edited
`1LevenJ. R:afi2ie§ms1E<i1
`‘Department 9-? 1% 51:35;
`1New Maxi-Q9 state 1
`A
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`L35 Crates,
`isfiexzas
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`>
`:3?!
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`C‘hemicai and Laser S<:ier1;:es.‘[3i'v%sion
`L03 Mamas Nat’ia3Ana,¥ ‘L3i3t3'Fa‘tt3rv~
`L03 Atamos, New Maxim
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`MARCEL DEKKER, INC.
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`New York" and Base!
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`Li%::ra.ry of CongressEafalggagix;g4i§141§n}3iit;ati(2n. Data .,
`
`;:‘§z§isi¢;a:1'i;, cixexnigzal, and hioicgical appficaii0ns.f e..c2ite-:3
`Lasexmiusze-ti V,;;1asm-as ::
`by Lewis
`Réxxiziemski, ’33a’x«’id 23;. iiremers.
`>>
`
`>
`‘
`
`.1." Rhdziexnski, Leon 1., ’ §9;'z3.s'3§
`
`’:‘;3awer.iasers.. ’
`
`0'13?
`
`This baak is prizwzd on sreiiiafree ip’:e2;:«e:r.
`
`Qopyrigh’-t © 1939; 1*:iARC.BL.DEKI{.ER. me. A1: Rights Reserved
`
`Neiiher this book no: any part may b,a_rep‘mdw:ed Q1‘ transnaitted in any form
`in by any means, eiexxtronizi or mechanicai, including plmtucopying, microfilming,
`and recording, or by any .inforrnation storage and retrieval sys-fem, without per
`mission in writing from the publisher.
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`MARCEL .DEK}{.B'R, INC‘
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`
`ii
`ii
`
`

`
`Céntents
`
`
`
`iii
`-xi‘
`
`36
`
`6]?
`
`6.Ԥ
`
`'33
`
`72
`
`7,5
`7’?
`
`88
`
`§2
`
`93
`
`:95
`
`99.
`
`I00
`
`101
`
`101
`
`105 M
`
`105
`
`110
`
`
`
`
`
`3 {ntro»duc£ion to Laser Piasma. Diagnostics
`H _ Allan A. Hans; and Hector A. Baldis
`
`?»1
`3.2
`
`Introduction
`
`Introduction to Optical Diagnostics
`
`ix
`
`fLaser-Infl11c=efl.. ’Br-eaiyfkzwzzz Au U‘§1sdat£:.
`
`;I§;;t;a:iu»c't:i;1n
`of Eicctrons
`.
`Eiemran €§'r{::§v£E1 in -.Ga$e»s
`Lasér~I:a;&.u::.:w;'z.',Eneraizzgmwxtx mi Solids am Liqzms
`.. {fim::»aiu.s:i:iz3g 'Rem_ar_i<s
` R:a:fm’*en:¢:.e:s
`
`{!(1€1iI}‘g.1§'f .P?us£—Br=eakti.ox&In Phenomena
`abexf
`Ki)-Qt
`
`Z’5:it.f<3»§i¥;:<:3;iiz:s:1
`Ciifizsatpifin 0f 21 ’P’mpagating flasma
`Absmrptian {Zhafanteristics Bf Hcatsni Gases
`Figattgrgs cf 1?fi:opagati.n_g Plasmas
`$3312.-~I}i1X1.Ensi0n.a} L:aser~S'u';3po1'1.ti:€3 ’CB1‘£fl3’H$1i0n Waves
`C3I.1e~Di.m.ensi0naI ’La.se:r~Suppcarted Detonzxtican Wave
`*One»13irj11.ans.ira’na} Laser~Suppin“te-d Radiation "Wave
`j:’i.‘ransi¥t'it3'r1 Regicms
`Radiai Ex;§arz.si:3‘n
`Thezfmal. Co;up1i.ng.
`523.3. Other Factors‘
`S’umn1a;fy
`References‘
`
`»
`
`»
`
`

`
`
`
`x
`
`3.3
`
`In_tmdu{:t_i_on to X—ray Diagnustics
`References
`
`4 I'.a3.se‘r#-Sxzstaixled P'¥as'}fias
`Dennis R. Keefe:
`
`4.1
`4.2
`.4,-3
`4.4
`$5
`
`Intmduction
`?r.incip1cs {sf Gpcratian.
`£&'1'm!;ylica1'MQdcLs
`Eagmrimental-S£13dii8S
`AppIi£.=atic;m.s of ‘fink: La_scr«S;:s£ai_t3_;$d P1351113.
`R-c{cr'e;nc£:_s
`_
`
`‘
`
`-
`
`5
`
`Infléftiailly-Ciuniinaifi Fusion
`Rat::e;rt- L. McC§{31'3_: angjcg. 3911;:
`
`'S0_1‘1'r'es
`
`-
`
`,
`
`I*Iisi_orica'i Oiverviexxg
`5.1
`'Laser—-'I*‘us'iorz Scaling Laws
`5.2
`$5.3 Camnal Physics
`5.4
`Xé-my‘ Genex‘-ati'orx by L-a_st:r«Pmduced Piasmas
`5.5
`Lam-<r—'Dzivcfl A'£1}'a:ti<_§:i
`,$_.§
`fiydrodyiiamio Stabiiity -afifiléiaiiveiy Dri=sz:_e'2:z._e$1_;1'¢II:r:
`5",‘?
`.Zr:.t‘atiiati_o11 Unfiifatirziiy}§ie>£g'1z3i&1Z1If:iitS'
`5.8-
`Impiosicén Ezxjgrerimeats
`Rtzfsarexzées
`'
`
`'
`
`6 Laser-Based Si2.zx1i€{m_é!11£f'i£tr 1%§>rimt.i;_:n
`;Iaseph'}E{. Wachteir
`
`6.1 Aspects of Semicandncter Fabrication
`6.2 Appiigations of Lasers in-the S<:mi__co£'1'dncto_r Industry
`6.3
`Research Areas
`6.4 Outiook
`Rcftarcnces
`
`'
`
`7 E S1m:_trochen1ical Anaiysis Using Laser }’}asma. Excitation
`Leon J. Radzian1sk'i and David A-. Cremers
`
`7.1
`
`Review
`
`-Methods. and Properties of Analysis Using Laser ?iasm-as
`7.2
`7.3 Analysis of Gases
`7.4 Analysis of Bulk Liquids
`7.5- Analysis of.Particle-.3
`7.6 Analysisbf Solids
`7.? Advances in Instrumentation
`
`
`
`Cements
`
`131
`161.
