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INTRODUCTION TO LASER:-
The word LASER is actually an acronym that stands for
Light Amplification by Stimulated Emission of Radiation .
Based on this principle, a very special kind of light is created,
of a form that doesnâ„¢t exist anywhere in nature. It is one
colour (monochrome) and appears as a tightly bundled,
directed beam. T.H. Maiman, a physicist from California,
USA, succeeded in building the first functioning
laser (ruby laser, with red light) in 1960.
The Flash Tube is just like a flash on a photo camera,
Its job is to inject the photons in to the ruby. The ruby
It self itâ„¢s the container of the atoms. The ruby was
Polished and was coated with silver, with the emitter
End of the ruby a little thinner, so some light could
escape out. The Quartz tube had the job of
reflecting the photons to maximize the number of
photons staying in the ruby.
A laser system generally consists of three important parts:
Â¢ An energy source (usually referred to as the pump or pump source).
Â¢ A gain medium or laser medium.
Â¢ A mirror, or system of mirrors, forming an optical resonator.
1. Pump source:-
The pump source is the part that provides energy to the laser system. Examples of pump sources include electrical discharges, flashlamps, arc lamps, light from another laser, chemical reactions and even explosive devices. The type of pump source used principally depends on the gain medium, and this also determines how the energy is transmitted to the medium
2. Laser medium:-
The gain medium is the major determining factor of the wavelength of operation, and other properties, of the laser. There are hundreds if not thousands of different gain media in which laser operation has been achieved. The gain medium is excited by the pump source to produce a population inversion, and it is in the gain medium that spontaneous and stimulated emission of photons takes place, leading to the phenomena of optical gain or optical amplification.
3. Optical resonator:-
The optical resonator, or optical cavity, in its simplest form is two parallel mirrors placed around the gain medium. Light from the medium, produced by spontaneous emission, is reflected by the mirrors back into the medium, where it may be amplified by stimulated emission. The light may reflect from the mirrors (and thus pass through the gain medium) many hundreds of times before exiting the cavity.
TYPES OF LASERS:-
There are five types of lasers, which are classified according to the lasing materials employed. The laser type depends on the material used in creating the laser. They are,
Solid state lasers:-
The solid substance that is used for lasing is generally
stimulated by a flashlight or other type of light.
Depending on whether the stimulation is continuous
or intermittent, we will get solid lasers that are in a
continuous beam or a pulsed beam.
Ex:- neodymium-yttrium-aluminum garnet, ruby, Erbium-Holmium,
Titanium sapphire etc.
Gas state lasers:-
In this type of laser, the lasing material is a gaseous material. Helium and helium-neon are the two gases most popularly used to create gas lasers. When CO2 is used, the laser created is an infrared laser. Gas lasers are typically red in color
The medium is a dye solution, as a result of which the colour
of the laser light can be varied over a wide range.
These lasers are not solid state lasers and are also referred
to as diode lasers. A semi conductor laser is not very powerful
on its own, and is thus generally used in combination with
Some organic dyes, such as the very oft used rhodamine G6, have molecules that can be easily excited, because of which tunable lasers with many different frequencies can be achieved. Lasers created from dyes that are either liquid dyes or suspension materials, are known as dye lasers.
ADVANCED PERTINENCES/APPLICATIONS OF LASERS:-
Laser finds its pertinences in many fields such as military, biomedical, scientific,
industrial, optical communications etcÂ¦
Directed energy weapons
Space laser satellite defense system
A laser designator is a laser light source which is used to designate a target. Laser designators provide targeting for laser guided bombs, missiles or precision artillery munitions, such as the pave way series of bombs, Lockheed-Martinâ„¢s hellfire or the copperhead round, respectively. When a target is marked by a designator, the beam is invisible and does not shine continuously. Instead, a series of coded pulses of laser-light are fired. These signals bounce off the target into the sky, where they are detected by the seeker on the laser guided munitions, which steers itself towards the centre of the reflected signal. Unless the people being targeted possess laser detection equipment or can hear aircraft overhead, it isextremely difficult for them to tell whether they are being marked or not. Laser designators work best in clear atmospheric conditions. Cloud cover, rain or smoke can make reliable designation of targets difficult or even impossible.
Directed energy weapons:-
The Boeing YAL-1 Airborne Laser Tested, (formerly Airborne Laser) weapons system is a megawatt-class chemical oxygen iodine laser (COIL) mounted inside a modified Boeing 747-400F. It is primarily designed as a missile defense system to destroy tactical ballistic missiles (TBMs), while in boost phase. The aircraft was designated YAL-1A in 2004 by the U.S. Department of Defense.
The YAL-1 with a low-power laser was test-fired in flight, at an airborne target in 2007.A high-energy laser was used to intercept a test target in January 2010.
The ABL does not burn through or disintegrate its target. It heats the missile skin, weakening it, causing failure from high speed flight stress. If proven successful, seven ABL-armed 747s will be built and assigned to two combat theaters. The aircraft were originally slated to enter service in 2008, but development has been slower and costlier than planned. The current plan calls for a prototype ABL to attempt to shoot down a test missile in 2009.
