Temperature Tracing Of The Pulsed Laser Ablation Zones On Solid Surface

With the maturation of high-power laser technology,laser ablation and heat treatment of materials,as a new material processing technology,the physics and materials science process has become a research hotspot in many disciplines.Among them,the ablation plasma generated on the surface of high-power laser irradiated materials and the corresponding heat-affected zone are the frontier research directions in plasma physics and technology.The heating of material surfaces by high-power pulsed lasers is the primary physical process of laser irradiation.The process of converting laser energy into thermal energy is still worth studying.The energy of short-pulsed lasers（mainly consisting of nanosecond pulses,picosecond pulses,and femtosecond pulses）is focused by the lens on a small area of the solid surface,resulting in an extremely high energy density field(10^12-15 W/m²)near the solid surface.It is generally believed that solid free electrons and bound electrons in the light field transform the laser energy into electron kinetic energy quickly and efficiently through the inverse toughening process,and then turn into heat energy through the relaxation process between the electron and the crystal lattice.The deposition of laser energy causes the surface temperature of the material to swell so that the surface of the solid rapidly liquefies,vaporizes,and thermally ionizes to form a high-density thermal plasma composed of electrons,ions,and neutral atoms,and diffuses outward from the surface of the substrate to form an ablation plasma.At present,the main research direction for laser ablation plasma is the modification of the material surface by the thermal action of the laser and the use of ablative plasma,including material processing such as laser welding,cutting,and quenching,and plasma-based thin film deposition technology.（PLD）and so on.However,as a basic physics problem,the rapid heating and temperature field distribution and evolution induced by pulsed laser irradiation on solid surfaces have not been given enough attention and detailed research.The reason for this is that there is no effective tracking technique for the temperature and evolution of the laser ablation zone.In this paper,after analyzing the main characteristics of the temperature parameters generated by pulsed laser irradiation on solid surfaces,a temperature tracking method based on infrared radiation is proposed,and several representative solid materials are selected to rapidly accelerate the surface temperature of the laser ablation zone.Changes were tracked and explored to study the applicability of the temperature tracking method.Firstly,the distribution of pulsed laser energy when irradiating solid surface was experimentally studied.Especially by measuring,calculating and analyzing the radiation intensity of pulsed laser ablation plasma,the distribution ratio of laser energy in plasma generation and radiation and its influencing factors are analyzed.The plasma radiant intensity of different materials and the effect of laser energy on ablation radiation were compared and studied.Experiments have found that the intensity of plasma radiation is positively correlated with the atomic number and laser energy of a solid target.Through the material’s laser reflection performance test,it was found that the material with the same surface finish has basically the same reflection characteristics as the laser.In the process of pulsed lasers and materials,their energy is mainly used to ablate material.The study of pulsed plasma radiation intensity and reflection characteristics of solid surface shows that the lower the atomic number of the target material when the pulsed laser heats different materials,the greater conversion of laser energy into material thermal energy.The pulsed output of ablative plasma is also an important indicator that can reflect the laser energy consumption.This paper analyzes the characteristics of the diffusion behavior of pulsed ablation plasmas.It is believed that this plasma diffusion is an atypical bipolar diffusion in which the rapid diffusion of electrons can form a separate diffusion current pulse.Based on this,a circuit is designed.Based on the principle of circuit measurement,an analysis method was developed to evaluate the pulsed laser ablation plasma production,and the main factors affecting the pulsed laser plasma production were analyzed and compared.In order to carry out follow-up measurement of rapidly evolving temperature in the ablation zone,based on the characteristics of high temperature in the ablation zone,based on the principle of infrared radiation temperature measurement,a two-color infrared temperature measurement program was designed based on the estimation of the most probable heat radiation band.The radiation temperature measurement system is composed of a filter system and an infrared sensor.After calibration of the temperature measurement system,the system was used to track and measure the temperature evolution of the material surface caused by pulsed laser ablation.Studies have shown that pulsed laser heating of materials is a rapid process,the surface temperature microsecond time scale can rise to several thousand degrees of temperature peaks,the temperature peak lags behind the peak time of laser energy,after the peak temperature is relatively late,sustainable for nearly a hundred microseconds.By comparing the evolution history of ablation temperatures of metals and non-metals,it is shown that the metal properties of ablated materials have a great influence on the temperature behavior.