Abstract

The gain coefficient depends on the differential oscillator strength at the peak of the lasing transition. Thus it depends directly on the spectral width of the transition. We discuss below the collisional broadening of hydrogenic transitions in plasmas. In a plasma, atomic and ionic transitions are broadened by collisions with electrons and ions. This effect tends to be particularly large for hydrogenic radiators, which experience a first-order Stark effect. In line-broadening, a hydrogenic radiator is one in which a level in the transition is quasi-degenerate with another level to which it is dipole-coupled, i.e., their energy separation is smaller than their homogeneous width. The Balmer-alpha (n = 3 → 2) transition of C⁵⁺ has been used by the Princeton x-ray laser group to achieve an enhancement of stimulated-to-spontaneous emission by a factor of ~100.¹ We have performed detailed calculations of the collisional broadening of this line and the Balmer-beta (n = 4 → 2) transition over a wide range of plasma conditions. The calculations include dynamic many-body ion collisions, which are the dominant broadening mechanism. For plasma conditions of current x-ray laser experiments,¹ the collisional width of Balmer-alpha is comparable with the Doppler width, and at higher densities it dominates.

© 1986 Optical Society of America