Population inversion of Alxi in a laser plasma

It was established experimentally that the population of the Al_xi levels with n = 4 and 5 became inverted relative to the n = 3 level in a recombining laser plasma at distances of ~ 50–500 μ from the target surface. The relative populations of the levels were determined from the intensities of the lines in the series of the 2p–nd transitions in Al_xi allowing for the self-absorption. The ratio of the populations of the 4d and 3d levels in the dense zone of the plasma with N_e10²⁰ cm^–3 was ~1.8, which corresponded to a population inversion of ΔN~10¹⁵ cm^–3. In this zone the gain for the 3d–4f line of Al_xi (λ ≈ 154Å) was estimated to be 0.1 cm^–1. An investigation was made of the recombination of He-like Al_xii ions and the electron temperature was determined as a function of the distance from the target surface, environment. Measurements indicate that the major impediment to the removal of this heat is the weak carrier-lattice interaction, (ii) Data are provided which allow an estimate to be made of the importance of current noise in the use of carbon composition resistance thermometers, (iii) For at least some carbon composition resistance thermometers, the temperature dependence of the resistance is given by the relation R = R₀exp(AT^–1/4) below ≈ 0.3 K.