Terahertz time-domain spectroscopy of Raman inactive phonon-polariton in strontium titanate

Abstract

The Raman inactive low-frequency phonon-polariton was studied in a quantum paraelectric strontium titanate crystal. The lowest frequency IR active T 1u mode was investigated by the reflectance and transmittance Terahertz Time-Domain Spectroscopy using the pulse coherent THz radiation from 0.2 to 5.0 THz. The complex dispersion relations were determined using the real and imaginary parts of a polariton wavevector calculated from the complex refractive index which reflects the T 1u symmetry phonon-polariton. The remarkable change of the dispersion relation was observed in the vicinity of TO and LO mode frequencies for both real and imaginary parts of a polariton wave vector. The observed complex dispersion relation of T 1u symmetry is in agreement within the experimental uncertainty with the dispersion curves fitted by the damped harmonic oscillator model.

Terahertz Spectroscopy in Advanced Materials Science

“…A 1 (TO1) modes are Raman inactive while infrared active and hyper-Raman active. The T 1u modes were studied by the far infrared spectroscopy [47], THz-TDS [48,49], and hyper-Raman scattering [50,51].…”

“…TOj and LOj (j = 1, 2, 3) denote the three TO and three LO modes of the T 1u symmetry, respectively [52]. The results of FTIR [52] and THz TDS [49] are shown by the solid line and the closed circles, respectively. The values of the hyper-Raman scattering [50,51] are shown by the closed circles and closed diamonds.…”

Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics

“…Therefore, the study of the 3T 1u modes is possible using infrared spectroscopy, including THz-TDS and hyper-Raman scattering. The lowest-frequency T 1u modes have been studied using far-IR spectroscopy [29] and THz-TDS [30][31][32].…”

“…The line of OQ denotes ν = ck/2π ε(∞). The results of FTIR [33] and THz-TDS [32] are shown by the solid line and the closed circles, respectively. The values of the hyper-Raman scattering reported in [34,35] are shown by the closed triangles and closed diamonds for comparison to the FTIR values.…”

THz-TDS parameter extraction: empirical correction terms for the analytical transfer function solution

“…Terahertz Time Domain Spectroscopy (THz-TDS) is a powerful analytical technique which is able to directly provide information on the real and imaginary components of a materials refractive index, providing a vital spectroscopy technique to investigate material properties such as biological samples [1][2][3][4], semiconductor manufacturing [5], pharmaceuticals [6][7][8][9], monitoring atmospheric pollution [10], and mineral science applications [11]. THz-TDS also has been used for interrogating light-matter interactions such as plasmons [12][13][14][15], polaritons [16][17][18], and charge carrier dynamics [19,20]. Future development of THz-TDS is seen to be a lucrative technology for industrial sensing and manufacturing applications [21]; however there remain several practical obstacles to overcome before mass industry uptake such as measurement speeds, accuracy of measuring layers of sub-wavelength thickness, and the speed and reliability of data analysis methods.…”