This work was supported in part by grants-in-aid KAKENHI from the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) Japan (#26104539, #26620020, #26810011, #15H03766, #15KT0060, #16H00826, and #16K13927); the Konica Minolta Science and Technology Foundation; the "Planting Seeds for Research" program of TokyoTech; the Imaging Science Project of the Center for Novel Science Initiatives (CNSI) at the National Institutes of Natural Sciences (NINS) (#IS261006); the RIKEN-IMS joint program on "Extreme Photonics;" and the Consortium for Photon Science and Technology (CPhoST).

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The authors have nothing to disclose.

本过程使我们能够捕获分子旋转的实时电影与基于狭缝2D成像设置。因为所观察到的离子穿过狭缝，步骤1.5是过程的关键步骤之一。狭缝刀片的边缘必须尖锐。时，有一个小缺陷，诸如在狭缝0.3mm的凹痕，划痕在离子图像中观察到的（ 图6）。在这种情况下，狭缝刀片应与2000砂砾湿砂纸打磨。 除了在图1所示的独特的摄像机角度，这种方法具有在3D成像检测器，这是以前用于旋转波包成像的唯一解决方案的几个优点。 首先，在本程序中，光束对准可以容易地通过监测原料离子的图像，如步骤4.1-4.2进行。 图7示出了在优化的泵-探针重叠条件的原始摄像机图像。当在pUMP-探测光束重叠丢失，各向异性或增强的图像签名不能被看见， 如图4A所示 。这一事实强调了在本方法步骤4.1-4.2的重要性。由于泵和探测光束的光点尺寸为10微米的量级，通常难以找到没有监测实时图像的最佳的重叠状态。在3D成像检测器的情况下，需要几秒钟，以形成具有当采用1000赫兹或更低的重复率激光足够的数据点（至少1000离子）的图像，因为计数速率被限制为少数的事件每个激光在3D拍摄的探测器。在本发明的方法，在另一方面，计数率基本上是无限的，并且每帧的离子的数量可以简单地通过延长曝光时间增加。在目前的情况下，超过1000离子在50毫秒的曝光时间内检测。 本方法的高计数率也导致<html>为更短的数据采集时间。因为相机的帧速率是250帧，它仅需〜40秒取分子运动的一个快照在特定的时间。用于测量在所述一个分子旋转复活时间（〜8.4 ps）的具有〜33-FS步骤，测量时间只有几个小时。这又是一个优点，因为实验数据将由激光器的有限的长期稳定性和整个实验装置劣化。在我们的设置，例如，持续时间随时间的变化，部分是由于在FS放大器的温度变化。 6小时内有3-K变化导致放大器的热膨胀，包括脉冲压缩光栅之间的距离的伸长，导致脉冲持续时间31的伸长率。激光束的漂移，这降低了泵诱导动力学的信号，〜8小时内也被检测到，虽然该漂移的来源没有被识别。 t"的&gt;本技术是一种2D成像的，限制在3D的信息。在一个库仑爆炸的情况下，只有在检测平面喷射离子的片段向图像，这意味着它是难以适用本发明的方法直接将复杂碎裂过程，如那些涉及符合成像研究25，32，33。我们注意到，与我们的方法中的信号强度的总和为正比于检测平面中的概率。这表示对间接信息尺寸不包括在成像平面11，12。 虽然我们专注于库仑爆炸成像在本文中，本方法可以，原则上适用于一般的带电粒子成像，如涉及光解研究14。在里面现有的成像过程，得到的带电粒子的3D牛顿球体的二维断层图像，光的偏振应平行于检测器表面。换句话说，摄像机的角度被限制到特定条件。另外，在本2D成像技术中，三维离子云被空间切片到2D切割，然后被成像。与此切片成像，摄像机角度的自由度将打开的方式来获得，有时会出现在激光传播方向26,34迄今-不可观测信息。

