A laser is a device that intensifies light. Put in simple terms, the atoms of the laser material serve as energy storehouses. Atoms can only store energy in very specific “packet” sizes. These energy portions are transported in the form of photons. Light of a specific wavelength is created by the photons, which transport a certain, predetermined energy quantity.

If an atom has free storage space for a packet of energy of a certain size and a photon flies by with an energy packet of that exact size, the atom can absorb and store the energy packet the photon is transporting. This is referred to as absorption.

 Once an atom has stored an energy packet, at some point it will emit this energy in the form of a photon. This photon will fly in an undetermined direction. The process described here is called spontaneous emission.

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