%0 Journal Article
%K Model
%K Target
%K Measurements
%K Measurement
%K USA
%K Surface
%K Emission
%K Pulse
%K Velocity
%K Experimental
%K Algorithm
%K Interferometry
%K Material
%K Ablation
%K Laser
%K Laser ablation
%K Laser ablation
%K Breakdown
%K Time-resolved
%K Time
%K Ca
%K E
%K Form
%K Plasma
%K Solids
%K Number
%K Pulses
%K Vapor
%K C
%K Metals
%K Ionization
%K Electron number densities
%K Plasmas
%K Picosecond
%K Picosecond laser
%K Picosecond laser ablation
%K Density
%K Pulsed laser
%K Pulsed laser
%K Targets
%K Electron
%K Electron number density
%K Number density
%K Order
%K Ha
%K Metal
%K Dynamics
%K Results
%K Expansion
%K Plume
%K Atmosphere
%K Physics
%K Air
%K Air breakdown
%K Electron emission
%K Electron-emission
%K Forms
%K Heat transfer
%K Laser plasma
%K Laser plasmas
%K Pulsed laser ablation (PLA)
%K Pulsed laser ablation (PLA)
%K Theoretical-model
%K Vapor plume
%A Samuel S Mao
%A Xianglei Mao
%A Ralph Greif
%A Richard E Russo
%B Applied Physics Letters
%D 2000
%F Laser
%G eng
%N 16
%P 2464-2466
%R 10.1063/1.1318239
%T Initiation of an early-stage plasma during picosecond laser ablation of solids
%V 77
%2 LBNL-46390
%8 10/2000
%X <p>Picosecond time-resolved images of plasma initiation were recorded during pulsed-laser ablation of metal targets in an air atmosphere. An early-stage plasma was observed to form before the release of a material vapor plume. Close to the target surface, interferometry measurements indicate that the early-stage plasma has an electron number density on the order of 10<sup>20</sup> cm<sup>-3</sup>. The longitudinal expansion of the ionization front for this plasma has a velocity 10<sup>9</sup> cm/s, during the laser pulse. In contrast, a material-vapor plume forms approximately 200 ps after the laser pulse, and it moves away from the target at 10<sup>6</sup> cm/s. The experimental observations of the early-stage plasma were simulated by using a theoretical model based on a two-fluids description of laser plasmas. The results indicate that the initiation of the plasma is due to air breakdown assisted by electron emission from the target.</p>