Kinds Of Pulses Research Articles

Linear and Nonlinear Optics of Broad-Band Laser Pulses: Diffraction.

The typical spectrally limited laser pulse in the near-infrared region is narrow-band up to 40-50 fs. Its spectral width Δk is much smaller than the carrying wavenumber k0 (Δk ≪ k0) . For such kinds of pulses, on distances of a few diffraction lengths, the diffraction is of a Fresnel's type and their evolution can be described correctly in the frame of the well-known paraxial evolution equation. The technology established in 1985 of amplification through chirping of laser pulses triggered remarkable progress in laser optics along with the construction of femtosecond (fs) laser facilities producing high intensity fields of the order of 1015-1021 W/cm2. However, the duration of the pulse was quickly shortened from picoseconds down to 5-6 fs, which have a broad-band nature (Δk ∼ k0). The linear and nonlinear propagation dynamics of broad-band pulses is quite different form their narrow-band counterparts. Here, we review the appropriate theoretical approach to study the evolution of the pulse. Moreover, we shed light on the different diffraction regimes inherent to both narrow-band and broad-band laser pulses and compare them to unveil the main differences. Using this very method, in subsequent papers, we will investigate the influence of the dispersion and nonlinearity on the laser pulse propagation in isotropic media.

In vitro digestion and fermentation characteristics of eight kinds of pulses and suggestions for different populations.

Pulse-based diets are attracting attention for their potential in combating diet-related non-communicable diseases. However, limited research studies have focused on the digestive and fermentative properties of pulses, which are crucial for exerting benefits. Here, we investigated the in vitro digestibility of starch/protein, along with the fermentation characteristics, of eight pulses and their pastes, including white kidney beans, adzuki beans, cowpeas, broad beans, mung beans, chickpeas, white lentils, and yellow peas. The findings indicated that pulse flours and pastes were low GL food (estimated GL < 10) and had a low degree of protein hydrolysis during simulated gastrointestinal digestion. During in vitro fermentation, pulses flours and pastes decreased the fermentation pH, increased the level of short-chain fatty acids (mainly consisting of valeric acid, followed by acetic acid, propionic acid, butyric acid, isobutyric acid, and isovaleric acid), and positively modulated the microbiota composition over time, specifically reducing the ratio of Firmicutes to Bacteroidetes. In addition, we found that boiling could affect the in vitro digestion and fermentation characteristics of pulses, possibly depending on their intrinsic nutrient characteristics. This research could provide a comprehensive summary of the nutrient content, digestibility, and fermentation of eight pulses and their pastes. Guided by factor analysis, for different individuals' consumption, pulses, cowpeas, broad beans, white lentils, and white kidney beans were preferred for diabetic individuals, yellow peas and white lentils were preferred for intestinal homeostasis disorders, and white lentils, broad beans, white kidney beans, and cowpeas were suitable for obese individuals, in which white lentils were considered healthier and suggested for healthy adults.

Theory of Generation of Various Dark and Negative Pulses From an FM Mode-Locked Laser

We show theoretically that various kinds of dark pulses and negative pulses can be generated from an FM mode-locked laser. First, we classify optical pulses into two groups, namely a positive pulse group, which has an electric field with a positive amplitude, and a negative pulse group, which has an electric field with a negative amplitude. We classify them into two further groups; one has a positive offset with a CW electric field and the other has a negative offset. Therefore, we have a total of four kinds of pulses, which we denote as positive bright, positive dark, negative bright, and negative dark pulses. We show that these pulses can be successfully generated by employing FM mode-locking with specific optical filters that we newly propose here. We generate various dark pulses including Gaussian, sech, double-sided exponential, rectangular, triangular, parabolic, and even dark Nyquist pulses, where we can precisely control their width, depth, and repetition rate. We also describe dark triangular and dark parabolic pulses with an intensity expression. Finally, we generate a tanh( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t/T$ </tex-math></inline-formula> ) pulse, which is an odd function and a dark soliton solution of the nonlinear Schrödinger equation. Since this pulse has different amplitudes with ± signs on the wings, conversion from an odd function to an even function plays an important role in achieving FM mode-locking.

