Coherent Multi-Quantum Multi-Dimensional Spectroscopy

相干二维(2D)电子能谱是研究超快时间尺度上激子动力学、能量和电荷输运或化学反应的有力手段。为激励和检测提供频率分辨率可以分离在一维瞬时吸收中重叠的贡献。2D方法揭示了光-物质相互作用的全三阶响应函数。在这里，我们系统地将这个概念扩展到更高的非线性阶、更高的量子相干性和更高的维度。这提供了关于激子的独特信息，这些激子是通过其他技术无法获得的。利用发展的方法，我们计划研究分子和超分子物种以及量子点中电子激发态的结构、动力学和相互关系。这将通过飞秒脉冲整形和以1 kHz的激光重复频率进行的快照到快照调制来实现。因此，我们可以在不改变光束几何形状的情况下，通过“相位循环”从相同的原始数据集中提取各种非线性信号贡献。快速扫描显著提高了信噪比，减少了总的数据采集时间。我们的第一种方法是基于全共线激发和荧光检测，避免了非共振溶剂贡献。我们将实现1*4*4-、1*6*6-和1*8*8倍相位循环，以分别确定四阶、六阶和八阶信号。因此，可以提取电子相关能或激子结合能。在1*5*5*5=125倍的相位循环下移动到四脉冲序列，揭示了15个不同的四阶和六阶三维光谱中的动态信息，这些光谱将各种零、一、二和三量子相干相互关联。第二种方法采用泵浦-探测几何结构，测量相干发射的信号。在这里，我们将使用五阶激子-激子-相互作用2D光谱来揭示超分子参数如链长、几何形状或组成的系统变化下的激子输运。我们还将研究沿一维、二维或三维发生传输的系统。最后，我们计划通过在同一系统中使用相同的激光参数来比较这两种激发几何。这应该会解决关于2D荧光光谱解释的争论。此外，我们通过部署多达六个脉冲来研究四维和五维光谱学的潜力。这可以解开高达六阶的所有信号贡献，并分离例如在传统2D测量中重叠的不同电子态上的波包动力学。

Coherent two-dimensional (2D) electronic spectroscopy is a powerful method for investigating exciton dynamics, energy and charge transport, or chemical reactions on ultrafast time scales. Providing frequency resolution both for the excitation and the detection separates contributions that overlap in one-dimensional transient absorption. The 2D method reveals the full third-order response function of light-matter interaction.Here we extend the concept systematically to higher nonlinear orders, higher quantum coherences, and higher dimensions. This offers unique information on excitons not accessible via other techniques. Using the developed methods, we plan to study the structure, dynamics, and correlations of electronically excited states in molecular and supramolecular species as well as quantum dots. This will be accomplished by femtosecond pulse shaping with shot-to-shot modulation at the 1-kHz repetition rate of the laser. Thus we can extract various nonlinear signal contributions via “phase cycling” from the same raw data set without changing the beam geometry. Rapid scanning significantly improves the signal-to-noise ratio and reduces the total data acquisition time.Our first approach is based on all-collinear excitation and fluorescence detection that avoids nonresonant solvent contributions. We will implement 1*4*4-, 1*6*6-, and 1*8*8-fold phase cycling to determine fourth-, sixth-, and eighth-order signals, respectively. Thus one can extract electron correlation energies or exciton binding energies. Moving to four-pulse sequences at 1*5*5*5=125-fold phase cycling reveals dynamic information within 15 different fourth- and sixth-order three-dimensional spectra that correlate various zero-, one-, two-, and three-quantum coherences with each other.A second approach employs a pump-probe geometry with measurement of the coherently emitted signal. Here we will use fifth-order exciton-exciton-interaction 2D spectroscopy to reveal exciton transport under systematic variation of supramolecular parameters such as chain length, geometry, or composition. We will also investigate systems in which transport may occur either along one, two, or three dimensions.Finally, we plan to compare the two excitation geometries by employing them on the same system using identical laser parameters. This should resolve a debate on the interpretation of 2D fluorescence spectra. In addition, we investigate the potential of four- and five-dimensional spectroscopy by deploying up to six pulses. This can disentangle all signal contributions up to sixth order and separate, for example, wavepacket dynamics on different electronic states that overlap in conventional 2D measurements.