L. A. S. E. R. technology allows for the creation of a diverse series of systems capable of emitting a beam of light defined as coherent in space, permitting collimation over time so that the emission spectrum is very narrow (monochromatic) by means of an optical amplification based on a emission process stimulated by electromagnetic radiation, hence the name: Light Amplification (by) Stimulated Emission (of) Radiation. The term has become so widespread that in the English language it has taken on the characteristics of a verb (“to lase”), so that “lasing” indicates the very activity of emission of a laser beam.
In traditional physics, light is considered as a superposition of electromagnetic oscillations. Until the mid-twentieth century, despite efforts to manipulate light in such a way as to make it versatile and functional in different fields of application, it was not possible to counteract the limit of its polychromaticity: optical expedients (such as filters, for example) almost succeeded in giving a coherence to the radiations, but not without considerably attenuating the intensity of the beam.
In reality, not even laser beams are perfectly monochromatic, but are able to concentrate almost all of their energy in a very narrow spectral band and this brings considerable advantages in a wide range of applications.
We can say that it was precisely with the advent of laser that light took on a new role in the industrial world: the enormous potential of this technology immediately began to offer important ideas for application and research.
The parameters of frequency (in Hertz), wavelength (in micrometers), average power and peak power and the pulse energy are used to measure an industrial laser.
The wavelengths that mostly involve laser technology range from 0.3 (UV) to 10 µm (CO2), or rather they cover a range that goes from ultraviolet to visible light up to infrared.
The history of laser undoubtedly began in 1916 with Albert Einstein, who hypothesized that three processes essentially intervene in the formation of an atomic spectral line: spontaneous emission, stimulated emission and absorption. To each of them he associated a coefficient (later called “Einstein’s”), which represents an estimate of the probability that the process takes place.
From these first studies carried out by the genius, we must then wait however until 1950 for the team of C. H. Townes to create the first working device that, in practice, made use of Einstein’s theories: the technology in question was called M. A. S. E. R., which stands for Microwave Amplification by Stimulated Emission of Radiation.
Subsequent studies, derived from a desire to extend the principles of MASER to the field of infrared and visible light, we owe to the multifaceted Theodor H. Maiman who completed the first pulsed ruby laser in 1960.
Since then, the laser has prevailed in many fields and research has been directed towards both the development of new laser sources and the improvement of the characteristics of existing ones.
Authorship of invention of the laser has not yet been attributed with certainty and opinions in this regard profoundly conflict with each other; so much so that the laser has been the subject of a patent dispute for thirty years.
We have already mentioned that it was Theodore H. Maiman who resumed Einstein’s studies: on 16 May 1960, the Californian engineer operated the first working laser in the Hughes Research laboratories in Malibu.
It was a solid-state laser that made use of the ruby crystal, capable of producing a red laser beam with a wavelength of 694nm, a frequency of 4 x 1014 Hz.
Also in 1960, Ali Javan, William R. Bennett and Donald Herriott built the first laser made with helium and neon, called a gas optical MASER, capable of producing an infrared beam.
Three years later in New Jersey, K. Patel developed the carbon dioxide laser at Bell Laboratories.
Among all involved, perhaps the best-known leading figure is physicist Gordon Gould who, following a conversation with Townes, had taken note of the optical use of MASERs and on the use of an open resonator, a detail that later became common in many lasers.
Considering himself the inventor of the laser, Gordon Gould had registered his notes with a notary, but he was not recognized as the author for the invention by the patent office in the legal dispute that arose.
In 1977, he achieved a small success with attribution of the Patent for optical pumping. In the following years, he collaborated in the elaboration of numerous documents that describe the great variety of possible applications of the laser, including heating and vaporization of materials, welding, drilling, cutting and various photochemical applications.
In conclusion, we can say that, although he has never been credited with the invention of the laser, Gordon Gould has collected millions in royalties, both for his subsequent patents and for the studies of other researchers who went on to find all those applications for the laser that we know today.
Lasers make use of an active medium, which has the ability to emit electromagnetic radiation (photons) when activated. The emission wavelength depends on the active medium.
The active medium can be gaseous (for example carbon dioxide, mixture of helium and neon), liquid (solvents, such as methanol, ethanol or ethylene glycol, to which chemical dyes such as coumarin, rhodamine and fluorescein are added) or solid (ruby, neodymium or semiconductors). The pumping system provides energy to the active medium, bringing it to excitation with emission of photons. Excitation can take place through:
The radiations emitted are normally concentrated through an optical cavity with reflective internal walls and a semi-reflective output area. This latter surface is the only one that allows exiting of the beam, which is then worked and repositioned through a series of lenses and mirrors to ensure that the resulting beam has the desired position, concentration and width.
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