Normal-incidence reflectivity data for β′ CuZn has been subjected to a Kramers—Kronig analysis for its optical constants in the spectral region 2 eV ≤hω≤3 eV (4140 Å ≤λ≤ 6200 Å) in order to explain the nature of an observed reflectivity edge at 5000 Å. Extrapolations of the data into the infrared and ultraviolet were made. The frequency dependence of the optical constants indicates a plasma resonance at 2.52 eV (4920 Å), shifted and damped from its classically predicted value by the influence of interband transitions occurring at approximately the same energy. The spectral behavior of the optical constants in this region is not very sensitive to the exact nature of the extrapolation.
KEITH H. JOHNSON and ROBERT J. ESPOSITO, "Plasma-Interband Coupling in β′ CuZn," J. Opt. Soc. Am. 54, 474-477 (1964)