本研究基於局部熱力學平衡的假設下建立一個二維軸對稱之雷射引發鐵金屬蒸氣(laser induced Fe plume)物理模型，探討雷射加工參數對於鐵金屬蒸氣生成機制之效應，著重於雷射功率對於蒸氣的流場、溫度場以及鐵原子密度分佈之影響，另外鐵金屬蒸氣中之電子對於雷射能量的吸收亦是研究的另一個重點，在數值模擬方面使用計算流體力學套裝軟體Fluent對雷射引發鐵金屬蒸氣製程中的多種物理性質進行分析，而實驗方面利用光譜分析技術量測溫度，另外進行穿透率實驗推估鐵金屬蒸氣中所包含的顆粒密度。
　　研究結果顯示出，當雷射功率增加，材料蒸發所需的時間越短，而熔池表面和鐵金屬蒸氣間的溫度、壓力、密度之比值會隨著溫度上升而增加，當熔池溫度到達 之後，由於鐵金屬蒸氣的流場結構由次音速(subsonic)轉變為超音速(supersonic)，熔池表面和金屬蒸氣間的比值將維持一定，而鐵金屬蒸氣的電子密度和雷射功率成正比，造成Inverse-Bremsstrahlung吸收係數大幅上升，鐵金屬蒸氣對於雷射能量的吸收也越多，是造成溫度上升的主要機制，所以鐵金屬蒸氣的溫度、壓力及速度都會升高，使得鐵原子的擴散通量(diffusion flux)及影響範圍也越大，另外，實驗及數值計算之結果都顯示出在靠近板件表面處，蒸氣中的鐵金屬顆粒密度最大。

　　This work was based on the assumptions of local thermodynamics equilibrium to establish a 2D axisymmetric lasers induced Fe plume model, and then to explore the impact of some laser parameters on the formation mechanism of Fe plume. The author put great emphasis on the influence of laser power for flow field, temperature field and Fe concentration in the plume. The absorption of laser energy by electrons in plume will be discussed too in this study. A series of numerical computation will be performed by a commercial software Fluent to evaluate the flow field characteristics of laser induced plume. In the experiment, the author use a spectrometer to measure the plume temperature, and proceed the transmittance measurement in order to estimate the iron particle density in the plume.

　　The result shows that the time to vaporize is shorter with higher laser power. the ratios of temperature, pressure, and density between melting pool surface and plume will increase when the melting pool temperature achieve 4500K. The flow construction of plume will change from subsonic to supersonic at 4500K, and the ratios of the above parameters remain. In the other hand, the electronics density is proportional to the laser power and causes a significant rising of Inverse-Bremsstrahlung absorption coefficient, so the laser energy absorption by plume is significant. It is a major mechanism that causes the increase of temperature, pressure and plume velocity, and all of them will enlarge the diffusion flux and affected zone. In the experiment and simulation, the results show that the iron particle density is maximum, of the plume near the substrate surface.

[1]Dwight R., Nicholson., Introduction to plasma theory, Wiley, New York, 1983.
[2]Steen W. M., Laser material processing, Springer-Verlag, London, 1991.
[3]Matsunawa A., Ohnawa T., Beam-plume interaction in laser materials processing,
Trans. JWRI, Vol. 20, No. 1, pp. 9-15, 1991.
[4]Wang H. X., Chen X., Three-dimensional modeling of the laser-induced plasma
plume characteristics in laser welding, J. Phys. D: Appl. Phys., Vol. 36, pp.
628-639, 2003.
[5]Chen X., Wang H. X., Prediction of the laser-induced plasma characteristics in
laser welding: a new modeling approach including a simplified keyhole model,
J. Phys. D: Appl. Phys., Vol. 36, pp. 1634-1643, 2003.
[6]Rockstroh T., Mazumder J., Spectroscopic studies of plasma during cw laser
materials interaction, J. Appl. Phys., Vol. 61, No. 3, pp. 917-923, 1987.
