Journal of Modern Physics, 2011, 2, 109-112
doi:10.4236/jmp.2011.23017 Published Online March 2011 (http://www.SciRP.org/journal/jmp)
The Enhanced Measurements of Laser Micro-Jet
Processing
Xizhao Lu, Haihe Xie, Chun Lin, Yuanqing Huang
Department of Mechanical & Electrical Engineering Xiamen University, Xiamen, China
Received November 15, 2010; revised January 11, 2011; accepted January 13, 2011
Abstract
In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure
water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the
small nozzle of water chamber enhance the laser power density ,at the same time, the laser beam transport in
the wave guided water with the proper total reflection angle. The laser power which depended on the proper-
ties of the diameter, the coupling water chamber and the coupling efficiency of the micro-jet and laser beam
expect of the properties of laser.
Keywords: Focusing Lens, Focal Spot Size, Nozzle of Water Chamber, Laser Micro-Jet, Flat-Topped，
Breakdown Threshold
1. Introduction of Laser Micro-Jet
Processing
Talking about the methods of precise processing, the
laser micro-jet system became a hot topic in recent years.
The laser micro-jet is utilized in the precise processing,
such as semiconductors, MEMS, hard metal, surgical
operation and medical stents etc. [1]. More and more
practical applications would be developed. This tech-
nology needed to overcome the difficulty consisted in
two elements-the micro-jet processing and the laser
processing. While the diameter of the nozzle was large
enough to the laser wavelength, the micro-jet was com-
parable to a multimode fiber.
In this paper, a new focusing lens with the appropriate
bulk of nozzle of water chamber would reform the focal
spot into a less one. As a result, the higher power density
can be obtained. Micro-jet with stability fluent like pure
water is adopted in order to achieve a processing sharp
cutter.
It shall be a more focal laser beam in water micro-jet
processing. The experiment of laser micro-jet is carried
out to make reliable proof. The design of optical path
integrated the focusing lens would reduce the focal spot
size within the breakdown threshold. The quality of
working laser beam was improved with compressing the
width of flat-topped of laser beam. During the laser
processing, laser micro-jet could be considered as laser
wave guided, which dues to the total internal reflection at
the water-air interface [2].
Above all, the character of laser beam and the stability
water-jet pressure are the key technologies of micro-jet.
The liquid fiber with variable length was available with
some certain stabile pressure applied into water chamber,
while the length of water column depended on the pres-
sure and the design of water chamber and the nozzle. The
laser beam is fully reflected at the water-jet surface,
similar to transmit the laser within a fiber.
The structure of focusing lens is showed in the Figure
1. The focusing lens will get a small diameter beam spot.
The principle of water-jet guided laser is shown in
Figure 2.
The good laser is focused and collimated into a nozzle
while passing through a low pressure water chamber and
then laser beam was projected to the surface of working
Figure 1. The focusing lens applied in the system.

X. Z. LU ET AL. 110
Figure 2. The principle of laser micro-jet [4].
piece. The total reflection angle is 41.25° [5]. If the de-
sign is good, we can couple the beamThe low-pressure
water beam was emitted from the nozzle guided the laser
beam by means of total internal reflection in the water
column, in a manner similar to that of glass fibers. When
system are performing the cutting function, the material
melts absorbing the laser energy, at the same time, the
water under low pressure removed the molten from the
cutting work piece,
2. The Distribution of Micro-Jet Laser is
Reformed by the Integrated Nozzle and
Focusing Lens
From the Figure 2 the working laser beam output the
single mode or the multi mode is shaped by inverted
Galileo telescope. After that, the beam is collimated with
a appropriate convex lens. Pure water with adjustable
pressure is needed in the laser micro-jet system. The pure
water which owns a higher breakdown threshold is nec-
essary [5], too. In fact, the single mode laser was not
very often utilized in the processing. In the experiments,
the LCS2 000 Laser Optical Analyzer and a reformative
water chamber which owned a 300 μm nozzle in Figure
3 which own N/A = 50/3 are utilized. The wavelength of
working Nd:YAG laser is 1 064 nm.
The laser beam was described by well-known rela-
tionship:

