Single-atom-response to a Partially Coherent Intense Laser Field

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通过梯形激光场和半周期场的合成扩展高次谐波截止频率

本文提出了一个在少周期梯形激光场上叠加半周期场来扩展高次谐波谱截止频率的方案。通过采用求解含时薛定谔方程,理论模拟了一维模型氢分子离子体系在不同激光场条件下的高次谐波谱,并结合时频分布图,分析了半周期场对高次谐波产生的影响。计算结果表明,使用梯形激光和半周期场的组合方法,可以有效实现扩展谐波截止频率的目的。     

通过梯形激光场和半周期场的合成扩展高次谐波截止频率

本文提出了一个在少周期梯形激光场上叠加半周期场来扩展高次谐波谱截止频率的方案.通过采用求解含时薛定谔方程,理论模拟了一维模型氢分子离子体系在不同激光场条件下的高次谐波谱,并结合时频分布图,分析了半周期场对高次谐波产生的影响.计算结果表明,使用梯形激光和半周期场的组合方法,可以有效实现扩展谐波截止频率的目的 .     

小波变换应用于谐波谱线的噪声滤除与基线校正

红外光谱谐波检测系统中的噪声与基线漂移问题一直是光谱处理的热点,提出一种采用小波变换的Mallet分解算法, 解决谐波检测中各种复杂噪声以及基线漂移的问题。选取适当小波函数及分解层次将谐波曲线中含有的噪声和基线漂移与有用信号分解到不同频带;分析频带信息,设定一个检测信息频带, 应用阈值处理及系数置零的方法使频率处于此频带的信息保留下来。小波变换方法可以在一次分解与重构过程中同时去除谐波信号的噪声与基线的双重干扰,从而将谐波信号有效地测量出来。实验证明,应用小波变换进行谐波校正的方法可应用于不同的谐波检测系统,具有普遍适用性。     

强激光啁啾脉冲中原子的高次谐波辐射

数值计算了强激光啁啾脉冲中原子的谐波辐射。啁啾效应使谐波发生移动和展宽，即相对于无啁啾冲情形，负啁啾脉冲中谐波平台的前半部分发生兰移，而后半部分谐波谱则发生红移。     

Analysis of broadband third harmonic generation with non-collinear angular dispersion in KDP crystals

A new scheme with non-collinear sum frequency generation (SFG) process of broadband third harmonic generation (THG) with two KDP crystals (one doubler and one mixer) using angular dispersion was proposed. The principle of broadband harmonic generation with non-collinear angular dispersion was presented. The comparison between the schemes of non-collinear and collinear SFG process was performed. The effects of the angular dispersion on the conversion efficiency, the pulse shape and the spectrum of the third harmonic field were discussed. The results show that, if proper angular dispersion is added to the fundamental and the second harmonic field outside the mixing KDP crystal, respectively, the broadband third harmonic conversion efficiency can be improved significantly. However, the difficulty of this scheme arises due to the requirement of two gratings with different angular dispersion outside the mixer. With the new scheme, it can be simpler that only one grating is needed to realize the broadband phase matching in the non-collinear SFG process. Although the fundamental and the second harmonic field inside the mixing crystal are non-collinear except the center wavelength, a blazing grating with proper angular dispersion for the fundamental field (twice as that for second harmonic field) can yield the well compensation for phase mismatching in the SFG process. Consequently, the conversion efficiency and the characteristics of the third harmonic field for the broadband third harmonic generation can be improved significantly.     

通过双色场和静电场的合成来拓宽高次谐波谱

本篇文章提出了一种通过双色激光场和静电场合成来拓宽高次谐波谱平台区域的方案.我们针对氦原子数值求解了一维含时薛定谔方程,并且得到了不同合成激光场条件下的高次谐波谱,并结合了经典电离-回碰动能分布图和时频分布图分析了静电场对高次谐波谱产生过程的影响.计算结果表明,通过在双色激光场上叠加一个静电场,可以有效地拓宽高次谐波谱的平台区域,从而得到一个频带宽度为358eV的超连续谱.     

Coupled Two-Dimensional Atomic Oscillation in an Anharmonic Trap

In atomic dynamics,oscillation along different axes can be studied separately in the harmonic trap. When the trap is not harmonic, motion in different directions may couple together. In this work, we observe a twodimensional oscillation by exciting atoms in one direction, where the atoms are transferred to an anharmonic region. Theoretical calculations are coincident to the experimental results. These oscillations in two dimensions not only can be used to measure trap parameters but also have potential applications in atomic interferometry and precise measurements.     

Optimization of multi-color laser waveform for high-order harmonic generation

With the development of laser technologies,multi-color light-field synthesis with complete amplitude and phase control would make it possible to generate arbitrary optical waveforms.A practical optimization algorithm is needed to generate such a waveform in order to control strong-field processes.We review some recent theoretical works of the optimization of amplitudes and phases of multi-color lasers to modify the single-atom high-order harmonic generation based on genetic algorithm.By choosing different fitness criteria,we demonstrate that:(i) harmonic yields can be enhanced by 10 to 100 times,(ii) harmonic cutoff energy can be substantially extended,(iii) specific harmonic orders can be selectively enhanced,and(iv) single attosecond pulses can be efficiently generated.The possibility of optimizing macroscopic conditions for the improved phase matching and low divergence of high harmonics is also discussed.The waveform control and optimization are expected to be new drivers for the next wave of breakthrough in the strong-field physics in the coming years.     

