Tip-enhanced Raman spectroscopy (TERS) provides the sensitivity required to obtain the vibrational fingerprint of few molecules. While single molecule detection has been demonstrated in UHV experiments, the sensitivity of the technique in ambient, liquid and electrochemical conditions is still limited. In this work, we present a new strategy to increase the signal-to-noise in TERS by spatial light modulation. We iteratively optimize the phase of the excitation beam employing two different feedback mechanisms. In one optimization protocol, we monitor the spectral changes upon aberration correction and tight far-field focusing. In a second protocol, we use a phase-optimization strategy where TER spectra are directly used for feedback. Far-field tight focusing results in average signal enhancements of a factor of 3.5 in air and has no impact on TER signals obtained from solid/liquid interfaces. Using the TER spectrum as direct feedback, we obtain average signal enhancements between a factor of 2.6 in liquid and 4.3 in air. In individual cases, some bands increase by more than one order of magnitude in intensity upon spatial light modulation. Importantly, phase modulation in addition allowed the retrieval of bands that were initially not discernible from the noise. The proposed beam-modulation strategy can be easily implemented in existing TERS instruments and can help to push the detection limit of the technique in applications where the signal-to-noise level is low.

中文翻译：

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尖端增强拉曼光谱中用于像差控制和信号增强的光束调制

尖端增强拉曼光谱 (TERS) 提供了获得少数分子振动指纹所需的灵敏度。虽然单分子检测已在 UHV 实验中得到证明，但该技术在环境、液体和电化学条件下的灵敏度仍然有限​​。在这项工作中，我们提出了一种通过空间光调制提高 TERS 信噪比的新策略。我们使用两种不同的反馈机制迭代优化激发光束的相位。在一种优化协议中，我们监测像差校正和紧密远场聚焦时的光谱变化。在第二个协议中，我们使用相位优化策略，其中 TER 光谱直接用于反馈。远场紧密聚焦导致平均信号增强 3 倍。5 在空气中，对从固/液界面获得的 TER 信号没有影响。使用 TER 频谱作为直接反馈，我们获得了液体中 2.6 倍和空气中 4.3 倍之间的平均信号增强。在个别情况下，某些波段在空间光调制后强度增加了一个数量级以上。重要的是，相位调制还允许检索最初无法从噪声中辨别出来的频带。所提出的光束调制策略可以很容易地在现有的 TERS 仪器中实施，并且有助于在信噪比低的应用中推动该技术的检测极限。一些波段在空间光调制后强度增加了一个数量级以上。重要的是，相位调制还允许检索最初无法从噪声中辨别出来的频带。所提出的光束调制策略可以很容易地在现有的 TERS 仪器中实施，并且有助于在信噪比低的应用中推动该技术的检测极限。一些波段在空间光调制后强度增加了一个数量级以上。重要的是，相位调制还允许检索最初无法从噪声中辨别出来的频带。所提出的光束调制策略可以很容易地在现有的 TERS 仪器中实施，并且有助于在信噪比低的应用中推动该技术的检测极限。