High power diode lasers (HPDLs) have been applied in more and more fields, such as material processing, pumping of solid-state lasers and fiber lasers, medical therapy. With the improvement of output power, efficiency and reliability, thermal management has been one of most critical issue for HPDLs. The junction temperature of a diode laser package has critical effects on laser characteristics, affecting wavelength, output power, threshold current, slope efficiency, and operating lifetime. Lower junction temperature is an effective means to achieve high output power and high electrooptical conversion efficiency of diode lasers. In recent years, high-power diode lasers operated at cryogenic temperature have attracted academic interests. Herein, high power diode lasers suitable at cryogenic temperature and a measurement setup at cryogenic temperature have been developed. The optical-electrical performance of microchannel cooled high power diode lasers from 0℃ ~ -60℃ have been studied theoretically and experimentally. The output power increases 18% and the conversion efficiency increases 6.3% from 0 ºC to -60 ºC. The high diode laser bars operated at cryogenic will be applied in pumping high energy lasers in the future.
High power diode laser arrays have found increasing applications in the field of pumping solid-state lasers and fiber lasers. Due to the thermal crosstalk across diode laser arrays and non-uniformity of local flow rate within microchannel cooler, junction temperature distribution becomes inhomogeneous, consequently leading to spectrum broadening and large beam divergence of diode laser pumping sources. In this work, an analytical method and numerical heat transfer based on finite volume method were employed to optimize the inner structure of microchannel cooler so as to obtain low thermal resistance and uniform junction temperature distribution for the diode laser arrays. Three-dimensional numerical models were developed to study the fluid flow and heat transfer of copper stacked microchannel coolers with different dimensions and arrangements of inner channels and fins. More uniform junction temperature distribution of diode laser array package could be achieved by self-heating compensation with specific coolant covering width. These results could provide significant guidance for the design of microchannel coolers of high power diode laser arrays for better performance.
A novel marco channel cooler (MaCC) has been developed for packaging high power diode vertical stacked (HPDL) lasers, which eliminates many of the issues in commercially-available copper micro-channel coolers (MCC). The MaCC coolers, which do not require deionized water as coolant, were carefully designed for compact size and superior thermal dissipation capability. Indium-free packaging technology was adopted throughout product design and fabrication process to minimize the risk of solder electromigration and thermal fatigue at high current density and long pulse width under QCW operation. Single MaCC unit with peak output power of up to 700W/bar at pulse width in microsecond range and 200W/bar at pulse width in millisecond range has been recorded. Characteristic comparison on thermal resistivity, spectrum, near filed and lifetime have been conducted between a MaCC product and its counterpart MCC product. QCW lifetime test (30ms 10Hz, 30% duty cycle) has also been conducted with distilled water as coolant. A vertical 40-MaCC stack product has been fabricated, total output power of 9 kilowatts has been recorded under QCW mode (3ms, 30Hz, 9% duty cycle).
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