Measurement And Reconstruction Of Extreme Ultraviolet Attosecond Pulse Trains Based On High Harmonic Radiation

The discovery of high-order harmonics from strong laser field interaction with gases provided the basis for generating attosecond pulses.The initial creation of attosecond pulses in the extreme ultraviolet range paved the way for the observation of sequences of attosecond pulses through various experimental measurement methods.The isolation of individual attosecond pulses from these sequences heralded the emergence of attosecond science as a novel area of ultrafast research,sparking a surge in attosecond time-resolved dynamics investigations.Attosecond science’s capacity to address electron motion on a natural time scale offers the potential for analyzing ultrafast dynamics of electrons and nuclei in atoms,molecules,and solids.This thesis focuses on generating and characterizing attosecond pulse trains through measurement.A home-built attosecond extreme ultraviolet beam-line is utilized in experiments to generate high-order harmonics by sending the femtosecond pulses(with a central wavelength of 800 nm and a pulse width of 35 fs)into a gas cell.The reconstruction of attosecond beating by interference of two-photon transitions(RABBITT)experiment is designed and executed based on the pump-probe detection principle.RABBITT photoionization spectra of He atoms are recorded with varying IR laser intensities and polarizations,the attosecond pulse trains(APTs)generated from Ar and Ne gas are compared.To extract phase information,a timing jitter-independent phase extraction technique(TURTLE)is introduced that relies on the correlation data between distinct sidebands.TURTLE technique overcomes the need for pump-detection delay stabilization and eliminates the impact of timing jitter on experimental accuracy.The efficiency of the technique is validated by comparing the TURTLE fit with the sin fit.Furthermore,the study reveals that TURTLE fitting remains useful in situations where the sin fitting fails to extract the phase difference caused by non-jitter factors’ sideband oscillation instability.This study employs the extended laminar reconstruction iteration engine(e PIE)algorithm to characterize and reconstruct the measured APTs.The impacts of IR laser intensity,IR laser polarization,and varying photon energies of different atoms on XUV pulse reconstruction are analyzed separately.The results confirm that the two-photon ionization transition remains valid in a range of IR light intensities,without the interference of higher frequency oscillations,leading to more uniform reconstructed attosecond pulse widths.When examining RABBITT photoionization spectra under different IR laser polarizations,it is observed that sidebands become more visible at smaller polarization angles and disappear gradually as polarization approaches 60°.This suggests that the atomic time delay and the continuous-continuous delay in the sideband oscillation function,caused by the IR pulse’s changing polarization of the IR field,cannot be neglected,leading to a certain angular dependence.Finally,comparing higher energy harmonics radiation produced by different atoms Ar and Ne in distinct photon energy ranges,it is found that the harmonic energy and width of radiation also affect attosecond pulse train reconstruction.The measurements indicate that shorter attosecond pulse widths are achieved for atoms with higher photon energy ranges.The generation and calibration of attosecond pulses have tremendous significance for advancing attosecond scientific research in atomic and molecular systems.It allows for a deeper understanding of electron motion,electron-nuclear coupling,and the natural evolution of quantum systems on an ultrafast scale.