WO2002018919A1 - Tete de detection a reflexion totale attenuee - Google Patents

Tete de detection a reflexion totale attenuee Download PDF

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Publication number
WO2002018919A1
WO2002018919A1 PCT/GB2001/001536 GB0101536W WO0218919A1 WO 2002018919 A1 WO2002018919 A1 WO 2002018919A1 GB 0101536 W GB0101536 W GB 0101536W WO 0218919 A1 WO0218919 A1 WO 0218919A1
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WO
WIPO (PCT)
Prior art keywords
sensing head
radiation
transmissive body
atr
probe
Prior art date
Application number
PCT/GB2001/001536
Other languages
English (en)
Inventor
Ian Weaver
Original Assignee
Central Research Laboratories Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Central Research Laboratories Limited filed Critical Central Research Laboratories Limited
Priority to AU2001248511A priority Critical patent/AU2001248511A1/en
Publication of WO2002018919A1 publication Critical patent/WO2002018919A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor

Definitions

  • the present invention relates to an attenuated total reflectance sensing head. It relates particularly, but not exclusively, to an attenuated total reflectance sensing head for use in mid-infrared spectroscopy.
  • infra-red radiation gives extremely useful information about the molecular structure of that material. If infra-red radiation is directed through a material, some wavelengths will be absorbed and some will be transmitted. Analysis of the resulting absorption spectrum can reveal details about the molecular groups present in the material, and can therefore be used to identify the material. This technique is known as infra-red spectroscopy, and is commonly used in the pharmaceutical, agro- chemical, chemical and food industries to analyse substances.
  • Liquids absorb very strongly in the mid infra-red region of the electromagnetic spectrum, with optical path lengths through the liquid of more than a few tens of micrometers leading to complete absorption of the radiation. This means that it is extremely difficult to use conventional cuvettes to obtain absorption spectra.
  • the attentuated total reflectance (or ATR) technique was developed to alleviate this problem, as well as enabling in-situ measurements to be carried out.
  • the basis of the ATR technique is that a crystal element is brought into contact with the material to be analysed. Infra-red radiation is passed through the crystal element and directed towards the crystal element/material interface at an angle greater than the critical angle. This leads to total internal reflection of the radiation and the formation of a non-propagating evanescent wave which extends into the material over a distance approximately equal to the wavelength of the radiation. In the presence of an absorbing medium the evanescent wave is subject to wavelength dependent attenuation or absorption. This causes an associated change in the totally internally reflected radiation. The totally internally reflected radiation is then monitored to yield the absorption spectrum of the material.
  • ATR crystal elements are commonly made of infra-red transmitting material such as zinc selenide, silicon or germanium, with zinc selenide being the most common.
  • such crystals are not suitable for use with corrosive substances such as strong acids or bases and, due to their potential toxicity, they are also not suitable for use in the food industry.
  • This problem is overcome by the use of an ATR element made of diamond, which is transparent to mid infra-red radiation. Diamond is also suitable as it can be used with corrosive substances, and is non-toxic.
  • utilisation of diamond is not simple as the crystals are extremely expensive, and are therefore only used in relatively thin sheets.
  • a problem with the use of thin flat ATR elements made of diamond is that in general, at least two interacting internal reflections at approximately 45° at the ATR element/absorbing medium interface are required to effect adequate absorption.
  • This combined with the fact that the element is mounted at the end of a long narrow cylindrical probe for insertion into a reaction vessel, means that it is a non-trivial problem to pass the radiation into and out of the thin diamond element located at the end of the narrow probe. This is because the radiation must be directed towards the flat diamond ATR element at the required angle of incidence.
  • This problem is alleviated by the use of cheaper ATR elements such as zinc selenide from which a corner cube prism can be made, thereby facilitating a simpler compact retro-reflector design.
  • a composite attenuated total reflectance (ATR) element is disclosed in US Patent No. 5,773,825 (Axiom Analytical Inc.).
  • This ATR element is bi-layered, having a diamond layer which contacts the sample to be analysed, and a layer used to support the diamond layer which is made of an infra-red transparent material such as zinc selenide.
  • the width of the supporting zinc selenide layer has to be relatively wide in order to provide two interacting internal reflections at the ATR element/absorbing medium interface. This ATR element is therefore not suitable for use in a very narrow probe due to the shape of the two layers of the element.
  • An aim of the present invention is to provide an ATR sensing head suitable for use in the analysis of corrosive materials such as, for example, strong acids or bases.
  • a further aim of the invention is to provide an ATR sensing head suitable for use in a narrow probe.
  • an attenuated total reflectance sensing head as claimed in claims 1 to 10.
  • Figure 1 shows a cross-sectional view of a first attenuated total reflectance sensing head
  • Figure 2a shows a perspective view of a portion of the first attenuated total reflectance sensing head
  • Figure 2b shows a perspective view of the attenuated total reflectance sensing head
  • Figures 3 a and b show a cross-sectional view of a probe and the first attenuated total reflectance sensing head
  • Figure 4 shows a cross-sectional view of a second attenuated total reflectance sensing head
