This work investigates transport phenomena and mechanisms of droplet formation during a pulsed laser interaction with thin films. The surface of the target material is altered through material flow in the molten phase induced by a tightly focused laser energy flux. Such a process is useful for developing a laser-based micromachining technique. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the process. As with many machining techniques, debris is often generated during laser-material interaction. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exists for “clean” structures to be fabricated. The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation and droplet formation are attributed to the surface-tension-driven flow, and the recoil pressure effect plays an insignificant role in the surface topography development. [S0022-1481(00)02903-0]

Issue Section:
Microscale Heat Transfer
Keywords:
laser beam effects, drops, surface topography, melting, heat transfer, surface tension, photography, thin films, Heat Transfer, Instability, Laser, Surface Tension, Visualization
Topics:
Drops, Lasers, Thin films, Flow (Dynamics), Surface tension, Fluid dynamics, Transients (Dynamics), Photography
1.
Brailovsky
,
A. B.
,
Gaponov
,
S. V.
, and
Luchin
,
V. I.
,
1995
, “
Mechanisms of Melt Droplets and Solid-Particle Ejection From a Target Surface by Pulsed Laser Action
,”
Appl. Phys. A: Mater. Sci. Process.
,
61
, pp.
81
–
86
.
2.
Balandin
,
V. Yu.
,
Otte
,
D.
, and
Bostanjoglo
,
O.
,
1995
, “
Thermocapillary Flow Excited by Focused Nanosecond Laser Pulses in Contaminated Thin Liquid Iron Films
,”
J. Appl. Phys.
,
78
, No.
3
, pp.
2037
–
2044
.
3.
Dimitrov
,
D. A.
,
1995
, “
Some Observations on Laser Trimming Platinum Thin Films
,”
Platinum Met. Rev.
,
39
, No.
3
, pp.
129
–
132
.
4.
Bennett
,
T. D.
,
Krajnovich
,
D. J.
,
Grigoropoulos
,
C. P.
,
Baumgart
,
P.
, and
Tam
,
A. C.
,
1997
, “
Marangoni Mechanism in Pulsed Laser Texturing of Magnetic Disk Substrates
,”
ASME J. Heat Transfer
,
119
, pp.
589
–
596
.
5.
Willis
,
D. A.
,
Xu
,
X.
,
Poon
,
C. C.
, and
Tam
,
A. C.
,
1998
, “
Laser-Assisted Surface Modification of Thin Chromium Films
,”
Opt. Eng.
,
37
, No.
3
, pp.
1033
–
1041
.
6.
Chandrasekhar, S., 1961, Hydrodynamic and Hydromagnetic Stability, Oxford University Press, London.
7.
Shamsundar
,
N.
, and
Sparrow
,
E. M.
,
1975
, “
Analysis of Multidimensional Conduction Phase Change Via the Enthalpy Model
,”
ASME J. Heat Transfer
,
97
, pp.
333
–
340
.
8.
von Allmen, M., 1987, Laser-Beam Interactions With Materials (Springer Series in Materials Science 2), Springer-Verlag, Berlin, pp. 146–151.
9.
Grosse
,
A. V.
,
1963
, “
High Temperature Research
,”
Science
,
140
, pp.
781
–
789
.
10.
Brandes, E. A., and Brook, G. B., 1992, Smithells Metals Reference Book, 7th Ed., Butterworth-Heinemann, Oxford.
11.
Allen
,
B. C.
,
1964
, “
The Surface Tension of Liquid Chromium and Manganese
,”
Trans. Metall. Soc. AIME
,
230
, pp.
1357
–
1361
.
12.
Allen, B. C., 1972, “The Surface Tension of Liquid Metals,” Liquid Metals, Chemistry and Physics, S. Z. Beer, ed., Marcel Dekker, New York, pp. 161–212.
13.
Vitol
,
E. N.
, and
Orlova
,
K. B.
,
1984
, “
The Surface Tension of Liquid Metals
,”
Russ. Metall.
,
4
, pp.
34
–
40
.
14.
Tret’yakova
,
E. E.
,
Baum
,
B. A.
,
Tyagunov
,
G. V.
,
Klimenkov
,
E. A.
, and
Tsepelev
,
V. S.
,
1986
, “
Surface Tension of Molten Steel
,”
Russ. Metall.
,
4
, pp.
25
–
28
.
15.
Filippov
,
K. S.
,
1992
, “
Density and Surface Tension of Iron and Fe-Cu-S Melts
,”
Russ. Metall.
,
1
, pp.
46
–
48
.
16.
Bostanjoglo
,
O.
, and
Nink
,
T.
,
1997
, “
Liquid Motion in Laser Pulsed Al, Co and Au Films
,”
Appl. Surf. Sci.
,
109/110
, pp.
101
–
105
.
17.
Chung
,
W. B.
,
Nogi
,
K.
,
Miller
,
W. A.
, and
McLean
,
A.
,
1992
, “
Surface Tension of Liquid Cr-O System
,”
Mater. Trans., JIM
,
33
, No.
8
, pp.
753
–
757
.
18.
Martynyuk
,
M. M.
,
1983
, “
Critical Constants of Metals
,”
Russ. J. Phys. Chem.
,
57
, No.
4
, pp.
494
–
501
.
19.
Barin, I., 1993, Thermochemical Data of Pure Substances, Part I, Ag–Kr, VCH, Weinheim, Germany, pp. 418–419.
20.
Incropera, F. P., and DeWitt, D. P., 1990, Fundamentals of Heat and Mass Transfer, 3rd Ed., John Wiley and Sons, New York, p. A3.
21.
Hunter, W. R., and Lynch, D., 1991, “An Introduction to the Data for Several Metals,” Handbook of the Optical Constants of Solids II, E. D. Palik, ed., Harcourt Brace Jovanovich, Boston, Part II, Subpart I, pp. 374–385.
22.
Boyer, H. E., and Gall, T. L., 1983, Metals Handbook Desk Edition, American Society for Metals, Metals Park, OH, p. 2.19.
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