电子信息专业英语（第二版）课件：Laser

LasersPassageAWhatisaLaser?

PassageBIntroduction:Super-tool

PassageCLasers

PassageAWhatisaLaser?

InH.G.Wells’sTheWaroftheWorlds,publishedin1898,extraterrestrialalienswreakdestructiononourplanetwiththeir“heatray”,abeamofenergysohot,sopowerful,thatitdestroysanythingittouches.“Suddenlytherewasaflashoflight,”wroteWells.“Itwassweepingroundswiftlyandsteadily,thisflamingdeath,thisinvisible,inevitableswordofheat.”Wells’sheatray,whichinspiredgenerationsofscience-fictionwriterstoimagineraygunsanddeathrays,wasachillinglyaccuratepremonitionofplanstousethehigh-energyinfraredlaserasaweapon.

Whenreallasersfinallyarrived—in1960—writersandmoviemakersimmediatelyleapedupontheirdestructivepowerandsubstitutedtheword“laser”forraygun.AlaserwasoneoftheleadingpiecesofmachineryintheJamesBondtechno-spythrillerGoldfingerintheearly1960s.Asyoumayrecall,Bond(SeanConneryplayedtheroleatthetime)wastieddowntoametaltablebythevillainGoldfinger,hislegsspreadapart,whilealasermadeitswaydirectlytowardhisgenitals.Thelaser’sbright,red,thickbeameasilycutaswaththroughthetable.Itobviouslyhadthepowertotearhimasunder,lengthwise.

Thisis,alas,themostpopularimageofthelaser.Araygun.Adeathray.Andindeed,somelasersdocutthroughmetalandsomecanbeusedasweapons.Butthisimageofthelaserisareflectionmoreoftheneedfordramainworksoffictionthanofthelaser’spotentialusefulnessinoursociety.Mostlaserbeamscan’tcutorburnandareatbestfaintpencillinesintheair,lightscatteredbydust.Thenicesharppicturesoflaserbeamsinthisbookaretakenbyprojectingthebeamsthroughcloudsofsmoke,whichscattertheirlightenoughtoallowthemtobeseenandphotographed.

Sohowshouldyouthinkofthelaser?Thinkofitsimplyasatool.Onethatuseslightinsteadofmechanicalenergy.Andatoolthatallowsitsusertocontroltheformandamountofenergydirectedataparticularplace.Thelasercancutthroughatwo-inch-thicksheetofsteelordetectasingleatom.Itcanperformataskasdramaticasignitingathermonuclearfusionreactionorasseeminglymundaneasdrillingaholeinababy-bottlenipple.

Alaserisadevicethatproducesaveryspecialkindoflight.Youcanthinkofitasasuperflashlight.Butthebeamthatcomesoutofalaserdiffersfromthelightthatcomesoutofaflashlightinfourbasicways:

· Laserlightisintense.Yetonlyafewlasersarepowerful.That’snotthecontradictionyoumightthink.Intensityisameasureofpowerperunitarea,andevenalaserthatemitsonlyafewmilli-wattscanproducealotofintensityinabeamthat’sonlyamillimeterindiameter.[1]Infact,itcanproduceanintensityequaltothatofsunlight.Anordinarylightbulbemitsmorelightthanasmalllaserlikethis,butthatlightspreadsoutallovertheroom.Somelaserscanproducemanythousandsofwattscontinuously;otherscanproducetrillionsofwattsinapulseonlyabillionthofasecondlong.

· Laserbeamsarenarrowandwillnotspreadoutlikeordinarylightbeams.Thisqualityiscalleddirectionality.Youknowthateventhemostpowerfulflashlightbeamwillnottravelfar.Aimoneatthesky,anditsbeamseemstodisappearquickly.Thebeambeginstospreadoutassoonasitleavestheflashlight,eventuallydispersingsomuchastobeuseless.Ontheotherhand,beamsfromlaserswithonlyafewwattsofpowerwerebouncedoffthemoon,andthelightwasstillbrightenoughtobeseenbackontheearth.Oneofthefirstlaserbeamsshotatthemoon—in1962—spreadoutonlytwoandahalfmilesonthelunarsurface.Notbadwhenyouconsiderthatithadtraveledaquarterofamillionmiles!

