Thermal management of diode laser arrays

Abstract

High-power lasers are in demand in the consumer, medical and defense sectors. The semiconductor diode laser, due to some outstanding properties, such as high optical conversion, will be important in the development of high-power laser energy sources. This paper will focus on the thermal analysis of using spray-cooled diode laser arrays to power solid-state lasers such as Nd:YAG and Yb:YAG. Even though the diode lasers have high optical efficiencies between 10 to 60%, a modest amount of heat is generated. The heat must be dissipated from the microscopic footprint of the device, which drives the heat flux density to extreme values on the order of kW/cm/sup 2/. The performance reliability of these diode lasers can degrade severely because of the difficulty in removing waste heat generated within the diode laser. Higher operating temperatures also reduce the lifetime of the diode lasers. The diode laser wavelength increases with an increase in temperature. That is, to have high overall optical conversion efficiency in a pumping application, the temperature is required to be quite uniform throughout the diode arrays. Precise and uniform temperature control of the diode lasers can be achieved using spray cooling through evaporation at a constant boiling point over the entire cooling surface. The isothermality and temperature control allow maintenance of precise laser wavelength, higher output efficiency and lower thermally induced stresses.