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International Day of Light

The world's first 'Day of Light'

On 16 May we are celebrating "World Day of Light" for the first time. The action day proclaimed by UNESCO is to draw attention to the central role of light in science, culture, art, education, sustainable development, medicine, communication and energy. Numerous events and exhibitions are taking place in Germany. For example, you can see the first laser, built by Theodore Maiman, at the Max Planck Institute of Quantum Optics in Garching. Further information on "World Day of Light" can be found here.

Nothing works without light - discoveries and innovations in the field of light

There are few things that at first glance seem so obvious and clear and at second glance as diverse and complex as light. Albert Einstein already commented: "Fifty years of intensive reflection have not brought me closer to the answer to the question 'What is light?' Of course, every dimwit today imagines he knows the answer. But he's mistaken."

In the beginning was the question: waves or particles?

For several hundred years man has been trying to get to the bottom of the nature of light. The decisive question is whether light consists of waves or particles. The English physicist Isaac Newton established his "corpuscle theory" in 1672: Accordingly, light consists of small corpuscles (particles) which are pushed through space in a straight line by the sun. The light particles can bounce off obstacles and change the direction of their trajectory. On the other hand, there were phenomena with light that only occur with waves: Interference and diffraction. This prompted Newton's contemporary Christiaan Huygens to regard light as a wave. But it was not until 1802 that the English physician Thomas Young was able to prove the wave characteristics of light.

Around 1900, the German physicist and director of the newly created Physikalisch-Technische Reichsanstalt Max Planck established his "Quantenphysik". Planck discovered during experiments that the light of an incandescent lamp is not emitted in waves, but in the smallest, indivisible energy packages, the so-called quanta.

Finally, Albert Einstein discovered the photoelectric effect in 1905: This means that electrons are released from a metal plate irradiated with short-wave light. The photons penetrate the metal and release all their energy to the electrons on the metal surface. Albert Einstein received his Nobel Prize in 1922 for explaining this effect and not for his much better known theory of relativity. The photoelectric effect is used, for example, by semiconductors, image converters, digital cameras and solar cells. The laser's mode of operation is also derived from the photoelectric effect, without which many devices in consumer electronics, information technology, analytics or medical technology would not exist.

Race for the first laser

Abbildung eines Masers

Illustration from patent specification US 2929922 A, "Masers to the Maser Communications System", 1960

Here, too, Einstein is regarded as a mastermind, after all, as he wrote to a friend in 1916, "a splendid light had risen". Thus, with his thesis of "stimulated emission" of light, he laid the theoretical foundations for the laser. The emission of a photon (light particle) is triggered by another photon.

However, it was not until the 1950s that various research groups developed the first independent MASER (Microwave Amplification by Stimulated Emission of Radiation). The technology is similar to that of the laser, but uses microwaves instead of light. Such a device can be used, for example, to receive signals from space probes billions of kilometres away. These signals can be made audible by focusing and amplifying microwaves.

Illustration from patent specification US 3 353 115 A, "Ruby Laser Systems" 1967

At the beginning of the 1960s, numerous laboratories worldwide were working on transferring the technology to light waves. While a team around Arthur Schawlow and Wolfgang Kaiser at Bell Laboratories relied on helium-neon gas as the amplifying medium for the light waves, Theodore Maiman experimented at Hughes Research Laboratories with ruby crystals, i.e. solids. On 16 May 1960 Maiman won the race. For the first time in the world, he succeeded in detecting a stimulated amplification of visible light in a ruby crystal. In November 1967 he was granted the patent US 3 353 115 A for this.

From 1960 the development of the laser progressed in giant steps: within a few years, fiber lasers, helium-neon lasers, semiconductor lasers, Nd:YAG lasers and CO2 lasers were developed and registered for patent.

What Theodore Maiman could not foresee: laser technology offers numerous applications ranging from simple light pointers, distance measuring devices, cutting and welding tools, the playback of optical storage media such as CDs, DVDs and Blu-ray Discs, message transmission, medical devices to high-speed Internet via laser.

Picture 1: iStock.com/schaffert, Bild 2: DPMA, Bild 3: DPMA

Last updated: 14/08/18 

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