final report

• 1. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 1IntroductionA laser is a device that emits light through a process of optical amplification based onthe stimulated emission or electromagnetic radiation. The term "laser" originatedas acronyms for Light Amplification by Stimulated Emission of Radiation.Lasers differ from other sources of light because they emit light coherently. Spatialcoherence allows a laser to be focused to a tight spot, enabling applications like laser cuttingand lithography. Spatial coherence also allows a laser beam to stay narrow over longdistances (collimation), enabling applications such as laser pointers.Lasers can also have high temporal coherence which allows them to have a verynarrow spectrum i.e., they only emit a single color of light. Temporal coherence can be usedto produce pulses of lightas short as a femto second.Fig.1.1 laser lightLaser beams can be focused to very tiny spots, achieving a very high irradiance, or they canbe launched into beams of very low divergence in order to concentrate their power at a largedistance.Lasers are distinguished from other light sources by their coherence. Spatial coherence istypically expressed through the output being a narrow beam which is diffraction- limited,often a so-called "pencil beam." Laser beams can be focused to very tiny spots, achieving avery high irradiance, or they can be launched into beams of very low divergence in order toconcentrate their power at a large distance.ME-DEPARTMENT SRMGPC LKO 1 | P a g e

2. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYProperties of laser1. The light emitted by lasers is different from that produced by more common light sourcessuch as incandescent bulbs, fluorescent lamps, and high-intensity arc lamps. Anunderstanding of the unique properties of laser light may be achieved by contrasting itwith the light produced by other, less unique sources.2. Highly directional nature of light produced by a laser. "Directionality" is thecharacteristic of laser light that causes it to travel in a single direction within a narrowcone of divergence.3. It consists of an extremely narrow range of wavelengths within the red portion of thespectrum. It is said to nearly monochromatic, meaning that it consists of light of almostsingle wavelength.4. Coherence is the most fundamental property of laser light and distinguishes it from thelight from other sources. Thus, a laser may be defined as a source of coherent light. Sothat laser light is highly coherent, means that phases at every instant of time are alwayssame.ME-DEPARTMENT SRMGPC LKO 2 | P a g eFig. 1.2First, let's discuss the properties of laser light and then we will go into how iscreated. Laser light is monochromatic, directional, and coherent.Fig.1.3 3. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 2History of laserMax Plank published work in 1900 that provided the understanding that light is a form ofelectromagnetic radiation. Without this understanding the laser would not have beeninvented.The principle of the laser was first known in 1917, when physicist Albert Einstein describedthe theory of stimulated emission. However, it was not until the late 1940s that engineersbegan to utilize this principle for practical purposes. At the onset of the 1950s severaldifferent engineers were working towards the harnessing of energy using the principal ofstimulated emission.At the University of Columbia was Charles Townes, at the Univers ity of Maryland wasJoseph Weber and at the Lebedev Laboratories in Moscow were Alexander Prokhorov andNikolai G Basov. At this stage the engineers were working towards the creation of what wastermed a MASER (Microwave Amplification by the Stimulated Emission of Radiation),A device that amplified microwaves as opposed to light and soon found use in microwavecommunication systems. Townes and the other engineers believed it to be possible to createan optical maser,A device for creating powerful beams of light using higher frequency energy to stimulatewhat was to become termed the lasing medium. Despite the pioneering work of Townes andProkhorov it was left to Theodore Maiman in 1960 to invent the first Laser using a lasingmedium of ruby that was stimulated using high energy flashes of intense light.Townes and Prokhorov were later awarded the Nobel Science Prize in 1964 for theirendeavors.Fig 2.1 scientist who developed laserThe Laser was a remarkable technical breakthrough, but in its early years it was something ofa technology without a purpose. It was not powerful enough for use in the beam weaponsenvisioned by the military, and its usefulness for transmitting information through theatmosphere was severely hampered by its inability to penetrate clouds and rain. Almostimmediately, though, some began to find uses for it. Maiman and other engineers developedlaser weapons sighting systems and powerful lasers for use in surgery and other.ME-DEPARTMENT SRMGPC LKO 3 | P a g e 4. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYAlbert Einstein first explained the theory of stimulated emission in 1917, which became thebasis of Laser. He postulated that, when the population inversion exists between upper andlower levels among atomic systems, it is possible to realize amplified stimulated emissionand the stimulated emission has the same frequency and phase as the incident radiation.However, it was in late 1940s and fifties that scientists and engineers did extensive work torealize a practical device based on the principle of stimulated emission. Notable scientistswho pioneered the work include Charles Townes, Joseph Weber, Alexander Prokhorov andNikolai G Basov.Initially, the scientists and engineers were working towards the realization of a MASER(Microwave Amplification by the Stimulated Emission of Radiation) ; a device that amplifiedmicrowaves for its immediate application in microwave communication systems. Townesand the other engineers believed it to be possible create an optical maser, a device forcreating powerful beams of light using higher frequency energy to stimulate what was tobecome termed the lasing medium. Despite the pioneering work of Townes and Prokhorov itwas left to Theodore Maiman in 1960 