Space laser satellite defense system:-
The satellites would be powered by built-in nuclear warheads â€œ in theory, the energy from the warhead detonation would be used to pump a series of laser emitters in the missiles or satellites, allowing each satellite to shoot down many incoming warheads simultaneously. The attraction of this approach was that it was thought to be faster than an optical laser, which could only shoot down warheads one at a time, limiting the number of warheads each laser could destroy in the short time 'window' of an attack.
Brilliant Pebbles was a non-nuclear system of satellite-based,watermelon-sized mini-missiles designed to use a high-velocity kinetic warhead. It was designed to operate in conjunction with the Brilliant Eyes sensor system and would have detected and destroyed missiles without any external guidance.
Satellite known as Delta Star to test several sensor related technologies. Delta Star carried an infrared imager, a long-wave infrared imager, an ensemble of imagers and photometers covering several visible and ultraviolet bands as well as a laser detector and ranging device. The satellite observed several ballistic missile launches including some releasing liquid propellant as a countermeasure to detection. .
The laser has in most firearms applications been used as a tool to enhance the targeting of other weapon systems. For example, a laser sight is a small, usually visible-light laser placed on a handgun or a rifle and aligned to emit a beam parallel to the barrel. Since a laser beam by definition has low divergence. The laser light appears as a small spot even at long distances; the user places the spot on the desired target and the barrel of the gun is aligned (but not necessarily allowing for bullet drop, windage and the target moving while the bullet travels).
A radar gun or speed gun is a small Doppler radar unit used to detect the speed of objects, especially trucks and automobiles for the purpose of regulating traffic, as well as pitched baseballs, runners or other moving objects in sports. A radar gun does not return information regarding the object's position. It relies on the Doppler Effect applied to a radar beam to measure the speed of objects at which it is pointed. Radar guns may be hand-held or vehicle-mounted.
Most of today's radar guns operate at X, K, Ka, IR Band (infrared), and (in Europe) Ku bands. An alternative technology, LIDAR, uses pulsed laser light.
The radar gun was invented by Bryce K. Brown in March 1954.
Laser spectroscopy has led to advances in the precision with which spectral line frequencies can be measured, and this has fundamental significance for our understanding of basic atomic processes. This precision has been obtained by passing two laser beams through the absorption sample in opposite directions, selectively triggering absorption only in those atoms that have a zero velocity component in the direction of the beams.
Laser fusion, also called inertial confinement fusion, is the most frequent fusion reaction on Earth. It is commonly used for experiments relevant to hydrogen bombs. Is relatively simple and cheap in comparison to tokamaks but didnâ„¢t allow continuous fusion and can be ignited discontinuously only.
Laser fusion process:
Now a days, mostly eye surgeries are done by using the laser technology.Although the terms laser eye surgery and refractive surgery are commonly used as if they were interchangeable, this is not the case. Lasers may be used to treat non-refractive conditions (e.g. to seal a retinal tear).
Surgical removal of tissues:-
The tissues in the human bodies are removed by using
the laser technology.Without touching the body,
we can remove the tissue.
Low level laser therapy (LLLT, also known as photobiomodulation, cold laser therapy and laser biostimulation) is a medical and veterinary treatment which uses low-level lasers or light-emitting diodes tostimulate or inhibit cellular function. The technique is also known by other terms such as laser therapy, "cold laser" and phototherapy (though the latter more accurately refers to light therapy), which may also be used to describe other medical techniques.
Holography (from the Greek, -hÃƒÂ³los whole + af-grafe writing, drawing) is a technique that allows the light scattered from an object to be recorded and later reconstructed so that it appears as if the object is in the same position relative to the recording medium as it was when recorded. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the recorded image (hologram) appear three dimensional.
LIDAR (Light Detection And Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses.
Â¢ Upcoming technologies:-
'The laser will ultimately fulfill its promise in the huge field that was called analytical chemistry, and become increasingly prolific in diagnostic medicine. Spectral properties and spatial coherence will assure this as the lab shrinks to chip scale. The future world of pharmagenomics will rely on lasers for genetic typing and perhaps for activation of the appropriate therapeutic course.â„¢
Laser has got many applications or pertinences in many fields such as military, scientific, medical, industrial etcÂ¦. This technology has been enhanced a lot in the past 40 years. This laser technology has many advantages such as eye surgeries, holograms, therapies etc and at the same it can be used for the destructive and devastative purposes also. So, we have to use this full-fledged laser technology in our positive Endeavourâ„¢s only.
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31-03-2010, 06:20 AM
LASERS:AN ADVANCED TECHNIQUE AND ITS APPLICATION
In modern era,there are many techniques which bring a revolution in manâ„¢s life.whether it is a field of science, medical etc.One of the majoruseful techniques(which is being used in every aspects of life)LASER which is an acronym for LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION.This is the device which proved to be boon for human life. LASER, invented in 1960 by Gordon Gould had the battle of his life receiving credit for his laser invention. It is a device by which an intense ,monochromatic ,collimated and highly coherent light beam can be obtained.
HISTORY OF LASERS:
The history of the laser began with a little boy and an Erector set. A little boy by the name of Gordon Gould was the son of Kenneth Miller and Helen Gould. He was born in New York City on July 17, 1920. The Erector set is a construction kit that children use to put things together and take them apart. After watching his mother use the set to construct various things, Gordon began to construct things himself and take them apart. So this was the beginning of taking things apart and fixing them for a creative child. With the help of his brothers, he began to take clocks apart piece-by-piece and attempt to fix them.
