Number of AXE photons at the end of the medium (<em>z</em> = 5 mm) for the pre-aligned 〈cos <sup>2</sup>ζ〉 = 0.64 (a) and isotropic (b) CO ensembles as a function of the XFEL pump pulse duration τ Victor Kimberg Song Bin Zhang Nina Rohringer 10.6084/m9.figshare.1012423.v1 https://iop.figshare.com/articles/figure/_Number_of_AXE_photons_at_the_end_of_the_medium_em_z_em_5_mm_for_the_pre_aligned_cos_sup_2_sup__0_64/1012423 <p><strong>Figure 8.</strong> Number of AXE photons at the end of the medium (<em>z</em> = 5 mm) for the pre-aligned 〈cos <sup>2</sup>ζ〉 = 0.64 (a) and isotropic (b) CO ensembles as a function of the XFEL pump pulse duration τ. The peak pump intensity 4.5 <b>×</b> 10<sup>16</sup> W cm<sup>−2</sup> is the same for all calculations. The results are compared for the C 1s<sup>−1</sup> → <em>X</em> (\full) and O 1s<sup>−1</sup> → <em>B</em> (−− − −) transitions.</p> <p><strong>Abstract</strong></p> <p>We theoretically demonstrate the feasibility of x-ray lasing in the CO molecule by the core ionization of the C K- and O K-shell by x-ray free-electron laser sources. Our numerical simulations are based on the solution of generalized Maxwell–Bloch equations, accounting for the electronic and nuclear degrees of freedom. The amplified x-ray emission pulses have an extremely narrow linewidth of about 0.1 eV and a pulse duration shorter than 30 fs. We compare x-ray lasing transitions to the three lowest electronic states of singly ionized CO. The dependence of the lasing efficiency on the spectral width of the x-ray fluorescence band, value and orientation of the electronic transition dipole moment, lifetime of the core-excited state and the duration of the pump pulse is analysed. Using a pre-aligned molecular ensemble substantially increases the amplified emission. Moreover, by controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization, the control of the emitted x-ray radiation is achievable. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on stimulated x-ray emission on bound transitions.</p> 2013-08-13 00:00:00 CO ensembles moment polarization radiation C 1 AXE photons lasing efficiency vibrational quantum state fluorescence band O 1 emission core ionization 30 fs xfel transition pulse duration source alignment CO molecule C K Atomic Physics Molecular Physics