Physics – Optics
Scientific paper
Feb 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........69h&link_type=abstract
Thesis (PH.D.)--STANFORD UNIVERSITY, 1991.Source: Dissertation Abstracts International, Volume: 52-09, Section: B, page: 4934.
Physics
Optics
2
Uranium, Aluminum
Scientific paper
Measurements of the optical constants and thermal radiative properties of three metals; tungsten (in the solid phase) and uranium and aluminum (both in the liquid phase) have been made using a new instrument which includes two independent optical systems and surface control and analysis capability. The two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity, operate over the wavelength range 0.4 to 10mum with sample temperatures between 940 and 1630 K. The surface science capabilities of the instrument permit the preparation of high purity samples of known composition in-situ. The device includes two 5 KeV argon ion sputter guns, an ultra-high vacuum pumping system and an Auger spectrometer. The ellipsometric optical system uses a novel radiation source (a carbon composite filament), refractive optics (CaF_2) and both calcite and wire grid polarizers to cover the wavelength range. The system for measuring the normal spectral emissivity uses reflective optics and an integral blackbody cavity located in the wall of the crucible holding the liquid sample. The two measurement techniques allow independent determinations of normal spectral emissivity, and thus allow unbiased estimation of errors. The sensitivity of six techniques for determining the complex index of refraction of molten metals (including the ellipsometric method used here) is analyzed over the wavelength range of interest. It is shown that only methods measuring both the phase shift and the amplitude attenuation upon reflection provide adequate accuracy over the full spectral range of interest. For tungsten, the measurement made using the two optical systems agreed well with each other and with previously published works. For aluminum, only the ellipsometric technique was employed, because the vapor pressure of aluminum prevented attaining sample temperatures high enough for accurate emissivity measurements, but these agreed well with expectations from the Drude model and with published results for the optical constants of molten aluminum. For uranium, for which published values for the optical constants of the liquid do not exist, the results from the two techniques agree well.
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