Effect of gas pressure on ionization of ambient gas

第19卷第3期原子与分子物理学报Vol.19,N.3002年7月CHINESE JOURNAL OF ATOMIC AND MOLECULAR PHYSICS2002Article Il:1000036(2002)3027205Effect of gas pressure on ionization of ambient gasSONG Guang-le, song Yi-zhong(l. Department of Physics Linyi Teachers University Linyi 2760052. Biomaterials Lab, Department of materiel science the southen zone, Shandong University Jinan 250061Abstract: An Nd: YAG pulsed laser( 145 m] )was used to ablate aluminum target and Ar was used as protecting gasTime-and space-resolved spectra of the plasmas under pressure 100 Pa, 1 kPa, 10 kPa and 100 kPa were acquired withtime-and space-resolved technique. The characteristics of the plasma radiating under each pressure were briefly describedand the laws of Ar characteristical radiaton were analyzed in detail. Based on the profile of Ar characteristical radiation underthese pressure the relation between protecting gas pressure and its ionization was briefly discussed and explained withquantum theory. Farther more the mechanism of ambient gas ionization was investigated. As the result, it was suggestedthat the main mechanism inducing protecting gas to ionize should be the absorption of the plasma continuum radiation by theKeywords: Laser ablating Time-and space-resolved spectrum Characteristic line Mechanism of ionization; QuantumCLC number :0433. 54Document code:: AINTRODUCTIONThis effect must be taken into account when higher purefilms were required 78. lonization of ambient gas was anIt was often encountered that ionization of ambientimportant phenomenon during the plasma evolvingas should occurred when a plasma was produced withradiating. Investigating the mechanism oflaser ablating a target. Many articles reported thisphenomenon conduce to the under standing of mechanismphenomenorfI-43, but few investigated it in detuil of plasma evolving radiating and provide theoreticalfarthequantum explanation for the plsustain for farther applications of plasma spatteringwas much fewer. Not only did ionization of ambient gasinduced by laser ablating target. In this work, theabsorb energy of the plasma, but also intervene radiating mechanism of ambient gas ionization would be discussedpetra of the plasma as an outside electric field. Thewith quantum theoryionization would disturb the analysis of target compositionwhen chemistry analysis was carried out assisted with the 2 EXPERIMeNtplasma radiations 6].When theinduced by laser ablating target was as a specialExperimental setup was shown in Fig. 1, thetechnique used to depositing thin film the ionization of desmbient protecting gas would induce gas ions into film. hasTH中国煤化工 process of acquiring dataCNMHGpape! 4a Received date 22001-10-24ang-le( 1962-)MaleRizhao city Shandong province associate professor, Department of Physics Linyi Teachers第19卷第3期SONG Guang-le et al : Effect of gas pressure on ionization of ambient gas2733 RESULTS AND DISCUSSIONesultsNd: YAG LASERLaser beamdiodeYIME DELAY SETOSCILLOSCOPEFASTGATEPULSE SETPRERINTERL:SPECTROMETEHR·320gas inCONTROLDETECTORSYSTEMPUMPPLOTTERFig 1 Schematic diagram of the experimental setup10ns30ns70ns400sons110ns130ns170ns200ns220ns250ns300ns200Ah390420390420390420390420390420中国煤化工Fig. 2 Time-resolved emission spectra of the plasmas obtof the surfaceunder pressure 100 Pa, laser pulse energy 145YHaCN MH gme to eachspectrum had been marked in it, respectivelyThe radiating spectra of the plasma were shown in kPa, 100 kPa were shown in Fig 3. Here only those withFig. 2, which were acquired with ambient gas pressure setdiating signal were given outupt100数据 e obtained under pressure1kPa,:10274原子与分子物理学报2002年3.2 AnalysisAr+ started after 30 ns delayed and died away after 300As shown in Fig. 2, continuum radiation of the ns delayed or so. At whole radiating stage of the plasmaplasma was quite strong after Ins delayed. Within 30 ns the radiation of ions was much weaker than that offter laser beam reaching the surface of target, the plasma continuum. After 100 ns delayed radiation of aluminumradiation mainly consisted of continuum radiation. Afterhad been quite strongetion30 ns delayed, the radiation of aluminum, atom Ar, ion kept stabilization, and continuum radiation went onArt appeared. scale for the spectra had been given in ourdeclining. Within 220 ns delayed, characteristic radiatiorelative works 9] all characteristic radiation addedgot gradually stronger and became main radiation of thecontinuum radiation, and they began lagging the latter plasma. After 220ns delayed, radiation of aluminum30 ns or so. With delayed time increasing, the began to decline continuum got weaker farther more butcharacteristic radiation became stronger and stronger,onthe first declined slower than the latter. After 350 nsthe contrary the continuum got weaker and weakerdelayedoIseWithin 90 ns delaved, the characteristic radiation was aluminum decayed slower so that it was still strong aftermuch weaker than continuum The radiation of r and500 ns delyedLMMi WVWavelength(nm)(a)10 kP(b)1 kPa(c)100 kPaFig 3 Time-resolved emission spectra bearing Ar* characteristic emission, obtained at z=0. 1 mm in front of the suface,er pulse energy 145 mJ/pulse in Ar, the delayed time to each spectrum had been marked in it, respectively,under pressure3. 4 Discussionndicated that there were lots of Art, and that Ar,aseen from Fig. 2 it was easily to be found out thatambient gas deeply absorbed the energy of the plasmaere was a broad dent adding to continuum on almostFrom Fig. b), under pressure 1 kPa, there were lots ofspectrum. The d elines of Ar+ too. These characteristic lines were clearabsorbing spectrum which derived from aluminum sharp but weaker. This indicated that there were manyresonantly absorbed continuum radiation 10 JArt, and that the absorption of plasma by Ar was3. 