LASER TECHNOLOGY AND IT`S APPLICATIONS

ABSTRACT

      

This paper emphasis on the principle of operation of LASER technology, the simulated emission that generate the signal, it`s uses and role in information technology, it`s safety measures and warnings signs.

INTRODUCTION

        A LASER is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons.

         The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation. in modern usage "light" broadly denotes electromagnetic radiation of any frequency, not only visible light, hence infrared laser, ultraviolet laser, X-ray laser, and so on. The emitted laser light is notable for its high degree of spatial and temporal coherence.

        Spatial coherence is typically 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 a very high irradiance, or they can be launched into beams of very low divergence in order to concentrate their power at a large distance.

 

PRINCIPLES OF OPERATION

   Lasers generate light by storing energy in particles called electrons inside atoms and then inducing the electrons to emit the absorbed energy as light. Atoms are the building blocks of all matter on Earth and are a thousand times smaller than viruses. Electrons are the underlying source of almost all light.

   Light is composed of tiny packets of energy called photons. Lasers produce coherent light: light that is monochromatic (one color) and whose photons are “in step” with one another.

   White light, such as that produced by an incandescent bulb, is composed of many colors of light—each with a different wavelength—and spreads out in all directions. Laser light consists of a single color (a single wavelength) and moves in one direction with the peaks and troughs of its waves in lockstep.

 

LIGHT

   Light, form of energy visible to the human eye that is radiated by moving charged particles.

   Light Absorption and Emission

   When a photon, or packet of light energy, is absorbed by an atom, the atom gains the energy of the photon, and one of the atom’s electrons may jump to a higher energy level. The atom is then said to be excited. When an electron of an excited atom falls to a lower energy level, the atom may emit the electron’s excess energy in the form of a photon.

   The energy levels, or orbitals, of the atoms shown here have been greatly simplified to illustrate these absorption and emission processes. For a more accurate depiction of electron orbitals, see the Atom article. To understand the nature of light and how it is normally created, it is necessary to study matter at its atomic level. Atoms are the building blocks of matter, and the motion of one of their constituents, the electron, leads to the emission of light in most sources.

   Light can be emitted, or radiated, by electrons circling the nucleus of their atom. Electrons can circle atoms only in certain patterns called orbitals, and electrons have a specific amount of energy in each orbital.

 

   The amount of energy needed for each orbital is called an energy level of the atom. Electrons that circle close to the nucleus have less energy than electrons in orbitals farther from the nucleus. If the electron is in the lowest energy level, then no radiation occurs despite the motion of the electron. If an electron in a lower energy level gains some energy, it must jump to a higher level, and the atom is said to be excited. The motion of the excited electron causes it to lose energy, and it falls back to a lower level. The energy the electron releases is equal to the difference between the higher and lower energy levels. The electron may emit this quantum of energy in the form of a photon.

 

Stimulated Emission

   Lasers are different from more familiar sources of light. Excited atoms in lasers collectively emit photons of a single colour, all travelling in the same direction and all in step with one another. When two photons are in step, the peaks and troughs of their waves line up. The electrons in the atoms of a laser are first pumped, or energized, to an excited state by an energy source. An excited atom can then be “stimulated” by a photon of exactly the same colour (or, equivalently, the same wavelength) as the photon this atom is about to emit spontaneously.

 

   If the photon approaches closely enough, the photon can stimulate the excited atom to immediately emit light that has the same wavelength and is in step with the photon that interacted with it. This stimulated emission is the key to laser operation. The new light adds to the existing light, and the two photons go on to stimulate other excited atoms to give up their extra energy, again in step. The phenomenon snowballs into an amplified, coherent beam of light: laser light.

 

LASER DESIGN WAY

   Lasers are possible because of the way light interacts with electrons. Electrons exist at specific energy levels or states characteristic of that particular atom or molecule. The energy levels can be imagined as rings or orbits around a nucleus. Electrons in outer rings are at higher energy levels than those in inner rings. Electrons can be bumped up to higher energy levels by the injection of energy-for example, by a flash of light. When an electron drops from an outer to an inner level, "excess" energy is given off as light.

 

        The wavelength or colour of the emitted light is precisely related to the amount of energy released. Depending on the particular lasing material being used, specific wavelengths of light are absorbed (to energize or excite the electrons) and specific wavelengths are emitted (when the electrons fall back to their initial level).

Rubby LASER

           For a ruby laser, a crystal of ruby is formed into a cylinder. A fully reflecting mirror is placed on one end and a partially reflecting mirror on the other. A high-intensity lamp is spiraled around the ruby cylinder to provide a flash of white light that triggers the laser action. The green and blue wavelengths in the flash excite electrons in the chromium atoms to a higher energy level.

 

         Upon returning to their normal state, the electrons emit their characteristic ruby-red light. The mirrors reflect some of this light back and forth inside the ruby crystal, stimulating other excited chromium atoms to produce more red light, until the light pulse builds up to high power and drains the energy stored in the crystal.

 

TYPES OF LASERs AND OPERATING PRINCIPLE

          Gas LASERs. Gas lasers using many different gases have been built and used for many purposes. The helium-neon laser (HeNe) is able to operate at a number of different wavelengths Commercial carbon-dioxide (CO₂) lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot.

          Chemical LASERs. Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the Hydrogen fluoride laser

 

 

          Excimer LASERs.Excimer lasers  are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer, or more precisely an exciplex  in existing designs. These are molecules which can only exist with one atom in an excited electronic state. Once the molecule transfers its excitation energy to a photon, therefore, its atoms are no longer bound to each other and the molecule disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a population inversion. Excimers currently used are all noble gas compounds; noble gasses are chemically inert and can only form compounds while in an excited state.