为更深入地了解和更好地利用分子的动态性质，有必要清楚地可视化的兴趣的分子运动。时间分辨库仑爆炸成像是强大的方法来达到这个目的1，2，3中的一个。在这种方法中，感兴趣的分子动力学由泵超短激光场开始，并且然后由一个时间延迟的探测脉冲探测。当探头照射下，分子被电离乘法和分成由于库仑斥力碎片离子。喷射的离子的空间分布是在探头照射的分子结构和空间取向的量度。测量扫描泵浦 - 探测延迟时间的序列导致创建一个分子的电影。值得注意的是，对于最简单的情况 - 双原子分子 - 所喷射的离子的角分布直接反映了分子轴分布（ 即平方转动波函数）。 对于泵的过程，在使用超短激光场分子运动的相干控制最近的进展已经导致建立高度控制的旋转波包4，5。此外，旋转方向可以积极地通过使用偏振控制的激光字段6，7，8来控制。因此，已经期望分子的旋转，包括波性质的详细的图片，可以当库仑爆炸成像技术与这种泵过程9，10，11，12，13结合可视化。然而，我们的一些次遇到与现有成像方法相关联，如下所述试验的困难。本文的目的是提出克服这些困难，创造分子转动波包的高品质电影的新方式。分子旋转的第一个实验电影本的方法拍摄，它的物理意义以来，我们在以前的文章11作了介绍。发展的背景下，本成像技术的详细的理论方面中，并且与其他现有技术的比较将在即将纸张进行说明。在这里，我们将主要集中在该过程的实际和技术方面，包括典型的泵浦 - 探测光学装置的组合和新的成像装置。如前面的纸，将目标系统单向地旋转氮分子11。 的主要实验难度现有的成像设置， 如图1示意性示出，具有与检测器的位置，或者相机角度做。因为旋转轴与激光感生分子旋转激光传播轴6，7，8一致，这是不实际的沿着旋转轴线安装的检测器。当安装了检测器，以避免激光照射，摄像机角对应于旋转的侧面观察。在这种情况下，这是不可能重建从预计（2D）离子图像14分子的原始方向。三维成像检测器14，15，16，17，18，19，与该到达时间顶端检测器和离子IMPAC吨的位置可以测量的，提供了一个独特的方式来直接观察分子旋转使用库仑爆炸成像10,12。然而，每激光照射可接受离子计数是在3D检测器低（典型地&lt;10离子），这意味着它是难以建立一个长的电影具有高图像质量14分子运动。检测器（通常纳秒）的死区时间也影响图像分辨率和成像效率。它也不是一件简单的工作通过监测实时离子图像与&lt;〜1kHz的激光重复率，使一个很好泵浦 - 探测光束重叠。尽管几个组已经观察到使用3D技术的旋转波包，该空间信息是有限的和/或直接和波性质的详细可视化，包括复杂的节点的结构，没有实现10,12。 的精髓新的成像技术是使用图1中的"新摄像机角度"的。在这种配置，避免了激光光束照射的检测器，而2D检测器平行于旋转平面，从而从旋转轴方向观察。狭缝只允许在转动平面内的离子（激光脉冲的偏振面），以向一个图像。二维检测器，其提供了比一个三维检测器的更高的计数率（通常为〜100离子），都可以使用。电子设备的设置比在三维检测的情况下更简单，而测量效率更高。耗时数学重建，如阿贝尔变换14，也没有必要提取角度信息。这些特征导致测量系统的容易的优化和生产高品质的电影。一个标准的2D / 3D带电粒子成像装置可以容易地修改本设置无覆盖UT斯达康使用昂贵的设备。

