Nonlinear Thomson scattering of an ultrashort laser pulse

The nonlinear scattering of an ultrashort laser pulse by free electrons is considered. The pulse is described in the “Mexican hat” wavelet basis. The equation of motion for a charged particle in the field of a plane electromagnetic wave has an exact solution allowing, together with the instant spectrum approximation, the calculation of the intensity of nonlinear Thomson scattering for a high-intensity laser pulse. The spectral distribution of scattered radiation for the entire pulse duration is found by integrating with respect to time. The maximum of the emission spectrum of a free electron calculated in 10¹⁹–10²¹ W/cm² fields lies in the UV spectral region between 3 and 12 eV. A part of the continuous spectrum achieves high photon energies. One percent of the scattered energy for the field intensity 10²⁰ W/cm² is concentrated in the range ħω > 2.7 × 10² eV, for a field intensity of 10²¹ W/cm² in the range ħΩ > 7.9 × 10² eV, and for an intensity of 10²² W/cm² in the range ħΩ > 2.45 × 10⁵ eV. These results allow us to estimate nonlinear scattering as a source of hard X-rays.     

Compton散射对短脉冲强激光在次临界等离子体中自聚焦的影响

应用相对论理论和多光子非线性Compton散射模型,研究了Compton散射对短脉冲强激光在次临界等离子体中自聚焦的影响,提出了将入射光和Compton散射光作为形成激光自聚焦的新机制,给出了三级电流密度满足的修正方程,并进行了数值模拟。结果表明,相对论效应使等离子体中的短脉冲强激光自聚焦趋势减缓,而散射则加速了自聚焦的发展,总自聚焦趋势比无相对论时来得快一些,主要原因是由于散射光和入射光形成的耦合光频率较入射光频率增大,散射效应补偿了因相对论效应引起的自聚焦减缓效应的缘故。     

Compton散射对短脉冲强激光在次临界等离子体中自聚焦的影响

应用相对论理论和多光子非线性Compton散射模型,研究了Compton散射对短脉冲强激光在次临界等离子体中自聚焦的影响,提出了将入射光和Compton散射光作为形成激光自聚焦的新机制,给出了三级电流密度满足的修正方程,并进行了数值模拟。结果表明,相对论效应使等离子体中的短脉冲强激光自聚焦趋势减缓,而散射则加速了自聚焦的发展,总自聚焦趋势比无相对论时来得快一些,主要原因是由于散射光和入射光形成的耦合光频率较入射光频率增大,散射效应补偿了因相对论效应引起的自聚焦减缓效应的缘故。     

周期量级脉冲线性Thomson散射特性

利用经典电磁辐射理论研究周期量级线偏振激光脉冲的90°Thomson线性散射。结果表明,脉冲所包含的光周期数越少,散射能谱越宽,谱中心处强度越小;谱宽度与电子相对论因子的平方及入射光脉冲频率成正比;谱强度与归一化光场强度和相对论因子乘积的平方均成正比,载波包络函数使光场中电子运动的时间和空间周期减小;进一步展宽散射能谱,使谱对称性变好,消除散射谱振荡;低于某一频率时,谱强度随载波包络初相的增大而减小,高于此频率时,谱强度随载波包络初相的增大而增大;电子进入光场初相的增大削弱了散射谱的强度。     

周期量级脉冲线性Thomson散射特性

 利用经典电磁辐射理论研究周期量级线偏振激光脉冲的90°Thomson线性散射。结果表明,脉冲所包含的光周期数越少,散射能谱越宽,谱中心处强度越小;谱宽度与电子相对论因子的平方及入射光脉冲频率成正比;谱强度与归一化光场强度和相对论因子乘积的平方均成正比,载波包络函数使光场中电子运动的时间和空间周期减小;进一步展宽散射能谱,使谱对称性变好,消除散射谱振荡;低于某一频率时,谱强度随载波包络初相的增大而减小,高于此频率时,谱强度随载波包络初相的增大而增大;电子进入光场初相的增大削弱了散射谱的强度。     

超短激光脉冲驱动的Thomson散射空间分布特性

研究了超短激光脉冲驱动的Thomson散射的辐射空间分布. 发现辐射的空间分布对称性显著地依赖于超短脉冲的载波相位η₀，在η₀＝0，π时，辐射的空间分布呈现出二重或一重对称性；而在其他载波相位时，这些空间分布对称性遭到破坏. 辐射光的准直性也依赖于驱动脉冲的载波相位，在η₀＝±π/2时辐射光的准直性最好. 这些结果表明可以通过改变驱动激光脉冲的载波相位来控制辐射光的空间分布，也可以利用辐射空间分布对相位的依赖特性来测量超短激光脉冲的载波相位. 关键词： Thomson散射 空间分布 载波相位     