· Laserlightiscoherent.Thismeansthatallthelightwavescomingoutofalaserarelinedupwitheachother.Anordinarylightsource,suchasalightbulb,generateslightwavesthatstartatdifferenttimesandheadindifferentdirections.It’slikethrowingahandfulofpebblesintoalake.Youcausesometinysplashesandafewripples,butthat’saboutall.Butifyoutakethesamepebblesandthrowthemonebyone,atexactlytherightrate,atthesamespot,youcangenerateamoresizeablewaveinthewater.Thisiswhatalaserdoes,andthisspecialpropertyisusefulinavarietyofways.Putanotherway,alightbulboraflashlightislikeashotgun;alaserislikeamachinegun.

· Lasersproducelightofonlyonecolor.Or,tosayitinamoretechnicalway,thelightismonochromatic.Ordinarylightcombinesallthecolorsofvisiblelight(i.e.,thespectrum).Mixedtogether,theycomeoutwhite.Laserbeamshavebeenproducedineverycoloroftherainbow(redisthemostcommonlasercolor),aswellasinmanykindsofinvisiblelight,buteachlasercanemitonecolorandonecoloronly.Therearesuchthingsastunablelasers,whichcanbeadjustedtoproduceseveraldifferentcolors,buteventheycanemitonlyonecoloratatime.[2]Afewlaserscanemitseveralmonochromaticwavelengthsatonce—butnotacontinuousspectrumcontainingallthecolorsofvisiblelightasalightbulbdoes.Andthentherearemanylasersthatprojectinvisiblelight,suchasinfraredandultravioletlight.NOTES

[1] Intensityisameasureofpowerperunitarea,andevenalaserthatemitsonlyafewmilli-wattscanproducealotofintensityinabeamthat’sonlyamillimeterindiameter.

强度是每单位面积上能量的度量，即使一个仅产生几毫瓦能量的激光器也能产生一个直径只有1毫米的高强度光束。

·后半句的主句为alaser…canproducealotofintensityinabeam…。［2］Laserbeamshavebeenproducedineverycoloroftherainbow(redisthemostcommonlasercolor),aswellasinmanykindsofinvisiblelight,buteachlasercanemitonecolorandonecoloronly.

激光束可以是彩虹中的每一种颜色(红色是最常见的激光颜色),还可以是许多种看不见的光,但每个激光器能且只能发出一种颜色的光。Exercises

1. Fillintheblanks.

(1)Whenreallasersfinallyarrived—in1960—writersandmoviemakersimmediately

theirdestructivepowerandsubstitutedtheword“laser”forraygun.

(2) Thelaser’sbright,red,thickbeameasilycutaswath

thetable.

(3) Onethatuseslight

mechanicalenergy.

(4)  Butthebeamthat

alaserdiffersfromthelightthatcomesoutofaflashlightinfourbasicways.

(5) Intensityisameasureofpowerperunitarea,andevenalaserthatemitsonlyafewmilli-wattscanproduce

intensityinabeamthat’sonlyamillimeter

.

(6) Thebeambeginstospreadout

itleavestheflashlight,eventuallydispersing

tobeuseless.

(7) Afewlaserscanemitseveral

wavelengthsatonce—butnotacontinuousspectrumcontainingallthecolorsofvisiblelightasalightbulbdoes.

