| Laser induced breakdown spectroscopy(LIBS)technology has advantages of rapidity analysis,multi-element analysis simultaneously and so on.Meanwhile,the LIBS technique still has vulnerabilities in such grounds as low precision of analysis and poor stability.Therefore,a globe effort was focused on how to improve the signal intensity and the accuracy of LIBS.To enhance the soil plasma and lead copper alloy plasma radiation intensity,laser-induced crater confinement method and self-hole confinement method are proposed in this paper.The main achievements are as the following:First,to investigate the enhancement effect of the laser-induced crater on radiation intensity of soil plasma,sequential laser pulses with different pulse durations(500μs,80μs and 8ns)were used to act on the same position of soil sample surface,respectively.(1)Laser-induced crater has best enhancement effect on plasma by 500μs laser pulses.The best enhancement times for emission intensities of PbⅠ405.78 nm and CrⅠ425.44 nm was about 4.74 and 14.87,meanwhile,the best enhancement times for spectral signal-to-background ratio was about 40.53 and 88.60.(2)The experimental results showed that when the numbers of sequential laser pulses(80μs)increase,the electron temperature is gradually increasing and reaching the strongest at 25 th laser pulse and then weakened.Compared with the plasma electron temperature at 5th laser pulse,the plasma electron temperature went up 171.23 K.The temperature of plasma increased and the distribution of temperature becomes uniform under crater confinement,which may be the reason for being able to effectively reduce the level of self-absorption effect of FeⅠ422.64 nm.(3)The 500μs laser pulse induced plasma has a longer overall life time(about 220~270μs),and the relative standard deviation was 2.21%~6.35% concluded by 8 times repeated experiments,which shows better stability of soil plasma by using the long-pulse laser.The detection limits of Pb and Cr calculated are 34.7mg/kg and 40.0mg/kg by using the internal standardization method.Second,self-hole confinement method was used to improve the spectral quality of laser-induced lead copper alloy sample.The conical holes were prefabricated by drilling on sample surface with variable diameters and heights.The enhancement effects will vary with different holes size and pulse duration.(1)Laser induced breakdown spectroscopy by 80μs laser pulse was used to generated plasma of HPb59-1 lead copper alloy sample in air.Overall,the best signal intensity can be obtained with a confinement self-hole with 3 mm diameter and 1.5 mm depth.The emission intensities of Cu Ⅰ 427.51 nm and Pb Ⅰ 405.78 nm with confinement were increased around 38.3% and 35.4% than without confinement;spectral signal-to-background ratio increased about 200.2% and 137.5%,respectively.(2)Laser induced breakdown spectroscopy by 8ns laser pulse was used to generated plasma of HPb59-1 lead copper alloy sample in air.Overall,the best signal intensity can be obtained with a confinement self-hole with 3 mm diameter and 2 mm depth.The emission intensities of Al Ⅰ 396.15 nm and Pb Ⅰ 405.78 nm with confinement were increased around 48.4% and 19.0% than without confinement;spectral signal-to-background ratio increased about 96.7% and 32.8%,respectively.At last,the enhancement effect of the self-spatial confinement on plasma radiation intensity by different pulse durations was investigated.The study results showed that increased interaction time between laser and sample contributed to the formation of “stable and lasted longer state plasma”,which can be acquires much better enhancement factor with self-spatial confinement.These self-spatial confinement is sample and easy to operate,and avoids the interference coming from the internal surface pollution of additional confinement setup of the experiment results,so they have a very broad space for application prospects. |
PDF Full Text Request