Raman spectroscopy is used to study the vibrational, rotational and other low frequency modes in a system. They typically employ lasers as a source of monochromatic light, which is scattered by phonons or other excitations from the system. This results in a shift in the energy of the laser phonons, which in turn yields information about the system in question, more specifically the chemical bonds and the symmetry of molecules. The technique is valuable for studying changes in chemical bonding and can be performed on very small sample areas.