Pulse Formation Research Articles

3D random-modulated pulse lidar based on a gain-switched semiconductor laser with a recirculating delay lines interferometer

This study presents the development of a 3D random-modulated pulse lidar based on a gain-switched semiconductor laser with a recirculating delay lines interferometer (RDLI). The random-modulated pulses are generated by homodyning the frequency-shifting gain-switched pulses with multiple self-delays. While they exhibit anti-interference characteristics similar to those in previously developed chaos-modulated lidar, there is no need for external pulse formation and wavelength-sensitive filtering components in the current configuration. By varying the injection currents in gain-switching and the delay lengths in the RDLI, we experimentally investigated the transient dynamics of the generated random-modulated pulses. We demonstrated how these operating parameters influence the modulation in their waveforms and spectra. The detection performance was quantified by calculating the effective bandwidths, signal-to-noise ratios, Cramér-Rao lower bounds, range precision, self-interference peaks, and detection probability. We identified two key operating conditions: the best-precision condition and the precision-interference balanced condition. Compared to a previously investigated delay self-homodyne interferometer (DSHI) scheme, which homodynes the gain-switched pulses with just a single delay, the RDLI scheme achieved a precision as low as 0.46 mm, approximately 1.5 times better than the DSHI scheme. To demonstrate its superior performance and feasibility for detection, we integrated the RDLI into a 3D lidar imaging system and compared its performance to the DSHI and chaos lidar schemes. To highlight its improved precision and robustness to temperature variations, we evaluated its precision under varying average output power and changes in laser temperature. With the developed lidar system, we successfully achieved high-quality face profiling of a person with millimeter-level precision.

Detection, identification and removing of artifacts from sEMG signals: Current studies and future challenges.

Surface electromyography (sEMG), a non-invasive technique, offers the ability to identify insights into the activities of muscles in the form of electrical pulses. During the process of recording, the sEMG signals frequently become contaminated by a multitude of different artifacts, the origin of which may be attributed to numerous sources. These artifacts affect the reliability and accuracy of the pure sEMG activity, and subsequently reduce the quality of analysis and interpretation. This can lead to a misinterpretation of sEMG signals, incorrect diagnostic, or a false decision in the case of human-machine interfaces (HMI), etc. Currently, several approaches have been developed to remove or reduce the effect of artifacts on the sEMG activity. In this paper, a comprehensive review of the current studies dealing with identification, detection, and removal of artifacts from sEMG signals is proposed. In addition, this study presents different features used to characterize the artifacts from that of the clean sEMG recordings. Finally, in order to improve the quality of denoising methods, the associated challenges of detection and artifact removal approaches are discussed to be addressed carefully in the future works.

Breathers in Mode-Locked Lasers Based on Saturable Absorbers

Breathing pulses, as a unique nonlinear pulse phenomenon, play a key role in laser performance optimization, nonlinear optical processes, and complex signal transmission. Unlike stable solitons, the energy of breathing pulses fluctuates periodically over time, exhibiting periodic changes in both pulse frequency and amplitude. Through appropriate nonlinear effects, lasers can generate stable breathing pulses, achieving a mode-locked state that demonstrates a periodic "breathing" pattern. Based on this, a fiber laser incorporating a saturable absorber as the mode-locking element was designed and built, and stable breathing states were successfully observed at lower pump power levels. High-speed detection techniques and time-stretched dispersive Fourier transform (TS-DFT) technology were used to time-amplify and spectrally analyze the rapid pulses, while monitoring the evolution of the breathing pulse in both time and frequency domains. Experimental results indicate that changes in pump power significantly affect the periodic modulation induced by additional oscillations, thereby controlling the breathing ratio and ultimately leading to the formation of a stable soliton. When the pump power is between 470 <i>mW</i> and 480 <i>mW</i>, the formation of the breathing pulse was first observed, with a breathing ratio of up to 4.5. As the pump power increases, the breathing effect gradually diminishes, and at 510 <i>mW</i>, it completely disappears, with the breathing ratio dropping to 1.<br>These results confirm the critical role of pump power in controlling the breathing pulse state and its transition, demonstrating the potential for controlling pump power in ultrafast laser technology and nonlinear optics. The breathing pulse phenomenon, as a periodic pulse behavior, reflects the complex dynamical characteristics between nonlinear optical effects and cavity parameters. When combined with the natural synchronization system formed between the breathing frequency and the cavity frequency (determined by the cavity length), the periodic change of the breathing pulse becomes a crucial factor for controlling laser output. By adjusting parameters such as the laser’s nonlinearity and dissipation, the characteristics of the breathing pulse and breathing ratio can be precisely controlled, thus achieving precise control of the laser output. The periodic oscillatory characteristics of the breathing pulse inside the laser cavity lead to the non-uniform distribution of pulses, a feature that demonstrates enormous potential in pulse shaping, ultrashort pulse generation, and precise frequency comb control. Additionally, the presence of the breathing pulse may impact the stability and energy conversion efficiency of the laser, offering new perspectives for laser design and optimization.