Then it happened in 1973 when he won his first court victory. The courts decided the documentation for the laser provided by Townes and Schawlow did not reflect the instructions for building a laser. Good news was heard in October of 1977. Gouldâ„¢s optic pump was finally given a patent. The good news did not stop with the optic pump. The United States Patent Office Appeals Board overturned all objections in 1986. This is something that Gould had been waiting to hear for years. Gould was 67 years old and his dream was finally coming true.
History was made with Gouldâ„¢s invention of the laser and the world reaps its benefits almost every day. Lasers can measure the distance to the moon and are being used in communications. The Universal Product Code we see on items is associated with the laser. The laser is responsible for compact disks, which contain recorded sound. Gould will be remembered as the inventor who was the most influential in the 20th century.
In order to understand the basics of LASERS , following terms should be known which are as follows:-
STIMULATED AND SPONTANEOUS EMISSION
Three kinds of transitions involving electromagnetic radiation are possible between two energy levels,Eo and E1,in an atom (fig a).If the atom is initially in the lower state Eo,it can be raised to E1 by absorbing aphoton of energy E1-Eo =hv.This process is called stimulated emission.If the atom is initially in upper state E1,it can drop to Eo by emitting a photon of energy hv. This is spontaneous emission.
Einstein, in1917,was the first to point out a third possibility, stimulated emission,in which an incident photon of energy hv causes transitionfrom E1 to Eo .In stimulated emission, the radiated light waves are exactly in phase with the incident ones, so the result is an enhanced beam of coherent light. Einstein showed that stimulated emission has the same probability as stimulated absorption . That is ,a photon of energy hv incident on an atom in the upper state E1 has the same likelihood of causing the emission of another photon of energy hv as its likelihood of being absorbed if it is incident on atom in the lower state Eo.
He introduced stimulated emission and used it to arrive at the form of Planckâ„¢s radiation law in an elegantly simple manner . By the early 1920s this idea together with what had becomeknown about the physics of the atom would have enabled the laser to have beeen invented then ,but ,somehow nobody connected the dots until over 30 years.
Consider two energy states ina particular atom, alower one i and an upper one j (fig b).If the atom is initially in state i ,it can be raised to state j by absorbing a photon of frequency
V = Ej â€œEi / h Â¦Â¦Â¦. (1)
Now imagine an assembly of Ni atoms in state i and Nj atoms in j state,all in thermal equillibrium at the temperature T with light of frequency v and energy density u(v),The probability that an atom in state I absorbs aphoton is proportional to the energy densityu(v) and
also to the properties of states i and j ,which can include in some constant Bij .Hence the number Ni->j of atoms per second that absorb photons is given by Number of atoms that absorb photons Ni->j =Nbij u(v) Â¦Â¦Â¦..(2)
An atom in the upper state j has a certain probability Aij to spontaneously drop to state i by emitting a photon of frequency v . Also a photon frequency v can somehow interact with an atom in state j to induce its transition to the lower state I .An energy density of u(v) therefore means a probability for stimulated emission of Bij u(v),where Bij ,like Bij and Aij, depends on the properties of states i and j. Since Nj is the number of atoms per seconds that fall to lower state i is
Number of atoms that emit photons
Ni->j = Nj [ Aij + Bij u(v) ] Â¦Â¦Â¦Â¦Â¦(3)
Stimulated emission has a classical physics analog in the behaviour of a harmonic oscillator. Of course, classical physics often doesnot apply on atomic scale ,but it is not assumed that stimulated emission does occur, only that it may occur. If this assumption is wrong , ultimately it is found that Bij = 0.
Since the system here is in equillibrium ,the number of atoms per seconds that go from state i to j must equal the number that go from j to i. Therefore
Ni Bij u(v) = Nj [ Aji + Bji u(v) ]
Dividing both side of the latter equation by Nj Bji and solving for u(v) gives
(Ni/ Nj) (Bij /Bji) u(v) = Aji / Bji + u(v)
u(v) = Aji/Bji /(Ni/ Nj) (Bij /Bji -1 Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦.(4)
Finally ,the numbers of atoms of energies Ei and Ej in a system of these atoms at the temperature T, which can be written as
Ni = C e
Nj = Ce
Hence _( Ei â€œ Ej) /kt ( Ej â€œ Ei ) /kt hv/ kt
Ni/Nj = e = e = e (from eq 1) Â¦Â¦Â¦(5)
And so hv/ kt
u(v) = Aji / (Bij / Bji )e -1 Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦.(6)
This formula gives the energy density of photons of frequency v in equillibrium at the temperature T with atoms whose possible energies are Ei and Ej .
Equation (6) is consistent with the Planck radiation law of Eq if
Bij = Bji
Aji / Bji = 8phv3 / c3 Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦Â¦(7)
Following conclusions can be drawn :
1. Stimulated emission does occur and its probability for a transition between two states is equal to the probability for absor ption.
2. The ratio between the probabilities for spontaneous and stimulated emission varies with v3 ,so the relative likelihood of spontaneous emission increases rapidly with the energy difference between two states .
