Pulse Coupling Research Articles

Ultrasound-assisted water-confined laser micromachining (UWLM) of metals: Experimental study and time-resolved observation

This paper reports the experimental studies and time-resolved observations of the ultrasound-assisted water-confined laser micromachining (UWLM) process on metal workpieces using 532-nm nanosecond laser pulses. UWLM is a new machining process proposed by the corresponding author (Wu, 2014). During UWLM, a laser beam interacts with a workpiece’s front surface location immersed in water to ablate the workpiece, and in-situ ultrasonic waves in water are also applied (for example, from above the front surface using an ultrasonic horn) to the laser ablation site (which energize the water and generate cavitations) to improve the machining process. This paper reports the experimental study of the UWLM process on multiple types of metal workpieces and time-resolved in-situ observations of the process. This kind of study on UWLM has been rarely reported in the literature. Under the studied conditions, it has been found that the ablation depths produced by UWLM at 200 laser pulses are about 2.3–3.8 times the depths by laser ablation in water without ultrasound. Through in-situ time-resolved shadowgraph imaging observations, it has been found that one important likely underlying mechanism for the enhanced material removal rate in the studied UWLM process is that the in-situ ultrasound in UWLM can reduce the material cloud resulted from the previous laser pulse ablation that lingers around laser ablation site, which can enhance the coupling of the subsequent laser pulse(s)’ energy to the workpiece.

Anomalous time delays and quantum weak measurements in optical micro-resonators.

Quantum weak measurements, wavepacket shifts and optical vortices are universal wave phenomena, which originate from fine interference of multiple plane waves. These effects have attracted considerable attention in both classical and quantum wave systems. Here we report on a phenomenon that brings together all the above topics in a simple one-dimensional scalar wave system. We consider inelastic scattering of Gaussian wave packets with parameters close to a zero of the complex scattering coefficient. We demonstrate that the scattered wave packets experience anomalously large time and frequency shifts in such near-zero scattering. These shifts reveal close analogies with the Goos–Hänchen beam shifts and quantum weak measurements of the momentum in a vortex wavefunction. We verify our general theory by an optical experiment using the near-zero transmission (near-critical coupling) of Gaussian pulses propagating through a nano-fibre with a side-coupled toroidal micro-resonator. Measurements demonstrate the amplification of the time delays from the typical inverse-resonator-linewidth scale to the pulse-duration scale.

Phase space analysis of secondary beams generated in hadron–photon collisions

Present availability of high brilliance photon beams in combination with intense TeV hadron beams makes it possible to conceive the generation of low emittance TeV-class energy pion/muon beams via photoproduction in a highly relativistic Lorentz boosted frame. We analyze the secondary beams brightness achievable by the coupling of advanced high efficiency high repetition rate FEL pulses and Large Hadron Collider or Future Circular Collider hadron beams. The phase space distributions of the pion and muon beams are obtained by means of an event generator code and the characteristics, such as emittance and energy spread, are benchmarked against analytical expressions.

Synergistic interactions between temporal coupling of complex light and magnetic pulses upon melanoma cell proliferation and planarian regeneration

ABSTRACTSynergisms between a physiologically patterned magnetic field that is known to enhance planarian growth and suppress proliferation of malignant cells in culture and three light emitting diode (LED) generated visible wavelengths (blue, green, red) upon planarian regeneration and melanoma cell numbers were discerned. Five days of hourly exposures to either a physiologically patterned (2.5–5.0 μT) magnetic field, one of three wavelengths (3 kLux) or both treatments simultaneously indicated that red light (680 nm), blue light (470 nm) or the magnetic field significantly facilitated regeneration of planarian compared to sham field exposed planarian. Presentation of both light and magnetic field conditions enhanced the effect. Whereas the blue and red light diminished the growth of malignant (melanoma) cells, the effect was not as large as that produced by the magnetic field. Only the paired presentation of the blue light and magnetic field enhanced the suppression. On the other hand, the changes following green light (540 nm) exposure did not differ from the control condition and green light presented with the magnetic field eliminated its effects for both the planarian and melanoma cells. These results indicate specific colors affect positive adaptation that is similar to weak, physiologically patterned frequency modulated (8–24 Hz) magnetic fields and that the two forms of energy can synergistically summate or cancel.

Jittering waves in rings of pulse oscillators.

