Fig. 1. MPC and CMPC schematic and configuration regimes. (A) Standard MPC mode. (B) CMPC mode without and with folding. In the unfolded geometry the CMPC is typically longer than a comparable MPC, reducing to much shorter length Leff after folding. (C) Typical configuration regimes and corresponding fluence characteristics of MPC and CMPC within the stability range.

Fig. 2. Schematics of standard MPC and CMPC. (A) Standard MPC geometry and beam pattern considering a linear beam pattern alignment (FM1/2: focusing mirrors). View of the beam path from the front (i) and from the top (ii). (iii) Resulting patterns for circular/linear alignment on FM1/2. (B) CMPC geometry and beam patterns. (i) Front view with additional planar mirrors (PM1/2) behind FM1/2. (ii) Top view onto the CMPC with beam folding ratio Γ=9. The numbers (1–5) are indicating the order of reflections of the first pass. (iii) Beam patterns on the mirrors FM1/2 and PM1/2. The black line follows the beam reflections 1–5 on the mirrors. (C) Photographs of experimental beam patterns with N=11, k=3, and Γ=25. POM: pick-off mirror.

Fig. 3. Energy scaling characteristics: calculated pulse energy acceptance Emax as a function of effective length Leff. The solid black line indicates a standard MPC as reported in Ref. [29] [Eq. (2)]. Each colored solid line represents a CMPC with a folding ratio Γ [Eq. (4)]. The gray line indicates an effective length of 10 m. The dashed lines show the corresponding pulse energies for selected values of Γ. We set the threshold fluence to Fth=0.5  J/cm2.

Fig. 4. Experimental setup. The CMPC input beam is indicated in red, and the output beam in orange. FM: focusing mirror. PM: planar mirror. POM: pick-off mirror. Min: input/output mirror. MM: mode-matching. DCM: double-chirped mirror. CCD: camera. z0: reference point for stability measurements. TFP: thin-film polarizer. wdg: wedge. (A) Beam input, telescope, and diagnostics used in the experiment. (B) CMPC setup with vacuum chamber.

Fig. 5. Measured and simulated pulse characteristics after CMPC spectral broadening and subsequent compression in 1 bar of air. (A) Reconstructed input and output temporal pulse. (B) Measured input spectrum and broadened spectrum. The inset shows the measured broadened spectrum along with simulated spectrum. (C) Measured FROG trace (FT). (D) Retrieved FROG trace (FROG error=0.73% on a 1024×1024 grid).

Fig. 6. Spectral broadening of 6.5 mJ pulses in 1 bar of Krypton. CMPC input (gray line) and measured output (dark blue line) spectra are shown. The inset shows the simulated spectrum along with the measured output spectrum.

Fig. 7. Beam position and spectral stability, measured in 1 bar of air. (A), (B) Scatter-plots of the beam position of input (A) and output (B) beams. Measurements are taken separately; the data span for each measurement is 7.5 min and 4000 data points, with a few minutes between measurements. In both measurements, the camera is placed at exactly 42 cm distance from the common reference point z0 (Fig. 4). Circles indicate deviations of 50, 100, and 150 μm from the mean value. The measurements are in accordance with the medium-term beam position stability measurements defined in EN ISO 11670:2003. (C) Measured broadened spectrum recorded over 5 min with 10 points per minute at full broadening (logarithmic scale). The RMS deviation of the FTL amounts to 0.65%.

Fig. 8. Measured spatio-spectral beam characteristics. (A) Measured and simulated average spectral overlap Vavg and simulated accumulated nonlinear phase ϕNL(1) as a function of peak power P normalized to the critical power Pc. (B) Example data set of a single measurement point, indicated by a circle in (A). (i), (ii) Spectral distribution of the pulse over the spatial x-direction, integrated over the y-direction and vice versa. (C) Corresponding STC traces for a standard MPC with similar broadening. wx and wy represent the 1/e2 beam radii.

Fig. 9. CMPC simulation for 200 mJ pulses. (A) Input pulse and simulated compressed output pulse. (B) Input spectrum and simulated broadened spectrum.

Fig. 10. CMPC geometry.

Fig. 11. Spectral homogeneity V(x,y) [Eq. (A6)] for each Vavg data point shown in Fig. 8 in the main text. The circles indicate the area of integration for the calculation of Vavg [Eq. (A7)].

Fig. 12. Spectral homogeneity V(x,y) [Eq. (A6)] for spectral broadening in air at 8 mJ. The circle indicates the area of integration for the calculation of Vavg [Eq. (A7)].

Fig. 13. Spectral homogeneity V(x,y) [Eq. (A6)] for the MPC comparison measurement shown in Fig. 8(C) in the main text. The circle indicates the area of integration for the calculation of Vavg [Eq. (A7)].