`
`.169
`
`169
`1_'??2.
`- 182
`139
`19.6
`20,3
`
`_
`
`_
`
`20?
`
`207
`2211
`217
`224
`227
`239'
`.243
`251
`260
`
`269
`
`269
`276
`283
`299
`291
`
`2.95
`
`295
`
`296
`302
`306
`309
`3 13
`318
`
`

`
`xi
`
`321
`.323
`
`.32?
`
`32?
`312.’?
`
`33%}
`
`335
`"341
`
`3944
`
`343
`
`347'
`
`34-’?
`350
`-
`353
`
`2363
`"365
`369
`3'22 _
`"376
`376
`
`385
`
`385
`
`386
`413
`
`
`
`Prognosis
`References
`
`-
`
`m'1g§a'men};3{s=of.A§§1ysis {if Sniiés by laser-Produced
`Iasiizas
`_
`
`flrrgzinimzitian
`I'mr'o'::meti.<.:in
`
`'
`
`
`
`. fiwmmmyy
`..
`9561?}: Sz1e(ifiaI.:__, Pats: Mitchell, and .Nichn‘las .-S. Nogar
`
`Clonvzniisfinai gdiid -Samgie ixitroéuetian fer Atomic
`Spe_cir£}sei3py
`Laser. Ablafibn £3f'St3iid Sampies.
`fi_L_b1at__f_'<:>2j1 -fur Sarx1j_§_1a‘_Z‘,-:_z_1‘r..'~*;2'::'Z:__:<:'1'i';'.7¢1;1 in Atomic.
`-Spgwaetzfsasntsgky
`Rgaiatis/Q NfIi‘:i'1’it;:3f;' GHQ.-a&?!:.3'f‘ Kbiaiifin fur Sa.n'.I'pic 1'n£r<3x:¥.u<:£'i'021
`in Atso':31iz_: Spfictmssopy
`-
`Laser S::su_rce.sf{3r Mass Spectrometry
`Applications :'_of Laser 'M§crap-robe
`Appligatirms of'1..3ser Des<'3r'ptic'm and Postionization
`Conclnsion
`Rcfeftmces
`
`Current New Applications of Laser fiasmas
`Allan A. "I-Iauexglfbavid W. Forsiund, Colin J. McKinstri.e,
`Iustin S". Wark, Philip J. I-Iargis, .I'r., Roy A. Hamil, and Joseph
`M. "Kinda!
`
`10.1 Introduction.
`10.2 Appfications -of Laser-P'Ias1na-Ge.nerat‘ed Xvrays and
`Particles
`10.3 Laser~Pfasma Acceleration 0fPartic1es
`
`7
`
`-
`
`'
`
`'
`
`
`
`

`
`xii
`
`_
`
`b
`
`.
`
`=£3;:m'teri{.s
`
`1114 Lasem-Puistad Power Sxvitching
`Refierances
`
`Index‘
`
`%
`
`-
`
`1»
`
`£324
`432
`
`437
`
`
`
`

`
`4
`La%§eriii?Susteaine Pleesmas
`
`
`ifienzfzis R.
`Carrier"far Lzaser
`Univeeizy of';Teze2£§3*e¢ 59¢: iérstiktzfe
`'3.¥I:.I{§i?t‘e:'ix'£3; Yéiznéssee
`
`4-.1
`
`INTROIJUCTION
`
`fi!.."’-SI -033-=
`’%?%¢'3€»
`Piasmas created -by the .raéi.ie£_iui;iff:Gfia ;fQ:<jZmS%13 =1a$fi'1:
`served with the .a£ivt_:'nt' 431:’ “Lgiiant guise” £2;-mvitehed, riiby lasers by Maker
`et "a3. (1963). These piaemas
`.‘h:y_gas breakziowrz at
`the focus oi 21 fees and. were -:s'I'1?.%§ti*~..iii,1..‘~§.:‘;'I.;I*>“1:_.t'i_}'4*' .§er‘-
`.‘di%fafi.en'ef iyhelasfcir
`pulse. Piasmas w'ere- also G5;S$f?fi%?i in farm en the -szvrfaties oi 1.1'&aiér3aT¥s:ir¥
`radiated by'higTh~p£1*wer pulsed or :cem?tim_iox;es.}aeer'3'aft1£¥ ‘fie greyagaie into
`the imzziciem ‘Beam at see:s=eniz'. z.:r':s_:;pez.s_9fi.¢
`the advent of
`
`mnti.nuous, high-power mt§_:><':'n=ti3iie,:::'.ifie 1 _ei.:'£, i§¥;h§éa2:1e_;pe;ssiib.iie tie‘ siistaizt
`a pzasma in a steatiy-state ::o::<5I'iti{m
`the f.£’&..i?5.!;1§ cf a=..2aee_;r
`and’ £116
`fi¥3t.experin1.e.Iita1 ebsexivatigjn cf 21 -"‘-eeniinuous 'ep_t’iea1 tiisehaege” was r_e~
`ported by Generaiov et el. (1933). -’I.‘ii"e- centixxucms, laser-sustained gpiasma
`(LS1?) is often referred to as a ce:z_fi;1';x;<>j;1$ epticai disc_I;‘2_a1*ge (C(31)) anti it.
`has .3 Irumber of unique 'pr0p8rtie£- 212:3: n§a1;e;iz=an'in:.erestin_g candidate fer
`a variety Uf applicatiens.
`_
`'
`The laser-sustained plasma shares many characteristics with other gas
`discharges, as explained in dezaii by Raizer (19813) 1‘n his compreh ensive. re.-
`view, but "it is sustained t11ro-ugh a't_§s.orpt;i'on of power frem an "optical beam
`by the pmcessof inverse brems'strahIung.- Since the optical frequency of the
`sustaining beam is greater than the piasma-frequency, the beam is capableof
`propagating well into the interior of the piasma where it is absorbed at high
`intensity near the focus. This is in contrast to plasmas sustained by high.»
