Development of Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy and Its Application to Interfacial Dynamics

Abstract

Interfaces play important roles in various fields such as catalytic chemistry, electrochemistry, biochemistry, and atmospheric chemistry. However, molecular-level understanding of structure and dynamics of their interfaces is still limited due to technical difficulties. Vibrational sum frequency generation (VSFG) spectroscopy is based on a second-order nonlinear optical process and provides interface-specific information. While conventional homodyne-detected VSFG measures the square of second-order nonlinear susceptibility (|χ⁽²⁾|²), heterodyne-detected (HD-) VSFG enables us to directly measure the imaginary part of χ⁽²⁾ (Imχ⁽²⁾), which corresponds to Imχ⁽¹⁾ obtained with absorption spectroscopy in bulk. We realized the first time-resolved (TR-) HD-VSFG measurement by combining HD-VSFG spectroscopy and pump-probe technique. This review introduces the principle of TR-HD-VSFG spectroscopy and its applications to interfacial dynamics at the metal, water, and lipid monolayer interfaces.