Optimized energetic particle emissions from Xe clusters in intense laser fields
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Abstract:
We have probed the interaction of intense laser fields with Xe clusters by measuring the energy and charge state distributions of emitted ions and electrons using ultrafast 20-fs pulses. This work demonstrates that the energetic particle emissions from laser-cluster interactions can be optimized by manipulating the character of ultrafast laser pulses, i.e., pulse duration and sign of chirp. The mean and maximum ion energies as high as 0.1 and 2 MeV, respectively, are achieved when Xe clusters are irradiated by 500-fs pulses with negative chirp as an optimal condition under a laser peak intensity of $2\ifmmode\times\else\texttimes\fi{}{10}^{17}{\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}.$ The mean ion energy obtained from 500-fs pulses with negative chirp is found to be about 1.6 times larger than that with positive chirp.Keywords:
Chirp
Picosecond
Ultrafast optics
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In the paper the autocorrelation error caused by the pulse chirp is analyzed.After analyzing the theory,the influence of linear chirp,quadratic chirp is simulated respectively.According to a method of revising quadratic chirp,the same result is gotten with the experiment.
Chirp
Chirp spread spectrum
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본 논문은 Chirp 신호가 변조된 UWB frequency slope를 이용한 거리 측정 기술 및 통신 시스템을 제안하였다. 오직 up-chirp 만 사용하거나 혹은 (주파수 간) 동일한 주파수 변화도(Frequency sweeping rate)를 가진 down-chirp 만 사용하는 대신에, 제안된 시스템은 주파수 도약을 이용하여 서로 다른 주파수 변화도를 가지는 여러 Chirp 신호를 사용한다. 제안된 시스템은 데이터 전송 속도를 증가시킬 수 있고 동시에 사용자들이 사용한 sequence 간에 간섭도 줄일 수 있기 때문에 기존 통신 거리 측정 전략보다도 성능이 좋다. 본 논문에서는 연구의 타당성을 보이기 위해 MATLAB을 이용한 UWB 통신 시스템의 시뮬레이션을 제시한다.
Chirp
Chirp spread spectrum
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摘要: 在方向依赖的阵元复增益条件下，该文提出一种宽带chirp信号二维角估计新方法。该方法基于信号时变阵列流形结构分析，构造出一种阵列流形时频变换，无需估计和补偿即可消除阵元幅相不一致误差的影响，实现宽带chirp信号二维角闭式解析估计。仿真实验表明了新方法的有效性。 关键词: 宽带chirp信号 / 二维到达角估计 / 阵列误差校正
Chirp
Wideband
Chirp spread spectrum
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According to the semi-classical theory of lightmatter interaction,by appling an accurate and efficient fourth-order Runge-Kutta method,we solved the modified Bloch equations with chirped terms.The numerical results show that the chirp and pulse area of different pulse shape have different modulation effects.The different shape chirped pulse controlled the reversion population by adjusting chirp and pulse area.
Chirp
Chirped pulse amplification
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By taking into account the interactions between SPM and GVD,we obtained an analytic expression of chirp induced by both blue remove chirp and red remove chirp.the results show that the feature of chirp according to z and T is identified completely for certain L D and L NL .With different ratio of L D/L NL ,the feature of chirp have obvious changes.We found that unchirp propagation can be obtained by controlling the input power of pulse in fiber and the stability of pulse also can be maintained.
Chirp
Chirp spread spectrum
Feature (linguistics)
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Based on the generalized nonlinear Schrodinger equation desiring pulse propagation in fiber,the propagation properties of self-similar parabolic pulse in high nonlinear fiber are investigated by numerical methods.The results show that when the pulses have the different initial energy and chirp parameters,the pulse in the high nonlinear fiber can evolve into the self-similar parabolic pulse,and with the increase of the normalized length,the self-similar factor of the pulse decreases from 0.0796 to about 0.0720.It is further investigated that the chirped Gaussian pulse transmission in fiber is widen gradually.The effect of the negative chirp on the self-similar evolution is greater than that of the positive chirp.The high energy positive and negative chirp pulses are evolved into the flat-top parabolic pulse and triangular pulse.
Chirp
Self-phase modulation
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This paper presents performance evaluation of a positioning system using pulsed chirp signal as the cooperative signal over a relatively small area. The aim is to investigate potential advantages of chirp pulse in localizing active RFID with high positioning accuracy in an approximate indoor environment. Positioning performance of chirp signal is compared with that of normal pulsed sine wave signal using Time of Arrival (TOA) location method. The numerical results show that chirp pulse outperforms sine wave signal in terms of much higher positioning accuracy in small coverage area.
Chirp
Chirp spread spectrum
SIGNAL (programming language)
Sine
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Chirp has good performance of compress and resolution, so this pulse compress signal is being applied widely. The ways of producing chirp hardware and software based on DDS are introduced. The results in practice indicate that the chirp signal has good stability, high-resolution, and anti-interference, can satisfy the demand of engineering.
Chirp
SIGNAL (programming language)
Pulse compression
Chirp spread spectrum
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Chirp reversal consists of transmitting first a chirp with upsweep frequencies (UPF) then a second chirp with downsweep frequencies (DNF). We have shown that contrast bubbles react differently to these chirps allowing the use of chirp reversal for ultrasound contrast imaging. The aim of the current study is to explore how chirp reversal can be optimized in terms of transmit frequency, bubble size, acoustic pressure and frequency bandwidth. Simulations were carried out to determine ultrasound parameters that provide largest differences in bubble's response to UPF and DNF chirps. Scattered pressures were calculated using a modified Rayleigh-Plesset equation. To evaluate the performance of chirp reversal for bubble detection, the echo from an UPF chirp was correlated to the time reversed echo from a DNF chirp for each scanning parameter. Simulations and optical measurements allow for an optimization of chirp reversal and demonstrate a potential application for contrast imaging when appropriate scanning parameters are selected.
Chirp
Chirp spread spectrum
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