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Concept Paper

Attenuated Total Reflection at THz Wavelengths: Prospective Use of Total Internal Reflection and Polariscopy

1
Research Institute for Material and Chemical Measurement, National Metrology Institute of Japan (AIST), Tsukuba Central 3, 1-1-1 Umezono, Tsukuba 305-8563, Japan
2
CREST-JST and School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
3
Optical Sciences Centre and ARC Training Centre in Surface Engineering for Advanced Materials (SEAM), School of Science, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
4
THz Beamline, ANSTO-Australian Synchrotron, Clayton, VIC 3168, Australia
5
Australian Centre for Electromagnetic Bioeffects Research, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
6
World Research Hub Initiative (WRHI), School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Edik U. Rafailov
Appl. Sci. 2021, 11(16), 7632; https://doi.org/10.3390/app11167632
Received: 18 June 2021 / Revised: 13 August 2021 / Accepted: 16 August 2021 / Published: 19 August 2021
Capabilities of the attenuated total reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials are presented. The penetration depth of a THz evanescent wave in biological samples is dependent on the wavelength and temperature and can reach 0.1–0.5 mm depth, due to the strong refractive index change ∼0.4 of the ice-water transition; this is quite significant and important when studying biological samples. Technical challenges are discussed when using ATR for uneven, heterogeneous, high refractive index samples with the possibility of frustrated total internal reflection (a breakdown of the ATR reflection mode into transmission mode). Local field enhancements at the interface are discussed with numerical/analytical examples. Maxwell’s scaling is used to model the behaviour of absorber–scatterer inside the materials at the interface with the ATR prism for realistic complex refractive indices of bio-materials. The modality of ATR with a polarisation analysis is proposed, and its principle is illustrated, opening an invitation for its experimental validation. The sensitivity of the polarised ATR mode to the refractive index between the sample and ATR prism is numerically modelled and experimentally verified for background (air) spectra. The design principles of polarisation active optical elements and spectral filters are outlined. The results and proposed concepts are based on experimental conditions at the THz beamline of the Australian Synchrotron. View Full-Text
Keywords: ATR; THz; synchrotron radiation; diagnostics; polariscopy; four polarisation method ATR; THz; synchrotron radiation; diagnostics; polariscopy; four polarisation method
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MDPI and ACS Style

Ryu, M.; Ng, S.H.; Anand, V.; Lundgaard, S.; Hu, J.; Katkus, T.; Appadoo, D.; Vilagosh, Z.; Wood, A.W.; Juodkazis, S.; Morikawa, J. Attenuated Total Reflection at THz Wavelengths: Prospective Use of Total Internal Reflection and Polariscopy. Appl. Sci. 2021, 11, 7632. https://doi.org/10.3390/app11167632

AMA Style

Ryu M, Ng SH, Anand V, Lundgaard S, Hu J, Katkus T, Appadoo D, Vilagosh Z, Wood AW, Juodkazis S, Morikawa J. Attenuated Total Reflection at THz Wavelengths: Prospective Use of Total Internal Reflection and Polariscopy. Applied Sciences. 2021; 11(16):7632. https://doi.org/10.3390/app11167632

Chicago/Turabian Style

Ryu, Meguya, Soon Hock Ng, Vijayakumar Anand, Stefan Lundgaard, Jingwen Hu, Tomas Katkus, Dominique Appadoo, Zoltan Vilagosh, Andrew W. Wood, Saulius Juodkazis, and Junko Morikawa. 2021. "Attenuated Total Reflection at THz Wavelengths: Prospective Use of Total Internal Reflection and Polariscopy" Applied Sciences 11, no. 16: 7632. https://doi.org/10.3390/app11167632

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