[7]Greses J., Hilton P. A., Barlow C. Y., Steen W. M., Plume attenuation under
high power Nd-YAG laser welding, Proceedings of ICALEO’02, Sec. C, 2002.
[8]Herziger G., The Industrial Laser Annual Handbook, ed Belforte D., Levitt M.,
PennWell, Tulsa, 1986.
[9]Tix C., Fratzke U., Simon G., Absorption of the laser beam by the plasma in
deep laser beam welding of metals, J. Appl. Phys., Vol. 78, No. 11, pp.
6448-6453, 1995.
[10]Miller R., DebRoy T., Energy absorption by metal-vapor-dominated plasma
during carbon dioxide laser welding of steels, J. Appl. Phys. Vol. 68, No. 5,
pp. 2045-2050, 1990.
[11]Szymanski Z., Kurzyna J., Kalita W., The spectroscopy of the plasma plume
induced during laser welding of stainless steel and titanium, J. Phys. D:
Appl. Phys., Vol. 30, pp. 3153-3162, 1997.
[12]Griem H., Plasma Spectroscopy , McGraw-Hill, New York, 1964.
[13]Nonhof. C. J., Material Processing with Nd-Lasers, Electrochemical
Publications Ltd, 1988.
[14]Beck M., Berger P., Hugel H., The effect of plasma formation on beam focusing
in deep penetration welding with CO2 lasers, J. Phys. D: Appl. Phys., Vol.
28, pp. 2430-2442, 1995.
[15]Kim K. R., Farson D. F., CO2 laser–plume interaction in materials
processing, J. Appl. Phys., Vol. 89, No. 1, pp. 681-688, 2001.
[16]Tsubota s., Ishide T., Nayama M., Shimokusu Y., Fukumoto S., Development of
10kW class YAG laser welding technology, Proceedings of ICALEO’00, C-219,
2001.
[17]Mundra K., DebRoy T., Calculation of weld metal composition change in
high-power conduction mode carbon dioxide laser-welded stainless steels, Met.
Trans. 24B:145, 1993.
[18]Matsunawa A., Katayama S., Susuki A., Ariyasu T., Laser production of
metallic ultrafine particles, Trans. JWRI, Vol. 15, No. 2, 1986.
[19]Lacroix D., Jeandel G., Solution of the radiative transfer equation in an
absorbing and scattering Nd-YAG laser-induced plume, J. Appl. Phys., Vol. 84,
No. 5, pp. 2443-2449, 1998.
[20]馮學深，雷射誘發鎂電漿光譜，國立中央大學物理與天文研究所碩士論文，民國79年。
[21]Ready J. F., Effects of high-power laser radiation, Academic Press, New York,
1971.
[22]Matsunawa A., Kim J. D., Takemoto T., Katayama S., Spectroscopic studies on
laser induced plume of Aluminum alloys, Proceedings of ICALEO’95, pp. 719,
1995.
[23]Szymanski Z., Kurzyna J., Spectroscopic measurements of laser induced plasma
during welding with CO2 laser, J. Appl. Phys, Vol. 76, No. 12, pp. 7750-7756,
1994.
[24]Lacroix D., Jeandel G., Spectroscopic characterization of laser-induced
plasma created during welding with a pulsed Nd-YAG laser, J. Appl. Phys.,
Vol. 81, No. 10, pp. 6599-6606, 1997.
[25]Trayner C., Glowacki M. H., A new technique for the solution of the Saha
equation, Journal of Scientific Computing, Vol. 10, No. 1, pp. 139-149,1994.
[26]Paik S, Pfender E., Argon plasma transport properties at reduced pressures,
Plasma Chemistry and Plasma Processing, Vol. 10, No. 2, pp291-304, 1989.
[27]Ready J. F., Industrial applications of lasers, Academic Press, New York,
1997.
[28]Farson D. F, Kim K. R., Generation of optical and acoustic emissions in laser
weld plumes, J. Appl. Phys., Vol. 85, No. 3, pp. 1329-1336, 1998.
[29]FLUENT 6.1 User Guide, Fluent Inc., 2003.
