Metal working – Method of mechanical manufacture – Heat exchanger or boiler making
Reexamination Certificate
2000-01-11
2001-07-31
Rosenbaum, I Cuda (Department: 3725)
Metal working
Method of mechanical manufacture
Heat exchanger or boiler making
C029S890030
Reexamination Certificate
active
06266881
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to cooling devices and more particularly to a cooling device of a high-power laser diode array and a fabrication process of such a cooling device. Further, the present invention relates to a high-power laser diode array that is equipped with such a cooling device.
In high-power solid lasers for use in various industrial applications, it is advantageous to use a laser diode array for optical pumping. By pumping a solid laser by such a high-power laser diode array that produces an output optical beam bundle with a characteristically narrow laser oscillation spectrum, in place of a conventional xenon lamp, an efficient pumping of the solid laser becomes possible.
When a laser diode array is used for such pumping purposes, it is required that the laser diode array is capable of producing the desired high-power laser beam bundle continuously with an optical power of several tens of Watts. As such a continuous high-power operation of the laser diode array causes a severe heating therein, an efficient cooling device is indispensable in a laser diode array of such high-power applications. In addition, in order that the use of a high-power laser diode array is accepted in the art of high-poser solid lasers, it is necessary to reduce the cost of the laser diode array per unit optical power as much as possible, including the cost of the cooling device.
FIG. 1
shows the construction of a conventional cooling device
10
disclosed in the U.S. Pat. No. 5,105,429 for cooling a laser diode array for high-power applications.
Referring to
FIG. 1
, the cooling device
10
includes a lower plate
1
and an upper plate
3
each formed with a channel of cooling water, wherein the lower and upper plates
1
and
3
are assembled so as to sandwich therebetween an intermediate plate
2
made of an insulating material such as a glass slab. The lower plate
1
includes an inlet opening
1
A and an outlet opening
1
B of the cooling water, while the upper plate
3
is formed with an inlet opening
3
A and an outlet opening
3
B of the cooling water similarly to the lower plate
1
. Further, the top surface of the lower plate
1
carries a branched channel
1
C of the cooling water, wherein the channel
1
C has a first end in communication with the foregoing cooling water inlet
1
A and a plurality of second ends in correspondence to a plurality of branches of the branched water channel
1
C.
The intermediate plate
2
, on the other hand, is formed, along a front edge
2
a
thereof, a slit
2
C in correspondence to the foregoing branched second ends of the water channel
1
C, wherein the slit
2
C acts as a channel of the cooling water flowing across the intermediate plate
2
from a lower side thereof to an upper side thereof. Further, cooling water channels
2
A and
2
B are formed in the intermediate plate
2
respectively in correspondence to the cooling water inlet
1
A and the cooling water outlet
1
B.
Further, the upper plate
3
carries, on the bottom surface thereof, micro-channels (not shown) along a front edge
3
a
of the upper plate
3
in communication with the outlet opening
3
B, and the micro-channels are formed with a reduced pitch as compared with the pitch of the water channel
1
C.
The upper plate
3
carries on a top surface thereof a laser diode array
4
along the foregoing front edge
3
a
, and the micro-channels are formed on the bottom surface of the plate
3
right underneath the laser diode array
4
.
The lower plate
1
, the intermediate plate
2
and the upper plate
3
are assembled with each other as explained already and are fixed by a clamping bolt inserted through aligned central openings
1
D-
3
D, which are formed in the plates
1
-
3
respectively. Each of the laser diodes in the laser diode array
4
are driven by a driver
5
.
In the conventional cooling device
10
of this prior art, it should be noted that the plates
1
and
3
are formed of a single crystal Si substrate, and the channel
1
C on the plate
1
as well as the micro-channels on the plate
3
are formed by a photolithographic patterning process that uses a resist process. Thereby, each of the grooves forming the micro-channels on the plate
1
or
3
has a width of about 25 &mgr;m and a depth of about 125 &mgr;m, and is defined by a crystal surface characteristic to a wet-etching process that is used in the photolithographic patterning process. By using such a micro-channels having a very small width, the formation of boundary layer in the cooling water along the surface of the channel is suppressed effectively and the efficiency of cooling by the cooling water through the micro-channels is enhanced substantially.
In the cooling device
10
of
FIG. 1
, it should be noted that the photolithographic process used to form the micro-channels requires an expensive exposure apparatus and various associated facilities. Thus, the cooling device of
FIG. 1
has a drawback of high production cost. Further, the Si substrate used for the upper and lower plates
1
and
3
or the glass slab forming the intermediate plate
2
is a brittle material, and the cooling device of this prior art suffers from the problem of low yield of production. It should be noted that the front edge
2
a
of the glass plate
2
, which is defined by the slot
2
C, is particularly fragile and vulnerable. Because of the mechanical fragileness, the plates
1
-
3
cannot be tightened when stacked to form the cooling device
10
. Thus, the cooling device
10
tends to suffer from the problem of water leakage even when a silicone rubber packing is interposed between adjacent plates. This problem becomes particularly serious in a long-duration operation of the laser diode array.
The cooling device
10
of
FIG. 1
further suffers from the problem of increased serial resistance when driving the laser diode array
4
by a driving current that is supplied through the plates
1
-
3
. As the cooling device
10
uses a glass slab for the intermediate plate
2
, and because of the fact that a rubber packing material is interposed between the plates
1
-
3
for eliminating water leakage, it is not possible to supply the drive current to the laser diode array
4
through the plates
1
-
3
, unless a conductor path is provided so as to bypass the plates
1
-
3
.
Thus, it is proposed to provide a metallization layer or a conductive clip on a side wall of the layered body of the plates
1
-
3
in combination with the use of a conductive rubber packing material in place of using an ordinary insulating rubber packing material for eliminating the water leakage. However, none of these approaches are sufficient to eliminate the problem of increased serial resistance of the laser diode array, and the problem of unwanted Joule heating has been inevitable.
In addition, the cooling device
10
of
FIG. 1
has a drawback in that the cooling device
10
does not use the part other than the part where the micro-channels are formed effectively for the cooling of the laser diode array
4
. Associated therewith, the efficiency of cooling of the cooling device
10
is not high as is expected.
More specifically, the plate
1
or plate
3
, which is formed of Si, has a thermal conductivity substantially smaller than a thermal conductivity of a metal, and thus, the efficient cooling of the laser diode array
4
through the plate
1
or plate
3
by heat conduction is not expected. In addition, no substantial heat conduction is expected through the glass intermediate plate
2
. Making things worse, the front edge part
2
a
of the glass intermediate plate
2
is thermally isolated from the rest of the glass plate
2
by the slot
2
C, and thus, no effective cooling is expected for the front edge part
2
a
, while this front edge part
2
a
, being located right underneath the laser diode array
4
, collects majority of the heat produced by the laser diode array
4
.
Thus, the cooling device
10
of
FIG. 1
relies solely on the micro-channels for cooling the laser diode array
4
, and thus, it is necess
Nishikawa Yuji
Takigawa Hiroshi
Armstrong Westerman Hattori McLeland & Naughton LLP
Cuda Rosenbaum I
Fujitsu Limited
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