Hard-X-Ray-Induced Multistep Ultrafast Dissociation

Creation of deep core holes with very short (τ≤1  fs) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few- femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1s→σ∗ excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon

Detail showing the transmission near (2,0)₄ for a column density of ~68 <b>×</b> 10¹⁷ cm⁻²

<p><strong>Figure 4.</strong> Detail showing the transmission near (2,0)₄ for a column density of ~68 <b>×</b> 10¹⁷ cm⁻². The series limit converging on He⁺(<em>n</em> = 2) is at 18.96 nm. The inset shows the single-shot spectra with the highest peak intensities at the positions of the He** absorption profiles along with the calculated average transmission (black trace).</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p

Detail showing the transmission near (2,0)₃ for a column density of ~68 <b>×</b> 10¹⁷ cm⁻²

<p><strong>Figure 3.</strong> Detail showing the transmission near (2,0)₃ for a column density of ~68 <b>×</b> 10¹⁷ cm⁻². The inset shows the two single-shot spectra with the highest transmitted intensities at the wavelengths of zero cross-section (red, blue), along with the calculated average transmission (black).</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p

Filter bandwidths using the (2,0)_<em>n</em> absorption profiles as functions of helium column density

<p><strong>Figure 6.</strong> Filter bandwidths using the (2,0)_<em>n</em> absorption profiles as functions of helium column density. For <em>n</em> = 2 (red) the two half-widths (dashed lines) are shown along with the full-width at half-maximum. Only the FWHMs are shown for <em>n</em> = 3 (blue), <em>n</em> = 4 (green), and <em>n</em> = 5 (purple). The dashed vertical lines show the maximum column density used in this work (68 <b>×</b> 10¹⁷ cm⁻²) and the column density which would correspond to 2 m of gas at atmospheric pressure (5 <b>×</b> 10²¹ cm⁻²). The solid black circles show the bandwidths obtained in the spectra plotted in figures <a href="http://iopscience.iop.org/0953-4075/46/16/164021/article#jpb465316f3" target="_blank">3</a> and <a href="http://iopscience.iop.org/0953-4075/46/16/164021/article#jpb465316f4" target="_blank">4</a>.</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p

Absorption cross-section σ (red, left-hand <em>y</em>-axis), and transmission (right-hand <em>y</em>-axis) for different column densities (/10¹⁷ cm⁻²)

<p><strong>Figure 1.</strong> Absorption cross-section σ (red, left-hand <em>y</em>-axis), and transmission (right-hand <em>y</em>-axis) for different column densities (/10¹⁷ cm⁻²).</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p

Single-shot simulation at a column density of 68 <b>×</b> 10¹⁷ cm⁻² near the <em>n</em> = 3 and <em>n</em> = 4 resonances

<p><strong>Figure 5.</strong> Single-shot simulation at a column density of 68 <b>×</b> 10¹⁷ cm⁻² near the <em>n</em> = 3 and <em>n</em> = 4 resonances. The upper panel shows the simulated SASE wavelength profile (red), the transmission of the gas cell (black, same <em>x</em>-axis), the phase due to absorption (black, right-hand <em>y</em>-axis), and the transmitted wavelength profile (blue). The lower panel shows the time profile of the electric field before (red) and after (blue) the gas cell.</p> <p><strong>Abstract</strong></p> <p>Using the third harmonic of the FEL radiation from the SPring-8 compact SASE (self-amplified stimulated emission) source SCSS we have studied the effects on SASE pulses with central wavelengths near 20 nm due to passage through a helium gas cell. The positions of zero ionization cross-section close to wavelengths corresponding to double-excitations allow operation as an efficient wavelength filter, with effectively 100% transmitted peak intensity until the Doppler-broadening limit is reached. We discuss how the time profile of the SASE pulses is affected, and discuss potential applications.</p