In 1917 Albert Einstein, in his paper Zur Quantentheorie der Strahlung On the Quantum Theory of Radiation, laid the foundation for the innovation of the optical maser and its predecessor, the maser, in a ground-breaking rederivation of Max Planck ‘s jurisprudence of radiation based on the constructs of chance coefficients ( subsequently to be termed ‘Einstein coefficients ‘ ) for the soaking up, self-generated emanation, and stimulated emanation of electromagnetic radiation.
In 1928, Rudolph W. Landenburg confirmed the being of stirred emanation and negative soaking up. In 1939, Valentine A. Fabrikant predicted the usage of stirred emanation to magnify “ short ” moving ridges.
In 1947, Willis E. Lamb and R. C. Rutherford found evident stirred emanation in H spectra and made the first presentation of stirred emanation.
In 1950, Alfred Kastler ( Nobel Prize for Physics 1966 ) proposed the method of optical pumping, which was by experimentation confirmed by Brossel, Kastler.
In 1957, Charles Hard Townes and Arthur Leonard Schawlow, so at Bell Labs, began a serious survey of the infrared optical maser. As thoughts were developed, infrared frequences were abandoned with focal point on seeable light alternatively. The construct was originally known as an “ optical maser ” . Bell Labs filed a patent application for their proposed optical maser a twelvemonth subsequently. Schawlow and Townes sent a manuscript of their theoretical computations to Physical Review, which published their paper that twelvemonth.
The first page of Gordon Gould ‘s optical maser notebook in which he coined the acronym LASER and described the indispensable elements for building one.
At the same clip Gordon Gould, a alumnus pupil at Columbia University, was working on a doctorial thesis on the energy degrees of aroused Tl. Gould and Townes met and had conversations on the general topic of radiation emanation. Afterwards Gould made notes about his thoughts for a “ optical maser ” in November 1957, including proposing utilizing an unfastened resonating chamber, which became an of import ingredient of future optical masers.
In 1958, Prokhorov independently proposed utilizing an unfastened resonating chamber, the first published visual aspect of this thought. Schawlow and Townes besides settled on an unfastened resonating chamber design, seemingly incognizant of both the published work of Prokhorov and the unpublished work of Gould.
The term “ optical maser ” was foremost introduced to the populace in Gould ‘s 1959 conference paper “ The LASER, Light Amplification by Stimulated Emission of Radiation ” . Gould intended “ -aser ” to be a postfix, to be used with an appropriate prefix for the spectrum of visible radiation emitted by the device ( x-rays: xaser, UV: uvaser, etc. ) . None of the other footings became popular, although “ raser ” was used for a short clip to depict radio-frequency breathing devices.
First working optical maser was made by Theodore H. Maiman in 1960 at Hughes Research Laboratories in Malibu, California, crushing several research squads including those of Townes at Columbia University, Arthur Schawlow at Bell Labs, and Gould at a company called TRG ( Technical Research Group ) . Maiman used a solid-state flashlamp-pumped man-made ruby crystal to bring forth ruddy optical maser visible radiation at 694 nanometers wavelength. Maiman ‘s optical maser, nevertheless, was merely capable of pulsed operation due to its three-level pumping strategy.
The construct of the semiconducting material optical maser rectifying tube was proposed by Basov and Javan. The first optical maser rectifying tube was demonstrated by Robert N. Hall in 1962. Hall ‘s device was made of Ga arsenide and emitted at 850 nanometer in the near-infrared part of the spectrum. The first semiconducting material optical maser with seeable emanation was demonstrated subsequently the same twelvemonth by Nick Holonyak, Jr. As with the first gas optical masers, these early semiconducting material optical masers could be used merely in pulsed operation, and so merely when cooled to liquid N temperatures ( 77 K ) .
In 1970, Zhores Alferov in the Soviet Union and Izuo Hayashi and Morton Panish of Bell Telephone Laboratories independently developed laser rectifying tubes continuously runing at room temperature, utilizing the heterojunction construction.
