The laser microprobe as an instrument for sampling and generation of optical emission spectra for elemental analysis presents special noise problems. The microprobe vaporizes a sample, usually 10<sup>−12</sup>-10<sup>−6</sup> g range, depending on the laser energy employed, and leaves a microscopic crater. While the duration of a <i>Q</i>-spoiled laser beam is usually less than 100 nsec and most of the optical noise occurs during this interval, the optically emitting plasma may persist for microseconds. Therefore such commonly used noise reduction techniques as signal averaging, tuned frequency detection, and derivative spectroscopy are not applicable. Since all photons of a given wavelength have the same energy, energy differentiation techniques cannot be employed.
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