Study On Energy Model For The Interaction Between Femtosecond Laser And Material And Processing Morphology

Compared with traditional continuous laser,femtosecond laser has its unique advantages in micromachining because of its ultrashort pulse duration,ultrahigh peak power and extremely wide frequency range.Femtosecond laser can input its total energy into the object region,which can avoid the effects of the linear absorption,energy transfer and diffusion during femtosecond laser process.The ultrafast energy input changes the interaction process of femtosecond laser and material compared with traditional laser.Thus,femtosecond laser micromachining has quite high precision and resolution.In this study,the scanning electron microscope images of the processed region by femtosecond laser were obtained.By analyzing the morphology and size of the processed region,the effects of femtosecond laser parameters and energy input on the morphology and size of processed region were discussed.In this study,the way and amount of femtosecond laser energy which is absorbed by the substrate is studied.The absorbed energy model of any point in the processed region is deduced.In addition,by calculating the absorbed energy distribution which is perpendicular to the scanning direction of femtosecond laser,the method of predicting the width of the ablated channel and the method of calculating the ablated threshold are delivered.The calculated threshold by this model approximate the threshold which is calculated by traditional method and the error could be ignored.On the other hand,the predicted width of the ablated channel approximate the experimental result.And the error could be ignored too.The method to calculate the absorbed energy of femtosecond laser,the width of ablated channel and the ablated threshold is suitable for any material.When the processed region is only melted,the process of femtosecond laser can be regard as autogenous welding.The welds are smooth at small scanning speeds of femtosecond laser.In order to avoid the long crack in the weld process,the weld processed by femtosecond laser must be added shielding gas or carried out in vacuum,which is different from the ablated processed.The input energy of femtosecond laser can be increased by increasing the mean power and decreasing the scanning speed of femtosecond laser.The size of the welds will be increased accordingly.However,the input energy must be less than the ablation threshold of materials.The effect of femtosecond laser mean power on the size of the weld is larger than that of femtosecond laser scanning speed.The cross sectional area of stainless steel weld has a good linear relationship with the scanning speed of femtosecond laser with a certain range of scanning speed,when the mean power is constant.The slope of the regression line is negative and the larger of femtosecond laser mean power the larger of the absolute value of the slope.The linear relationship can be used to predict the size of the weld cross section.There is a small component transition zone at the boundary between the weld and the base material.