Spontaneous emission and stimulated emission differ in an important respect. Spontaneous emission is a completely random process , and the emitted photons are in coherent , which means that their phases and propagation direction are random .In stimulated emission, the phase and direction of propagation are the same as that of the incident photon. This is referred as coherent photon emission . A light bulb is an incoherent photon source.The phase relation between individual photons is random , and because the propagation direction the photons is random ,the intensity of the source falls off as the square of the distance. A LASER is a coherent source of radiation. All photons are in phase ,and because they have the same propagation direction ,the divergence of the beam is very small. This explains why laser beam that is reflected from the moon still has a measurable intensity when it returns to earth .
It describes an assembly of atoms in which the majority are in energy levels above the ground state ,normaly the ground state is occupied to the greatest extent.
A number of ways exist to produce a population inversion .One of them, called optical pumping illustrated in (fig ).Here an external light source is used some of whose photons have the right frequency to raise ground state atoms to the excited state that decays spontaneously to the desired metastable state.
PRINCIPLE AND WORKING :
In order for a laser to function properly, more atoms with stored energy must be present than atoms with free storage space, as more photons on average would otherwise be absorbed than the number of new ones being added. This state is known as inversion. In order to achieve this state, atoms are kept in an excited state by pumping the laser, 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.
To make some of the photons pass through the laser medium more than once, a so-called resonator is used: Two mirrors are positioned to reflect and amplify the light between them before it leaves the laser as the output beam. One mirror is almost perfectly reflective and the second reflects only most of the incoming photons, allowing some of the photons to pass through it. This forms the laser beam.
Fig( ) :The principal of the laser
WORKING PRINCIPLE :
Two coherent laser beams derived from a single source intersect at a fixed angle. The intersection volume of the two beams is positioned on the sample surface. The wavefronts of the two beams interfere in the intersection volume and form an interference pattern. The fringes of the pattern have a known distance depending on the wavelength of the laser and the angle between the two beams.
For simplicity, assume that an element with a velocity component perpendicular to the center axis is moving through the intersection volume. The element will scatter light with its amplitude modulated by the local intensity contrast. The frequency of the modulation is proportional to the velocity of the element.
Thus when recording the intensity signal the motion of elements within the observation area can be calculated. A typical sample with its natural roughness contains scattering elements everywhere on its surface which allows the measurement of the amount of material moving through the observation area.
By simultaneous measurement at two points of the sample surface the relative motion between these two points can be determined. This allows the use of the measuring arrangement as an extensometer.
In other words , principle at which laser works can be understood as the no atoms of a substance are in their ground state .When they are given energyu by some external source,they are excited and reach some higher energy state.An atom can persist in an excited state only for 10n (n = -8 ) seconds after which it returns to its original state. In this process, the atom emits light photons of frequency v ,where
hv = E2 - E1
where E2 and E1 are the energies in the higher and the lower energy states respectively.The
process called spontaneous emission . This ian irregular emission and takes place at different times for different atoms. So, the light obtained by spontaneous emmission from different atoms is incoherent.
If ,however ,when an atom is in an excited state E2,alight photon of the same frequency which is to be emitted by the atom ,falls upon it,then the atom immediately comes down to its normal state E1 and estimulates the incident light by emitting the photon of exactly the same frequency.this is called as stimulated emission which is completely coherent with the incident light.Now the stimulated and the incident light photons cause coherent stimulated light emission from the excited atoms.If the substance has a good number of excited atoms ,then this process gets multiplied . Thus, an intense ,coherent light beam is emitted from the substance.
TYPES OF LASERS
According to their sources:
1. Gas Lasers
2. Crystal Lasers
3. Semiconductors Lasers
4. Liquid Lasers
Â¢ According to the nature of emission:
1. Continuous Wave
2. Pulsed Laser
Â¢ According to their wavelength:
1. Visible Region
2. Infrared Region
3. Ultraviolet Region
4. Microwave Region
5. X-Ray Region
INSTRUMENTATION OF RUBY LASERS
A laser is constructed from three principal parts:
Â¢ An energy source (usually referred to as the pump or pump source),
Â¢ A gain medium or laser medium, and
Â¢ Two or more mirrors that form an optical resonator.
The pump source is the part that provides energy to the laser system. Examples of pump sources include electrical discharges, flashlamps, arc lamps, light from another laser, chemical reactions and even explosive devices. The type of pump source used principally depends on the gain medium, and this also determines how the energy is transmitted to the medium. A helium-neon (HeNe) laser uses an electrical discharge in the helium-neon gas mixture, a Nd:YAG laser uses either light focused from a xenon flash lamp or diode lasers, and excimer lasers use a chemical reaction.
Gain medium / Laser medium
The gain medium is the major determining factor of the wavelength of operation, and other properties, of the laser. There are hundreds if not thousands of different gain media in which laser operation has been achieved. The gain medium is excited by the pump source to produce a population inversion, and it is in the gain medium that spontaneous and stimulated emission of photons takes place, leading to the phenomenon of optical gain, or amplification.
Examples of different gain media include:
Â¢ Liquids, such as dye lasers. These are usually organic chemical solvents, such as methanol, ethanol or ethylene glycol, to which are added chemical dyes such as coumarin, rhodamine and fluorescein. The exact chemical configuration of the dye molecules determines the operation wavelength of the dye laser.