Theory: -The rule of a optical maser is based on two separate characteristics:
a ) a light emitting/amplifying medium B ) an optical resonating chamber ( normally defined by two parallel mirrors ) .
The physical procedure responsible for the light elaboration is supposed to be the stimulated ( induced ) emanation procedure which is assumed to happen in instance of a population inversion between two atomic provinces in a radiation field of the corresponding frequence. This would take to the atomic emanation magnifying the incident radiation field precisely in stage ( coherently ) which would immensely increase the amplitude of the end point wavetrain compared to an incoherent ( random ) superposition ( because for N emitters it would be relative to N instead than aE†A?N ) .
Now there is in my sentiment a cardinal conceptual job with the premise of the being of a stimulated ( induced ) emanation: atomic natural philosophies distinguishes two different mechanisms for radiative passages between two degrees i, K of an atom:
a ) Spontaneous emanation that occurs with a chance given by the decay changeless Ai, K, B ) induced emanation or soaking up due to an external radiation field. Resonant sprinkling is for case normally considered as soaking up of a photon which lifts an negatron to a higher energy degree followed by the re- emanation of a photon when the negatron falls spontaneously back once more. However, both a theoretical consideration and experimental grounds shows that this image of a two-step procedure is non right and that resonant sprinkling has to be described as a coherent procedure ( i.e. a forced oscillator with muffling changeless Ai, K ) . Unlike photo ionisation or excitement by electron/ion impact, dispersing involves hence no atomic energy alterations as no work as being done.
With respect to the optical resonating chamber ( e.g. mirrors ) , classical optical maser theory assumes now that it ( apart from concentrating the visible radiation ) serves as a agency to enable all atoms in the light breathing medium to radiate in stage, viz. if its length is a multiple of half the wavelength. In this instance of optical resonance, a standing moving ridge will be set up for a strictly sinusoidal signal, and it is assumed that this circumstance enables the proposed procedure of stirred emanation to magnify all emanations in stage. It is normally argued here that the per se self-generated and random emanation develops into a moving ridge with a unambiguously defined stage because one of the initial emanations ‘overwhelms ‘ all the others and hence defines the stage of the radiation field. However, this is merely a manus beckoning statement which in fact defies common sense ( as it would go against the superposition rule for case ) . Even if a stirred emanation procedure exists, it is merely possible that the initial ‘photons ‘ nowadays before the state of affairs of a population inversion are being amplified in stage individually when meeting an atom in an aroused province. Although a standing moving ridge will be set up for each of these coherently amplified ‘photons ‘ individually in the optical resonating chamber, this has really no consequence on acquiring farther emanations in stage as this would go on anyhow ( laser or maser effects do seemingly besides occur in natural media without any optical resonating chamber every bit long as there is a important population inversion ) . The lone consequence the optical resonating chamber has here is to magnify each of the wavetrains by turn uping it back into itself if it is long plenty. This, non surprisingly, is easy the instance for all optical maser passages as these arise typically from ( quasi- ) metastable provinces with really long life times. For a moving ridge train with length L the attendant amplitude would hence be L/l if cubic decimeter is the distance between the mirrors ( provided the mirror coefficient of reflection allows that many contemplations ; otherwise the amplitude would be determined.The attendant moving ridge train is now consequently shorter ( in consequence ) but this will in many instances non be so of import for the subsequent interaction with affair as the increased moving ridge amplitude. However, as all N standing moving ridges are indiscriminately out of stage, the elaboration is evidently much less than for a consistent superposition of all emitters ( L/l is normally much smaller than N ) .
Two coherent optical maser beams derived from a individual beginning intersect at a fixed angle. The intersection volume of the two beams is positioned on the sample surface. The wave fronts of the two beams interfere in the intersection volume and organize an intervention form. The peripheries of the form have a known distance depending on the wavelength of the optical maser and the angle between the two beams.
For simpleness, assume that an component with a speed constituent perpendicular to the centre axis is traveling through the intersection volume. The component will disperse light with its amplitude modulated by the local strength contrast. The frequence of the transition is relative to the speed of the component.
