhage induced by acoustic radiation force impulse in clinical settings

Background Acoustic radiation force impulse (ARFI) has recently become widespread in clinical practice as ultrasound elastography. However, the safety of the modality is yet to be confirmed. Although we have already reported the alveolar hemorrhage induced by ARFI on rabbit lung tissue, these experiments were conducted with much longer pulse duration (PD) compared with that in clinical use. Therefore, we introduced a new ARFI exposure system that can confirm a targeting focal spot on a B mode image and adjust a focal depth with a good alignment precision. This time, we conducted a series of animal experiments with the setup which is equivalent to the clinical condition. Methods 10 rabbits were anesthetized and placed in spine position. Tracheal intubation was performed to control ventilation. A focused 5.2 MHz linear probe that transmitted ARFI was placed in precordial and subcostal regions bilaterally and determined appropriate locations for exposure of the lung through two paths (transhepatic and transthoracic) respectively. Exposure settings were varied in the cases and included: mechanical index (MI) 0.6∼1.4, PD 0.3 or 1.0ms, pulse repetition time (PRT) 3s, exposure time 90s. One case was conducted with ultrasound contrast agent. After exposure, the lungs were removed for macrophotography and histopathologic study. Results A red spot was observed on the surface of the lung corresponding to the area of exposure in each animal (17 at transhepatic and 19 at transthoracic path out of 20 and 19 exposures respectively). The size of red spots varied from 2 mm to 22 mm. The damage was not aggravated with use of ultrasound contrast agent. Microscopic findings confirmed alveolar hemorrhage in each red spot. Discussion Ultrasound exposure has been known to induce lung injury in animal experiments. In this study, ARFI induced lung injury under the acoustic output regulation value of MI ( Conclusion Lung hemorrhage was induced under regulation value of MI and with shorter PD of 0.3ms equivalent to that in clinical use of ARFI. These results identify a potential risk of lung injury associated with the elastography when the lung is unintentionally exposed to ultrasound from the probe, especially for liver or breast imaging.

1H-Detected quadrupolar spin-lattice relaxation measurements under magic-angle spinning solid-state NMR.

Proton detection and phase-modulated pulse saturation enable the measurement of spin-lattice relaxation times of "invisible" quadrupolar nuclei with extensively large quadrupolar couplings. For nitrogen-14, efficient cross-polarization is obtained with a long-duration preparation pulse. The experiment paves the way to the characterization of a large variety of materials containing halogens, metals and more.

Effect of Crystal Structure on Fabrication of Fine Periodic Surface Structures with Short Pulsed Laser

In recent years, nanostructures have been required for industry and medical services, to perform functions such as reduction in friction, control of wettability, and enhancement in biological affinity. Ultrashort pulsed lasers have been applied to meet these demands, and have been actively studied both experimentally and theoretically in terms of phenomena and principles. In this study, to clarify the phenomenon of the fabrication of laser-induced periodic surface structures (LIPSS), and its application to industry, experiments were conducted on SUS304, titanium, and nickel-phosphorus by a short pulsed laser that has a longer pulse duration, higher cost-effectiveness, and higher stability than ultrashort pulsed lasers. The results confirmed that while LIPSS were fabricated on Ti and Ni-P workpieces, a uniform fine periodic structure was not fabricated on the whole irradiated surface of SUS304, and crystal grain boundaries appeared with low energy density and irradiation number because SUS304 is an alloy composed of Fe, Cr, and Ni. Further, the short pulsed laser has a low power and long pulse duration, inducing the thermal effect. We clarified the effect of crystal structure on fabricating fine periodic surface structures with short pulsed laser.

