Two-photon laser induced fluorescence and amplified spontaneous emission atom concentration measurements in O2 and H2 discharges

Multiphoton laser-induced fluorescence (LIF) and amplified spontaneous emission (ASE) are used to detect ground-state atoms in oxygen and hydrogen glow discharge plasmas. Experimental results and modeling are analyzed to establish the validity criteria for the use of LIF and ASE as diagnostic probes in the measurements of ground-state atom concentrations. An absolute calibration of the LIF signals is obtained by vacuum ultraviolet absorption experiments, either on the 130 nm resonant line of the atomic oxygen, or the 125 nm resonant line of the hydrogen atom. Under typical operating conditions of dc glow discharges, that is, for gas pressure between 0.5 and 5.0 Torr and discharge current from 1 to 50 mA, the densities of the atomic species are measured in the range 1013 cm−3–1015 cm−3. Under the same conditions the hydrogen atom temperature varies from (336±43) K to (1580±90) K.