Coherent pump pulses in Double Electron Electron Resonance spectroscopy.
Coherent pump pulses in Double Electron Electron Resonance spectroscopy.
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DOI：
10.1039/c6cp03555h
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发表时间：
2016-07-21
期刊：
影响因子：
--
通讯作者：
Stoll S
中科院分区：
文献类型：
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作者：
Tait CE;Stoll S
最近引入的形状脉冲双电子电子共振（DEER）光谱通过增加激发带宽和改进对自旋动力学的控制，导致灵敏度显著增强。到目前为止，DEER的应用依赖于非相干泵浦通道的存在来平均泵浦脉冲对观察者自旋的大多数不希望的相干效应。然而，在越来越多地用于产生形状脉冲的全相干EPR光谱仪中，相干泵脉冲的存在意味着需要明确考虑这些影响。在本论文中，我们研究了相干矩形泵浦脉冲和相干塞赫/丹泵浦脉冲在多达三个泵浦脉冲的DEER实验中的影响。我们表明，即使在观测器和泵浦脉冲激发带宽没有明显重叠的情况下，涉及两种脉冲类型的相干转移路径也会产生相当强度的自旋回波。这些回声会引入人工制品，如果不加以识别和去除，很容易导致误解。我们证明，观测到的回波可以使用一个简单的自旋量子动力学方法，包括仪器传递函数进行定量建模。在分析回波交叉伪影的基础上，提出了有效的相位循环抑制方案。这使得在新型全相干EPR光谱仪上使用先进的DEER实验具有高灵敏度和更高的长距离测量精度。
The recent introduction of shaped pulses to Double Electron Electron Resonance (DEER) spectroscopy has led to significant enhancements in sensitivity through increased excitation bandwidths and improved control over spin dynamics. The application of DEER has so far relied on the presence of an incoherent pump channel to average out most undesired coherent effects of the pump pulse(s) on the observer spins. However, in fully coherent EPR spectrometers that are increasingly used to generate shaped pulses, the presence of coherent pump pulses means that these effects need to be explicitly considered. In this paper, we examine the effects of coherent rectangular and sech/tanh pump pulses in DEER experiments with up to three pump pulses. We show that, even in the absence of significant overlap of the observer and pump pulse excitation bandwidths, coherence transfer pathways involving both types of pulses generate spin echoes of considerable intensity. These echoes introduce artefacts, which, if not identified and removed, can easily lead to misinterpretation. We demonstrate that the observed echoes can be quantitatively modelled using a simple spin quantum dynamics approach that includes instrumental transfer functions. Based on an analysis of the echo crossing artefacts, we propose efficient phase cycling schemes for their suppression. This enables the use of advanced DEER experiments, characterized by high sensitivity and increased accuracy for long-distance measurements, on novel fully coherent EPR spectrometers.