  • Figure 5 shows a cross-sectional view of another attenuated total reflectance sensing head.
  • FIG. 1 there is shown a cross-sectional view of an attenuated reflectance sensing head (10a) which comprises a first TR transmissive portion (12) made of diamond, and a second, supporting IR transmissive portion (14) made, for example, of zinc selenide.
  • the zinc selenide portion (14) is a rectangular solid block with a front face (16a), back face (16b) (not shown), upper face (16c), and lower face (16d), the rectangular solid having a truncated wedge-shaped cut-away portion extending from the upper face (16c) of the rectangular block towards the centre of the block to form an upper recess (18a), and a larger truncated wedge-shaped cut-away portion extending from the lower face (16d) of the rectangular block towards the centre of the block to form a lower recess (18b). Both cut-away portions extend from the front face (16a) to the back face (16b) of the block.
  • the diamond portion (12) of the sensing head (10a) is of a complimentary shape to, and is disposed within, upper recess (18a) (i.e., it is a hexahedron having a trapezoid vertical cross-section). It is separated from the zinc selenide portion (14) by a small air gap (20) at its lower surface (44). This arrangement is shown in Figure 2b.
  • the tapered surfaces of the diamond and the zinc selenide portions of the sensing head are in optical contact. These surfaces may be coated with an anti-reflection coating, if required.
  • the probe (22) in which the sensing head (10a) is disposed is formed from an elongated tube of circular cross-section.
  • the ATR sensing head (10a) is located at its distal end. As shown in Figures 3a and 3b, the ATR sensing head (10a) is kept in place by way of a lip (24) located at the end of the probe.
  • the lip (24) protects the zinc selenide portion (14) from, but exposes the diamond portion (12) to, the material under test.
  • a sealing member (26) is disposed on the underside of the lip (24) to prevent material from entering the probe (22) and coming into contact with the supporting portion (14). In the present example, the sealing member is in the form of a ring.
  • infra-red radiation is generated in the main body of the spectroscope and is directed along the body of the probe (22) via, for example, fibre optic connections (28a,b).
  • the radiation is then collimated by a first lens (30a) into the lower recess (18b) and onto a sloped lower inner surface (32a) of the zinc selenide portion (14), whereupon a portion of the radiation (34) is refracted into the zinc selenide portion, and a portion of the radiation (36) is reflected back into the lower recess.
  • the angle of slope, ⁇ , of the lower inner surface (32a) of the zinc selenide portion (14) is such that the infra-red radiation (36) reflected by this surface is at right angles to the refracted infra-red radiation (34).
  • a polarized beam of infra-red radiation gives more accurate attenuated total reflection spectra than non-polarised beams because the depth of the evanescent wave into the absorbing medium, and hence the fraction of light absorbed, is polarisation dependent.
  • the required angle, ⁇ , of slope of the lower inner surface (32a) is approximately equal to that required to yield a refracted beam of 45° off the original direction of the radiation. This angle of 45° is the desired angle for propagation of the radiation through the sensing head.
  • the refracted beam of radiation (34) passes through the zinc selenide towards the outer surface (16e) of the second portion (14).
  • the outer surfaces (16e,f) (i.e., the side faces of the rectangular block) of the zinc selenide portion (14) are substantially parallel to the original direction of propagation of the infra-red beam.
  • the refracted radiation (34) is totally internally reflected at the outer surface (16e) of the zinc selenide portion (14), at an angle, ⁇ x , of 45°.
  • the outer surface (16e) could be mirrored so that total internal reflection does not have to take place at this surface.
  • the beam (34) passes through the zinc selenide towards the upper recess (18a).
  • the inner surfaces (38) of the zinc selenide portion which define the upper recess (18a) are also sloped.
  • the angle of the slope is such that the beam exits from the zinc selenide portion (14) of the sensing head and enters the diamond portion (12) at an angle, ⁇ 2 , of 90° to both the upper inner surface (38) of the zinc selenide portion, and the sloping side surface (40) of the diamond portion. This ensures that refraction across the diamond/zinc selenide interface does not occur.
  • An index matching fluid may also be used at this interface to improve optical coupling.
  • the length of the upper face (42) of the diamond portion (12) of the sensing head which comes into contact with the material to be analysed is made equal to four times the thickness, t, thereof. This results in the infra-red beam being totally internally reflected three times, as shown in Figure 1. Two of these reflections occur at the diamond/sample interface. Again, the lower surface of the diamond part (12) may be mirrored so that total internal reflection is not an absolute requirement.
  • the radiation passes back into the zinc selenide portion (14) of the sensing head.
  • the exit route of the infra-red beam is in the opposite direction to the input route.
  • the radiation exits the ATR sensing head (10a) and enters the lower recess (18b).
  • the exiting radiation is focused onto a fibre optic connection (28b) by a further lens (30b), and is directed to the main spectrometer for further processing and subsequent analysis.
  • FIG. 4 Another embodiment of the invention is shown in Figure 4.
  • the structure of the ATR sensing head (10b) is the same as the aforedescribed ATR sensing head (10a), except that the lower surface (44) of the diamond (12) is in contact with the zinc selenide portion (14) of the sensing head.