СПОСОБИ ПІДВИЩЕННЯ ЕФЕКТИВНОСТІ ІМПУЛЬСНИХ ПРИСТРОЇВ СИЛОВОЇ ЕЛЕКТРОНІКИ

The paper examines demonstrative magnetic-semiconductor pulse generators (MSPGs), including their improved assemblies and a unipolar current voltage regulator. The advantages are given: MSPGs -1 with a modernized DC/AC input unit; MSPGs -2 with a throttle output unit for the formation of single-stroke pulses; MSPGs -3 with a transformer output unit for the formation of single-cycle pulses in comparison with known analogues, in which unipolarization of bipolar pulses is carried out at their high-voltage output using numerous semiconductor devices (MSPGs -SD). It was established that the reliability of MSPGs -2 and MSPGs -3 is, at least, an order of magnitude greater than the reliability of MSPGs -SD. In addition, with the help of MSPGs -SD, it is impossible to implement functions related to galvanic isolation, synchronization of loads, simplification of load protection and uncomplicated matching of MSPGs -SD with low-resistance and capacitive loads. It is shown that the AC voltage regulator is able to regulate the voltage on the load from zero to the maximum value, block the load, divert unused electricity, process pulses from nanosecond to millisecond ranges. As a result, materials were obtained for the further processing of the generalized complex synthesis for the improvement of the above-mentioned devices and other impulse devices of power electronics. Ref. 5, fig. 4.

Stabilized 30 µJ dissipative soliton resonance laser source at 1064 nm

We demonstrate the first successful stabilization of a dissipative soliton resonance (DSR) mode-locked (ML) laser source using straightforward techniques. Our setup employed a figure-8 (F8) resonator configuration and a nonlinear optical loop mirror (NOLM) to achieve stable mode-locking, generating 1064 nm rectangular pulses with a 3 ns duration at a repetition frequency of ~ 1 MHz. The pulses were boosted in an all-fiber amplifier chain and reached 30 µJ and 10 kW peak power per pulse at 30 W average output power. We addressed a critical gap in the literature by actively stabilizing key DSR pulse parameters: average output power (improved by a factor of 51), pulse repetition frequency (improved by 7583 using cross-phase modulation for synchronization), and pulse duration (improved by a factor of ~ 4). Additionally, we included a numerical analysis to explore the pulse formation mechanisms in DSR ML lasers working in a F8 configuration. Our findings show that non-complex all-in-fiber DSR ML lasers can reliably produce high-energy pulses with stable, repeatable parameters, making them suitable for future applications e.g. in nonlinear frequency conversion, laser micromachining, or LIDAR.