<table><tbody><tr><td>CMOS camera</td><td>Toshiba TELI</td><td>BU-238M-ES</td><td>equipped with SONY IMX174 sensor</td></tr><tr><td>High voltage switch</td><td>Behlke</td><td>HTS-41-03-GSM</td><td></td></tr><tr><td>High voltage switch</td><td>Behlke</td><td>HTS-80-03</td><td></td></tr><tr><td>Digital delay generator</td><td>Stanford research systems</td><td>DG535</td><td></td></tr><tr><td>Digital delay generator</td><td>Stanford research systems</td><td>DG645</td><td></td></tr><tr><td>Microchannel plate</td><td>Photonis</td><td>3075</td><td></td></tr><tr><td>Pulsed valve</td><td>LAMID LTD</td><td>Even-Lavie valve&amp;nbsp;</td><td>High repetition, room temperature model</td></tr><tr><td>Molecular beam skimmers</td><td>Institute for Molecular Science</td><td>13C11</td><td>3 and 1.5 mm center hole, 25 degrees full inner angle, and ~50 mm length</td></tr><tr><td>Optical Comparator</td><td>Nikon</td><td>V-24B</td><td></td></tr><tr><td>DPSS laser</td><td>Lighthouse Photonics</td><td>Sprout</td><td></td></tr><tr><td>Femtosecond Ti:Sapphire oscillator</td><td>KMLabs</td><td>Halcyon</td><td></td></tr><tr><td>Femtosecond Ti:Sapphire amplifier</td><td>Quantronix</td><td>Odin-II HE</td><td></td></tr><tr><td>Motorized linear stage</td><td>Sigma Koki</td><td>KST(GS)-100X</td><td></td></tr><tr><td>Manual X-stage</td><td>Sigma Koki</td><td>TSD-601S</td><td></td></tr><tr><td>High resolution mirror mount</td><td>Newport</td><td>Suprema SX100-F2KN-254</td><td></td></tr><tr><td>High resolution mirror mount</td><td>LIOP-TEC GmbH</td><td>SR100-100R-2-HS</td><td></td></tr><tr><td>Polarization checker</td><td>Paradigm Devices, Inc.</td><td>O-tool VIS</td><td></td></tr><tr><td>Instrument communication interface</td><td>National Instruments</td><td>NI-MAX</td><td></td></tr><tr><td>Graphical development environment for measurement programs</td><td>National Instruments</td><td>LabVIEW 2014</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>CVI/LEO</td><td>TLM2-400/800-45UNP</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>Altechna</td><td>Low GDD Ultrafast mirror</td><td></td></tr><tr><td>Laser line dielectric mirror</td><td>Altechna</td><td>Low GDD Ultrafast mirror</td><td></td></tr><tr><td>Femtosecond polarizer</td><td>Advanced Thin Films</td><td>PBS-GVD</td><td></td></tr></tbody></table>

direct imaging of laser-driven ultrafast molecular rotation

我们提出了一个可视化的激光诱导，超快分子转动波包动力学的方法。我们已经开发，其中迄今-不切实际摄像机角度实现一个新的2维库仑爆炸成像设置。在我们的成像技术，双原子分子照射具有圆偏振光强激光脉冲。喷射的原子的离子垂直地加速到激光传播。卧在激光偏振面的离子通过使用机械狭缝的选择并具有高通量成像的，二维探测器平行安装的偏振平面。因为圆极化（各向同性）库仑爆炸脉冲时，被排出的离子的观察角度分布直接对应于平方旋转波函数在所述脉冲照射的时间。创建分子旋转的实时电影，本成像技术是用飞秒泵浦 - 探测O组合ptical设置在该泵脉冲创建单向旋转分子合奏。由于高图像可以通过我们的检测系统，所述泵 - 探针实验条件可以容易地通过监测实时快照优化。其结果是，观察到的电影的质量是足够高的可视化的运动的详细波性质。我们也注意到，本技术可以在现有的标准离子成像设置来实现，提供用于分子系统的新相机角度或视点而不需要大量修改。

