LASER IS THE MAJOR INVENTIONS IN THE 21ST CENTURY
The name LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation. In 1917, Albert Einstein first theorized about the process which makes lasers possible called "Stimulated Emission."
In 1954, CharlesTowns and Arthur Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - the maser was invented before the (optical) laser, however, the technology is very close but not a visible light laser.
In 1958, Towns and Arthur Schawlow theorized about a visible laser, an invention that would use infrared and/or visible spectrum light.
Ted Maiman invented the ruby laser (light laser) considered to be the first successful optical laser. Many historians claim that Maiman invented the first optical laser, however, there is some controversy.
Gordon Gould was the first person to use the word "laser". There is good reason to believe that Gordon Gould made the first light laser. Gould was a doctoral student at ColumbiaUniversity under CharlesTowns, the inventor of the maser. Gould was inspired to build his optical laser starting in 1958. He failed to file for a patent his invention until 1959. As a result, Gould's patent was refused and his technology was exploited by others. It took until 1977 for Gould to finally win his patent war and recieve his first patent for the laser.
The first gas laser (helium neon laser) was invented by Ali Javan.
Albert Einstein
Albert Einstein was born in Germany in 1879. He enjoyed classical music and played the violin. One story Einstein liked to tell about his childhood was of a wonder he saw when he was four or five years old: a magnetic compass. The needle's invariable northward swing, guided by an invisible force, profoundly impressed the child. The compass convinced him that there had to be "something behind things, something deeply hidden."
Even as a small boy Albert Einstein was self-sufficient and thoughtful. According to family legend he was a slow talker, pausing to consider what he would say. His sister remembered the concentration and perseverance with which he would build houses of cards.
In 1933, he joined the staff of the newly created Institute for Advanced Study in Princeton, New Jersey. He accepted this position for life, living there until his death. Einstein is probably familiar to most people for his mathematical equation about the nature of energy, E = MC2.
Albert Einstein wrote a paper with a new understanding of the structure of light. He argued that light can act as though it consists of discrete, independent particles of energy, in some ways like the particles of a gas. A few years before, Max Planck's work had contained the first suggestion of a discreteness in energy, but Einstein went far beyond this. His revolutionary proposal seemed to contradict the universally accepted theory that light consists of smoothly oscillating electromagnetic waves. But Einstein showed that light quanta, as he called the particles of energy, could help to explain phenomena being studied by experimental physicists. For example, he made clear how light ejects electrons from metals.
There was a well-known kinetic energy theory that explained heat as an effect of the ceaseless motion of atoms; Einstein proposed a way to put the theory to a new and crucial experimental test. If tiny but visible particles were suspended in a liquid, he said, the irregular bombardment by the liquid's invisible atoms should cause the suspended particles to carry out a random jittering dance. One should be able to observe this through a microscope, and if the predicted motion were not seen, the whole kinetic theory would be in grave danger. But just such a random dance of microscopic particles had long since been observed. Now the motion was explained in detail. Albert Einstein had reinforced the kinetic theory, and he had created a powerful new tool for studying the movement of atoms.
Uses of Laser:
Lasers are everywhere. In your computer CD-ROM, your CD player, at supermarket checkouts and in laser light shows. As far as technologies go, they have been one of the inventions most quickly absorbed into society.
The laser was invented in 1958 and the first working ruby laser began operation in 1960 and was a heavy complicated piece of machinery. Now some lasers are the size of a pinhead and cost a few dollars to produce.
Laser Light is Special
The light we see is usually a mixture of all the different colors of light, bouncing off objects around us and eventually ending up at our eyes. Laser light is quite different for a few reasons. The most important are listed below and for each one, there is a simplified version of the properties of lasers and then a more exact but more complex version.
1. Laser light is monochromatic
Simple version: This means that the light coming from a laser is all one color. If we split up white light, we can see all the colors of the rainbow but if we try to split up laser light, we find there is nothing except the single laser color.
Complex version: Laser light is actually a small range of colors, far too similar to distinguish with the human eye and that is why we often say it is one color.
2. Laser light is unidirectional
Simple version:Light from a bulb or most other sources of light spreads out in many directions. Laser light is quite different in that all the light is directed the same way. Beams of laser light can be extremely tight over quite long distances.
Complex version: Laser light will always spread out a bit but it forms a much tighter beam than any other form of light.