Generation of dark pulses in mode-locked erbium-doped fiber ring laser using Ti2SnC absorber

Abstract We report the experimental observation of domain-wall type dark solitons in an all-fiber ring cavity erbium-doped fiber laser (EDFL) mode-locked with a Titanium Tin Carbide (Ti2SnC) saturable absorber (SA). The SA, featuring a modulation depth of 8.2%, was created by incorporating Ti2SnC particles into a polyvinyl film. Dark pulse formation is attributed to cross-phase coupling resulting from cavity birefringence. The mode-locked laser operates at 1559 nm with pump power ranging from 30.9 mW to 90.0 mW, achieving a maximum pulse energy of 1.73 nJ, a repetition rate of 1.78 MHz, and a pulse width of 261.2 ns.

Study of the parametric effect of the wave profiles of the time-space fractional soliton neuron model equation arising in the topic of neuroscience

Time-space fractional nonlinear problems (T-SFNLPs) play a crucial role in the study of nonlinear wave propagation. Time-space nonlinearity is prevalent across various fields of applied science, nonlinear dynamics, mathematical physics, and engineering, including biosciences, neurosciences, plasma physics, geochemistry, and fluid mechanics. In this context, we examine the time-space fractional soliton neuron model (TSFSNM), which holds significant importance in neuroscience. This model explains how action potentials are initiated and propagated by axons, based on a thermodynamic theory of nerve pulse transmission. The signals passing through the cell membrane (CM) are proposed to take the form of solitary sound pulses, which can be represented as solitons. To investigate these soliton solutions, nonlinear fractional differential equations (NLFDEs) are transformed into corresponding partial differential equations (PDEs) using a fractional complex transform (FCT). The Kudryashov method is then applied to determine the wave profiles for the TSFSNM equation. We present 3D, 2D, contour, and density plots of the TSFSNM equation, and further analyze how fractional and time-space parameters influence these wave profiles through additional graphical representations. Kink, singular kink and different types of soliton solutions are successfully recovered through the Kudryashov method. The outcomes of various studies show that the applied method is highly efficient and well-suited for tackling problems in applied sciences and mathematical physics. Graphical representations, coupled with numerical data, reinforce the validity and accuracy of the technique. The proposed method is a convenient and powerful tool for handling the solution of nonlinear equations, making it particularly effective in exploring complex wave phenomena in diverse scientific fields.

Dephasingless two-color terahertz generation

A laser pulse composed of a fundamental and an appropriately phased second harmonic can drive a time-dependent current of photoionized electrons that generates broadband THz radiation. Over the propagation distances relevant to many experiments, dispersion causes the relative phase between the harmonics to evolve. This “dephasing” slows the accumulation of THz energy and results in a multi-cycle THz pulse with significant angular dispersion. Here, we introduce a novel optical configuration that compensates the relative phase evolution, allowing for the formation of a half-cycle THz pulse with almost no angular dispersion. The configuration uses the spherical aberration of an axilens to map a prescribed radial phase variation in the near field to a desired longitudinal phase variation in the far field. Simulations that combine this configuration with an ultrashort flying focus demonstrate the formation of a half-cycle THz pulse with a controlled emission angle and 1/4 the angular divergence of the multi-cycle pulse created by a conventional optical configuration.

Reverse-Engineered Exact Control of Population Transfer in Lossy Nonlinear Three-State Systems

We introduce a reverse-engineered scheme for achieving the precise control of population transfer in nonlinear quantum systems characterized by a 1:2 resonance. This scheme involves the use of two resonant laser pulses that transition from initial and final states to an intermediate level exhibiting irreversible losses. In comparison to alternative techniques, our approach offers computational efficiency advantages. Notably, the analytically defined form of the pump pulse enables tailored control strategies, enhancing robustness against decoherence and imperfections. This flexibility extends to choosing dump pulses and designing time evolution scenarios. These features open doors for practical implementation and scalability in quantum technologies, with potential applications in quantum information processing, quantum computing, and quantum communication.