`frequency electrical fields (microwave and electredeiess discharges) that
`operate at frequencies below the plasma frequency and sustain the plasma
`through absorption within a thin "layer near t-heplasma surface. This funda-
`mentai difference in the power absorption mechanism makes it possible to
`
`189
`
`

`
`‘I70
`
`_
`
`Keefer
`
`£3
`
`genome steady-Etazcu pia'smas.1?.a.v.ing .rx1ax.im.:i.'m temperatures of IGQOOOK or
`xnore-in '21 #1331 «name near-:zhc--Edens oi a ism.-far -away from any tic-nifining
`strum.-ixxm. A photo of.a._p1a33_;I;a. sustained by 3 “Ease; beam focused with a lens
`3% shown in Fig.
`I‘ A EEOW fiaussian beam from a. carbon dioxide
`
`:_3_._ 19
`1215:? was f;'G£’£‘.3_.‘I_‘$4'§-‘:3
`'I':'1___f<_3czi3 [3e.n_'gt"h ‘1o3‘2_s into 2 aitm of flowing at»
`gon. Fig; 4..1(b§_):s}i=oivs _s'c'h_er:1_a:icaZiy how tm piasrna forms-vdtliin t11c.fI'3.'f:81'
`rayon.
`3 Vania‘-ty of
`$i1£3,s;_‘_Q_aS ._hav.€: been produced
`(3-..¥33?£.t'i§2t13£3'x33}‘,f6'.I..’:$‘i3;S
`é.;trn'11§i.t?g!Ea£¥>€3z1 t_'3i.0dtido1a$ers'operati11g‘a_'t
`_‘g"3l$;€‘;;S at
`‘1 ti¥_L1
`£i%o§.2:1.25 W to several 1:-ilaiwatzs. Most
`;of‘1.(3‘_.6
`:4
`of these rcxpefiriiexiié-were-pcifozmcd;.i_n Qi;.'3.€:'I‘1..aii"
`cr.1_a.2:ge_ -chambers-wim
`_l'_i$:_i3¢..floi:sz, for iI1=a'_t‘ gr-ovideszi by naiural afmveéciion, hm recon!‘ ox»
`;$éc—‘_§:_}3$i'I_r;z§=£}§;€Q $1‘-ail. (19873)? Wells; ‘ea -31,.
`98‘?)_,_ and. Cross-‘and
`mics» -dezaioirnitaiaéd 't’E;:at. the LS? can be <7.;3t":*2*'.fit€2d
`'sI1;;<*J:'c%ss*
`-ccfixrcctivg
`'i:iiS$?éi¥é£z"'g"e;$ iiaaz operate" zizii -ia? _f£iwi:::;g
`fully in 2:
`environment have been caiied “'fp‘2$i5mj£;§r-fins” in t1‘1_c_ Soviet fitoratura, and
`the laser-sustained p'}a'x_'z_n'a..is_ often referred to as an "optical p1asmatro;1_.”'
`'Z_-‘$119,362
`'?xa‘&*§-de,n:Ioz2sirat_ed ihai p'Iasma..coxaditions arc stxéongiy
`
`dgpahdcnt on
`._ifi;€:3I:' of‘-{ho ~;21a;ns:r'iaa Mtiiiiz t‘he- s.i'zstaii1in'g Imam, -and
`that .t}1£%:'¥;>ifii§i2:9;_-
`Egcocgroigcigd .3 xsriiie. ranjge of c;ondi:tions 1';s—
`ing-.aip§ropri_a£o..;;£$133}:ii1a;tinns n'f"1é‘s_er powcr-,_ flow, and optical configura.
`tion.
`-
`..
`_.
`.
`.
`_fIfia«ie;z1::i§gn&.:zai:I::‘Iit;g% to stzxstain a;::1as.:n_a wiiiliia -ac.---small. i_soia:te'<i VOIIXIR6
`a§r;¢1_?1Kf3Yé‘;Iy '
`;31ii‘5§$'?v‘§j11‘B$- and'_-;«ton}pc:atu':e5:.h:as s1'zg_geSt_cd =21 zn2:nbe_r of
`poicaiiai -3-‘153;I3.iQ§\_2i1£?$§$ for £h&_1a$.§f~suS'.£ai2i€fi piasma. since {kc
`can
`operate. in porn hydzngcn and the
`<:_az1 be beamed remwcciy, it has.
`been '.pxopnso'_cj_§ that tho. coziid be used for high specif2c—.=impulse- space;
`propzfisidrx; .g9g_';;g;;';1b81' of papers h'a"v'ode'a2t-with this opp2i‘cation_, and “it was
`the. snhjcct of a jr-oqicsv bjy Ginnii: a:v:1"K_rier (1984). Thompson at al. (19%)
`described oxporimonts in which "laser energy was converted into c¥_cctrica'i'
`cncrgr using a -Iascr~sustainod argon. "plasma. Cromers at a}. ('19_8_5) have
`sixggefiied the L8? as a. source £01’. s;3octro£-éhenzicai analysis and given some
`experimexzta} result; Cross and Cromers (1986) fiavc sustained "pl-asrnas in
`tho throat of a small nozzle to produce atomic oxygen having a directed
`velocity of sevoral km/sec for the laboratory study of surface interactions at
`energies and particle fluxes similar to those experienced by satellites in" low»
`egarth orbit. Other applications are suggested by anaiogy to other plasma
`devices including light aourccs, piasma ch cmistxy, and matcriais processing.
`The physical proccsses that determine the u_niq_ue characteristics of the
`LSP will bodiscnsscd in Sec. 4,2, and the theoretical analyses that have been
`used to describe the LS1? will he a'ddress_ed in Sec. 4.3. Experimental results
`obtained will be presentod in Sec. 4.4 and compared with the theoretical
`predictions. Sec. 4.5 will consider some possible applications.
`
`€
`

`
`Laser-sustainegs Piasmas
`
`‘
`
`171
`
`(:3).
`
`(3) Fhotogr-aph of a plasma sustained by in 600 W _ca.rboz_z dinxittie iascr
`Figure" 4.1
`beam {unused with a 191 ‘mm fecal length lens. (13) Schematic representation shew-
`ing haw the plasma forms within. the focal volume.
