High-resolution spectroscopy with reciprocal-space analysis: Application to isotopically pure Si

We discuss a new Fourier-transform approach that has recently been developed to optimize the determination of critical point parameters in optical spectra. In this approach, segments of direct (energy or frequency) space spectra are Fourier transformed into reciprocal (Fourier-inverse) space, and the endpoint-discontinuity artifacts that result are eliminated by subtracting corresponding coefficients of low-order Legendre polynomials determined by least-squares fitting these coefficients to the transformed data in the white-noise region. We apply this approach to determine the extremely small effect of isotopic mass on the energy of the E1 critical point of crystalline Si from low-temperature spectroscopic ellipsometric data.

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