Tectono-magmatic evolution of the Indian crust in western Himalayas during Paleoproterozoic: Insights from Nanga Parbat and Indus syntaxis in northern Pakistan

The Paleoproterozoic tectono-magmatic history of the Indian plate has been modelled mostly based on investigations of the Indian parts with limited studies considering the Pakistani domains of the mountain range. In this study we investigate basement rocks and younger intrusions of the Indian crust from within the core of the Indus Syntaxis and the Nanga Parbat Syntaxis in northern Pakistan, with the goal of establishing a chronology for the entire tectono-magmatic progression of northwestern Indian plate margin, including the source rocks that were ultimately involved in the formation of younger magmatic pulses. We present in-situ zircon U-Pb geochronology and O-isotopes complemented by whole rock geochemistry of granitoids and paragneisses that yielded evidence for two distinct, large-scale Paleoproterozoic magmatic events that took place in ∼ 1860 Ma and ∼ 2200 Ma in the Indian crust. Later, leucogranites (6.4 ± 0.1 Ma) intruded into the Nanga Parbat basement that were the result of melting of the basement induced by rapid uplift. The δ18OSMOW compositions of zircons from our basement samples range between 7.5 to 9.1 ‰, indicating the derivation of parental magma from the crustal source while the younger leucogranite is somewhat lighter with δ18O ranging between 7.06 to 8.23 ‰. Geochemical data show extensional tectonic settings for the basement rocks that have an A-type affinity, again pointing to a crustal precursor. We propose little to no δ18O exchange took place between the young anatectic melt and basement rocks during crustal evolution. Moreover, geochemical signatures record the crystallization of basement rocks dominated the northwestern margin of Indian plate in a post-orogenic setting in an overall extensional tectonic realm. Based on these observations, we infer that the northwestern Indian margin has experienced a large-scale magmatism during Paleoproterozoic associated with the amalgamation of the Columbia supercontinent.

Experimental studies on penetration process of high-speed water-jet into ballistic gelatin

To reveal the penetration mechanism and present the penetration characteristics of high-speed micro-jet with injection volume larger than 0.3 mL into soft tissue, the present study conducted experimental research on high-speed water-jet penetration into ballistic gelatin. The free jet dynamics of an air-powered needle-free injector that can emit up to 1.27 mL of liquid at once and the penetration dynamics were visualized to reveal the details of the penetration process. In the early unstable stage, the jet is emitted in the form of pulses, and the first jet pulse can rapidly generate an initial slender channel in gelatin in a very short time. In the subsequent stable stage, energy input produces dispersion and further increases the penetration depth slowly. Changing the driving pressure by the power source mainly changes the penetration depth increment by dispersion; while changing the nozzle diameter mainly affects the penetration depth in the initial stage. The central position of the dispersion area in the injection direction was firstly defined in the present work and it was found that an approximate linear relationship between this position and the maximum penetration depth exits for different nozzle diameters and driving pressures when injecting the same liquid dose. These research results can provide a basis for a thorough understanding of the penetration characteristics of high-speed micro-jet with injection volume larger than 0.3 mL into soft tissue, as well as the design and operation of the air-powered needle-free injector.

High order Fano resonance in the time domain for a freezing water microdroplet

Fog is a collection of micro drops of water suspended in the air, formed as a result of cooling of moist air. In supercooled air, water droplets freeze, forming ice fog at air temperatures below − 10–15° C. As the ice drop freezes, it forms a core-shell structure. In such a particle, a high-Q Fano resonance is possible, which entails the formation of a magnetic pulse. Our theoretical calculations have predicted the time-dependent formation of Fano resonances in a freezing the outside in water droplet. Time-varying unconventional Fano resonance with magnetic field enhancement yield new method to manipulate light–matter interactions in a freezing water droplet. To the best of our knowledge this mechanism was not discussed previously.