`'
`
`
`
`

`
`‘:72
`
`Keefer
`
`4.2 PRINCIPLES OF {JPERATXON
`
`:_.;;. ';:cms;:_._i22
`
`iasers {,‘(a;_£i ht‘.' génerate:j,_in._a variety
`Plasmas that are created 0:‘ st-3sta_i_r£et:1'
`of ‘farms-, <1lc:{2t:"I3](i'irIg,.-eat!‘th%i1'ara£:t§;§;i§£ics Bf ftha laser and optical gimme.
`1:}; used to generate theméi F.ii'gh»»finéjf§Y-pn-3S€:d_l2'1sn'rs can ge11cra£e_p}asma
`breaicdtawn d_ir$ct;iy wiziiég;-aigas'§§:;a§__rw1.iliSi.n atransi{zntexpa13din'g';§}'asma
`similar to an expiosian._-1:52
`1£!}§_e,r _3'_jI.1.t€;:;3siiie5 and lvrzgar puIs£_°- timezs,
`-piasmas may 1>e'i:1iti'atcii__3_£i7t_
`Q .$I3x‘i'ix£‘Lt%$;an:i than 'prnpaga;te'into the gas.
`t"ai'ni::g "ht-.a'm a.t—.sn;:er3oni'?¢‘§vé1;:;;_ tics as-:2; _a{&€"r~s'n$taihad detonatian (LSD)
`wave or snhscxzic ve1ox:i_i;ix=:s_as‘ "'Ta___1.__:»3_’_;:%"'<=:£-'ar.'ia'3§:aiiz:2:t;i ébzfihustibn (ESQ) wave-.
`These transient plasmas Imvai Baez:
`Rafzier {$950) "and xvii} not
`be tmazed _here_:. If the 1338? is
`and tI'1"_¢_ a§tiié'a}
`
`
`
`figéamfitry, flaw,
`:a.%m,;% iézgaétykéfétata 1.3.?-may
`The :;:on.ii_n;n‘ensiy- maiihtainjagéi-at_ =‘a'1_'p§1‘:n§téi;:i'3z n_;:a£r_‘tfiej_'.fi3eu$ of the beam. The
`intensity that ié -availaifiie
`a"'cGiit3:zuo‘u;£;1ast:t-is‘ insufficient to cause
`breakdmem in thagaa, _.‘:2owever, and an..axm_iiimf3z semrce must‘ 133-233;}. to 3m.
`flats thepiasma. .& skstch -of a—St;£aZ€iy-.stata'.1a.st:.t~—si1sta'incd gaiasma is shown
`in Fig. _4.3(b). The plasma -may-he siminecz vziilhiii an xxmfining cizamber tr‘:
`ccnxml {I16 flaw and prmysi:re- at in 993:1 air-'01‘ a large. chamber where the
`fiQw"i_$ cI:etEi‘mine'db:y tlrzgrmgafi buexfincya
`.
`_
`in many ways, 'the3asex«suszaingc_:2.p1asma is si11:.1i}_aI'. ta direct current 01'
`law-frzquaizcy e3ec§rx;}d§I¢s§_='=a:_;'gs and ':ni§.::i:9.vax_re, :§is§:§1arga_s't¥3at-are apar-
`ated in simiiar gases
`'2tfi51a'r-_pra$snx;e$..-Htisvexasr, the LS? vsriI1.g¢ner-
`any ha _7':_xt:£::r{;e- 'c£3§i‘.i}2aci5 and
`Ifighér
`'¥;.<:'t1‘;'1fa€:r_atIz;ra
`'t11a:;1.o't§1er
`-czmtinmaus arc -s£$n'{c.¢$-iiiidl Q-‘an-.135 susitainaé in a steady Mate with away fram.
`containing. boundarics. A fnn_d'an1€:f£ii‘a1difi’eI'6nce in the way in which en-
`acrgy is absorbed by the p}a_sma.is r6sp£3;15§b.2€'>.f£3£'i§1c$f3'11ni:£}'iIfi characifirifififis
`c.f'the LSR
`
`4.2.1 Basic I’hysicai i’ro(-(«asses
`
`In a direct current (dc) arc or in an inzinctivciy c-cmplcd pkisma (ICP‘), en-
`ergy is absorbed through ohmic heating produced by. {he low-frequency or‘
`direct currents flowing in the plasma. The eim'.':£rical Conductivity of an ideal
`plasma is. given by -(Shka1.'ofsky at al., 1966)
`
`neg
`
`If —Eu)
`
`°' “ 32:; (V2 +3")
`
`(4-13
`
`where :1 is the electron‘ density, e the electronic charge, m the electron mass,
`as the radian frequency of the applied electric fieid, V the eifective collisien
`frequency for electrons, and i the'squarc root of «1. In the. dc arc (LG = 0),
`the currents are‘ transmitted through the plasma between electrodes and
`
`

`
` §
`
`:3;:3
`:2:3
`iii
`-35"-53‘H
`2:“
`-3:?125-8.3-l‘S
`
`av
`.33.:
`35%
`
`3:55:2»!
`2;'1!5:1!5.?!
`2-,»:
`
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`:55
`‘:3aa
`23
`E3
`
`
`m{m'm=o-.w¢-4m...-.2«
`
`
`Laser—$.z-malned Wasmas
`
`'
`
`-.
`
`.
`
`1'2‘-3
`
`the size of the plasma is deiorrnined by the Sim and spacing of the olectroflo
`and t.¥1e.£:<:'n.fi'12ing' bO3lI.1da-fi§:'S_.
`In the ICP? the currents are induced. in._';.o
`the p}ai3flfi.a from aitornatiiig cuzrents flowing in. a surrounding soianoiiial
`coii. The are is su§g§ino;3._3gsvi'thin a container ‘that determines the _pIaSiIia
`diameter, wheroas tiie lenfifla of the piasma is detormined.'hy the. iength of
`£133 soieizoid,
`In
`’I'i1e..I§:3P operaios at-freqoenggies. woii beiow the piasma frequency
`
`1%W
`
`_
`
`_ (4.2)
`
`'-‘fl-116176.60 is-the of fkoo-.s_pace. In this frequency range», the 613%
`tro'm'ag:'1etic= 'fi£§I.Ei does :;-go‘? progziaggito as‘ a wave. 'witt2'ih the plasma, but is
`a..::3n.;ia:§d. as;
`avanesomi-:wave'(Ho1tand Haskéii, 1965) avg: dis'£a;11c£:s
`c'a.f:;1.a.:e m:c'{e.r <':f~t:he skin fifijfith
`'
`-
`-
`
`
`
`(4.3;
`
`whom 6 is tiara. s-peed. of lights "I‘}:u.s, z}:¢'...pIasma is. sustained by exam’--afia
`sorbed within a.5r;na§1.iay£;r "near its outer surface that produces a r_athcr:f1at
`temperainie '§r;ofi;i§¢ wiih'i'1_1__ t'ho_p‘§asmja_ and limits the maximum. temgera.»
