Research on Reducing the Smile Effect of High Power Diode Laser Based on Optimizing the Reflow Curve of Indium Solder Welding

Due to the existence of a very large temperature gradient during the operation of the laser, thermal stress is generated due to the mismatch between the linear thermal expansion coefficients of the gallium arsenide substrate material and the heat sink material. Thermal stress causes displacement of each light-emitting unit in a diode laser perpendicular to the direction of light propagation, resulting in the light-emitting units not being in a straight line and causing them to bend, which is called the smile effect. The stress generated between diode lasers and heat sink materials can strain and introduce dislocations or defects in the active region, deteriorating the opto-electronic characteristics of the laser and reducing its lifespan. If the stress is further increased, it may even cause diode fracture and result in sudden failure of the laser. The Smile effect can have an adverse effect on beam alignment, causing the collimated beam to bend.