Atomic absorption spectra are created when light passes through gaseous elements and atoms. The gas absorbs the light waves from the light source and emits a characteristic absorption spectra.
An absorption spectrum is a spectrum of light that changes depending on the gaseous elements present. For an element or an atom to produce an absorption spectrum, the gas must be both cold and dilute. Next, light can be shone through the gas. Photons from the light are absorbed by the cold, dilute gas, and the atoms in the gas produce distinctive frequencies of light that is re-emitted to form an absorption spectrum.