UMM

08/11/15Advanced Manufacturing ChoicesENG 165-265Spring 2015, Class 4 Thermal Energy Based Remoing Te!hni"#es108/11/15$Sin%er ele!&ri!al dis!harge ma!hining 'E()* and +ire E()$,aser -eam ma!hining$Ele!&ron -eam ma!hining$.lasma ar! !#&&ing$/ha& is a laser0208/11/15Thermal Removing Techniques$ 1n&hermalremoingpro!esses,&hermalenergy,proided-ya hea& so#r!e, mel&s and2or apori3es &he ol#me o4 &he ma&erial &o -e remoed5 $ 6mong &hermal remoal me&hods,ele!&ri!al dis!harge ma!hining or E() is &he oldes& and mos& +idely #sed5 Ele!&ron--eam 'EB)* andlaser-eamma!hining',B)*arene+er&hermal&e!hni"#es also +idely a!!ep&ed in ind#s&ry &oday5 .lasma-ar! !#&&ing #sing a plasmaar!&or!hismos&ly#sed4or!#&&ingrela&iely&hi!% ma&erials in &he range o4 7 &o 85 mm and is less per&inen& &o mos& miniari3a&ion s!ien!e appli!a&ions5 $ 1n&hermalremoalpro!esses,ahea&-a44e!&ed3one'96:*, some&imes!alledare!as&layer,isal+aysle4&on&he+or%-pie!e5 1nele!&ron--eam,laser,andar!ma!hiningdeposi&ionas+ellas remoal me&hods are aaila-le5308/11/15Electrical Discharge Machining - EDM$ 1n die-sin%ing E() sys&ems, &he ele!&rode '!#&&ing &ool* and +or%-pie!e are held -y &he ma!hine &ool5 6 po+er s#pply !on&rols &he ele!&ri!al dis!harges and moemen& o4 &he ele!&rode in rela&ion &o &he +or%-pie!e5 $ (#ring opera&ion &he +or%-pie!e is s#-merged in a -a&h o4 diele!&ri! 4l#id 'non-!ond#!&ing*5 '(ie-Sin%ing E() is also !alled Sin%er, ram E(), Conen&ional, .l#nge or ;er&i!al E()*5 SEE %t ca' )% c$os%' to r%act c$%&ically ;it$ t$% ;or5pi%c% to produc% $%at a'd acc%l%rat% t$% cutti'* sp%%d !,.CE"2d7 4.8 7 '%ody&iu&-dop%d yttriu& alu&i'u& *ar'%t is a crystal t$at is us%d as a lasi'* &%diu& (or solid-stat% las%rs 1808/11/15Laser Beam Machining$ 6laserma!hine!onsis&so4&helaser,somemirrorsora4i-er4or-eam g#idan!e,4o!#singop&i!sandaposi&ioningsys&em5Thelaser-eamis 4o!#sedon&o&he+or%-pie!eand!an-emoedrela&iely&oi&5Thelaser ma!hiningpro!essis!on&rolled-ys+i&!hing&helaseronando44, !hanging&helaserp#lseenergyando&herlaserparame&ers,and-y posi&ioning ei&her &he +or%-pie!e or &he laser 4o!#s5$ ,aserma!hiningislo!ali3ed,non-!on&a!&ma!hiningandisalmos& rea!&ion-4or!e4ree5.ho&onenergyisa-sor-ed-y&arge&ma&erialin&he 4orm o4 &hermal energy or pho&o!hemi!al energy5 )a&erial is remoed -y mel&ing and -lo+n a+ay 'long p#lsed and !on&in#o#s-+ae lasers*, or -y dire!& apori3a&ion2a-la&ion '#l&ra-shor& p#lsed lasers*5 6ny ma&erial &ha& !anproperlya-sor-&helaserirradia&ion!an-elaserma!hined5The spe!&r#mo4laserma!hina-lema&erialsin!l#deshardand-ri&&le ma&erials as +ell as so4& ma&erials5 The ery high in&ensi&ies o4 #l&ra-shor& p#lsed lasers ena-le a-sorp&ion een in &ransparen& ma&erials5 1908/11/15w ~ beam waistor 1/e2 radius~be careful, 1/e radius isused for calculatingelectric field~m to mm~20 to 40 m for Nd:Y! "armonic lasers w o#ticsLaser Beam Machining$ .#lsed lasers '-eam +ais&*@2220) (wre I r I $0 ~ a%ial intensit&w ~ beam waist 'i(e( 1/e2 radius)t r * w, t"e $'r) is at 1/e2 '1+(,-) of t"e a%ial intensit&, $0(2008/11/15Laser Beam Machining.$ Eor a gien -eam, 10 +ill -e a& a ma=im#m in &he 4o!al plane +here + N +0, &he minim#m -eam +ais&52002020222 ) (22wPII wPdr r e I dA r I Ptotaltotalwrtotal 21Laser Beam Machining.$ The parame&er +'3* approa!hes a s&raigh& line 4or 3 OOO3R $ The angle -e&+een &his s&raigh& line and &he !en&ral a=is o4 &he -eam is !alled &he diergen!e o4 &he -eam5 1& is gien -y08/11/1511]1