Therefore when entering the strength signal the gesture of elements within the observation country can be calculated. A typical sample with its natural raggedness contains dispersing elements everyplace on its surface which allows the measuring of the sum of stuff traveling through the observation country.
By coincident measuring at two points of the sample surface the relation
gesture between these two points can be determined. This allows the usage of the mensurating agreement as an extensometer.
TYPES OF LASER
[ I ] Based on its pumping strategy a optical maser can be classified as
[ a ] Optically pumped optical maser
[ B ] Electrically pumped optical maser
[ II ] On the footing of the operation manner, laser autumn into categories of
[ a ] Continuous Wave Lasers
[ B ] Pulsed Lasers.
[ III ] Harmonizing to the stuffs used to bring forth laser visible radiation, optical masers can be divided into three classs:
[ a ] Gas Lasers
[ B ] Solid State Lasers
[ degree Celsius ] Semiconductor Lasers
[ vitamin D ] Other Laser Devicess
Brief inside informations of type
( I ) Gas Laser:
Gas optical masers by and large have a broad assortment of features. For illustration, some gas optical masers emit lame power below 1mW, but other commercial gas optical masers emit power of the order of kW. Some optical masers can breathe uninterrupted beam for old ages, others emit pulsations enduring a few nanoseconds. Their end products range from deep in the UV through the seeable and infrared to millimetre moving ridges.
( a ) . Helium- Ne ( HeNe )
The optical maser medium is a mixture of He and Ne gases. An electrical discharge, in the signifier of direct current or radio frequence current, is used to excite the medium to a higher energy degree. The pumping action takes topographic point in a complex and indirect mode. First the He atoms are excited by the discharge to two of the aroused energy degrees These two degrees go on to be really near to the 3s and 2s degrees of the Ne atoms. When the aroused He atoms collide with the Ne atoms, energy is exchanged, pumping the Ne atoms to the several degrees. The atoms at the Ne 3s degree finally drops down to the 2p degree, as a consequence of stirred emanation, and visible radiation of wavelength 632.8 nanometer is emitted. The atoms at the 2s degree, on the other manus, drops to the 2p degree by breathing visible radiation at 1.15 nanometer. However, the atoms at the 3s degree may alternatively drop down to the 3p degree, by breathing visible radiation at 3.39 millimeter. 632.8nm is in the seeable scope.
( B ) . Gallium Arsenate ( GaAs ) Laser
( two ) . Solid province optical maser:
A solid province optical maser is one in which the atoms that emit light are fixed within a crystal or a glassy stuff. The first optical maser invented by Maiman in 1960, the ruby optical maser, was a solid province optical maser. The atoms that emit light in solid province optical masers are dispersed in a crystal or a piece of glass that contains many other elements. The crystal is shaped into a rod, with reflecting mirrors placed at each terminal. Light from an external beginning ( such as a pulsed flash lamp, a bright uninterrupted discharge lamp, or another optical maser ) enters the optical maser rod and excites the light-emitting atoms. The two mirrors form a resonating pit and the upside-down population in the optical maser rod, provided the feedback needed to bring forth a optical maser beam that emerges through the end product mirror.
As the photons traverse the crystal, they stimulate the emanation of extra photons until adequate energy is available for a pulsation of photons to interrupt through the thinly mirrored terminal on the right of the optical maser crystal.
The Nd: YAG optical maser is a good illustration of the most normally used solid province optical masers. The optical maser medium is made up of yttrium- aluminium-garnet, with trivalent Nd ions present as drosss. The optical maser passage involved corresponds to a wavelength of 1.06 millimeter, in the close infrared part
( three ) . Semiconductor Laser:
A unique, and possibly the most of import, type of optical maser in footings of opto- electronics applications is the semiconducting material optical maser. It is alone because of its little dimensions ( mm x millimeter x millimeter ) , and its natural integrating capablenesss with micro electronic circuitry, Furthermore, the light elaboration by the procedure of stirred emanation is non precisely in the signifier that we have described before.
