飞秒荧光光谱技术及其在生命科学中的应用

频率上转换荧光光谱技术在生物大分子的结构、功能以及动力学研究方面具有广泛的应用。近年来,随着超快激光技术的发展以及相关光电子设备的升级和更新,尤其是飞秒激光的出现,频率上转换技术的时间分辨率达到了飞秒量级,为生物、化学和医学等领域的研究带来了新的发展契机。本文介绍和回顾了频率上转换荧光光谱技术的基本原理,在自行组建的一套频率上转换飞秒荧光光谱实验系统基础上,重点分析了整体系统的关键设计因素。介绍了频率上转换飞秒荧光光谱技术在生命科学领域,尤其是蛋白质、DNA动力学研究中的一些应用。

化学反应飞秒相干动力学与激光相干控制——1999年诺贝尔化学奖介绍

文章主要介绍了１９９９ 年诺贝尔化学奖得主艾哈默德·泽维尔（Ａｈｍｅｄ．Ｈ．Ｚｅｗａｉｌ） 教授的获奖工作———用飞秒技术和飞秒光谱的方法研究化学反应飞秒相干动力学，叙述了它们的原理、方法和应用，并简要介绍了其获奖背景、重要意义、相关研究及应用展望．

光子晶体光纤飞秒激光放大器抽运方式的研究

对不同抽运方式下光子晶体光纤飞秒脉冲放大器中的脉冲演变过程进行了数值模拟和实验验证。在数值模拟上,采用了速率方程和非线性薛定谔方程相结合的理论模型;该模型考虑到端面抽运引起光纤中的非均匀增益分布、群速度色散和自相位调制三者之间的相互作用。模拟结果表明,相比于前向抽运放大方式,采用背向抽运放大方式不仅输出功率高,而且放大脉冲具有更窄的时域和光谱宽度,即较小的时间带宽积和更少的非线性积累。在验证实验上,搭建了基于前向和背向抽运方式的光子晶体光纤飞秒激光放大器;获得的实验结果与数值模拟结论一致,并对放大脉冲演变过程的物理机制进行了讨论。

Investigation of Ultrafast Electronic Transfer Process on Organic/Inorganic Heterojunction by Femtosecond Transient Absorption

We detect a relaxation process of excited SQ02 dye in the chlorobenzene solution and an- chor SQ02 on Al2O3 and TiO2 film, so as to investigate the photophysical properties of pristine SQ02 in the monodisperse system, aggregation state, and the corresponding inter- facial electron transfer process. The experimental data show that the lifetime of SQ02 in the monondisperse system is ～2.0 ns, but that of SQ02 anchored on the Al2O3 film could obviously decrease to ～21 ps. The time of electron transfer from excited SQ02 to TiO2 film is estimated to be ～2.6 ps and the yield of electron injection is estimated to be ～89.1%, which matches the incident photon to current efficiency of dye-sensitized solar cell based on SQ02. In addition, some dyes are found to pack on the other dyes anchored on the nanocrystal film, and their relaxation time could reach ～60 ps. They couldn＇t participate in the interfacial electron transfer, since they are far away from the TiO2 interface.

Detection Techniques of Femtosecond Lasers

The measurement techniques of femtosecond spectroscopy are effective method to investigate ultrafast dynamics, they are widely used in the fields of physics, chemistry and biology. In this paper, the principle, experiment setup and the approaches to deal with the experiment data were presented. Then different measurement techniques such as transient absorption spectroscopy, photon echoes, optical Kerr effect and degenerate four-wave mixing were explained with special examples. At last, the application prospect of measurement techniques of femtosecond spectroscopy was forecasted.

激光化学

O644.18 1001010264化学反应飞秒相干动力学与激光相干控制:1999年诺贝尔化学奖介绍=Femtosecond coherent dynamicsof chemical reactions and laser coherentcontrol:the 1999 Nobel Prize in chemistry[刊,中]/罗莉,周建英(中山大学超快速激光光谱学国家重点实验室.广东,广州(510275))∥物理.-2000,29(3).-141-147介绍了采用飞秒技术和飞秒光谱的方法研究化学反应飞秒相干动力学,叙述了它们的原理、方法和应用,并简要介绍了其获奖背景、重要意义、相关研究及应用展望。图4参7(李瑞琴)

Impact of substrate on opto-thermal response of thin metallic targets under irradiation with femtosecond laser pulses

Femtosecond pulsed lasers have been widely used over the past decades due to their capability to fabricate precise patterns at the micro-and nano-lengths scales. A key issue for efficient material processing is the determination of the laser parameters used in the experimental set ups. Despite a systematic investigation that has been performed to highlight the impact of every parameter independently, little attention has been drawn on the role of the substrate material on which the irradiated solid is placed. In this work, the influence of the substrate is emphasised for films of various thicknesses, which demonstrates that both the optical and thermophysical properties of the substrate affect the thermal fingerprint on the irradiated film while the impact is manifested to be higher at smaller film sizes. Two representative materials, silicon and fused silica, have been selected as typical substrates for thin films(gold and nickel) of different optical and thermophysical behaviour and the thermal response and damage thresholds are evaluated for the irradiated solids. The pronounced influence of the substrate is aimed to pave the way for new and more optimised designs of laserbased fabrication set ups and processing schemes.

