千米小说网

Chapter 7 Lighting the frontiers（第2页）

&ytodothisiisfullyquantummeicalallowsstiststoexploreiesofmatterthatarerelevaypesofmaterials（forexample，solid-statemetaloxides）overwhichitisdifficulttoexertthesamedegreeofpretrola。Inicgasesitisnowpossibletolookatatomsiesindividuallyaheyaredoingasgesaremadetotheire。

Itispossibletoexplorethislimewithmakindsofatoms，andtobuildplicatedtrappingstructuresusinglight。Theideaofusingsto‘simulate’otherquantumsystemsisatareaofresearch。Itallowsexplorationofplexproblemsthatotbesolvedinotherectedtoleadtoaandingofmaterialsandstructuresthataeshelpiandandevendesigsthatwillbeusedforapplissuchasdatasteforagiagingmaesforhealthcare，orevenfriotorsforlevitatingtrains。

Ultrafast

Lightpulsesbeextremelybrief。Iatedthattheybeasshortasasiheopticalfield。Fhtinthevisibleregiorum，that’sabout2fs。Fhtiremeultraviion，whichisthandhigherfrequeionsbemuchshorter。Theshortestyetmeasuredislessthan100as（10-18s）long。Thesearetlytheshortestpulsesthattrollablygehoughweobserveeventsthathappenonamuescalebymeansofparticlecolliders）。AndwiththeadventofburstsoflightintheX-rayregiorum，ectthateveimescalesarepossible。

&hesenumbersaresomind-bogglinglysmall，itishelpfultoputthemiheageoftheuniverseisapproximately5×1017s。Thustheratioofoheageoftheuniverseisapproximatelythesameastheratioofooonesed。Ortoputitinaneitext，ifthenatioheUSisequivalehewouldbeequivaleosethisscale，asiosedisvirtuallyworthless。

WhatsortofthingsonthistimesChapter4，Iintroducedasimplemodelofanatom—calledtheBohrmodel—irons‘orbit’anatomiucleus，attractedtoitbyeleuchthesamelatheSun，attractedbygravitatioimetakeheseorbitsforsimpleatoms（thatis，thosewithorons）isabout150as。Soifwewanttolookatthismotioousepulsesshorterthanthis，sowedon’tjustseeablur。

Theideaofthestroboscopeistheooourstory，sinceavariantisusedbyresearcherstodaytolookatthereallyspeedygesthatgoonatthefuallevelofatomsandmolethisapplithelightpulsesfromalaseraresplitintotwo（ormore）parts，withadelayiweepulseinthesequenatesthesample，aisabsorbed。This‘triggers’somethesystem—eleovearouom，orbondsvibrateinmoleculesorsolids。Aninstahesedpulsearrivesaisagaihesampleaed。

Asthedelaybetweewopulsesinrepeatedrunsofthisexperimeedscatteredlightmapsoutthedynamigesofthesample。Imakesa‘movie’oftheatomormoleculeorsolidasitges。This‘pump-and-probe’schemehasbeeisofens，forinstangachemicalrea，whentwomoleculesarerefiguredbytheiriioicatedversionsofthiskindofapproachexistusipulses。Theseapprusednowtoexploremauresofextremelyiingandpuzzlingmaterials，fratomsauresuperductorstobiologicalsystems。

&hattheshortestpulseitispossibletogeeisasiheopticalfield。Itturnsoutthatyoudeviseaomeasuretheossoftheopticalelectricfieldusiremeultraviolet（EUV）pulsesproducedbyhighharmoion。Whatisomeasurethepulsefieldisaveryfastproethatismuchfasterthaicalcycleitself。Thatbeprovidedbyapulsewithmuchshths，abouttwentyorthirtytimesshorterthanthatoftheopticalwavelength。Pulsesofsuchbrevityaregeedwheronisrippedoffanatombymeansopticalpulse。Thisrequiresanopticalfieldwhthisparabletothebindiheeleiucleus。Suchpulsesarereadilyavailablebyaddingopticalamplifierstotheoutputofamode-lockedlaser。

&heeleisliberatedbysutefiinginarapidlyosgelectricfield，and，ifitsliberationoearatimewhenthefieldhaszeroamplitude，theele‘surf’alocycleoftheopticalwave，takinganexawayfromtheatom，andthenba。Wheismovi，arecollideswiththeatomitberecapturedbyemittingallofitsextraenergyaslight。Inthiscaseaveryshortpulseisemittedastheelebines，haviwavelengthofperhapsafewtensofbillionthsofametre，intheEUVregiorum，abouttweerthaicalwavethatge。

NowimagihisEUVpulseshiheratom。Ithasasuffitlyshortwavelengthsuchthatitisabsorbedbytheatom，andknoele，whisitsom。Imagiheatomissimultaneouslyillumiheshortopticalpulseweseektomeasure。ThefieldofthispulseacceleratestheeleoionoranotherdependioftheopticalcycleatwhichtheeleisliberatedbytheEUVpulse。BygthedelaybetweentheEUVpulseaicalpulse，theacoftheelebemeasuredsirons，whichhavebeeree，havemy。Inthisossibleto‘see’anopticalpulsefield（Figure33），despitetheextraordinarilyshorttimescaleoftheossofthefield。