初始相位对周期量级激光脉冲Thomson散射特性的影响

 用电子Thomson散射的经典理论,研究了周期量级激光脉冲作用下电子Thomson散射的特性,讨论了不同激光强度下,激光脉冲的初始相位对电子辐射的空间分布以及特定方向上频谱分布特性的影响。计算表明:对弱激光脉冲,电子辐射的空间分布类似于偶极天线的对称双叶结构,初始相位对电子的辐射几乎没有影响;而对强激光脉冲,电子辐射的空间分布出现了三叶结构,初始相位对电子的辐射影响非常显著。     

周期量级激光脉冲的Thomson散射

用经典辐射理论对线偏振周期量级激光脉冲的线性Thomson散射进行分析，从理论上得到它可产生亚阿秒脉冲的结论. 计算显示，在电子相对论因子为50、激光脉冲中心波长为1μm、归一化光场强度为0.01的情况下，用包含1.5个光周期的激光脉冲，可获得0.2as(半高全宽)的散射脉冲输出. 还对光场载波包络初相φ_ce和电子进入光场的初相φ_in对散射脉冲的影响作了分析讨论，结果表明，在适当的φ_ce和φ_in条件下，能实现单个阿秒脉冲输出，并可对脉冲宽度和频率进行调谐. 关键词： 线性Thomson散射 周期量级激光脉冲 载波包络初相 阿秒脉冲     

X-ray radiation from nonlinear Thomson scattering of an intense femtosecond laser on relativistic electrons in a helium plasma

We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a(0). This radiative process is dominant for a(0) greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.     

On the theory of nonlinear Thomson scattering of a highly focused laser pulse

The problem of nonlinear Thomson scattering of an ultrashort laser pulse on free electrons from a sharp focus is solved within the test particle approach. To describe the laser beam fields, an exact solution to the Helmholtz equation is used, which allows simulation of the electron dynamics and emission when the paraxial approximation is certainly inapplicable. Characteristics of attosecond electromagnetic pulses of secondary emission from test electrons during their motion near the laser focus are studied.     

ALP production through non-linear Compton scattering in intense fields

We derive production yields for massive pseudo-scalar and scalar axion-like-particles (ALPs), through non-linear Compton scattering of an electron in the background of low- and high-intensity electromagnetic fields. In particular, we focus on electromagnetic fields from Gaussian plane wave laser pulses. A detailed study of the angular distributions and effects of the scalar and pseudo-scalar masses is presented. It is shown that ultra-relativistic seed electrons can be used to produce scalars and pseudo-scalars with masses up to the order of the electron mass. We briefly discuss future applications of this work towards lab-based searches for light beyond-the-Standard-Model particles.     

Post-transient relaxation in graphene after an intense laser pulse

High intensity laser pulses were recently shown to induce a population inverted transient state in graphene [T. Li, et al., Phys. Rev. Lett. 108, 167401 (2012)]. Using a combination of hydrodynamic arguments and a kinetic theory we determine the post-transient state relaxation of hot, dense, population inverted electrons towards equilibrium. The cooling rate and charge-imbalance relaxation rate are determined from the Boltzmann-equation including electron-phonon scattering. We show that the relaxation of the population inversion, driven by inter-band scattering processes, is much slower that the relaxation of the electron temperature, which is determined by intra-band scattering processes. This insight may be of relevance for the application of graphene as an optical gain medium.     

Compton散射对斜入射激光脉冲在等离子体中传输的影响

应用多光子非线性Compton散射模型和等效折射指数模型,研究了Compton散射对斜入射激光脉冲在等离子体中传输特性的影响,提出了将入射光和Compton散射光形成的耦合光脉冲作为在等离子体中传输的新机制,用等效耦合折射指数和折射定律分别计算和数值模拟了等离子体中耦合光的反射和折射,结果表明,散射使等离子体中法拉第效应增强,产生了一个与折射界面平行的、较小等幅度附加折射波平面;使等效耦合折射指数的实部和虚部的实参数、折射角和等效折射指数之间的差异明显减小;使用等效耦合折射指数和折射定所得到的反射系数几乎均表现出相同的先增大后迅速减小的规律;使等离子体的反射系数随碰撞频率的增大而迅速减小,透射增强,透射增强的频率位置向高频明显移动。     

