High order harmonic radiation source for multicolor extreme ultraviolet radiography of carbon plumes

Multicolor radiography is used for the characterization of atoms, ions, and molecules of carbon plasma plumes formed by focusing a 200 ps Ti:sapphire laser pulse on a solid graphite target. The radiography of the plume was carried out using a high order harmonic generation based radiation source consisting of the 11th (λ ≈ 72.7 nm) to 21st (λ ≈ 38 nm) odd harmonic orders of the Ti:sapphire laser pulse. The density profile of CI, CII, and carbon dimer molecule (C2) is estimated from the 2D-transmission profile of the harmonics, recorded after passing through the carbon plume. The peak densities of CI, CII, and C2 at a 50 ns delay are estimated to be 8 × 1024 m−3, 4 × 1024 m−3, and 3.5 × 1023 m−3 at distances of 150 μm, 170 μm, and 120 μm away from the target surface, respectively. The expansion speed of the plasma plume front is estimated to be 2 × 104 m/s and the speed of the C2 molecule to be 4 × 103 m/s at a laser intensity of 1011 W cm−2. The present study demonstrates ultrafast multicolor radiography as a simple and versatile tool for a simultaneous estimation of the density profile of neutral atoms, ions, and molecular species of the plasma plume.

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