  • the lower surface (44) of the diamond and/or the adjacent zinc selenide portion of the sensing head can be coated with a highly reflective layer of, for example, gold to reflect IR radiation at this coated surface.
  • the second portion (14) can be made from a material other than zinc selenide, but there will now be a different angle of slope, ⁇ , of the inner surface (32) in order for the beam to be reflected by 45° at the outer surface (16e). It can be shown that the angle, ⁇ , of the slope of the lower inner surface (32a) of the second portion (14) which is composed of a material of refractive index n 2 , in order to provide a 45° refracted beam, is given by:
  • the second portion (14) of the sensing head is made of a material with a different refractive index to zinc selenide, the Brewster condition will not be satisfied, and therefore the radiation will only be partially polarized.
  • the attenuated total reflectance sensing head (10c) comprises a first diamond portion (12), and a second, supporting portion (14), as previously described.
  • the second portion (14) of the sensing head has a rectangular cut-away portion in the upper face (16c) of the block, rather than a truncated wedge.
  • the diamond portion (12) of the ATR sensing head (10c) is of a complimentary shape to, and sits in, upper recess (18a).
  • the zinc selenide and diamond have virtually the same refractive index over the mid infra-red region, where the second portion (14) of the sensing head is made of zinc selenide there will be no significant refraction of the infra-red beam as it travels across the zinc selenide/diamond interface.
  • the zinc selenide and the diamond should be in optical contact. If they are not in optical contact, total internal reflection would occur in the zinc selenide portion, and the radiation would be unable to propagate from the zinc selenide to the diamond.
  • the angle, ⁇ , of the slope of the lower inner surface (32a) of the zinc selenide portion is the same as for the aforedescribed ATR sensing heads (10a,b), i.e., 112.45°.
  • the second portion (14) may have an air gap (20) behind the diamond, or the lower surface (44) of the diamond may be coated with a highly reflective coating, as discussed previously.
  • the second portion (14) of the ATR sensing head (10c) is made of a material which does not have the same refractive index as diamond, refraction of the infra-red beam will occur as it crosses the supporting crystal/diamond interface. If the angle of incidence, ⁇ i , within the diamond (12) is required to be 45°, which is desirable, then the angle, ⁇ , of the slope of the lower inner surface (32a) of the second portion (14) of the sensing head can be shown to be given by:
  • n x is the refractive index of diamond
  • n 2 is the refractive index of the material from which the second portion (14) of the sensing head is made.
  • the surface (46) of the second portion (14) of the sensing head which defines the upper boundary of the lower recess (18b) may be roughened. This stops reflections from the bottom of the diamond portion (12) from being specularly reflected at this surface. If this surface is not roughened, it could possibly lead to specular reflections being detected by the infra-red detector, giving false readings.
  • ATR sensing heads (10a,b,c) are: 1) polarisation of infra-red radiation incident upon the ATR sensing head (10a,b,c) occurs automatically for a zinc selenide supporting portion without the need for additional polarisers; and 2) the shape of the ATR sensing head (10a,b,c) means that a narrow probe can be used.
  • the surfaces (32) of the second portion of the sensing head where refraction occurs are sloped.
  • the sides (16e,f) of the second portion where reflection occurs are flat.
  • the remaining outer surfaces of the second portion of the sensing head could be curved, leading to a cylindrical second portion with two flats polished on the outer sides.
  • the second portion (14) of the sensing head could have only one (lower) recess formed therein which receives incoming IR radiation.
  • the diamond (12) could have a rectangular cross section and may extend across the whole upper surface (16c) of the second portion of the sensing head.
  • the second portion (14) of the sensing head described herein is composed of zinc selenide, it could be made from any material transparent to the wavelength of interest. It could, for example, be zinc sulphide or germanium.
  • the lower inner surfaces (32) of the second portion (14) of the sensing head could be coated with an anti- reflection coating. This would prevent losses due to reflection of infra-red radiation at the ATR sensing head (10a,b,c) surfaces, but the infra-red beam will not be polarised.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention concerne une tête de détection (10) à réflexion totale atténuée (RTA) destinée à une utilisation en spectroscopie infrarouge (IR). Ladite tête de détection comporte un premier élément transmissif par infrarouge pourvu d'une partie prismatique (12) présentant une surface de détection (42) destinée à entrer en contact avec un échantillon, et un deuxième élément transmissif par infrarouge (14). La partie prismatique (12) présente de premières surfaces d'entrée et de sortie infrarouge (40) s'amincissant l'une en direction de l'autre lorsque la distance par rapport à la surface de détection augmente, ladite partie prismatique étant logée dans une cavité formée dans le deuxième élément transmissif par infrarouge. Ce deuxième élément transmissif par infrarouge présente au moins deux surfaces (38) optiquement couplées aux premières surfaces d'entrée et de sortie infrarouge (40). Les angles des surfaces des premier et deuxième éléments transmissifs par infrarouge provoquent une propagation du rayonnement polarisé au travers de la tête de détection à réflexion totale atténuée. Ainsi, il est possible de réaliser des mesures plus précises.
PCT/GB2001/001536 2000-09-01 2001-04-03 Tete de detection a reflexion totale attenuee WO2002018919A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001248511A AU2001248511A1 (en) 2000-09-01 2001-04-03 Attenuated total reflectance sensing head

