Abstract
We show that attosecond metrology has evolved from proof-of-principle experiments to a level where complex processes can be resolved in time that cannot be accessed using any other existing technique. The cascaded Auger decay following ionization and excitation of the 3d-subshell in Kr with subfemtosecond 94 eV soft x-ray pulses has been energy- and time-resolved in an x-ray pump–infrared probe experiment. This Auger cascade reveals rich multi-electron dynamics, which despite the fact that there are many experimental and theoretical data available, is not yet fully understood. We present time-resolved data showing the sequence of the temporal dynamics in the cascaded Auger decay. The decay time of several groups of lines has been measured, including the lines at the low-energy part of the spectrum, which are predominantly produced by the second-step Auger transitions. Our experimental data reveal long lifetimes (up to 70 fs) of the subvalence excited ionic (intermediate) states in the cascaded resonant Auger decay. Extensive theoretical calculations within the multiconfiguration Dirac–Fock (MCDF) approach show that the observed long lifetime may be attributed to the second-step Auger decay of the resonantly excited 3d−1np states with n = 6,7. Furthermore, our experimental data show that the electrons with a kinetic energy around 25 eV (generally assigned as M4,5N1N1 1S0 normal Auger lines) have a component corresponding to the second-step Auger decay of the ion after resonant Auger transition 3d−1np → 4s2 4p3 4dnp → 4s2 4p4 with a lifetime of 26 ± 4 fs.
Highlights
We show that attosecond metrology has evolved from proof-ofprinciple experiments to a level where complex processes can be resolved in time that cannot be accessed using any other existing technique
Using the schematic energy diagram, it is possible to identify which of the observed Auger lines have to belong to the first step of the Auger decay and which may possibly be emitted in the second step of the Auger cascade
The observed large decay time of 74 ± 20 fs of the Auger electrons with a kinetic energy around 12 eV can be attributed to the second-step transitions in a resonant Auger cascade with possible assignment 4s4p5np → 4s24p4 or 4s2 4p3 4dnp → 4p4 with n = 7 or higher, according to our theoretical calculations
Summary
The laser system used in the experiment is a 5 kHz Ti:sapphire chirped pulse amplifier (CPA), delivering 0.8 mJ, 25 fs pulses. A two-component annular Mo/Si multilayer mirror focuses the IR and XUV pulses with a controllable delay onto the krypton target. Show the measured spectrum at large negative delay (where the IR probe precedes the XUV pump pulse) with bars at the known line positions taken from [9, 10, 12,13,14]. Using these line positions we fitted the spectrum and obtained the relative line strengths for our experimental conditions. Measured signal (XUV after IR) photoionization of valence shells resonant Auger lines normal Auger lines
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