Cooling techniques for laser diode arrays

Abstract

High-power laser diodes are desired in the consumer, medical and defense sectors. The performance and reliability of these lasers can degrade severely because of the difficulty in removing the waste heat generated within the laser diode. Higher operating temperatures also reduce the lifetime of the laser diodes. This paper investigates various cooling techniques for thermally managing laser diode arrays. Two ideal candidates for high heat flux removal are microchannel cooling and spray cooling. MicroChannel cooling requires large fluid velocities and large pressure gradients to remove waste heat. In addition, the fluid absorbs thermal energy as it flows through the channel introducing a temperature gradient along the surface. When using laser diode arrays to pump a solid state laser gain media it is essential to maintain a consistent wavelength throughout the array. Therefore, it is necessary to maintain a uniform temperature for all emitters in the array. Spray cooling allows maintenance of precise laser wavelength, higher output efficiency and lower thermally induced stresses. Nomenclature A Area (m) AC Cross-Sectional Area (m) Cp Specific Heat (J/kgK) f Darcy friction factor g Gravitational Constant (m/s) h Convection heat-transfer coefficient (W/mK) hfg Latent Heat of Vaporization (kJ/kg) k Thermal conductivity (W/mK) 18 Mass Flow Rate (kg/s) p Pressure (N/m) q Heat Flux (W/cm) Q Heat(W) ReD Hydraulic Diameter Reynolds Number T Temperature (°C or K) p Fluid Density (kg/m) p_l Liquid Density (kg/m) p_v Vapor Density (kg/m) /j. Fluid Viscosity (Ns/m) a Surface Tension (N/m) /I Wavelength (nm)