How a Laser Works The Basics of an Atom

Everything we see within the universe is made up of an infinitely large number of combinations of the 100 different kinds of atoms. The arrangement and bonding of these atoms determines what material/object they constitute.

Atoms are constantly in motion. They continuously vibrate and move. Although all atoms are vibrating to a degree, atoms can be in a different state of excitation (i.e. they can have different levels of energy). If a large degree of energy is applied to an atom then it can leave what is referred to as ground-state energy level and go to an excited level. The level of excitation is proportional to the amount of energy applied.

A simple atom as shown in Figure 1 consists of a nucleus, which consists of protons and neutrons and what is often referred to as an electron cloud. For a simplistic interpretation of the atom model it is easy to think of the electrons within the electron cloud following discrete paths or orbits within the cloud. This analogy suits our purpose as we can then consider these orbits to be the different energy levels that make up the atom. If we add some form of energy to the atom we can assume that electrons from me lower-energy orbitals will transfer to the higher-energy orbitals at a greater distance from the nucleus, resulting in a higher level of excitation.

Electron Nucleus orbit

Fig.1. Simple Atom Model

When atoms reach a higher-energy orbital they eventually seek to return to the ground-state energy level. Upon returning to ground-state energy level the excess energy is released in the form of a photon - a particle of light.