Fig. 1. A schematic view of the experimental setup (WS, wavelength separator; FS, fused silica). The 800 nm beam is focused by a convex lens to the BBO crystal and its substrate. Afterward, the second harmonic beam is isolated and collimated before being sent to a chirped-mirror compressor. The beam profile was measured at the focus of an uncoated fused-silica lens with a focal length of 500 mm.

Fig. 2. (a) Measured spectrum distribution as a function of the BBO position with respect to the focusing lens. (b) The bandwidth (FWHM) and the signal intensity of the second harmonic beam as a function of the BBO position with respect to the focusing lens. (c) Measured spectra of the second harmonic beam for three different BBO positions.

Fig. 3. (a), (b) The measured and reconstructed SD-FROG traces. The reconstructed temporal intensity and phase of the pulse are shown in (c) together with the temporal profile of the Fourier-transform limited pulse.

Fig. 4. (a) The pulse energy of the compressed SHG pulse as a function of the fundamental pulse energy with a power function fitting. (b) A summary of pulse durations and energies for experimentally demonstrated intense sub-10 fs 400 nm pulses.

Fig. 5. Single-shot measurements of pulse energy stability (a), and beam pointing along the horizontal () and vertical () directions (b), (c) over 8 hours for the compressed second harmonic beam. The histograms of the normalized stability distributions are plotted on the corresponding right-hand side panels.