Study of elementary processes for the lower laser level of the copper vapor laser

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In the powerful and highly efficient copper vapor laser, the lower levels of the laser transitions are metastable states. The detailed knowledge of their relaxation processes is therefore of practical importance to improve the laser performance. In this study the diffusion and electron-collisional de-excitation processes for the metastable copper atoms were investigated, which determine the lifetime of the metastable atoms in the discharge.Copper vapor was produced in a discharge tube with a copper hollow cathode by cathodic sputtering. The diffusion coefficients for metastable copper atoms in Ne and Ar were determined from their density decay in the afterglow measured by using laser absorption spectroscopy. The diffusion coefficients for ground-state copper atoms in He, Ne, Ar were also determined by using absorption spectroscopy with a copper hollow cathode lamp used as a light source. It was found that the diffusion coefficients for the metastable and the ground-state copper atoms w … More ere essentially of the same magnitude, contrary to a reported result.A new method was developed to determine the lifetimes of metastable atoms in a steady-state discharge. The method is based on saturated absorption spectroscopy, in which a strong pump laser beam excites metastable atoms and a weak probe beam measures the reduction of their population due to the pump beam ; the analysis of the results with the aid of rate equations enables one to determine the lifetime of the metastable atoms. As was demonstated by experiments, the long lifetime of metastable atoms prevents the pump beam from causing hole burning in the velocity distribution of the atoms through collisional mixing of the populations with different velocities ; this allows one to use the rate-equation analysis. The obtained lifetime of the metastable copper atoms decreased with increasing discharge current. This indicates that their lifetime is mainly determined by electron-collisional destruction rather than by diffusion. This method of determining metastable-atom lifetime can be combined with electron density and temperature measurements to yield de-excitation rate constant for metastable atoms. Less