Doppler-free measurement of the calcium 4 s21S0-4 s4 p1P1 transition at 422.673 nm by degenerate four-wave mixing in a demountable cathode discharge atomizer

Abstract

Doppler-free laser spectroscopic measurement of the calcium 4 s 2 1 S 0-4 s4 p 1 P 1 transition at 422.673 nm by degenerate four-wave mixing is reported using an excimer-pumped dye laser as the excitation light source. The use of a demountable hollow cathode discharge cell operated at relatively low pressure levels (1–10 torr) minimizes Lorentzian (pressure) broadening and hence further improves the Doppler-free signal. The analyte (as small as 0.32 μg calcium) is deposited inside the cylindrical microcathode where the three input laser beams are directed. Important characteristic properties of degenerate four-wave mixing are discussed, including cubic energy dependence, quadratic concentration dependence, and dependence of signal on different discharge gases, buffer gas pressure and discharge current.