Line profiles of Ni-like collisional XUV laser amplifiers: Particle correlation effects

Abstract

We present a detailed analysis of the different processes that contribute to the spectral broadening of the Ni-like Ag XUV laser line, including the effects of particle correlations on the broadening due to the radiator motion (Doppler broadening). We consider two different regimes of collisional excitation pumping: the transient pumping for which ionic temperature is relatively low (the plasma coupling parameter is large), and the quasi steady-state pumping for which the ionic temperature is higher and the plasma coupling parameter is of the order of 1. In both cases, by using classical molecular dynamics simulation techniques, we show that ionic correlations actually modify the radiatormotion broadened profiles and cannot be neglected in evaluating the Doppler effect. The subsequent narrowing of the Doppler component is small compared to the overall linewidth, which includes the effect of homogeneous collisional broadening. However ionic correlations will also affect the amplification of the lasing line, especially when the laser enters the saturation regime, because it will lead to an homogenization of the spectral profile.

Inversion density threshold for Rabi oscillations and modified small-signal gain in extreme-ultraviolet lasers

“…Equations (2) and (3) assume the same value of the transition frequency ω for all ions, or in other words, inhomogeneous broadening can be neglected (see [11,12] for a discussion of that point). The relevant atomic quantities, namely, γ, the pumping population fluxes R i , and excitation/decay rates γ ij are obtained from an outside collisional-radiative package.…”

“…As mentioned previously, they rely on different pumping techniques, leading to significantly different conditions in the lasing region and gain values achieved. Relevant parameters for each case, as drawn from the literature [2,10,12,[15][16][17][18]; the calculated threshold gain G ad and the equivalent adiabatic gain G ad recovered from the measured value G are gathered in Table 1. The G gain values shown are derived from experimental measurements of the exponential increase of the XUV laser intensity with the plasma amplifier length.…”