Expanding the capabilities of Sum-frequency Generation Vibrational Spectroscopy

Sum-frequency generation vibrational spectroscopy (SFG-VS) is a nonlinear optical spectroscopy used to probe the vibrations of molecules at interfaces. SFG-VS can be applied to study a vast number of interfacial systems to gain information which could not be obtained through other means. Methods of acquiring phase-sensitive sum-frequency generation (PS-SFG) and two-dimensional sum-frequency generation (2D SFG) measurements were developed for use in SFU Chemistry. PS-SFG measurements were enabled through phase-shifting interferometry, allowing for the extraction of complex PS-SFG spectra revealing the orientations of molecular groups at interfaces. Phase-shifting was accomplished by rotating dispersive optics in the beam path of a secondary SFG source used to interfere with the SFG of the sample. 2D SFG measurements were enabled through the use of a novel implementation of the Michelson interferometer. A custom motion controller was designed and implemented for precise control over the interferometer arm lengths. A calibration procedure was developed for the interferometer which uses spectral interferometry. The ability of the interferometer to produce a 2D SFG spectrum is demonstrated with reference measurements. The ability to produce a 2D SFG spectrum of a vibrationally-resonant sample was not demonstrated due to insufficient laser power.