`taxes that ::;a:é'be;-:i.}a:a“ij::e:i.
`-
`_ carbon tiioio
`'
`The f1‘€£}‘§l§§Ii6;{ of this-;op‘tioBi fielfis (2-8 ‘EH3 for the: 1846-
`ido iasor) used."-.f0r'fhe. LS?-.is.-gre.a'tcr than -the 'piasma'£rcqnoncy,- and-t§2e*re~
`"fore 2:113 ir'zci"-d"e;r1£ 1353:
`Ii‘;-an "propagate weii into the interior‘ before
`it is s'ignii‘ii:aI3..’£1.34’ -ifi3§QI¥§i.5d' E}1r€!'i!gh the process of inverse bromsstrahlxmg
`(Siikatofsky -set. a}., 1956). Sincothe focusing of the laser beam prodxicrsd
`by a lens or mi£'.ro'r is e-ssomialiy preserved as tho "beam propagates into fiche
`plasma‘, very largofiolcl strengths may be produced within the piasma near
`the beam -foc1i$..- It is ilxejsie large field strengths that lead to peak _io_1npera-
`turcs in't11e_ LS1’ that are generally groator "than those obtained with either-
`dc arcs or the ICP aizdmake it ‘possible to sustain a smali V0i'1III1f3 of plasma
`near the focus, well away from anyconfining walls.
`Inverse bremsstrahlung- is a process in which the plasma electrons ab~
`sort) photons from the laser beam dur.ing'ine1a_1s.ti'c collisions with ions, new
`trals, and other electrons. The collisiohs between electrons and ions are
`‘tile _doii1in.a-nt. process for the LSP and the absorption Coeflicient is 'given'1'a.y
`(Shkarofsky et 3.1., 1966')
`
`M ms‘ 3n.S[,G 1—e“”"’”‘T
`
`Q-(.9) "ET
`
`(“<3
`
`

`
`374
`
`’
`
`,ij<.e»efer
`
`where E is Planck’s constant divided by zar, k B0i:am.a:§.:1’s c»£3*n»St23Iil?a 8137
`-the t£:mp€’:.r.alure ofl:hee1e.c:rons. T113 factor G‘ is the Gmmt faster and the
`Easter 3:59 isgiveu by
`
`
`A. 3
`3
`15;.
`.22
`
`. L‘
`.
`.
`.3133 "~'-’—" *“** nflfin
`3 H1203’
`.47n°.g
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`112
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`
`(4-5).
`’
`
`»
`
`-.
`mg "‘iw imam.
`’-
`32.32:’ i
`;i§’gi-v“c.m» by ear’: law
`
`£acmr,.is. a
`T where Z is the ionic cha:rge and 3,, the ion -dezxsilzy. ‘The
`mecfiaaniclail currectioxi tea the -::.1as.si.c.al theary,-_’amil aztiensiire ”!.:£i’xhies
`
`have} been given "by Karzais and Latter
`Fdr f
`‘
`"
`"
`’ ” " ’
`the phgtofn energy is ’mm.:.h lass than than
`’
`bmzzketalzi term in
`(4.4) is zmarily .in<3e.;§e:1 \.
`.
`cIc:=efiieient:"ls ess.enl;ial2y»pmpz3r:i:mai "t=G”l:ha.$§;1;2a£::. :3.
`size ef the
`will Clepefld an several féctflfis
`_2g;:;a:a.n:et:y;, 1aser»:pcs:ver, and a}}s£2rp.ti»c3’:x cnefifieiant.
`szaf. the-..1aser ‘imam as it prupagrates v2i:thin the
`
`_
`
`
`
`.
`
`“~=«' -val’
`
`‘
`
`..
`
`(.4-E6)
`
`F.EE3‘: abaargzl
`’
`~ where s is tha distance alnng the local :i.i.rex;:.ian £§i’5_;3:’:iii3
`.
`tinnifiength Life: is a daminantlength scaia fc:r’t}'.1s‘3.
`,,
`. 288 it :c§.e=;:rl-:‘*;r’. ma-..s .
`"H133 r:§'is_t;anc=e.-oyggr xvhigah tE:’a’p~{3w€;£,iS absGx*beé¥ frgm {?h:e’bai:am., F&r'tFhis’r:§caa
`2:
`:59-n,»t"1%m dimension Qftha»§ii’gii~:a3It1;}a£aI£iifa ;é2£¥2s:>3éb§i:z_.‘
`"<2:
`piiaatxza
`
`alcmg tha laser beam will he of the cider’ taf ;h:¢;»a¥3sar;):t:»c:n itzzzgiiz. ésiihaiigh
`it is {he absorption 3.Emg1:h that determines ‘tlilailangtii ief-tha»;3}asma»a1:an;g the 7
`Exam fixigs, :1. is the laser beam »cI.iarmeter amt. diziezmiizxes ti-1:2: galasma ’§fi33.I§§?e¢'
`tar; ’I”i1e’;31£1s:11a expands to fill the. begin £:i3.11”eI .ui§:'1.”ti:r:e it
`able fie «21?3$*c«fl3
`pawar, than rapicliy ciaszzmazscs in tenzperazure. m:tsi.:§::: tihes: lsaam ti1rau1_gTh
`thermal <:a.n::1uction.a.nd radiativs lass .machan.isms..
`The pnsition‘ 9f the
`relative to the facal paint is tiriiicai in deiermirb
`ing its sitruciure andilie range cf para.mcters far which it ‘cat; The .maintaine€1.
