Population inversion in laser-produced plasmas stagnating on a radiative coolant of solid density.
Population inversion between the n = 3 and n = 2 levels of the Mg(+11) ion (the wavelength of the transition is 4.5 nm) was observed in a laser-produced plasma that was stagnated and rapidly cooled on a high-Z (Au) plate. The ratio of the population inversion was determined to be 1.4 - 1.8 when the opacity effect was taken into account. From the dependence of the inversion on the coolant's Z number, we found that the major cooling mechanism is radiative heat loss rather than thermal conduction to a cold inner part of the plate.
Kodama
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Mochizuki
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