图4A示出N个2+离子在探头照射（库仑爆炸）喷出，采取一个探针激光照射的一个只探针的原始图像。每一个亮点都对应一个离子。 图4B示出万二进制化原料相机图像的相加图像。这些图像表明，我们的成像设置可以监视在偏振面的所有取向角度的分子。 图4C示出了对应于图4B的归一极坐标图。由于旋转控制（泵）脉冲是不存在，分布是各向同性的（ 图4C示出了一个圆）。 在图4B中 ，由于检测器的不均匀性小缺陷所用的椭圆的底部可以看到。这种缺陷总是出现在图像的同一位置上。因此，Ç一个可以通过用一个仅探针图像（步骤4.5.3.7）标准化观察到的图像进行补偿。 图中选择的两个泵浦脉冲的照射后拍摄快照5所示。从而改善的理解，不仅观察到的离子的图像，但也相应极坐标图和"哑铃型"模型的照片被示出为的探测时间的函数。在极坐标图在步骤4.5.3.5创建。的哑铃图象是各种取向角度哑铃的重叠图象，和他们的权值（不透明度）是观察到的角度概率。图像的序列形成单向分子旋转的清晰的电影。运动的波动性可以看作是复杂的节点结构和分散性，其中包括一个"X"形形状形成。 图6示出了具有受损的狭缝和AP截取的离子图像带凹痕狭缝边缘hotograph。小缺陷在很大程度上影响观察图像。在这样的情况下，重复步骤1.5是必要的。这其实也是在讨论中讨论。 图7示出了在优化的泵-探针重叠条件的原始摄像机图像。通过监测这种光束重叠信号，光路可以被优化。这导致了明显的电影，如在图5中 。 <img alt="图1" src="/files/ftp_upload/54917/54917fig1.jpg" /> 图1: 在不实用，典型和新配置中的摄像机角度的概念示图。在典型的相机角度，一个检测器被安装，以避免激光照射，但离子的喷射角度不能从2D投影图像重建。在目前新的拍摄角度，旋转平面（激光polarizat离子平面）平行于检测器的表面，因此适合于可视化的旋转运动。典型偏置电压2,500伏，1799伏，1846伏，253伏，0伏，3500伏，-800伏，4500 V代表离子光学1，2，3，4，和5所示，脉冲推斥，所述微通道板和荧光屏，分别。离子光学编号起始于底部电极。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig1large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图2" src="/files/ftp_upload/54917/54917fig2.jpg" /> 图2:2D成像单元的示意图。 （ 一 ）探测器系统的示意图。在橙色的圆板是其中其它部件安装用螺栓的基板。 （B）中的狭缝组件的示意图。右图解释了缝隙的运动。尺寸值以毫米。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图3" src="/files/ftp_upload/54917/54917fig3.jpg" /> 图3: 本泵浦-探测光学装置的示意图。用于旋转激励所述泵脉冲的光路是由红色线表示，而该探针（成像）脉冲的由蓝色线表示。 NLC，非线性晶体的二次谐波产生; HWP，半波片; QWP，四分之一波片; DM，分色镜; BS，50:50分束器; HRM:高分辨率镜座。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig3large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> ithin页="1"&gt; <img alt="图4" src="/files/ftp_upload/54917/54917fig4.jpg" /> 图4: 原材料和分析库仑爆炸离子图像。 （A）N个典型的原始图像2+采取一个探头拍摄。 （B）10000二值化用照相机图像概括图像。摄像机图像的尺寸为1200点¯x750像素。相应的现实空间大小为80毫米×50毫米。 （C）从求和图像构造的归一极坐标图。在原始和相加的图像，添加假彩色显示信号的强度。度的极角沿圆周所示。径向值是一个角度依赖性概率（任意单位）。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig4large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> 4917fig5.jpg"/&gt; 图 5: 激光诱导旋转波包动力学的选定快照。在每一个时间延迟，在上面板示出了椭圆形状已被转换成一个圆圈的离子图像。中间的面板显示相应的极坐标图。底部面板显示的角分布的哑铃模型。此哑铃图像是从不同的定向角的哑铃的重叠图象，和他们的权值（不透明度）是观察到的角度概率。极坐标图使用相同的单元和比例， 如图4。离子图像采用变换后的坐标，如在步骤4.5.3.4。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig5large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图6" src="/files/ftp_upload/54917/54917fig6.jpg" /> 图6:影响的实验离子图像上的缝隙缺陷。 （ 一 ）观察探针n只有2+有损坏的缝隙拍摄的图像。具有亚毫米凹痕狭缝边缘的（B）的照片。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig6large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图7" src="/files/ftp_upload/54917/54917fig7.jpg" /> 图7: 在优化的泵-探针重叠条件原始摄像机图像。探测时间被设定在t =第一泵脉冲照射后4.0 ps的。此时，分子取向的最大程度的实现。摄像机图像的尺寸为1200点¯x750像素。相应的现实空间大小为80毫米×50毫米。 <a href="http://ecsource.jove.com/files/ftp_upload/54917/54917fig7large.jpg" target="_blank">请点击</a>此处查看该图的放大版本。