Â¢ Gases, such as carbon dioxide, argon, krypton and mixtures such as helium-neon. These lasers are often pumped by electrical discharge.
Â¢ Solids, such as crystals and glasses. The solid host materials are usually doped with an impurity such as chromium, neodymium, erbium or titanium ions. Typical hosts include YAG (yttrium aluminium garnet), YLF (yttrium lithium fluoride), sapphire (aluminium oxide) and various glasses. Examples of solid-state laser media include Nd:YAG, Tiapphire, Crapphire (usually known as ruby), Cr:LiSAF (chromium-doped lithium strontium aluminium fluoride), Er:YLF, Nd:glass, and Er:glass. Solid-state lasers are usually pumped by flashlamps or light from another laser.
Â¢ Semiconductors, a type of solid, in which the movement of electrons between material with differing dopant levels can cause laser action. Semiconductor lasers are typically very small, and can be pumped with a simple electric current, enabling them to be used in consumer devices such as compact disc players. See laser diode.
The optical resonator, or optical cavity, in its simplest form is two parallel mirrors placed around the gain medium which provide feedback of the light. The mirrors are given optical coatings which determine their reflective properties. Typically one will be a high reflector, and the other will be a partial reflector. The latter is called the output coupler, because it allows some of the light to leave the cavity to produce the laser's output beam.
Light from the medium, produced by spontaneous emission, is reflected by the mirrors back into the medium, where it may be amplified by stimulated emission. The light may reflect from the mirrors and thus pass through the gain medium many hundreds of times before exiting the cavity. In more complex lasers, configurations with four or more mirrors forming the cavity are used. The design and alignment of the mirrors with respect to the medium is crucial to determining the exact operating wavelength and other attributes of the laser system.
Other optical devices, such as spinning mirrors, modulators, filters, and absorbers, may be placed within the optical resonator to produce a variety of effects on the laser output, such as altering the wavelength of operation or the production of pulses of laser light.
Some lasers do not use an optical cavity, but instead rely on very high optical gain to produce significant amplified spontaneous emission (ASE) without needing feedback of the light back into the gain medium. Such lasers are said to be superluminescent, and emit light with low coherence but high bandwidth. Since they do not use optical feedback, these devices are often not categorized as lasers.
Characteristics of Laser
1. Highly Monochromatic:
* Laser ray is highly pure beam of light with respect to the wavelength and the frequency of the photons forming it.
2. Highly Directional
* laser beam is highly intense and very narrow beam this is because its divergence is very small.
* Laser beam transfers in straight lines approximately parallel to each other.
3. Highly Coherent
* The laser photons are coherent,in phase and have the same direction.
APPLICATIONS OF LASERS:
There are many scientific, military, medical and commercial laser applications which have been developed since the invention of the laser in the 1958. The coherency, high monochromaticity, and ability to reach extremely high powers are all properties which allow for these specialized applications.
In science, lasers are used in many ways, including:
Â¢ A wide variety of interferometric techniques
Â¢ Raman spectroscopy
Â¢ Laser induced breakdown spectroscopy.
Â¢ Atmospheric remote sensing
Â¢ Investigating nonlinear optics phenomena
Â¢ Holographic techniques employing lasers also contribute to a number of measurement techniques.
Â¢ Laser based LIght Detection And Ranging (LIDAR) technology has application in geology, seismology, remote sensing and atmospheric physics.
Â¢ Lasers have been used aboard spacecraft such as in the Cassini-Huygens mission.
Â¢ In astronomy, lasers have been used to create artificial laser guide stars, used as reference objects for adaptive optics telescopes.
Lasers may also be indirectly used in spectroscopy as a micro-sampling system, a technique termed Laser ablation (LA), which is typically applied to ICP-MS apparatus resulting in the powerful LA-ICP-MS.
The principles of laser spectroscopy are discussed by DemtrÃƒÂ¶der and the use of tunable lasers in spectroscopy are described in Tunable Laser Applications.
Most types of laser are an inherently pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful design of the laser components, the purity of the laser light (measured as the "linewidth") can be improved more than the purity of any other light source. This makes the laser a very useful source for spectroscopy. The high intensity of light that can be achieved in a small, well collimated beam can also be used to induce a nonlinear optical effect in a sample, which makes techniques such as Raman spectroscopy possible. Other spectroscopic techniques based on lasers can be used to make extremely sensitive detectors of various molecules, able to measure molecular concentrations in the parts-per-trillion (ppt) level. Due to the high power densities achievable by lasers, beam-induced atomic emission is possible: this technique is termed Laser induced breakdown spectroscopy (LIBS).
Lunar laser ranging
Main article: Lunar laser ranging experiment
When the Apollo astronauts visited the moon, they planted retroreflector arrays to make possible the Lunar Laser Ranging Experiment. Laser beams are focused through large telescopes on Earth aimed toward the arrays, and the time taken for the beam to be reflected back to Earth measured to determine the distance between the Earth and Moon with high accuracy.
Laser cutting, laser welding, laser brazing, laser bending, laser engraving or marking, laser cleaning, weapons etc. LIA has edited a book on most of these topics: "Handbook of Laser Materials Processing".
