Low THz absorption of Na3La9B8O27 crystal

THz time-domain spectrum of the Na
3
La
9
B
8
O
27
(NLBO) crystal had been measured. The absorption spectrum and other optical constants had been gained through Fourier transform. The absorption coefficient α(ω) is less than 20/cm from 0.1 to 3.0 THz. With the increasing of the frequency, the refractive index n(ω) and the real of dielectric constant ε
1
(ω) steadily and monotonically increase. The n(ω) changes from 3.55 to 3.78, and the ε
1
(ω) changes from 12.7 to 14.2. The imaginary of dielectric constant ε
2
(ω) is less than 0.1 from 0.5 to 2.0 THz.