利用超快强光场产生的高次谐波获得相干软X射线辐射

报道了在本实验室建立的４５ｆｓ－２ＴＷ级超短超强钛宝石激光装置上，以Ａｒ气为非线性工作介质进行的高次谐波实验的初步结果。研究了激光能量和气体密度对高次谐波的影响。目前得到的最高次谐波为２５次，相应波长为３１．４ｎｍ，深入的实验研究正在进行之中。     

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。     

飞秒激光在氦气中的高次谐波

利用中心波长在795nm的线偏振的钛宝石超短脉冲激光除为抽运源，在拟气中观察到40nm-160nm第5－17次谐波的软X射线激光辐射，着重研究了高次谐波谱线强度随气压的变化规律，发现高次谐波谱线强度随充气气压的增加而增强，实验中考虑到如果充气气压过高，探测仪器可能受到损害，充气气压没有达到最佳值。     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

超强激光作用下相对论电子振荡所导致的谐波辐射

研究发现，在超强激光作用下电子运动的相对论效应可导致高次谐波辐射，采用单电子模型计算分析了不同偏振微光作用下的高次谐波发射，表明圆偏振激光较线偏振激光更有利于高次谐波产生。     

Electron‐Nuclear Dynamics in Molecular Harmonic Generation Driven by a Plasmonic Nonhomogeneous Field

Electron (z)‐nuclear (R) dynamics in the molecular high‐order harmonic generation (MHHG) from H₂⁺ driven by the plasmonic nonhomogeneous field, generated by the surface plasmon polaritons in the bowtie‐shaped nanostructure, have been theoretically investigated through solving the two dimensional time‐dependent Schrödinger equation with the Non‐Bohn‐Oppenheimer approximation. It is found that (i) due to the plasmonic enhancement of the laser intensity, the harmonic cutoff can be extended when the spatial position of H₂⁺ is away from the gap center of the nanostructure. However, due to the limit of the gap size, the threshold value of the harmonic cutoff can be obtained at a given position of H₂⁺. (ii) Due to the asymmetric enhancement of the laser intensity in space, the extended higher harmonics are respectively from E(t) > 0 a.u. or E(t) < 0 a.u. for the cases of the positive and the negative spatial position of H₂⁺. As a result, the intensities of the extended higher harmonics are different and can be controlled by changing the carrier‐envelope phase and the pulse duration of the laser field. (iii) In the few‐cycle pulse duration, the MHHG mainly comes from the multi‐photon resonance ionization (MPRI), while as the pulse duration increases, the MPRI, the charge‐resonance enhanced ionization (CREI) and even the dissociative ionization (DI) are contributed to the MHHG. Moreover, as the spatial position of H₂⁺ moves, the contributions of the MHHG from the MPRI, the CERI and the DI can be controlled. (iv) The contributions of the MHHG from the two‐H nuclei have been investigated and found that when E(t) > 0 a.u., the intensities of the harmonics from the negative‐H is higher than those from the positive‐H; while when E(t) < 0 a.u., the intensities of the harmonics from the positive‐H plays the main role in the MHHG. Moreover, the multi‐minima, caused by the two‐center interference can also be found. (v) Finally, by superposing a properly selected harmonics, a single isolated attosecond pulse (SIAP) with the full width at half maximum (FWHM) of 34 as can be obtained.     

阈上电离与高次谐波

通过数值求解一维含时薛定锷方程，研究阈上电离与高次谐波随激光强度的变化关系，结果表明，两者具有相同的特性，都具有平台区和截止位置，但两者又有差别，较低激光强度作用下，谐波谱有平台而光电了能谱为单调下降的，激光强度较高时，两者都平台，对应的平台区和截止位置相同。     

隧道电离产生的高次谐波

用隧道电离模型，研究了激光和气体相互作用中，不同气体密度及激光强度下，气体电离及激光能量损耗物过程，并研究了这种效应引起的高次谐波。     

Two Methods of Amplification of Coherent Extreme Ultraviolet Radiation During Harmonic Generation in Plasmas

Different recently revealed approaches of harmonic enhancement in plasmas are reviewed. The 4-step analytical model of resonant enhancement of high-order harmonic generation is extended to the systems possessing resonant transitions of inner-shell electrons. Role of inelastic scattering is discussed by simulation of excited state’s population dynamics. The enhancement of harmonics in the In plasma using different pumps is analyzed to prove the concept. We also discuss the plasma emission and harmonic generation spectra in the case of resonance enhancement of single harmonic using various laser-produced plasmas. The analysis of these spectra showed that the enhancement of harmonics depended on the oscillator strengths of the nearby ionic transitions rather than the plasma emission transitions. Finally, we review some recent experimental studies of the phase-matching of high-order harmonic generation in multi-jet plasmas.     

