The name LASER is an acronym for Light Amplification by the Stimulated Emission of Radiation.
Lights are really a electromagnetic waves. Each wave has brightness and color, and vibrates at a certain angle, so-called polarizations. These are also true for lasers light but it is more parallel than any other light source. Every parts of the beam have (almost) the exact same directions and the beams will therefore diverge very little. With the good laser an object at a distance of 1 km (0.8 mile) can be illuminated with about 65 mm in radius.
As these is so parallel it can also be focused to very small diameters where the concentrations of these light energies becomes so great that you can t cut, drill or turn with the beams. This also make them impossible to illuminates and examines very tiny details. It is the property that is used for operation appliances and in DVD players.
These are also be made very monochromatic, that just one light wavelength is present. These are not the cases with ordinary light sources. White light contain the colours in these spectrum, but even a color light, such as a blue LED contain a continuous interval.
Laser light emissions are not usually very weak when it comes to energy content. Very powerful lasers of the kinds that uses in a laser show do not give of most light that an ordinary road light.
Before the Laser there was the Maser
In 1955, Charlee Townes and Arvin Schawlow invented the maser (microwave amplification by stimulated emission of radiation), using ammonia gas and microwave radiation - these masers were invented before the lasers. The technologies are very close but do use a visible light. The masers were used to amplify radio signals and ultrasensitives detectors for space researches.
Many materials can be used as lasers. Like the ruby laser, emits shortest pulses of laser lights. Other, like neither helium-neon gas lasers nor liquid dye lasers emit a continuous beam of light.
Laser is possible due to the way light interact with the electrons. Electron may be present at specific energies levels or states characteristics of the particular atoms or molecules. These energy levels could imagine as ring and orbit around the nucleus. Electron at outer ring is at high energy levels than those in inner ring. Electrons can be jumped up to higher energy levels by the injections of energy. When these electrons drop from outer to inner level, excess energy is given as light. These wavelengths or colors of the emitted light are precisely related to these amounts of energy release. Depending on the particulars laser material being used, specifics wavelength of lights are absorbed and specific wavelengths are emitted.
In the cylinder, a fully reflected mirror placed on end and a partially reflect mirror on the other. High-intensity lamps are spiraling around the ruby cylinder and provide a flash of white lights that trigger the laser. The green and blue wavelengths in the flash excite electrons in the atoms to a higher energy level. On return to the original state, the electron are emitting their characteristics in ruby-blue light. The mirrors are reflecting many of this light back and forth inside the ruby crystal, stimulating other excited chromium atoms to produce more red light, until the light pulse builds up to high power and drains the energy stored in the crystal. High-voltage electricity causes the quartz flash tubes on emit an intense burst of light, exciting some of the atoms in the ruby crystal to more energy levels. At a specific energy level, some atoms emit particles of light called photons. First the particles are emitted in many directions. Particles from one atom stimulate emission of photons from other atoms and the light intensities are more rapidly amplified. Mirrors at every end are reflecting the photons back and forth, continuous process of stimulated emission and amplification. The photons leave through the partially silvered mirror at one end. It is a laser light.
EINSTEIN THEORY OF LASER
As Einstein did not discovered the laser, but still his work lay the foundation. That was Einstein who gave out that stimulated emissions of radiation could happen within spontaneous emission. He used his photon mathematics to examine the case of a large collection of atoms full of excess energy and ready to emit a photon at some random time in a random direction. If a stray photon passes by, then the atoms are stimulated by its presence to emit their photons early. More remarkably, the emitted photons go in the same direction and have exactly the same frequency as the original photon. Moreover as the small crowd of identical particles is moving through the rest of the atoms, large number of photons will have to leave their atoms early.
It took to invent the laser was for someone to find the right kind of atoms and to add reflecting mirrors to help the stimulated emission along .The acronym LASER means Light Amplification by (using Einstein's ideas about) Stimulated Emission of Radiation.
Another type's of photo-conjugated electron transits in an atom is stimulated emission. Suppose an electron is in a higher energy level and a photon comes along with energy equal to the difference between the electron's energy and a lower energy. Then the particle will stimulate the electron to fall into a low energy state, therefore emitting a particle.
The ejected photons have the same energy as the original photon, and viewed as waves we will then have two waves emerging from the atom in phase with the same frequency. Such waves will constructively interfere, leading to a more intense wave. This is the principle behind the laser light. In a laser atoms are kept in an excited state by pumping the lasers, and some photons are inserted. This causes some atoms to undergo stimulated emission, and the resulting photons cause other atoms to undergo stimulated emission, leading to a chain reaction. The resultant light is very intense and coherent (composed of one frequency), and can be easily focused.
TYPES OF LASER
ON THE BASIS OF ENERGY LEVEL
- Two level: In this photon from meta stable state jumps to second level on excitation
- Three level: In this photon from meta stable state jumps to third level on excitation
- Four level: In this photon from meta stable state jumps to fourth level on excitation
ON THE BASIS OF MATERIAL USED
Helium Neon Laser- used in Interferometer, holography, spectroscopy, barcodes scanner, optical demonstrations.
