Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
1999-06-11
2001-05-08
Davie, James W. (Department: 2881)
Coherent light generators
Particular temperature control
Heat sink
C372S109000
Reexamination Certificate
active
06229831
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to light-sources including an array of diode-laser bars. The invention relates to a bright, diode-laser-light-source including a plurality of diode-laser bars spaced apart from each other in the laser-light emission-direction thereof, emitted laser-light being coupled into an optical delivery system for delivery to an output-aperture of the light-source.
DISCUSSION OF BACKGROUND ART
Diode-lasers provide a most efficient and compact means of light generation and are attractive as light-sources in many applications, particularly those in which light is required only in a limited range of wavelengths. Such applications include, for example, medical applications such as photodynamic therapy and depilation; machining, welding, and heat treating using light; providing pump-light-sources for solid state lasers; and simply providing illumination.
Diode-laser-light-sources are frequently in the form of a “bar” which includes a plurality of individual lasers on a single semiconductor substrate. The lasers emit from the edge of the bar in a direction perpendicular to the length of the bar. Where one bar is insufficient to provide a desired power or brightness, an array of bars is used, one stacked above the other in a direction perpendicular to the emission-direction. Such an arrangement is usually referred to as a stacked-bar array, or a two dimensional array of emitters.
One relatively simple way of mounting such a stack of diode-laser bars is disclosed in U.S. Pat. No. 5,040,187. Here, in what may be described as a back-plane cooling arrangement, the diode-laser bars are mounted in metalized grooves in a common heat-sink of conductive ceramic material such as beryllia or alumina. In more elaborate arrangements each diode-laser bar is provided with an individual cooler and mechanical arrangements are provided for holding the bars and coolers in a unified array. In all such arrangements, the closer the bars are stacked, i.e., the more compact the output-aperture of the array, the brighter the array will be. Where the closely stacked bars are operated at high power or rapid pulse rates, however, problems are often encountered in removing heat generated during operation of the bars.
One prior-art solution to these problems has been to construct diode-laser bar arrays in which the diode-laser bars are separated horizontally as well as vertically. Such arrays are disclosed, for example, in German patent DE 2,153,969, and in Japanese patent JP 4,426,789. The disclosed arrays include a heat-sink having a stepped mounting surface with a diode-laser bar mounted on each step. Vertical spacing is comparable or even closer than in the case of arrays in which diode-laser bars are only vertically separated, while the horizontal spacing provides greater physical separation which facilitates cooling. The stepped mounting surface of the heat-sink, however, can be expensive to fabricate and also creates difficulty in using fluid-cooling arrangements, in particular microchannel-cooler arrangements, for the surfaces or steps on which the diode-laser bars are mounted. There is a need for a diode-laser-light-source in which diode-laser bars can be relatively widely spaced while still being effectively cooled and while still delivering light from a compact output-aperture.
SUMMARY OF THE INVENTION
The present invention is directed to providing an array of diode-laser bars, the collective laser-light output of which is used to provide a light-source. The invention is further directed to providing such a light-source wherein the diode-laser bar array is configured to avoid concentration of heat generated by the diode-laser bars.
In one aspect, a light-source in accordance with the present invention comprises a heat-sink having a flat surface and a plurality of diode-laser bars thermally coupled to the flat surface. Each of the diode-laser bars has a front surface. The front surface has a plurality of diode-laser emitting-area-areas therein. Laser-light is emitted from the emitting-areas in an emission-direction generally perpendicular to the front surface of the diode-laser bars. The diode-laser bars are arranged on the flat surface of the heat-sink parallel to each other and spaced apart from each other in the emission-direction.
An optical delivery system is provided for collecting laser-light emitted by the diode-laser bars and delivering the collected laser-light to an output-aperture of the light-source.
In one embodiment of a light-source in accordance with the present invention, the diode-laser bars are mounted on the flat surface such that the emission-direction is at an acute angle to the plane of the flat surface of the heat-sink. The acute angle and the emission-direction-spacing of the diode-laser bars are selected such that laser-light emitted from one of the diode-laser bars is directed over an adjacent one of the diode-laser bars in the emission-direction.
In one example of a light-source in accordance with this embodiment of the present invention, the optical delivery system includes a plurality of rectangular optical-waveguides, one thereof associated with each of the diode-laser bars. The optical-waveguides have an entrance-face and an exit-face. The entrance-face is arranged to collect laser-light from each of the diode-lasers in the bar with which it is associated. The exit-faces of the plurality of optical-waveguides are collectively arranged to provide the output-aperture of the light-source.
In another example of a light-source in accordance with the above-described embodiment of the present invention, the optical delivery system includes a plurality of cylindrical lenses, one thereof associated with each of the diode-laser bars and arranged to collect laser-light only from the diode-laser bar with which it is associated. The lenses may be arranged alternatively to collimate or focus the collected light in the fast axis thereof and direct the collimated or focused light to the output-aperture of the light-source.
In another embodiment of a light-source in accordance with the present invention, the emission-direction is parallel to the plane of the flat surface of the heat-sink. The optical delivery system includes a plurality of rectangular optical-waveguides, one thereof associated with each of the diode-laser bars and arranged such that an entrance-face thereof collects laser-light only from the diode-laser bar with which it is associated. Each of the optical-waveguides located rearward of an adjacent one of the optical waveguides is shaped such that light collected thereby is transported thereby over the adjacent diode-laser bar and any waveguides associated therewith. The optical waveguides are shaped such that exit-faces thereof are collectively arranged to provide the output-aperture of the light-source.
Light-sources in accordance with the present invention may be formed from any above-described diode-laser array and optical delivery system arrangements, stacked, one above the other, or side by side, to increase the number of diode-laser bars in the inventive light-source
In one preferred method for forming a light-source in accordance with the present invention a heat-sink having a flat surface is provided. A plurality of diode-laser bars is provided each thereof having a front surface including a plurality of diode-lasers emitting-areas, laser-light being emitted from the emitting-areas in an emission-direction generally perpendicular to the front surface.
A plurality of wedge-shaped submounts is provided, one thereof for each of the plurality of diode-laser bars. Each submount has a thick-end and a thin-end and a wedge-angle, the wedge-angle being an acute angle. Each diode-laser bars is attached to one of the wedge-shaped submounts with the front surface of the diode-laser bar closest the thick-end of the wedge-shaped.
The diode-laser bars and submounts attached thereto are arranged on the flat surface of the heat-sink such that the diode-laser bars are parallel to each other, spaced apart in the emissi
Hmelar Michael
Nightingale John L.
Coherent Inc.
Davie James W.
Stallman & Pollock LLP
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