This webpage contains an interactive simulation that allows users to explore the physics behind lasers. Two simulations are available, the first showing the optical excitation of a single atom and the second showing the result of interactions between multiple atoms. The single atom simulation allows users to view a model atom absorbing and releasing photons. One and two energy level models can be selected along with the intensity the incoming radiation and the radiative lifetimes of the levels. The multiple atom simulation shows the population inversion and build-up of photons that can lead to lasing. Users can also control the energy levels of atoms and the reflectivity of the mirrors. The internal and output power production is shown. A link is included to a picture of a real laser, allowing users to compare the parts of the simulation to a real world example.