Some laser systems, through the process of modelocking, can produce extremely brief pulses of light - as short as picoseconds or femtoseconds (10-12 - 10-15 seconds). Such pulses can be used to initiate and analyse chemical reactions, a technique known as photochemistry. The short pulses can be used to probe the process of the reaction at a very high temporal resolution, allowing the detection of short-lived intermediate molecules. This method is particularly useful in biochemistry, where it is used to analyse details of protein folding and function.
A technique that has had recent success is laser cooling. This involves atom trapping, a method where a number of atoms are confined in a specially shaped arrangement of electric and magnetic fields. Shining particular wavelengths of laser light at the ions or atoms slows them down, thus cooling them. As this process is continued, they all are slowed and have the same energy level, forming an unusual arrangement of matter known as a Bose-Einstein condensate.
Some of the world's most powerful and complex arrangements of multiple lasers and optical amplifiers are used to produce extremely high intensity pulses of light of extremely short duration. These pulses are arranged such that they impact pellets of tritium-deuterium simultaneously from all directions, hoping that the squeezing effect of the impacts will induce atomic fusion in the pellets. This technique, known as "inertial confinement fusion", so far has not been able to achieve "breakeven", that is, so far the fusion reaction generates less power than is used to power the lasers, but research continues.
Confocal laser scanning microscopy and Two-photon excitation microscopy make use of lasers to obtain blur-free images of thick specimens at various depths. Laser capture microdissection use lasers to procure specific cell populations from a tissue section under microscopic visualization.
Additional laser microscopy techniques include harmonic microscopy, four-wave mixing microscopy and interferometric microscopy.
Military uses of lasers include applications such as target designation and ranging, defensive countermeasures, communications and directed energy weapons. Directed energy weapons such as Boeingâ„¢s Airborne Laser which can be built inside a 747 jet can burn the skin off enemy missiles.
On March 18, 2009 Northrop Grumman announced that its engineers in Redondo Beach had successfully built and tested an electric laser capable of producing a 100-kilowatt ray of light, powerful enough to destroy cruise missiles, artillery, rockets and mortar rounds. An electric laser is theoretically capable, according to Brian Strickland, manager for the United States Army's Joint High Power Solid State Laser program, of being mounted in an aircraft, ship, or vehicle because it requires much less space for its supporting equipment than a chemical laser.
Defensive countermeasure applications can range from compact, low power infrared countermeasures to high power, airborne laser systems. IR countermeasure systems use lasers to confuse the seeker heads on heat-seeking anti-aircraft missiles. High power boost-phase intercept laser systems use a complex system of lasers to find, track and destroy intercontinental ballistic missiles (ICBM). In this type of system a chemical laser, one in which the laser operation is powered by an energetic chemical reaction, is used as the main weapon beam (see Airborne Laser). The Mobile Tactical High-Energy Laser (MTHEL) is another defensive laser system under development; this is envisioned as a field-deployable weapon system able to track incoming artillery project and implimentationiles and cruise missiles by radar and destroy them with a powerful deuterium fluoride laser.
Another example of direct use of a laser as a defensive weapon was researched for the Strategic Defense Initiative (SDI, nicknamed "Star Wars"), and its successor programs. This project and implimentation would use ground-based or space-based laser systems to destroy incoming intercontinental ballistic missiles (ICBMs). The practical problems of using and aiming these systems were many; particularly the problem of destroying ICBMs at the most opportune moment, the boost phase just after launch. This would involve directing a laser through a large distance in the atmosphere, which, due to optical scattering and refraction, would bend and distort the laser beam, complicating the aiming of the laser and reducing its efficiency.
Another idea to come from the SDI project and implimentation was the nuclear-pumped X-ray laser. This was essentially an orbiting atomic bomb, surrounded by laser media in the form of glass rods; when the bomb exploded, the rods would be bombarded with highly-energetic gamma-ray photons, causing spontaneous and stimulated emission of X-ray photons in the atoms making up the rods. This would lead to optical amplification of the X-ray photons, producing an X-ray laser beam that would be minimally affected by atmospheric distortion and capable of destroying ICBMs in flight. The X-ray laser would be a strictly one-shot device, destroying itself on activation. Some initial tests of this concept were performed with underground nuclear testing; however, the results were not encouraging. Research into this approach to missile defense was discontinued after the SDI program was cancelled.
Main article: Laser designator
A target designator
Another military use of lasers is as a laser target designator. This is a low-power laser pointer used to indicate a target for a precision-guided munition, typically launched from an aircraft. The guided munition adjusts its flight-path to home in to the laser light reflected by the target, enabling a great precision in aiming. The beam of the laser target designator is set to a pulse rate that matches that set on the guided munition to ensure munitions strike their designated targets and do not follow other laser beams which may be in use in the area. The laser designator can be shone onto the target by an aircraft or nearby infantry. Lasers used for this purpose are usually infrared lasers, so the enemy cannot easily detect the guiding laser light.
Smith & Wesson revolver equipped with laser sight mounted on trigger guard.
The laser has in most firearms applications been used as a tool to enhance the targeting of other weapon systems. For example, a laser sight is a small, usually visible-light laser placed on a handgun or a rifle and aligned to emit a beam parallel to the barrel. Since a laser beam by definition has low divergence, the laser light appears as a small spot even at long distances; the user places the spot on the desired target and the barrel of the gun is aligned (but not necessarily allowing for bullet drop, windage and the target moving while the bullet travels).
