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have been measured for photon energies between 0.3 and 4.5 eV at temperatures above and below each material's superconducting critical temperature. The amplitude of the characteristic optical structure near the screened plasma frequency of each sample in the normal-state TDR spectrum varies approximately linearly with temperature, T, indicating that the temperature-dependent optical scattering rate in these materials scales with temperature as T 2 . From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal-state reflectance ratio, R S /R N , has been obtained. In all of these spectra, there are significant deviations from unity in R S /R N at photon energies on the order of 2.0 eV. This optical structure cannot be accounted for using the conventional Mattis-Bardeen description of the optical properties of a superconductor or its strong-coupling extension where electron-pairing interactions are limited to energies less than 0.1 eV. However, both the temperature and energy dependence of the structure in the R S /R N spectra may be adequately described within Eliashberg theory with an electron-boson coupling function which consists of both a low-energy component ͑Ͻ0.1 eV͒ and a high-energy component located between 1.6 and 2.1 eV.

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We have previously measured the temperature dependent thermal difference reflectance (TDR) spectra of several high-temperature superconducting thin films. From the TDR spectra collected above and below the critical temperature of each sample, the superconducting to normal state reflectance ratio, RS/RN, has been obtained. We observe significant deviations from unity in this reflectance ratio at photon energies on the order of 2.0 eV. Both the temperature dependence and location of this structure in the RS/RN spectra may be described by solving the Eliashberg integral equations with an electron-boson coupling function that includes both an eleciron-phonon interaction and an interaction located at approximately the energies of known charge transfer excitations in these materials (-2.0 eV). We found remarkably good agreement between the experimental data and the results of our calculations based upon this description of the superconducting state. We also use the technique of TDR spectroscopy to probe the superconducting proximity effect. By measuring the 1DR spectra of the silver layer in a Ag-(BiPb)SrCaCu3O1 bi-layer junction or the indium layer in a In-Ag-(BiPb)SrCaCu3O1 in-layer junction, at temperatures above and below the critical temperature of the high temperature superconductor, we hope to observe structure due to a proximity induced gap function in the normal metal.