3D few cycle optical pulses in carbon nanotube-based photonic crystal with allowance for mechanical stress

This paper constructs and numerically analyzes a theoretical model of three-dimensional few cycle optical pulse dynamics in semiconductor carbon nanotube-based spatially-modulated refractive index medium. It takes into account external deformation in terms of the gauge theory. It identifies the stable propagation of that kind of pulses in photonic crystal. The paper also reveals the dependence of pulse dynamics on photonic crystal characteristics (refractive index depth and modulation period in particular).

Single-Event Transients in an IEEE 802.15.4 RF Receiver for Wireless Sensor Networks.

This paper presents a procedure to analyse the effects of radiation in an IEEE 802.15.4 RF receiver for wireless sensor networks (WSNs). Specifically, single-event transients (SETs) represent one of the greatest threats to the adequate performance of electronic communication devices in high-radiation environments. The proposed procedure consists in injecting current pulses in sensitive nodes of the receiver and analysing how they propagate through the different circuits that form the receiver. In order to perform this analysis, a Complementary Metal Oxide Semiconductor (CMOS) low-IF receiver has been designed using a 0.18 μm technology from the foundry UMC. In order to analyse the effect of single-event transients in this receiver, it has been studied how current pulses generated in the low-noise amplifier propagate down the receiver chain. The effect of the different circuits that form the receiver on this kind of pulse has been studied prior to the analysis of the complete receiver. First, the effect of SETs in low-noise amplifiers was analysed. Then, the propagation of pulses through mixers was studied. The effect of filters in the analysed current pulses has also been studied. Regarding the analysis of the designed RF receiver, an amplitude and phase shift was observed under the presence of SETs.

Improved neural networks based on genetic algorithm for pulse recognition

Pulse diagnosis is an important part of Chinese medicine and has played an important role in the development of Chinese medical science. However, the pulse is traditionally determined by cutting it off, which leads to a lack of objective standard pulse identification methods and affects their accuracy and feasibility. This research has studied and discussed the processing and identification of four kinds of pulse: normal pulse, wiry pulse, smooth pulse, and thready pulse. Four frequency-domain characteristics of the pulse wave and six kinds of wavelet scale energy characteristic information were extracted, and a three-layer BP (backprocessing) neural network was established. The LM (Levenberg–Marquard) algorithm and a genetic algorithm were used to improve the BP neural network, to train on and predict experimental samples, and to obtain classification accuracies of 90% and 95% respectively. Moreover, improved BP neural network based on a genetic algorithm has shown highly superior performance in terms of convergence speed and low error rate.

Antioxidant Capacities of Plant-Derived Foods Commonly Consumed in Japan.

To provide reliable data for high quality epidemiological studies examining the relationship between health and antioxidant intake from daily foods, 107 plant-derived food items (12 rice, bread and noodles, 5 potatoes and starches, 9 pulses, 6 nuts/seeds, 29 vegetables, 22 fruits, 5 mushrooms, 7 algae, and 12 beverages) were selected as commonly consumed foods in Japan based on dietary records, and their antioxidant capacities were evaluated by validated hydrophilic- and lipophilic-oxygen radical absorbance capacity (H-ORAC and L-ORAC) methods. The food items covered more than 60% of total food intake for each category on a weight basis. The H-ORAC and L-ORAC values were widely distributed at 0-210 and 0-30 μmol-Trolox equivalent/g, respectively. The foods possessing potent antioxidant capacities were found in vegetables and fruits as well as other plant-derived foods. In most foods measured, the H-ORAC values were much larger than the L-ORAC values, except for certain kinds of pulses, nuts/seeds, mushrooms, and algae. The ORAC data shown here is sufficient to accurately estimate the antioxidant intake from plant-derived foods in Japan, and should be useful in future epidemiological studies aiming to clarify the biological significance of ORAC values.