A semiconducting material optical maser uses particular belongingss of the passage part at the junction of a p-type semiconducting material in contact with an n-type semiconducting material. In semiconducting material stuffs, because of the extended interaction of energy between atoms, the energy degrees form sets. Energy set diagrams for an n-type and a p-type semiconducting material are depicted in The energy spread between the valency set and the conductivity set is designated by Eg and is measured in electronvolts, e.g. , the Fermi degree Ef is the degree that divides the occupied from the unoccupied degrees.
In a p-n junction, as shown in the energy degrees readjust in conformity with thermodynamics so that the Ef set is the same through the junction. The valency set Evv and the conductivity set Ec of the p-type semiconducting material are higher than the corresponding sets of the n-type semiconducting material. If a positive electromotive force is applied on the p side ( the alleged positive prejudice ) , the negatrons on the n side will be attracted by the applied electromotive force and will traverse into the junction part. There they recombine with the holes that have been pushed into the junction part by the positive prejudice. This procedure will go on every bit long as the external circuit is on, because the negatrons and holes that have recombined are continuously replenished.
When the negatrons and holes recombine, they emit energy in the signifier of photons. The junction passage part in which this takes topographic point is hence the beginning of radiation, and may be viewed as equivalent to the E2 and E1 passage degrees which we discussed earlier.
To obtain stirred emanation and elaboration from this part, the equivalent of the population inversion needs to be created, for which a high denseness of negatrons and a high denseness of holes must be at the same time in the junction part. To accomplish this, to a great extent doped p-n junctions are used in semiconducting material optical masers.
shows the attendant energy degrees. When a positive prejudice is applied on the p-side, there is a passage part with a high concentration of negatrons and holes, as shown in This part serves as a population upside-down medium, which amplifies the radiation emitted within it through electron – hole recombination. A p-n junction semiconducting material optical maser is illustrated schematically in The shaded country is the passage part where the optical maser action takes topographic point. This part is about 1-2 millimeter midst, and 10s of microns long. As a consequence, the emanation is squeezed into a thin plane, taking to an egg-shaped cross-section of the beam.
( four ) Other Laser devices:
( a ) . Ion and Metal Vapour Laser: -Operated at high temperatures to maintain the metals ( e.g. , Cu, gold etc. ) vaporized and produced laser visible radiation in the infrared, seeable or ultraviolet parts. They are first-class beginnings of short, high-intensity optical maser pulsations at really high pulse-repetition rates. The mixture of metal vapor and baronial gases are excited by electrical discharges. Example is copper vapor optical masers which produces green and xanthous visible radiation from a mixture of Cu vapor with He and Ne.
( B ) . Carbon Dioxide Laser.
( degree Celsius ) . The excimer Laser.
( vitamin D ) . The liquid ( dye ) Laser: Dye optical masers use liquid organic dyes.
Dye optical masers can bring forth a wide and about uninterrupted scope of colourss, chiefly in the seeable portion of the spectrum. With proper optical system any coloring material can be selected or tuning from one coloring material to another can be done. That is why dye optical masers are peculiarly suited for applications in which a precise coloring material is required. Normally another optical maser beginning e.g. , Cu vapor optical masers are used to excite the dye.
( vitamin E ) . The Free Electron optical maser.
Applications of optical maser: –
There are a big no of applications of optical maser in our day-to-day life
1: -Spectroscopy: – Most types of optical maser are an inherently pure beginning
of visible radiation ; they emit nearmonochromatic visible radiation with a really good defined scope of wavelengths. By careful, the pureness of the optical maser visible radiation ( measured as the “ linewidth ” ) can be improved more than the pureness of any other light beginning. This makes the optical maser a really utile beginning for spectrometry. The high strength of visible radiation that can be achieved in a little, good collimated beam can besides be used to bring on a nonlinear optical consequence in a sample, which makes techniques such as Raman spectroscopy possible. Other spectroscopic techniques based on optical masers can be used to do highly sensitive sensors of assorted molecules, able to mensurate molecular concentrations in the parts-per-trillion ( ppt ) degree. Due to the high power densenesss accomplishable by optical masers, beam-induced atomic emanation is possible: this technique is termed Laser induced breakdown spectrometry ( LIBS ) .