`Whan the plasma is initiatad near the beam foam, it pmpagataa into. the
`sustaining beam and seeks a stable. _position. The pasitidn nf stability will be
`.locat»e»d‘wher:: the imam intensity is ‘just sujffizziimt t11at.1:.ha ‘a’bsm“ba»x;l power
`will balance tlxalosses due to convection, thermal ccynfiuctinn, and.therm.a1
`radiation. A _number of factors cmnbine to determine this pcssiilcm of sta-
`bilitylncluding the transverse pmfile of the incident beam, t.hefoca1.leng-tl1
`and aberrations of‘ the focusing lens or mirror, the plasma bprassura, and the
`incident flow velocity (Keefer at 211., 1986; Walla at 211., 1987).
`The power per unit volume that is absorbedby the plasma is given by
`
`
`
`P == crl
`
`V
`
`(4.7)
`
`

`
`.=.:-(7-::.-'-av:-;-.:;£
`:\\:9<s<’.s<o,~;z;.z:¢§%<‘?‘}-§4::>.n.:.s-\?»>'.2.e-t~}:-2;:2z:§3<za§iz<;;$=§§§3i§t%§&%%o2&2uz;::zEEi£E§.iii:zii:.zné$.:fi$'a.$i:$;£¢L$:2£i.i$2
`
`s:$::'-3-5:55:53-.:sa\m:«\.
`
`i.aser«$u3'xainet! Plasmas‘
`
`375
`
`where I is the. local irradia1,1C€. of t1:1fi..1aSe.I boarn. Since I depentia on -the
`transverse profiie, of the-‘incidfimz
`as W833 as tho focal Iongth and aber-
`rations of the lens, these ohametcrisiios wi}l.infi:1_£:11_ce theiloraation within
`the focai region at wh_;§;_x ihggzahfimnm sus£ainin,g' i'1.1tensit_y is located. For
`exampie, far a small. f{:iumb£§f‘:3§‘éi1$».$13.6-'-iz1£f=Ii$it3i éiecreaaes _r.ap'id_1y'wi£h in-
`creasing distance £2-um..zhe-=fos:x:s-.anci't1,a¢: gsiaisma-will smbiiize:-nc'ar the focas.
`‘For a larger .finum‘ber system?
`1335 ¥a_p"Ed1y‘aIid the-
`plasma will -stgbifizc ai .a::po's§fiia<:r ';fu_1;‘iih¢;r ;aaazay:fiiTr£é3.:%ix.t:E1a£_ocx;;§. Izideoxzi, for
`
`fiiifiicienéiy 1m'3g=-"fecal ._1:s1.:2.g'-th._S axis?
`Kasai:
`j
`ob-
`served to p1-op'a_ga;te many-:meters {Raz§§£;.;1§39.)=as “lasaresnpgxqnad cam-
`'bu51ion waves" at sumqnio
`r:¥e;;;6:z:1i3‘1:‘m§.i':I9‘y the. intarm
`The éetaiiad sgéatial
`fgrmaijc of
`iafioxrss betwaan-iheogfiicai
`piafiina,
`I11‘: gas; and the flew-'t'hmugii ¥21;e»fi._;ii'9«sza;B.:a.;. 1% W322 ‘pain:--wiiisin
`absorbaé.
`th6teI.3IP$‘6i;r;"aturé§.an;df fims: ':a':i%_:t£:=a}:3§_uat.:fi
`that
`from the‘ laser
`with -the ins: tfirongh zzammizion-, zwzzduzation,
`and thermal :adiati't:m. file position :i:1.t}m“§béea;§2__re;_1atiyo to {lag focal point
`at which the 'p}asma siabflizos
`the structure
`of tho plasmamat-,.-in tum fietorninitew am ggmfiifinns txf__p£:"w;::3 grcssurg,
`ai1<3.fiW'£hjr'12?11.i.c:h a st.a.ih§¢'p'1:as'fi1a
`out inside-large
`Most of tho eariy
`was: detzsnxained
`chambers or £1: gzpen-a"it§'W§1ef!E8
`by the effects of thermal} bnnganay, ZI?‘_‘meé_.f'€?3£.:=Eii geoinjetriaass mm naezi and
`thy; 13ri?;‘;s'S2'1te- and laser
`ééfiiié f$3§,i1€3i$i$ of
`aixd
`Wheté-it was poxsiléiié to s:z:zm'i11.t21“£s.;I;;SP=..ii: aéwariexy -of gases _(;:-kn-
`eidaiov ct-£1}.-, 1912;. xcmav at _ai.,--
`'*Fhasé.. mtpezimmts
`indicated that ‘there were nppar ané
`iimits ffirfhoifi _powe.r and
`pressure at which the 1.5? -coifiti
`susminéd.
`.
`Genoralov et a1. (1972) suggested that tho upper limit for power was a re-
`sult of forming the LS? .w.i.th a hotizonzai beam. In this gemixetzy, thermal.
`buoyancy -induces a flow transverse to £1123 optiaal axis, The induced flow
`carries the piasma up and out of the beam when.'hig'l1er'1asiér_p.t3w&r muses
`the plasma to stabilize f'art'_}1cx from the. focus. They were unable to estab-
`Iish an upper“ power‘ f_limi£-when tho experiment was oper_ated with the beam '
`pro_p'agatinTg -vertically upward. Kozlov et ;a'{. (19%) deyelopoéi a radiative
`mode] for the [SP and explained the upper power limit on the basis that
`the plasma must stabilize close enough to'th'e> "focal point that the geomet-
`ric increase of Iaser beam -intensity going into the plasma was greater than
`the loss of intansity due to absorpfiion. They specuiated that the failure of
`Gcneraiov at al. (1972) to observe this limit -in a vertical beam was due to
`‘rapid extinction and reignition of the plasma.
`It is clear from the experi.men't_s of Generalov er al. (1972) that flow can
`have a large effect on the range ‘of pressure andlaser power that will support
`
`

`
`‘W6
`
`Keefer
`
`
`
`Fiastxnas sust-a.i.nsd in tho frat: jot issuing from a nozzio have
`a szabio
`boon studied by Gerasimenko at 31. (198.3) who n1aa'.sured the discharge
`’%;s*f&3e%?i‘3 nnincigy alozxyg {ha bean: andxannges for the existenizn of a $toa€iy~st=ate'
`
`d;‘is's»;:h
`..Rn;:::nn1.%i§»
`y
`nonts’ havn been oozxcixxctnd in confined tubes
`
`:.vha1%e’=»£.0i1:ced nnnyactinn :1 :ni'nat€-ni nu: flow (‘Wane oz 211.,
`:£9{87_). 1:; was
`.:f0’unr?: ihaifi-n addition. in power and §}f$S.Si1f-£3, both the flow and nptiycai ge-
`OYII.
