Study Of Spectral Characteristics And Precision On Laser Induced Breakdown Spectroscopy At Low Pressure

Laser-induced breakdown spectroscopy is widely used because of its advantages of remote detection and rapid analysis.However,there are still some shortcomings such as low sensitivity and poor precision.In order to explore a method to improve the sensitivity and precision of LIBS technique effectively,spectrum of induced alloy and soil plasma was collected with different pulse width lasers,different laser energies and different wavelengths under low pressure.By analyzing the signal-to-background ratio,linewidth,self-absorption phenomenon,relative standard deviation(RSD)and plasma characteristics,calibration curve,detection limit and so on,the spectral characteristics and precision of laser induced alloy and soil plasma impact were studied.On the one hand,the effects of low pressure on the spectral characteristics and precision of three pulse width laser were studied,by using Q-switched laser(8ns pulse width)and two long pulse width(500?s,80?s).The results showed that the appropriate low pressure atmosphere had obviously enhancement and improvement effect on the three kinds of pulse width laser-induced alloy plasma spectra.Compared with the normal pressure,the signal-to-background ratio of the plasma spectrum increased significantly under the appropriate low pressure,the width of spectral line was obviously reduced,the precision of spectral intensity was obviously increased,the self absorption phenomenon was obviously weakened,and the fitting accuracy of the calibration curve was improved.The effect of low pressure on improving and enhancing the spectrum of plasma induced by pulse width 8ns laser(532nm)was the most obvious:Compared with the standard atmospheric pressure,the signal-to-background ratio of the two kinds of energy(100mJ,40mJ)increased by 11.23 and 12.62 times respectively under the pressure of 5.0×10~4Pa;Spectral line width was 19%,20%of line width under atmospheric pressure;The RSD of spectral line intensity decreased by 53%and 77%respectively.Under the pressure of 8.0×10~4Pa,the fitting coefficient of calibration curve of Fe element in alloy with pulse width(8ns)laser(1064nm)reached 0.9692,which was improved by 15%.On the other hand,the effects of low pressure on spectral characteristics and precision of laser-induced soil plasma were studied by using two pulse width(8ns?500?s)laser(1064nm)as excitation light source.The results showed that the soil plasma spectrum induced by nanosecond laser could be significantly enhanced and improved under the appropriate low pressure.At the atmospheric pressure of 8.0×10~4Pa,the signal-to-background ratio of Pb induced by the nanosecond laser increased by 1.69times,the electron density increased by 4.2%and the precision of spectral line increased by 68%,the coefficient of fitting curve was increased,the detection limit decreased by40%,reaching 57.27mg/kg.The precision of soil plasma spectrum induced by long pulse width(500?s)laser had a significant improvement with the appropriate low pressure.The RSD of Ca in soil plasma spectrum reached the minimum at pressure of1.0×10~4Pa,decreasing by 66%.The RSD of three Cr plasma spectrum reached its minimums at pressure of 1.0×10~3Pa,decreasing by31%,31%and 32%respectively.The results showed that the laser-induced plasma spectroscopy could be significantly enhanced,the spectral quality could be improved significantly,the detection sensitivity of LIBS technology could be increased,the detection limits of elemental analysis could also be improved,the accuracy and precision of quantitative spectral analysis could be increased under the appropriate low pressure environment.