Study Of The Influence Of Temperature On “Smile” In High Power Diode Laser Arrays

High power diode lasers with numerous features,such as small size,light weight,high wall-plug efficiency,high reliability and etc.,have become promising products as a credible photon source for wide applications in industry,military,entertainment display,material processing,medical and cosmetic and other fields.With the continuous advancement of chip technology and driven by more applications requiring lower cost and longer lifetime,there emerges new technology development trend of high power diode lasers,namely,output power scaling,high brightness,indium free bar bonding,narrow spectrum,and low “smile”.“Smile” effect in high power diode laser arrays,or called near field non-linearity,refers to the bending of output light in fast axis direction.During die/bar bonding process,thermal stress induced by the coefficients of thermal expansion(CTE)mismatch between the laser bar and mounting heatsink is the primary source of “smile”.“Smile” effect poses significant challenges in beam collimating,shaping and optical coupling,and has become one of the major bottlenecks in wider applications of high power diode lasers.As thus,it is rather important to study the influence factors of “smile”.Up to now,the relevant research of “smile” mainly includes how to measure “smile” accurately and reduce it,the effect of “smile” on beam quality,the general mechanism of “smile” and etc.Whereas,the influence of temperature on “smile” is still not clear yet.This thesis mainly studies the influence of temperature on “smile” in high power diode laser arrays.For the reason that “smile” is primarily related with the thermal stress induced during packaging process and operation,it is necessary to study the thermal stress in the laser bar when studying the influence of temperature on “smile”.For this subject,the main job of this thesis includes:(1)By experiment test,the influences of temperature on the output performances of high power diode laser arrays are studies comprehensively and systematically,such as threshold,slope efficiency,output power,spectrum,wavelength,etc.(2)By finite element method(FEM),the thermal stress and displacement in the diode laser bar induced during packaging process and operation are simulated respectively.By numerical modeling,the distribution curves of thermal stress and displacement in the laser bar after packaging are achieved.In addition,the distribution curves of thermal stress and displacement in the laser bar operating under different heatsink temperatures are calculated,and thus the variation of thermal stress and displacement with the increasing heatsink temperature are obtained.The simulation results provide theoretical guidance for explaining experiment results.(3)In the experiment,conduction-cooled indium solder bonded 60 W 808 nm diode laser arrays are prepared.In pulsed condition 100 ?s at 100 Hz(duty cycle1%),the spatial spectrum of the products are tested separately.According to the spatial spectrum distribution,the thermal stress distribution across the laser bar is predicted,which is accordance with the simulation results.In practice,temperature at the bottom of heatsink is controlled by thermoelectric cooler(TEC).By changing the temperature of TEC,“smile” of the experimental products are measured in the temperature range of 20 °C to 65 °C.Combined the numerical simulation results with experiment results,the rules and mechanism of “smile” varying with the temperature are analyzed.(4)By experimental test,the influence of packaging technology on thermal stress across the laser bar and “smile” is investigated.Furthermore,some strategies are put forward to control thermal stress and achieve low “smile”,which provide guidance for improving the performance of high power diode lasers.