`in ”
`' gvg-:2:pi”GfBfindinflnen'c:-3 on the cfharactmisiicsyof tho =
`
`
`
`
`tho L-SP <:s:;:;.:icif2_:»’c=;, susta.i-nan are ya}
`y
`_y
`._
`o~:nIy:.;Eor the gmriicziiar.-experimental’ gjeomntrynsed to obtain ithkem.
`
`
`
`when tho pins
`inn ‘ iasma -
`
`
`
`
`
`
`thnft itiho ’3=1e-2* absorbed fmm £235. tzeoam, given byis balanced-’
`‘fine: convective; con§’uc'§i9<7.o, .a‘nd irafiiation Ioiss-es. -Sincies, in generai, "the ‘in,
`
`
`' _ T, the B33122, the p1asma.wi11 a.<:ijust.._;i‘z"2 size, snap»
`
`
`
`
`
`
`2!; rBs:1x‘F:...nf‘E3onn3i4h:o:nn:i iransitinns,» rosniting in lino ’rar}ia£,ion am: absnr
`tion, =and..frno;~?§:onn£i amzi fies-afrose téran:si‘tions’that resin}: in .m'ntin'unzn vraciz
`a’iiQn»-afifi: ahsoafpt
`Qve; §I1e.op£_ioaI§_y thinportion of the spectrum, ‘chi
`ran.1.am>.n xvii? : stmngiy ;i?::$i:rbaii by the plasma or sn:‘ronnr3ing nifinm.
`regions and wii} sinxpiy osc;ap»c from the plasma. (Ether Iportions of the spec» b
`mam will
`sirongiy absorbed, 1‘e2:'uking in a transport of energy within the :
`plasma. In the oniiizaiiy ii1ick1'imiI:,_this resu1‘ts;in a diffusive energy trans“
`p-Cart that is similar to thermal coimtiuction, but may be significantly larger.
`Detailed cn1Acui.ations. of the LS? (long and Keefer, 1986) indicate that this
`radiative trzmsporz is a szionxinant factor in the determination of the stmo
`turn and position of the LSP. In particular, it is the radiative transport that
`’ determines the t7ompe'ratur,e gmdiont in the upstream .fr.ont of thoplasma,
`thereby determining the position in the beam for which convection losses
`are balanced by -absorption.
`The position of stability for the LSP also depends on the plasma px'os~
`sure, The absorption coefiicientis a strong function of plasma density, as
`soon from Eq. .(4.4).. If the pressure is inczroasocl and the absorption ooe:ffi«
`cient increases, than the plasma can absorb more power from the beam and
`will move away from the focus to a lower intensity region in the beam. At the
`
`
`
`

`
`f‘.-aser=~Sust\a_!ne£i Piasmas
`
`'
`
`1‘???
`
`same time, the plasma lengt-h along the beam decmases "because ‘cf the dd»
`£;1f$as‘a in abs<3rptia11-icngth, but the diflmfiifli increases ta fill the-la:-gar -crgssg
`sectiegm (if the ‘heath. Thus-, for the same. laser beam co2zc¥§tio¢’!'$,- "a .h.i'g“hex.-
`pressure LS1"-’ will stéfiilizc _a_ point farther away -from the focal _poi3::t and
`have 51 sift}allfir.-length-1o»dihme1e'r ratin than a iower~pres.$ure
`iI'I£:idant.'ia_se'r pawn":-,_. as well as the ffnumher and aberratio'_ns.{1f the ff.)-
`mssing t:3pt.ir:s_,- will -(flax: infiuance the ;':,_<,3;sIi_i.'-5.911 at which the: LS? st;rib_i}izes-
`"within.-me .ftm'a'::t2, ,F3':m':'1 jzfie forégqing éiiscussian, iris‘ aim that -as the-'b_ea.a1:
`}3.!3W£:2"." is incxeased, the plasma -wiflmavc up the
`away from the £6331
`T5113 distance ihatxit masses is ciatcrmiaed fir the flnmnbgu‘ (ztatiimf
`fq«ns1.‘im.1g;3:.2- to tixt:
`diézinvzerz 'ine.i:3'$m_1m thaj-f:m::.:~:éi:_g §;!e‘ftI.1ar1£3- 'f8;f'i31.13
`;3pt§€:’E§I
`sings the rate <'>f_ch.;a:ige: in main -fixtensiiiy
`iimixzai
`axis
`xvii?! ah iz1{;:ea,s<~3':in fffmmhtzr;
`aihmifflfliflnse '¢a,I1.-83$£#'§1s&’V3-
`cm _p13;sma pcasii'i'orz (Keefmf. et 31.,
`In pill!’-'¥':i'£‘.‘1_I__l&x, syhm-an an-
`:1tI1;a'r mm {mm an ugstabze laser izfiéiil-3:3: is. -fézusfea by 3 syn-atical lens,
`it.pr§3£diti€>_t?is an annular piiefoczzs region hafdre -reaching thefacai
`azni
`_ £1t€:. intensity $31
`r:'egi'_r;:n xzaagr "be. $x1ffii:.iL=:.n‘£' t_o snstaifi an .=a:;-§;_m2'a.z"
`Efrem-t§§1e.£3l3sanratians discussed aibme, fit is Eifiiai‘ ihai"'§-hfi':f):ji3Sii3€3f1 9f
`the: glasma relaiivs in the {ma} win:
`E1".piflffilind-Eiff£§t§i'£}31"'§}1§'}§La8111a
`éizazafiiéziristicsa fiat tffle ‘apps: i.1'i2*n'.im pf-s_ta7bi¥i1y fer
`'iasaw'_r-=
`ana-
`-,p:£‘a3X*£Iii"£*:_; '-it‘ a§5.'§J%éi"2*-S that £33332 pl:;~'3$_n1a Baeebmes .11xista'iiZe.'w}m'n i3t"mmes-
`f8f'f}'.‘§3£££ ifhé fi:3.GaZ'p{3§I1_t. T111‘; mayba due ta‘-{ha fat-:1, as ;_;:gpp3ad;hyf§<§I€S$1Qv
`6% a1. {-19%}, that as the priasm-a maws sufficiently far-away
`film
`file" ram {sf incraase of the beam .i1'}.£821S§__ty in £231: é1j§r_ac;t;i_c3;1 Qf-ygfiyggfiigxg.