Rings of oscillators with delayed pulse coupling are studied analytically, numerically, and experimentally. The basic regimes observed in such rings are rotating waves with constant interspike intervals and phase lags between the neighbors. We show that these rotating waves may destabilize leading to the so-called jittering waves. For these regimes, the interspike intervals are no more equal but form a periodic sequence in time. Analytic criterion for the emergence of jittering waves is derived and confirmed by the numerical and experimental data. The obtained results contribute to the hypothesis that the multijitter instability is universal in systems with pulse coupling.

Towards manipulating relativistic laser pulses with micro-tube plasma lenses.

Efficient coupling of intense laser pulses to solid-density matter is critical to many applications including ion acceleration for cancer therapy. At relativistic intensities, the focus has been mainly on investigating various laser beams irradiating initially overdense flat interfaces with little or no control over the interaction. Here, we propose a novel approach that leverages recent advancements in 3D direct laser writing (DLW) of materials and high contrast lasers to manipulate the laser-matter interactions on the micro-scales. We demonstrate, via simulations, that usable intensities ≥1023 Wcm−2 could be achieved with current tabletop lasers coupled to micro-engineered plasma lenses. We show that these plasma optical elements act as a lens to focus laser light. These results open new paths to engineering light-matter interactions at ultra-relativistic intensities.

Jittering regimes of two spiking oscillators with delayed coupling

Abstract A system of two oscillators with delayed pulse coupling is studied analytically and numerically. The so-called jittering regimes with non-equal inter-spike intervals are observed. The analytical conditions for the emergence of in-phase and anti-phase jittering are derived. The obtained results suggest universality of the multi-jitter instability for systems with delayed pulse coupling.

The emergence of synchrony behavior in weakly coupled electrochemical oscillators via a ‘metallic plate’

We have made an effort to investigate thoroughly the coupled behavior of a spatio-temporal system of two limit cycle electrochemical oscillators (Fe/H2SO4) in the absence and presence of a metallic plate (using copper and platinum). The oscillators exchange information via the common electrolyte solution and the magnitude of information exchange varies with the distance (d) between the oscillators, i.e. the lesser the d the more will be the coupling strength and vice-versa. The presence of metallic plate between the working electrodes (Fe) enhances the magnitude of potential distribution in the solution which leads to the increase in entrainment area, i.e. the product of distance between the oscillators d and their parameter mismatch. To explain the experimental findings numerically, the pulse coupling mechanism based on the delta function (Kronecker) has been introduced.

Simple transmission line model suitable for the electromagnetic pulse coupling analysis of twisted-wire pairs above ground

Simple transmission line model suitable for the electromagnetic pulse coupling analysis of twisted-wire pairs above ground

Characteristics of THz Pulse Propagation on Teflon Covered Two-Wire Lines

We report efficient direct coupling of THz dipole antenna pulses onto air spaced two-wire transmission lines and Teflon covered two-wire lines. The air spaced two-wire lines show TEM mode propagation with very small group velocity dispersion (GVD) and relatively low attenuation. The Teflon covered two-wire lines showed comparatively much higher attenuation and GVD. However, the Teflon covered two-wire lines show a very good guiding property when the lines are curved. Although the lines are circled only 5.0 cm in diameter, there is no additional attenuation compared to straight the lines.

Numerical simulation of the coupling of ultra-wide band electromagnetic pulse into landmine by aperture**Project supported by the Postdoctoral Science Foundation of China (Grant No. 2014M552610).

The modern landmine’s electronic fuse is susceptible to strong interference or can even be damaged by the ultra-wide band electromagnetic pulse (UWB-EMP). The finite-difference time-domain (FDTD) method in lossy media with cylindrical coordinates is used to study the interactions of the UWB-EMP with the landmine. First, the coupling of UWB-EMP into the landmine shielding shell through an aperture is numerically simulated. Second, the coupled electromagnetic field of mine shells made of different shielding materials and with apertures of different sizes is plotted. Third, the aperture coupling laws of UWB-EMP into shells are analyzed and categorized. Such an algorithm is capable of effectively preventing ladder similar errors, and consequently improving the calculation precision, and in addition to adopting the message passing interface (MPI) parallel method to divide the total calculating range into more sub-ranges, the overall calculating efficiency is greatly increased. These calculations are surely a constructive reference for modern landmine design against electromagnetic damage.

