2021 年 15 巻 1 号 p. A0116-
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.
