Calculation of optical absorption in Al across the solid-to-liquid transition

We calculate the optical-absorption spectrum of solid and liquid Al for temperatures between 0 and 1800 K with an empirical pseudopotential technique. It is found that a prominent peak in the spectrum of the solid (at $\hslash \omega \sim 1.5\mathrm{eV}$) smoothly disappears as the temperature is raised above $T_{\mathrm{melt}}=938\mathrm{K}$. This is in agreement with earlier measurements on solid and liquid Al, but is in disagreement with more recent measurements on the liquid, in which the peak was seen to remain at $T=1550\mathrm{K}$. Our results suggest that in situ optical constants measurements may be used as a diagnostic for the shock melting of Al.

Figure 1

(a) EPM-RPA and (b) LDA-RPA results for the imaginary part of the long-wavelength dielectric function vs photon energy for fcc Al at 0 K, and for a single snapshot at 300 K. Both 0 K and 300 K configurations are at a density corresponding to the density at 300 K.

Figure 2

Calculated Al optical spectra for $T=0\mathrm{K}$, 100 K, 200 K, 300 K, 400 K, 550 K, 750 K, 900 K, 950 K, 1400 K, and 1800 K. Bold solid curves indicate $T=0\mathrm{K}$, 750 K, and 950 K. For the purpose of identifying the curves, note that ${ϵ}_2(\hslash \omega =1.0\mathrm{eV})$ is monotonically increasing with $T$.

Figure 3

Measured Al optical spectra for $T=198\mathrm{K}$ (solid line), 298 K (long-dashed line), 404 K (short-dashed line), 552 K (dot-dashed line) from Ref. 4, and 1550 K from Ref. 5 (shaded diamonds) and Ref. 6 (open circles). Data of Ref. 4 were originally presented as individual points. All data were originally given as ${\sigma }_1\left(\omega \right)$ vs photon energy. We have converted them using the relation: ${ϵ}_2\left(\omega \right)=(4\pi ∕\omega ){\sigma }_1\left(\omega \right)$.