Modelling Microtiming Beat Variations with Pulse-Coupled Oscillators

Patterns of microtiming variation at the beat level are known to be associated with music that evokes an experience of groove. The microtiming of Clyde Stubblefield’s drum break on James Brown’s track The Funky Drummer exhibits a pattern of variation in individual beat periods, but bar durations are unaffected. The aim of the study was to model the production of these two apparently paradoxical attributes. In the computational model presented here, microtiming variations at the beat level emerge together with uniform bar durations, due to the interaction of two oscillators via pulse coupling. The two coupled oscillators can be seen as abstractions of entrainment processes in the brain, and implications for a general model of musical entrainment are discussed.

Inhibitory and excitatory pulse coupling of two frequency-different chemical oscillators with time delay

Dynamical regimes of two pulse coupled non-identical Belousov-Zhabotinsky oscillators have been studied experimentally as well as theoretically with the aid of ordinary differential equations and phase response curves both for pure inhibitory and pure excitatory coupling. Time delay τ between a spike in one oscillator and perturbing pulse in the other oscillator plays a significant role for the phase relations of synchronous regimes of the 1:1 and 1:2 resonances. Birhythmicity between anti-phase and in-phase oscillations for inhibitory pulse coupling as well as between 1:2 and 1:1 resonances for excitatory pulse coupling have also been found. Depending on the ratio of native periods of oscillations T2/T1, coupling strength, and time delay τ, such resonances as 1:1 (with different phase locking), 2:3, 1:2, 2:5, 1:3, 1:4, as well as complex oscillations and oscillatory death are observed.

High-efficiency quantum state transfer and quantum memory using a mechanical oscillator

We analyze an optomechanical system that can be used to efficiently transfer a quantum state between an optical cavity and a distant mechanical oscillator coupled to a second optical cavity. We show that for a moderate mechanical Q-factor it is possible to achieve a transfer efficiency of $99.4\%$ by using adjustable cavity damping rates and destructive interference. We also show that the quantum mechanical oscillator can be used as a quantum memory device with an efficiency of $96\%$ employing a pulsed optomechanical coupling. Although the mechanical dissipation slightly decreases the efficiency, its effect can be significantly reduced by designing a high-Q mechanical oscillator.

On-chip picosecond pulse detection and generation using graphene photoconductive switches.

We report on the use of graphene for room temperature on-chip detection and generation of pulsed terahertz (THz) frequency radiation, exploiting the fast carrier dynamics of light-generated hot carriers, and compare our results with conventional low-temperature-grown gallium arsenide (LT-GaAs) photoconductive (PC) switches. Coupling of picosecond-duration pulses from a biased graphene PC switch into Goubau line waveguides is also demonstrated. A Drude transport model based on the transient photoconductance of graphene is used to describe the mechanism for both detection and generation of THz radiation.

Remote Sensing Image Fusion using PCNN Model Parameter Estimation by Gamma Distribution in Shearlet Domain

Abstract Here the proposed approach deals with some adaptive parameters in pulse coupled neural network (PCNN) model which are highly suitable in image fusion. Initially, the source images are separately decomposed into multi-scaled and multi-directional bands by shearlet transform (ST). Later, the PCNN model is mapped between the decomposed low pass ST sub-bands which depends on linking pulse response and coupling strength with regional statistics of ST coefficients. The process of different high pass ST sub-bands and utilization of singular value decomposition (SDV) have been discussed in details. Finally, we have obtained fusion results by the inverse shearlet transformation (IST). The experimental results on satellite images show that the proposed method has good performance and able to preserve spectral information and high spatial details simultaneously like the original source images. The objective evaluation criteria and visual effect illustrate that our proposed method has a better edge over the prevalent image fusion methods.

Pulse-coupled BZ oscillators with unequal coupling strengths.