偶氮化合物中级联作用引起的高阶多波混频的研究

用三维简并四波混频的实验装置，在偶氮化合物中观察到了多波混频效应，在接收屏上，除了三个泵浦光斑，还观察到了由于多波耦合产生的另外１４个排列整齐的信号光斑，这个现象可望被广泛用光计算，信息处理和光互连中。     

Higher Harmonic Generation of Coherent Sub-THz Radiation at Lifshitz Transition in Gapped Bilayer Graphene

Journal of Experimental and Theoretical Physics - The microscopic quantum theory of nonlinear interaction of strong coherent electromagnetic radiation with gapped bilayer graphene is used for...     

The Exact Solution,Berry's Phase and Coherent State for the Driven Generalized Time-Dependent Harmonic Oscillator

The Lewis'invariant and exact solution for the driven generalized time-dependent harmonic oscillator is found by making use of the Lewis-Riesenfeld quantum theory. Then, the adiabatic asymptotic limit of the exact solution is discussed and the Berry's phase for thirr system is obtained. We then proceed to use the exact solution to construct the coherent state and calculate the corresponding exact classical phase angle. This phase angle can give the Hannay's angle in the adiabatic limit. The relation between the exact Lewis'phase and the corresponding classical phase angle L'discusrred.     

强激光和超薄等离子体薄膜相互作用产生高次谐波

通过一维粒子（particle in cell,简称PIC）模拟，研制了超薄等离子体薄膜在两列旋转方向相反的圆偏振激光脉冲作用下的高次谐波辐射。在10^21W/cm^2强度的激光作用下，可以获得200次以上的高次谐波。当激光脉冲宽度较短时，由于等离子体薄膜被压缩所导致的多普勒频移对高次谐波产生了显著的频率调制。而这种多普勒频移可以通过对抽运光脉冲引入频率啁啾来补偿。     

飞秒互相关时间选通技术用于光学层析成像的实验研究

利用飞秒互相关二次谐波信号时间选通技术。实现了对埋藏在高度散射介质中物体的透射成像和反射以析成像。互相关选通门有效地选出携带物体信息的弹道光子和蛇行光子，排除了给成像带来背景噪声的温射光子，分别获得了散射介质中物体的二次谐波一维和二维图像。     

Theoretical Study of High-Order Harmonic Generation From a Coherent Superposition State in a Chirp-Free Pulse Combined with a Chirped Control Pulse

In this paper, we theoretically investigate high-order harmonic generation (HHG) from a helium atom prepared in a coherent superposition state in a two-color laser field. Numerical results show that the emission efficiency of the harmonic spectrum in a coherent superposition state is enhanced by approximately eight orders of magnitude compared with the case of the ground state. In addition, the effect of the initial population of the excited state on the HHG is presented to reveal the physical origin of the enhancement of HHG. By adjusting the laser parameters of the driving pulse, such as the chirping parameter, the relative phase, and the intensity of the driving pulse, an ultrabroad continuum with a width of 275 eV can be observed. Finally, an isolated 12-as pulse is generated after phase compensation.     

7 fs超快强激光驱动Ar原子产生支持单个阿秒脉冲的高次谐波连续谱

采用脉冲宽度为7 fs,脉冲能量为0.4 mJ的超快强激光脉冲与气体盒子中Ar原子作用获得了高次谐波截止区连续谱,并发现当驱动激光稳定在不同的载波包络相位时,高次谐波的谱结构、谱调制深度和连续谱的带宽都有很大区别。在某些载波包络相位时获得了平滑的连续谱,调制深度小于17%,连续带宽达10 eV,从而支持时域上获得变换极限500 as的单个阿秒脉冲。     

脉冲形状对氢原子高次谐波的影响

在含时密度泛函理论框架下,采用经典和量子相结合的模型,模拟了氢原子在超强飞秒激光脉冲作用下的高次谐波产生现象,并研究了激光脉冲形状对氢原子高次谐波的影响.结果表明,氢原子的高次谐波谱具有典型的原子谐波谱的特征;具有“下降－平台－截止”的结构和偶次谐波被禁闭仅出现奇次谐波的选择性特征;不同的脉冲形状会导致高次谐波的截止频率和谱线强度的变化.     

数控高精度PWM调制特种电源

介绍了两种斯特林制冷机数控驱动源,分析了单极性驱动方式与双极性驱动方式对红外探测芯片产生的干扰情况,并根据与系统的联试比较了两种数控驱动源的优缺点.说明了数字滤波技术、PID控制算法及V/F转换电路在提高温控精度和减少电源对探测芯片干扰中的优势.