General Normalizing Approach for Broadband Infrared Sum-Frequency Generation Spectroscopy via a Transmitted Signal in α-Quartz

Sum-frequency generation vibrational spectroscopy (SFG-VS), a second-order nonlinear spectroscopic technique, has extensive applications in interface science. Accurate normalization of the incident laser beam intensity is essential, particularly for buried interfaces, where incident lasers are absorbed before reaching the interface. We introduce a novel normalization method that exploits both the transmitted and reflected SFG signals from alpha-quartz, leveraging its benefits in signal amplification and phase referencing. This method shows versatility for both chiral and achiral molecules at interfaces and is extendable to electronic or doubly resonant SFG spectroscopy. We have demonstrated this normalization method by examining the SFG vibrational spectra of sodium dodecyl sulfate molecules on quartz and deducting the IR absorption from CO2 in the gas phase.