Study On Thermal Stress/strain Characteristics Of High Power Semiconductor Laser Arrays

High-power diode lasers play an irreplaceable role in material molding,aerospace,medical cosmetology,and all-solid-state laser pumping.The developing trend of high-power diode lasers is to increase power,efficiency,and reliability.The key factors that limit the performance and reliability of high-power diode lasers are laser diode chip and packaging.Packaging is closely related to heat dissipation efficiency and stress/strain of the device,and has a decisive influence on the photoelectric performance and reliability of diode lasers.In order to improve the beam quality and reliability of the diode laser array,deeply understand the influence mechanism of external factors on chip thermal stress and the "Smile",understand the transient temperature,stress,strain behavior of the laser under quasi-continuous wave high power under different working conditions,the steady-state and transient temperature and thermal stress/strain behavior of hard-solder packaged diode lasers and microchannel-cooled diode lasers are studied,and the key factors and solutions that restrict the stress/strain in diode laser packages are proposed.The "sandwich" packaging structure is firstly proposed in this article,which use the material with the same thermal expansion coefficient of the chip as the negative electrode and the secondary heat sink.The thickness of the two layers is the same,and the chip is sandwiched in the middle.This new structure can significantly optimize thermal stress in AuSn packaged high power diode lasers.We first introduce the mechanism of thermal stress,and build a thermal stress mechanical model based on Suhir's multilayer stack structure.Based on this,the influence of different materials on the thermal stress/strain characteristics of the device is studied through the finite element simulation method.Based on the simulation results,a “sandwich” package structure in which both the negative electrode and the secondary heatsink are copper diamond is proposed.Compared with the conventional hard solder packaged diode laser,the thermal stress in the chip layer can be reduced by 44%.Then the effect of anode structure and sub-heat sink size on the thermal stress/strain characteristics of AuSn packaged high power semiconductor lasers is investigated by finite element method.It is revealed that the cause of “Smile” is not the stress in the chip layer,but the copper heat sink bending.The simulation results show that the stress in the chip layer monotonously decreases with the increase of the thickness of the secondary heat sink,but the “Smile” value increases with the thickness of the secondary heat sink first and then decreases,and the turning point is 29% of the thickness of the copper heat sink.The simulation results are verified experimentally,and the luminescence spectra and "Smile" values are measured.The experimental results show that the stress of the chip layer decreases with the increase of the thickness of the secondary heat sink,and the “Smile” value increases with the thickness of the secondary heat sink.Finally,transient thermal stress/strain behavior of microchannel water-cooled lasers operating in a quasi-continuous state is studied.The "hysteresis effect" between the stress and the "Smile" under QCW mode is found.The change of the “Smile” is not synchronized with the stress,which increases with the thermal load applied in each pulse,and decreases after unloading.With the increase of pulse number,the stress value gradually decreases and finally stabilizes."Smile" peaks after three pulses of stress change and then decreases within three pulses.The "Smile" amplification decreases as the number of cycles increases,and finally stabilizes.Increasing the operating temperature of the coolant in the microchannel does not affect the heat dissipation capability of the device,but can reduce the stress and “Smile” in the chip.