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&omsareough，theydoobelocatedatthesame‘site’ie，sdistributionofatomsisverylikeafulleggateachsite，asshowninFigure32b.Inthiscasethereisy，siomsliketostayput.Itismorelikean‘insulator’，asnothiuriyupanddownitispossibletoexplorethisiraweeelyfreeflowandnoflo>
&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.
NowimagihisEUVpulseshiheratoIthasasuffitlyshortwavelengthsuchthatitisabsorbedbytheatom，andknoele，whisitsoImagiheatomissimultaneouslyillumiheshortopticalpulseweseektomeasure.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.
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