2. True/False.

(1) AlaserwasoneoftheleadingpiecesofmachineryintheJamesBondtechno-spythrillerGoldfingerintheearly1970s.()

(2) Thisis,alas,themostpopularimageofthelaser.Araygun.Adeathray.Andindeed,somelasersdocutthroughmetalandsomecanbeusedasweapons.()

(3) Mostlaserbeamscancutorburnandareatbestfaintpencillinesintheair,lightscatteredbydust.()

(4) Itcan’tperformataskasdramaticasignitingathermonuclearfusionreactionorasseeminglymundaneasdrillingaholeinababy-bottlenipple.()

(5) Anordinarylightbulbemitsmorelightthanasmalllaserlikethis,butthatlightspreadsoutallovertheroom.()

(6) Anordinarylightsource,suchasalightbulb,generateslightwavesthatstartatdifferenttimesandheadindifferentdirections.()

(7) Therearesuchthingsastunablelasers,whichcanbeadjustedtoproduceseveraldifferentcolors,buteventheycanemitonlyonecoloratatime.()PassageBIntroduction:Super-tool

WhatAreLasersGoodFor?

Therangeofusesforthelaserisstriking,goingfarbeyondtheoriginalideasofthescientistswhodevelopedthefirstmodels(thoughtheydon’tliketoadmitthis),aswellasvastlybeyondthevisionsoftheearlyscience-fictionwriters,whomoreoftenthannotweresimplylookingforafuturisticweapon(thoughtheytooarenotabouttoadmittheirlackofvision).[1]

Thewidevarietyoflasersisalsostriking.Atoneendofthescale,therearelasersmadefromtinysemiconductorchipssimilartothoseusedinelectroniccircuits,nolargerthangrainsofsalt(akindoflaserthatGordonGould,oneofthepioneersofthefield,sayssurprisedhimwhenitwasintroduced).Attheotherend,therearethebuilding-sizelaserweaponsthatthemilitaryistesting,quitedifferentfromthehand-heldraygunsofscience-fictionwriters.

Ourpurposeinthisbookisnotonlytoexplainlasersbuttotellyouaboutallthewaysinwhichthey’renowused—andwillbeusedinthenearfuture—andabouthowlaserswillthereforeaffectourlives.Thetasksthatlasersperformrangefromthemundanetotheesoteric,buttheyusuallyhaveacommonelement:theyaredifficultorimpossiblewithanyothertool.[2]Lasersarerelativelyexpensivetoolsandareusuallybroughtintodoajobonlybecausetheycandelivertherequiredtypeandamountofenergytothedesiredspot.CharlesH.Townes,oneoftheinventorsofthelaserandaNobelprize-winner,toldusrecentlythathebelievesthelaser“isgoingtotouchonaverygreatnumberofareas.Thelaserwilldoalmostanything.Butitcosts.Thatistheonlylimitation.”The$50,000ScalperandTelevisionFibers

Atypicalsurgicallaser,forexample,costsfrom$30,000to$50,000andup,oraboutathousandtimesmorethanagoodconventionalscalpel.Andtobehonest,formanyoperationsascalpelmaybebetterthanalaser.Butifyouhaveadetachedretina,aconditionthatcouldleadtoblindness,youmaybehappythattheseexpensivescalpelsexist.Alasercandowhataknifecan’t:weldtheretinabacktotheeyeball.Noincisionisrequiredforthisdelicatesurgery,whichcanbeperformedrightinthedoctor’soffice.Thelaserbeamshinesthroughthelensofthepatient’seyeandisfocusedontheretina,producingasmalllesionthathelpsholdittotheeyeball.Exoticasthissounds,asimilarlasertreatmenthasbecomeastandardwayofcuringblindnesscausedbydiabetes.(CharlesTownesfindsthisapplicationofthelaseramazing.Headmittedtousrecentlythattheadaptationofthelaserformedicalusestookhimbysurprise,especiallythedetachedretinaprocedure.)