Argon Laser- used in retinal phototherapy (for diabetes), lithography, microscopic, spectroscopic pumping other laser light.
Krypton Laser-This laser is used in scientific research, mixed with argon to create "white-light" lasers, light shows.
Xenon ion Laser - used in scientific research. In this type of laser many lines throughout visible spectrum extend into the UV and IR.
Nitrogen Laser- It is used in Pumping of dye lasers, measure pollutions, and science research. Nitrogen lasers could be operated super radiate (without a resonator cavity).
Carbon Dioxide laser- It is used in material processes (cut, weld, etc.),operaation.
Excimer Laser- This type of laser is produced by exciter combination via electrical charging. It is used in Ultraviolet lithography for conductor manufacturing, laser surgery, LASIK.
These types of lasers are used as directed-energy weapons like
Hydrogen Fluoride laser: It is formed by Chemical reaction in a burning jet of ethylene and hydrogen tetra fluoride (NF3) and is used in researching for light weapon by the America, operates on continuous wave mode, can have power in the megawatt range.
Deuterium fluoride laser: - It is used in MIRACL, Pulsing Energies Projecting & Tactical Higher Energies Laser.
COIL (Chemical oxygen-iodine laser): It is produced by Chemical reaction in a jet of double delta oxygen and neon and is used in Laser weapon, science and materialing research, light is used in the military's Airborne laser in continuing wave mode, could have power in the m watt range.
These types of lasers are used in Research, spectroscopy, birthmark removal, isotope separation. The tuning range of the laser depends on which dye is used.
Helium-cadmium (HeCd) metal-vapor laser: - They are used in Printing and typesetting applications, fluorescence excitation examination (ie. in U.S. paper currency printing), scientific research.
Helium-mercury (HeHg) metal-vapor laser: - They are used in Rare, scientific research, amateur laser construction.
Helium-silver (HeAg) metal-vapor laser, Neon-copper (NeCu) metal-vapor laser:-
They are used in scientific research.
Copper vapor laser: - It is used in Dermatological uses, high speed photos, pumping for dye lasers.
Gold vapor laser: - This type of laser is used in dentistry and photodynamic therapies used
Ruby laser : Used in Holography, tattoo removal.
Nd: YAG laser : used in Material processing, ranging finding, laser target designation, surgery, research, pumping other lasers. One of the common high power lasers.
Er: YAG laser: used in Peridontal scaling, dentist work.
Neodymium YLF (Nd: YLF) solid-state laser: Mostly used for pulsed pump having certain types of pulsed Ti: sapphire lasers, combined with frequencies doubling.
Neodymium doped Yttrium orthovanadate (Nd: YVO4) laser : Mostly used for continuous pumping of mode-locked Ti:sapphire or dye lasers, in combination with frequency doubling. Also used pulsed for marking and micromachining. A frequency doubled nd:YVO4 laser is also the normal way of making a green laser pointer.
Neodymium glass (Nd: Glass) laser: Used in extremely low power, high energy (mega joules) team systems for inertial confinement fusion. Glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.
Cerium doped lithium strontium (or calcium) aluminum fluoride (Ce: Li SAF, Ce:Li CAF):- Used in far atmosphere sensing, optical research.
Erbium doped and erbium-ytterbium co doped glass lasers: These are made in rod, plate/chip, and optical fiber form. Erbium doped fibers are commonly used as optical amplifiers for telecommunications.
Semiconductor laser diode has working wavelength between 0.4-20m, depending on active region and are used in Telecommunications, holography, printing, weapons, machining, welding, pump. There are many different types of semiconductor lasers like:
Alga As : used in Optical discs, laser pointers, data communications. 780 nm Compact Disc player laser is the most common laser type in the world. Solid-state laser pumping, machining, medical.
Inga Asp : used in Telecommunications, solid-state laser pumping, machining, medical.
Quantum cascade laser : used in Researches ,Future applications including collision-avoidance radar, industrial-process control and medical diagnostics such as breath analyzers.
Other types of lasers
Free electron laser : This type of laser is having a broad wavelength range (about 100 nm - several mm); one free electron laser may be tunable over a wavelength range and is basically used in atmospheric research, material science, medical applications.
Gas dynamic laser : - used In Military applications; can operate in CW mode at several megawatts optical power and is produced by Spin state population inversion in carbon dioxide molecules caused by supersonic adiabatic expansion of mixture of nitrogen and carbon dioxide.
"Nickel-like" Samarium laser : It has pumping source Lasing in ultra-hot samarium plasma formed by double pulse terawatt scale irradiation fluences created by Rutherford Appleton Laboratory's Nd:glass Vulcan laser and first demonstration of efficient "saturated" operation of a sub-10 nm X-ray laser, possible applications in high resolution microscopy and holography, operation is close to the "water window" at 2.2 to 4.4 nm where observation of DNA structure and the action of viruses and drugs on cells can be examined.
Raman laser, using elastic stimulated scattering in a non linear media, mostly nylon fiber, for amplification. It finds its applications in complete 1-2 m wavelength coverage; distributed optical signal amplification for telecommunications; optics solutions generation and amplification.