A General Sub-Nyquist Sampling System for Pulse Streams

The recent finite rate of innovation (FRI) framework has shown that pulse streams can be sampled at the rate of innovation and recovered from a set of Fourier coefficients. However, due to the individual variation of the pulse frequency spectrum, previous FRI sampling systems vary owing to different pulse shapes. In this paper, we propose a general sub-Nyquist sampling and recovery method for pulse streams that is available for many kinds of pulses. The proposed scheme exploits the spread-spectrum technique from a random demodulator (RD), in which an analog mixing front end aliases the spectrum. Such a technique allows for recovery of an arbitrary pulse with the baseband of the frequency spectrum, which greatly improves the flexibility of the sampling system. But unlike the fast switching rate of the mixing signal in RD, the proposed method has a lower rate requirement and is simpler to implement in practice. To recover the unknown parameters of the pulse streams from the obtained aliased Fourier coefficients, we quantize the analog time axis with a fit number of uniform bins and propose a sparsity-based recovery algorithm. Finally, simulation results demonstrate the effectiveness and robustness of the proposed method.

Detection and parameter estimation of weak pulse signal based on strongly coupled Duffing oscillators

Pulse signal detection is widely used in nuclear explosion electromagnetic pulse detection, lightning signal detection, power system partial discharge detection, electrostatic discharge detection, and other fields. The signal strength becomes weak with the increase of the detection distance and may be submerged in strong Gaussian noise for remote detection. Therefore, the detection and recovery of the weak signals, especially the weak pulse signals, have important applications in signal processing area. Some methods have been reported to detect and estimate weak pulse signals in strong background noise. Coupled Duffing oscillators are usually used in processing periodic signals, though it is still in an exploration stage for aperiodic transient signals. There remain some problems to be solved, for example, the system performance depends on some initial values, results are valid only for the period-doubling bifurcation state, the waveform time domain information cannot be accurately estimated, etc. In this paper, we explain the reasons why there exist these inherent defects in the current weakly coupled Duffing oscillators. In order to solve the above-mentioned problems, a new signal detection and recovery model is constructed, which is characterized by coupling the restoring force and damping force of the two oscillators simultaneously. A large coupling coefficient is applied to the two Duffing oscillators, and a generalized " in-well out-of-synchronization”phenomenon arises between the oscillators which conduces to detecting and recovering the weak pulse signals, and also overcoming the defects mentioned above. Using the metrics of signal-to-noise ratio improvement (SNRI) and waveform similarity, the effects of amplitude and period of periodic driving force, coupling coefficient, step size and damping coefficient on signal detection and waveform recovery are studied. Finally, experiments are performed to detect and recover the following three kinds of pulses: square wave pulses, double exponential pulses, and Gaussian derivative pulses. The input SNR thresholds of these three waveforms are –15, –12, and –16 dB, respectively, under the detection probabilities and waveform similarity all being greater than 0.9 simultaneously. The maximum error of the pulse amplitude and pulse width are both less than 5% of their corresponding true values. In summary, the strongly coupled Duffing system has advantages of being able to operate in any phase-space state and being no longer limited by the initial values. Especially, the time domain waveform of weak pulse signals can be well recovered in the low SNR case, and the error and the minimum mean square error are both very low.