`snaialifir. Sizzce £;h"e. tfinapéiétizra <35 ihé p31a;*s;ijrxa1.:ni;;:s:,-fat:-irea:ze..ca:s.tI::e
`prqpagam into the ;'zp.str'c.a1I'I1 ezige £}_5f‘theé"}}las;;;iai t;ii'3- ixstensizy nf--the.
`’beam='mns'£ 3359 increase. At-some paint, ihe;_dccreas'<: of tlzehfiam intensity
`éizzes tC:=-aifistirptiem is greater than the itzcreeasa due {<3 focusing, 33 the plasma
`Imsiahle and exzinguishes. Rcceni izaiczflaticans by 3'_cng.and "Keefer
`(198-?a), hawavcr, infiicate that there. may exist local regiszns wititin the LS?
`where the-‘bazim .intensi'ty dec:re3se,s.'as it psnetraies the plasma.
`. A'£:£3:1s§'(ierabic dagree 01’ control of the structure. and positing‘ of the L3?
`can be gainzd throllgh both optical geometry and flew, in additian to 1353:
`pnwcr and "pressure. Utilization of these: addétional parameters makes "it
`possible to successfully operate the LSP over a wider range of experimental
`conditions, enabling a wider .range of potential app'iicati0.ns.
`
`
`
`4.2.2
`
`§’ias.ma Characteristics
`
`Laser-sustained plasmas "have been operated in a variety of molecular and
`rare gases at press'_u1'e5 from I to more than 200 aim. The resulting plasmas
`have characteristics that are similar to are plasmas operated at similar pres-
`
`

`
`177:8
`
`-
`
`-Keefer
`
`am usually somewhat highs:
`sures, {mt the pcak tenupcraturcs in the
`than these for the ccmparable arc, Ra:¥iati=on "item the plasma can be a Sig-
`nificant 'fI‘aCiiO’I1 of the total pzawar ,iz?:pI.1.t, and .rar3.iaii0n transp.r;:2r!: plays 2.-
`majcr tale in t:‘ctctminin_ the structure‘ of thc plasma. Co1::tinuu.rn —abscr-p—
`tion processes are cf13attici3lar,1’mp0.ttatzce in these ;plasm.as since thcpower
`to wstain the plasma is aiascrbati -tlzrctzglz these. me.-chanisms,
`The» .caniin1mm ahccttzztizm putiizccss iinyclvcs both l:}{)'i3I1fi.~fi‘€f3 trans.ition.s
`('p}:»0tci£>nizatii}n) anti ft'.6c».f£'cc transifticns (invcrsc bt‘fimsst.f’ahluéng) in
`wlzich phm:tmjs are absorbcd. fmm the»»l.a4scr’l::eam. Thu .fr<w-ices. transitions
`iI1?t:tlv6=»‘:flectron ccllisicms with 56:13, Gthfif éclcctrcns, and .’ncutr:al particles’
`{siziiaamfslfty c: .31., 3;’9‘§S-;;; £3:r.i‘c:m, ’19fi4}..
`i39mi'nan:t abscrption process
`
`for than is fiiiffliligli cc?ll§3_ion.§ ihctwcteti
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`;xft.s 3-m3”icns, ,ar1d*t,hc a_b%m:p~
`-tiozt cccfiicicnt far this ptcccsa: is» given by Eq.
`For the usual Case in
`the 'LSP, kw ~.»:<:::k:'1’~and the ~a'?bs£33.fpii<:;I1’ is; appraximatcly‘ garcgtortianal to the
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`Tltcrttzal r,a>di:a>fi!>01Et>..iS iizaiiilie cf thfit ::1}I£:st.’.i;2:;§c:’ta:z’1 c'ha:;acterisiics of the
`LSF. Thermal -rad_.i.a1:ion jO3t.ffG1'3Il.’ih3}313$'ifi3 can ai_:c0’nnt fer nearfzy all
`that ;;=t3wc1' abimribcd by the 'f3l’a,s.Ii”1a what} £115:- flow througlz the plasma is
`small anti. will account for :a s.igx.1ilicant fmciie'n of absorbed pews: even
`whcn thc ccnvcctlvc lcsscs are large. Thjc thermal rradiation. consists of
`continuum radiation resulting from _reccx1il3i1*;ati0n (free-bound transitions)
`and bramsstrahlnng (fffifi-’fI‘-fifi tr-ansitionfl) as well as line radiation (:bC}1.,1I1(3*
`buund transititms). Calculatitzn of this radi.atit::n is straightfcrward, ab
`though rather tctiieus, when the plasma is in local thermodynamic equ£~
`librimm (LTE) (Gricm, 1964).
`‘Local tltcrmcaclynamic equilibrium is es»
`tablishcd when the clcctmn colclisional rate proccsscs dominate the pro-
`cesses of radiative decay and recombination. When LTE is c~st.ab.lishcd
`in the plasma, the density -in specific quantum states is the same as a sys~
`team in complete thermal -equilibrium having the same total density, tern»
`peraturc, ancl chcmicalv.c_ompc3iti0:1.
`It should be emphasized that this
`does not imply that the radiation is similar ta a blackbody at the plasma
`temperature. In general, that: spectrum of the Iadiaticm from the plasma
`will have a complex structurc consisting of the superposition of relatively
`narrow spectral lines and a continuum having a complex. spectral struc-
`ture.
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`Laser»-SuszaIn'e<i Piasmas
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`Tho a’tisor;;;tiozx- cooflicient in the plasma depends on the waveigcngth, and
`for the o}tr'avi_€$1e12--portiian of the spectrum below the wavelength of the 35350-
`nancio-iines (trans-iiions iiwqiving the ground state), the raciiazion is strongly
`absorbed. by the pizififizxa
`the: cooler s_u:rozmdi.ng. gas. This rosuits in a
`sat-onjg radiative far-{3.:1$port“m