高精度相位分辨SFG光谱法检测界面微弱信号
Detecting Weak Signals from Interfaces by High Accuracy Phase-Resolved SFG Spectroscopy
摘要：
在过去的25年里，大量的工作表明，界面特定的，alloptical技术，振动和频产生（V-SFG）光谱，往往是唯一能够表征的结构和动态的界面物种。在这样的测量中所需的信息是复杂的二阶极化率，其引起来自界面分子的非线性响应。检测仅对磁化率产生小贡献的分子种类的能力同时受到可以确定光谱相位和振幅的精度的限制。在这项研究中，我们描述了一种新的光谱仪设计，提供了前所未有的相位和振幅精度，同时显着提高了技术的灵敏度。结合一个完整的共线光束的几何形状的技术，使复杂的样品和参考光谱的同时测量，在参考相位和幅度的不确定性被证明是大大减少。此外，我们表明，使用平衡检测，信噪比可以增加一个数量级。光谱仪的能力通过从z切石英的体占主导地位的非线性光学响应中分离出小的各向同性表面信号来证明。我们的光谱仪所达到的精度使得目前在v-SFG光谱中不可行的测量成为可能。
英文摘要：
Much work over the last 25 years has demonstrated that the interface-specific, alloptical technique, vibrational sum frequency generation (v-SFG) spectroscopy, is often uniquely capable of characterizing the structure and dynamics of interfacial species. The desired information in such a measurement is the complex second order susceptibility which gives rise to the nonlinear response from interfacial molecules. The ability to detect molecular species yielding only small contributions to the susceptibility is meanwhile limited by the precision by which the spectral phase and amplitude can be determined. In this study we describe a new spectrometer design that offers unprecedented phase and amplitude accuracy while significantly improving the sensitivity of the technique. Combining a full collinear beam geometry with a technique enabling the simultaneous measurement of the complex sample and reference spectrum, uncertainties in the reference phase and amplitude are shown to be greatly reduced. Furthermore, we show that using balanced detection, the signal to noise ratio can be increased by one order of magnitude. The capabilities of the spectrometer are demonstrated by the isolation of a small isotropic surface signal from the bulk dominated nonlinear optical response of z-cut quartz. The achieved precision of our spectrometer enables measurements not currently feasible in v-SFG spectroscopy.
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