Watch this Scientific Journal Video about Direct Imaging of Laser-driven Ultrafast Molecular Rotation at JoVE.com

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

激光驱动的超快分子旋转直接成像

We present a method for visualizing laser-induced, ultrafast molecular rotational wave packet dynamics. We have developed a new 2-dimensional Coulomb ...

direct-imaging-of-laser-driven-ultrafast-molecular-rotation

Nanyang Technological University

Research

Education

JoVE Journal

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Chemistry

Chemical Bonding: Molecular Geometry and Bonding Theories

SCIENTISTS IN ACTION

9.7K 次观看.  Tokyo Institute of Technology. We present a protocol for creating a real-time movie of a molecular rotational wave packet using a high-resolution Coulomb explosion imaging setup.

视频: Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular events. Viscosity is one of the key parameters affecting the diffusion of molecules and proteins, and changes in viscosity have been linked to disease and malfunction at the cellular level.1-3 While methods to measure the bulk viscosity are well developed, imaging microviscosity remains a challenge. Viscosity maps of microscopic objects, such as single cells, have until recently been hard to obtain. Mapping viscosity with fluorescence techniques is advantageous because, similar to other optical techniques, it is minimally invasive, non-destructive and can be applied to living cells and tissues.
Fluorescent molecular rotors exhibit fluorescence lifetimes and quantum yields which are a function of the viscosity of their microenvironment.4,5 Intramolecular twisting or rotation leads to non-radiative decay from the excited state back to the ground state. A viscous environment slows this rotation or twisting, restricting access to this non-radiative decay pathway. This leads to an increase in the fluorescence quantum yield and the fluorescence lifetime. Fluorescence Lifetime Imaging (FLIM) of modified hydrophobic BODIPY dyes that act as fluorescent molecular rotors show that the fluorescence lifetime of these probes is a function of the microviscosity of their environment.6-8 A logarithmic plot of the fluorescence lifetime versus the solvent viscosity yields a straight line that obeys the F&ouml;rster Hoffman equation.9 This plot also serves as a calibration graph to convert fluorescence lifetime into viscosity.
Following incubation of living cells with the modified BODIPY fluorescent molecular rotor, a punctate dye distribution is observed in the fluorescence images. The viscosity value obtained in the puncta in live cells is around 100 times higher than that of water and of cellular cytoplasm.6,7 Time-resolved fluorescence anisotropy measurements yield rotational correlation times in agreement with these large microviscosity values. Mapping the fluorescence lifetime is independent of the fluorescence intensity, and thus allows the separation of probe concentration and viscosity effects. 
In summary, we have developed a practical and versatile approach to map the microviscosity in cells based on FLIM of fluorescent molecular rotors.

Fluorescence Lifetime Imaging (FLIM) has emerged as a key technique to image the environment and interaction of specific proteins and dyes in living cells. FLIM of fluorescent molecular rotors allows mapping of viscosity in living cells.

在活细胞中的荧光寿命成像分子转子

Diffusion is often an important rate-determining step in chemical reactions or biological processes and plays a role in a wide range of intracellular ...

科研

生物工程

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

分子构象器和星团的空间分离

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

工程学

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, low pressure reference cell. The resulting beat between the known and unknown laser frequencies is monitored by a metal-insulator-metal point contact diode detector whose output is observed on a spectrum analyzer. The beat frequency between these laser emissions is subsequently measured and combined with the known reference frequencies to extrapolate the unknown far-infrared laser frequency. The resulting one-sigma fractional uncertainty for laser frequencies measured with this technique is &#177; 5 parts in 107. Accurately determining the frequency of far-infrared laser emissions is critical as they are often used as a reference for other measurements, as in the high-resolution spectroscopic investigations of free radicals using laser magnetic resonance. As part of this investigation, difluoromethane, CH2F2, was used as the far-infrared laser medium. In all, eight far-infrared laser frequencies were measured for the first time with frequencies ranging from 0.359 to 1.273 THz. Three of these laser emissions were discovered during this investigation and are reported with their optimal operating pressure, polarization with respect to the CO2 pump laser, and strength.

