Coherent light generators – Particular temperature control – Liquid coolant
Reexamination Certificate
2000-07-27
2003-11-04
Ip, Paul (Department: 2828)
Coherent light generators
Particular temperature control
Liquid coolant
C372S034000, C372S036000
Reexamination Certificate
active
06643302
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cooling device, and more particularly to a cooling device for cooling laser diode arrays that release large quantities of heat and to a surface emitting device, configured from laser diode arrays, which comprises that cooling device.
2. Description of the Related Art
One application for the laser diode array is seen in light sources for exciting high-output solid lasers. In general, in such a high-output solid laser, when a high average output at the kW level is sought, it is necessary (a) that continuous laser light having a high intensity of 100 W/cm
2
or greater be generated in the laser diode array used as the excitation light source, and (b) that a large emitting surface area of several tens of cm
2
be available. Given the constraints of realizing a large light emitting surface area, a cooling device is indispensable in order both to release heat generated at a density of 100 to 200 W/cm
2
and to control the rise in temperature of the laser diode array.
In order for surface emitting light sources configured from such high-output laser diode arrays to be widely used in this field, it is very important that the cost per unit of light output be kept down.
FIG. 1A
is a diagram of a surface emitting device
118
comprising a plurality of conventional one-dimensional laser diode arrays (hereinafter called laser bars), while
FIG. 1B
represents the configuration of the main parts of such a cooling device
119
for that surface emitting device.
As diagrammed in
FIG. 1B
, the heat generated by a laser bar
22
is conducted by a laser bar support plate
120
, from there passes through an insulating plate
121
and a heat sink
122
, and is discharged after heat exchange with a cooling liquid
123
. For that reason, the thermal resistance between the laser bar
22
and the cooling liquid
123
will inevitably become comparatively high, so that the temperature of the laser bar
22
readily rises due to heat generation.
However, with a surface emitting device
118
that employs a cooling device
119
structured so that it cools the back surface of a two-dimensional laser diode array configured from a plurality of such laser bars
22
, a configuration that makes almost the entire surface a light emitting surface is possible, as seen from the light emitting surface side, as diagrammed in
FIG. 1A
, wherefore, when an attempt is made to deploy an even larger plurality of these surface emitting devices to configure a surface emitting light source having a larger light emitting surface area, there are restrictions such as the degree of layout freedom being low and it being difficult to realize a surface emitting light source having few non-emitting parts.
FIG. 2
gives an exploded view representing the configuration of another type of a surface emitting device
124
comprising a plurality of conventional laser bars
22
. As diagrammed in
FIG. 2
, each of the plurality of laser bars
22
is thermally connected to a separate cooling unit
125
. The cooling liquid is made to flow into the cooling units
125
from a cooling liquid induction port (not visible in
FIG. 2
) that is connected to an intake opening
8
provided commonly for each of the cooling units
125
, passes more or less directly below the positions where the laser bars
22
are deployed, and is then discharged from a cooling liquid discharge port
17
that is connected to an outlet opening
9
provided commonly for each of the cooling units
125
. Hence the thermal resistance between the laser bars
22
and the cooling liquid can be made lower, and it becomes possible to hold down temperature rises in the laser bars
22
due to heat generation to a low level.
However, with a surface emitting device
124
wherein cooling devices are employed that have a structure that cools with cooling liquid immediately below the individual laser bars
22
in this manner, the non-emitting areas as seen from the light emitting surface side become great because of the deployment, on the outside of the stacked plurality of cooling devices, of an induction pipeline
14
for inducting the cooling liquid in from the intake opening and a discharge pipeline
16
for discharging the cooling liquid from the outlet opening, and the deployment of a tightening bolt
20
to prevent leakage of cooling liquid from between the cooling units
125
and
125
. For that reason, when an attempt is made to deploy an even larger plurality of these surface emitting devices to configure a surface emitting light source having a larger light emitting surface area, there are restrictions such as the degree of layout freedom being low and it being difficult to realize a surface emitting light source having few non-emitting parts.
In
FIG. 2
, the intervals in the cooling device are represented as being wider than at the time of actual use, in the interest of making the configuration easy to understand, and the diagram shows neither the sealing material used to prevent the cooling liquid from leaking out from between the cooling units
125
and
125
nor the wiring connection board connecting to an electrode on the side of the laser bars not connected to the cooling devices.
FIG. 3
provides an exploded view of an example configuration of the cooling device diagrammed in FIG.
2
. As diagrammed in
FIG. 3
, the cooling unit
125
is made up of a first thin plate
126
, a second thin plate
127
, a third thin plate
128
, a fourth thin plate
129
, and a fifth thin plate
130
, stacked sequentially from the top.
A cooling liquid intake opening
8
and outlet opening
9
are formed in the first thin plate
126
.
In the second thin plate
127
, an outlet opening
8
is formed in a position corresponding to the outlet opening
9
in the first thin plate
126
. A cooling liquid flow channel
131
is also formed therein, extending from a position corresponding to the intake opening
8
of the first thin plate
126
such that the width thereof widens as the front end surface
12
is approached. Microchannels
133
are also formed therein, near a front end surface
12
, along that front end surface
12
.
In the third thin plate
128
, an intake opening
8
and an outlet opening
9
are formed at positions corresponding to the cooling liquid intake opening
8
and outlet opening
9
of the first thin plate
126
. A slit
132
is also formed therein, near the front end surface
12
, along that front end surface
12
.
In the fourth thin plate
129
, an intake opening
8
is formed at a position corresponding to the intake opening
8
of the third thin plate
128
. A cooling liquid passage
131
is also formed so as to extend from a position corresponding to the outlet opening
9
of the third thin plate
126
towards the front end surface
12
while increasing the width thereof.
In the fifth thin plate
130
, an intake opening
8
and an outlet opening
9
are formed at positions corresponding to the cooling liquid intake opening
8
and outlet opening
9
of the first thin plate
126
.
The first to fifth thin plates
126
to
130
described above, respectively, are made of a highly thermally conductive material such as copper, for example, and are mutually stacked together. Cooling liquid inducted from the intake openings
8
passes through the microchannels
133
in the second thin plate and is discharged from the outlet openings
9
. When this occurs, the laser bar (not shown) deployed along the front end surface
12
of the fifth thin plate
130
is cooled. In the microchannels
133
, very fine flow channels, having a width of 20 &mgr;m or so, are formed, by laser processing or the like, in order to prevent the heat exchanging efficiency from falling due to a cooling liquid boundary layer.
FIG. 4
is an exploded view of the configuration of a cooling device disclosed in Japanese Patent Application Laid-Open No. 209531/1998. This cooling device is a different type from that diagrammed in
FIG. 3
which is for cooling one one-dimensional laser diode array.
As diagrammed in
FIG. 4
, the coolin
Nishikawa Yuji
Takigawa Hiroshi
Fanuc Ltd.
Ip Paul
Nguyen Phillip
Staas & Halsey , LLP
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