Fig. 1. The experimental setup for a demonstration of the post-compressor within the ELFIE interaction chamber. OAP is the off-axis parabolic mirror and TCC is its focus position.

Fig. 2. Images of the focused laser beam after traversing no material (left), 5 mm fused silica glass (center) and 2 mm COP (right).

Fig. 3. Simulations of spectral broadening for pulses interacting with 5 mm fused silica, based on ELFIE laser parameters. The top row (a)–(c) considers the resultant spectra and pulse temporal shape for the compressed pulse as a function of the input pulse energy. Middle column: pulse shape for the dispersion compensation = –6000 fs. Right-hand column: FL pulse shapes. In (d), the dotted red and blue lines describe the duration of the FL compressed pulse (red solid) and fixed fs² (blue solid), respectively. (e) The measured input spectrum (blue) and output spectrum (dotted red) for 4.8 J pulse energy. (f) The corresponding reconstructed shape for input (300 fs, blue) and output (170 fs, dotted red) pulse.

Fig. 4. The spectral broadening occurring due to self-phase modulation (SPM) with no material (red line), fused silica (green line) and COP (orange line) is compared with the laser spectrum measured before the interaction (blue dashed) in (a)–(c). The initial pulse spectrum measured with no material presented in (a) shows no significant change in the spectra. In (b), a 4.8 J pulse interacts with 5 mm of fused silica, and (c) shows the result of a 3.9 J pulse passing through 2 mm of COP. The autocorrelator measurements shown in (d) and (e) give the FWHM fit in the case of no material (0.50 ± 0.05 ps) and fused silica (0.41 ± 0.9 ps), which correspond to pulse durations for the specific cases shown of 0.34 and 0.2 ps, respectively. In (f), the resulting spectral FWHM bandwidth in nm is measured relative to the input pulse chirp, as defined by the variation of the laser compressor grating separation ( [mm]). The initial FWHM bandwidth measured with no material (red vertical line) remains fairly constant at 5.1 nm despite the change in the separation of the laser compressor gratings. With the FS, the compressor position becomes optimized when the broadened bandwidth (green dot) is maximized relative to the measured laser bandwidth (blue circle).

Fig. 5. Beam profile comparison between the reference (a) and FS (b); in (c) the power spectrum of two separate laser regions (regions I and II, denoted by black and green, respectively), before and after the nonlinear interaction. The ratio of the power spectra, relative to the initial corresponding reference, gives the relative gain in the spatial modulation instabilities (SMIs) in (d).