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History of lasers
What is a laser ?
You could compare the laser hardware with an air compressor.The comparison looks a bit stupid but air is compressed by mechanical interaction into a buffer tank ready for use.
The laser is compressing light into a burst of short pulses or even a continuous stream off light.The creation/compression of this light is done in such a way that the light gets specific characteristics. Normal light is disperse and travels in every direction like a radiating sfere. Light is in fact a traveling electromagnetic wave which can travel true air,water and space.
White light is a composure of a lot of different wavelengths falling on surfaces and objects which will absorb specific wavelengths to create a surface color.
Again laser light is a special case of light because it consist of one primal wavelength, it has one moving direction and all waves are a phase travelling true air. Because of the one direction wave characteristic this wave is having a concentrated beam of energy. With optical element like lenses and beam collimators one can concentrate and tailor pinpoint the amount of energy to a surface or let it travel true air, space and water.
How is laser light created ?
Laser light is an electromagnetic wave created by exiting a specific lasing material. Mostly this is Yttrium aluminium garnet base, being highly purified glass doped with a laser-active rare-earth ion such as Nd3+ (neodymium), Yb3+ (ytterbium) or Er3+ (erbium). This lasing material can be a cristal rod or a fiber.
These doping elements have electrons moving around there mass core witch can be exited to there next electron level.To do so we need the exact amount of energy (eV) to let this electron jump to the next level. This amount of energy is brought by an external light source (flash lamp, lower grade laser or diodes) pumping energy into the glass garnet tube doped with the right element and getting exited by this external energy amount.The electron jumps to the next energy level but this is only a momentary stable position as all system try to get a minimal energetic status. The electron falls back to his original energy position by releasing his energy under the form of an electromagnetic wave called a photon.This is the first stage reaction. These photons are travelling in an opto-electro system and bouncing back and forth. If the falling back of an electron is hit by a traveling photon the system is creating an extra photon, now we are creating more photons and more energy into the system.This is in basic the creation of a bunch of photons with all the same wavelength and equal energy level closed in an optical material being a YAG rod or a fiber. Now the photon are guided towards the exit of the optical laser pump injected in a transport fiber or freely true air.
YAG versus Fiber laser ?
We distinguished in history tree types of lasers :
Gas lasers (CO2) (old type)
Solid state lasers also called YAG (old type)
fiber lasers
The most know and oldest laser is the gas laser so called CO2 laser. This laser could deliver high energy quantities but need maintenance and regularly gas replacement.Further the high energetic light beam could not be transported over a transport fiber, so reflection mirrors where used.
The solid state or YAG laser was a well used laser sources by research labs over the world. Its development was huge but this type of laser source needed a lot of attention. Due to the construction,the cooling was always a limiting factor to really push thru in industrial applications which required 24/24 7 days a week production. They are very sensitive to vibrations and temperature changes.But they went very far and still important in a lot of applications.They can deliver high puls energy and a flat top energy distribution. The puls frequencies are limited and the puls duration is depending on the frequency.
The fiber laser is in fact also a solid state laser but a special case, due to the fact the photons are created in one part of the fiber with several pumping diodes at the beginning.After the laser light creation in the first section all the light strings are coupled into one transport fiber.So the laser light is always staying in a fibre which results in a very high energy efficiency, low cooling, high laser light quality and electronically tunable in varies ways.
Pulsed versus continuous ?
The above principals are used to create pulsed and continuous wave lasers. By pulsing the external energy to make the electron jump we can create a discontinue pulsed laser beam. Here we can compare again with our air compressor. By compressing the light in a short time delay we can generate high energy pulses . A 1mj pulse can be compressed in a 100 nanosecond delay creating 10KW of peak power. This can be variated in every direction opening complete new application fields like surface structuring till eye surgery.
Pulsed laser are more expensive than continuous wave lasers, as long you choose for fiber lasers you have no maintenance to the source. So fiber lasers are you choice for industrial applications.
