High power water-cooled horizontal array diode lasers are critical components in laser cutting systems for the compact line beam shape. Because of heat spreading effect of heatsink and thermal crosstalk effect among the laser bars, local thermal resistance for each bar is different, leading to unhomogeneous output power for each bar and non-uniform intensity distribution for laser line beam. In this paper, heat transfer and pressure drop as function of water flow rate in a single bent microchannel is firstly studied by computational fluid dynamics. For reaching same local thermal resistance, numerical simulation is used to determine local heat transfer coefficient (HTC) distribution for microchannels within the horizontal array heatsink. The water inlet or outlet structure respectively in the upstream and downstream of distributed channels is designed to compensate the distributed pressure drop so that each flow path from inlet to outlet has same pressure drop. This work gave the basic thermal design rule for horizontal array diode lasers to reach uniform junction temperature.
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.
High power diode lasers have been widely used in many fields. To meet the requirements of high power and high reliability, passively cooled single bar CS-packaged diode lasers must be robust to withstand thermal fatigue and operate long lifetime. In this work, a novel complete indium-free double-side cooling technology has been applied to package passively cooled high power diode lasers. Thermal behavior of hard solder CS-package diode lasers with different packaging structures was simulated and analyzed. Based on these results, the device structure and packaging process of double-side cooled CS-packaged diode lasers were optimized. A series of CW 200W 940nm high power diode lasers were developed and fabricated using hard solder bonding technology. The performance of the CW 200W 940nm high power diode lasers, such as output power, spectrum, thermal resistance, near field, far field, smile, lifetime, etc., is characterized and analyzed.
A new beam-shaping technique is proposed to improve the beam quality of a high-power diode laser area light source. It consists of two staggered prism arrays and a reflector array, which can cut the slow axis beam twice and rearrange the divided beams in fast axis to make the beam quality of both axes approximately equal. Furthermore, the beam transformation and compression can be carried out simultaneously, and the assembly error of this technique induced by the machining accuracy of prism’s dimensions also can be greatly decreased. By this technique, a fiber-coupled system for one three-bar laser diode stack is designed and characterized. The experimental results demonstrate that the laser beams could be transformed into the required distribution with ∼93.4% reshaped efficiency and coupled into a 400 μm/0.22 NA fiber, which are consistent with the theory.