Measurements And Analysis On The Mechanical Effect Of High-power Laser And Material Interaction

The mechanical effect, the ultrasonic effect, laser-generated bubble dynamics, the plasma emission spectrum and the laser-induced plasma shock wave during the high-power laser and matter interaction are systemically investigated by experiments.A novel optical system including a negative axial prism and a lens system is first designed to generate a non-diffraction beam with changeable spot size. The system acts as the focusing system to laser processing. It is proposed that the system has naught sensitivity to the position error of work in the range of non-diffraction, high adaptability to the smoothness of work and can satisfy various processing requirements by replacing the general spherical lens. The potential applications of the system are also proposed.The spatial shape and the transportation of ablated material during the process of laser ablates target material is studied by the mean of synchrostep shadowgraph. Light field force is first proposed. As a result, the speed distribution of ablated materials when they leaving target material surface is determined by the mechanism of ablation. The transportation behavior of ablated materials during the action of working laser is controlled by diffusion mechanism and light field force mechanism. The transportation behavior is determined by diffusion mechanism only after the action of laser.Based on the optical probe method, a system is designed to detect the plasma emission spectrum. The characteristic spectral line flight spectrum of Al atoms in excited state is investigated by experiment and the flight velocity is calculated.By the beam deflection technique based on surface shape change effect, a laser ultrasonic detector is developed. Lamb wave, surface wave and longitudinal wave aredetected.An instrument based on the beam deflection principle by refractive index effect is designed to detect the laser-induced plasma shock wave and the shock wave in transparent solid is first measured by beam deflection technique.Based on Hooke Law, a fiber transient mechanical sensor is first proposed. And the mechanical effect of target during the action of laser with various energy working on the target under water is investigated. The result shows that three transient pulse forces stress the target in turn. The generation and the impact force of cavitation liquid-jet depend on the bubble energy and non-dimension parameters. The efficiency of laserslotting in air and water is also investigated by experiment. The experimental results show that the efficiency in water is much higher than that in air. The reasons have been analyzed.According to the spherical cavitation bubble dynamic model considering the bubble energy dissipation, the impulsive motion of laser-generated bubble is calculated numerically. Then based on beam deflection by the variation of refractive index on the boundary surface between air and water, a system is designed to measure laser-generated bubble linear dimension geometric size. The maximum radius and the minimum radial distance of the bubbles near the target surface induced by laser with different pulse energy are investigated by this system. Furthermore, the results from numerical calculation and experiment have been matched.These research results will develop laser applications and corresponding detection techniques.