This Month in Physics History
December 1958: Invention of the Laser
Charles Townes
Arthur Schawlow
Every now and then, a scientific breakthrough occurs that has a revolutionary impact on daily life. One example of this is the invention of the laser, which stands for light amplification by stimulated emission of radiation. Few people realized at the time of its invention that it would prove to be such a useful (and lucrative) device, but the laser ultimately launched a new scientific field and opened the door to what is today a multi-billion dollar industry.
The principle of the laser dates back to 1917, when Albert Einstein first described the theory of stimulated emission, but the practical device has its roots in the 1940s and early 1950s, particularly the work on microwave spectroscopy-a powerful tool for discovering the characteristics of a wide variety of molecules-by physicists Charles Townes, Arthur Schawlow and others, and the subsequent invention of the maser (microwave amplification by stimulated emission of radiation).
After World War II had ended, Townes was intrigued by the possibility of using stimulated emission to probe gases for molecular spectroscopy. As the wavelength of the microwave radiation grew shorter, its interactions with molecules became stronger, making it a more powerful spectroscopic tool. Townes and colleagues at Columbia University demonstrated a working maser in 1953, two years after similar devices were independently invented by researchers at the University of Maryland and Lebedev Laboratories in Moscow.
However, Townes realized that the wavelengths of infrared and optical light, because they were shorter, would be even more powerful tools for spectroscopy, and mentioned the idea of extending the maser principle to shorter wavelengths to Schawlow while visiting the latter at Bell Labs. Schawlow came up with the idea of arranging a set of mirrors, one on each end of the device's cavity, to bounce the light back and forth, thus eliminating the amplification of any beams bouncing in other directions. He thought that this would enable them to adjust the dimensions so that the laser would only have one frequency which could be selected within a given line width, and that the mirror size could be adjusted so that even slight off axis motion could be damped. He also suggested using certain solid state materials for the lasers.
Eight months later, the two men wrote a paper on the proof of concept for their work, published in the December 1958 issue of the Physical Review (Vol. 112, No. 6, pp. 1940-1949), and received a patent for the invention of the laser two years later-the same year the first working laser was built by Theodore Maiman at Hughes Aircraft Company. Townes was a co-recipient of the 1964 Nobel Prize in Physics for his fundamental work in quantum electronics that provided the basis of the maser/laser principle. Schawlow's recognition came much later; he shared the 1981 Nobel Prize for his contributions to the development of laser spectroscopy.
While Townes and Schawlow are the names most often associated with the invention of the laser because of their 1958 paper and subsequent patent, numerous others made vital contributions. Perhaps that is why the question of who really invented the laser has proven to be a fairly litigious one, due in large part to the efforts of Gordon Gould, a scientist at Columbia and later with Technical Research Group (TRG), to earn patent rights based on his research notebook. An entry on his initial ideas for the laser was dated and notarized November 1957. Gould fought for decades, and in 1973 the US Court of Customs and Patent Appeals ruled that the original patent awarded to Schawlow and Townes was too general, and did not supply enough information to create certain key components. Gould was finally granted patent rights, receiving his fourth and final patent on lasers in 1988.
Although it was a remarkable technical breakthrough, in its early years the laser did not have many practical applications, since it was not powerful enough for use in beam-based weaponry, and its ability to transmit information through the atmosphere was severely hampered by its inability to penetrate clouds and rain. But it didn't take long for researchers to develop the first laser sighting systems and the first tools for laser surgery.
Today, lasers are ubiquitous in the commercial marketplace, used in CD players, in corrective eye surgery, tattoo removal, industrial assembly lines, supermarket scanners, optical communications, and optical data storage.
Further Reading:
source APS advandce phycics
Bromberg, Joan L., "The Birth of the Laser", Physics Today, October 1988, pp. 26-33.
"A Laser Patent That Upsets the Industry," Business Week, 24 October 1977, pp. 121-130.
Hecht, Jeff, "Winning the Laser Patent War," Laser Focus World, December 1994, pp. 49-51.
