Fig. 1. (a) Schematic of the experimental setup. Two identical off-axis parabola mirrors, OAP1 and OAP2, are used to focus and recollimate the laser beam. The laser pulse temporal profiles are measured with SHG-FROG and Sequoia. W1, W2 are wedged fused silica plates, and M1–M4 are HR mirrors. M2 is mounted on a motorized linear stage. PM stands for plasma mirror. (b) The laser contrast measurement in a 60 ps window using Sequoia. The inset is the zoom-in profile from −1 to 0.5 ps. The ‘a’ and ‘b’ correspond to the estimated PM trigger times for laser fluences Fpm of 140.0  J/cm2 and 6.5  J/cm2, respectively. Example results of (c) retrieved FROG trace and (d) the corresponding Wigner distribution of laser pulse without a PM.

Fig. 2. Wigner distribution (left axis) and temporal profiles (right axis) of the laser pulse after reflection from the PM with Fpm equal to (a) 140.0  J/cm2, (b) 50.0  J/cm2, (c) 23.8  J/cm2, (d) 14.0  J/cm2, (e) 9.2  J/cm2, and (f) 6.5  J/cm2. The intensity is normalized to the peak value at t=0  fs. The shaded area in each plot is due to the shot-to-shot fluctuations.

Fig. 3. (a) Pulse durations measured with FWHM (TFWHM) and the second-order moment (Tvar) methods. The solid lines are drawn to guide eyes. (b) Integrated reflectivity of the PM-reflected laser pulse as a function of Fpm.

Fig. 4. Retrieved spectral intensity (red line) and phase (black line) of the PM-reflected laser beam with the same laser fluence as in Fig. 2. The shaded area in each plot is due to shot-to-shot fluctuations.

Fig. 5. Modulation depth Γ (black line) and group delay t (red line) for two laser fluence examples of (a) Fpm=50.0  J/cm2 and (b) Fpm=9.2  J/cm2. The dashed lines are the reference group delays for the laser pulse without a PM. The shaded areas are the standard deviations due to shot-to-shot fluctuations.