3. Laser light is coherent
Complex version:This is a little harder to explain. Light can be considered to be act like waves in some circumstances but particles in other circumstances. One way to think about laser light is to think of particles of light that have a wave-like nature. The important thing about laser light is that the wave parts of every particle are lined up perfectly. This is called coherent light. It isn't so important for laser pointers and laser light shows but absolutely vital for many uses of lasers.
About the Structure of Atoms
To understand how a laser works, we need to know a bit about what atoms are like so that we can understand how light interacts with atoms and then how that light becomes laser light.
1. Electrons orbit a nucleus
Simple version: You can think of atoms as being made of electrons orbiting around a central nucleus. The electrons can only orbit at certain places because of the rules of quantum mechanics. Electrons will stay in orbit until they are knocked out of place. This could happen by zapping them with electricity or by shining light on them. The electrons orbit around at different distances out from the nucleus, like planets orbiting the sun.
Simple version / Complex versionComplex version: Electrons are not like little planets at all. In reality they are a spread out fuzz surrounding the nucleus. However, each electron has a very particular type of fuzzy positioning around the nucleus that corresponds to a particular amount of energy. The details of electrons are dictated by the theory of quantum physics.
Light Interacts with Atoms
Light can interact with atoms in a variety of ways but the most important thing to know is that a particle of light, or photon, can give its energy to an electron, forcing it jump to a higher energy orbit. The color of the photon needed to do this depends on the energy separation of the orbits (also called energy levels).
We can represent this with a diagram. This first one shows an electron absorbing a photon and jumping to a higher energy level. We draw the energies of the levels as straight lines here to save having to draw the whole atom again.
The opposite of this process can also occur. The electron can suddenly drop down to a lower energy level at random (spontaneous emission) and when it does, it gives off a photon.
These aren't the only processes that go on when a photon interacts with an atom but it is the starting point. There is another special type of interaction that we will look at next.
The "SE" part of LASER
The whole idea of a laser depends on a particular interaction between light and atoms. The process is referred to in the name of a laser. LASER stands for Light Amplification by Stimulated Emission of Radiation. The meaning of this is that light is made more intense or amplified by a particular process involving radiation (which also refers to light). It is the SE or stimulated emission part that is critically important. In this process, an excited atom (one with the electron in a high energy level) is hit by a photon. That photon causes another photon to be emitted as the electron drops down to the lower energy level. The two photons that are given out are identical and exactly in step with each other.
Lasers Work
Laser light has several features that are significantly different from white light. To begin with, light from most sources spreads out as it travels, so that much less light hits a given area as the distance from the light source increases. Laser light travels as a parallel beam and spreads very little.
Furthermore, laser light is monochromatic and coherent. White light is a jumble of colored light waves. Each color has a different wavelength. If all the wavelengths but one are filtered out, the remaining light is monochromatic. If these waves are all parallel to one another, they are also coherent: the waves travel in a definite phase relationship with one another. In the case of laser light, the wave crests coincide and the troughs coincide. The waves all reinforce one another. It is the monochromaticity and coherency of laser light that makes it ideal for recording data on optical media such as a CD as well as use as a light source for long haul fiber-optic communications.
The laser uses a process called stimulated emission to amplify light waves. (One method of amplification of an electromagnetic beam is to produce additional waves that travel in step with that beam.) A substance normally gives off light by spontaneous emission. One of the electrons of an atom absorbs energy. While it possesses this energy, the atom is in an excited state. If the electron gives off this excess energy (in the form of electromagnetic radiation such as light) with no outside impetus, spontaneous emission has occurred.
If a wave emitted by one excited atom strikes another, it stimulates the second atom to emit energy in the form of a second wave that travels parallel to and in step with the first wave. This stimulated emission results in amplification of the first wave. If the two waves strike other excited atoms, a large coherent beam builds up. But if they strike unexcited atoms, they are simply absorbed, and the amplification is then lost. In the case of normal matter on Earth, the great majority of atoms are not excited. As more than the usual number of atoms become excited, the probability increases that stimulated emission rather than absorption will take place.
Laser resurfacing:
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A. DinakaranV. Rajesh R.Ganesh K. ArumugamK. Kathick
BY VIII STD FROM T.V. NAGAR HIGH SCHOOL