to invent the first Laser using ruby as a lasing mediumthat was stimulated using high energy flashes of intense light.The development of Lasers has been a turning point in the history of science and engineering.It has produced a completely new type of systems with potentials for applications in a widevariety of fields. During sixties, lot of work had been carried out on the basic development ofalmost all the major lasers including high power gas dynamic and chemical lasers. Almost allthe practical applications of these lasers in defense as well as in industry were also identifiedduring this period. The motivation of using the high power lasers in strategic scenario was agreat driving force for the rapid development of these high power lasers. In early seventies,megawatt class carbon dioxide gas dynamic laser was successfully developed and testedagainst typical military targets. The development of chemical lasers, free electron and X-raylasers took slightly longer time because of involvement of multidisciplinary approach.The major steps of advances or breakthroughs in Laser research are given below: Dates,Contributors and events:1917: Einstein, A. - Concept and theory of stimulated light emission1948: Gabor, D. - Invention of holography1951: Charles H Townes, Alexander Prokhorov, Nikolai G Basov, Joseph Weber - Theinvention of the MASER (Microwave Amplification of Stimulated Emission of Radiation) atColumbia University, Lebedev Laboratories, Moscow and University of Maryland.1956: Bloembergen, N. - Solid-state maser- [Proposal for a new type of solid state maser] atHarvard University.1958: Schawlow, A.L. and Townes, C.H. - Proposed the realization of masers for light andinfrared at Columbia University.ME-DEPARTMENT SRMGPC LKO 4 | P a g e 5. A STUDY ON THE APPLICATION OF LASER TECHNOLOGY1960: Maiman, T.H. - Realization of first working LASER based on Ruby at HughesResearch Laboratories.1961: Javan, A., Bennet, W.R. and Herriot, D.R. - First gas laser: Helium- Neon (He-Nelaser) at Bell Laboratories.1961: Fox, A.G., Li, T. - Theory of optical resonators at Bell Laboratories.1962: Hall,R. - First Semiconductor laser (Gallium-Arsenide laser) at General Electric Labs.1962: McClung,F.J and Hellwarth, R.W. - Giant pulse generation / Q-Switching.1962: Johnson, L.F., Boyd, G.D., Nassau, K and Sodden, R.R. - Continuous wave solid-statelaser.1964: Geusic, J.E., Markos, H.M., Van Uiteit, L.G. - Development of first working Nd:YAGLASER at Bell Labs.1964: Patel, C.K.N. - Development of CO2 LASER at Bell Labs.1964: Bridges, W. - Development of Argon Ion LASER a Hughes Labs.1965: Pimentel, G. and Kasper, J. V. V. - First chemical LASER at University of California,Berkley.1965: Bloembergen, N. - Wave propagation in nonlinear media.1966: Silfvast, W., Fowles, G. and Hopkins - First metal vapor LASER - Zn/Cd - atUniversity of Utah.1966: Walter, W.T., Solomon, N., Piltch, M and Gould, G. - Metal vapor laser.1966: Sorokin, P. and Lankard, J. - Demonstration of first Dye Laser action at IBM Labs.1966: AVCO Research Laboratory, USA. - First Gas Dynamic Laser based on CO21970: Nikolai Basov's Group - First Excimer LASER at Lebedev Labs, Moscow based onXenon (Xe) only.1974: Ewing, J.J. and Brau, C. - First rare gas halide excimer at Avco Everet Labs.1977: John M J Madey's Group - First free electron laser at Stanford University.1977: McDermott, W.E., Pehelkin, N.R,. Benard, D.J and Bousek, R.R. - Chemical OxygenIodine Laser (COIL).1980: Geoffrey Pert's Group - First report of X-ray lasing action, Hull University, UK.1984: Dennis Matthew's Group - First reported demonstration of a "laboratory" X-ray laserfrom Lawrence Livermore Labs.1999: Herbelin,J.M., Henshaw, T.L., Rafferty, B.D., Anderson, B.T., Tate, R.F., Madden,T.J., Mankey II, G.C and Hager, G.D. - All Gas-Phase Chemical Iodine Laser (AGIL).2001: Lawrence Livermore National Laboratory - Solid State Heat Capacity Laser (SSHCL).ME-DEPARTMENT SRMGPC LKO 5 | P a g e 6. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYDevelopment of lasernd Stimulated Light1. In 1905 German scientist Albert Einstein announced his own theory about light, namelythat it is made up of both particles and waves. Einstein claimed that the particles, calledphotons (from the Greek word for "light"), move along in wavelike patterns. Later, otherscientists performed experiments that proved Einstein was right. Einstein himself thenwent on to predict some more startling things about light, first and foremost how photonsare made. He agreed with some other scientists of his day about how light sources (likecandles, light bulbs, or the sun) produce photons. The researchers thought that atoms (thetiny particles that make up all material in the universe) give off photons. Some form ofenergysuch as heat, electricity, or chemical energymight "excite" an atom, or make itmore energetic. It would then emit (give off) a photon. Afterward, the atom would goback to its normal, unexcited state. Because there are huge numbers of atoms, they giveoff equally large numbers of photons. A 100-watt light bulb gives off about 10 trillionphotons every second.2. 1951, while sitting on a park bench, Townes had a brilliant idea. He realized it might bepossible to use molecules of ammonia to produce a powerful microwave beam. (Amolecule consists of two or more atoms that are connected together.) Townes reasonedCharles Townes (left) and James P. Gordon proudly display their maser, a device thatgreatly amplifies microwaves. That when molecules of ammonia became excited (byheat, electricity, or chemical energy), they could be stimulated to emit microwaves of thetype he was working with. He knew this process would be almost identical to the oneEinstein described for stimulating visible light. The only difference was that Towneswould be using microwaves instead of light. He calculated that if the ammonia moleculescould be kept in an excited state long enough, they might be stimulated to produce moreand more microwaves. Eventually, the waves would become concentrated and morepowerful. In short, the microwaves would be amplified.Townes decided to try to build aworking model. He enlisted the aid of two other researchers, Herbert J. Zigler and JamesP. Gordon. Working diligently, by 1954 the three men had a working device that operatedin the following way: First, some ammonia gas was heated until many of the moleculesbecame excited and then were separated from the unexcited molecules. Next, the excitedME-DEPARTMENT SRMGPC LKO 6 | P a g e 7. