Abstract
Two effects have been recently observed by the authors for the copper sample melted in a rarefied argon atmosphere. The first of these effects is a strong decrease in the normal reflectance of a copper sample with time just after the beginning of melting. A partially regular crystal structure was also formed on the surface of the solid sample after the experiment. Both effects were explained by generation of a cloud of levitating nanoparticles. Additional experiments reported in the present paper show that the rate of decrease in reflectance increases with pressure of argon atmosphere and the surface pattern on the solid sample after the experiment depends on the probe laser radiation. It is theoretically shown for the first time that the dependent scattering effects in the cloud of copper nanoparticles are responsible for the abnormal decrease in normal reflectance and also for the observed significant role of light pressure in deposition of nanoparticles on the sample surface. The predicted minimum of normal reflectance is in good agreement with the experimental value.
Highlights
The experimental and theoretical study presented here was started in connection with the traditional task of determining the change in spectral optical properties of chemically pure copper during its melting
Laboratory experiments in a vacuum chamber at a very low pressure of argon showed that the specular reflection of the probe laser radiation from the copper sample strongly decreases, almost immediately after the beginning of copper melting
A preliminary explanation of the decrease in normal reflectance of the copper sample in Reference [1] was based on the Mie scattering of light by small copper particles
Summary
The experimental and theoretical study presented here was started in connection with the traditional task of determining the change in spectral optical properties of chemically pure copper during its melting. The qualitative explanation of the observation, proposed by the authors, was associated with the condensation of copper vapor with formation of sub-micron particles of the melt above the sample surface. In contrast to Reference [1], a physically more sophisticated model for the effect of a cloud of copper nanoparticles on a strong decrease in the reflection of probe laser cloud of copper nanoparticles on a strong decrease in the reflection of probe laser radiation radiation is developed in the present paper. Special attention is paid to the deposition of of particles on the sample surface at the end of the experiment. The dependent scattering of closely spaced particles particles is a physical basis of the model developed.
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