Spectroscopy is the characterization of matter through themeasure-

ment of its interaction with light. The discovery by Isaac Newton of

the sprawl of colors (dispersion) of sunlight by a prism has been

the foundation of further developments of spectroscopy. Joseph von

Fraunhofer used a diffraction grating for the same goal and observed

dark bands in the spectrum of the sunlight. Walter N. Hartley

contributed to make the link between the position of atoms in the

periodic table and the observed bands in spectra. The invention of

the spectroscopy has induced a fantastic advanced in knowledge

of universe due to its ability to determine the composition of the

sun and stars. It has been then possible to analyze not only remote

materials, but also the light sources, gas, and liquids in laboratories

since the end of the nineteenth century. The twentieth century

saw the development of new spectroscopic techniques and the

improvement of the sensitivity of the devices in order to detect

smaller and smaller concentrations of chemical components. The

basis of spectroscopy is given considering the distinction between

elastic and inelastic scattering, before investigating the way to

improve the sensitivity of devices by field enhancement.