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+ 22021Rzzw ww0 * min( waist. * wfwaist in t"e focal #lane/0 ~ 0a&leig" range 'orconfocal #arameter)n ~ inde% of refraction'a##ro%( 1 for air)0 ~ free s#ace wa1elengt"2208/11/15Laser Beam Machining.inf ow n fw w 0t / * 0, t"e minimum beamwaist, w0'wf), is:w"erewf 21/e2 beam waist in t"e focal #lanef 2 focal lengt" of lenswin 2 beam waist into t"e lens'at / * 3f)n 2 inde% of refraction'a##ro%( 1 for air)2308/11/15Laser Beam Machining!D"#$%.&RAt z = zR:so I0 is decreased by 2X.02 2 w w wf 11]1

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+ 22021Rzzw w( ) 2022ftotalwPIT$% dista'c% )%t;%%' t$%s% t;o poi'ts is call%d t$% confocal parameter or depth of focus of the beam:2408/11/15Laser Beam Machining$ 14 a Pper4e!&P lens 'no spheri!al a-erra&ion* is #sed &o 4o!#s a !ollima&ed laser -eam, &he minim#m spo& si3e radi#s or &he 4o!#sed +ais& '+0* is limi&ed -y di44ra!&ion only and is gien -y '4 is &he 4o!al leng&h o4 &he lens* @$ /i&h d0 N 12e2 &he diame&er o4 &he 4o!#s 'N 2+0* and +i&h &he diame&er o4 &he lens (lensN2+lens 'or &he diame&er o4 &he laser -eam a& &he lens M+ha&eer is &he smalles&* +e o-&ain@ w0 fwlens d0 4fDlens1.27fDlensLaser drilling hole2508/11/15$ Th#s, &he prin!ipal +ay o4 in!reasing &he resol#&ion in laser ma!hining, as in pho&oli&hography, is -y red#!ing &he +aeleng&h, and &he smalles& 4o!al spo& +ill -e a!hieed +i&h a large-diame&er -eam en&ering a lens +i&h a shor& 4o!al leng&h5$ QT+i!e &he Raleigh range or 2 3R is !alled &he Pdep&h o4 4o!#sP -e!a#se &his is &he &o&al dis&an!e oer +hi!h &he -eam remains rela&iely parallel, or Pin 4o!#sP 'seeEig#re*5RGrad#a&e onlyS $ Br also, &he dep&h o4 4o!#s or dep&h o4 4ield '(BE* is &he dis&an!e -e&+een &he al#es +here &he -eam is T2 &imes larger &han i& is a& &he -eam +ais&5 This !an -e deried as 'see also earlier* @$ )a&erial pro!essing +i&h a ery shor& dep&h o4 4o!#s re"#ires a ery 4la& s#r4a!e5 14 &he s#r4a!e has a !orr#ga&ed &opology, a sero-loop !onne!&ed +i&h an in&er4erome&ri! a#&o ranging dei!e m#s& -e #sed5Laser Beam Machining DOF =1.27/NA22608/11/15Laser Beam Machining$ ,asera-la&ionis&hepro!esso4 remoalo4ma&&er4romasolid-y meanso4anenergy-ind#!ed &ransien&dise"#ili-ri#min&he la&&i!e5The!hara!&eris&i!so4&he releaseda&oms,mole!#les,!l#s&ers and4ragmen&s'&hedryaerosol* dependon&hee44i!ien!yo4&he energy!o#pling&o&hesample s&r#!re,i5e5,&hema&erial-spe!i4i! a-sor-an!eo4a!er&ain+aeleng&h, &he elo!i&y o4 energy deliery 'laser p#lse+id&h*and&helaser !hara!