Electron beam energy deposition and VUV efficiency measurements in rare gases

Reliable techniques for the determination of the energy/cm³ deposited by an e-beam into a gas as well as the energy/cm³ radiated have been developed in order to obtain dependable data on the VUV fluorescence efficiency for rare gas excimers. Spatially resolved total stopping calorimetry in the gas at the cell foil was used to characterize the energy distribution in the e-beam (∼ 200 kV, few Amp/cm², ∼ 1 µsec) transmitted by a “hibachi”-supported 1-mil Ti foil. By using these data, suitable input for a 3-D Monte Carlo electron transport code (SANDYL) was generated. The spatial distribution of energy deposition in the gas was then calculated taking into account multiple scattering and cell geometry. The validity of the SANDYL technique is substantiated by excellent agreement between the measured and calculated energy flux on a vertical stack of five fast risetime (< 1 msec) calorimeters at several depth positions [0 < Z(cm) < 15] in the gas [1 < P(atm) < 3]. Calibrated optical components were used in a well defined geometry that permitted calculation of the effective radiating volume observed. By using the above techniques, high absolute efficiencies (10–30%) have been measured for rare gas VUV continua emission which can photolytically produce group VI metastables [e.g., 0(¹S),S(¹S)] of interest as fusion visible-laser candidates.