Measurements of Temporal Summation of Heat Pain: a Pilot Investigation in Healthy Humans

Temporal summation of pain (TSP) is a promising tool for measuring the pain modulation processes in healthy subjects and patients with chronic pain. We tried to find optimal stimulation parameters in order to elicit a robust reproducible TSP phenomenon. Twenty healthy volunteers (15 women and 5 men) completed four sessions/conditions of pulsating heat pain stimulation, applied to the left forearm with a frequency of 0.33–0.4 sec–1 using a contact heat-evoked potential stimulator. The stimulation temperature (step +0.5°C or +1.0°C up to the pain threshold, pain tolerance), pulse duration (500, 800, or 1000 msec), and number of stimuli (60 or 90) were varied. The participants rated the pain intensity at the first and every 10th heat pulse, using a numeric rating scale (NRS) 0–100. The TSP was calculated as the difference between the lowest rating and the rating of the last stimulus and was compared between conditions. The optimal condition (19 out of 20 participants responded with TSP) showed temperature at pain tolerance, pulse duration of 800 msec, and 90 stimuli. In addition, this condition showed weaker side effects (painful discomfort) than those with less (60) but longer (1000 msec) stimuli presented 1.0 degree above the pain threshold. The protocol with a relatively high stimulus repetition and a moderate pulse duration seems to be the optimal protocol to reproduce TSP. Heat stimulation with longer pulse durations and higher stimulation temperatures was less feasible.

How do chronic nutrient loading and the duration of nutrient pulses affect nutrient uptake in headwater streams?

Our study aimed to analyze the effects of chronic nutrient loading on the capacity of headwater streams to retain phosphorus and ammonium pulses of different duration. For this purpose, we selected nine headwater streams located across a gradient of increasing agricultural land use and eutrophication. In each stream, we performed sequential plateau additions with increasing nutrient concentrations in summer 2015 and instantaneous slug additions in summer 2016 under similar hydrological conditions. We modelled kinetic uptake curves from the slug additions via the Tracer Additions for Spiraling Curve Characterization method and calculated ambient uptake parameters. Ambient uptake rates generally increased (1.4–20.8 µg m−2 s−1 for NH4–N and 0.3–10.3 µg m−2 s−1 for SRP, respectively), while ambient uptake velocities decreased from oligotrophic to polytrophic streams (1.8–14.0 mm min−1 for NH4–N and 1.6–9.9 mm min−1 for SRP, respectively). However, correlations between ambient uptake parameters and background concentrations were weak. Concentration-dependent uptake rates followed either a linear or a Michaelis–Menten saturation model, regardless of the degree of nutrient loading. Uptake rate curves showed counter-clockwise hysteresis in oligotrophic streams and clockwise hysteresis in streams of higher trophic states, indicating a reduced significance of hyporheic uptake with increasing nutrient loading. Comparisons of slug and plateau additions revealed that oligotrophic streams were most efficient in uptake during short nutrient pulses, while eutrophic streams profited from longer pulse duration. The results indicate that nutrient uptake is increasingly transport-controlled in polluted streams where increased biofilm thickness and clogging of sediments restrict nutrient transport to reactive sites.

Indirect approaches for estimating the efficiency of the cold metal transfer welding process

ABSTRACTIn this work, two indirect approaches are compared to estimate the efficiency of the cold metal transfer welding process with two different current waveforms. The first approach is based on an analytical heat transfer model coupled with thermocouple measurements. The second method includes numerical heat transfer simulation of aluminium filler on the galvanised steel sheet. Then a diffusional-growth model allows evaluating the thickness of the Fe–Al intermetallic layer that was compared it to that of the experimental one. Results show that both methods give very similar process efficiencies. The process efficiency reaches a high value (0.92) with current waveforms using high-intensity pulses of short duration, whereas it decreases to 0.78 with current waveforms using low-intensity pulses of long duration.

Matched-Filter Loss From Time-Varying Rough-Surface Reflection With a Small Effective Ensonified Area

