Fig. 1. Development of generation techniques for isolated attosecond pulse

Fig. 2. Effect of strong laser field on photoelectrons ionized by attosecond pulses. Dashed line presents velocity distribution without laser field while solid line with laser field^[63]

Fig. 3. Attosecond streaking camera scheme. (a) Attosecond streaking camera scheme diagram; (b) experimental streaking spectrogram of IAP; (c) ionized from noble gas atoms by XUV pulses, photoelectrons are then accelerated in infrared/near-infrared (IR/NIR) field and collected by TOF

Fig. 4. Characterization of PCGPA, LSGPA and ePIE for experimental spectrogram. (a) Reconstruction results with 20000 iterations from PCGPA, LSGPA and ePIE, together with experimental result; (b) retrieved NIR streaking fields, XUV pulse envelope intensities and phases from PCGPA, LSGPA and ePIE^[96]

Fig. 5. Diagram of PROOF. (a) Photoelectrons are ionized from ground states to continuum by IAP. Continuum states separated by laser frequency are coupled, leading to oscillation of spectrogram with time delay. (b) Signal peaks by Fourier transform from photoelectrons in (a) at certain energy, lying at laser frequencies of zero, ωL and 2ωL, whereas ωL oscillation component is selected by using band-pass filter. (c) Spectrogram retrieved from inverse Fourier transform of filtered ωL component of oscillation, which encodes phase angle α(v)^[93]

Fig. 6. Characterization of 67 as IAP. (a) Experimentally obtained streaking electron spectrogram; (b) comparison of filtered IωL component (left) with retrieved one (right); (c) experimental photoelectron spectrum (thick solid), PROOF retrieved spectra and phase (solid) and FROG-CRAB ones (dashed); (d) reconstructed temporal profiles and phases by PROOF (solid) and FROG-CRAB (dashed)^[30]

Fig. 7. Reconstruction of 71 as experimental IAP by PROOF and qPROOF. (a) Experimental IAP spectrogram; (b) IAP spectrum and retrieved spectral phases by PROOF (solid line) and qPROOF (dashed line); (c) experimental extracted (Exp.) and retrieved (Retr.) OOF phases by PROOF (αP) and qPROOF (αqP); (d) reconstructed IAP temporal envelopes from PROOF (dashed line) and qPROOF (solid line), and retrieved temporal phases from PROOF (blue triangles) and qPROOF (red circles)^[22]

Fig. 8. Reconstruction of 43 as IAP spectrogram. (a) Experimentally measured attosecond streaking spectrogram with target gas xenon; (b) reconstructed spectrogram and mid-IR vector potential by ML-VTGPA; (c) reconstructed (blue) and Fourier transform limited (FTL) (red dashed) IAP temporal amplitude with temporal phase (black), where inset shows retrieved spectrum (blue) compared with measured spectrum (red) and retrieved spectral phase (black); (d) reconstructed mid-IR vector potential (blue), FTL pulse amplitude (red dashed) and TG-FROG measured amplitude (green dotted)^[27]

Fig. 9. PROBP-AC method. (a), (b) Autocorrelation (AC) patterns extracted from experimental and reconstructed spectrogram from literature; (c) AC pattern retrieved by PROBP-AC; (d)‒(f) reconstructed results from ML-VTGPA in literature compared with PROBP-AC for IAP envelope, spectral phase and IR vector potential^[99]