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Generation of Electromagnetic Pulses from Plasma Channels Induced By

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Generation of Electromagnetic Pulses from Plasma Channels Induced By Generationofelectromagneticpulsesfromplasmachannels inducedbyfemtosecondlightstrings Chung-ChiehCheng,E.M.Wright,andJ.V.Moloney ArizonaCenterforMathematicalSciences,andOpticalSciencesCenter,UniversityofArizona, Tucson,AZ85721 December04,2000 We present a model that elucidates the physics underlying the generation of an electromagneticpulsefromaplasmachannelresultingfromtheionizationofairbya femtosecond laser pulse. By a new mechanism analogous to nonlinear optical rectification,thelaserpulseinducesadipolemomentintheplasmawhichsubsequently oscillates at the plasma frequency and radiates an electromagnetic pulse with a peak frequency within the far-infrared to microwave region, depending on the electron density,withabandwidtharoundhundredsofgigahertz. PACS:33.80.WzOthermultiphotonprocesses 42.65.ReUltrafastprocesses;opticalpulsegenerationandpulsecompression 52.40.DbElectromagnetic(nonlaser)radiationinteractionswithplasma Recentinvestigationsofthepropagationofintensefemtosecondinfrared(IR)laser pulsesinairshowthatthedynamicalinteractionbetweennonlinearself-focusing, plasmadefocusing,andgroup-velocitydispersioncancauseaninitialbeamtobreakup spatiallyintoseveralfilaments,orlightstrings,withdiametersaroundahundred micronsthatcanmaintainthemselvesoverlongdistances[1,2,3,4,5].Ithasbeen observedexperimentallythatfemtosecondlightstringsinturnproduceplasma channelsbymulti-photonionization(MPI)alongtheirdirectionofpropagationwith lengthsrangingfromtensofcentimeterstoseveralmeters[6,7,8].Observationsofthe electromagneticpulses(EMPs)fromlightstringinducedplasmassuggestthatthese channelsattaindipolemomentsduringthelaserpulsewhichsubsequentlyoscillateat theplasmafrequencyandradiate[6].Thelifetimeoftheobservedplasmachannelsis aroundananosecondinkeepingwiththedurationoftheobservedEMP,thoughtheir frequencycontenthasnotbeendeterminedexperimentallyasofyet. 1 ¢¡¤£¦¥¨§ © £¦£¦ ¤ © ¡¨£¨ ¦ !"$#&%' ¡¨ ()£¦§ ¡¤¦*+¦ £¦© ,-¡¨. § %'¥¨£¨©£¦§ ¡¨% § ¡¨/,- . 0©)© £¦1 /,-§2)£¦ £¦¥¨ /¡¨ 3'§ ¡¨%4¥¨3'©§ ,-©5)§ ¡¤)£¦§ ,-/ )¥¨6£¦¥¨ § ¡¨§ £¦§ ) § ¡¨£¨§ © /,- .§ ¡¤£¦¥¨ )©7,-¥¨)¡¨¡¨ 0¡¨.£¦¥¨ £¦§ © ¨£¦¥¨ 8)§ )£¦ !"$#:9 ¢¡¤£¦¥¨§ © ,-£¦¡¨© )¡¨.§ ¡¨© ) § ¡¨§ £¦§ ) 34,- )£¦ <;=34"$# >/ £?1£¦¥¨ § %'¥¨£ ©£¦§ ¡¨%'5))¡¨.§ ¡¨£¨§ © ©/@;=© AB/ ¡¨£¦ 34§ ¡¨/,- .§2¡¤£¦¥¨ )© ;=34£¦¥¨ CB ,-§ £¦3'D £¢¥¨§2© ¦,- ,-¡¨£¦)§ ¡¨© © H,-¡¨D ¡¨ ¡¨£¨E ¡¨£¦F¦ ,- '9 G' )© ¦§ .¨¦ A'/ ¡¨,-3 ω §2¡¤)§ £¦§ ¡¤£¦1 6¦ A'/ ¡¨,-34,-¡¨ ¡¨£¨)¡¨) %'/© £¦ ¥¨)¡¨§ ,I,-¡¨ ¡¨£¨)£¨J ω ,-£¦§ ¦§ ,-)£¦§ ¡¤§ ¡¤¡¨¡¨ § ¡¨ )£¦§ ,-©K 9 ¢£¨§ © £¦¥¨§ © 6¦ A'/ ¡>,-34£¦ +£¦¥¨)£¨,- H£¦ © £¦¥¨ § ¡¨§ £¦§ ) 9L § ¡¨£¨§ ¡¤£¦¥¨ )©,-¥¨0¡¨¡¨ M;=34 ¡¨%'§ £¦/§ ¡¨) 34© ))£¦§ ¡¨%4£¦¥¨ § %'¥¨£¨ ,-£¦*¡¨© ¦+£¦¥¨ ¥¨ )CB34§N¡¨© ¡¤£¦¥¨ ©¥¨£B£¦§ ©,-) ¨£¦¥¨ § %'¥¨£¨©£¦§ ¡¨%O9G ¤§ ¡¨%4£¦¥¨ )© / © £¦¥¨ ,-£¦¡¨D¦§ ¡¤©3'©£¦ +£¦¥¨ ¡¤©£¦)*£¦© £¦1©,-§ )£¦ ¡¨%'§N£¦/§ ¡¨) 34)£¨£¦¥¨ )©¦ A'/ ¡¨,-3 )¡¨.%' ¡¨ )£¦ © )¡¤!"$#&)%'H£¦§ ¡¨%4)§ ) 34)¤)34?+£¦¥¨ )©,-¥¨)¡¨¡¨ P9 QR ©£¦ ©© £¦¥¨)£¨£¦¥¨§ © ,-¥¨)¡¨§ ©S+¦,- )£¦§ ¡¨%4§ ¡¨£¨§ ¡¤ )©§ © ¡¨ 60¡¨.§ ©£¦§ ¡>,-£¨¦ £¦¥¨)£¨/ £¦1£¦¥¨ >¡¨ £¦§ CB ¦ ,- ¦+£¦§ %'¥B£¦ 34¦,-/© .T7)/©©§ 0¡;= )UK 10,11,12]: G' § %'¥B£¨©£¦§ ¡¨%'© ¨§ ) £¦ (V)W)W§ ,-¡¨© )¡¨.¦ 6,- ¡¨£¦§ £¦ © ¡¨%'£¦¥¤£¦¥¨ ¡¨ £¦§NCB ¦ ,- ©¥¨/ <;= ¡¨ %' § %'§ ;= '9 ¢¡¤/ ¤ ,-¡¨©§ ¦ £¦© ,-¡¨. )© / © § ¡¨ ) 34 )§ F) .) ¡¨%4£¦¥¨ X@D § ,-£¦§ ¡¨5))¡¨.)%')£?§ ¡¨%4§ ¡¤)§ ) ¡¨%1£¦¥¨ F)D¦§ ,-£¦§ ¡¨5)¤§ £¦¥¤,- ¡¨£¦) ¢YZ¤)CB ¡B%'£¦¥¤ ] )¡¨. 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