Lasermedicineprobablyhasn’ttouchedyoupersonally(you’dknowifithad),butlasercommunicationhasundoubtedlyservedyoualready.Ifyouwatchedthe1980WinterOlympicsfromLakePlacid,NewYork,oranyrecentfootballgamefromTampaBay(Florida)Stadiumontelevision,yousawsignalsthatweretransmittedpartofthewaytoyourhomebylaser.Laserscarrytelephonesignalsindozensofplacesaroundthecountry.Inbothcases,lightfromthelasersiscarriedthroughhair-thinfibersofglass—fiberoptics—atechnologythatcouldultimatelybringamultitudeofnewcommunicationservicesintoyourhome.DeathRays,Drills,NuclearFusion

Lasersarealreadycommonplaceitemsamongourmilitary,butprobablynotinthewayyouthink.Theirmainfunctioninthebusinessofwaristhatofrangefinderandtargetdesignator,notraygun.Lasersmeasurethedistancestotargetsorpinpointthemwitha“bull’s-eye,”helpingeithergunsormissilestohomeinontheenemy.Andyes,inanoffshootofH.G.Wells’sidea,theU.S.militaryisalsospendingabout$300millionayeartryingtobuildlasersabletodestroytargetsrangingfromhelicopterstoballisticmissilesandsatellites.TheSovietUnionhasacomparableprogramandisbelievedtohavealreadyusedalasertotemporarilyblindthesensitiveelectronic“eyes”ofaU.S.spysatellite.

Infactoriesaroundtheworld,lasersarenowusedroutinelytodrillholesindiamonds,labelautomotiveparts,andweldbatterycasesforheartpacemakers.Laserquality-control“inspectors”sitever-vigilantonassemblylines,makingsurethatthesizesofpartsdonotdeviatefromanacceptablerange.

Oneofthehopesforendingourenergyproblemsisthermounuclearfusion,theprocessbywhichoursungeneratesitsenergy.Onewayofcreatingfusionhereonearthistoheatandcompresspelletscontaininghydrogentothetemperaturesandpressuresneededtofusethenucleiofthehydrogenatomstogether,creatingtinyhydrogenbombsandthusgeneratingincrediblepower.[3]Whatcancompressthesepellets?Lasers,ofcourse.Three-dimensionalImagesandSuperReaders

Lasersarewhatmakehologramspossible—thosethree-dimensionalimagesthatseemtofloatbeforeyou,suspendedinspace.Butholographyhasmanyseeminglymundaneapplicationsaswell,fromtestingthequalityofaircrafttirestomeasuringheatflowtoaidinginthedesignofsuchthingsashairdryers.

Lasershavemadenewartandnewentertainmentformspossible,evenbeyondholography.Laserlightshows,thebestknownofwhichisLaserium,havebeenseenbymillionsofpeoplearoundtheworld.Alaserisalsoattheheartofonetypeofvideodiskplayer,thatnewdevicethatplaysbackmoviesandtelevisionprogramsprerecordedonphonographlikedisks.

Laserscanread.Thosecrypticbarcodesonfoodpackagesinsupermarketsarereadbyscanningthemwithalaserbeam.Thepatternofreflectedlightisdecodedtotellacomputerinthebackofthestorewhatthelabelsays.Thisnotonlytabulatesthepriceonthecashregisterbutautomaticallyregistersinthecomputer’sinventorymemory.Lasersalsoreadspecialtypewriterfaces,sothatmanuscriptscanbetypesetautomatically,withouthumanaid.

Andlasercanwrite.It’ssimpleforacomputertocontrolalaser,makingitwriteonfilm,specialpaper,orthedrumofacopyingmachine,forlatertransfertopaper.Laserexposeprintingplatesfornewspapersandprintstatementsforinsurancecompaniesandmutualfunds.NOTES

[1] Therangeofusesforthelaserisstriking,goingfarbeyondtheoriginalideasofthescientistswhodevelopedthefirstmodels(thoughtheydon’tliketoadmitthis),aswellasvastlybeyondthevisionsoftheearlyscience-fictionwriters,whomoreoftenthannotweresimplylookingforafuturisticweapon(thoughtheytooarenotabouttoadmittheirlackofvision).

