OPTICAL-PROPERTIES OF LIQUID ALUMINUM IN THE ENERGY-RANGE 1.2-3.5 EV

The optical properties of clean liquid aluminum were investigated in the energy range 1.2-3.5 eV using pulsed-dye-laser spectroscopic ellipsometry. Aluminum specimens were electromagnetically levitated and melted, and any residual aluminum oxide and nitride phases were vaporized at high temperatures (T > 1850 K). An automated dual-detector rotating analyzer ellipsometer that moved to a set of fixed azimuths was employed to measure the optical constants, using a nitrogen laser-pumped dye laser as the light source for wavelengths from 360 to 990 nm. Measurements were obtained over the full wavelength range at ca. 1550 K and at five wavelengths over the temperature range 1200-1800 K. Liquid aluminum exhibits an absorption peak near 1.4 eV (ca. 885 nm) like that of the solid which arises from interband transitions in the same energy range. This existence of an absorption peak at 1.4 eV is supported by the results of previous electron-induced x-ray emission, electron energy loss, and NMR experiments as well as theoretical analyses of the structure of liquid aluminum. The reasons that this peak was not observed in the previous ellipsometric work are discussed.