Fig. 1. (a) Laser temporal profiles in three simulated cases; (b) two-dimensional profile of electron density of the target plasma.

Fig. 2. Time-integrated energy spectra of fast electrons with three laser waveforms (a dashed line is utilized to indicate the temperature slope). The black line indicates the positive skew case. The red line indicates the Gaussian case. The blue line indicates the negative skew case.

Fig. 3. Phase space (X, P_X) distribution of the electrons. (a) Positive skew pulses, 200 fs; (b) Gaussian pulses, 500 fs; (c) negative skew pulses, 850 fs.

Fig. 4. Distribution of electrons’ longitudinal momentum when the laser peak reaches the target surface. (a) Positive skew pulses, 150 fs; (b) Gaussian pulses, 500 fs; (c) negative skew pulses, 850 fs.

Fig. 5. Evolution of the maximum longitudinal momentum at the target surface for different laser waveforms. The black square line indicates the positive skew case. The red square line indicates the Gaussian case. The blue square line indicates the negative skew case.

Fig. 6. Distribution of plasma density along the x direction when the laser peak reaches the front surface of the target for the different laser waveforms.

Fig. 7. Time evolution of the total energy of electrons in the simulation box with different energy ranges for the three pulses. (a) For positive skew pulses; (b) for Gaussian pulses; (c) for negative skew pulses. Comparison of the energy of electrons under the three pulses. (d) For electrons with E > 500 keV; (e) for electrons with E > 1 MeV; (f) for electrons with E > 5 MeV.