| A tunable, distributed-Bragg reflector diode laser operating in the 1083 nm region was used to measure several properties of the 23 S1 helium metastable in a simple dc and pulsed dc electrical discharge by absorption spectroscopy. Among these were the spatial variation of the metastable density, the dependence of the density on the applied current, the diffusion of the metastables in the discharge and the role of the higher-order diffusion terms in the observed density decay following pulsed excitation. The spatial distribution of the metastables was measured in a dc, wall-less, parallel-plate discharge with capped electrodes at 1, 3 and 5 Torr total gas pressure. The discharge was run in the normal (8 muA-cm-2) to abnormal (175 muA-cm-2) glow regimes. Abel inversion of the data provided a spatial distribution of the 23 S1 metastable density that shows a region that has near one-dimensional character. The axial metastable density ranged from 5 x 109--1.2 x 1011cm-3 for current densities of 8--175 muA-cm-2, respectively. Measurements of the decay of the metastables due to diffusion was carried out in a pulsed-dc, walled, parallel-plate discharge at 2 and 5 Torr total gas pressure. The measured value derived from this work was 471 +/- 22cm2-sec-1 by fitting to the long-time decay data. Also found in the pulsed discharge was evidence of higher-order diffusion modes. An analytical model of the higher-order modes was used to quantify their effects. To the best of our knowledge, this is the first reported measurement of these modes. The diffusion coefficient measured in this way was found to be 471 +/- 15 cm2-sec-1. |