Anexampleofanappliethodsofpump-arosbiochemistryisthestudyofthefirststepsintheprocessofphotosynthesis，bywhitsverttheairintooxygenusingsunlightasanenergysource。Theprocessesbywhichthishapperanspenergyaroundabigbiologicalmoleculewithremarkablyhighefficy。Themeansbywhichthishappenshassomeveryiingandpoorlyuoodfeatures—itisfasterthaexpedmuchmoreeffit。Ifwecouldlearnfromsystemsthathaveevolvednaturallyovereonshowtodothis，perhapswouldeoapplyittothingslikeimprovingthedesignofsolarcells，whichwouldhaveanenormousimpasociety。

33。Directimageoftheelectricfieldofanopticalpulse。Thetimebeteaksisapproximately2。5fs。

Ultra-intense

Yourelectricitybilltellsyouhowmuergyyouusedinthepreviousmonth。Itismeasuredinunitsofkilowatt-hours（kWh），andyedforeaitthatyoue。Let’ssaythatyouused220kWhihisistheaveragemonthlyenergyptionintheUK）。Now，youcoulduseallthisehesamerateacrossallfourweeksofthemonth。Oryoucoulduseitiweek，ahinginthesubsequentthreeweeks。Butagiallinamillionbillionthofased?You’dohaveanawfullotofappliaousethatmuergyinsue，andyou’doswitandoffimpossiblyquickly。Butthepeakrateorpowerwouldbeimmeispossiblethtpulsesthatachievethis。Thatis，theyareincrediblybriefandthisamounty。Infact，itispossibletoproduceapulsethatdeliversearateequaltotheeygeingcapacityoftheplaagiveninstant。Butthelightsinyourhousewon’tgoout，becausethepulsesaresobriefthatthetyinthemisverysmall。

&producepulsesofthiskindaremassiveis，oglargebuildingsthatareasignifitfraofafootballfieldinsize。OheVULlaserattheRutherfordAppletonLabland。VULproducespulseswith500Joulesy（1J=kulseof500fsduration。500Jistheeedbya100Wlightbulbinfiveseds。YetthebrevityofthepulsemeansthattheiyofthelightbeashighasamillionsutheNationalIgnitionFaIF）inLivermore，uch，muchbiggerthanthis。AndtheprhtInfrastructureprojectissettodeliverasystemcapableofeveerpeakpowerthanthatatNIF。

Suchverybrief，veryiburstsbeusedtoalterstatesofmatter。Theelectricfieldatthemostiofthelightpulseislargerthaivefieldbetweeronsaholdsatomstogether。Soitispossibletostriptheelesofftheatomstoformaer—aplasma。Andit’spossibletodothisinaninstahetimeoverwhiiumove，sothattheplasmaisverydehesamedensityasinasolidbloaterialsuchasapieceofglass，exowattwomilliondegreesCelsius。

&hesihecoresofthegiasaars:veryhigh-densityplasmaswithparticlesgwitheachhspeedandatpressuresofamillioofourohere。Itispossibletousethisory-accessiblestateofmatterfs。Forinstanbegiandhohattheirlifecydtocharacterizetheirstagesofevolution，suchassupernovaeexplosionsandwhitedwarfs。Othersituatiooastrophysicistsarealsoamealexplorationusirophysicistsalsousesuchplasmastoprobethefrontiersofplaarysstaispossibletoiionofthegasgiantsfromtheirmassaoowhichmatterpressedatsuchhighpressuresisknown。

Somelaserfacilitiesgeepulsesusinglightofveryshortwavelengths。Thesepulsesareproducedbyageleaghatthey‘wiggle’fromsidetosideastheywhizdowor。ThisprodudofsynradiationgofshortburstsofX-rays。Oftenthesekindsoflasersuseteiques，andindeedhardware，fromparticleaplesofthesearetheStanfordLinearChtSource（LdtheHamburgX-rayFreeEleLaser（XFEL）。

&eiquesaffordedbythemostintenselaserpulses，inwithshortburstsofX-rays，eodiagnoseplasmasinawiderangeofs。Further，theimmensepressureexertedbylasersbetweenatomiucausethem，us，tofusetalargeamouheprocess。This‘nuclearfusion’isapossibleroutetoanalmostunlimitedsourergy。Thisapplioflasersisextremelyteicallydemanding，awomethodsthatarebeioachievefusioherdoesnotiexceptasawaytomonitortheproakeuseofdenseplasmas。

Asthelaserpulsesmhtheseplasmas，theygeeawave，verysimilartothewakethattrailsaboatmovingacrossawatersurface。Theelectricfieldsintheplasmawavereachmorethan100，000Vover10-6m（that’sabouttehevoltageinthebigpowerlinesonpyloahahofahumanhair’sbreadth。）Thesefieldstre1，000timesbiggerthaingfieldsusedinthewestmaesffuicles，suchastheLargeHadronCollider（LHimaybepossibleusihodseventuallytobuildtable-topdevicesthataccelerateeleilarenergiesastlypossibleintheLHC。

Itisalsopossibletoaccelerateheavierparticles，suearaordinarilystroricfieldsgeheiionoflaserpulsesrotonbeamsaretlybeingexploredasacertreatmehedeliveryofheavyparticlestodiseasedtissueorepredatgreaterdepthsthalypossibleusiypesofradiationtherapy。

&raordiiesoflightuetoenablenewrealmsofdiscovery，acrossawiderangeoffields。Lightisaubiquitoustoolforsdteology。