TY - JOUR KW - Model KW - Profiles KW - Surface KW - Pulse KW - Power KW - Evaporation KW - Ablation KW - Laser KW - Time KW - Glass KW - Glasses KW - Mass KW - Mass spectrometry KW - Plasma KW - Sample KW - Samples KW - Ablated mass KW - Ablation rate KW - Brass KW - Dependence KW - Atomic emission spectrometry KW - Density KW - Thermal KW - Aluminum KW - Inductively-coupled plasma KW - Laser power density KW - Coefficient KW - Absorption KW - Light KW - Profile KW - Thermal evaporation KW - Plume KW - Plasma shielding KW - Laser radiation KW - Inverse bremsstrahlung KW - Solid materials KW - Radiation AU - Xianglei Mao AU - Richard E Russo AB -

Mass ablation rate increases with laser power density following a power law dependence and a significant change occurs at 0.3 GW/cm2. A reflected laser temporal profile was measured from a brass sample. When the power density is greater than 0.3 GW/cm2+, the temporal profile changes. The transmitted laser-pulse temporal profile through a glass sample also was measured. When the power density is greater than 0.3 GW/cm2, the later part of laser pulse becomes truncated. The power density at which the laser temporal profile changes for each case is same as the power density that the mass ablation rate coefficient changes. The ablated mass can absorb incoming laser radiation through inverse Bremsstrahlung. The mass becomes thermally ionized and opaque to the incident radiation, preventing laser light from reaching the surface. A model based on thermal evaporation and inverse Bremsstrahlung absorption was developed. Calculations show that plasma shielding occurs at approximately 0.3 GW/cm2. The experiments and model suggest that the significant change observed in mass ablation rate coefficient is caused by plasma shielding.

AD -

LAWRENCE BERKELEY LAB,BERKELEY,CA 94720

BT - Applied Physics A-Materials Science & Processing DA - 12/1996 DO - 10.1007/s003390050437 IS - 1 LA - eng LB - Laser N2 -

Mass ablation rate increases with laser power density following a power law dependence and a significant change occurs at 0.3 GW/cm2. A reflected laser temporal profile was measured from a brass sample. When the power density is greater than 0.3 GW/cm2+, the temporal profile changes. The transmitted laser-pulse temporal profile through a glass sample also was measured. When the power density is greater than 0.3 GW/cm2, the later part of laser pulse becomes truncated. The power density at which the laser temporal profile changes for each case is same as the power density that the mass ablation rate coefficient changes. The ablated mass can absorb incoming laser radiation through inverse Bremsstrahlung. The mass becomes thermally ionized and opaque to the incident radiation, preventing laser light from reaching the surface. A model based on thermal evaporation and inverse Bremsstrahlung absorption was developed. Calculations show that plasma shielding occurs at approximately 0.3 GW/cm2. The experiments and model suggest that the significant change observed in mass ablation rate coefficient is caused by plasma shielding.

PB - Springer-Verlag PY - 1997 SP - 1 EP - 6 T2 - Applied Physics A-Materials Science & Processing TI - Observation of plasma shielding by measuring transmitted and reflected laser pulse temporal profiles VL - 64 SN - Print ISSN: 0947-8396; Online ISSN: 1432-0630 ER -