4.1 Radiating lines of ionslighter, From Fig 3(c), under pressure 100 kPa,thereAt the stage of Ar radiating, there were many中国煤化工 These lines had broadradiating lines of Ar+. These characteristic lines had styleCNMHGindicated that there werelear sharp line style but were very weaka few Ar, and that the absorption was quite lightrom Fig 3( a), under gas pressure 10 kPa,thereBased on the analysis above we could conclude aswere many radiating lines of Ar+. These characteristic followes were而点教ap, and quite stron.ThiuationThere were the most characteristic lines of Al第19卷第3期SONG Guang-le et al : Effect of gas pressure on ionization of ambient gas275under pressure 10 kPa, farther more, under this the plasma formed continuum radiation of the plasmasituation, Ar+ have strongest radiation. with gas pressure started at once 11). Effected by the continuumdecreased, the number and style of the characteristic lines Ar atoms were ionized into Ar+. Just after cechanged little but radiation decayed sharply. With gas on the one hand Ar'absorbed the continuum radiatinpressure increased the number of the lines declined photons transiting to excited state. The Ar+ which wasquickly and radiation got weaker and weaker the style in excited state was unstable and emitted characteristicof the lines became worse and worseradiation photons transiting to lower or ground state with3.4.2 Mechanism analysiscertain photons given out so characteristic radiation ofWhat resulting in the results shown in Fig. 2 and Art came into being. This could be shown as formulaFig 3 were the compound reaction of Ar and e and the (4 ). On the other hand, Ar* would take part inhanism of plasma energy absorption by Ar and Ar. compound reactionantum theory the energy ofAr+eAr+ hAt high pressureenunE=nhro=nu个s(1) densities but flew slowly 9. So they had stronger effectof electric attraction. Because of this effect they made forWhere n is the number of photons in one pulsedeach other and compounded. As the result, Ar had littlelaser beam Ao is the wavelength of laser photon. If Ewas given we can obtain n[ 101situatimpound betweenThe radiation of art couldn 't be detectewas dominant but radiating action of Ar+ was secoband observed until Ar+ absorbed three laser photons at so at the gas pressure of 100 kPa the characteristicthe same timeradiation was weak, the number of characteristic lines wasE+3ho→EAt→E+hr(2) less and the lines were broade contrarybothhere r is the frequency of photons in the bandhad low number densities and moved quickly]. So theyobserved, its value limitedchance to compound with e. As the result Ar went on42Xm)7≤373mm)absorb some phonons to conform characterthe probability of multi-photons after coming into being. In this situation radiating actionabsorption is very little so this isnt the main mechanism of Ar* was dominant, but compound between Art and ef energy absorption by Arwas secondary. so at the gas pressure of 100 Pa thereAnother manner of absorption of plasmma energyby were many characteristic lines, and the lines were clAr is absorbing continuum radiating photons of the and sharp but because of low number densities of Arthe characteristic radiation was weak, result in fig. 2 andhr→E(3)EAr++ hro +hr'(4)CONCLUSIONsay, continuum radiation photons arenodulated by inherent frequency of Art, so that RamanThe relation between ionization of Ar and the gasscatteringoccurred. This manner is the main mechanofmaH中国煤化工ring time resolved spectraCNMHG100 Pa. 1 kPa, 10 kPaThe process of Ar+ radiation could be brand 100 kPa. As the result we found that Ar+ radiatedescribed as followstrongest at 10 kPa and that with pressure increasingShortly after the laser beam bombarded onto the compound between Ar and e became more dominantsurface of farge, F plasma came into being. As soon as but ionization of Ar got weaker, and that, with pressure原子与分子物理学报2002年decreasing radiation of Ar got more and more[JI. Spectroscopy and Spectral Analysis, 2000. 20( 1 ): 25ominant ionization of Ar became deeper and deeperAfter Ar+ coming into geing they took part in both [5JKichirl Kagawa. Sadahiro Yoko. Application of the Nz laser tocompound with e and radiation with characteristic photorlaser microprobe spectrochemical analysis[ J ] Spectrochimicagiven out. The relation between the two actions madeActa.1981B3x9):789~795characteristic radiation of Ar+ strong or weak. The [6]WF HO, CWNG, N H Cheung Spectrochemical analysisof liquids using laser-induced plasma emissions effects of laserabsorption of continuum radiation by Ar was the mainwavelengtH]. Applied Spectrosc. 1997 51(1)87-91echanism for ar ionization and radiation[7]J. Gonzalo, C. N. Afonso, J. Perrier. Influence of laserenergy density on the plasma expansion dynamics and filmREFERENCESstoichiometry during laser ablation of BiSrCaCu(J].J. Applys.,19967910)8042~8[1]M Kuzuya, H Matsumoto, H. Takechi et al.. Effect of laser [8]ZHANG Ya-ping, GAO Jia-cheng, WEN Jing. Preparaenergy and atmosphere on the emission characteristics of laser-composing bioceramic layer on titanium alloy by laserinduced plasma J ]. Applied Spectrosc. 1993 Ax 10 ) 1 659cladding J ] Chinese Journal of Materials Research. 1998, 12~1664(4)423-4262 J Yong-ILL Lee, Samuel P Sawan Terry L. Thiem et al[9 ]SONG Yi-zhong, LI Liang, ZHANG Yan-hui. 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