Study Of High-resolution LIBS System Based On Far-field Optics

Laser probe, namely laser-induced breakdown spectroscopy (LIBS), is a vital methodof elements detection. Currently, its low resolution, which is limited by optical diffractionlimit, makes laser probe have no advantages in comparison with the electron probe orenergy spectrum analyzer. In order to further improve the resolution, the laser probeoptical system based on far-field optical technology, including coaxial laser focusing,coaxial monitoring and illumination, coaxial indicator and spectral collecting, wasdesigned and optimized. The results are shown as bellows:The ultimate resolution of the laser probe based on far-field optics was studiedsystematically. Using the reflex objective (N.A=0.4) to focus the incident532nm laserbeam, under the condition of appropriate energy, the resolution of2.26μm and1.87μm onpure Al and Fe samples surface was obtained, respectively. Under this system, theeffective Al and Fe atomic spectrum can be acquired with intensity three times of thebackground noise, respectively.A set of coaxial monitoring system with coaxial illumination was designed andrealized, which the monitoring area is286215μm2, and the field magnification is24.7.The results showed that, the coaxial illumination system can improve the sharpness andidentification of the graphics with resolution not less than228lines per millimeter.A coaxial spectral collection system with indicator was invented, which can maintainthe alignment error within10μm between the plasma and the coaxial collection system. Inthe coaxial monitoring area and combining with an X-Y axis scanning system, a spectralmatrix with63points on the plasma surface can be acquired, whcih the images of plasmaspatial resolution could be obtained as well.Finally, the scheme of a high resolution LIBS system based on far-field optics wasaccomplished. The laser probe has the resolution below3μm with the functions of coaxialmonitoring and spectral coaxial collection, as well as the spectrum within micro area ofthe plasma can be acquired accurately. These results mentioned above would prompt LIBSto industrial application.