Sum‐frequency spectroscopy on bulk and surface phonons of noncentrosymmetric crystals

Abstract Infrared‐visible sum‐frequency spectroscopy is shown to be an effective tool to probe not only bulk phonons, but also microscopic surface phonons of noncentrosymmetric crystals. Results on α‐quartz are presented as an example. The observed surface phonons of the (0001) surface agree well with the calculated surface structure.