&eris&i!s'-eamenergy pro4ile,energydensi&yor4l#en!y and &he +aeleng&h*5 Laser ParameterInfluence on Material Processing Power (average)Temperature (steady state) Process throughput Wavelength (m)Optical absorption, reflection, transmission, resolution, and photochemical effects Spectral line width (nm)Temporal coherence Chromatic aberration Beam size (mm)Focal spot size Depth of focus Intensity Lasing modesIntensity distribution Spatial uniformity Speckle Spatial coherence Modulation transfer function Peak power (W)Peak temperature Damage/induced stress Nonlinear effects Pulse width (sec)Interaction time Transient processes Stability (%)Process latitude Efficiency (%)Cost ReliabilityCost 2708/11/15Laser Beam Machining$ )orespe!i4i!ally4or mi!roma!hiningp#rposes,&he +aeleng&h,spo&si3eQi5e5,&he minim#mdiame&ero4&he4o!#sed laser-eam,d0,aeragelaser-eam in&ensi&y,dep&ho44o!#s,laserp#lse leng&h and sho&-&o-sho& repea&a-ili&y 's&a-ili&y and relia-ili&y in &he Ta-le* are&hesi=mos&impor&an& parame&ers &o !on&rol5 $ 6ddi&ionalparame&ers,no&lis&edin &he Ta-le , !on!erns laser ma!hining ina?e&o4+a&erandlaserassis&ed !hemi!al e&!hing ',6CE*-see -elo+5PHB stent2808/11/15Laser Beam Machining!'eat Affected &one - 'A&$ Themos&4#ndamen&al4eareo4laser2ma&erial in&era!&ion in &he long p#lse regime 'e5g5, p#lse d#ra&ion Uns,energy055mV*is&ha&&hehea&deposi&ed-y&he laserin&hema&erialdi44#sesa+ayd#ring&hep#lse d#ra&ionC&ha&is,&helaserp#lsed#ra&ionislonger&han &hehea&di44#sion&ime5Thismay-edesira-le4orlaser +elding,-#&4ormos&mi!roma!hining?o-s,hea& di44#sionin&o&hes#rro#ndingma&erialis#ndesira-le andde&rimen&al&o&he"#ali&yo4&hema!hining 'h&&p@22+++5!lar%-m=r5!om*5 $ 9ere are reasons +hy one sho#ld aoid hea& di44#sion 4or pre!ise mi!roma!hining@A 9ea&di44#sionred#!es&hee44i!ien!yo4&hemi!roma!hining pro!essasi&&a%esenergya+ay4rom&he+or%spo&Renergy &ha&+o#ldo&her+isegoin&oremoing+or%pie!ema&erial5 The higher &he hea& !ond#!&ii&y o4 &he ma&erial &he more &he ma!hining e44i!ien!y is red#!ed5 2908/11/15Laser Beam Machining!'eat Affected &one - 'A&A 9ea&-di44#sion a44e!&s a large 3one aro#nd &he ma!hining spo&, a 3one re4erred &o as&hehea&-a44e!&ed3oneor96:5Thehea&ing'ands#-se"#en&!ooling*+aes propaga&ing&hro#gh&he96:!a#seme!hani!als&ressandmay!rea&emi!ro !ra!%s'orinsome!ases,ma!ro!ra!%s*in&hes#rro#ndingma&erial5These de4e!&sareP4ro3enPin&hes&r#!re+hen&hema&erial!ools,andins#-se"#en& ro#&ine#se&hese!ra!%smaypropaga&edeepin&o&he-#l%o4&hema&erialand !a#se premare dei!e 4ail#re5 6 !losely asso!ia&ed phenomenon is &he 4orma&ion o4are!as&layero4ma&erialaro#nd&hema!hined4eare5Thisresolidi4ied ma&erial o4&en has a physi!al and2or !hemi!al s&r#!re &ha& is ery di44eren& 4rom &he#nmel&edma&erial5Thisre!as&layermay-eme!hani!ally+ea%erandm#s& o4&en -e remoed5 A 9ea&-di44#sionissome&imesasso!ia&ed+i&h&he4orma&iono4s#r4a!esho!% +aes5Thesesho!%+aes!andamagenear-ydei!es&r#!resordelamina&e m#l&ilayerma&erials5/hile&heamplideo4&hesho!%+aesaries+i&h&he ma&erial-eingpro!essed,i&isgenerally&r#e&ha&&hemoreenergydeposi&edin &he mi!roma!hining pro!ess &he s&ronger &he asso!ia&ed sho!