Chapter 9 - Heterodyne-detected chiral vibrational sum frequency generation spectroscopy of bulk and interfacial samples

Abstract

Chiral vibrational sum frequency generation (VSFG) is a highly sensitive method to detect the chirality of materials. This method applies to both randomly oriented bulk and azimuthally isotropic interfaces. Chiral VSFG spectroscopy is more sensitive than the conventional chiral vibrational spectroscopies, such as vibrational circular dichroism (VCD) and Raman optical activity (ROA) because it relies on the electric dipole interaction and the signal is obtained in a background-free manner. The introduction of a heterodyne-detection technique permits detecting the phase of the VSFG signal field, by which the chirality senses of samples are distinguished. The technique also enhances the sensitivity of the method. The sensitivity can be further improved by conducting chiral VSFG under electronic resonant conditions. In this article, we describe the basic theory of chiral VSFG spectroscopy, the multiplex heterodyne-detected (HD) chiral VSFG spectrometer that we have developed, and introduce the applications of HD chiral VSFG to various bulk and interfacial samples.