Most laser sights use a red laser diode. Others use an infrared diode to produce a dot invisible to the naked human eye but detectable with night vision devices. The firearms adaptive target acquisition module LLM01 laser light module combines visible and infrared laser diodes. In the late 1990s, green diode pumped solid state laser (DPSS) laser sights (532 nm) became available. Modern laser sights are small and light enough for attachment to the firearms.
In 2007, LaserMax, a company specializing in manufacturing lasers for military and police firearms, introduced the first mass-production green laser available for small arms. This laser mounts to the underside of a handgun or long arm on the accessory rail. The green laser is supposed to be more visible than the red laser in bright lighting conditions because, for the same wattage, green light appears brighter than red light.
A non-lethal laser weapon was developed by the U.S. Air Force to temporarily impair an adversaryâ„¢s ability to fire a weapon or to otherwise threaten enemy forces. This unit illuminates an opponent with harmless low-power laser light and can have the effect of dazzling or disorienting the subject or causing him to flee. Several types of dazzlers are now available, and some have been used in combat.
There remains the possibility of using lasers to blind, since this requires much lower power levels, and is easily achievable in a man-portable unit. However, most nations regard the deliberate permanent blinding of the enemy as forbidden by the rules of war . Although several nations have developed blinding laser weapons, such as China's ZM-87, none of these are believed to have made it past the prototype stage.
In addition to the applications that crossover with military applications, a widely known law enforcement use of lasers is for lidar to measure the speed of vehicles.
See also: laser medicine
Â¢ Cosmetic surgery (removing tattoos, scars, stretch marks, sunspots, wrinkles, birthmarks, and hairs): see laser hair removal. Laser types used in dermatology include ruby (694 nm), alexandrite (755 nm), pulsed diode array (810 nm), Nd:YAG (1064 nm), Ho:YAG (209|Er]]:YAG (2940 nm).
Â¢ Eye surgery and refractive surgery
Â¢ Soft tissue surgery: CO2, Er:YAG laser
Â¢ Laser scalpel (General surgery, gynecological, urology, laparoscopic)
Â¢ Photobiomodulation (i.e. laser therapy)
Â¢ "No-Touch" removal of tumors, especially of the brain and spinal cord.
Â¢ In dentistry for caries removal, endodontic/periodontic procedures, tooth whitening, and oral surgery
Industrial and commercial
Lasers used for visual effects during a musical performance. (A laser light show.)
Â¢ Cutting and peening of metals and other material, welding, marking, etc
Â¢ Guidance systems (e.g., ring laser gyroscopes)
Â¢ Rangefinder / surveying,
Â¢ LIDAR / pollution monitoring,
Â¢ Digital minilabs
Â¢ Barcode readers
Â¢ Laser engraving of printing plate
Â¢ Laser bonding of additive marking materials for decoration and identification,
Â¢ Laser pointers
Â¢ Laser accelerometers
Â¢ Optical communications (over optical fiber or in free space)
Â¢ Optical tweezers
Â¢ Writing subtitles onto motion picture films.
Â¢ Space elevator, a possible solution transfer energy to the climbers by laser or microwave power beaming
Â¢ 3D laser scanners for accurate 3D measurement.
Â¢ Laser line levels are used in surveying and construction. Lasers are also used for guidance for aircraft.
Â¢ Extensively in both consumer and industrial imaging equipment.
Â¢ In laser printers: gas and diode lasers play a key role in manufacturing high resolution printing plates and in image scanning equipment.
Â¢ Diode lasers are used as a lightswitch in industry, with a laser beam and a receiver which will switch on or off when the beam is interrupted, and because a laser can keep the light intensity over larger distances than a normal light, and is more precise than a normal light it can be used for product detection in automated production.
Â¢ Laser alignment
Â¢ Additive manufacturing
In consumer electronics, telecommunications, and data communications, lasers are used as the transmitters in optical communications over optical fiber and free space.
Â¢ To store and retrieve data in optical discs
Â¢ Laser lighting displays (pictured) accompany many music concerts.
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09-04-2010, 09:06 PM
LASER GUIDED DOOR OPENERppt.pptx (Size: 490.09 KB / Downloads: 266)
LASER GUIDED DOOR OPENER ,AS THE NAME SUGGESTS THE DOOR OPENING OPERATION IS DONE WITH HELP OF A LASER
i.e. PHOTO SIGNAL .AND THIS SIGNAL IS NOTHING BUT THE ANOLOG INPUT .HERE AS LONG AS THE INPUT ANOLOG SIGNAL IS GIVEN THE DIODE IS IN REVERSE BIASED AND THE CIRCUIT LL NOT BE CLOSED ,AND WHEN A INTERUPT HAS TAKEN PLACE THE PHOTO INPUT DOES NOT REACH THE DIODE SO THE DIODE NOW CONNECTS AS FORWARD BIASED AND THE CIRCUIT IS CLOSED AND AT THAT PARTICULAR MOMENT THE MOTOR STARTS ROTATING AND THIS MOTOR IS LATER CONNECTED TO ELECTROMECHANICAL DOORS AND THUS THE ROTATION OPERATION TAKES PLACE .
