Measurement of the Soft-Mode Dispersion in SrTiO3by Terahertz Time-Domain Spectroscopic Ellipsometry

We have measured the soft-mode dispersion of SrTiO3 bulk single crystals by terahertz time-domain spectroscopic ellipsometry (THz-TDSE). The real and imaginary parts of the dielectric function of the sample are independently derived from the complex amplitude reflectivities of p- and s-polarized terahertz pulses. The TO1 soft-mode resonance is clearly observed at 2.62 THz (87 cm-1). The spectra of the complex dielectric function agree well with those predicted using the general harmonic oscillator model with parameters obtained from conventional Fourier-transform far-infrared (FT-FIR) reflection measurements. THz-TDSE developed in this study can be employed to investigate low-frequency dielectric dispersions.