Active sonar sensing often entails propagation paths that include a surface reflection, particularly in shallow-water scenarios. Surface reflection loss, which degrades sonar performance, depends on how rough the surface is with respect to the sensing wavelength and grazing angle. The Rayleigh roughness measure quantifies this relationship with small values representing an acoustically smooth surface and large values an acoustically rough surface. Models predicting surface reflection loss are generally derived assuming the surface shape is not varying over the time in which the pulse is reflecting from it and that the ensonified region of the surface is large in extent relative to the spatial correlation length of the surface. While these models are often appropriate for short-duration narrowband pulses, they are not necessarily applicable to long-duration broadband pulses, which are the focus of this paper. By assuming the effective ensonified area after matched filtering is smaller in extent than the spatial correlation length, a surface-reflection-loss model is derived as a function of pulse duration relative to surface wave period when the net surface displacement is Gaussian distributed. As might be expected the matched filter loss for the small-ensonified-area scenario increases with the Rayleigh roughness, the number of consecutive surface reflections, and the ratio between pulse duration and the surface wave period. With respect to the latter, the loss is predicted to saturate when the pulse duration exceeds one surface wave period. The model was compared with data measurements from the 2013 Target and Reverberation Experiment, as reported by Hines et al. (“The dependence of signal coherence on sea surface roughness for high and low duty cycle sonars in a shallow water channel,” IEEE J. Ocean. Eng. , vol. 42, no. 2, pp. 298–318, Apr. 2017). The data represent both short- and long-duration pulses with respect to the surface wave period. For the short-duration pulses, the model corroborates the data analysis by Hines et al. in predicting a very small matched filter loss. It also compared very favorably with the data for the long-duration pulses in both level and slope as a function of surface roughness. The models presented in this paper should be useful in sonar-equation analysis for predicting surface reflection loss with broadband waveforms when pulse duration is on par with or exceeds the surface wave period.

Computational and experimental study on hole evolution and delamination in laser drilling of thermal barrier coated nickel superalloy

Computational study related to thermal stress and hole formation in laser percussion drilling of thermal barrier coated nickel alloy based on a thermal-mechanical coupled model, combined with experimental work, was conducted in this paper. The effects of laser parameters (pulse duration and laser power) and material property (elastic modulus) on delamination were discussed based on thermal stress analysis. Laser drilling with higher peak power density (>1e11W/m2) can quickly get a through-hole of 2.3 mm within 10 pulses. Stress mutation and thermal stress shock near the interfaces are responsible for the crack formation. For the case with low peak power density, solidification rate and solidification sequence between materials should also be considered. Under the same pulse duration, the thermal stress would be enhanced with increasing of laser power. With the same pulse energy, a more intense thermal stress shock in pulse cycles can be produced under a longer pulse duration. And this shock effect near the interfaces can be alleviated when laser source is far from the interfaces. Heat accumulating effect induced by stagnation phenomenon, mainly due to lower peak power, can contribute to crack extension along the interfaces. Thus, breaking through the first two layers with high drilling efficiency is an effective way to restrain/prevent the delamination and viable parameters are also determined in the paper. Furthermore, it would offer great benefits for delamination prevention that make sure the elastic modulus of TBC and BC close to each other along the thickness with a gradually approaching method in their preparations.

XUV pulse effect on signal modulations of harmonic spectra from H $$_{2}^{+}$$ 2 + and T $$_{2}^{+}$$ 2 +

The effects of signal modulations on the molecular high-order harmonic generations in $$\hbox {H}_{2}^{+ }$$ and $$\hbox {T}_{2}^{+}$$ have been theoretically investigated. It is found that with the introduction of the XUV pulse, due to the absorption of the extra XUV photons in the recombination process, multiplateaus on the harmonic spectra, separated by the XUV photon energy can be found. Moreover, this multiplateau structure is insensitive to the wavelength of the XUV pulse. In shorter pulse duration, the intensities of the multiplateaus from $$\hbox {H}_{2}^{+}$$ are higher than those from $$\hbox {T}_{2}^{+}$$ ; while in longer pulse duration, the opposite results can be found. Finally, by changing the delay time of the XUV pulse, the signal modulations (including the amplitude and the frequency modulations) of the multiplateaus can be controlled.

Base-isolation systems for the seismic retrofitting of r.c. framed buildings with soft-storey subjected to near-fault earthquakes

More studies are needed to evaluate the effectiveness of the base-isolation in seismic retrofitting of reinforced concrete (r.c.) framed structures in the case of masonry infills (MIs) not uniformly distributed in elevation. Moreover, amplification of the inelastic demand is generally expected for base-isolated structures located in a near-fault area, in the event of long-duration velocity pulses. In order to understand the nonlinear seismic behaviour of masonry-infilled base-isolated r.c. framed structures, first a six-storey r.c. framed building is primarily designed (as fixed-base) in compliance with a former Italian seismic code, for a medium-risk zone. Then it is retrofitted by the insertion of a base-isolation system with elastomeric and sliding bearings to meet the requirements of the current Italian code, in a high-risk seismic zone. Failure mechanisms of totally and partly infilled structures are compared by considering three structural models: (i) bare structure with nonstructural MIs; (ii) infilled structure with in-elevation uniform distribution of structural MIs; (iii) infilled structure with in-elevation uneven distribution of structural MIs. Nonlinear dynamic analysis of the original (fixed-base) and retrofitted (base-isolated) structures is carried out by a lumped plasticity model describing the inelastic behaviour of the r.c. frame members, while nonlinear force-displacement laws are considered for the elastomeric and sliding bearings. A pivot hysteretic model is assumed to predict the nonlinear force-displacement law of the equivalent diagonal strut adopted for modelling the MIs. Finally, near-fault ground motions with significant horizontal pulses are selected and scaled on the basis of the design hypotheses adopted for the test structures.

