Complete phase retrieval of photoelectron wavepackets

Abstract

Coherent, broadband pulses of extreme ultraviolet (XUV) light provide a new and exciting tool for exploring attosecond electron dynamics. Using photoelectron streaking, interferometric spectrograms can be generated that contain a wealth of information about the phase properties of the photoionization process. If properly retrieved, this phase information reveals attosecond dynamics during photoelectron emission such as multielectron dynamics and resonance processes. However, until now, the full retrieval of the continuous electron wavepacket phase from isolated attosecond pulses has remained challenging. Here, after elucidating key approximations and limitations that hinder one from extracting the coherent electron wavepacket dynamics using available retrieval algorithms, we present a new method called Absolute Complex Dipole transmission matrix element reConstruction (ACDC). We apply the ACDC method to experimental spectrograms to resolve the phase and group delay difference between photoelectrons emitted from Ne and Ar. Our results reveal subtle dynamics in this group delay difference of photoelectrons emitted form Ar. These group delay dynamics were not resolvable with prior methods that were only able to extract phase information at discrete energy levels, emphasizing the importance of a complete and continuous phase retrieval technique such as ACDC. Here we also make this new ACDC retrieval algorithm available with appropriate citation in return.

Absolute delay calibration by analytical fitting of attosecond streaking measurements

“…A common assumption of pulse retrieval algorithms is the wavepacket approximation [36][37][38]. From equation ( 1), the dependence of the dipole moment of the XUV-induced transitions on the IR vector…”

Attosecond resolution from free running interferometric measurements

“…These two techniques not only have been used to characterize attosecond pulses but also to resolve electron ionization dynamics in atoms [7][8][9][10][11][12][13][14][15], small molecules [16][17][18], up to biomolecules [19] and solids [20,21]. Streaking traces have to be analysed in the time-domain and relay on reconstruction algorithms with different approximations [22][23][24][25], whereas the interference nature of the RABBITT-method allows for a more direct retrieval of the spectral phases [14,26]. However, both methods require an attosecond pump-probe delay control, which remains challenging and any XUV-IR pulse timing jiiter with uncontrolled fluctuations of the pump-probe delay can reduce the temporal resolution.…”