Fig. 1. Schematic of the experimental setup: (a) laser source and pre-amplifiers of the HERA laser facility; (b) Sagnac interferometer used for parallel amplification and coherent combining; (c) diagnostics for energetic, spatial and temporal single-shot analysis of the combined and the uncombined beams.

Fig. 2. Near-field profiles at low energy through the alignment procedure at 10 Hz: (a)–(c) images show the profiles of the combined channel, while (d)–(f) images show those of the uncombined channel. Each column represents an acquisition with a progressively smaller misalignment angle ( = 168, 84 and 0 μrad) converging to 0. Each image is normalized to have a scale consistent with its energy.

Fig. 3. Combined output energy and combining efficiency as a function of Sagnac interferometer input energy. Measurements are taken for pulses durations of 3 ns (blue) and 15 ns (orange), respectively. The total-energy amplification curve follows the Frantz–Nodvik model (dashed green line).

Fig. 4. Spatial profiles of the Sagnac interferometer output beam: (a) near field of the combined beam; (b) near field of the uncombined beam; (c) far field of the combined beam; (d) horizontal cut of (a) and (b) compared to the reference beam without CBC. The profiles shown in (a)–(c) have been obtained simultaneously with the highest energy (21.1 J, = 92%).

Fig. 5. Temporal profiles of the input pulse just after the regenerative amplifier (green line not to scale for better visibility), the combined pulse (blue) and the uncombined pulse (orange line). The instantaneous combining efficiency (t) is plotted as the red line. (a) For a square input profile of 15 ns. (b) For an input profile of 15 ns shaped to pre-compensation saturation. These measurements are made for a total output energy higher than 20 J.

Fig. 6. Spatial considerations on the Sagnac interferometer with large beams: (a) optical path of P and S beams; (b) differential wavefront measurement of the two counter-propagating beams in the interferometer.