Resolution along both infrared and visible frequency axes in second-order Fourier-transform vibrational sum-frequency generation spectroscopy

Vibrational sum frequency generation (SFG) spectroscopy is a versatile technique in surface science, which enables the study of physical and chemical properties of interfaces at the molecular scale. This technique reliably measures molecular vibrational resonances. However, utilization of the SFG spectroscopy in its conventional implementation to reveal correlations between vibrational and electronic resonances at interfaces meets substantial practical limitations. The limitations can, in principle, be overcome by using Fourier-transform SFG (FT SFG) spectroscopy and resolving both frequency axes for the second-order nonlinear optical susceptibility. Here, we experimentally demonstrate this approach using two model systems, quartz and a decanoic acid monolayer at the water/air interface. Implementation of the FT SFG spectroscopy requires heterodyne detection and, thus, the technique can provide the phase-resolved response of molecular resonances. To this end, we develop the phasing procedure for this spectroscopy.