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# Fredrick Brown-Laser Systems.ppt

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### Fredrick Brown-Laser Systems.ppt

1. 1. Laser SystemsLaser Systems Fredrick BrownFredrick Brown ELEC 6750ELEC 6750 Spring 2004Spring 2004
2. 2. QuestionsQuestions  What is a laser?What is a laser?  What are the primary parts of a gas laserWhat are the primary parts of a gas laser system?system?
3. 3. OverviewOverview  Primary Parts of a laserPrimary Parts of a laser  Population InversionPopulation Inversion  Gases Used in lasersGases Used in lasers  SummarySummary  Answers to questionsAnswers to questions
4. 4. Primary PartsPrimary Parts  A laser consists of two primaryA laser consists of two primary parts: a cavity consisting of atparts: a cavity consisting of at least two mirrors and a gasleast two mirrors and a gas discharge tube with a means ofdischarge tube with a means of establishing a populationestablishing a population inversion.inversion.  The mirrors in a gas laser areThe mirrors in a gas laser are highly specialized and will be usedhighly specialized and will be used to form the ends of the laserto form the ends of the laser cavity. They are coated with thincavity. They are coated with thin films that make them highlyfilms that make them highly reflective for the exact wavelength.reflective for the exact wavelength. One of the mirrors is 100%One of the mirrors is 100% reflective while the other is aboutreflective while the other is about 99%. This will allow a thin beam to99%. This will allow a thin beam to be reflected from the difference inbe reflected from the difference in the 1%.the 1%. http://vcs.abdn.ac.uk/ENGINEERING/lasers/gas.html Figure 1. Diagram of a laser beam reflecting between mirrors in tube.
5. 5. Population InversionPopulation Inversion  A population inversion is whenA population inversion is when molecules or gas particles are excitedmolecules or gas particles are excited to a higher energy state larger thanto a higher energy state larger than that of a lower energy state.that of a lower energy state.  The gas inside of the cavity will amplifyThe gas inside of the cavity will amplify the number of photons that are put in,the number of photons that are put in, for example, for every photon whichfor example, for every photon which passes through the substance, twopasses through the substance, two others leave it creating an extremelyothers leave it creating an extremely coherent beam of light all in phase.coherent beam of light all in phase.  The process of exciting molecules toThe process of exciting molecules to create the population inversion is callcreate the population inversion is call “pumping”. Electrons in a gas“pumping”. Electrons in a gas discharge do the job of excitingdischarge do the job of exciting molecules from low energy states tomolecules from low energy states to high energy states.high energy states. http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/lasgas.html Figure 2. Example of population inversion of gas particles.
6. 6. GasesGases  Helium-NeonHelium-Neon  Argon-IonArgon-Ion  Carbon DioxideCarbon Dioxide
7. 7. Helium-NeonHelium-Neon  The most common andThe most common and inexpensive gas laser isinexpensive gas laser is the HeNe. It is usuallythe HeNe. It is usually constructed to operate inconstructed to operate in the red wavelength atthe red wavelength at 632.8nm. It can also632.8nm. It can also produce laser action inproduce laser action in the green at 543.5nm andthe green at 543.5nm and in the infrared at 1523nm.in the infrared at 1523nm. Also, it contains aboutAlso, it contains about 85% helium and 15%85% helium and 15% neon gas and aboutneon gas and about 1/300 of atmospheric1/300 of atmospheric pressure.pressure. http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/lasgas.html
8. 8. HeNe (Cont.)HeNe (Cont.)  The lighter Helium atomsThe lighter Helium atoms are excited by collisionsare excited by collisions with electrons in thewith electrons in the discharge. Next, thedischarge. Next, the Helium atoms collide withHelium atoms collide with the heavier Neon atomsthe heavier Neon atoms which excites them towhich excites them to their metastable statetheir metastable state where populationwhere population inversion builds up.inversion builds up. Bridges, W.B. and Chester, A.N. "Ionized Gas Lasers," in handbook of lasers. Presley, R.J. editor. Chemical Rubber Co., 1971
9. 9. Argon-IonArgon-Ion  The Argon-Ion laser isThe Argon-Ion laser is capable of producingcapable of producing approximately 10approximately 10 wavelengths in thewavelengths in the ultraviolet and up to 25 inultraviolet and up to 25 in the visible region, rangingthe visible region, ranging from 275-363.8nm andfrom 275-363.8nm and 408.9-686.1nm.408.9-686.1nm.  The typical Argon laserThe typical Argon laser has a high melting pointhas a high melting point and allows the laser toand allows the laser to operate at a higher poweroperate at a higher power level with longer tube lifelevel with longer tube life than the HeNe.than the HeNe. http://vcs.abdn.ac.uk/ENGINEERING/lasers/gas.html
10. 10. Argon-Ion (Cont.)Argon-Ion (Cont.)  An unfortunate side effect of the highAn unfortunate side effect of the high discharge current and the low gasdischarge current and the low gas pressure employed by the Argon-Ion laserpressure employed by the Argon-Ion laser is an extremely high plasma electronis an extremely high plasma electron temperature, which generates a significanttemperature, which generates a significant amount of heat. Therefore, this lasersamount of heat. Therefore, this lasers system are water cooled through ansystem are water cooled through an external chiller or an efficient fan.external chiller or an efficient fan.
11. 11. Carbon DioxideCarbon Dioxide  CO2 laser emits an invisibleCO2 laser emits an invisible infrared beam of a singleinfrared beam of a single wavelength in the form of awavelength in the form of a small, intense beam.small, intense beam. Specifically, CO2 emitsSpecifically, CO2 emits photons at 10.6 and 9.6um.photons at 10.6 and 9.6um.  The beam produces a veryThe beam produces a very high temperature that may behigh temperature that may be used for engraving, cutting,used for engraving, cutting, drilling, marking, welding anddrilling, marking, welding and in various medical applicationsin various medical applications such as dermatology and as asuch as dermatology and as a medical tool for producingmedical tool for producing clean cuts with little bleeding.clean cuts with little bleeding. http://www.repairfaq.org/sam/lasercc2.htm
12. 12. CO2 (Cont.)CO2 (Cont.) http://www.repairfaq.org/sam/lasercc2.htm
13. 13. SummarySummary  In conclusion, energy in the form of heat, light,In conclusion, energy in the form of heat, light, and chemical reaction can be used to exciteand chemical reaction can be used to excite electrons within atoms and push them to higherelectrons within atoms and push them to higher energy states within a laser system to create aenergy states within a laser system to create a population inversion. The relaxation of electronspopulation inversion. The relaxation of electrons to lower energy states, ultimately, to their groundto lower energy states, ultimately, to their ground state using the correct primary parts canstate using the correct primary parts can produce ultraviolet light, visible light, and infraredproduce ultraviolet light, visible light, and infrared radiation in a laser system.radiation in a laser system.
14. 14. AnswersAnswers  What is a laser?What is a laser? Light Amplification byLight Amplification by Stimulated Emission of RadiationStimulated Emission of Radiation..  What are the primary parts of a gas laserWhat are the primary parts of a gas laser system?system? A cavity consisting of at least 2A cavity consisting of at least 2 mirrors and a gas discharge tubemirrors and a gas discharge tube..