scholarly journals Characterisation of Biological Materials at THz Frequencies by Attenuated Total Reflection: Lard

2020 ◽  
Vol 10 (23) ◽  
pp. 8692
Author(s):  
Zoltan Vilagosh ◽  
Alireza Lajevardipour ◽  
Dominique Appadoo ◽  
Soon Hock Ng ◽  
Saulius Juodkazis ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Evanescent Wave ◽  
Total Internal Reflection ◽  
Complex Refractive Index ◽  
Biological Tissues ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Frustrated Total Internal Reflection ◽  
Model Sample ◽  
Difference Time

The penetration depth of an evanescent wave in Attenuated Total Reflection (ATR) is dependent on the wavelength of the radiation utilised. At THz frequencies, the penetration depth into biological tissues is in the order of 0.1 to 0.5 mm; rendered pig lard was used as a model sample in this study. A method for the direct measurement of the evanescent wave penetration depth is presented which allows for the estimation of the dispersion of the complex refractive index by using the reflection of the evanescent wave from varying sample depths. The method employs frustrated total internal reflection, and has been demonstrated by using the THz/Far-IR beamline at the Australian synchrotron, and modelled using finite difference time domain (FDTD) simulations.

scholarly journals Attenuated Total Reflection at THz Wavelengths: Peculiarities of Total Internal Reflection and Polariscopy

2021 ◽  
Author(s):  
Meguya Ryu ◽  
Soon Hock Ng ◽  
Vijayakumar Anand ◽  
Stefan Lundgaard ◽  
Jingwen Hu ◽  
...  
Keyword(s):  
Refractive Index ◽  
Biological Samples ◽  
Total Internal Reflection ◽  
Refractive Index Change ◽  
High Refractive Index ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Internal Reflection ◽  
Optical Elements ◽  
Frustrated Total Internal Reflection

Capabilities of the Attenuated Total Reflection (ATR) at THz wavelengths for increased sub-surface depth characterisation of (bio-)materials is 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 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 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 was used to model behaviour of absorber-scatterer inside materials at the interface with ATR prism for realistic complex refractive indices of bio-materials. Modality of ATR with polarisation analysis is proposed and its principle 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 revealed. Design principles of polarisation active optical elements and spectral filters are outlined. The results and concepts are based on experiments carried out at the THz beamline of the Australian Synchrotron.

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

2021 ◽  
Vol 11 (16) ◽  
pp. 7632
Author(s):  
Meguya Ryu ◽  
Soon Hock Ng ◽  
Vijayakumar Anand ◽  
Stefan Lundgaard ◽  
Jingwen Hu ◽  
...  
Keyword(s):  
Refractive Index ◽  
Biological Samples ◽  
Total Internal Reflection ◽  
Refractive Index Change ◽  
High Refractive Index ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Internal Reflection ◽  
Experimental Conditions ◽  
Frustrated Total Internal Reflection

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.

On the Nature of the Evanescent Wave

2013 ◽  
Vol 67 (2) ◽  
pp. 126-131 ◽  
Author(s):  
Milan Milosevic
Keyword(s):  
Theoretical Result ◽  
Experimental Method ◽  
Evanescent Wave ◽  
Research Topic ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Entire Field ◽  
Mental Picture ◽  
Basic Understanding ◽  
Atr Spectroscopy

This is an unusual paper in that it does not address a particular research topic or present a novel experimental method or a new theoretical result. This paper addresses our basic understanding of the nature of the evanescent wave, the wave that is the basis of the entire field of Attenuated Total Reflection (ATR) spectroscopy. I recently had the opportunity to reexamine the foundations of ATR spectroscopy and was surprised to have had to change my own mental picture of the evanescent wave that I have built over the last 25 years. Over the years I have had numerous discussions with a large number of workers in the field as well as with my former mentor, and one of the originators and the principal developer of ATR spectroscopy, the late N.J. Harrick. Everything brought up in all these discussions was perfectly consistent with my old mental picture of the evanescent wave. Thus, I believe that the picture of the evanescent wave that I had is virtually universally held by workers in the field. This paper describes the new picture of the evanescent wave that emerged from said reexamination process.

scholarly journals Using Attenuated Total Reflection (ATR) Apparatus to Investigate the Temperature Dependent Dielectric Properties of Water, Ice, and Tissue-Representative Fats

2021 ◽  
Author(s):  
Zoltan Vilagosh ◽  
Alireza Lajevardipour ◽  
Dominique Appadoo ◽  
Saulius Juodkazis ◽  
Andrew Wood
Keyword(s):  
Refractive Index ◽  
Dielectric Properties ◽  
Liquid Water ◽  
Complex Refractive Index ◽  
Rapid Change ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Temperature Dependent ◽  
Minimal Sample ◽  
Emulsified Water

A novel method of investigating the temperature dependent variation of aspects of the complex refractive index n* in samples in the THz range using continuous, non-polarised, synchrotron radiation is presented. The method relies on the use of ATR apparatus, and retains the advantage of minimal sample preparation, which is a feature of ATR techniques. The method demonstrates the viability of rapidly monitoring temperature reflectance whilst continuously heating or cooling samples by using a temperature variable Thermal Sample Stage. The method remains useful when the refractive index of the sample precludes attenuated total reflection study. This is demonstrated with the water reflectance experiments. The temperature dependent ATR reflectance of tissue-representative fats (lard and Lurpak® butter) was investigated with the novel approach. Both are within the ATR range of the diamond crystal in a “true” ATR mode. Lard showed no clear temperature variation between -15 0C and 24 0C at 0.7 to 1.15 THz or 1.70 to 2.25 THz. Lard can be regarded as having invariable, constant, dielectric properties within mixtures when biological substances are being assessed for temperature dependent dielectric variation within the stated THz ranges. Lurpak® butter (water content 14.7%) displayed temperature dependent reflectance features with a steady decline in reflectivity with increasing temperature. This is in line with the temperature-dependent behaviour of liquid water. There is no rapid change in reflectance, even at -20 0C, suggesting that emulsified water retains liquid-water-like THz properties at freezing temperatures.

Novel Attenuated Total Reflection Fourier Transform Infrared Microscopy Using a Gem Quality Diamond as an Internal Reflection Element

2005 ◽  
Vol 59 (10) ◽  
pp. 1236-1241 ◽  
Author(s):  
Sanong Ekgasit ◽  
Pimthong Thongnopkun
Keyword(s):  
Fourier Transform ◽  
Total Internal Reflection ◽  
Fourier Transform Infrared ◽  
Normal Incidence ◽  
Total Reflection ◽  
Attenuated Total Reflection ◽  
Internal Reflection ◽  
The Novel ◽  
Infrared Microscope ◽  
Ft Ir

A novel technique for attenuated total reflection Fourier transform infrared (ATR FT-IR) spectral acquisition by an infrared microscope with a gem-quality faceted diamond as an internal reflection element (IRE) is introduced. Unlike conventional IREs, the novel diamond IRE has a sharp tip configuration instead of a flat tip configuration. Light at normal incidence was coupled into the diamond while the transflected radiation from the diamond was collected through the table facet by the built-in 15× Cassegrainian objective. The number of reflections in the novel diamond IRE equals two. The evanescent field generated under total internal reflection at the pavilion facet was exploited for ATR spectral acquisition of materials attached to the IRE. The observed ATR spectra were compared to those obtained via a traditional zinc selenide IRE.

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