Development of Virtual Pulse Simulation for Pulse Diagnosis Studies

Pulse signals can be used to observe the early sign of patients' health problems. From medical researches, monitoring the characteristic of arterial pulse waveform shows some risk indicator of specific diseases, e.g., hypertension, cardiovascular and heart failure diseases. A simple way to get arterial pulse wave is by using fingers to touch the radial artery position on the wrist. In the traditional Chinese medicine, a physician can use the information of arterial pulse wave-form to identify diseases based on the physician’s ability and experience. The improvement of the skill in pulse measurement can be improved by training using various kinds of pulses that represent each disease. This paper proposes a development of the virtual pulse simulation using Augmented Reality (AR) and haptic device for pulse diagnosis studies under various situations. The pulse simulation generates arterial pulse waveforms based on Sine and Gaussian functions. In this study, the mathematical model can generate the pulse wave like human pulse by setting up specific parameters. We can generate pulse waveform which representing different kinds and states of diseases by varying the mathematical model and parameters such as pulse rate or pulse pressure. The features of this work include how to generate force feedback from the mathematical models using the haptic device and how the virtual 3D can display visual feedback. The pulse simulation is useful for the health sciences students, especially the nursing students in training to identify some diseases. The evaluation of the system was carried out by first-year nursing students regarding usability, satisfaction, and performance.

Legume production at Cyrene in the Hellenistic period: epigraphic evidence

AbstractLegumes seem to have been cultivated and to have formed an essential part of the human diet during the Greek and Roman periods. This paper examines the cultivation of pulses in Cyrenaica during the Hellenistic era. It considers the regional production capacity for legumes to meet local needs and argues the involvement of different kinds of pulses in interregional commerce alongside cereals and other dry grains. This study has been implemented via investigating Hellenistic epigraphic evidence from Cyrene. It has traced the cost of pulses mentioned in inscriptions of the fourth and third/second centuries BC and compared them with that of wheat and barley. Pulses and cereal costs indicated by Diocletian's ‘Edict on Maximum Prices of AD 301’ have also been investigated to assess the general trend of their prices over time. The examination demonstrates that varieties of pulses were produced in Cyrenaica during the Hellenistic era and were likely as significant as wheat and barley. It also indicates that they were probably traded from the region alongside other dry commodities.

Synthesis of ultrashort laser pulses for high-order harmonic generation

We present a technique for the synthesis of ultrashort laser pulses with approximately one cycle (FWHM) of temporal duration. These pulses are characterized by a certain degree of chirp. We show that these pulses produce both an enhancement of the high-order harmonic generation (HHG) cutoff and a noticeable increase of the yield, when interacting with an atomic system. Additionally, the asymmetric nature of the driven pulses plays an important role in the efficiency and cutoff extension of the high-order harmonics generated. Starting from the HHG spectra, we demonstrate it is possible to retrieve isolated attosecond pulses by spectral filtering. The analysis and interpretation of the different characteristics present in the HHG driven by this kind of pulse was carried out invoking classic arguments. Furthermore, a more complete description and validation of the HHG properties is performed by a quantum analysis, based on the integration of the time-dependent Schr\odinger equation in full dimensionality.

Robust generation of entangled state via ground-state antiblockade of Rydberg atoms

We propose a mechanism of ground-state antiblockade of Rydberg atoms, which is then exploited to prepare two-atom entangled state via three different kinds of pulses. First we use the pulses in the form of sin2 and cos2 functions and obtain a maximally entangled state at an accurate interaction time. Then the method of stimulated Raman adiabatic passage (STIRAP) is adopted for the entanglement generation, which is immune to the fluctuations of revelent parameters but requires a long time. Finally we capitalize the advantages of the former two methods and employ shortcuts to adiabatic passage (STAP) to generate the maximal entanglement. The strictly numerical simulation reveals that the current scheme is robust against spontaneous emission of atoms due to the virtual excitation of Rydberg states, and all of the above methods favor a high fidelity with the present experimental technology.