We describe the generation of far-infrared radiation using an optically pumped molecular laser along with the measurement of their frequencies with heterodyne techniques. The experimental system and techniques are demonstrated using difluoromethane (CH2F2) as the laser medium whose results include three new laser emissions and eight measured laser frequencies.

表征远红外激光辐射及其频率的测量

The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radio astronomy, and ...

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish between enantiomers (stereoisomers) of simple chiral species on the level of individual molecules. In this approach, a gaseous molecular jet of the sample expands into a vacuum chamber and intersects with femtosecond (fs) laser pulses. The high intensity of the pulses leads to fast multiple ionization, igniting a so-called Coulomb Explosion that produces several cationic (positively charged) fragments. An electrostatic field guides these cations onto time- and position-sensitive detectors. Similar to a time-of-flight mass spectrometer, the arrival time of each ion yields information on its mass. As a surplus, the electrostatic field is adjusted in a way that the emission direction and the kinetic energy after fragmentation lead to variations in the time-of-flight and in the impact position on the detector.
Each ion impact creates an electronic signal in the detector; this signal is treated by high-frequency electronics and recorded event by event by a computer. The registered data correspond to the impact times and positions. With these data, the energy and the emission direction of each fragment can be calculated. These values are related to structural properties of the molecule under investigation, i.e. to the bond lengths and relative positions of the atoms, allowing to determine molecule by molecule the handedness of simple chiral species and other isomeric features.

For small chiral species, Coulomb Explosion Imaging provides a new approach to determine the handedness of individual molecules.

作为一种工具来区分立体异构体的库仑爆炸成像

This article shows how the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) or the "reaction microscope" technique can be used to distinguish ...

化学

Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

We present a parametric driving method to cool an ultracold Fermi gas in a crossed-beam optical dipole trap. This method selectively removes high-energy atoms from the trap by periodically modulating the trap depth with frequencies that are resonant with the anharmonic components of the trapping potential.

通过定期行驶冷却光学被困超冷费米气体

We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

观测 Photoresponsive 液晶结构动力学的新方法

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the wavelength of the strong-field ionizing pump pulse from the commonly used 800 nm into the near-infrared (1200-1600 nm), the contribution of adiabatic electron tunneling to the ionization process increases relative to multiphoton absorption. Adiabatic ionization results in predominant population of the ground electronic state of the ion upon electron removal, which effectively prepares a coherent vibrational state (&#34;wave packet&#34;) amenable to subsequent excitation. In our experiments, the coherent vibrational dynamics are probed with a weak-field 800 nm pulse and the time-dependent yields of dissociation products measured in a time-of-flight mass spectrometer. We present the measurements on the molecule dimethyl methylphosphonate (DMMP) to illustrate how using 1500 nm pulses for excitation enhances the amplitude of coherent oscillations in ion yields by a factor of 10 as compared to 800 nm pulses. This protocol may be implemented in existing pump-probe setups through the incorporation of an optical parametric amplifier (OPA) for wavelength conversion.

We present a protocol for probing ultrafast vibrational coherences in polyatomic radical cations that result in molecular dissociation.

强场绝热电离多原子自由基阳离子超快振动相干的测量

We present a pump-probe method for preparing vibrational coherences in polyatomic radical cations and probing their ultrafast dynamics. By shifting the ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

轻型金纳米旋转电机系统的施工与运行

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Light-driven Molecular Motors on Surfaces for Single Molecular Imaging

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces are demonstrated. This work requires careful design, considerable synthetic effort, and proper analysis. The rotary motion of the molecular motor in solution is shown by 1H NMR and UV-vis absorption spectroscopy techniques. In addition, the method to graft the motor onto an amine-coated quartz is described. This method helps to gain more insight into molecular machines.

The manuscript describes how to synthesize and graft a molecular motor on surfaces for single molecular imaging.

表面光驱动分子电机的单分子成像

The design and synthesis of a synthetic system that aims for the direct visualization of a synthetic rotary motor at the single molecule level on surfaces ...

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Here, we present a protocol to perform sensitive, spatially resolved gas spectroscopy in the mid-infrared region, using degenerate four-wave mixing combined with upconversion detection.

用于定量气体传感的红外退化四波融合与上转换检测

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species ...