Fig. 1. (a) Experimental scheme for generating three collinearly propagating time-delayed probe pulses, based on NOPA. BS, beamsplitter; L, lens; A, attenuator; AL, achromatic lens; SP, sapphire window; DL, delay line; DM, dichroic mirror; SM, spherical mirror. (b) Schematic representation of the temporal overlap of the WLC with the pump pulses in a single-stage BBO: the description schematically shows which pump pulses are controlled by specific delay lines. P1–P3, pump pulses. (c) WLC after narrowband amplification. S1–S3, probe pulses.

Fig. 2. Normalized spectra of probe pulses S1, S2 and S3. Cut-on wavelengths of the dichroic BS used for spatial separation of the pulses are shown as vertical lines. The dashed curves show the transmission function of the BPF in front of the cameras.

Fig. 3. Measured group delay of the WLC, centered to probe pulse S2. The error bars correspond to the measured delay of central wavelengths related to the probing pulse. A 95% prediction interval estimates the total error of measurement. The respective delays between the center wavelengths of the three generated probe pulses are also shown.

Fig. 4. Plasma channel captured at two different delays of the driver beam with respect to the probe operating at the wavelength of 560 nm. Each picture corresponds to one shot and shows the plasma channel at three different times. The top subpicture corresponds to probe S1, the middle subpicture shows the plasma channel recorded by probe S2 and the bottom subpicture corresponds to the channel recorded by probe S3. The solid cyan line marks the middle of the frame and the dashed magenta line indicates the end of the developed channel captured at a specific time point.

Fig. 5. (a) Plasma channel captured at the global delay of +0.1 ps at three different times, where the delay between probes follows the definition introduced in Figure 3. (b) Relative phase shift recalculated from the raw data normalized to the maximum value in the picture.

Fig. 6. Calculated amplification bandwidth of a probe pulse with the central wavelength ranging from 480 to 650 nm. The seed FWHM duration is equal to 1.95 ps and the pump FWHM duration is equal to 50 fs in a 1 mm thick BBO crystal. The measured values refer to the probes shown in Figure 2.

Fig. 7. Calculated amplification bandwidth for a range of the pump pulse lengths between 30 and 120 fs and the chirped WLC pulse length between 1.5 and 2.5 ps (the values refer to the FWHM durations). The central wavelength of the amplified signal was set to 560 nm.