School of Analytical Sciences Adlershof, Humboldt Universität zu Berlin, Albert-Einstein-Str. 5-11, 12489 Berlin, Germany.
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Str. 2a, 12489 Berlin, Germany.
J Chem Phys. 2018 Mar 14;148(10):104702. doi: 10.1063/1.5016629.
Broadband vibrational sum-frequency generation (BB-VSFG) spectroscopy has become a well-established surface analytical tool capable of identifying the orientation and structure of molecular layers. A straightforward way to boost the sensitivity of the technique could be to increase the laser repetition rate beyond that of standard BB-VSFG spectrometers, which rely on Ti:sapphire lasers operating at repetition rates of 1-5 kHz. Nevertheless, possible thermally induced artifacts in the vibrational spectra due to higher laser average powers are unexplored. Here, we discuss laser power induced temperature accumulation effects that distort the BB-VSFG spectra of 1,2-diacyl-sn-glycero-3-phosphocholine at an interface between two transparent phases at repetition rates of 5, 10, 50, and 100 kHz at constant pulse energy. No heat-induced distortions were found in the spectra, suggesting that the increase in the laser repetition rate provides a feasible route to an improved signal-to-noise ratio or shorter data acquisition times in BB-VSFG spectroscopy for thin films on transparent substrates. The results have implications for future BB-VSFG spectrometers pushing the detection limit for molecular layers with low surface coverage.
宽带振动和频发生（BB-VSFG）光谱学已经成为一种成熟的表面分析工具，能够确定分子层的取向和结构。提高该技术灵敏度的一种直接方法是将激光重复率提高到标准 BB-VSFG 光谱仪的重复率以上，标准 BB-VSFG 光谱仪依赖于重复率为 1-5 kHz 的钛宝石激光器。然而，由于更高的激光平均功率，可能会出现热诱导的振动光谱伪影，这方面还没有得到探索。在这里，我们讨论了激光功率引起的温度积累效应，该效应会在两个透明相之间的界面处扭曲 1,2-二酰基-sn-甘油-3-磷酸胆碱的 BB-VSFG 光谱，在重复率为 5、10、50 和 100 kHz 时，在恒定脉冲能量下。在光谱中未发现热诱导的失真，这表明增加激光重复率为在透明衬底上的薄膜的 BB-VSFG 光谱学中提供了一种可行的途径，可以提高信噪比或缩短数据采集时间。这些结果对未来的 BB-VSFG 光谱仪具有重要意义，可以提高具有低表面覆盖率的分子层的检测极限。