Compton散射对斜入射激光脉冲在等离子体中传输的影响

应用多光子非线性Compton散射模型和等效折射指数模型,研究了Compton散射对斜入射激光脉冲在等离子体中传输特性的影响,提出了将入射光和Compton散射光形成的耦合光脉冲作为在等离子体中传输的新机制,用等效耦合折射指数和折射定律分别计算和数值模拟了等离子体中耦合光的反射和折射,结果表明,散射使等离子体中法拉第效应增强,产生了一个与折射界面平行的、较小等幅度附加折射波平面;使等效耦合折射指数的实部和虚部的实参数、折射角和等效折射指数之间的差异明显减小;使用等效耦合折射指数和折射定所得到的反射系数几乎均表现出相同的先增大后迅速减小的规律;使等离子体的反射系数随碰撞频率的增大而迅速减小,透射增强,透射增强的频率位置向高频明显移动。     

Attosecond X-ray pulse obtained from linear Thomson scattering

Linear Thomson scattering by a relativistic electron of a short pulse laser has been investigated by computer simulation. Under a laser field with a pulse of 33.3-fs full-width at half-maximum, and the initial energy of an electron of γ₀=10, the motion of the electron is relativistic and generates an ultrashort radiation of 76-as with a photon wave length of 2.5-nm in the backward scattering. The radiation under a high relativistic energy electron has better characteristic than under a low relativistic energy electron in terms of the pulse width and the angular distribution.     

Thomson scattering from ultrashort and ultraintense laser pulses

The Thomson scattering in an ultraintense ( approximately 10(18) W cm(-2)) and ultrashort (20 fs) laser field is calculated that demonstrates different characteristics from those of the low-intensity field case. The electron trajectory no longer conforms to a figure-eight pattern, and the spectra demonstrate complex shifting and broadening to suggest that Thomson scattering can be used for characterizing pulsed lasers. The initial phase at the electron entrance of the field can critically affect the Thomson scattering, but its effect is weighted by the intensity profile of the field. As a result, the fourfold symmetry of the radiation pattern breaks down when the electron enters the field closer to the pulse peak. The relationship between the Thomson scattering and Compton scattering in the high field is analyzed.     

Compton scattering and electron-atom scattering in an elliptically polarized laser field of relativistic radiation power

Presently available laser sources can yield powers for which the ponderomotive energy of an electrons can be equal to or even larger than the rest energy mc ² of an electron. Therefore it has become of interest to consider fundamental radiation-induced or assisted processes in such powerful laser fields. In the present work we consider laser-induced Compton scattering and laser-assisted electron atom scattering in such fields, assuming that the laser beam has arbitrary elliptic polarization. We investigate in detail the angular and polarisation dependence of the differential cross-sections of the two laser-induced or laser-assisted nonlinear processes as a function of the order N of absorbed or emitted laser photons . The present work is a generalization of our previous analysis of Compton scattering and electron-atom scattering in a linearly polarized laser field [Phys. Rev. A 65, 022712 and 033408 (2002)].Received: 3 November 2002, Published online: 29 April 2003PACS: 34.50.Rk Laser-modified scattering and reactions - 34.80.Qb Laser-modified scattering - 32.80.Wr Other multiphoton processes     

X-ray-boosted photoionization for the measurement of an intense laser pulse

Investigations show that X-ray-boosted photoionization(XBP) has the following advantages for in-situ measurements of ultrahigh laser intensity I and field envelope F(t)(time t,pulse duration τL,carrier-envelope-phase Φ):accuracy,dynamic range,and rapidness.The calculated XBP spectra resemble inversely proportional functions of the photoelectron momentum shift.The maximum momentum p and the observable value Q(defined as a double integration of a normalized photoelectron energy spectrum,PES) linearly depend on I1/2 and τL,respectively.Φ and F(t) can be determined from the PES cut-off energy and peak positions.The measurable laser intensity can be up to and over 1018 W/cm2 by using high energy X-rays and highly charged inert gases.     

利用Compton散射对自由电子激光器的研究

通过坐标变换的方法，利用康普顿散射对自由电子激光器(FEL)的自发辐射进行了研究，精确地推导了FEL的自发辐射的波长公式，其近似式就是经典散射理论推导的自发辐射波长公式；对自发辐射的辐射功率也进行了近似推导，结果与经典散射理论公式一致。     

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By using the model of multi-photon nonlinear Compton scattering, the nonlinear dispersion relation and Karpman’s model, the influences of the modulation instability on Compton scattering to the linear polarized light in relativistic plasma were studied, the revised equations on the nonlinear dispersion, the control and the growth rate of the modulation instability were given out, and these equations are simulated. The results show that under the same perturbation wave numbers, the even big rate of the modulation instability near the plasma surface are taken place by Compton scattering along with the decreasing of the numbers of the no gauge frequency than before Compton scattering, and the even marked growth rate of the modulation instability near the plasma surface are taken place near the plasma surface than other places. Because the plasma nonlinear is increased by the scattering, the self-focusing and self-turned fine silk are formed.