Characterization and application of a narrow band Lyman-alpha light source

The Lyman-α emission line shape of dissociated hydrogen atoms in a high pressure Ne environment is studied. Vacuum ultra-violet absorption spectroscopy using the emitted Lyman-α radiation allows for the measurement of trace concentrations of ground state deuterium atoms in a hydrogen environment.; Near resonant energy transfer from Ne excimer molecules to dissociative excitation of hydrogen molecules is utilized to generate excited state, n = 2, hydrogen atoms. Plasmas are generated in systems containing 250 to 600 [Torr] Ne with an admixture of 0.10 [Torr] H₂ using a 12 [keV] electron beam. Experimental data on the upper states of the Lyman-α transition is collected via a new application of the dc opto-galvanic effect in low temperature, high pressure plasmas. A model line shape containing a non-thermal equilibrium atomic velocity distribution and pressure effects is developed. Excess energy from second continuum Ne excimers is imparted primarily to the dissociated hydrogen atoms giving the excited atoms a large excess velocity component. The dominant pressure effect is van der Waals interactions between the excited hydrogen atoms and ground state Ne atoms. Adjustable model parameters are optimized to fit the experimental data. Pressure broadening is observed to be non-linear, with the largest deviations from the predicted widths occurring at the lowest Ne pressures, while pressure shifting is linear in Ne pressure. The higher pressure data approaches the theoretical ratio between pressure width and shift for van der Waals interactions. Smooth extrapolation of the fit parameters, toward the theoretical limit, allows for the calculation of a Lyman-α emission line shape at a Ne pressure of 760 [Torr].; Hydrogen is replaced with deuterium in the system to provide a light source for absorption spectroscopy of ground state deuterium atoms. A discharge tube is filled to 3.5 [Torr] with H₂ after introduction of a small admixture of D₂. A discharge is ignited and absorption of the deuterium Lyman-α radiation is measured at various D₂ partial pressures. The system clearly demonstrates sensitivity to variation in the D₂ partial pressure in a constant pressure H₂ environment. Projected sensitivity for this simple, inexpensive measurement system is approximately 180 delta around mural abundance.