Spatial profile measurement of electron number densities and analyte line intensities in an inductively coupled plasma

A versatile instrument for spatial profile measurement has been developed and applied to the measurement of electron number densities and analyte emission intensities in an inductively coupled plasma (ICP). A precise Y-Z stage on which the ICP source was mounted was set on a rail-based optical bench. By translating the ICP source with a precision of ± 0.01 mm, the H_β Stark broadening and analyte line intensities were measured with the use of a silicon intensified target (SIT) and a photomultiplier (PMT). Micro-computer assisted data acquisition allowed it to measure a large number of emission profiles in a short period. The ease of acquisition enabled to build up complete contour maps of electron number densities, Ca neutral atom (Ca I) and Ca ion (Ca II) line intensities, and intensity ratios of the Ca II and Ca I lines. The maximum electron number density was 4 × 10¹⁵ cm^?3 occurring low in the plasma and 5 mm off axis. In a contour map of the electron number densities a hollow region was found low in the plasma, and the distribution pattern looked like a deep “trench”. Along the central channel of the ICP, the peak position of Ca II emission occurred higher than that of Ca I emission, and the spatial distribution of Ca II emission was wider and taller than that of Ca I emission. It has been verified that Ca I is emitted mainly at the region where the electron number density is less than 1 × 10¹⁴ cm^?3.