Absorption measurements on a low-pressure, inductively coupled argon-mercury discharge for lighting purposes: 1. The gas temperature and argon metastable states density

The gas temperature and the absolute density of the argon 4S 3P2 level in an 80 W inductively coupled low-pressure argon - mercury plasma are determined for three different argon filling pressures. This is done by measuring the line profile of the 4S 3P2 -> 4P 3D3 transition in argon, using a tuneable laser diode. Since the width of this argon line is found to depend on the kinetic heavy particle temperature only, radial profiles of the gas temperature can be obtained. It turns out that the maximum gas temperature in this discharge (550 - 810 K depending on the filling pressure) is significantly higher than that in a common tubular fluorescent lamp. From the radial distribution of the argon 4s density it can be concluded that the maxima of the electron density and of the electron temperature are situated close to the coil. It is also found that the position of these maxima depends on the argon filling pressure.