Attosecond electron dynamics

Abstract

This research investigates ultrafast electron dynamics in the interaction of an ultrafast laser with matter. The study encompasses three main areas. Attosecond XUV generation and characterization in a gas medium, Photoemission time delay in solid materials through attosecond streaking, and Simulation for population inversion from the inner shell of atoms for an Atomic X-ray laser. For the attosecond XUV generation and experiments, the experimental setup involves employing a stabilized Carrier-Envelope Phase (CEP) few- cycle laser to focus on ultrafast science, particularly sensitive to the shape of the few-cycle pulse. High Harmonic Generation (HHG) is achieved by focusing the laser into a gas cell with neon gas. The CEP dependence of is verified through spectral measurements. The isolated single attosecond XUV pulse is generated by spectral filtering. This isolated single attosecond pulse is further utilized in pump- probe streaking experiments, where the attosecond XUV pulse and few- cycle IR pulse propagate coaxially and are reflected by a double mirror setup. The resulting temporal characteristics are analyzed through spectrogram retrieval using FROG-CRAB (ATTOGRAM), confirming the single-isolated nature of the attosecond XUV pulse. The attosecond XUV pulse is employed to investigate ultrafast electron dynamics in solid graphene. Simulations are conducted to understand the time delay between emitted electrons from the 2s and 2p orbitals, arising from anisotropic potential and angular momentum. The simulations align well with experimental results, confirming a time delay of approximately 20 attoseconds. Streaking measurements on graphene validate the observed time delay, aligning with expectations from both simulation and experiment. Finally, the study addresses challenges faced by X-ray Free Electron Lasers (XFELs) by proposing an X-ray atomic laser approach. The SCFLY method is employed to simulate population inversion from inner-shell states, considering various materials and achieving higher gain under specific conditions. The simulation results indicate the potential of an atomic X-ray laser.