Radiation efficiency of Hg-Ar surface wave discharges

The radiation efficiency of Hg-Ar low-pressure surface wave (SW) discharges has been measured in a broad range of Ar pressures (40 mTorr-12 Torr), Hg partial pressures ( approximately 1-100mTorr) and excitation frequencies (200-1000 MHz). Gas filling and tube geometry (26 mm outer diameter) were chosen to allow a comparison with the conventionally excited Hg-Ar low-pressure discharge used for general lighting purposes in the well known fluorescent lamp. The study focuses on the quantitative measurement of the two Hg UV resonance lines at 185 and 254 nm. The RF power input into the plasma column extending outside the surfatron coupling structure was determined quantitatively. This was done by measuring the power dissipated in the part of the plasma column hidden within the surfatron by a calorimetric method. The measurements of the Hg UV radiation efficiency are supplemented by radial scan experiments of a visible Hg line, and by the study of phenomena occurring at a higher power density such as saturation and standing wave formation.