          Solid-State LASERs. Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required energy states

          Fiber LASERs. Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a single mode optical fibber  are instead called fiber lasers. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam.

         Photonic Crystal LASERs. Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density of optical states (DOS) structure required for the feedback to take place

 

         Semiconductor LASERs. Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain. Reflection from the ends of the crystal form an optical resonator, although the resonator can be external to the semiconductor in some designs.Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm. Low to medium power laser diodes are used in laser pointers, laser printers and CD/DVD players. Laser diodes are also frequently used to optically pump other lasers with high efficiency

 

 

          Dye LASERs. Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses (on the order of a few femtoseconds)

        Free Electron LASERs. Free electron lasers, or FELs, generate coherent, high power radiation, that is widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type.

 

         Bio LASERs. Living cells can be genetically engineered to produce Green fluorescent protein (GFP). The GFP is used as the laser's "gain medium", where light amplification takes place. The cells are then placed between two tiny mirrors, just 20 millionths of a metre across, which acted as the "laser cavity" in which light could bounce many times through the cell. Upon bathing the cell with blue light, it could be seen to emit directed and intense green laser light

        Exotic LASER Media. In September 2007, the BBC News reported that there was speculation about the possibility of using positronium annihilation to drive a very powerful gamma ray laser. Dr. David Cassidy of the University of California, Riverside proposed that a single such laser could be used to ignite a nuclear fusion reaction, replacing the banks of hundreds of lasers currently employed in inertial confinement fusion experiments

 

USES OF LASER TECHNOLOGY

Ø Medicine: Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry

Ø Industry: Cutting, welding, material heat treatment, marking parts, non-contact measurement of parts

Ø Military: Marking targets, guiding munitions, missile defence, electro-optical countermeasures (EOCM), alternative to radar, blinding troops.

Ø Law enforcement: used for latent fingerprint detection in the forensic identification field

Ø Research: Spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry, LIDAR, laser capture microdissection, fluorescence microscopy

Ø Product development/commercial: laser printers, optical discs (e.g. CDs and the like), barcode scanners, thermometers, laser pointers, holograms, bubblegrams.

 

 

Ø Laser lighting displays: Laser light shows

 

 

Ø Cosmetic skin treatments: acne treatment, cellulite and striae reduction, and hair removal.

 

DEFENSIVE COUNTERMEASURES

   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 projectiles and cruise missiles by radar and destroy them with a powerful deuterium fluoride laser.

 

The continuous or average power required for some uses:  Table 1

Safety of LASER

   Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight, when the beam from such a laser hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time. Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is:

 

 

Ø Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players.

Ø Class II/2 is safe during normal use; the blink reflect of the eye will prevent damage. Usually up to 1 mW power, for example laser pointers.

Ø Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.

Ø Class IIIb/3B can cause immediate eye damage upon exposure.

Ø Class IV/4 lasers can burn skin, and in some cases, even scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.

 

 

   The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength. Certain infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as being "eye-safe".

CONCLUSION

   In conclusion, LASER technology as we have seen is a technology that have great effect and has enhance good living in human life in this century and has improve the standard of life. Is a Technology that has enhance our Medical, Engineering and all round of our lives. Even the EVC NASENI recommended that some of the parts in the made in Nigeria motorcycle should be sharpened and made neat with LASER.

REFERENCES

Ø  A journal paper from www.mellegriot.com.

Ø  LASERs, how do the work? By a PH-223 student.

Ø  Optics and LASER technology by Elsevier

Ø  LASER and it`s Application. From popular & science series.

Ø  The basic principles LASER technology, its uses and safety measures

Ø  Microsoft Encarta on LASER technology

Ø  Www.google.com

Ø  LASER-induced breakdown spectroscopy( fundermentals and application) by

      Andrzej m. Mizioick

     Vincenzo palleschi

     Isreal Schecter.

 

REFERENCES 

 Duarte F. J.; Hillman, L.W. (1990). Dye Laser Principles, with Applications. Boston: Academic Press. ISBN 0-12-222700-X.

  Polanyi, T.G. (1970). "A CO₂ Laser for Surgical Research". Med. & Biol. Engng. 8: 541–548. doi:10.1007/bf02478228.

 "Soft-Tissue Laser Surgery - CO2 Surgical Laser - LightScalpel". LightScalpel. Retrieved 2016-04-04.

 Loevschall, Henrik (1994). "Effect of low level diode laser irradiation of human oral mucosa fibroblasts in vitro". Lasers in Surgery and Medicine 14 (4): 347–354. doi:10.1002/lsm.1900140407.

 Costela A, Garcia-Moreno I, Gomez C (2016). "Medical Applications of Organic Dye Lasers". In Duarte FJ. Tunable Laser Applications (3rd ed.). Boca Raton: CRC Press. pp. 293–313. ISBN 9781482261066.

 Popov S (2016). "Fiber Laser Overview and Medical Applications". In Duarte FJ. Tunable Laser Applications (3rd ed.). Boca Raton: CRC Press. pp. 263–292. ISBN 9781482261066.

 Duarte FJ (2016). "Broadly Tunable External-Cavity Semiconductor Lasers". In Duarte FJ. Tunable Laser Applications (3rd ed.). Boca Raton: CRC Press. pp. 203–241. ISBN 9781482261066.