Coupled chemical oscillators are usually studied with symmetric coupling, either between identical oscillators or between oscillators whose frequencies differ. Asymmetric connectivity is important in neuroscience, where synaptic strength inequality in neural networks commonly occurs. While the properties of the individual oscillators in some coupled chemical systems may be readily changed, enforcing inequality between the connection strengths in a reciprocal coupling is more challenging. We recently demonstrated a novel way of coupling chemical oscillators, which allows for manipulation of individual connection strengths. Here we study two identical, pulse-coupled Belousov-Zhabotinsky (BZ) oscillators with unequal connection strengths. When the pulse perturbations contain KBr (inhibitor), this system exhibits simple out-of-phase and complex oscillations, oscillatory-suppressed states as well as temporally periodic patterns (N : M) in which the two oscillators exhibit different numbers of peaks per cycle. The N : M patterns emerge due to the long-term effect of the inhibitory pulse-perturbations, a feature that has not been considered in earlier works. Time delay was previously shown to have a profound effect on the system's behaviour when pulse coupling was inhibitory and the coupling strengths were equal. When the coupling is asymmetric, however, delay produces no qualitative change in behaviour, though the 1 : 2 temporal pattern becomes more robust. Asymmetry in instantaneous excitatory coupling via AgNO3 injection produces a previously unseen temporal pattern (1 : N patterns starting with a double peak) with time delay and high [AgNO3]. Numerical simulations of the behaviour agree well with theoretical predictions in asymmetrical pulse-coupled systems.

New type of excitatory pulse coupling of chemical oscillators via inhibitor

We introduce a new type of pulse coupling between chemical oscillators. A constant inflow of inhibitor in one reactor is interrupted shortly after a time delay after a sharp spike of activity in the other reactor. We proved experimentally and theoretically that this reversed inhibitory coupling is analogous to excitatory coupling. We did this by analyzing phase response curves, dependences of different synchronous regimes of the 1 : 1 resonance on time delay, and other resonances of two coupled chemical oscillators. Dynamical rhythms of two Belousov-Zhabotinsky oscillators coupled via "negative" inhibitory pulses were investigated.

Dynamical regimes of two frequency different chemical oscillators coupled via pulse inhibitory coupling with time delay

Resonance regimes of two frequency different chemical oscillators coupled via pulsed inhibitory coupling with time delay τ have been studied theoretically and experimentally. The Belousov-Zhabotinsky reaction is used as a chemical oscillator. Regions of the 1: 1, 2: 3, 1: 2, 2: 5, and 1: 3 resonances, as well as complex oscillations and a regime in which one oscillator is suppressed have been found in the parameter plane “the ratio between the T2/T1-τ.” For the 1: 2 resonance, a sharp transition from one synchronized regime (called “0/0.5”) to the other one (called “0.2/0.7”) has been found. This transition (reminiscent to the transition between in-phase and anti-phase oscillations in case of the 1: 1 resonance) is controlled by time delay τ and the coupling strength.

Efficient coupling of nanosecond laser pulses with the cluster medium: Generation of hydrogen-like [C](5+) atomic ions.

Clusters exhibit diverse photochemical behavior as a function of laser parameters, i.e. wavelength, pulse duration and intensity. One such aspect of cluster photochemistry is the generation of energetic multiply charged atomic ions, upon efficient interaction of clusters with intense laser pulses. In the present work, mass spectrometric investigations have been carried out on clusters of tetrahydrofuran (THF, C4 H8 O) - a saturated cyclic ether - subjected to nanosecond laser pulse (spanning from UV to IR wavelength range) with the aim of shedding light on the complex mechanism of laser-cluster interactions, which is still ambiguous. THF clusters, generated via supersonic expansion of room-temperature THF vapours seeded in argon, were subjected to gigawatt intensity laser pulses (355, 532 and 1064 nm) obtained from a nanosecond Nd:YAG laser. The ions generated upon laser-cluster interaction were characterized using a time-of-flight mass spectrometer. At 355 nm, THF clusters exhibit the usual multiphoton dissociation/ionization behavior while, at 532 nm, observation of multiply charged atomic ions of carbon (up to [C](4+) ) and oxygen (up to [O](3+) ) was ascribed to Coulomb explosion of THF clusters. For studies carried out at 1064 nm, multiply charged atomic ions of carbon up to [C](5+) having an ionization energy of ~392 eV were observed, at a laser intensity of 10(10) W/cm(2) . The observation of [C](5+) atomic ions signifies efficient coupling of the laser energy with the cluster medium, using a nanosecond laser pulse. The results have been rationalized on the basis of a three-stage cluster ionization mechanism, suggesting the crucial role of the threshold laser intensity for initiating ionization within the cluster and generation of optimum charge centers for efficient extraction of energy from the laser pulse.