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)

Sub-1 cm(-1) high-resolution broadbandsum-frequencygeneration vibrational spectroscopy (HR-BB-SFG-VS) using synchronizedpicosecond and femtosecond lasers at 1 kHz was first reported overa decade ago, and many advantages of HR-BB-SFG-VS over the conventionalBB-SFG-VS have been well-documented. A highly efficient and much lower-costversion of HR-BB-SFG-VS is needed for broader adoption of this powerfulinterface-specific spectroscopic technique. Here, we report the realizationof such sub-1 cm(-1) HR-BB-SFG-VS with a tunable repetitionrate of around 100 kHz. Instead of synchronization of an additionalexpensive 90 ps laser for enough power to achieve high spectral resolutionSFG measurement, a chirped volume Bragg grating (CVBG) is implementedwith the second-harmonic band compression (SHBC) unit to generatean intense 90 ps laser pulse at 517 nm with a bandwidth of about 0.16cm(-1) from a 150 fs laser pulse at & SIM;1034 nm,with an efficiency of & SIM;26%. The effectiveness of this new SFGsystem is demonstrated through the SFG spectra obtained with a spectralresolution of 0.6 cm(-1) and excellent line shapefrom the air/DMSO (dimethyl sulfoxide) aqueous solution interfacesand the air/water interface, without an apparent surface heating effect.This development provides much lower-cost and easy-to-implement powerfulHR-BB-SFG-VS instrumentation for broad applications in structure anddynamics studies on illusive molecular surfaces and interfaces.