AND ALONG WITH THIS WE PLACE ONE PIEZO ELECTRIC BUZZER ON THE GROUND COVERED WITH CARPET .
PIEZO ELECTRIC BUZZER â€œTHE ONE WHICH TAKES THE PHYSICAL FORM OF ENERGY AS INPUT SIGNAL AND GIVES OUT ELCETRICAL OUTPUT SIGNAL .
USING THIS A CONNECTION IS SET FOR MAKING DESIRED SOUNDS .
Laser guided vehicles
Laser Guided Vehicles - LGV / Automated Guided Vehicles - AGV
A LGV - Automated Guided Vehicle physically moves the goods and acts as the link between the different machines within the warehouse environment. The vehicle combines many different systems to ensure reliability and efficiency, including Energy, Safety, Fork/load handling and Guidance and Control systems. General technical features of LGVs All the LGVs can be equipped with special waterproof devices which enable them to work outdoors, even in all-weather conditions.
Laser guide bombs
Two basic types of laser guidedmissiles exist on the modern battlefield. The first type "reads" the laser lightemitted from the launching aircraft/helicopter. The missile's electronic suite issues commands to the fins (called control surfaces) on its body in an effort to keep it on course with the laser beam. This type of missile is called a beam rider as it tends to ride the laser
beam towards its target.The second type of missile uses on-board sensors to pick up laser light reflected from the target. The aircraft/helicopter pilot
selects a target, hits the target with a laser beam shot from a target designator, and then launches the missile. The missile's sensor measures the error between its flight path and the path of the reflected light. Correction messages are then passed on to the missile's control surfaces via the electronics suite, steering the missile onto its target.Regardless of type, the missile designer must run computer simulations as the first step of the design process. These simulations assist the designer in choosing the proper laser type, body length, nozzle configurations, cavity size, warhead type, propellant mass, and control surfaces. The designer then puts together a package containing all relevant engineering calculations, including those generated by computer simulations. The electronics suite is then designed around the capabilities of the laser and control surfaces. Drawings and schematics of all components can now be completed; CAD/CAM (Computer-Aided Design/Manufacture) technology has proven helpful with this task. electronics systems are then designed around the capabilities of the aircraft's laser and the missile's control surfaces. The following step consists of generating the necessary schematic drawings for the chosen electronics system. Another
computer-assisted study of the total guided missile system constitutes the final step of the design process.
Laser guided saw
The laser guidance allows periodic checks to establish the
accuracy of the actual cut to the intended cutting line.
Whether youâ„¢re making straight cuts, cutting profiled surfaces,
cutting difficult to mark surfaces, trimming a thin slice from a
section, or making complex compound mitre cuts the guidance system
provides improved accuracy and increased confidence.
Laser guided bullets
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09-10-2010, 12:52 PM
Green Lasers.pptx (Size: 414.03 KB / Downloads: 70)
What the world needs now !
Its a semiconductor laser that's good, cheap, long-lasting, powerful, and truly green.
Which can give us affordable televisions with bigger, more dazzling pictures than the best available today.
The hunt for a true green solid-state laser has stymied researchers around the world for decades.
How it evolved !
In 1995 ,a Japaneese engineer fabricated the world's first gallium nitride laser, a device that emitted ultraviolet radiation.
Though a green laser has many advantages, the biggest market of all would arguably be for use in television sets.
By 2003 the researchers had produced a 480-nm laser—still blue but at least leaning toward green.
By 2008 ,researchers had hit 488 nm and commercialized that device, which the company describes as 'blue-green.
In building of laser the first thing to be done is building the pump cavity.
Revolutionize information display
Improve opthalmological therapies
Give us the best TVs, with bigger more dazzling pictures.
Laser light shows
Industrial process control.
DNA sequencing machines
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17-03-2011, 09:31 AM
Laser Final.pptx (Size: 3.21 MB / Downloads: 61)
Laser and its applications
Theory of Lasing
Introduction (Brief history of laser)
The laser is perhaps the most important optical device to be developed in the past 50 years. Since its arrival in the 1960s, rather quiet and unheralded outside the scientific community, it has provided the stimulus to make optics one of the most rapidly growing fields in science and technology today. The laser is essentially an optical amplifier. The word laser is an acronym that stands for “light amplification by the stimulated emission of radiation”. The basic concept of laser was given by Einstein and Townes.
Einstein’s quantum theory of radiation
In 1916, according to Einstein, the interaction of radiation with matter could be explained in terms of three basic processes: spontaneous emission, absorption and stimulated emission. The three processes are shown below:
Essential Elements of Laser
The laser device consists of basically of three elements:
External source (pump), Amplifying medium and optical cavity (resonator( .
Types of lasers
Solid State Lasers
Electron Beam Lasers
Properties of Laser
Applications of Laser
1.Laser in Industry
2. Laser in Military
Laser Range Finder
3. Medical Application of Laser
4. Domestic Application of Laser
High Speed Photography
Since lasers were introduced in the 1960's, research and development has produced ever more portable, powerful, and reliable systems. Today lasers are found in a wide range of applications. It is apprehended that lasers will be used in nanotechnology and micro-mechanical systems in the near future.