Study on the coupling characteristics of water-jet guided high-power laser based on negative defocus coupling alignment method

Water-jet guided laser machining is an innovative hybrid laser processing technique known for its minimal heat-affected zone, precise grooving, and high depth-to-width ratio. A critical factor in achieving high machining quality is the precise alignment of the laser and water-jet, especially in high-power applications where maintaining stable coupling and ensuring thermal safety present significant challenges. A negative defocus coupling method is proposed to enhance the laser-water-jet coupling tolerance and improve system stability. Using ray tracing simulations and experiments, the laser spot distribution within the water-jet under different defocusing conditions was analyzed. The results demonstrate that negative defocus coupling effectively reduces laser power density at the optical window and nozzle, protecting them from thermal damage. Additionally, negative defocus coupling improves laser and water-jet coupling efficiency and increases the system’s tolerance to higher laser power levels. These findings validate the feasibility and benefits of negative defocus coupling, offering a reliable solution for efficient, water-jet guided high-power laser machining with enhanced component protection and machining quality.