The influence of the reference potential on the operation of the pulse formation system of a 12-pulse controlled rectifier

The influence of the reference potential on the operation of the pulse formation system of a 12-pulse controlled rectifier

Fault‐Valve Instability: A Mechanism for Slow Slip Events

AbstractGeophysical and geological studies provide evidence for cyclic changes in fault‐zone pore fluid pressure that synchronize with or at least modulate slip events. A hypothesized explanation is fault valving arising from temporal changes in fault zone permeability. In our study, we investigate how the coupled dynamics of rate and state friction, along‐fault fluid flow, and permeability evolution can produce slow slip events. Permeability decreases with time, and increases with slip. Linear stability analysis shows that steady slip with constant fluid flow along the fault zone is unstable to perturbations, even for velocity‐strengthening friction with no state evolution, if the background flow is sufficiently high. We refer to this instability as the “fault valve instability.” The propagation speed of the fluid pressure and slip pulse, which scales with permeability enhancement, can be much higher than expected from linear pressure diffusion. Two‐dimensional simulations with spatially uniform properties show that the fault valve instability develops into slow slip events, in the form of aseismic slip pulses that propagate in the direction of fluid flow. We also perform earthquake sequence simulations on a megathrust fault, taking into account depth‐dependent frictional and hydrological properties. The simulations produce quasi‐periodic slow slip events from the fault valve instability below the seismogenic zone, in both velocity‐weakening and velocity‐strengthening regions, for a wide range of effective normal stresses. A separation of slow slip events from the seismogenic zone, which is observed in some subduction zones, is reproduced when assuming a fluid sink around the mantle wedge corner.

Coherent Radio Emission from “Main-sequence Radio Pulse Emitters”: A New Stellar Diagnostic to Probe 3D Magnetospheric Structures

Main-sequence radio pulse emitters (MRPs) are magnetic early-type stars that produce coherent radio emission observed in the form of periodic radio pulses. The emission mechanism behind this is the electron-cyclotron maser emission (ECME). Among all kinds of magnetospheric emission, ECME is unique due to its high directivity and intrinsically narrow bandwidth. The emission is also highly circularly polarized and the sign of polarization is opposite for the two magnetic hemispheres. This combination of properties makes ECME highly sensitive to the three-dimensional structures in the stellar magnetospheres. This is especially significant for late-B and A-type magnetic stars that do not emit other types of magnetospheric emission such as Hα, the key probe used to trace magnetospheric densities. In this paper, we use an ultra-wideband observation (0.4–2 GHz) of a late B-type MRP HD 133880 to demonstrate how we can extract information on plasma distribution from ECME. We achieve this by examining the differences in pulse arrival times (“lags”) as a function of frequencies and qualitatively comparing those with lags obtained by simulating ECME ray paths in hot stars’ magnetospheres. This reveals that the stellar magnetosphere has a disk-like overdensity inclined to the magnetic equator with a centrally concentrated density that primarily affects the intermediate frequencies (400–800 MHz). This result, which is consistent with the recent density model proposed for hotter centrifugally supported magnetospheres, lends support to the idea of a unifying model for magnetospheric operations in early-type stars, and also provides further motivation to fully characterize the ECME phenomenon in large-scale stellar magnetospheres.

Chitosan/CNDs coated Cu electrode surface has an electrical potential for electrical energy application

Polymers and nanomaterials had been widely applied at electrochemical chemosensor and biosensor. Developing technical energy is still much needed, especially using natural environmental friendly material. Both chitosan of biopolymer and carbon nanodots (CNDs) of nanomaterials are highly studied due to their extraordinary properties. The research focus on chitosan and chitosan/CNDs nanocomposite surface that was applied for electrical energy. Nanocomposite was coated on Cu electrode surface by using electroplating method. The coated electrode was dipped into oil samples. The dipped nanocomposite then was characterized by FTIR, XRD, SEM, and Chemosensor. Nanocomposite structure is still maintain its chemical compound, confirmed by FTIR and XRD, which still maintain amine group; hydroxyl group; and crystalinity of chitosan after CNDs intercoporation. Nanocomposite surface morphology show magnetite particle distribution that spreaded on the surface of electrode for both chitosan and CNDs nanocomposite, which is confirmed by SEM. The free dipping method is based on the sensitive material chitosan/CNDs as a chemosensor; the pressure process on the surface of the chitosan/CNDs sensitive material causes the interaction of metal ions and acid compounds, which involves an iontophoresis process where oil atoms that have been excited in the evaporation process will experience atomic vibrations due to electron transport which then the active groups on the Chemosensor directly absorb and bind metals and acids in oil use a chemisorption process which leads to the transfer of charge from the adsorption particles to the chemosensor surface to fill the holes so that a potential difference occurs in the form of electrical pulses which will then be captured by the Arduino system which will be converted into digital data. This process makes technological energy production in the form of electrical energy faster.

