Generation of time-dependent ultra-short optical pulse trains in the presence of self-steepening effect

Starting from the extended nonlinear Schrodinger equation in which the self-steepening effect is included, the evolution and the splitting processes of continuous optical wave whose amplitude is perturbed into time related ultra-short optical pulse trains in an optical fibre are numerically simulated by adopting the split-step Fourier algorithm. The results show that the self-steepening effect can cause the characteristic of the pulse trains to vary with time, which is different from the self-steepening-free case where the generated pulse trains consist of single pulses which are identical in width, intensity, and interval, namely when pulses move a certain distance, they turn into the pulse trains within a certain time range. Moreover, each single pulse may split into several sub-pulses. And as time goes on, the number of the sub-pulses will decrease gradually and the pulse width and the pulse intensity will change too. With the increase of the self-steepening parameter, the distance needed to generate time-dependent pulse trains will shorten. In addition, for a large self-steepening parameter and at the distance where more sub-pulses appear, the corresponding frequency spectra of pulse trains are also wider.

Generation and propagation of subpicosecond pulse train

Higher-order nonlinear Schrodinger equation with the Hirota constraint conditions is considered, and an analytic solution, which can describe the modulational instability process, is presented. Based on the solution, a new pulse train without continuous wave （CW） background is generated in quadratures and the propagation of the pulse train is discussed in detail by simulating numerically. The results show that, unlike the propagation of the picosecond pulse train, under the effects of the higher-order terms, the pulse train cannot propagate along the fibre when the energy is very high; however, for some medium energy the pulse train can stably propagate. We also investigate the stability of the pulse train against violation of the Hirota conditions, and the results show that the pulse train can still propagate stably when the Hirota conditions are broken.

Attosecond pulse trains driven by IR pulses spectrally broadened via supercontinuum generation in solid thin plates

We utilized a set of fused silica thin plates to broaden the spectrum of 1kHz,30 fs Ti:sapphire amplified laser pulses to an octave.Following the compression by chirped mirror pairs,the generated few-cycle pulses were focused onto an argon filled gas cell.We detected high order harmonics corresponding to a train of 209 as pulses,characterized by the reconstruction of attosecond beating by interference of two-photon transition(RABITT)technique.Compared with the conventional attosecond pulse trains,the broad harmonics in such pulse trains cover more energy range,so it is more efficient in studying some typical cases,such as resonances,with frequency resolved RABITT.As the solid thin plates can support high power supercontinuum generation,it is feasible to tailor the spectrum to have different central wavelength and spectral width,which will make the RABITT source work in different applications.

A Chaotic Pulse Train Generator Based on Henon Map

The Henon map forms one of the most-studied two-dimensional discrete-time dynamical systems that exhibits chaotic behavior.The Henon map takes a point(Xn,Yn)in the plane and maps it to a new point(Xn+1,Yn+1).In this paper,a chaotic pulse generator based on the chaotic Henon map is proposed.It consists of a Henon map function subcircuit to realize the Henon map and another subcircuit to perform the iterative operation.The Henon map subcircuit comprises operational amplifiers,multipliers,delay elements and resistors,whereas,the iterative subcircuit is implemented with a simple design that comprises of an edge forming circuit followed by a monostable multivibrator and a voltage controlled switch without the use of any clock control.The proposed design can be used to realize the Henon map and also to generate a chaotic pulse train,with a controllable time interval and pulse position.The proposed circuit is implemented and simulated using Multisim 13.0 and MATLAB R2019b.The chaotic nature of the generated pulse train and also the time interval between the consecutive pulses is verified by the calculation of its Lyapunov exponents.

Producing High Intense Attosecond Pulse Train by Interaction of Three-Color Pulse and Overdense Plasma

Amplifying the attosecond pulse by the chirp pulse amplification method is impossible. Furthermore, the intensity of attosecond pulse is low in the interaction of laser pulse and underdense plasma. This motivates us to propose using a multi-color pulse to produce the high intense attosecond pulse. In the present study, the relativistic interaction of a three-color linearly-polarized laser-pulse with highly overdense plasma is studied. We show that the combination of ω1, ω2 and ω3 frequencies decreases the instance full width at half maximum reflected attosecond pulse train from the overdense plasma surface. Moreover, we show that the three-color pulse increases the intensity of generated harmonics, which is explained by the relativistic oscillating mirror model. The obtained results demonstrate that if the three-color laser pulse interacts with overdense plasma, it will enhance two orders of magnitude of intensity of ultra short attosecond pulses in comparison with monochromatic pulse.

