Laser stands for Light Amplification by the Stimulated Emission of Radiation. Lasers work by producing an intense beam of bright light that travels in one direction. The laser has the unique ability to produce one specific color or wavelength of light, which can be varied in its intensity and pulse duration. The newest laser systems have become remarkably precise and selective, allowing treatment results and safety levels not previously available.
All lasers contain an energized substance that can increase the intensity of light that passes through it. This substance is called the amplifying medium and it can be a solid, a liquid or a gas. Einstein can be considered as the father of the laser. 80 years ago he postulated photons and stimulated emission and won the Nobel Prize for related research on the photoelectric effect. This section discusses the historical evolution from microwave lasers to optical lasers and finally to x-ray lasers and lasers discovered in space.
Some theorists were on the right track, especially Planck, who proposed that nature acted by using “quanta” of energy. But it was the young, unknown Albert Einstein who explained everything and started the field of quantum mechanics with his paper on the photoelectric effect. Einstein showed that light does not consist of continuous waves, nor of small, hard particles. Instead, it exists as bundles of wave energy called photons. Each photon has an energy that corresponds to the frequency of the waves in the bundle.
The higher the frequency (the bluer the color), the greater the energy carried by that bundle. Einstein’s Nobel Prize was not awarded for either one of his relativity theories – the Nobel Committee thought them too speculative at the time. Rather Einstein won the prize for explaining the photoelectric effect. Two of Einstein’s 1905 papers were on the theory of atoms and molecules, yet there were still many scientists in 1905 who did not believe in atoms or molecules. There are many lasers such as the carbon dioxide laser or CO2 laser, and many forms of this too.
In contrast to the old carbon dioxide lasers, the newest generation of the CO2 laser delivers short bursts of extremely high-energy laser light. In a neodymium YAG (Nd:YAG) laser, the amplifying medium is a rod of yttrium aluminum garnate (YAG) containing neodymium ions. In a dye laser, it is a solution of a fluorescent dye in a solvent such as methanol. In a helium-neon laser, it is a mixture of the gases helium and neon. In a laser diode, it is a thin layer of semiconductor material sandwiched between other semiconductor layers.
The factor by which the intensity of the light is increased by the amplifying medium is known as the gain. The gain is not a constant for a particular type of medium. It depends critically upon the wavelength of the incoming light, the length of the amplifying medium and also upon the extent to which the amplifying medium has been energized. In order to increase the intensity of the light, we would need to energize the amplifying medium, or in other terms, pumping. There are several ways of pumping an amplifying medium.
When the amplifying medium is a solid, pumping is usually achieved by irradiating it with intense light. This light is absorbed by atoms or ions within the medium and raises them into higher energy states. Often, the pumping light comes from xenon-filled flash tubes that are positioned alongside the amplifying medium. Passing a high voltage electric discharge through the flash tubes causes them to emit an intense flash of white light, some of which is absorbed by the amplifying medium. A laser that is pumped in this way will have a pulsed output.
Pumping an amplifying medium by irradiating it with intense light is usually referred to optical pumping. In some cases, the source of the pumping light is another laser. Gaseous amplifying media have to be contained in some form of enclosure or tube and are often pumped by passing an electric discharge through the medium itself. The mechanism by which this elevates atoms or molecules in the gas to higher energy states depends upon the gas that is being excited and is often complex. In many gas lasers, the end windows of the laser tube are inclined at an angle and they are referred to as brewster windows.
Brewster windows are able to transmit a beam that is polarized in the plane of the diagram without losses due to reflection. Such a laser would have an output beam that is polarized. This remarkable technology is used in many fields such as surgery, military purposes, and accurate measurement in both speed and distance. Many people these days spend thousands on their low self-images by using laser surgery to enhance their looks and rid them of their blemishes. In a military point of view, lasers are a potential weapon and an extremely useful defense mechanism.
Even now, sci-fi tales of the laser gun have been told, we are not far off to its development. The laser has been used in the medical field as well. This revolutionary technology actually vaporizes the undesired skin tissue, one layer at a time, revealing fresh skin underneath. The CO2 lasers highly focused aim enables the dermatological surgeon to gently remove the skins surface with a low risk of scarring and complications in properly selected patients. The laser beam can gently vaporize and remove wrinkles, scars and blemishes, seal blood vessels or cut skin tissue.
Lasers can also be used in defense. For example the use of the laser attatched onto a satellite would enable us to destroy incoming or airborne missiles before they reach their target. Even though our government wasted millions of taxpayers money on the laser defense systems, they could waste more on developing new and improved satellites, or maybe even working ones too. An alternate technique for boost-phase interception requires that space interceptors be constantly over the enemy territory.
Keeping a sufficient number of interceptors continuously ready for action and over the enemy territory is costly, although not impossible. Advances in technology — lasers, neutral particle beams, non-nuclear “smart” weapons — make it possible to attack missiles as they rise. The laser is also a key tool used in measurement as well. The use of measuring with a laser is used in many fields such as measuring the distance between objects to even the speed of gases. An instrument called the iterferometer is used to measure very small changes in distance .
Todays scientist on the San Adreas fault is actually using this instrument in order to find slight movements created by the fault. Just like radar the laser can be used to measure long distances as well, but a even more accurately. Prior to the astronauts arrival on the moon, a mirror has been left in order to judge the distance between the moon and the earth by pulses of laser light aimed at the mirror. The reflection back is then divided by half, just like radar, to find the distance.