Recent progress on sum-frequency spectroscopy

Second harmonic generation (SHG) and sum frequency spectroscopy (SFS) have provided unique opportunities to probe surfaces and interfaces. They have found broad applications in many disciplines of science and technology. In recent years, there has been significant progress in the development of SHG/SFS technology that has significantly broadened the applications of SHG and SFS. In this article, we review the recent progress of the field with emphasis on SFS.