激光的用途极其广泛，令人瞩目，远远超出了设计第一代模型的科学家们的想像(尽管他们不愿承认)，也极大地超出了早期科幻小说家的想像，这些小说家只是单纯地寻找一种未来武器(尽管他们也不愿承认自己缺乏想像力)。

[2] Thetasksthatlasersperformrangefromthemundanetotheesoteric,buttheyusuallyhaveacommonelement:theyaredifficultimpossiblewithanyothertool.

激光器能完成从平凡到神秘的多种任务，但这些任务通常都有一个共同点：它们很难或不可能由其他工具来完成。

·句中的两个they均指thetasks。

[3] Onewayofcreatingfusionhereonearthistoheatandcompresspelletscontaininghydrogentothetemperaturesandpressuresneededtofusethenucleiofthehydrogenatomstogether,creatingtinyhydrogenbombsandthusgeneratingincrediblepower.

在地球上实现熔合的途径是对含有氢气的气团加温加压，以达到使氢原子熔合的温度和压力，产生小型氢弹，因而出现难以想像的巨大能量。Exercises

1. Fillintheblanks.

(1) Atoneendofthescale,therearelasers

tinysemiconductorchipssimilartothoseusedinelectroniccircuits,nolargerthangrainsofsalt.

(2) CharlesH.Townes,oneoftheinventorsofthelaserandaNobelprize-winner,toldusrecentlythathebelievesthelaser“isgoingtotouchon

areas”.

(3) Thelaserbeamshinesthroughthelensofthepatient’seyeandis

theretina,producingasmalllesionthathelpsholdittotheeyeball.

(4) Inbothcases,lightfromthelasersis

hair-thinfibersofglass—fiberoptics—atechnologythatcouldultimatelybringamultitudeofnewcommunicationservices

yourhome.

(5) Thepatternofreflectedlightisdecodedtotellacomputer

thestorewhatthelabelsays.

2. True/False.

(1) Laserscarrytelephonesignalsindozensofplacesaroundthecountry.()

(2)Lasersmeasurethedistancestotargetsorpinpointthemwitha“bull’s-eye,”helpingeithergunsormissilestohomeinontheenemy.()

(3)  Infactoriesaroundtheworld,lasersarenowusedroutinelytodrillholesindiamonds,labelautomotiveparts,andweldbatterycasesforheartpacemakers.()

(4)  Lasersarewhatmakehologramsimpossible—thosethree-dimensionalimagesthatseemtofloatbeforeyou,suspendedinspace.()

(5)  Laserexposeprintingplatesfornewspapersandprintstatementsforinsurancecompaniesandmutualfunds.()

(6)  Laserscan’tcauseandcontrolchemicalreactionsandsomedaymightevenpropelrocketsandaircraft.We’llcoverallthesethingsinthefollowingpages.()PassageCLasers

Tounderstandwhatalaser(LightAmplificationbyStimulatedEmissionofRadiation)is,onehastounderstandhowlightgenerated.Lightcomesfromtheelectronswhichsurroundthenucleusofeverynormalatom.Whentheatom,letussay,ofsodium,isinitsunexcitedstatetheelectronsthatsurroundthesodiumnucleusareintheirnormalenergylevels.Ifthissodiumatomabsorbssomeenergyfromoutside,oneormoreoftheelectronsjumpsfromalowenergyleveltoahigherenergylevel.Theatomthenremainsinthisexcitedstateuntilitisabletoreleasetheenergyithastemporarilystored.Whenthisreleaseoccurstheelectroninthehighenergylevelfallsbacktothelowenergylevel.Butasitdoessoitemitstheextraenergyasapulsewemayseeaslight.

Thelaserbeamismadebyexcitingtheatoms