Formation of quasi unipolar pulses in nonequilibrium magnetized plasma channels

The possibility of controlling both the spectral and polarization properties of THz pulses propagating in strongly nonequilibrium extended magnetized plasma channels formed by intense UV femtosecond laser pulses in nitrogen (air) is analyzed. The formation of quasiunipolar pulses with a nonzero electric area and a specific state of polarization is discussed. The transformation of such pulses upon leaving the region of a static magnetic field is analyzed.

Development of Figure‐of‐Nine Laser Cavity for Mode‐Locked Fiber Lasers: A Review

AbstractArtificial saturable absorbers (SA) are nonlinear optical devices widely employed in mode‐locked lasers. Among the artificial SAs are nonlinear polarization evolution (NPE) and nonlinear amplifying loop mirrors that can work in either figure‐of‐eight (Fo8) or figure‐of‐nine (Fo9) laser cavities. The NPE technique is highly sensitive to environmental perturbations. Both Fo8 and Fo9 laser cavities exhibit a higher environmental stability than the NPE technique. Here the recent advances of the Fo9 laser cavity, with a focus on the pulse formation mechanisms and the role of different cavity parameters that can enable ultrafast mode‐locking analyses are discussed. Besides, the recent development of using the Fo9 laser cavity to generate high‐energy rectangular laser pulses through either dissipative soliton resonance or noise‐like pulse regimes is also reviewed. In conclusion, the current issues and challenges of pulse formation through the Fo9 laser cavity are highlighted and recommendations for future research directions are proposed. This review is expected to provide a deeper insight into the Fo9 laser cavity as the next generation of artificial SA with interesting cavity structures, laser features, and output performances.

Statistical features of the response of a superconducting hot-electron bolometer to extremely weak terahertz pulses of picosecond and nanosecond duration

We study the statistical distributions of the output signals of a superconducting hot-electron bolometer (HEB) detector exposed to weak photon pulses of 1 THz (terahertz) frequency. Pulses with variable photon numbers were generated through strongly non-degenerate parametric downconversion (PDC) in a LiNbO3 crystal at 4.8 K. Fundamental differences in histograms are found between two PDC pumping modes, with pulse widths of 28 ps and 10 ns. HEB response to a picosecond THz pulse was detected in the form of a single elementary electrical pulse (SEP), with the average amplitude proportional to radiation intensity and dispersion relative to the bolometer's dark current. HEB responses to extremely weak radiation intensities have been recorded using nanosecond pulsed illumination. We found that nanosecond histograms are asymmetrical and broaden as radiation intensity increases, indicating that the nanosecond response consists of several SEPs. Poisson–Gauss approximation of histograms indicates that not only the average number of SEPs increase but also the average amplitude of a SEP increases with increasing power of incident THz radiation.

Diffraction efficiency in acousto-optical interaction with short radio pulses

Development of acousto-optic modulators with high diffraction efficiency, which is achieved by using multi-frequency acoustic signals, is of great interest. In this regard, it seems interesting to study the possibility of implementing highly efficient diffraction for wideband signals in the form of radio pulses with short duration. The goal of presented article is to develop a mathematical model based on a quantum description of the interaction between a photon and a phonon, simulate various operating modes of an acousto-optical modulator and compare theoretical results with experimental ones. A comparison between experimental and theoretical results was made, demonstrating the possibility of obtaining high diffraction efficiency (more than 90%) for wideband signals. The proposed method makes it possible to determine the conditions under which maximum diffraction efficiency is observed, and it also seems possible to determine the parameters of the pulse sequence.