R6G单分子表面增强共振拉曼散射光谱探测研究

以共焦显微系统为平台,研究了不同浓度的R6G银溶胶的表面增强共振拉曼散射(SERRS)光谱, 结果表明不同浓度溶液中的R6G分子表现出了不同的光谱特性。在浓度为10-13mol·L-1的R6G银溶胶中 得到了R6G单分子的表面增强共振拉曼散射光谱,观察到了一些光谱非均匀变化现象,如谱色散、谱线的 强度起伏、拉曼谱的偏振化以及分子的闪烁等,并对这些现象进行了分析,证明得到的是R6G单分子的 SERRS光谱。文章还对单分子检测中的一些关键问题进行了分析与讨论,确定了单分子SERRS光谱检测的 适当条件。     

Simulating resonance-mediated two-photon absorption enhancement in rare-earth ions by a rectangle phase modulation

Improving the up-conversion luminescence efficiency of rare-earth ions via the multi-photon absorption process is crucial in several related application areas. In this work, we theoretically propose a feasible scheme to enhance the resonance-mediated two-photon absorption in Er~(3+) ions by shaping the femtosecond laser field with a rectangle phase modulation. Our theoretical results show that the resonance-mediated two-photon absorption can be decomposed into the on-resonant and near-resonant parts, and the on-resonant part mainly comes from the contribution of laser central frequency components, while the near-resonant part mainly results from the excitation of low and high laser frequency components.So, the rectangle phase modulation can induce a constructive interference between the two parts by properly designing the modulation depth and width, and finally realizes the resonance-mediated two-photon absorption enhancement. Moreover, our results also show that the enhancement efficiency of resonance-mediated two-photon absorption depends on the laser pulse width(or laser spectral bandwidth), final state transition frequency, and intermediate and final state absorption bandwidths. The enhancement efficiency modulation can be attributed to the relative weight manipulation of on-resonant and near-resonant two-photon absorption in the whole excitation process. This study presents a clear physical insight for the quantum control of resonance-mediated two-photon absorption in the rare-earth ions, and there will be an important significance for improving the up-conversion luminescence efficiency of rare-earthions.     

Two-color laser wavelength effect on intense terahertz generation in air

Near-IR femtosecond lasers have been proposed to produce high-field terahertz radiation in the air via the laser-plasma interaction, but the physical mechanism still needs to be further explored. In this work, we theoretically investigate the effect of the two-color laser wavelength on the terahertz generation in the air based on a transient photocurrent model.We show that the long wavelength laser excitation can greatly enhance the terahertz amplitude for a given total laser intensity. Furthermore, we utilize a local current model to illustrate the enhancement mechanism. Our analysis shows that the terahertz amplitude is determined by the superposition of contributions from individual ionization events, and for the long wavelength laser excitation, the electron production concentrates in a few ionization events and acquires the larger drift velocities, which results in the stronger terahertz radiation generation. These results will be very helpful for understanding the terahertz generation process and optimizing the terahertz output.     

最优化“调控”区间分离密度泛函理论的研究进展

发展精确、高效的交换-关联泛函一直是密度泛函理论工作者所追求的神圣目标。传统密度泛函被证实在计算原子或分子体系的某些基态和激发态性能时存在困难,而且预测不具有普适性;另一方面,一些高水平方法如耦合簇（CC）理论和基于格林函数（G）和屏蔽库仑作用（W）近似的多体微扰理论（MBPT）,尽管相对精确但往往需要消耗昂贵的计算成本,因而其研究体系的尺寸和实用性受到了很大的限制。近年来,“最优化”调控区间分离泛函的发展在一定程度上使得上述问题得到改善,尤其是在消耗较少的计算成本前提下能够达到与高水平方法相媲美的预测精度,引起了越来越多的关注。本文首先简要回顾了密度泛函领域的理论背景,在区间分离密度泛函理论的基础上,重点介绍了最优化“调控”的概念;并且结合近期的理论工作对其在实际计算时的表现进行评价;最后,就最优化“调控”方法的前景和应用进行了展望。     

High-Resolution Selective Excitation of Resonance-Enhanced Multiphoton-Ionization Photoelectron Spectroscopy by Shaping Femtosecond Laser Pulses

Femtosecond laser-induced resonance-enhanced multiphoton-ionization photoelectron spectroscopy （REMPI-PS） is faced with two drawbacks of low spectral resolution and poor selective excitation due to the broad spectral bandwidth. We propose a scheme to obtain a high-resolution selective excitation of （2＋1） REMPI-PS by com- bining 7r and cosinusoidal phase modulation. Our theoretical results indicate that the （2＋1） REMPI-PS signals related to neighboring excited states can be differentiated from their indistinguishable photoelectron spectra by the 7r phase modulation, and then their selective excitation can be realized by supplementally adding the cosi- nusoidal phase modulation. Furthermore, the physical mechanism of the high-resolution selective excitation of （2＋1） REMPI-PS is explained by considering the two-photon power spectrum.     

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subelusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the ease of homonuelear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuelear clusters with larger sizes are required to achieve a greater neutron yield.     

两个双能级原子与辐射场的喇曼相互作用

研究了两个双能级原子与单模辐射腔场的喇曼相互作用。分别计算了两个原子与光场之间具有不同耦合常数和两个原子虽与光场具有相同耦合常数但同时考虑了原子间偶极-偶极相互作用两种情形下的辐射谱。分析了两个原子与辐射场之间耦合常数的相对大小和两原子间偶极作用的计入对辐射谱的影响。 关键词：     

Polarization and phase control of two-photon absorption in an isotropic molecular system

<正>We theoretically and experimentally study the polarization and phase control of two-photon absorption in an isotropic molecular system.We theoretically show that the two-photon transition probability decreases when the laser polarization changes from linear through elliptical to circular,and the laser polarization does not affect the control efficiency of two-photon transition probability by shaping the spectral phase.These theoretical results are experimentally confirmed in coumarin 480.Furthermore,we propose that the combination of the laser polarization with the spectral phase modulation can further increase the control efficiency of the two-photon absorption.     

飞秒强激光作用下Ar原子团簇离子能谱计算

研究了飞秒强激光与Ar原子团簇相互作用时的电离机制及库仑爆炸过程,建立了一个简化的模型计算相互作用产生的离子能谱,计算结果与实验结果较为吻合,可以较好地解释离子能谱高能端的主要特征。     

碰撞对钠分子梯形能级系统高位能级布居的影响

以氩气为缓冲气体,在实验上研究了碰撞过程对钠分子梯形能级系统高位能级两种布居过程的影响。对于双光子激发过程,由于消相碰撞,无多普勒加宽的洛伦兹尖峰随缓冲气体压力的增大而很快消失,加入少量缓冲气体时,碰撞激发过程对以多普勒宽度为特征的信号有一定的增强作用,但加入过量缓冲气体会由于消布居作用使信号减弱,对于主要通过碰撞实现高位能级布居的过程,加入缓冲气体对高位能级布居起关键作用,在速率方程近似下解释了上述结果。