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Thermomechanical behavior has an important effect on reliability and lifetime of high-power diode lasers (HPDLs). Finite-element analysis (FEA) model and analytical solution model of the conduction-cooled package (CS) HPDL are established to analyze the thermomechanical behavior including normal stress, shearing stress, and displacement in reflowing process and working process. Moreover, in order to simulate and analyze the thermomechanical behavior in total process, reflowing thermal stress and displacement are considered as the residual stress and the initial condition of working process. We find that shearing stress is the origin of other thermomechanical behavior due to coefficient thermal expansion (CTE) mismatch, while both CTE mismatch and temperature gradient cause the thermal stress and displacement in working process. Although thermal stresses and displacement induced in reflowing process are larger than working process, the working process has great impact on smile and causes much worse total smile. The influence of different working temperatures on smile is also studied in total process with analytical solution, FEA, and experiment. For analytical solution, the total smile value is inversely proportional to the working temperature, while for FEA the smile value is proportional to the working temperature and FEA result accords with experimental result.

Passively Q-switched solid-state laser is potentially a very advantageous light source for automotive LiDAR application. The key challenge is the ability of wide temperature range operation. In this work we investigated high-power diode laser bar pumped passively Q-switched Nd:YAG/Cr:YAG solid-state laser with a stable output over a wide temperature range. Firstly we studied the impact of the pump light wavelength and the laser crystal temperature on the pulse energy and threshold, and results showed that to obtain the stable output of a solid-state laser in a wide temperature range, both the diode output and the laser crystal temperature should be stabilized in a reasonable small range. Further we designed and fabricated solid-state laser modules with a single active temperature control for both laser diode and crystal, which had stable pulse energy of millijoules with a pulse width of about 2 ns and a repetition rate of 30 Hz over a wide temperature range from -30 oC to 90 oC.

High-power diode lasers are widely used in solid-state and fiber laser pumping. The spectral power distribution (SPD) of diode lasers should be perfectly matched with the absorption peak of gain materials. Spectral broadening would lead to a low optical-optical efficiency for the pump lasers. In this paper, a mathematical model based on multiple Gaussian functions was introduced to characterize the SPD of high-power diode lasers. The effect of temperature and the distribution on laser spectrum was specially included in this model. Temperature distribution in high-power diode lasers was calculated via an analytical three-dimensional thermal model. The temperature difference within the active region for diode lasers with different package structures and under different heat dissipation conditions was demonstrated. The intrinsic SPD for diode lasers with uniform junction temperature distribution was obtained from the experimental measurements in which a cold pulse current was injected into the diode lasers. SPDs for diode lasers under different injected currents were illustrated by this spectrum model, and compared to the experimental results for model validation. SPDs for the diode lasers with different chip architectures and packaging structures was calculated by coupling the analytical temperature fields into the spectrum model. Laser spectrum was verified to be independent of current density, but mainly depend on the junction temperature distribution in the experiments by comparing the spectra of the epi-up and epi-down packaged F-Mount single-emitters at same injected current.

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.

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.

Thermal stress is an influential factor for the reliability of HPDL and their optical properties. Two packages of conduction-cooled-packaged 60W HPDL were selected as the study samples. In order to investigate what reflow factors influence thermo-mechanical of HPLD, a COS model is established. In reflow process and working process, hard solder package suffers higher thermal stress. Thermal stress mainly comes from reflow process. In reflow process, copper mount will deteriorate thermo-mechanical of hard solder package. There exists shear stress in HPLD and it will convert TE-polarized power to TM-polarized power. In working process, uniaxial normal stress along the width direction of QW is mainly influenced by coefficient expansion thermal. The displacement of HCS along growth direction is larger than that of CS, whereas the “smile” value is smaller. “Smile” is mainly impacted by CTE of solder and submount.

The reliability is the important performance of high power semiconductor laser. Thermally accelerated ageing test is an important technology of lifetime evaluation and reliability analysis. In this study, three groups of thermally accelerated ageing tests of conduction-cooled-packaged 60W 808nm high power diode laser arrays packaged by Indium solder at constant current have been carried out. Analysis of ageing data suggest the extrapolated lifetime under room temperature to value device reliability. We also analyze and discuss the degradation modes. This work can provide guidance for optimizing the chip and package structure, is helpful for improving performance and enhancing reliability of high power semiconductor lasers.

Heat generation in the active region leads to high junction temperature that significantly affects electrical and optical properties, reliability and lifetime of high power diode laser arrays. It is of great importance to understand the thermal behavior to improve the devices. Compared to conduction cooling techniques, diode laser arrays packaged on microchannel heat sinks have superior capability to dissipate the large amount of heat so as to deliver higher output power and ensure high reliability. In this paper, numerical approach based on finite element method (FEM) and computational fluid dynamics (CFD) was employed to investigate thermal properties of microchannel cooled (MCC) high power diode laser arrays. The static and transient thermal behavior of the devices operated in continuous wave (CW) mode at different water flow rates have been studied in detail. The thermal resistance contributed from the laser chip, solder interface and MCC heat sink was revealed. The correlation between thermal resistance and water flow rate was analyzed. The thermal time constants were derived to characterize the three distinct heating processes related to active region, copper heat sink and copper/water interface. Non-uniformity of junction temperature across the diode laser array was discussed by thermal crosstalk employing the independent emitter analysis. Understanding thermal phenomena in diode laser arrays could offer useful guidelines in optimizing the operating conditions, MCC heat sink structures and packaging architectures for enhanced performance and reliability.

With the improvement of performance and reliability, high power semiconductor lasers have been widely applied in more and more fields. Thermal management is one of the most important issues effecting the optical-electrical performance of high power semiconductor laser. Compared with liquid-cooled techniques, conduction-cooled techniques have many advantages in some special applications because it could be adaptable for extreme environments, such as high temperature and low temperature. In this paper, a compact quasi-continuous wave (QCW) conduction-cooled high power semiconductor laser array was studied. The thermal behavior of the conduction-cooled semiconductor laser array with different structure and operation parameters were carried out using finite element method (FEM). The structure parameters of G-Stack semiconductor laser array was presented and optimized. Finally, A high power semiconductor laser array with superior performance was fabricated and characterized.

“Smile” in high power diode laser arrays is mainly caused by thermal stress generated during packaging processes and operation. By numerical modeling, a three-dimensional finite element model of a conduction-cooled packaged 60W high power diode laser array was established. Finite element method (FEM) was conducted to simulate and analyze the thermal and mechanical characteristic of the diode laser bar in different scenarios. According to the variation of thermal stress and displacement across the laser bar, the influence of temperature and driving current on “smile” was analyzed and discussed. Numerical simulation results show that “smile” will decrease with the increasing heatsink temperature and increase with the increasing driving current. In this paper, the corresponding quantitative relationships of smile with heatsink temperature and driving current were obtained. The work provides theoretical guidance for optimizing high power diode laser array design, packaging process and reducing “smile”.

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 similar to 93.4% reshaped efficiency and coupled into a 400 mu m/0.22 na fiber, which are consistent with the theory. (c) 2013 society of photo-optical instrumentation engineers (spie)