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYmolecules flowed into a chamber called the resonant cavity (or resonator) where thestimulation of the molecules took place. As the excited ammonia molecules began to emitmicrowave particles, the particles began to bounce back and forth inside the chamber.When one of these particles came near an excited molecule, the molecule suddenly gaveoff its own particle. Thus the particles themselves stimulated the production of moreparticles. Soon the number of particles doubled, and then doubled again and again untilthe microwaves in the chamber had become very powerful.3. By 1960 many scientists, including Townes and Schawlow, Basov and Prokhorov, andGould, had asked for laser patents. In addition, the paper published by Townes andSchawlow had caused widespread interest in lasers in the American scientificcommunity. Researchers in labs around the country raced to be first to construct aworking model. The first successful device appeared on July 7, 1960, built by apreviously unknown researcher who had worked totally on his ownTheodore H.Maiman of the Hughes Aircraft Company in Malibu, California. Maiman's laser wassmall (only a few inches long) and not very complicated. The core of the device consistedof an artificial ruby about one and a half inches long, so Maiman called his invention the"ruby laser."4. The first gas laser (helium neon) was invented by Ali Javan, in 1960. The gas laser wasthe first continuous-light laser and the first to operate "on the principle of convertingelectrical energy to a laser light output." It has been used in many practical applications.5. In 1962, Robert Hall, created a revolutionary type of laser that is still used in many of theelectronic appliances and communications systems that we use every day.Fig. 2.2 laser research centerME-DEPARTMENT SRMGPC LKO 7 | P a g e 8. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 3Components of laserAll Lasers are comprised of these essential mediumEvery laser have a three basic components are;1 Active medium.2 External source.3 Optical resonator.Fig.3.1 components of laser1. The active medium is excited by the external energy source (pump source) to producepopulation inversion. In the gain medium that spontaneous and stimulated emission ofphotons takes place, leading to the phenomenon of optical gain, or amplification.Semiconductors, organic dyes, gases (He, Ne, CO2, etc.), solid materials ( YAG,sapphire(ruby) etc.) are usually used as lasing materials and often LASERs are named forthe ingredients used as medium.2. The excitation source, pump source provides energy which is needed for thepopulation inversion and stimulated emission to the system. Pumping can be done in twoways electrical discharge method and optical method. Examples of pump sources areME-DEPARTMENT SRMGPC LKO 8 | P a g e 9. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYelectrical discharges, flash lamps, arc lamps, light from another laser, chemical reactionsetc.3. Resonator guide basically provides the guidance about the simulated emission process.It is induced by high speed photons. Finally, a laser beam will be generated.In most of the systems, it consists of two mirrors. One mirror is fully reflective and otheris partially reflective. Both the mirrors are set up on optic axis, parallel to each other. Theactive medium is used in the optical cavity between the both mirrors. This arrangementonly filters those photons which came along the axis and others are reflected by themirrors back into the medium, where it may be amplified by stimulated emission.Electrons in the atoms of the lasing material normally reside in a steady-state lower energylevel. When light energy from the flash lamp is added to the atoms of the lasing material, themajority of the electrons are excited to a higher energy level -- a phenomenon known aspopulation inversion. This is an unstable condition for these electrons. They will stay in thisstate for a short time and then decay back to their original energy state. This decay occurs intwo ways: spontaneous decay -- the electrons simply fall to their ground state while emittingrandomly directed photons; and stimulated decay -- the photons from spontaneous decayingelectrons strike other excited electrons which causes them to fall to their ground state. Thisstimulated transition will release energy in the form of photons of light that travel in phase atthe same wavelength and in the same direction as the incident photon. If the direction isparallel to the optical axis, the emitted photons travel back and forth in the optical cavitythrough the lasing material between the totally reflecting mirror and the partially reflectingmirror. The light energy is amplified in this manner until sufficient energy is built up for aburst of laser light to be transmitted through the partially reflecting mirror.As shown in figure 4, a lasing medium must have at least one excited (metastable) statewhere electrons can be trapped long enough (microseconds to milliseconds) for a populationinversion to occur. Although laser action is possible with only two energy levels, most lasershave four or more levels.ME-DEPARTMENT SRMGPC LKO 9 | P a g e 10. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig. 3.2 Three level laser energy diagramA Q-switch in the optical path is a method of providing laser pulses of extremely short timeduration. A rotating prism like the total reflector in figure 3 was an early method of providingQ-switching. Only at the point of rotation when there is a clear optical path will light energybe allowed to pass.A normally opaque electro-optical device (e.g., a pockets cell) is now often used for a Q-switchingdevice. At the time of voltage application, the device becomes transparent; thelight built up in the cavity by excited atoms can then reach the mirror so that the cavityQuality, Q, increases to a high level and emits a high peak power laser pulse of a fewnanoseconds duration.When the phases of different frequency modes of a laser are synchronized (locked together),these modes will interfere with each other and generate a beat effect. The result is a laseroutput with regularly spaced pulsations called "mode locking". Mode locked lasers usuallyproduce trains of pulses with a duration of a few picoseconds to nanoseconds resulting inhigher peak powers than the same laser operating in the Q-switched mode.Pulsed lasers are often designed to produce repetitive pulses. The pulse repetition frequency,PRF, as well as pulse width is extremely important in evaluating biological effects.ME-DEPARTMENT SRMGPC LKO 10 | P a g e 11. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 4Types of laser1. Semiconductor laserThe laser diode is a light emitting diode with an optical cavity to amplify the light emittedfrom the energy band gap that exists in semiconductors as shown in figure 11. They can betuned by varying the applied current, temperature or magnetic field.Fig.4.1 Semiconductor laser diagram2. Gas laserGas lasers consist of a gas filled tube placed in the laser cavity as shown in figure 12. Avoltage (the external pump source) is applied to the tube to excite the atoms in the gas to apopulation inversion. The light emitted from this type of laser is normally continuous wave(CW). One should note that if Brewster angle windows are attached to the gas dischargetube, some laser radiation may be reflected out the side of the laser cavity. Large gas lasersknown as gas dynamic lasers use a combustion chamber and supersonic nozzle forpopulation inversion.Fig.4.2 Gas laser diagramME-DEPARTMENT SRMGPC LKO 11 | P a g e 12. A STUDY ON THE APPLICATION OF LASER TECHNOLOGY3. Dye laserFigure 13 shows a dye laser diagram. Dye lasers employ an active material in a liquidsuspension. The dye cell contains the lasing medium. Many dyes or liquid suspensions aretoxic.Fig.4.3 Common Dye Laser Diagram4. Free electron laserFree electron lasers such as in figure 14 have the ability to generate wavelengths from themicrowave to the X-ray region. They operate by having an electron beam in an optical cavitypass through a wiggler magnetic field. The change in direction exerted by the magnetic fieldon the electrons causes them to emit photons.ME-DEPARTMENT SRMGPC LKO 12 | P a g e 13. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig.4.4 Free Electron Laser Diagram5. Transverse electromagnetic laserLaser beam geometries display transverse electromagnetic (TEM) wave patterns across thebeam similar to microwaves in a wave guide. Figure 9 shows some common TEM modes ina cross section of a laser beam.Fig.4.5 Common TEM laser beam modesA laser operating in the mode could be considered as two lasers operating side byside. The ideal mode for most laser applications is the mode and this mode isnormally assumed to easily perform laser hazards analysis. Light from a conventional lightsource is extremely broadband (containing wavelengths across the electromagneticspectrum). If one were to place a filter that would allow only a very narrow band ofwavelengths in front of a white or broadband light source, only a single light color would beseen exiting the filter. Light from the laser is similar to the light seen from the filter.However, instead of a narrow band of wavelengths none of which is dominant as in the caseof the filter, there is a much narrower line width about a dominant center frequency emittedfrom the laser. The color or wavelength of light being emitted depends on the type of lasingmaterial being used. For example, if a Neodymium: Yttrium Aluminum Garnet (Nd:YAG)crystal is used as the lasing material, light with a wavelength of 1064 nm will be emitted.Table 1 illustrates various types of material currently used for lasing and the wavelengths thatare emitted by that type of laser. Note that certain materials and gases are capable of emittingmore than one wavelength. The wavelength of the light emitted in this case is dependent onthe optical configuration of the laser.ME-DEPARTMENT SRMGPC LKO 13 | P a g e 14. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYTable 1 Common Lasers and Their WavelengthsLASER TYPEWAVELENGTH(Nanometers)Argon Fluoride 193Xenon Chloride 308 and 459Xenon Fluoride 353 and 459Helium Cadmium 325 - 442Rhodamine 6G 450 - 650Copper Vapor 511 and 578Argon457 - 528 (514.5 and 488most used)Frequency doubled Nd:YAG 532Helium Neon 543, 594, 612, and 632.8Krypton337.5 - 799.3 (647.1 - 676.4most used)Ruby 694.3Laser Diodes 630 - 950Ti:Sapphire 690 - 960Alexandrite 720 - 780Nd:YAG 1064Hydrogen Fluoride 2600 - 3000Erbium:Glass 1540Carbon Monoxide 5000 - 6000Carbon Dioxide 10600Light from a conventional light source diverges or spreads rapidly show in fig 16. Theintensity may be large at the source, but it decreases rapidly as an observer moves away fromthe source.ME-DEPARTMENT SRMGPC LKO 14 | P a g e 15. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFigure 4.6 Divergence of Conventional Light SourceIn contrast, the output of a laser as shown in figure 17 has a very small divergence and canmaintain high beam intensities over long ranges. Thus, relatively low power lasers are able toproject more energy at a single wavelength within a narrow beam than can be obtained frommuch more powerful conventional light sources.Fig.4.7 Divergence of Laser SourceFor example, a laser capable of delivering a 100 mJ pulse in 20 ns has a peak power of 5million watts. A CW laser will usually have the light energy expressed in watts, and a pulsedlaser will usually have its output expressed in joules. Since energy cannot be created ordestroyed, the amount of energy available in a vacuum at the output of the laser will be thesame amount of energy contained within the beam at some point downrange (with some lossin the atmosphere).ME-DEPARTMENT SRMGPC LKO 15 | P a g e 16. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig. illustrates a typical laser beam. The amount of energy available within the samplingarea will be considerably less than the amount of energy available within the beam. Forexample, a 100 mW laser output might have 40 mW measured within 1 sample area.The irradiance in this example is 40 mW/ .Fig.4.8 Illustration of IrradianceME-DEPARTMENT SRMGPC LKO 16 | P a g e 17. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 5Working of laserThe electromagnetic spectrum consists of the complete range of frequencies from radiowaves to gamma rays. All electromagnetic radiation consists of photons which are individualquantum packets of energy. For example, a household light bulb emits about1,000,000,000,000,000,000,000 photons of light per second! In this course we will onlyconcern ourselves with the portion of the electromagnetic spectrum where lasers operate -infrared, visible, and ultraviolet radiation.Name WavelengthUltraviolet 100 nm - 400 nmVisible 400 nm - 750 nmNear Infrared 750 nm - 3000 nmFar Infrared 3000 nm - 1 mmEinstein was awarded the Nobel Prize for his discovery and interpretation of the formula -E=mc2 - right? Wrong.Fig 5.1Albert EinsteinHe won the Nobel Prize for his explanation of the phenomena referred to as the photoelectriceffect. When light (electromagnetic energy) is shined on a metal surface in a vacuum, it mayME-DEPARTMENT SRMGPC LKO 17 | P a g e 18. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYfree electrons from thatsurface.Fig.5.2These electrons can be detected as a current flowing in the vacuum to an electrode.The light was not always strong enough to cause this effect, however. When the scientistsmade the light brighter, no increase in electrons was seen. Only when they changed the colorof the light (the wavelength) did they see a change in photoemission of electrons.This was explained by Einstein using a theory that light consists of photons, each withdiscrete quantum of energy proportional to their wavelength.For an electron to be freed from the metal surface it would need a photon with enough energyto overcome the energy that bound it to the atom. So, making the light brighter would supplymore photons, but none would have the energy to free the electron.Light with a shorter wavelength consisted of higher energy photons that could supply theneeded energy to free the electron. Now, you ask, "What the heck does this idea of quantumenergy have to do with a laser? Well, with this background under our belts we willcontinue.ME-DEPARTMENT SRMGPC LKO 18 | P a g e 19. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 6Spectroscope of laser lightLine width:In fact emission and absorption depend on photon frequency and are characterized by a linewidthLine broadening types include:1. Natural, from finite lifetime (H)2. Phonon, from lattice vibrations (H)3. Collisional, in gases (H)4. Strain, from static lattice in homogeneities (I)5. Impurity ions in host crystal (I)6. Doppler, in gases (I)Line width EffectsA laser beam of intensity I (W/m2), propagating in the direction through a medium with gaincoefficient g (m-1) grows in intensity as I = I0 exp(gz) Since g depends on wavelength, thisprocess will increase the intensity for wavelengths near line-center faster than for those in thewings, leading to gain-narrowing of the spectrum.Line width propertiesAtoms in either upper or lower levels of the laser medium will not interact with a perfectlymonochromatic beam. This is the fact that all spectral lines have a finite wavelength orfrequency spread, i.e., (fluorescent or spectral line width). This can be seen in both emissionand absorption,And if we measured the emission of a typical spectral source as a function of frequency, wewill get bell-shaped curve illustrated. The precise shape of the curve is given by the lineshape function g(), which represents the frequency distribution of the radiation in a givenspectral line. The precise form of g() which is normalized so that the area under the curve isunity depends on the particular mechanism causing the spectral broadening.ME-DEPARTMENT SRMGPC LKO 19 | P a g e 20. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 7Applications of laserThe light beam produced by most lasers is pencil-sized, and maintains its size and directionover very large distances; this sharply focused beam of coherent light is suitable for a widevariety of applications. Lasers have been used in industry for cutting and boring metals andother materials as well as welding and soldering, and for inspecting optical equipment. Inmedicine, they have been used in surgical operations.CDs and DVDs read and written to using lasers, and lasers also are employed in laser printersand bar-code scanners. They are used in communications, both in fiber optics and in somespace and open-air communications; in a manner similar to radio transmission, thetransmitted light beam is modulated with a signal and is received and demodulated somedistance away. The field of holography is based on the fact that actual wave-front patterns,captured in a photographic image of an object illuminated with laser light, can bereconstructed to produce a three-dimensional image of the object.Lasers have been used in a number of areas of scientific research, and have opened a newfield of scientific research, nonlinear optics, which is concerned with the study of suchphenomena as the frequency doubling of coherent light by certain crystals. One importantresult of laser research is the development of lasers that can be tuned to emit light over arange of frequencies, instead of producing light of only a single frequency. Lasers also havebeen developed experimentally as weaponry.Sophisticated laser system concepts are increasingly being used to address high bandwidthfree space optical (FSO) communications needs and for sensing applications..Terrestrial and space based multi-mega/gigabit FSO links have been demonstrated but stillrequire advances in beam steering, detection schemes, adaptive optics and other methods ofmitigating atmospheric effects, and modulated laser encoding before wide applications are tobe realized. Optical sensors based on lasers are also progressing both in remote applicationsas well as in on chip sensing, in communities ranging from environmental sensing to medicaldiagnostics. Laser based sensing and free space communications both employ sophisticateddetection schemes. This meeting reports on the multiple applications of lasers in FSOcommunications as well as in advanced sensing applications.ME-DEPARTMENT SRMGPC LKO 20 | P a g e 21. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYLASER BEAM MACHININGFig.7.1Laser beam machining (LBM) is an unconventional machining process in which a beam ofhighly coherent light called a laser is directed towards the work piece for machining. Sincethe rays of a laser beam are monochromatic and parallel it can be focused to a very smalldiameter and can produce energy as high as 100 MW of energy for a square millimeter ofarea. It is especially suited to making accurately placed holes. It can be used to performprecision micro-machining on all microelectronic substrates such as ceramic, silicon,diamond, and graphite. Examples of microelectronic micro-machining include cutting,scribing & drilling all substrates, trimming any hybrid resistors, patterning displays of glassME-DEPARTMENT SRMGPC LKO 21 | P a g e 22. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYor plastic and trace cutting on semiconductor wafers and chips. A pulsed ruby laser isnormally used for developing a high power.Fig.7.2Extremely short pulses provide for minimal thermal damage to surroundingsME-DEPARTMENT SRMGPC LKO 22 | P a g e 23. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYCharacteristics of Femtosecond Laser Micromachining1. Very high peak powers in the range 1013W/cm2 provide for minimal thermal damage tosurroundings2. Very clean cuts with high aspect ratios3. Sub-micron feature resolution4. Minimum redeposition5. Possible to machine transparent materials like glass, sapphire etc.ADVANTAGES:1. Non-contact machining2. Very high resolution, repeatability and aspect ratios3. Localized heating, minimal redeposition4. No pre/post processing of material5. Wide range of materials: fragile, ultra-thin and highly reflective surfaces6. Process can be fully automated.Fig.7.3INTENSITY DISTRIBUTION:Fig.7.4Focal length of 9mm FOCAL LENGTH OF 40mm FocalME-DEPARTMENT SRMGPC LKO 23 | P a g e 24. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig 7.5APPLICATIONS IN MANUFACTURING1. CLEANINGEmerging process, particularly driven by art and monument restoration (I.e. NationalMuseums and Galleries on Merseyside (NMGM) conservation centre Metal surfaces are well-suited for many laser cleaning applications. Optimizedbeam settings will not metallurgically change or damage the laser treatedsurface. Only the coating, residue or oxide targeted for removal is affected as thelaser beam is precisely adjusted not to react with the underlying metal surface. Laser beam power density is accurately and easily adjusted to achieve cleaningresults impossible with all other options.ME-DEPARTMENT SRMGPC LKO 24 | P a g e 25. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig .7.62.ENGRAVING : Better engraving performance on metals Internal glass markingLaser engraving, and laser marking, is the practice of using lasers to engrave or mark an object.The technique does not involve the use of inks, nor does it involve tool bits which contact theengraving surface and wear out. These properties distinguish laser engraving from alternativeengraving or marking technologies where inks or bit heads have to be replaced regularlyFig.7.72. DRILLING: A high power pulsed Nd:YAG laser is normally used, occasionally a fiberlaser is chosen, or a CO2 laser can be used with non-metallic parts. Processing isaccomplished through either percussion drilling or trepanning. In the laser drillingME-DEPARTMENT SRMGPC LKO 25 | P a g e 26. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYprocess, high power density is accomplished by using a high power laser and a focusedspot size of 0.05 mm (0.002") to 0.75 mm (0.030").Fig.7.83. WELDING : Solid-state lasers operate at wavelengths on the order of 1 micrometer, muchshorter than gas lasers, and as a result require that operators wear special eyewear or use specialscreens to prevent retina damage. Nd:YAG lasers can operate in both pulsed and continuousmode, but the other types are limited to pulsed mode. The original and still popular solid-statedesign is a single crystal shaped as a rod approximately 20 mm in diameter and 200 mm long, andthe ends are ground flat.Fig.7.94. CUTTING: The parallel rays of coherent light from the laser source often fall in the rangebetween 0.060.08 inch (1.52.0 mm) in diameter. This beam is normally focused and intensifiedby a lens or a mirror to a very small spot of about 0.001 inches (0.025 mm) to create a veryME-DEPARTMENT SRMGPC LKO 26 | P a g e 27. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYintense laser beam. In order to achieve the smoothest possible finish during contour cutting, thedirection of beam polarization must be rotated as it goes around the periphery of a contouredworkpiece. For sheet metal cutting, the focal length is usually 1.53 inches (3876 mm)Fig7.10 Good edge quality (square ,clean and no burrs)OTHER POPULAR LASER APPLICATIONS ARE1. SpectroscopyMost types of laser are an inherently pure source of light; they emit near-monochromaticlight with a very well defined range of wavelengths. By careful design of thelaser components, the purity of the laser light (measured as the "linewidth") can be improvedmore than the purity of any other light source. This makes the laser a very useful sourcefor spectroscopy. The high intensity of light that can be achieved in a small, well collimatedbeam can also be used to induce a nonlinear optical effect in a sample, which makestechniques such as Raman spectroscopy possible. Other spectroscopic techniques based onlasers can be used to make extremely sensitive detectors of various molecules, able tomeasure molecular concentrations in the parts-per-1012 (ppt) level. Due to the high powerME-DEPARTMENT SRMGPC LKO 27 | P a g e 28. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYdensities achievable by lasers, beam-induced atomic emission is possible: this technique istermed Laser induced breakdown spectroscopy (LIBS).Fig.7.112. Heat TreatmentHeat treating with lasers allows selective surface hardening against wear with little or nodistortion of the component. Because this eliminates much part reworking that is currentlydone, the laser system's capital cost is recovered in a short time. An inert, absorbent coatingfor laser heat treatment has also been developed that eliminates the fumes generated byconventional paint coatings during the heat-treating process with CO2 laser beams.One consideration crucial to the success of a heat treatment operation is control of the laserbeam irradiance on the part surface. The optimal irradiance distribution is driven by thethermodynamics of the laser-material interaction and by the part geometry. Typically,irradiances between 500-5000 W/cm^2 satisfy the thermodynamic constraints and allow therapid surface heating and minimal total heat input required. For general heat treatment, auniform square or rectangular beam is one of the best options. For some special applicationsor applications where the heat treatment is done on an edge or corner of the part, it may bebetter to have the irradiance decrease near the edge to prevent melting.Fig.7.12ME-DEPARTMENT SRMGPC LKO 28 | P a g e 29. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYLunar laser rangingWhen the Apollo astronauts visited the moon, they planted retro reflector arrays to makepossible the Lunar Laser Ranging Experiment. Laser beams are focused throughlarge telescopes on Earth aimed toward the arrays, and the time taken for the beam to bereflected back to Earth measured to determine the distance between the Earth and Moon withhigh accuracy.PhotochemistrySome laser systems, through the process of mode locking, can produce extremely brief pulsesof light - as short as picoseconds or femto seconds (1012 - 1015 seconds). Such pulses can beused to initiate and analyses chemical reactions, a technique known as photo chemistry. Theshort pulses can be used to probe the process of the reaction at a very high temporalresolution, allowing the detection of short-lived intermediate molecules. This method isparticularly useful in biochemistry, where it is used to analyses details of protein folding andfunction.Fig7.13ME-DEPARTMENT SRMGPC LKO 29 | P a g e 30. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYLaser Barcode ScannersLaser barcode scanners are ideal for applications that require high speed reading of linearcodes or stacked symbols. From small products for embedded OEM applications to ruggedlaser barcode scanners for industrial use, Micro scan offers a wide range of quality productsto read linear barcodes and stacked symbols, with features such as high speed reading, widefield of view, symbol reconstruction, and aggressive decoding technology.Fig7.14Laser coolingA technique that has recent success is laser cooling. This involves atom trapping, a methodwhere a number of atoms are confined in a specially shaped arrangementof electric and magnetic fields. Shining particular wavelengths of laser light at the ions oratoms slows them down, thus cooling them. As this process is continued, they all are slowedand have the same energy level, forming an unusual arrangement of matter known as a Bose-Einstein condensate.Fig .7.15ME-DEPARTMENT SRMGPC LKO 30 | P a g e 31. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYNuclear fusionSome of the world's most powerful and complex arrangements of multiple lasers and opticalamplifiers are used to produce extremely high intensity pulses of light of extremely shortduration. These pulses are arranged such that they impact pellets of tritium-deuteriumsimultaneously from all directions, hoping that the squeezing effect of the impacts willinduce 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 generatesless power than is used to power the lasers, but research continues.ME-DEPARTMENT SRMGPC LKO 31 | P a g eFig7.16MicroscopyConfocal laser scanning microscopy and Two-photon excitation microscopy make use of lasers toobtain blur-free images of thick specimens at various depths. Laser capture microdissection uselasers to procure specific cell populations from a tissue section under microscopic visualization.Additional laser microscopy techniques include harmonic microscopy, four-wave mixing microscopyand interferometric microscopy. 32. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFig.7.17ME-DEPARTMENT SRMGPC LKO 32 | P a g e 33. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYWorking:A laser printer is a popular type of personal computer printer that uses a non-impact (keysdon't strike the paper), photocopier technology. When a document is sent to the printer, alaser beam "draws" the document on a selenium-coated drum using electrical charges. Afterthe drum is charged, it is rolled in toner, a dry powder type of ink. The toner adheres to thecharged image on the drum. The toner is transferred onto a piece of paper and fused to thepaper with heat and pressure. After the document is printed, the electrical charge isremoved from the drum and the excess toner is collected. Most laser printers print only inmonochrome. A color laser printer is up to 10 times more expensive than a monochromelaser printerSKIN TREATMENT.Fig.7.18If you have fine lines or wrinkles around your eyes or mouth or on your forehead, shallow scars fromacne, or non-responsive skin after a facelift, then you may be a good candidate for laser skinresurfacing.ME-DEPARTMENT SRMGPC LKO 33 | P a g e 34. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYThe two types of lasers most commonly used in laser resurfacing are carbon dioxide (CO2) anderbium. Each laser vaporizes skin cells damaged at the surface-level.The newest version of CO2 laser resurfacing uses very short pulsed light energy (known asultrapulse) or continuous light beams that are delivered in a scanning pattern to remove thin layersof skin with minimal heat damage. Recovery takes up to two weeks.Fig.7.19ME-DEPARTMENT SRMGPC LKO 34 | P a g e 35. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYFUTURE DEVELOPMENTIgnition of fuel through laser beamA method for igniting a fuel mixture in an internal combustion engine,1. The method comprising: Generating a laser beam.2. Transmitting the laser beam through a lens to form a focused laser beam. and3. Transmitting the focused laser beam through a prism to focus the laser beam on the fuelmixture supplied into a combustion chamber of the internal combustion engine, whereinthe lens moves linearly to transmit the laser beam.Fig.7.20ME-DEPARTMENT SRMGPC LKO 35 | P a g e 36. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYAnti-Missile Defence SystemFig7.21Current missile defenses consist of missiles fired at other missiles. If LockheedMartin has its way, that may change in a few years, with missiles being shot downby laser beamsThe advantage of laser-based defense over missile-based is that tracking is lesscomplex. Missiles need to calculate trajectories and even be able to maneuver (aswith Iron Dome) toward their target. Lasers do not. Plus, a laser beam moves at thespeed of light, so at a range of a mile, it can hit its target in less than five-millionthsof a second. Lastly, laser weapons cost less to fire, since they arent using up realammunition, jut power.ME-DEPARTMENT SRMGPC LKO 36 | P a g e 37. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYChapter 8The Future of the LaserModern technology is advancing so quickly that the average person simply cannot keep up with it.Even some scientists are occasionally unaware of discoveries being made in other fields. Lasers arevery much a part of this technology explosion. They help in the discovery of new knowledge, whichfurther fuels the explosion while, by advancing communications, they help spread the newknowledge to those who want it.Realistic Images in Homes and OfficesMany experts expect laser-computer advances to lead to the eventual perfection of holography,. Itwill be like watching old-fashioned 3D movies, only without the special glasses. Even holographictelevision will likely be developed, although it will be very difficult to construct because so muchinformation is needed to form a holographic image. To transmit the information of a singlehologram to a home, it will take a cable with the capacity of five hundred television channels. Oncethe hologram arrives in someone's living room, the television itself will have to be able to projectthe hologram, and this will require a screen with more than one thousand times more detail thantoday's TV screens.Computing at Light SpeedIn the mid-1990s the laser joined in a useful working partnership with the computer, but the laserstill only reads, writes, and memorizes for the computer. Some scientists think the laser could gofurther and bring about a drastic change in the way the computer is designed. The computer itselfconsists of wires, chips, connections, and other parts through which electrical signals flow. Expertspoint out that in the larger supercomputers sometimes too many pieces of information try to get tothe same place at the same time.Walking Electronics Stores?Advanced laser-based devices may also transform ordinary people into virtual walking electronicsstores. The fact that the beam of a laser can be focused to a microscopic point has already given itthe ability to create discs to store vast amounts of information, including video and audio discs ofhigh quality. Researchers are now working to expand this principle to the miniaturization ofelectronic devices so that they can be carried or even worn by the average person.Lasers and Nuclear FusionMost nuclear scientists believe that in the future nuclear power will be supplied by fusion, a nuclearreaction in which two atoms are combined. But starting a fusion reaction requires an enormousinitial force. Many scientists think that "laser chains" can supply that force. A laser chain consists ofseveral laser amplifiers over a hundred feet long, which intensify the power of laser beams. Thehigh-powered beams are directed through beam splitters and onto mirrors so that several beamsstrike a tiny fuel pellet from all sides at once. This causes an explosion powerful enough to trigger afusion reaction. The laser may provide a way to get a safe fusion reaction going. Experiments withlasers and fusion began in the late 1960s, but progress was slow for a long time. A majorME-DEPARTMENT SRMGPC LKO 37 | P a g e 38. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYbreakthrough occurred in August 2001 when researchers from Japan and the United Kingdomsucceeded in using a laser beam to compress a ball -likeFig8.1Twenty-four lasers are arranged for a nuclear fusion experiment. Controlled fusion has not yet beenperfected, but lasers may open the door to that important new technology.A World Transformed.In the twenty-first century and beyond, the laser promises to help raise human civilization to newheights. The supertool will build a storehouse of knowledge and put that knowledge within easyreach of most people. Laser light will illuminate a complex and computerized world, one in whichtechnology allows men and women to live increasingly productive and happy lives. Indeed, the lasermay one day harness the fire of the stars to give humanity clean, safe, and abundant energy forgenerations to come as well as access to alien knowledge that could transform the world in ways notyet imagined.ME-DEPARTMENT SRMGPC LKO 38 | P a g e 39. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYREFERENCES1. http://lasers.coherent.com/lasers/laser%20application%20in%20engineering%20field2. http://en.wikipedia.org/wiki/Medical_imaging3. http://en.wikipedia.org/wiki/Laser_printing4. http://www.scienceclarified.com/scitech/Lasers/The-Future-of-the-Laser.html5. http://www.howstuffworks.com/laser.htm6. http://en.wikipedia.org/wiki/Laser_engraving7. http://en.wikipedia.org/wiki/Laser_beam_machining8. www.sciencedirect.com/science/article9. drdo.gov.in/drdo/data/Laser%20and%20its%20Applications.10. hyperphysics.phy-astr.gsu.edu/hbase/optmod/lasapp.html11. www.google.com/images/heat treatment12. www.google.com/images/ microscopy13. www.google.com/images/ WELDINGME-DEPARTMENT SRMGPC LKO 39 | P a g e 40. A STUDY ON THE APPLICATION OF LASER TECHNOLOGYAPPENDIXPage no.1. Fig.1.1 Laser light 12. Fig.1.2-Fig1.3 Properties of light 23. Fig 2.1 Scientist who developed laser 34. Fig. 2.2 Laser research center 75. Fig.3.1 Components of laser 86. Fig.4.1-Fig4.8 Types of laser 11-167. Fig 5.1 Albert Einstein 178. Fig 5.2 Working of laser 189. Fig.7.1-Fig7.21 Applications of laser 21-3610. Fig8.1 Lasers and Nuclear Fusion 38ME-DEPARTMENT SRMGPC LKO 40 | P a g e