Thermal management is one of the most important factors affecting the performance of high power diode lasers. In this paper, transient thermal behavior of conduction-cooled high power diode lasers has been studied using finite element method. The effects of heat sink geometry, ceramics size on the junction temperature of high power diode laser packages have been analyzed. Based on the simulations, heat dissipation capability of high power diode laser packages is improved and compact conduction-cooled diode laser array packages with 3 bars and 5 bars are fabricated. The power ~ current and spectrum of the optimized high power diode laser array packages at different operation parameters are characterized at different pulse widths, repetition frequencies and TEC temperatures. The effects of temperature on the output power and spectrum are discussed. The lifetime test of high power diode laser array packages is also performed. It shows that the conduction-cooled high power diode laser array packages have good optical performance.
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.
Packaging is an important part of high power diode laser (HPLD) development and has become one of the key factors affecting the performance of high power diode lasers. In the package structure of HPLD, the interface layer of die bonding has significant effects on the thermal behavior of high power diode laser packages and most degradations and failures in high power diode laser packages are directly related to the interface layer. In this work, the effects of interface layer on the performance of high power diode laser array were studied numerically by modeling and experimentally. Firstly, numerical simulations using finite element method (FEM) were conducted to analyze the effects of voids in the interface layer on the temperature rise in active region of diode laser array. The correlation between junction temperature rise and voids was analyzed. According to the numerical simulation results, it was found that the local temperature rise of active region originated from the voids in the solder layer will lead to wavelength shift of some emitters. Secondly, the effects of solder interface layer on the spectrum properties of high power diode laser array were studied. It showed that the spectrum shape of diode laser array appeared “right shoulder” or “multi-peaks”, which were related to the voids in the solder interface layer. Finally, “void-free” techniques were developed to minimize the voids in the solder interface layer and achieve high power diode lasers with better optical-electrical performances.
9xx nm CW mini-bar diode lasers and stacks with high brightness and reliability are desired for pumping fiber lasers and direct fiber coupling applications. For the traditional cm-bar with 1mm-2mm cavity, it can provide CW output power up to 80W-100W and high reliability, whereas the brightness is relatively low. In comparison, mini-bar based diode lasers with 4mm cavity offer a superior performance balance between power, brightness, and reliability. However, the long cavity and large footprint of mini-bar diode laser renders its sensitivity towards thermal stress formed in packaging process, which directly affects the performances of high bright mini-bar diode lasers. In this work, the thermal stress correlating with package structure and packaging process are compared and analyzed. Based on the experiment and analysis results, an optimized package structure of CW 60W 976 nm mini-bar diode lasers is designed and developed which relieves thermal stress.
With the improvement of output power, efficiency and reliability, high power semiconductor lasers have been applied in more and more fields. In this paper, a conduction-cooled, high peak output power semiconductor laser array was studied and developed. The structure and operation parameters of G-Stack semiconductor laser array were designed and optimized using finite element method (FEM). A Quasi-continuous-wave (QCW) conduction-cooled G-Stack semiconductor laser array with a narrow spectrum width was fabricated successfully.
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.
High power semiconductor laser arrays have found increased applications in many fields. In this work, a hard soldering
microchannel cooler (HSMCC) technology was developed for packaging high power diode laser array. Numerical
simulations of the thermal behavior characteristics of hard solder and indium solder MCC-packaged diode lasers were
conducted and analyzed. Based on the simulated results, a series of high power HSMCC packaged diode laser arrays
were fabricated and characterized. The test and statistical results indicated that under the same output power the HSMCC
packaged laser bar has lower smile and high reliability in comparison with the conventional copper MCC packaged laser
bar using indium soldering technology.