[30]Poirier D. R., Geiger G. H., Transport phenomena in materials processing, ,
The Minerals Metals & Materials Society, Warrendale, 1994.
[31]Le H. C., Zeitoun D.E., Parisse J. D., Sentis M., Marine W., Modeling of gas
dynamics for a laser-generated plasma: propagation into low-pressure gases,
Phys. Rev. E, Vol. 62, No. 3, pp. 4152-4161, 1999.
[32]Knight Charles J., Theoretical modeling of rapid surface vaporization with
back pressure, AIAA Journal, Vol. 17, No. 5, pp. 519-523, 1979.
[33]林士隆，雷射震波蒸發生成金屬微粒之研究，國立成功大學機械工程研究所碩士論文，
民國92年。
[34]JANAF Thermochemical Tables, Dow Chemical Company, Midland, Mich., 1970.
[35]Yoshida T., Akashi K., Particle heating in a radio-frequency plasma torch, J.
Appl. Phys., Vol. 48, No. 6, pp. 2252-2260., 1977.
[36]DebRoy T., Basu S., Mundra K., Probing laser induced metal vaporization by
gas dynamics and liquid pool transport phenomena, J. Appl. Phys., Vol. 70,
No. 3, pp. 1313-1319, 1991.
[37]Vargaftik N. B., Tables on the thermophysical properties of liquids and
gases: in normal and dissociated states, Wiley, New York, 1975.
[38]Aden M., Beyer E., Herziger G., Kunze H., Laser-induced vaporization of a
metal surface, J. Phys. D: Appl. Phys., Vol. 25, pp. 57-65, 1992.
[39]He X., DebRoy T., Fuerschbach P. W., Alloying element vaporization during
laser spot welding of stainless steel, J. Phys. D., Vol. 36., pp. 3079-3088,
2003.
[40]He X., DebRoy T., Fuerschbach P. W., Probing temperature during laser spot
welding from vapor composition and modeling, J. Appl. Phys., Vol. 94., No.
10, pp. 6949-6958, 2003.
[41]Amara E. H., Bendib A., Modeling of vapour flow in deep penetration laser
welding, J. Phys. D: Appl. Phys., Vol. 35, pp272-280, 2002.
[42]Aden M., Beyer E., Herziger G., Laser-induced vaporization of metal as a
Riemann problem, J. Phys. D: Appl. Phys., Vol. 23, pp. 655-661, 1990.
[43]Poueyo-Verwaerde A., Fabbro R., Deshors G., Frutos A. M. de, Orza J. M.,
Experimental study of laser-induced plasma in welding conditions with
continuous CO2 laser, J. Appl. Phys., Vol. 74, No. 9, pp. 5773-5780, 1993.
[44]Greses J., Hilton P. A., Barlow C. Y., Steen W. M., Spectroscopic studies of
plume/plasma in different gas environments, Proceedings of ICALEO’01, E-808,
2001.
[45]Batteh J. J., Chen M. M., Mazumder J., A stagnation analysis of the heat
transfer and fluid flow phenomena in laser drilling, Journal of Heat
Transfer, Vol. 22, pp. 801-807, 2000.
[46]Finke B. R., Kapadia P. D., Dowden J. M., A fundamental plasma based model
for energy transfer in laser material processing, J. Phys. D: Appl. Phys.,
Vol. 23., pp. 643-654, 1990.
[47]王逸君，流體力學導論課堂筆記，國立成功大學機械工程研究所，民國92年。
[48]MAX C. E., Interaction laser-plasma/Laser-plasma interaction, ed Balian R.,
Adam J. C., North-holland publishing company, Amsterdam, 1980.
[49]Incropera F. P., DeWitt D. P., Fundamentals of heat and mass transfer, John
Wiley & Sons, New York, 1996.
[50]2002 product catalog, pp. 10, Ocean optics Inc, 2002.
[51]Van de Hulst H. C., Light scattering by small particles, Dover Publication
Inc, New York, 1981.
[53]Bennett A. A., American Institute of physics handbook, MacGraw-Hill, New York, 1957.