The main principle of atomic absorption spectroscopy is that atoms of different elements absorb and re-emit light in different ways. In this characterization technique, an extremely light-sensitive device called a photometer measures how much light passes through a material and how much is absorbed to identify the elements present.
Different elements absorb different wavelengths of light. These absorbed light waves excite the electrons of an element’s atoms, causing them to jump up to higher energy levels around the nucleus of the atom. In atomic absorption spectroscopy, a beam source emitting a set of known wavelengths or a continuous spectrum is shined up a thin sample or a solution. As the different wavelengths of light pass through the sample, they encounter different elements that either absorb or pass along the light, depending on the characteristic wavelength of the sample atoms.
Opposite to the beam source, a sensitive electronic detector of light measures the amplitude or intensity of different wavelengths of light after they pass through the sample. Regions of the spectrum with decreased intensity indicate the absorption of specific wavelengths. These specific wavelengths correspond to specific atoms, which can be identified by comparing these absent wavelengths with the elemental spectra listed in a table or electronic database. Atomic spectroscopy is commonly used to analyze the spectra of planets and stars to estimate the composition of these heavenly bodies.