The Birefringence and Extinction Coefficient of Ferroelectric Liquid Crystals in the Terahertz Range

Round 1

Reviewer 1 Report

Research on dielectric properties in the THz region has recently attracted attention. The authors' research may be useful. However, because there is so little information about liquid crystal alignment, the results of this hard-earned research cannot be put to good use. Please describe the following points in detail.

a) Why DHFLC and ESHFLC

There is no detailed explanation of why the author chooses spirally wound ferroelectric liquid crystals as the subject of this research.

b) Alignment and structure of DHFLC and ESHFLC

There is no description of the LC molecular alignment throughout the cell. It should be described clearly whether the director at the substrate surface is planar or vertical alignment. It should be also described clearly whether the helix in bulk is parallel or perpendicular to the substrate.

c) Photographs

Add the angle of the polarizer and the scale of the figure.

d) Validity of results

In order to discuss the validity of the results, please cite measurement examples of other research groups regarding E7 (or measurement examples using cyanobiphenyl liquid crystals). 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this manuscript, the authors examine the refractive index and extinction coefficient of two modes of FLC materials (ESHFLC and DHFLC) by the Terahertz (THz) time-domain spectroscopy system. Their large birefringence and low extinction coefficient show the possibility for their using in fast liquid crystal THz devices, for example imaging, sensing, wireless communication systems and photonic devices. To my knowledge, parameters of FLCs in THz wavelength have not been examined. This work is of great interest and I would like to recommend the acceptance of this work, after following questions and comments are addressed.

(1)   DHFLC 587 was produced by P. N. Lebedev Physical Institute of Russian Academy of Sciences but not by publicly available chemical companies. It is better to give chemical components in the manuscript.

(2)   Because FLCs are fast switching LC materials. I suggest the authors should elaborate what is the switching times for selected materials.

(3)   The cell gap of FLC samples is 150 μm. I am wondering whether FLC THz devices may need to operate at high voltage range with this cell gap.

(4)   Liquid crystals are an amazing soft-matter material. The authors may wish to introduce more about its other applications,  Nature Photonics, 2022, 16, 226；Responsive Materials 2023, 1, e20230005; Nature Communications 2023， 14, 3005；Advanced Materials 2023, 2306834； Light： Science & Applications 2015， 4，e253.

There exist some typos, for example, “FD4004N,” in the last paragraph in section 3 should be “FD4004N.”. The authors should carefully check these throughout the whole paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper was properly revised.