The laser microprobe is a useful tool for the analysis of specific sample areas of approximately 50 μ diameter. The auxiliary spark excitation of Brech and Cross increases spectrum intensity but results in a staining of metal sample surfaces in the area of analysis. Sample surface detail is thus obscured and selection of analysis sites for subsequent determinations is extremely difficult. The capability of the laser microprobe to selectively sample closely adjacent areas is thereby nullified. Deposition of the stain can be restricted to the dimensions of a central hole in a paper shield; however, placement of a shield is difficult even for plane surface samples.
H. N. Barton and J. Benallo, "Prevention of Laser Microprobe Staining of Analyzed Metals," Appl. Spectrosc. 24, 614-614 (1970)