22
2
22
max 2
2
ee
o
rr
o
Ir Iπ
2
o




 (1)
where ω0-waist radius of laser beam,
r - current radius,
I(r) - laser intensity function.
That total energy of laser beam is 1.
From the Formula (1), I(r) was increasing when ω0 is
increased or the value of r is decreased.
3. The Experiments of a Focusing Lens and
Enhanced the Laser Micro-Jet Beam.
The energy distribution of laser beam was shown like
Figure 3. The structure of the laser micro-jet system with
focusing lens and nozzle of water chamber.
(a)
(b)
Figure 4. a) The Nd:YAG laser coupled into the chamber
and nozzle without water; b) The 3D distribution model
(left) and x-profile (right) of Nd:YAG laser.
Figure 4(a) and 4(b), when the Nd:YAG laser beam is
coupled into the nozzle through chamber without water
under some certain pressure.
When the laser beam was coupled in the water cham-
ber, the quality of laser was ameliorated.
To concentrate the collimation laser before transmis-
sion into the water chamber, the width of waist radius
was about 16 μm. The flat width of flat-topped laser mi-
cro-jet is about 26 μm (under very low pressure, such as

X. Z. LU ET AL.111
(a)

(b)
Figure 5. (a) The Nd:YAG laser coupled in the micro-jet; (b)
The laser 3D distribution model (left) and X-profile (right)
in water.
0.1 Mpa)
In the Figure 6, some groups of lenses included the
Galileo shaper integrated into the water micro-jet system
are composed of some convex lenses and a concave lens.
Part of them worked like a Galileo telescope. The con-
cave lens would expand the laser. When those were in
appropriate positions, it would work as shaper which was
the good beam shaper. The system would average the
intensity of laser output before concentrated into water
chamber and nozzle, that is to say, it was another en-
hancement the stability of laser beam transmission in
micro-jet and minimal the heated affect core zone on the
surface of work piece in water column.
The Figure 6 showed the experiment equipment to
test the enhancement of quality of working laser mi-
cro-jet. In system, the Galileo telescope and the focusing
lens enhances the quality of laser worked as Figure 6.
After that, the performance of laser beam in the Fig-
ure 5(a) and Figure 5(b) were obtained through the
Galileo shaper and then the nozzle in water chamber.
Being the diameter of nozzle was 0.03 mm that power
intensity was less than 0.1 mm which was difficulty to
machine but owned some good performance in the ex-
periment. Above all, the laser spot would augment with
the increasing diameter of water column. That means the
same energy will increase the power intensity, as a result,
the power intensity would be lower than breakdown thres-
hold, which should banish the producing bubble in time.
The width of waist laser radius is about 24 μm, the
edge is sharper than the laser micro-jet (about 10 μm).
The consequence of the experiment of laser micro-jet
Figure 6. The theoretical experiment system.
which equipped the laser shaper showed the diameters of
waster laser radius was less than the one without shaper.
We can the consequence of working laser which was
made effect on the working piece depended on the fac-
tors which not only including peak of laser power but
also the power intensity [6]. In some sense, the power
intensity was more important than others to improve the
quality of laser processing. The spots would be bigger
than the one in traditional micro-jet without the shaper.
From the experiment and the Formula (1), it is no deny-
ing that the diameter of waster laser was reduced and the
intensity of laser power would increase.
W = P*T (2)
W - Pulse energy of working laser.
P - Power of laser pulse.
T - The width of laser pulse.
Through the expression (2), the conclusion of the
theoretical experiments was draw. Selecting the appro-
priate energy and the power needed to be lower than the
breakdown threshold played an important role as well
[5].
4. The Conclusion of Experiment
The laser micro-jet is a very fine and precise technique.
That stability water-jet is an important role to make a
successful processing. The appropriate pressure will en-
hance the stability of processing. It can cool the laser
working condition which the laser would cut the work
piece more area with high efficiency.
It was obvious that some certain pressure would give
some aspects advantages of laser processing. With
enough power intensity of processing form fine kerfs,
that is to say, the methods of shaper before the laser cou-
pled into nozzle of water chamber was still efficient to
processing in laser micro-jet.
The laser micro-jet with the focusing lens is efficient
in making a smooth cutting to enhance the processing
efficiency than before.

X. Z. LU ET AL. 112
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