Comments on “Optical properties of borate crystals in the terahertz domain”.

We comment on the recent paper by V.D. Antsygin et al. [Opt. Commun. 309 (2013) 333–337], in which for the first time dispersions of refractive indices n x , z in lithium triborate (LBO) were presented for the THz domain. Their claim of “ n x > n z ”, based on measurements by THz time-domain spectroscopy (TDS), is contrary to the well-known relationship for the maximum transparency region. [ABSTRACT FROM AUTHOR]