Efficient photoassociation of ultracold cesium atoms with picosecond pulse laser

ABSTRACTWe investigate theoretically the formation of ultracold Cs2 molecules via photoassociation (PA) with three kinds of pulses (the Gaussian pulse, the asymmetric shaped laser pulse SL1 with a large rising time and a small falling time and the asymmetric shaped laser pulse SL2 with a small rising time and a large falling time). For the three kinds of pulses, the final population on vibrational levels from v′ = 120 to 175 of the excited state displays a regular oscillation change with pulse width and interaction strength, and a high PA efficiency can be achieved with optimised parameters. The PA efficiency in the excited state steered by the SL1-pulse (SL2-pulse) train with optimised parameters which is composed of four SL1 (SL2) pulses is 1.74 times as much as that by the single SL1 (SL2) pulse due to the population accumulation effect. Moreover, a dump laser is employed to transfer the excited molecules from the excited state to the vibrational level v″ = 12 of the ground state to obtain stable molecules.

High-order harmonic generation driven by chirped laser pulses induced by linear and non linear phenomena

We present a theoretical study of high-order harmonic generation (HHG) driven by ultrashort optical pulses with different kind of chirps. The goal of the present work is perform a detailed study to clarify the relevant parameters in the chirped pulses to achieve a noticeable cut-off extensions in HHG. These chirped pulses are generated using both linear and nonlinear dispersive media.The description of the origin of the physical mechanisms responsible of this extension is, however, not usually reported with enough detail in the literature. The study of the behaviour of the harmonic cut-off with these kind of pulses is carried out in the classical context, by the integration of the Newton-Lorentz equation complemented with the quantum approach, based on the integration of the time dependent Schr\"odinger equation in full dimensions (TDSE-3D), we are able to understand the underlying physics.

The effective stimulating pulse for restoration of blink function in unilateral facial nerve paralysis rabbits, verified by a simple FES system.

The trains of 200ms biphasic square pulses with the width of 9ms delivered at 50Hz were found to be the most suitable and effective mean as stimulation in FES system of restoring the blink function in unilateral facial nerve paralysis rabbit model. FES system is a reliable tool for these patients. Facial paralysis affects thousands of people every year. Many will have long term facial difficulties and the loss of the ability to blink the eye, which can lead to potential loss of the eye. Although many treatments exist, no one approach corrects all the deficits associated with the loss of orbicularis oculi function. FES is a means of providing movement in paralysed muscles to assist with practical activities and one possible way of restoring blink and other functions in these patients. Although some previous researches had investigated the effect of simple FES system on restoration of paralyzed facial muscles, there is still controversy about the appropriate details of the most effective stimulating pulses, such as the frequency, wave pattern and pulse width. Our aim is to find out the parameters of the most appropriate and effective stimulatin verify it by a simple FES system. 24 healthy adult male New Zealand white rabbits were accepted the surgery of right side facial nerve main trunk transaction under general anesthesia as the unilateral facial nerve paralysis models. The platinum tungsten alloy electrodes were implanted in orbicularis oculi muscle. The parameters of stimulus pulses were set to a 200ms biphasic pulse with different waveforms (square, sine and triangle), different frequencies (25, 50, 100Hz) and different widths from 1 to 9ms. Next, we set up a simple FES system to verify the previous results as the stimulus signal. We observed the movement of the both sides of eyelid when eye blink induced by different kinds of pulses. In all animals, the three kinds of waveforms pulse with frequency of 25Hz could not evoke the smooth blink movement. But the pulses with frequency of 50 and 100Hz can achieve this effect. The voltage threshold of the square pulse was lower than that of the sine pulse and triangle pulse. With the increase of pulse width from 1 to 9ms, the voltage threshold decreased gradually. The voltage threshold of the pulse with frequency of 100Hz was obviously lower than that of 50Hz. But the amount of total charge of the stimulation pulse of 100Hz was significantly more than that of 50Hz. In addition, when the FES system was turned on, the eye blink on the affected side with the stimulation pulses that were set by the previous step results was successfully aroused by the blink movement as a trigger on the contralateral.

