Coherent light generators – Particular temperature control – Liquid coolant
Patent
1998-05-13
2000-07-18
Font, Frank G.
Coherent light generators
Particular temperature control
Liquid coolant
372 35, 372 36, 372 75, 257714, 257715, 257716, H10S 304, H10S 3091
Patent
active
060917466
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of assemblies of laser diode arrays and their cooling systems.
The fields of application of assemblies of laser diode arrays are numerous and can be grouped into two major families: (beams shaped by optics or carried by fibres) and essentially relating to the medical sector and the industrial sector (marking); optical pumping of laser media (energy storage media or nonlinear effect media), e.g. the optical pumping of crystalline materials, such as oxides or fluorides doped with ions of rare earths (Nd, Er, Tm, Ho, Yb, Pr, Ce, . . . ) or Cr, Co and similar ions, optical pumping of laser material, such as dyes and the interaction with nonlinear effect media (generation of harmonics, parametric amplifiers or oscillators).
2. Discussion of the Background
Laser diode arrays and in more general terms laser diodes, have an optical/electrical efficiency of approximately 25 to 33%. Consequently the power lost by heating represents 66 to 75% of the consumed electrical power. In a continuous 20 Watt array, the active volume (semiconductor) is generally very small (micrometric dimensions) and typically 0.5 to 1 mm.sup.3, whilst the thermal power density is between 60 and 160 kW/cm.sup.3. The array is generally welded to a base (made from brass or copper), which has several functions:
In all commercial laser diode arrays, heat conduction takes place from the bottom, through the substrate and in general the anode base. This base must be in contact with a cold source in order to remove the thermal power and limit the temperature rise in the semiconductor. The connection in the upper part (cathode) cannot generally ensure an adequate thermal conductivity and the heat exchange takes place by natural convection of the ambient air.
In order to create a cold source, it is either possible to use a metal (brass or copper) cold box, or a Peltier effect thermocouple.
These procedures assume a good contact between the base of the array and the cold source, in order to minimize the contact thermal resistivity. The Peltier effect technology is very widely used in low power applications and when there is only a limited number of diodes. There is no example of the use of this technology for continuous power arrays (typically 21 Watt on average).
A so-called "microchannel" technology is described in U.S. Pat. No. 5,105,429 and U.S. Pat. No. 5,105,430. This technology is based on the assembly of modules in order to form a bidimensional emitting structure, each module having a diode array placed on a substrate with microchannel cooling.
Improvements or variants have been made, relating to the internal architecture of the structure, the construction of the stacks or the way in which the cooling fluid circulates. The principle of cooling by a microchannel structure remains the same, there being the benefit of a large exchange surface (radiator) by having a network of fins in a conductive material. The material can be the actual semiconductor or a material having a good heat conduction, such as silicon, copper or diamond.
The microchannel radiator can be integrated into each array base in order to have an autonomous module, or can be common to assemblies of arrays (surface of bidimensional assembly).
The field of application of microchannel technology is that of stacks of arrays. 1 cm wide or wider array stacks make it possible to obtain emissive areas of several square centimeters. This is the most widely used alternative in connection with surface emission diode networks. For the reasons indicated below, the development of the microchannel method is very delicate.
Firstly, this microchannel method is only accessible by highly sophisticated etching technologies. The size of the channels is also approximately 100 microns, with a spacing of 50 to 150 microns. Therefore the cooling liquid must be filtered with great care so as not to clog the network of microchannels. This leads to a significant pressure loss which, for reasonable fluid flow rates of app
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Le Garrec Bruno
Raze Gerard
Commissariat a l''Energie Atomique
Compagnie Generale des Matieres Nucleaires
Flores Ruiz Delma R.
Font Frank G.
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