TY - JOUR KW - Energy KW - Target KW - Reduction KW - Measurements KW - Measurement KW - USA KW - Surface KW - Emission KW - Pulse KW - Efficiency KW - Copper KW - Material KW - Ablation KW - Laser KW - Laser ablation KW - Laser ablation KW - Breakdown KW - Time-resolved KW - Time KW - Ablation efficiency KW - Ca KW - E KW - Plasma KW - Fluence KW - Laser fluence KW - Vapor KW - C KW - Development KW - Picosecond KW - Picosecond laser KW - Picosecond laser ablation KW - Density KW - Electron KW - Energies KW - Nm KW - Order KW - Absorption KW - Dynamics KW - Expansion KW - Plume KW - Electron density KW - Circulation KW - Physics KW - Electron-density KW - Air KW - Air breakdown KW - Electron emission KW - Electron-emission KW - Vapor plume KW - Ablation plasma KW - Region KW - Solid-surface AU - Samuel S Mao AU - Xianglei Mao AU - Ralph Greif AU - Richard E Russo AB -

Using picosecond time-resolved shadowgrams and interferograms, we measured the lateral expansion of an early stage ablation plasma induced by a 1064 nm, 35 ps laser pulse on a copper target. The plasma was found to have an electron density on the order of 1020 cm-3 near the target surface. Prior to the expanding material vapor plume, this high density plasma originates from the breakdown of air, assisted by laser-induced electron emission from the target surface. The longitudinal expansion of the plasma was suppressed due to the development of a strong space-charge region. At postpulse times, the relation r∼t1/2 was found for the temporal lateral expansion of the radius of the plasma. Measurements of energy absorption by the plasma provide an interpretation for the experimentally measured reduction in ablation efficiency as the laser fluence increases beyond approximately 100 J/cm2.

AD -

Univ Calif Berkeley, Lawrence Berkeley Lab, Berkeley, CA 94720 USA

AN - 120 BT - Applied Physics Letters LA - eng LB - Laser N1 -

LNBL-44560 NOT IN FILE

N2 -

Using picosecond time-resolved shadowgrams and interferograms, we measured the lateral expansion of an early stage ablation plasma induced by a 1064 nm, 35 ps laser pulse on a copper target. The plasma was found to have an electron density on the order of 1020 cm-3 near the target surface. Prior to the expanding material vapor plume, this high density plasma originates from the breakdown of air, assisted by laser-induced electron emission from the target surface. The longitudinal expansion of the plasma was suppressed due to the development of a strong space-charge region. At postpulse times, the relation r∼t1/2 was found for the temporal lateral expansion of the radius of the plasma. Measurements of energy absorption by the plasma provide an interpretation for the experimentally measured reduction in ablation efficiency as the laser fluence increases beyond approximately 100 J/cm2.

PY - 2000 SP - 31 EP - 33 T2 - Applied Physics Letters TI - Dynamics of an air breakdown plasma on a solid surface during picosecond laser ablation VL - 76 ER -