Fig. 1. Diagram of experimental system

Fig. 2. Time resolved images of plasmas produced by the double-pulse. (a) 532 nm wavelength laser interferogram; (b) 1064 nm wavelength laser interferogram

Fig. 3. Electron density distribution diagram of plasma (Unit of the color bar is 10¹⁹cm⁻³)

Fig. 4. Cross sectional electron density distribution in plasma

Fig. 5. Comparison of plasma electron density induced by double-pulse laser and single-pulse laser

Fig. 6. Variation of electron density induced by double-pulse laser plasma with delay time

Fig. 7. Plasma electron density rise percentage

Fig. 8. Plasma electron density distribution diagram with different delay times at 130 ns (Unit of the color bar scale is 10¹⁹cm⁻³)