Investigation of time domain characteristics of negative capacitance FinFET by pulse-train approaches

The HfO2-based ferroelectric field effect transistors(FeFET)have been widely studied for their ability in breaking the Boltzmann limit and the potential to be applied to low-power circuits.This article systematically investigates the transient response of negative capacitance(NC)fin field-effect transistors(FinFETs)through two kinds of self-built test schemes.By comparing the results with those of conventional FinFETs,we experimentally demonstrate that the on-current of the NC FinFET is not degraded in the MHz frequency domain.Further test results in the higher frequency domain show that the on-state current of the prepared NC FinFET increases with the decreasing gate pulse width at pulse widths below 100 ns and is consistently greater(about 80%with NC NMOS)than the on-state current of the conventional transistor,indicating the great potential of the NC FET for future high-frequency applications.

Fiber laser with random-access pulse train profiling for a photoinjector driver

We report on the design and performance of a fiber laser system with adaptive acousto-optic macropulse control for a novel photocathode laser driver with 3D ellipsoidal pulse shaping. The laser system incorporates a threestage fiber amplifier with an integrated acousto-optical modulator. A digital electronic control system with feedback combines the functions of the arbitrary micropulse selection and modulation resulting in macropulse envelope profiling. As a benefit, a narrow temporal transparency window of the modulator, comparable to a laser pulse repetition period, effectively improves temporal contrast. In experiments, we demonstrated rectangular laser pulse train profiling at the output of a three-cascade Yb-doped fiber amplifier.

Method to reconnoiter pulse amplitude train for phased array radar based on Hausdorff distance

This paper presents a method to estimate beam pointing of phased array radar by the pulse amplitude train, which is significant in radar electronic reconnaissance and electronic support measure. Firstly, the antenna patterns modeling of the phased array system is exploited to build the radar sweeping model and the signal propagation model. Secondly, the relationship between the variation of the radiated power and the antenna beam pointing angles in the given airspace is analyzed. Based on the above two points, the sample with obvious amplitude characteristics of the pulse amplitude train can be screened out after detecting the train peaks. Finally, the sample is matched to the subsequent pulse amplitude train based on the Hausdorff distance. The proposed methods have less prior knowledge and higher efficiency and are easier to process. By cross correlating the sample of the pulse amplitude train with the sample data of the antenna follow-up radiation, the probability of detection of the beam pointing direction becomes larger in case that the subsequent antenna beam returns to the specific position.

Thermal characteristics of double-layer thin film target ablated by femtosecond laser pulses

Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 x 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04×103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.

Dynamic simulation and safety evaluation of high-speed trains meeting in open air

Dynamic responses of a carriage under excitation with the German high-speed low-interference track spectrum together with the air pressure pulse generated as high-speed trains passing each other are investigated with a multi-body dynamics method.The variations of degrees of freedom（DOFs：horizontal movement,roll angle,and yaw angle）,the lateral wheel-rail force,the derailment coefficient and the rate of wheel load reduction with time when two carriages meet in open air are obtained and compared with the results of a single train travelling at specifie speeds.Results show that the rate of wheel load reduction increases with the increase of train speed and meets some safety standard at a certain speed,but exceeding the value of the rate of wheel load reduction does not necessarily mean derailment.The evaluation standard of the rate of wheel load reduction is somewhat conservative and may be loosened.The pressure pulse has significan effects on the train DOFs,and the evaluations of these safety indexes are strongly suggested in practice.The pressure pulse has a limited effect on the derailment coefficien and the lateral wheel-rail force,and,thus,their further evaluations may be not necessary.

北京地区五种常见鸣虫的鸣声结构

本文对寒蝉、蚱蝉、鸣鸣蝉、锐声鸣螽和大扁头蟋五种鸣虫雄虫的鸣声结构进行了较系统的研究。这些昆虫鸣声节律以及声谱和声压的瞬时变化均有显著的不同。一种昆虫的鸣声频谱范围虽然很大,但不同频率的图象却都和主频率的图象一样。

Spectrum shuttle for producing spatially shapable GHz burst pulses

Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.

