Precise determination of optical parameter of highly absorptive liquid in THz region using Kramers-Kronig relations

A new approach for precise complex optical parameter of highly absorptive liquid is proposed for transmission THz time-domain spectroscopy. Due to the nature of liquid, indirect measurement of sample thickness increases inaccuracy in optical parameter. Here, we reduced uncertainty in optical parameter through an algorithm optimizing sample thickness by Kramers-Kronig relations. Less than 2% error in absorption coefficient of water at 1THz is achieved in proof-of-concept experiment. This analysis technique can be of use in studies of water-based liquid such as biomolecular solution.