Research On Microstructure Manufacturing By Femtosecond Laser

Femtosecond laser processing technology in complex internal structure of micro machine,micro system has obvious advantages,especially in the preparation of microfluidic chip with hollow three-dimensional structure has irreplaceable position.The femtosecond laser has the characteristics of high peak power,short pulse width,etc.,and can directly focus on the interior of the material to obtain a hollow microstructure during processing,which solves the problems of low processing efficiency,complicated processing technology,low sample success rate,and difficulty in preparation of the complexities of the conventional processing methods.So that femtosecond laser processing technology has been widely used.This article takes polymethyl methacrylate(PMMA)as the research object,and carries out numerical simulation and experimental research on femtosecond laser processing continuous hollow micro channels in its interior.The main contents and results are as follows:1.The temperature change of the material surface and the diffusion depth of 1/4,1/2,3/4,and 1 times after the femtosecond laser irradiation was studied.The temperature change of the material after femtosecond laser irradiation is not only related to the parameters of the laser,but also closely related to the material's absorption rate of the laser and the material's own characteristics.The results show that the thermal diffusion temperature firstly increases and then decreases,and the time at which the temperature rises to the highest point at each point below the surface lags behind.The maximum temperature that can be reached also decreases with depth.2.The processing mechanism of femtosecond lasers with different repetition frequencies was studied.The heat accumulation process in the process of femtosecond laser processing of transparent dielectric materials was studied,and the effects of different repetition frequencies on femtosecond laser processing were obtained.Studies have shown that when the number of femtosecond pulses is sufficient,there is no heat accumulation process regardless of the number of pulses emitted when the repetition frequency is low(1kHz);when the repetition frequency is increased(10kHz,100 kHz),the pulse interval time is smaller than the thermal diffusion time.Therefore,the heat generated by a single pulse will be accumulated,and the temperature will increase with the increase of the number of pulses;when the repetition frequency is higher(1MHz),the heat accumulation effect is more obvious,and the material temperature rise is faster.The maximum temperature that can be reached is also increasing.3.The relationship between different repetition frequencies and processing thresholds and processing efficiency was studied.Studies have shown that high repetition rate femtosecond lasers can make the threshold energy density decrease exponentially with increasing repetition frequency.The higher the repetition frequency,the lower the energy density required to reach the material destruction threshold.With the increase of repetition frequency,the shorter the time required for the material to reach the phase transition temperature,the higher the processing efficiency.4.The influence of different femtosecond laser processing parameters on the channel quality was studied.In the experiment,a bottom-up processing method was adopted,and a hollow three-dimensional microchannel was obtained by a laser direct writing method without any gas or liquid auxiliary conditions,and the laser power,processing speed,processing depth,and number of scans were specifically studied.Impact on the quality of the channel.Among them,the different laser power causes the cross-sectional circularity of the channel to change with it;with the increase of the scanning speed,the diameter of the channel increases first and then decreases;the laser power acting on the material increases with the increase of the processing depth.The laser deposition energy gradually decays with the depth,making the channel diameter decrease as the processing depth increases.When the femtosecond laser scans the channel several times,the focused laser will break down the gas in the hollow channel.The plasma is formed so that most of the energy of the laser is absorbed and the thermal energy is radiated to the surroundings.As a result,the microchannel structural destruction and decreases in photo permeability as the number of scans increases.5.By using Ti:sapphire femtosecond laser,a continuous hollow microchannel was prepared within the PMMA(polymethyl methacrylate)under the condition of no gas and liquid assisted,and the channel was proved to be smooth,transparent and hydrophilic through the injection experiment.