Change in Reflectivity of Metals under Intense Laser Radiation. Revision
Abstract
The reflectance behavior of a target surface during laser irradiation determines the laser energy which is directly absorbed. Experimentally, the reflectance of a metal surface has been reported to undergo a sharp and substantial decrease during an intense laser pulse. Explanations have been offered based on an increase in electron-photon collision frequency as the temperature of the metal surface rises to the melting point of the metal. For high conductivity metals such as copper, we have shown that the temperature dependence of a Drude-type free-electron model can not explain the substantial reflectance changes reported. Three other classes of explanations have been proposed: (1) deformation of the metal surface, (2) plasma formation in the front of the target, or (3) a nonlinear process causing enhanced absorption within the metal. Specular and total reflectances of metal surfaces during ruby laser irradiation have been measured at the Polytechnic. The laser energy absorbed has been calculated and the temperature history of the metal surface determined using a one-dimensional heat-conduction approach. Reflectance and temperature histories have been related to permanent changes observed in the metal target surface. Only at temperatures significantly above the melting point of the metal does a substantial decrease in the total reflectance occur. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1981
- Accession Number
- ADA102005
Entities
People
- William T. Walter