利用不变量本征算符求解二维耦合量子谐振子的能级间隔

目前不变量本征算符方法已成功地解决了某些量子系统哈密顿量能级问题.对于二维耦合量子谐振子,利用这一方法可以非常简捷有效地给出其能级信息,而不需要使其哈密顿量对角化.计算结果表明,不同耦合形式的二维耦合量子谐振子的能级间隔是不同的.     

混沌干扰中基于同步挤压小波变换的谐波信号提取方法

针对混沌干扰背景下多个谐波信号的提取问题, 提出了一种基于同步挤压小波变换(SST)的谐波信号抽取方法. 首先利用SST将混沌信号和谐波信号组成的混合信号分解为不同的内蕴模态类函数, 然后利用Hilbert变换对分离出的内蕴模态类函数进行频率识别, 从中分离出各谐波信号. 以Duffing混沌背景为例, 对混沌干扰下多谐波信号的提取进行了实验分析. 实验结果表明: 对于不同频率间隔的多个谐波分量, 本文方法的提取结果都具有较高的精度, 而且所提方法对高斯白噪声的干扰具有较好的鲁棒性, 综合提取效果优于经典的经验模态分解方法.     

Decoding the electron dynamics in high-order harmonic generation from asymmetric molecular ions in elliptically polarized laser fields

The high-order harmonic generation from an asymmetric molecular ion is theoretically investigated based on the Born-Oppenheimer model with two-dimensional electron dynamics. It is shown that the harmonic intensity changes periodically in elliptically polarized laser fields. The periodical character is ellipticity-dependent. By establishing the physical image, the periodicity of the harmonic intensity can be ascribed to the contributions of the ground state and the excited state. Furthermore, the electron dynamics from different electronic states can be selected via combining the elliptically polarized laser field with a static electric field. The harmonics dominated either by ground state or excited state are emitted once in an optical cycle in the combined laser field.     

High-order harmonic generation with a two-color laser pulse

We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field.We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation.We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays.We find that the width of the harmonic plateau can be extended when the control electric field is added,and a supercontinuum from 198 to 435 eV is generated,from which an isolated 61-as pulse can be directly obtained.     

变形谐振子势的能谱方程

讨论了3种变形谐振子势:左右两边不同参数的谐振子势、左边方形势加右边谐振子势和谐振子势中间加δ势中的能量本征态函数.这些函数都可以由厄米函数表示.由波函数及其一次导数在原点的衔接条件,得到了能谱方程.     

High-order harmonic generation with a two-color laser pulse

We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field. We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays. We find that the width of the harmonic plateau can be extended when the control electric field is added, and a supercontinuum from 198 to 435 eV is generated, from which an isolated 61-as pulse can be directly obtained.     

基于混频效应的宽带激光谐波转换理论

提出了一种新的宽带激光谐波转换理论,指出实际宽带激光谐波转换不能简单应用倍频理论,提出同时存在不同波长之间满足和频相位匹配情况,因而宽带谐波转换应该是一个倍频加和频的混合转换过程.在合理设计下,不同波长之间的和频效应可以在整个谐波转换中占主导地位,突破了传统允许波长的限制,这种理论和方法不仅适合二倍频,同时适合三倍频等高次谐波转换 关键词： 宽带激光 谐波转换 混频     

Evolution of spin-dependent atomic wave packets in a harmonic potential

We have investigated theoretically the evolution of spin-dependent atomic wave packets in a harmonic magnetic trapping potential. For a Bose-condensed gas, which undergoes a Mott insulator transition and a spin-dependent transport, the atomic wavefunction can be described by an entangled single-atom state. Due to the confinement of the harmonic potential, the density distributions exhibit periodic decay and revival, which is different from the case of free expansion after switching off the combined harmonic and optical lattice potential.     

利用谐波分量提高动态光谱法的信噪比

为了提高动态光谱法信号的信噪比,从信号和噪声能量的角度分析了动态光谱法以往采用的频域数据处理方法优点和缺陷,研究了了典型动态光谱系统噪声来源、频谱特点及其对动态光谱法信噪比的影响;并由此提出了增加多次谐波分量计入动态光谱的方法,并通过实验方法研究了实验中不同对照组的动态光谱相关系数与谐波次数逐渐增加时的变化趋势、确定了计入动态光谱的最佳谐波次数。实验证明,伴随频域处理中引入的谐波次数的增加,源自两个不同个体的动态光谱数据的相关系数会先减小后增加;而源自同一个体不同部位的动态光谱数据则一直增大。当引入的谐波次数为5时,可以得到最佳信噪比。所得到的动态光谱可以更加准确地反应血液成分信息,从而使动态光谱法的信噪比最大。     

任意偏振双色相干场高次谐波

系统地研究了任意偏振双色相干场高次谐波，结果表明单个圆偏振光不能产生高次谐波，在适当的条件下，某些谐波可以部分或完全消失，而某些谐波可以得到加强，产生更高次谐波高转换效率的条件是双色线偏振场的结合。