% +aes5 3008/11/15Long (ulse Laser Beam Machining$ Theario#s#ndesira-lee44e!&s asso!ia&ed+i&hlonglaserp#lse e&!hing are ill#s&ra&edhere5$ The p#lse d#ra&ionin &his e=ample is U ns and &heenergy 055 mV E=ample o4a 25 Dm '1mil* !hannel ma!hined in1mm'40mils*&hi!%1N;6R+i&h ananose!ondlaser51N;6Ris e=&remelys&a-le5Thissample+as ma!hined#singaWlongXp#lselaser5 6re!as&layer!an-e!learlyseen near&heedgeso4&he!hannel5,arge de-risarealsoseenin&hei!ini&yo4 &he !#&5 )htt*!++,,,.clar--m.r.com/.3108/11/150hort(ulse Laser Beam Machining$Gl&ra-shor&laserp#lseshaeopened#p manyne+possi-ili&iesinlaser-ma&&er in&era!&ionandma&erialspro!essing5The e=&remely shor& p#lse +id&h ma%es i& easy &o a!hieeeryhighpea%laserin&ensi&y+i&h lo+p#lseenergies5Thelaserin&ensi&y!an rea!h1014Y1015/2!m2+i&hap#lseZ1mV +hen a s#--pi!o-se!ond p#lse is 4o!#sed &o a spo& si3e o4 a 4e+ &ens o4 mi!rome&ers5 3208/11/15$ Gsingshor&p#lseslaserin&ensi&yeasilyrea!hes&heh#ndredso4 &era+a&&spers"#are!en&ime&era&&he+or%spo&i&sel45Noma&erial !an+i&hs&and&hea-la&ion4or!esa&+or%a&&hesepo+erdensi&ies5 This means &ha&, +i&h #l&ra4as& laser p#lses, ery hard ma&erials, s#!h asdiamond,as+ellasma&erials+i&he=&remelyhighmel&ingpoin&s, s#!hasmoly-den#mandrheni#m,!an-ema!hined5Themos& 4#ndamen&al4eareo4laser-ma&&erin&era!&ionin&heery4as&p#lse regimeis&ha&&hehea&deposi&ed-y&helaserin&o&hema&erialdoes no& hae &ime &o moe a+ay 4rom &he +or% spo& d#ring &he &ime o4 &he laserp#lse5Thed#ra&iono4&helaserp#lseisshor&er&han&hehea& di44#sion&ime5Thisregimehasn#mero#sadan&agesaslis&ed-elo+ 'h&&p@22+++5!lar%-m=r5!om2ind#s&rial2hand-oo%2in&rod#!&ion5h&m*@ 0hort(ulse Laser Beam Machining3308/11/150hort(ulse Laser Beam Machining$ Be!a#se &he energy does no& hae &he &ime &o di44#se a+ay, &he e44i!ien!y o4 &he ma!hining pro!ess is high5 ,aser energy piles #p a& &he leel o4 &he +or%ing spo&, +hose &emperare rises ins&an&ly pas& &he mel&ing poin& o4 &he ma&erial and %eeps on !lim-ing in&o +ha& is !alled &he plasma regime5 $ 64&er&he#l&ra-4as&laserp#lse!rea&es&heplasmaa&&hes#r4a!eo4&he +or%-pie!e,&hepress#res!rea&ed-y&he4or!es+i&hini&!a#se&he ma&erial &o e=pand o#&+ard 4rom &he s#r4a!e in a highly energe&i! pl#me orgas5Thein&ernal4or!es&ha&preio#slyheld&hema&erial&oge&herare as&lyins#44i!ien&&o!on&ain&hise=pansiono4highlyioni3eda&omsand ele!&rons4rom&hes#r4a!e5Conse"#en&ly,&herearenodrople&s&ha& !ondenseon&o&hes#rro#ndingma&erial56ddi&ionally,sin!e&hereisno mel&phase,&hereisnospla&&eringo4ma&erialon&o&hes#rro#nding s#r4a!e53408/11/15 0hort(ulse Laser Beam Machining$ 9ea&ing o4 &he s#rro#nding area is signi4i!an&ly red#!ed and, !onse"#en&ly, all &he nega&ies asso!ia&ed +i&h a 96: are no longer presen&5 No mel& 3one, no mi!ro !ra!%s, no sho!% +ae &ha& !an delamina&e m#l&ilayer ma&erials, no s&ress &ha& !an damage ad?a!en& s&r#!res, and no re!as& layer5 3508/11/15Laser Beam Machining$ 6dan&ages@A E=!ellen& !on&rol o4 &he laser -eam +i&h a s&a-le mo&ion sys&em a!hiees an e=&reme edge "#ali&y5 ,aser-!