Some of the universe ‘s most powerful and complex agreements of multiple optical masers and optical amplifiers are used to bring forth highly high strength pulsations of visible radiation of highly short continuance. These pulsations are arranged such that they impact pellets of tritium-deuterium at the same time from all waies, trusting that the squashing consequence of the impacts will bring on atomic merger in the pellets. This technique, known as “ inertial parturiency merger ” , so far has non been able to accomplish “ breakeven ” , that is, so far the merger reaction generates less power than is used to power the optical masers, but research continues.
( a ) .Cosmetic surgery ( taking tattoos, cicatrixs, stretch Markss, maculas, furrows, nevuss, and hairs ) : see laser hair remotion. Laser types used in dermatology include ruby ( 694 nanometer ) , alexandrite ( 755 nanometer ) , pulsed diode array ( 810 nanometer ) , Nd: YAG ( 1064 nanometer ) , Ho: YAG ( 2090 nanometer ) , and Er: YAG ( 2940 nanometer ) .
( B ) Eye surgery:
LASIK ( laser vision rectification )
LASEK ( laser-assisted sub-epithelial keratectomy )
PRK ( photorefractive keratectomy )
( degree Celsius ) .Soft tissue surgery: CO2, Er: YAG optical maser
( vitamin D ) .Laser scalpel ( General surgery, gynaecological, urology, laparoscopic )
( vitamin E ) .Dental processs
( degree Fahrenheit ) Photobiomodulation ( i.e. optical maser therapy )
( g ) ” No-Touch ” remotion of tumours, particularly of the encephalon and spinal cord.
( H ) In dental medicine for cavities remotion, endodontic/periodontic proc Es, tooth whiteningedur, and unwritten surgery.
Defensive countermeasures: –
Defensive countermeasure applications can run from compact, low power infrared countermeasures to high power, airborne optical maser systems. IR countermeasure systems use optical masers to confound the searcher caputs on heat-seeking anti-aircraft missiles. High power boost-phase intercept optical maser systems use a complex system of optical masers to happen, path and destruct intercontinental ballistic missiles. In this type of system a chemical optical maser, one in which the optical maser operation is powered by an energetic chemical reaction, is used as the chief arm beam ( see Airborne Laser ) . The Mobile Tactical High-Energy Laser ( MTHEL ) is another defensive optical maser system under development ; this is envisioned as a field-deployable arm system able to track incoming heavy weapon missiles and sail missiles by radio detection and ranging and destruct them with a powerful heavy hydrogen fluoride optical maser.
Another illustration of direct usage of a optical maser as a defensive arm was researched for the Strategic Defense Initiative ( SDI, nicknamed “ Star Wars ” ) , and its replacement plans. This undertaking would utilize ground-based or space-based optical maser systems to destruct incoming intercontinental ballistic missiles ( ICBMs ) . The practical jobs of utilizing and taking these systems were many ; peculiarly the job of destructing ICBMs at the most opportune minute, the encouragement stage merely after launch. This would affect directing a optical maser through a big distance in the ambiance, which, due to optical sprinkling and refraction, would flex and falsify the optical maser beam, perplexing the aiming of the optical maser and cut downing its efficiency.
In the April 2008 edition of Popular Science, there is an article showcasing a new combat optical maser, the Boeing Advanced Tactical Laser Beam, which will be carried in a big aircraft ( it is shown carried in a C-130 ) and fired at big marks ( vehicles or edifices. ) It is presently being tested at Kirtland Air Force Base in New Mexico. The optical maser itself is a chemical optical maser, and weighs 40,000 lbs. The scope is reported to be 5 stat mis, and it can quickly strike marks ( it uses rapid-fire instead than a uninterrupted beam to minimise the hazard of friendly fire. ) However, the paradigm cost $ 200 million, doing it dubious that this will be put to widespread usage. Baring the cost, it is expected to be in conflict within five old ages. The late introduced FIRESTRIKE optical maser system is little plenty ( 400lbs ) to suit into light vehicles.