Abstract-Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep

Da-Hye Choi, Il-Min Lee, Kiwon Moon, Dong Woo Park, Eui Su Lee, and Kyung Hyun Park

Fig. 1 Schematic of the experiment set-up. A beating signal generated from a tunable laser system is injected into the transmitter (Tx) for THz generation. The THz waves are divided by a beam splitter. The beams reflected from the two mirrors are focused on the receiver (Rx).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-10-14695

A terahertz continuous wave system is demonstrated for thickness measurement using Gouy phase shift interferometry without frequency sweep. One arm of the interferometer utilizes a collimated wave as a reference, and the other arm applies a focused beam for sample investigation. When the optical path difference (OPD) of the arms is zero, a destructive interference pattern is produced. Interference signal intensity changes induced by the OPD changes can be easily predicted by calculations. By minimizing the difference between the measured and the calculated signal against the OPD, the thicknesses of sub-100-μm-thick samples are determined at 625 GHz.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Electromagnon with Sensitive Terahertz Magnetochromism in a Room-Temperature Magnetoelectric Hexaferrite

Sae Hwan Chun, Kwang Woo Shin, Hyung Joon Kim, Seonghoon Jung, Jaehun Park, Young-Mi Bahk, Hyeong-Ryeol Park, Jisoo Kyoung, Da-Hye Choi, Dai-Sik Kim, Gun-Sik Park, J. F. Mitchell, and Kee Hoon Kim

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.027202

An electromagnon in the magnetoelectric (ME) hexaferrite ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{2.5}{\mathrm{Co}}_2{\mathrm{Fe}}_{24}{O}_{41}$ (${\mathrm{Co}}_{2}Z$-type) single crystal is identified by time-domain terahertz (THz) spectroscopy. The associated THz resonance is active on the electric field ($E^{\omega }$) of the THz light parallel to the $c$ axis ($\parallel \left[001\right]$), whose spectral weight develops at a markedly high temperature, coinciding with a transverse conical magnetic order below 410 K. The resonance frequency of 1.03 THz at 20 K changes $-8.7\%$ and $+5.8\%$ under external magnetic field ($H$) of 2 kOe along [001] and [120], respectively. A model Hamiltonian describing the conical magnetic order elucidates that the dynamical ME effect arises from antiphase motion of spins which are coupled with modulating electric dipoles through the exchange striction mechanism. Moreover, the calculated frequency shift points to the key role of the Dzyaloshinskii-Moriya interaction that is altered by static electric polarization change under different $H$.

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Abstract-Electromagnon with sensitive terahertz magnetochromism in a room-temperature magnetoelectric hexaferrite

Sae Hwan Chun, Kwang Woo Shin, Hyung Joon Kim, Seonghoon Jung, Jaehun Park, Young Mi Bahk, Hyeong Ryeol Park, Ji Soo Kyoung, Da-Hye Choi, Dae-Sik Kim, Gun-Sik Park, John F. Mitchell, and Kee Hoon Kim

https://journals.aps.org/prl/accepted/d0079Y40Oe81095739b74618cf6352f7426e0ff08

An electromagnon in the magnetoelectric (ME) hexaferrite Ba0.5Sr2.5Co2Fe24 O41 (Co2Z-type) single crystal is identified by time-domain terahertz (THz) spectroscopy. The associated THz resonance is active on electric field (E\omega ) of the THz light parallel to the c axis (\textbar \textbar [001]), whose spectral weight develops at a markedly high temperature, coinciding with a transverse conical magnetic order below 410 K. The resonance frequency of 1.03 THz at 20 K changes -8.7 {\%} and +5.8 {\%} under external magnetic field (H) of 2 kOe along [001] and [120], respectively. A model Hamiltonian describing the conical magnetic order elucidates that the dynamical ME effect arises from anti-phase motion of spins which are coupled with modulating electric dipoles through exchange striction mechanism. Moreover, the calculated frequency shift points to the key role of Dzyaloshinskii-Moriya interaction that is altered by static electric polarization change under different H.

Abstract-Improved thickness estimation of liquid water using Kramers–Kronig relations for determination of precise optical parameters in terahertz transmission spectroscopy

Heyjin Son, Da-Hye Choi, and Gun-Sik Park

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-4-4509&origin=search

In terahertz transmission spectroscopy, there is a typical problem of thickness uncertainty, which hampers to determine precise optical parameters of samples. In order to resolve this experimental problem, a method optimizing sample thickness using singly subtractive Kramers–Kronig relations is proposed. For tens of micrometers thick water samples, we improved the accuracy of sample thickness by an order of magnitude (up to sub-micrometer) using the algorithm leading to obtain precise optical parameters of water. The broad applicability of the method is demonstrated for measuring various materials in addition to highly absorbing liquid water in the spectral range from 0.3 to 1.6 THz.

© 2017 Optical Society of America