The influence of bat echolocation call duration and timing on auditory encoding of predator distance in noctuoid moths

Animals co-occur with multiple predators, making sensory systems that can encode information about diverse predators advantageous. Moths in the families Noctuidae and Erebidae have ears with two auditory receptor cells (A1 and A2) used to detect the echolocation calls of predatory bats. Bat communities contain species that vary in echolocation call duration, and the dynamic range of A1 is limited by the duration of sound, suggesting that A1 provides less information about bats with shorter echolocation calls. To test this hypothesis, we obtained intensity-response functions for both receptor cells across many moth species for sound pulse durations representing the range of echolocation call durations produced by bat species in northeastern North America. We found that the threshold and dynamic range of both cells varied with sound pulse duration. The number of A1 action potentials per sound pulse increases linearly with increasing amplitude for long-duration pulses, saturating near the A2 threshold. For short sound pulses, however, A1 saturates with only a few action potentials per pulse at amplitudes far lower than the A2 threshold for both single sound pulses and pulse sequences typical of searching or approaching bats. Neural adaptation was only evident in response to approaching bat sequences at high amplitudes, not search-phase sequences. These results show that, for short echolocation calls, a large range of sound levels cannot be coded by moth auditory receptor activity, resulting in no information about the distance of a bat, although differences in activity between ears might provide information about direction.

Effect of Pulse Duration on Corrosion and Impression Creep Properties of AA5083‐H111 Al–Mg Alloy Weldments Processed by P‐GTAW

In this work, the corrosion and impression creep properties of weldments are determined using potentiodynamic polarization test and impression creep test. It is evident that the shorter pulse duration results in comparatively finer grains and reduces the loss of magnesium in fusion zone, which facilitates an increase in precipitation of anodic β‐phase (Al3Mg2) and Mg2Si particles in the grain boundaries. It leads to the formation of pits by dissolving Mg atoms and propagate along the interdendritic region and finally corrode the surface thoroughly. On contrary, the increase in pulse duration results in uniform distribution of iron‐rich Al6(Fe,Mn) intermetallics as well as Fe and Mn particles in the interdendritic region which induce localized cathodic reaction and these localized cathodes assisted in achieving noble corrosion resistance by increasing the width of passive region. Also, an increase in creep resistance is attained with an increase in activation energy at a temperature of 573 K owing to the uniform dispersion of iron‐rich Al6(Fe,Mn) intermetallics in the grain boundaries of weldments processed with longer pulse duration. Hence, it is inferred from this research that the rise in pulse duration improves the corrosion and creep resistance of weldments by altering the morphology and surface distribution of intermetallics.

Pulse carving using nanocavity-enhanced nonlinear effects in photonic crystal Fano structures.

We experimentally demonstrate the use of a photonic crystal Fano resonance for carving-out short pulses from long-duration input pulses. This is achieved by exploiting an asymmetric Fano resonance combined with carrier-induced nonlinear effects in a photonic crystal membrane structure. The use of a nanocavity concentrates the input field to a very small volume leading to an efficient nonlinear resonance shift that carves a short pulse out of the input pulse. Here, we demonstrate shortening of ∼500 ps and ∼100 ps long pulses to ∼30 ps and ∼20 ps pulses, respectively. Furthermore, we demonstrate error-free low duty cycle return-to-zero signal generation at 2Gbit/s with energy consumption down to ∼1 pJ/bit and power penalty of ∼2 dB. The device physics and limitations are analyzed using nonlinear coupled-mode theory.