Microscopic Analysis Of Elements With Nanometer Scale Spatial Resolution By LA-LIBS

In laser-induced breakdown spectroscopy(LIBS)technique,the signal processing equipment,such as amplifier,is very easy to work out of the linear domain due to the inevitable and strong bremsstrahlung emission of the electrons,which severely limits the spectral analysis sensitivity and the lateral spatial resolution improvement of LIBS.Therefore,it is necessary to do something to eliminate this effect.Since the time duration of the background is much shorter than those of the atomic emissions in the plasma,time-resolved signal detection techniques can be used to enhance the signal-to-back ratio of the detection system and to improve the analytical sensitivity as well as spatial resolution.On the base of past research results of our laboratory,an orthogonal double-pulse dual-wavelength laser ablation(LA)LIBS experimental setup was built based on single Q-switched Nd:YAG laser.High sensitivity elements analysis of the samples with high spatial resolution analysis can be realized after using a gated amplifier circuit.Experimentally,the atomic emission was first selected by a monochromator and detected by a photomultiplier tube.The bremsstrahlung emission background of the electrons was then eliminated by a gated amplifier.The noise was suppressed by optimizing the circuit system.The signal analysis was successively carried out by using this gated amplifier followed with another commercial amplifier.A gated circuit was applied in LA-LIBS signal detection system experimentally.The working principle of this gated amplifier circuit and the design of the switching circuit were discussed.Then a switch circuit was designed with an N-channel MOS tube,the possibility of rejecting white light background interference with time-resolved signal detection technique was discussed.Finally,a gated amplifier circuit was designed by using an operational amplifier with disabled function.The weak atomic radiation signal from the plasma was selective amplified by setting appropriate trigger level and the signal to background ratio has been successfully improved in LIBS.While analyzing the major aluminum and minor copper in aluminum standard samples,the lateral spatial resolutions had reached ~ 0.90 μm and ~ 1.2 μm,respectively.These were much better than ~ 2.9 μm and ~ 6.2 μm results obtained only using normal photomultiplier tube followed with a commercial amplifier.The elements microanalysis under nanometer scale spatial resolution was successfully realized with low-cost orthogonal dual-pulse laser-ablation laser-induced breakdown spectroscopy.