Long Chain Fatty Acid Affects Excited State Branching in Bilirubin-Human Serum Protein Complex

After binding to human serum albumin,bilirubin could undergo photoisomerization and photoinduced cyclization process.The latter process would result the formation of a product,named as lumirubin.These photo induced behaviors are the fundamental ofclinical therapy for neonatal jaundice.Previous studies have reported that the addition of long chain fatty acids is beneficial to the generation of lumirubin,yet no kinetic study has revealed the mechanism behind.In this study,how palmitic acid affects the photochemical reaction process of bilirubin in Human serum albumin(HSA)is studied by using femtosecond transient absorption and fluorescence up-conversion techniques.With the addition of palmitic acid,the excited population of bilirubin prefers to return to its hot ground state(S_(0))through a 4 ps decay channel rather than the intrinsic ultrafast decay pathways(<1 ps).This effect prompts the Z-Z to E-Z isomerization at the S_(0) state and then further increases the production yield of lumirubin.This is the first time to characterize the promoting effect of long chain fatty acid in the process of phototherapy with femtosecond time resolution spectroscopy and the results can provide useful information to benefit the relevant clinical study.

Ultrafast Excited State Dynamics of t^rans-4-Aminoazobenzene Studied by Femtosecond Transient Absorption Spectroscopy

The ultrafast excited state dynamics of trans-4-aminoazobenzene （trans-4-AAB） in ethanol was investigated by femtosecond transient absorption spectroscopy. After being excited to the S2 state by 400 nm, trans-4-AAB decays from the S2 state to the hot S1 state by internal conversion with time constant of -70 fs. The photoisomerization through inversion mechanism on the S1 potential energy surface and the internal conversion from the S1 state to the hot So state are observed, respectively. The average timescale of these two decay pathways is -0.7 ps. And the vibrational cooling of the hot So state of cis- and trans-4- AAB occur with time constants of -4 and N13 ps, respectively. Furthermore, the ultrafast intersystem crossing process are also observed. The timescale of intersystem crossing from the S2 state to the T4 state is about 480 ps while from the S1 state to the T2 state is -180 ps.

Ultrafast Decay Dynamics of 2-Hydroxypyridine Excited to S_(1) Electronic State

The S_(1) state decay dynamics of 2-hydroxypyridine following UV excitation at a wavelength range of 276.9-250.0 nm is investigated using femtosecond time-resolved photoelectron imaging technique.Based on pump wavelength dependence of the decay dynamics,a refined decay picture is proposed.At pump wavelength of 276.9 nm,the S_(1) state is depopulated through intersystem crossing to lower triplet state(s).At 264.0 nm,both intersystem crossing to lower triplet state(s)and internal conversion to the ground state are in operation.At 250.0 nm,internal conversion to the ground state becomes dominated.

四维超快电子衍射及显微成像:机遇与挑战

随着近年来超快电子衍射和电子显微镜的发展,一个崭新的结构动力学时代即将到来,这对中国和世界都是一个令人激动的时刻,同时也意味着巨大的机遇。本文将介绍该项新技术的最新进展,以及从物理、化学到生物方面的最新突破。各种机遇和挑战也将会在报告中提到。

Progress in femtochemistry and femtobiology

Femtoscience offers a unique way to understand the dynamics in physics, chemistry and biology. This subject focuses on the process happening at femto-to pico-second time scale by femtosecond optical methods. Widely used in chemistry it reveals chemical reactions, including bond breaking, forming, and stretching, which happens at an ultrafast time scale. Femtoscience is also important in the biological system, for example, light harvesting system and vision system. Femtoscience in physics is also widely used, but it is not studied in this paper. Instead, we report new advances in femtochemistry and femtobiology, including structural dynamics, coherent control, enzyme function dynamics and hydration in the protein system. We also introduce attosecond science, focusing on electron dynamics at an extreme short time scale.

A Coulomb explosion theoretical model of femtosecond laser ablation materials

In this paper,a kinetic theory of Vlasov equation is proposed to depict electron and ion's nonequilibrium transport processes in a femtosecond time scale.A Coulomb explosion model of femtosecond laser ablation of materials is proposed and numerically simulated.The mechanism of surface Coulomb explosion induced by self-consisted electric field and the impact of laser parameters on the ablation of materials are quantitatively analyzed.The ablation depths calculated by the model are in good agreement with the experimental results.It is shown that,the intensity of self-consisted electric field generated on the dielectric material's surface is much greater than that generated on the metal or the semiconductor material's surface,and Coulomb explosion ablation is more easily to occur on the dielectric material's surface.