#& par&s hae a !ondi&ion o4 nearly 3ero edge de4orma&ion, or roll-o44 A 1& is also 4as&er &han !onen&ional &ool-ma%ing &e!hni"#es5A ,aser !#&&ing has higher a!!#ra!y ra&es oer o&her me&hods #sing hea& genera&ion, as +ell as +a&er ?e& !#&&ing5A There is "#i!%er rnaro#nd 4or par&s regardless o4 &he !omple=i&y, -e!a#se !hanges o4 &he design o4 par&s !an -e easily a!!ommoda&ed5 ,aser !#&&ing also red#!es +as&age5 $ (isadan&ages@A The ma&erial -eing !#& ge&s ery ho&, so in narro+ areas, &hermal e=pansion may -e a pro-lem5A (is&or&ion !an -e !a#sed -y o=ygen, +hi!h is some&imes #sed as an assis& gas, -e!a#se i& p#&s s&ress in&o &he !#& edge o4 some ma&erialsC &his is &ypi!ally a pro-lem in dense pa&&erns o4 holes5A ,asers also re"#ire high energy, ma%ing &hem !os&ly &o r#n5A ,asers are no& ery e44e!&ie on me&als s#!h as al#min#m and !opper alloys d#e &o &heir a-ili&y &o re4le!& ligh& as +ell as a-sor- and !ond#!& hea&5 Nei&her are lasers appropria&e &o #se on !rys&al, glass and o&her &ransparen& ma&erials53608/11/15Water 1et uided Laser Machining$ 1n+a&er?e&g#idedlaser ma!hining,a&hin?e&o4high-press#re +a&er '&he diame&er o4 &he ?e&is-e&+een40and100Dmand &he+a&erpress#reis-e&+een20 and500-ars*is4or!ed&hro#gha no33le'madeo4diamondor sapphire*5Thelaser-eamis 4o!#sed&hro#gha+a&er!ham-er '&he+a&erisde-ioni3edand 4il&ered*in&oano33leassho+nin &he Eig#re5$ Brie4lydis!#ss,6CEi5e5,laser assis&ed !hemi!al e&!hing 3708/11/15Electron Beam Machining$ Ele!&ron--eamremoalo4 ma&erials is ano&her 4as&-gro+ing &hermal&e!hni"#e51ns&eado4 ele!&ri!alspar%s,&hisme&hod #sesas&reamo44o!#sed,high-elo!i&yele!&rons4roman ele!&rong#n&omel&and apori3e&he+or%-pie!e ma&erial5 $ 1nEB),ele!&ronsare a!!elera&ed&oaelo!i&yo4 200,000%m2sornearly&hree-4o#r&hs &ha& o4 ligh&5 3808/11/15 (lasma Beam Machining$ .lasmaar!!#&&ing'alsoplasma ar!ma!hining,.6)*ismainly #sed4or!#&&ing&hi!%se!&ionso4 ele!&ri!ally!ond#!&iema&erials5 6high-&emperareplasma s&ream '#p &o 60,000HE* in&era!&s +i&h &he +or%-pie!e, !a#sing rapid mel&ing56&ypi!alplasma&or!his !ons&r#!&ed in s#!h a +ay &ha& &he plasmais!on4inedinanarro+ !ol#mn a-o#& 1 mm in diame&er5 3908/11/15(lasma Beam Machining$Theele!&ri!ally !ond#!&ie+or%-pie!eis posi&iely!harged,and &he ele!&rode is nega&iely !harged5Rela&ielylarge !#&&ingspeeds!an-e o-&ained@4ore=ample, 7U0mm2min4ora s&ainlesss&eelpla&e85 mm&hi!%a&anar! !#rren& o4 U00 65 $Toleran!eso4I05Umm!an -ea!hieedinma&erialso4 &hi!%nessesless&han25 mm,and&oleran!eso4I7 mmareo-&ained4orgrea&er &hi!%nesses5$ The96:4orplasmaar! !#&&ingaries-e&+een058 and5mmin&hi!%nessand &he me&hod is #sed primarily 4or4erro#sandnon4erro#s me&als5 4008/11/15What is a laser2$ The +ord ,6SER is an a!ronym +hi!h s&ands 4or ,igh& 6mpli4i!a&ion -y S&im#la&ed Emission o4 Radia&ion5 1& a!ally represen&s &he prin!iple i&sel4 -#& is no+adays also #sed &o des!ri-e &he so#r!e o4 &he laser -eam5 $ The main !omponen&s o4 a laser are &he laser a!