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1、1.TheLightoftheTwenty-firstCentury1.Thewordlaserstandsfor“lightamplificationbystimulatedemissionofradiation”.Tomanypeoplelasersareverymysteriousbutalaserissimplyadevicethatproducesaverystronglight.Thelightfromalaseriscalledcoherentlightbecauseitislightthatmovesinonlyonedirection.Incontrast,
2、incoherentlight,likethelightfromthesunoralightbulb,movesawayfromitssourceinalldirections,soitsstrengthisveryspreadout.Thelightfromalaser,movinginonlyonedirectionandconcentratedinanarrowbeam,ismuchstronger.2.Assoonasthelaserwasdeveloped,scientistsbeganthinkingofpracticalapplicationsforit.One
3、oftheearliestuseswastomakeextremelyprecisemeasurementsofdistanceandspeed.Forexample,thedistancetothemoonwasmeasuredtowithinafoot,andthespeedoflightwasmeasuredtowithinathousandthofamilepersecond.Astimepassed,manymoreapplicationsforthelaserweredeveloped.3.Someofthemostimportantusesoflasersare
4、inmedicine.Laserscanbeusedinsurgerytoopenandcloseincisionswithnodangerofinfection.Ineyeoperations,alasercanbeusedtoreattacharetinaandtopreventexcessivebleedingoftinybloodvesselintheeye.Lasersarealsoimportantinthetreatmentofcancer.Alaserbeamcancompletelydestroyacancerousgrowthwithoutleavingb
5、ehindanydangerouscancercellsthatcouldstartanewtumor.Morerecently,lasershavebeenusedtoremoveskindiscolorationslikefreckles,agespots,andbirthmarks.Somedentistshaveevenstartedusinglasersforpainlesstreatmentofteethandgums.4.Overthepasttwentyyears,personalcomputershavebroughttremendouschangestot
6、hehomeandtheworkplace,andmanyofthemostimportantdevelopmentsincomputertechnologyarebasedonlasers.Fromlaserprinters(includingthenewestcolonprinterstotechnologybywhichwholeencyclopediasofinformationcanbestoredonalaserdisk(calledaCD-ROM}andreadbyacomputer,toopticaldisksthathavehundredsoftimesas
7、muchmemoryasregularfloppydisks,lasersarerevolutionizingcomputers.5.Lasersalsohavemanyusesinbusinessandindustryandineverydaylife.Infactories,lasersareusedtocutclothandhardenmetals.Insupermarkets,alaseratthecheckoutcounterreadsthepricecodesonpackages.Laser