Unipolar and bipolar pulses emitted during the development of lightning flashes

AbstractBoth unipolar and bipolar magnetic or electric field pulses have been observed during preparatory stages of a lightning flash. We introduce a new simple analytical model to describe both kinds of pulses. We show how the polarity overshoot depends on the parameters of the model, including the propagation velocity of the current pulse, the step length, and the injected current waveshape. We observe that the expression for the radiation part of the magnetic field can be decomposed into two time‐shifted terms with opposite polarities. The time shift of the two terms is determined by the overall propagation time of the current pulse. The model well corresponds not only to observations of the bipolar preliminary breakdown pulses at time scales of tens of microseconds but also to both unipolar and bipolar dart‐stepped leader pulses at submicrosecond time scales.

Temporal and time-averaged Talbot effect of grating

Talbot effect of grating with the ultra-short pulsed laser illumination is studied in time domain and space domain. The theoretical formulas of the temporal and time-averaged diffraction intensity of grating illuminated by the pulsed laser are deduced on basis of the partial coherence theory. The influence of the duration time of pulse and the chirp coefficient on the Talbot image of grating is analyzed in detail. As the duration time is long enough, the temporal and the time-averaged Talbot image can be obtained. Moreover, the influence of the pulse shape on Talbot effect of grating is also discussed. The diffraction distributions of grating illuminated by three kinds of pulses with Gaussian, super-Gaussian and sech shapes are provided. Under the same condition, the diffraction of grating illuminated by the pulsed laser with super-Gaussian shape closes much more to the grating structure.

Experimental investigations of pulse shape control in passively mode-locked fiber lasers with net-normal dispersion

Pulse shape control in passively mode-locked fiber lasers with net-normal dispersion is investigated experimentally. Three kinds of pulses with different spectral and temporal shapes are observed, and their pulse-shaping mechanisms are discussed. After a polarization-resolved system external to the cavity, the maximum intensity differences of the two polarization components for the rectangular-spectrum (RS), Gaussian-spectrum (GS), and super-broadband (SB) pulses are measured as ∼20 dB, ∼15 dB, and ∼1 dB, respectively. It is suggested that the equivalent saturable absorption effect plays an increasingly important role from the RS to GS and then to SB pulses in the pulse-shaping processes, while the spectral filtering effect declines. This work could help in systematically understanding pulse formation and proposing guidelines for the realization of pulses with better performance in fiber lasers.

Recent progress in investigation and application of dissipative soliton in fiber lasers

Fiber lasers have promoted the development of scientific researches and technology applications for their excellent beam quality, high efficiency, compact structure, and high reliability. Ultra-short high-energy pulse fiber lasers can find important applications in the areas of optic communication, sensing, precision machining, material processing, ultra-fast diagnosis, biomedicine, and national defense. Consequently, how to increase the power and energy of the laser pulse, control and utilize the complex nonlinearity, and develop the key technologies for the applications of high-power, high-energy, and ultra-broadband all-fiber ultra-short pulse lasers become the important scientific issues for the exploration of new phenomena and schemes as well as the breakthrough of technical systems about fiber laser pulses. This article briefly reviews some key techniques and important progresses about mode-locked fiber lasers, discusses the merits and drawbacks of various fiber lasers and pulses, also introduces our research results in the past several years about how to improve the performance of fiber lasers and achieve novel kinds of pulses. We particularly discuss the typical behaviors of fiber lasers operating in different dispersion regimes, and demonstrate both experimentally and numerically the formation mechanisms, output features, and dynamic evolutions of conventional solitons as well as dissipative solitons. Moreover, several novel types of high-energy wave-breaking-free pulses are introduced. These results in the article may provide helpful theoretical and experimental fundamentals for the in-depth study of new high-energy pulses. Hopefully, our introductions and discussions can attract the researchers’ attentions to the exploration of new phenomena and mechanisms of ultra-short high-energy pulses based on novel mode-lockers, and bring the new understandings about nonlinear phenomenon of ultra-short high-energy pulses under extreme conditions.