The Introduction and Development of a New Method for Measuring the Optical Constants of Metals in the Soft X-Ray Range.
The future design and development of new optical techniques and instrumentation in the presently underexplored soft x-ray range (50 to 1200 eV) depend directly on the accurate characterization of the complex index of refraction of several classes of potentially useful materials: elements, alloys, and compounds. Orthodox metrological techniques in this energy range, based largely on the exploitation of Fresnel's equations, and consisting principally of transmissivity or reflectivity measurements made on thin-film samples of the materials of interest, are exceedingly hard to perform accurately at soft x-ray wavelengths, where undesirable scattering of the incident light can become significantly large. In addition, such techniques usually measure only one component of the complex index of refraction directly, relying on approximation and computation to deduce the complementary (unmeasured) component, a process which makes the results sensitive to a maximal number of systematic and computational errors. In our dissertation, we describe a new method discovered by us at Stanford for measuring the optical constants of metals (a significantly large and useful class of materials) in the soft x-ray range, a method which does not suffer from any of the principal limitations listed above. Under ideal experimental conditions, the method is independent of measurements of absolute light intensities, and it is also capable of directly yielding both parts of the complex index of refraction from only two measurements of the light diffracted off two suitable transmission gratings (which are composed of the material whose optical constants are to be established). Both optical constants, after suitable corrections, are deducible directly from the ratios of the first to the zeroth orders of the diffracted light. The new method has been experimentally tested and verified by us at the Stanford Synchrotron Radiation Laboratory, and the procedure is described in detail in the experimental section of our dissertation. The gratings for the experiment were composed of pure gold (the material whose optical constants we intended to measure) and were fabricated for us by IBM especially for this experiment. Based on the analysis of our data, we have extracted new optical constants of gold in the 280 to 640 eV range and the values, together with our error analysis, support the validity and accuracy of the new experimental technique.
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- Physics: Optics