10.6084/m9.figshare.1012418.v1 Victor Kimberg Victor Kimberg Song Bin Zhang Song Bin Zhang Nina Rohringer Nina Rohringer Number of photons in the C 1<em>s</em><sup>−1</sup> → <em>X</em> AXE channel as a function of the number of photons in the incoming XFEL pulse of a duration of 50 fs for an isotropic ensemble () and for pre-aligned ensembles with 〈cos <sup>2</sup>ζ〉 = 0.51() and 〈cos <sup>2</sup>ζ〉 = 0.64(▵) IOP Publishing 2013 CO molecule fluorescence band vibrational quantum state lasing efficiency C 1 radiation XFEL pulse ensemble moment polarization emission photon axe alignment source 50 fs transition 30 fs pulse duration core ionization C K Atomic Physics Molecular Physics 2013-08-13 00:00:00 Figure https://iop.figshare.com/articles/figure/_Number_of_photons_in_the_C_1_em_s_em_sup_1_sup_em_X_em_AXE_channel_as_a_function_of_the_number_of_p/1012418 <p><strong>Figure 3.</strong> Number of photons in the C 1<em>s</em><sup>−1</sup> → <em>X</em> AXE channel as a function of the number of photons in the incoming XFEL pulse of a duration of 50 fs for an isotropic ensemble () and for pre-aligned ensembles with 〈cos <sup>2</sup>ζ〉 = 0.51() and 〈cos <sup>2</sup>ζ〉 = 0.64(▵).</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>