Electron-density scaling of conversion efficiency of laser energy into L-shell X-rays - Fournier, K; Constantin, C; Back, C; Suter, L; Chung, H; Miller, M; Froula, D; Gregori, G; Glenzer, S; Dewald, E; Landen, O (JOURNAL OF QUANTITATIVE SPECTROSCOPY and RADIATIVE TRANSFER, 2006)