Argon-hydrogen-strontium discharge light source

Abstract

We report the observation of vacuum ultraviolet (VUV) emission in the region 40-560 nm from incandescently heated atomic hydrogen and atomized strontium that increased with argon. The observed plasma formed at low temperatures (e.g., /spl ap/10/sup 3/ K) from atomic hydrogen generated at a tungsten filament that heated a titanium dissociator and atomic strontium which was vaporized from the metal by heating. The emission intensity of the plasma generated by atomic strontium increased significantly with the introduction of argon gas only when Ar/sup +/ emission was observed. No emission was observed with hydrogen when sodium, magnesium, or barium replaced strontium or with hydrogen, hydrogen-argon mixtures, or strontium alone. The width of the 656.3-nm Balmer /spl alpha/ line emitted from gas discharge plasmas of hydrogen and mixtures of hydrogen with magnesium, strontium, and noble gases was measured. Significant line broadening corresponding to an average hydrogen atom temperature of 23-45 eV was observed for strontium-hydrogen, helium-hydrogen, argon-hydrogen, strontium-helium-hydrogen, and strontium-argon-hydrogen plasmas; whereas, pure hydrogen, krypton-hydrogen, xenon-hydrogen and magnesium-hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of /spl ap/4 eV. The power balance of a gas cell having vaporized strontium and atomized hydrogen from pure hydrogen or argon-hydrogen mixture (77/23%) was measured by integrating the total light output corrected for spectrometer system response and energy over the visible range. Hydrogen control cell experiments were identical except that sodium, magnesium, or barium replaced strontium. In the case of hydrogen-sodium, hydrogen-magnesium, and hydrogen-barium mixtures, 4000, 7000, and 6500 times the power of the hydrogen-strontium mixture was required, respectively, in order to achieve that same optically measured light output power. With the addition of argon to the hydrogen-strontium plasma, the power required to achieve that same optically measured light output power was reduced by a factor of about two. The power required to maintain a plasma of equivalent optical brightness with strontium atoms present was 8600 and 6300 times less than that required for argon-hydrogen and argon control, respectively. A plasma formed at a cell voltage of about 250 V for hydrogen alone and sodium-hydrogen mixtures, 140-150 V for hydrogen-magnesium and hydrogen-barium mixtures, 224 V for an argon-hydrogen mixture, and 190 V for argon alone; whereas, a plasma formed for hydrogen-strontium mixtures and argon-hydrogen-strontium mixtures at extremely low voltages of about 2 and 6.6 V, respectively.