Vibrational Spectra of Liquid Interfaces with a 100 kHz Sub-1 cm^–1 High-Resolution Broadband Sum-Frequency Generation Vibrational Spectrometer (HR-BB-SFG-VS)

Abstract

Sub-1 cm–1 high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) using synchronized picosecond and femtosecond lasers at 1 kHz was first reported over a decade ago, and many advantages of HR-BB-SFG-VS over the conventional BB-SFG-VS have been well-documented. A highly efficient and much lower-cost version of HR-BB-SFG-VS is needed for broader adoption of this powerful interface-specific spectroscopic technique. Here, we report the realization of such sub-1 cm–1 HR-BB-SFG-VS with a tunable repetition rate of around 100 kHz. Instead of synchronization of an additional expensive 90 ps laser for enough power to achieve high spectral resolution SFG measurement, a chirped volume Bragg grating (CVBG) is implemented with the second-harmonic band compression (SHBC) unit to generate an intense 90 ps laser pulse at 517 nm with a bandwidth of about 0.16 cm–1 from a 150 fs laser pulse at ∼1034 nm, with an efficiency of ∼26%. The effectiveness of this new SFG system is demonstrated through the SFG spectra obtained with a spectral resolution of 0.6 cm–1 and excellent line shape from the air/DMSO (dimethyl sulfoxide) aqueous solution interfaces and the air/water interface, without an apparent surface heating effect. This development provides much lower-cost and easy-to-implement powerful HR-BB-SFG-VS instrumentation for broad applications in structure and dynamics studies on illusive molecular surfaces and interfaces.

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