THz spectra of five borates crystals

Terahertz spectral responses have been studied for five borate crystals Na5B2P3O13] (NBP), Zn3BPO (ZBP), SrB4O7 (SBO), Na3La9O3(BO3)8 (NLBO) and PbB4O7 (PBO). It is found that the samples had good transmission in 0.25–1.5 THz region. Both SBO and NLBO have an absorption coefficient less than 10 cm 1. Among them, SBO has not only the smallest absorption coefficient but also a very flat dispersion in the frequency region under investigation. Distinct resonance absorption peaks are observed for ZBP at v 1 = 1.4 THz, v 2 = 2.0 THz and SBO at v = 2.4 THz. In the spectrum of PBO, two abnormal dispersions appear in the frequency regions 1.44–1.74 and 2.2–2.5 THz. The absorption coefficients and refraction indices of the five crystals are extracted from the THz time-domain (THz-TDS) spectra in 0.25–2.5 THz region. The properties and origins of the spectral responses are addressed. Supported by the National Natural Science Foundation of China (Grant Nos. 50672104 and 10390160)