Fig. 1. Schematic of the interaction between femtosecond laser and periodic fused silica plates

Fig. 2. Laser frequency spectrum after broadening by 20 fused silica plates with different period（2.5 cm，5 cm，7.5 cm），and thickness（0.1 mm，0.2 mm，0.4 mm）

Fig. 3. The evolution of laser pulse propagating through 10 fused silica plates，with period of 2.5 cm and thickness of 0.2 mm

Fig. 4. The frequency spectrum broadening in the second stage

Fig. 5. The frequency spectrum broadening in the third stage