What principle does light work on?

How does a laser work?

Atoms can emit light - for example whenever they have been supplied with additional energy by impact or light. Because particles give up the excess again and again; for example by getting rid of the energy in the form of a light wave.

In a fluorescent tube, mercury atoms are supplied with additional energy by electron bombardment, which they later release by emitting light. According to the laws of quantum physics, the emission of light takes place completely randomly. Until it is sent, it is completely indeterminate in which direction the light is emitted, or also when it will happen. Nature decides that spontaneously. This is the reason for the name of the effect: the spontaneous emission.

Light amplification with lasers: stimulated emission

Stimulated emission from light and atomic lasers

An atom with excess energy would spontaneously emit light after some time without further action, in which only the energy is fixed. This changes when it is shone with a light wave of the corresponding energy. Then there is a higher probability that the atom will simply copy the rest of the properties of the wave: It then emits light that oscillates in time with the original and propagates in the same direction.

In contrast to spontaneous emission, this effect is called stimulated emission. This effect ensures the light amplification in the laser and this is where the name comes from:Light Amplification by Stimulated Emission of Radiation.

Countless “copies” are made from just a few light waves. To do this, however, the light waves have to be guided past the atoms again and again. This is done with the help of mirrors. The light waves are caught in them - just in such a way that the individual waves lie on top of one another and vibrate in unison. Such a structure is called a standing wave.

But of course the atoms also have to be constantly supplied with new energy, for example with the help of a bright lamp. Lasers only work when there are more atoms with additional energy than without. This is an unnatural state called population inversion.

In summary, this means: A laser must be constantly supplied with energy from the outside in order to bring its atoms into an excited state. The atoms repeatedly fall into the state of low energy and give off the excess to the laser wave trains. One of the two mirrors is partially transparent so that part of the light can leave the laser. In this way the laser loses energy; and humans gain laser light.

The discovery of the principle

Albert Einstein laid the theoretical foundations for the laser in 1917. It was then that he discovered what is known as stimulated emission. But it wasn't until the 1950s that physicist Charles H. Townes showed that an extraordinary light source could be built with the help of stimulated emission. For this he was awarded the Nobel Prize in 1964.

The American physicist Theodore H. Maiman generated the first laser beam in 1960. At that time, a ruby ​​crystal was used as the laser medium. Two years later Maiman went into business for himself and founded the Korad Corporation, which deals with the development and manufacture of lasers.