We have developed high-precision machining based on high-power pulsed green lasers (30–40 ns pulse width) at multi-kHz repetition rate. Dynamics of material removal has been investigated using a copper vapor laser. We found that noticeable surface evaporation starts to appear as laser intensity exceeds 107 W/cm2. Material removal is then dominated by ablation at higher laser intensities. However, strong plasma absorption starts to appear as laser intensity exceeds 2 GW/cm2. This prolongs material heating by hot plasma via electron conduction, resulting in noticeable melt formation and expulsion. Maintaining laser radiance below the plasma-ignition threshold minimizes this melt formation. The optimum rate of ablation on metals was found to be ∼1 μm/pulse with a laser fluence of 50 J/cm2. Higher material removal rate can be achieved at higher fluence, but is mostly accompanied with unwanted melt formation and ejection. By keeping laser intensity within a few GW/cm2, we have demonstrated high-aspect-ratio machining with micron-scale accuracy and negligible heat affected zone. High-quality percussion drilling, trepanning, grooving, and slotting were demonstrated on metals and ceramics with a negligible heat affected zone. Straight holes with sizes varying from 500 to less than 25 μm were consistently drilled with a height-to-diameter ratio up to 40. The high quality machining with scalable machining speed promises expanded use of pulsed green lasers in micromachining.

Topics
Machining, Ceramics, Lasers, Plasmas, Trepanning
1.
X.
Chen
,
W.
Lotshaw
,
A.
Ortiz
,
P.
Staver
,
C.
Erikson
,
M.
McLaughlin
, and
T.
Rockstroh
, “
Laser drilling of advanced materials: effects and peak power, pulse format, and wavelength
,”
J. Laser Appl.
8
,
233
–
239
(
1996
).
Google Scholar
Crossref
Search ADS
 
2.
C. Paul
Christensen
, “
Waveguide excimer laser fabrication of 3D microstructures
,”
Proc. SPIE
2045
,
141
–
145
(
1994
).
Google Scholar
Crossref
Search ADS
 
3.
E.
Wiener-Avnear
, “
Laser cut microscopic paths with major potential
,”
Laser Focus World
July
75
–
80
(
1993
).
Google Scholar
 
4.
J.
Hobbs
, “
Electronics makers switch to precise micro machining tools
,”
Laser Focus World
March
69
–
72
(
1994
).
Google Scholar
 
5.
M. Knowles, R. Foster-Turner, and A. Kearsley, “Copper lasers go for industrial gold,” IEEE Circuits Devices Mag. Sep. 39–44 (1994).
6.
J.
Golden
, “
Green lasers score good marks in semiconductor material processing
,”
Laser Focus World
June
75
–
88
(
1992
).
Google Scholar
 
7.
J.
Chang
and
B.
Warner
, “
Laser–plasma interaction during visible laser ablation of metals
,”
Appl. Phys. Lett.
69
,
473
–
475
(
1996
).
Google Scholar
Crossref
Search ADS
 
8.
C. Boley and J. Early, “Computational model of drilling with high radiance lasers,” Proceedings of the International Congress on Applications of Lasers and Electro-Optics, ICALEO’94, Orlando, FL (Laser Institute of America, Orlando, FL, 1994), Vol. 79, pp. 499–508.
9.
A.
Zweig
, “
A thermal-mechanical model for laser ablation
,”
J. Appl. Phys.
70
,
1684
–
1691
(
1991
).
Google Scholar
Crossref
Search ADS
 
10.
J.
Chang
, “
Copper-laser oscillator with adjoint-coupled self-filtering injection
,”
Opt. Lett.
20
,
575
–
577
(
1995
).
Google Scholar
Crossref
Search ADS
PubMed
 
11.
S. Takeno, M. Moritasu, and S. Hiramoto, “Laser drilling by high-peak pulsed CO2 laser,” Proceedings of the International Congress on Applications of Lasers and Electro-Optics, ICALEO’92 (Laser Institute of America, Orlando, FL, 1992), pp. 459–468.
12.
C. Lehane and H. Kwok, “Laser drilling at large standoff distances using dual pulse Nd laser,” Proceedings of the International Congress on Applications of Lasers and Electro-Optics, ICALEO’94, Orlando, FL (Laser Institute of America, Orlando, FL, 1994), Vol. 79, pp. 230–239.
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© 1998 Laser Institute of America.
1998
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