Industrial Applications of Laser
Today, laser can be found in a broad range of applications within industry, where it can be used for such things as pointing and measuring. In the manufacturing industry, laser is used to measure the ball cylindricity in bearings by observing the dispersion of a laser beam when reflected on the ball.Lasers also working as a spirit level and could be used to indicate a flat surface by just sweeping the laser beam along the surface. This is for instance, used when making walls at building sites. In the mining industry, laser is used to point out the drilling direction.
Laser technologies have also been used within environmental areas. Another example is an ability to determine from a distance the environmental toxins in a column of smoke. Other examples are being able to predict and measure the existence of photochemical smog and ozone, both at ground level where it isn't wanted and in the upper layers of the atmosphere where it is needed. Laser is also used to supervise water purification.
Laser works as a light source in all fiber optics in use. It has greater bandwidth. It is insensitive to interference from external electrical and magnetic fields. Fiber optics is used increasingly often in data and telecommunications around the world.
Lasers are used in medicine to improve precision work like operations. Brain surgeries are an example of precision surgery that calls for the surgeon to reach the intended area precisely. To make sure of this, lasers are used both to measure and to point in the area in question. Birth, warts and discoloring of the skin can easily be removed with an unfocused laser. The operations are quick and heal quickly and, best of all, they are less painful than ordinary surgery performed with a scalpel.
A DVD player containing laser is used as it produces anti parallel beam, but due to the light emerges from a small point, which do enable to be focused on the different layers of the disc. The information, ones and zeros, is stored in several layers, and only one layer is to be read at a time. Every point on a particular layer is read during every revolution of the disc.
In order to make room for a lot of information on every disc, the beam has to be focused on as small an area as possible. This cannot be done with any other light source than a laser.
Lasers pointers are made from inexpensive semiconductors laser as together with lens produce a parallel beam of light that can be used to make a bright spot to point with. Their range is very large. If one points at a surface 200 meters (220 yards) distant in the dark, a person standing close to the object being pointed at will have no trouble seeing the shining spot (of course, someone else has to hold the laser). On the other hand, the one holding the pointer will have difficulty seeing the spot. The eternal question of range has more to do with the light's behavior on its way back to the sender than with the length of the beam.
Laser sights for rifles and guns can be based on several different principles. Some send a laser beam parallel to the trajectory so that the point of impact becomes visible. This method exposes the marksman. Some project a red dot inside a telescopic sight (instead of cross hairs). In both cases, the dot can be produced with a ring around it.
Speed Measurement Using Laser
The method the police use to measure car speed is based on a laser signal that is sent towards the target. This beam bounces back and is mixed with light that has not hit the car. The result is an oscillation - the same as when you tune a guitar - with higher frequency (more treble) the faster the target moves.
The speed has to be measured straight from the front or from the back. If it is measured at an angle, the speed is underrated. This means that you cannot get false values that are too high.
The measurement is dependent on the car having something that reflects well. The license plate is perfect, as are different types of reflecting objects. Fogged surfaces are okay, but reduce the maximum distance.
Laser Distance Meter
The primary use of laser distance meters today is surveyors and constructors, Least spectacular is the so-called parking assistance that helps the driver to estimate the distance to the car behind when parking. A more recent application measures the distance to the car in front of the driver when driving on highways or other roads. You simply lock in the distance to the car in front of you in order to maintain that distance. This makes driving more efficient and faster as long as it all works. This kind of laser is found in most robots with mechanical vision.
Bloembergen and Schawlow received the prize for their contribution to the development of laser spectroscopy. One typical application of this is nonlinear optics which means methods of influencing one light beam with another and permanently joining several laser beams (not just mixing them - compare the difference between mixing two substances and making them chemically react with one another).
These phenomena mean that a light beam can in principle be steered by another light beam. If in the future someone intends to build an optical computer (that could be much faster and much more efficient in storing data), it would have to be based on a nonlinear optic.
When using optical fibers, for example in broadband applications, several of the switches and amplifiers that are used require nonlinear optical effects.
Chu, Cohen-Tannoudji and Phillips et al. received the prize for their developments of methods to cool and trap atoms with laser light which is a method for inducing atoms to relinquish their heat energy to laser light and thus reach lower and lower temperatures.
When their temperature sinks very close to absolute zero, atoms form aggregates (make clumps) in a way that reveals some of the innermost aspects of nature. And that is the important application of laser cooling, namely to make us understand more of nature. Very soon after the discovery other scientists started to use the technique to further develop closely related areas.
Alferov and Kroemer were given the prize for their development within the field of semiconductor physics, where they had studied the type of substances that was first used to build semiconductor lasers, that is, the kind of miniature lasers that today have become the cheapest, lightest and smallest. The idea is to produce both the light source and energy supply and place the mirrors in one crystal (less than 1 mm facet, with many sequences). This has become not only the basis for many cheap and portable appliances, but also the foundation in optical information networks.
The CD player, laser writer, laser pointer and the bar code reader the cashier at the supermarket uses, are all based on their discovery.
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