&ie, ligh& ampli4ying medi#m and an op&i!al resona&or +hi!h #s#ally !onsis&s o4 &+o mirrors54108/11/15What is a laser2$ ,aser 6!&ie )edi#m@ ,aser ligh& is genera&ed in &he a!&ie medi#m o4 &he laser5 Energy is p#mped in&o &he a!&ie medi#m in an appropria&e 4orm and is par&ially &rans4ormed in&o radia&ion energy5 The energy p#mped in&o &he a!&ie medi#m is #s#ally highly en&ropi!, i5e5 ery disorganised, +hile &he res#l&ing laser radia&ion is highly ordered and &h#s has lo+er en&ropy5 9ighly en&ropi! energy is &here4ore !oner&ed in&o less en&ropi! energy +i&hin &he laser5 6!&ie laser media are aaila-le in all aggrega&e s&a&es@solid, li"#id and gas54208/11/15What is a laser2$ 1nersion@The laser &ransi&ion o4 an a!&ie medi#m o!!#rs -e&+een &+o de4ined leels or leel gro#ps - &he #pper 'E2* and &he lo+er 'E1*5 1mpor&an& in &erms o4 laser opera&ion is &ha& an iner&ed !ondi&ion is a!hieed -e&+een &he &+o energy leels@ &he higher energy leel m#s& -e more densely pop#la&ed &han &he lo+er5 $ 1nersion is neer a!hieed in sys&ems in &hermodynami! e"#ili-ri#m5 Thermal e"#ili-ri#m is &h#s !hara!&erised -y &he 4a!& &ha& &he lo+er energy leel is al+ays more densely pop#la&ed &han &he higher5 ,asers m#s& &here4ore opera&e in opposi&e !ondi&ions &o &hose +hi!h preail in &hermal e"#ili-ri#m54308/11/15What is a laser2$ ,asing prin!iple@ (#ring spon&aneo#s emission o4 pho&ons, &he "#an&a are emi&&ed in a random dire!&ion a& a random phase5 1n !on&ras&, &he a&oms emi&&ed d#ring s&im#la&ed emission are 4or!ed in&o phase -y &he radia&ion 4ield5 /hen a n#m-er o4 &hese in-phase +ae &rains oerlap ea!h o&her, &he res#l&an& radia&ion 4ield propaga&es in &he one dire!&ion +i&h a ery s&a-le amplide5 4408/11/15What is a laser2$ T+o !ondi&ions m#s& -e me& in order &o syn!hronise &his s&im#la&ed a&omi! emission@ 4irs&ly, &here m#s& -e more a&oms presen& in &heir higher, e=!i&ed s&a&es &han in &he lo+er energy leels, i5e5 &here m#s& -e an inersion5 This is ne!essary o&her+ise &he s&im#la&ed emissions o4 "#an&a +ill -e dire!&ly re-a-sor-ed -y &he a&oms +hi!h are presen& in lo+er energy s&a&es5 The iner&ed !ondi&ion does no& preail in nare@ &he lo+er energy leels are normally more densely pop#la&ed &han &he higher leels5 Some means o4 [p#mping\ &he a&oms is &here4ore needed5 54508/11/15What is a laser2$ ,aser p#mping is &he a!& o4 energy &rans4er 4rom an e=&ernal so#r!e in&o &he gain medi#m o4 a laser5 The energy is a-sor-ed in &he medi#m, prod#!ing e=!i&ed s&a&es in i&s a&oms5 /hen &he n#m-er o4 par&i!les in one e=!i&ed s&a&e e=!eeds &he n#m-er o4 par&i!les in &he gro#nd s&a&e or a less-e=!i&ed s&a&e, pop#la&ion inersion is a!hieed5 1n &his !ondi&ion, &he me!hanism o4 s&im#la&ed emission !an &a%e pla!e and &he medi#m !an a!& as a laser or an op&i!al ampli4ier5 The p#mp po+er m#s& -e higher &han &he lasing &hreshold o4 &he laser5$ The p#mp energy is #s#ally proided in &he 4orm o4 ligh& or ele!&ri! !#rren&, -#& more e=o&i! so#r!es hae -een #sed, s#!h as !hemi!al or n#!lear rea!&ions546