Semiclassical calculation of ionisation rate for Rydberg helium atoms in an electric field

The ionisation of Rydberg helium atoms in an electric field above the classical ionisation threshold has been examined using the semiclassical method, with particular emphasis on discussing the influence of the core scattering on the escape dynamics of electrons. The results show that the Rydberg helium atoms ionise by emitting a train of electron pulses. Unlike the case of the ionisation of Rydberg hydrogen atom in parallel electric and magnetic fields, where the pulses of the electron are caused by the external magnetic field, the pulse trains for Rydberg helium atoms are created through core scattering. Each peak in the ionisation rate corresponds to the contribution of one core-scattered combination trajectory. This fact further illustrates that the ionic core scattering leads to the chaotic property of the Rydberg helium atom in external fields. Our studies provide a simple explanation for the escape dynamics in the ionisation of nonhydrogenic atoms in external fields.

Novel method for radial velocity difference estimation of moving targets with wideband signals

For the frequency difference of arrival （FDOA） esti-mation in passive location, this paper transforms the frequency difference estimation into the radial velocity difference estimation, which is difficult to achieve a high accuracy due to the mismatch between the sampling period and the pulse repetition interval. The proposed algorithm firstly estimates the point-in-time that each pulse arrives at two receivers accurately. Secondly two time of arrival （TOA） sequences are subtracted. And final y the radial ve-locity difference of a target relative to two stations with the least square method is estimated. This algorithm only needs accurate estimation of the time delay between pulses and is not influenced by parameters such as frequency and modulation mode. It avoids transmitting a large amount of data between two stations in real time. Simulation results corroborate that the performance is bet-ter than the arithmetic average of the Cramer-Rao lower bound （CRLB） for monopulse under suitable conditions.

Dissipative Discrete System with Nearest-Neighbor Interaction for the Nonlinear Electrical Lattice

A generalized dissipative discrete complex Ginzburg-Landau equation that governs the wave propagation in dissipative discrete nonlinear electrical transmission line with negative nonlinear resistance is derived. This equation presents arbitrarily nearest-neighbor nonlinearities. We analyze the properties of such model both in connection to their modulational stability, as well as in regard to the generation of intrinsic localized modes. We present a generalized discrete Lange-Newell criterion. Numerical simulations are performed and we show that discrete breathers are generated through modulational instability.

低频脉冲电治疗联合等速肌力训练对脑卒中偏瘫患者肢体活动能力的影响

目的探究低频脉冲电治疗联合等速肌力训练对脑卒中偏瘫患者肢体活动能力的影响.方法纳入我院2019年12月—2021年12月收治的92例脑卒中偏瘫患者,按随机数字表法分为对照组和观察组,各46例.对照组予以常规康复训练,观察组在对照组基础上增加低频脉冲电治疗联合等速肌力训练,均持续干预4周.比较两组肌力恢复情况、肢体运动功能、平衡及生活能力.结果观察组干预后伸膝肌峰力矩(PT)(56.22±6.86)N?M、屈膝肌PT(36.49±6.21)N?M均高于对照组,Fugl-Meyer运动功能评估量表中上肢功能评分(40.11±6.84)分、下肢功能评分(19.15±3.64)分均高于对照组,Berg平衡量表评分(40.11±4.25)分、Barthel指数评定量表评分(76.38±6.39)分均高于对照组,组间差异有统计学意义(P<0.05).结论对脑卒中偏瘫患者采用低频脉冲电治疗联合等速肌力训练,能够有效增强肌力,改善肢体运动功能,提高平衡、生活能力.

Parametric generation and phase locking of multiple sidebands in the regime of full-back-conversion

Parametric interaction allows both forward and backward energy transfers among the three interacting waves.The back-conversion effect is usually detrimental when unidirectional energy transfer is desired.In this theoretical work,we manifest that the back-conversion effect underpins the direct generation of the picosecond pulse train without the need for a laser resonator.The research scenario is an optical parametric amplification(OPA)that consists of a second-order nonlinear medium,a quasi-continuous pump laser and a sinusoidal amplitude-modulated seed signal.The back-conversion of OPA can transfer the modulation peaks(valleys)of the incident signal into output valleys(peaks),which inherently induces spectral sidebands.The generation of each sideband is naturally accompanied with a phase shift of±π.In the regime of full-back-conversion,the amount and amplitude of the sidebands reach the maximum simultaneously,and their phase constitutes an arithmetic sequence,leading to the production of a picosecond pulse train.The generated picosecond pulse train can have an ultrahigh repetition rate of 40 GHz or higher,which may facilitate ultrafast applications with ultrahigh speed.