In the beginning there was Albert Einstein. In the early 20th century, the famous physicist took a close look at the phenomenon of light in his research, with one of his reflections revolving around the question of whether light could possibly consist of individual “energy packages” The quantum hypothesis by Planck was already known at this point. With the “principle of stimulated emission” resulting from these reflections, Einstein laid the foundation for the development of what we now know as laser technology. However, it was more than 40 years before the physicist Charles Townes put Einstein’s theoretical foundations into practice in terms of stimulated emission. Stimulated emission means that a laser-active medium can temporarily store energy by, for example, irradiation with light. This stored energy can be “forcefully” retrieved - thus the laser beam is amplified.
In the late 1940s, Townes experimented with microwaves and in 1951 he constructed a device that could generate and amplify these microwaves. Based on Einstein’s theory, Townes gave his discovery the name “Maser” - an acronym for “microwave amplification by stimulated emission of radiation”. What was possible with microwaves, i.e. the amplification by stimulated emission of radiation, should also be feasible for infrared or conventional light, knowing that as the wavelength decreases, the cost of constructing a laser greatly increases.
However, it was a few more years before a “light amplification by stimulated emission of radiation” (laser) was created from this assumption. At this stage all materials required to build a laser were known and available. The first laser, consisting of a flash lamp, a synthetically manufactured ruby doped with chromium and a metal sleeve, was finally created in the hands of physicist Theodore Maiman in 1960. However, this discovery was initially overlooked by experts. When Maiman wanted to have his findings printed in a journal, the editors refused to accept the text - the possibility of combining coherent light beams with high colour purity seemed trivial.
Only in years to come did it become clear what was possible with laser technology, with a wide range of laser systems currently in existence. All these laser machines are based on the principle that Einstein predicted in 1917 and Theodore Maiman experimentally demonstrated in 1960.
Once the principle of laser technology was known, the speed of development suddenly increased. As early as 1961, a ruby laser was used in opthalmology in the USA. Particularly in medicine, the invention quickly became an all-rounder and heralded the age of minimally invasive surgery.
In 1962, the semiconductor laser was also being researched in the USA. This ultra-compact laser can be used in continuous operation and is so easy to integrate into electronic components.
For a high beam power more suited to industrial use, the first CO2 laser was invented by Kumar Patel in 1964. Since then, this laser source has been used to cut, drill, mark or weld metals. Even today CO2 lasers are an indispensable part of modern production, more than 50 years after their discovery.
From 1966, laser physics became colourful. With the development of the dye laser, the wavelength of laser light along a spectrum of fluorescent dyes is freely selectable. Since then, dye lasers have mainly been used in spectroscopy.
While the popularity of CDs and CD-ROMs has declined, their creation was possible from 1972 onwards. With the invention of the semiconductor laser, laser physics finally penetrated the mass market. From the 1980s, the new technology of photonics, a combination of laser diodes and glass fiber transmission, became suitable for mass production and today ensures high data speeds on the Internet.
Finally, in 1998, the laser diodes became smaller than the wavelength of light that they emit. Since then, nanolasers have been used in data processing, medicine or optical signal transmission.
Lasers are used for a wide range of different applications today.
In the medical sector, laser beams can be used to remove tumour tissue in the field of laser-induced thermotherapy, and are used to attach detaching retina or treat varicose veins.
In cosmetics, lasers can be used for tattoo removal or for permanent hair removal through epilation. Due to the high heat radiation and the reaction products of the thermally altered/destroyed colour pigments, the use of lasers in removing tattoos is risky. Despite this, the technology has become a standard in the industry.
In tunnel construction, laser machines provide a directional beam that makes the extremely precise tunnelling of tunnelling machines possible.
Laser technology appears in all walks of life and is present in our everyday lives. The light beam burns CDs, prints paper or scans our purchases at the supermarket checkout. Laser pointers are also an important tool for presenters.
For manufacturing purposes, metals can be drilled, cut, marked or welded with a laser. Lasers are extremely precise even with the tightest geometries, where conventional processing methods such as turning or milling would fail.
In research, lasers are used in mass spectrometry to excite higher atomic or molecular states or are used to study the atmosphere.
The idea of energy production through lasers is still in its infancy. In the field of nuclear fusion, high-power lasers produce extremely dense plasmas of high particle density and temperatures up to 1 million degrees. However, it is still not clear when a stable, exothermic nuclear fusion can be established.