Lichtgedanken 04

S C HW E R P U N K T 13 04 | LICHT GEDANKEN Light is what we see: a small section from the spectrum of electromagnetic radiation for which the human body has developed two detectors—the eyes—over the course of evolution. In addition to high-energy radiation in the ultraviolet, X-ray and gamma rang- es, and low-energy radiation, for exam- ple infrared waves, microwaves and radio waves, the range of visible light constitutes only a fraction of the elec- tromagnetic radiation spectrum. Electromagnetic radiation consists of waves. The character of light waves can be demonstrated using the double split experiment. When a ray of light is split into two by a screen, it does not just split into two new rays of light; in- stead it is split into several rays with different levels of brightness. This is due to the wave characteristics of light. The point at which the crest and trough of the wave of the two resulting rays cancel each other out remains dark. The point where the two wave crests intensify one another is light. The dis- tance between the two neighbouring wave crests and troughs represents the wavelength, which is used to clas- sify the electromagnetic radiation. The wavelength of visible light ranges be- tween 380 nanometres (violet light) and 780 nanometres (red light). Particles with zero mass but maximum speed Why do humans perceive this very part of the huge spectrum of electro- magnetic radiation? The answer is a simple one: this part is equivalent to the frequency range in which the sun emits the most intense electromagnet- ic radiation. But there is more to light than that which is described as classic waves. It was back in the 17th century when Isaac Newton stated that light is made up of tiny particles. Albert Ein- stein then explained the photoelectric effect at the beginning of the 20th cen- tury: the energy of light, just as that for other electromagnetic radiation, is quantized in tiny portions known as photons. Thus, light is both waves and particles. In contrast to other compo- nents of matter, for example as elec- trons and protons, light particles have zero mass. They travel at speeds of al- most 300,000 kilometres per second in a vacuum—the maximum speed in the universe. Light is energy, a tool and information On average, the sun emits around 1,300 joules per second per square metre of the earth. Sunlight is the most relia- ble and greatest energy source that we have—utilizing it and storing it is one of the main challenges facing the grow- ing population. Researchers at the Jena Centre for Energy and Environmental Chemistry work with environmentally friendly solar cells and batteries to make energy from sunlight available to applications (p. 16 of this edition). Light is also the foundation of life in gener- al. Plants, algae, and some bacteria use sunlight for photosynthesis to convert carbon dioxide and water into ener- gy-rich organic compounds, e.g. sugar. Life-essential oxygen is a by-product of this process. Living organisms—from single-celled green algae to humans— use the light of the sun to synchronize their internal clocks. Botanists from the Matthias Schleiden Institute at the University of Jena are working to deci- pher how this clock works. Light has always been used as a tool. Nowadays, it is mainly lasers that are used in multiple fields as precision in- struments. Physicists in Jena use spe- cially pulsed laser light, which releases enormous amounts of energy in scarce- ly conceivable short flashes. Laser puls- es lasting just a few attoseconds (one quintillionth of a second) can be used to reproduce and thus decode ultrafast chemical processes (p. 20). The pulses that physicists use to light up air and thus display three-dimen- sional objects in free space are only fractionally longer, in the femtosecond range (p. 24). Laser beams are also be- ing used to digitalize antique clay tab- lets to present the millennia-old cunei- form scripts from Mesopotamia to the public in a contemporary way (p. 26). Light is information. Electromagnetic radiation from space that we detect on earth can provide information about distant stars and galaxies. Astrophys- icists from the University’s observatory look into the depths of the universe, and analyse starlight (p. 34) and star- dust (p. 40). Thus, light is not just illuminating the macrocosm. Light also provides in- sights into the microcosm: either living cells, nanoparticles, meteorite rock or polymer layer, a huge range of micro- scopic procedures are turning minute details into fascinating pictures, as demonstrated by the photo gallery in this edition (p. 30). Sources of enlightenment Science sheds »light on the dark«. Researchers have »a light-bulb moment«. The list of light-based meta­ phors in science goes on and on, and even includes the title of this research magazine—after all, LICHT­ GEDANKEN stands for illuminating thoughts, enlightened spirit and knowledge. Light, however, is more than just symbolism. Light, in all of its many facets, is one of the focuses of research at the Friedrich Schiller Uni­ versity Jena that brings together physicists, materials scientists, chemists, biologists, medics and computer scientists, and is not just limited to physical phenomena. BY UTE SCHÖNFELDER F E AT U R E