Figure 1

The effect of a narrow gate width ($\sim 1\mathrm{fs}$) on the generated attosecond pulse. In (a), the CE phase of the NIR laser means the freed electron recombines in a field of high ellipticity, severely limiting its recombination probability. In (b), the CE phase is more favorable for high attosecond pulse emission since the electron experiences a linear field for its full lifetime. The color gradient represents the ellipticity of the field with the darker being the most elliptical and white the most linear. The experimental evidence for this effect is shown in (c). The upper figure shows the energy spectrum as a function of the CE phase of the NIR laser while the lower plot shows the total signal integrated along the energy axis. The $2\pi$ periodic structure is the effects of the two-color gating in GDOG. (d) A streaked spectrogram when the CE phase is unlocked. (e) The temporal profile (solid line) and phase (dashed line) for the pulse shown in (d).Reuse & Permissions

Figure 2

Streaked photoelectron spectrograms for four different values of the CE phase. (a) $\sim 0\mathrm{rad}$, (b) $\sim \pi /2\mathrm{rad}$, (c) $\sim \pi \mathrm{rad}$, and (d) $\sim 3\pi /2\mathrm{rad}$. The images are normalized to the peak counts of (c).Reuse & Permissions

Figure 3

(a) The photoelectron energy spectrum for each of the streaked spectrograms of Fig. 2. (b) The temporal profiles (solid lines) and phases (dashed lines) for the spectrograms with phase 0 (black line) and $\pi$ [gray (red) line]. (c) The temporal profiles and phases for the spectrograms with phase $\pi /2$ (black line) and $3\pi /2$ [gray (red) line]. Each line corresponds to the spectra from (a). Panel (d) shows the extracted electric fields of each of the spectrograms from Fig. 2.Reuse & Permissions

Figure 4

(a),(b) Streaked spectrograms of attosecond pulses produced directly from an amplifier with an approximately $\pi$ shift between them. Panel (c) shows the temporal profiles of (a) and (b) while the inset shows the energy spectrum of (a) [gray (red) line] and (b) (black line). The electric fields extracted from (a) and (b) through Fourier filtering is shown in (d) for the phase of 0 gray (red) line] and $\pi$ (black line).Reuse & Permissions