The Study Of Millisecond Laser Interaction With Solid Target Induced Gasification And Molten Ejection

The interactions between laser and matters were foundations of applying laser to industry and military.In this paper,the gasification phenomenon of solid target by millisecond laser with a wavelength of 1064nm,the effect of laser drilling by gasification,and the process of molten liquid ejection were studied theoretically and experimentally.It was observed that gasification phenomenon and molten liquid ejection at both sides of silicon plate when millisecond laser irradiates to silicon.The sequence interference diagrams of the interaction between millisecond laser and silicon plate were obtained by Mach-Zehnder interferometer experimentally.The speed of the vapor was calculated by the interference fringes position and the time interval between the two interference diagrams.And then the vapor pressure at silicon plate surface was calculated in theory according to the Rankine-Hugoniot equation,the gas dynamics equation and the conservation equations(mass,momentum,and energy)in Knudsen layer by using the vapor speed as the initial condition.The Clapyron-Clausius equation was used to calculate the temperature at the silicon plate surface,and it was found that the temperature was above the boiling point of silicon to product the so-called "superheated liquid" in the irradiation region of laser.The finite element method(FEM)model of the interaction between the millisecond laser and the silicon plate was established.The enthalpy method was applied to demonstrate the melt phase transition process and the heat flow equation was used to calculate the energy loss of laser due to gasification.The process of interaction between silicon target and millisecond laser was simulated while the laser power density was 5×106W/cm2.The temperature field distributions,the gasification velocities and gasification depths were obtained by laser with different pulse width.The simulation results were compared with the drilling depth obtained in experiment,and it was concluded that the main mechanism of removing the material was molten liquid ejection.The performance ratios of punching under different laser energy densities were calculated based on the depths of the hole which were obtained by the interactions between millisecond laser and aluminum slab in experiment.The Quasi-steady state heat conduction equation was modified by adding the affect term of gasification,and the surface temperature of the aluminum slab was calculated theoretically,and the laser energies which consumed by gasification were obtained by the different energy densities during the drilling process.Results showed that the laser energies consumed by the gasification were increased with the incident laser energy density when the pulse widths were same,and the laser energies consumed by the gasification were decreased with the incident laser pulse width when the energy densities were same.The sequence shading photos of the interaction between the millisecond laser and the solid targets(silicon and aluminum)were recorded by high speed CCD.It was found that gasification and molten liquid ejection could be induced by millisecond laser in both solid targets.However,the gasification intensity,the morphology and luminescence of the molten liquid ejection were different because the effect of superheated boiling could be induced by millisecond laser in silicon target.The drilling depths of solid targets with millisecond laser which had same energy density were calculated.The theortical result showed that the silicon was more efficient than aluminium in laser drilling,it was agreed with experimental result.The research consequences may provide theoretical and experimental fundaments to the further study of the gasification and the molten metal ejection induced by millisecond laser,and promote the application of millisecond laser in industrial processing,manufacturing,military,etc.