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0021502.0 2000-09-01
GBGB0021502.0A GB0021502D0 (en) 2000-09-01 2000-09-01 An attenuated total reflectance sensing head

Publications (1)

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WO2002018919A1 true WO2002018919A1 (fr) 2002-03-07

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GB (1) GB0021502D0 (fr)
WO (1) WO2002018919A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103398948A (zh) * 2013-08-14 2013-11-20 武汉大学 一种用于傅里叶变换红外光谱仪的atr探头
EP2693200A1 (fr) * 2011-03-29 2014-02-05 Hamamatsu Photonics K.K. Spectromètre à ondes térahertz
US20150136986A1 (en) * 2012-05-29 2015-05-21 Hamamatsu Photonics K.K. Prism member, terahertz-wave spectroscopic measurement device, and terahertz-wave spectroscopic measurement method
US9080913B2 (en) 2011-03-29 2015-07-14 Hamamatsu Photonics K.K Terahertz-wave spectrometer and prism member
WO2017045998A1 (fr) * 2015-09-14 2017-03-23 Lorenz Sykora Élément de réflexion atr et procédé de spectroscopie atr
FR3117214A1 (fr) * 2020-12-07 2022-06-10 Seb S.A. Element optique pour un dispositif de determination de la brillance relative d’une pluralite de fibres capillaires
WO2024011021A1 (fr) * 2022-07-08 2024-01-11 Daylight Solutions, Inc. Ensemble de cellules de test comprenant un réflecteur total atténué

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0624785A1 (fr) * 1992-10-07 1994-11-17 Sumitomo Electric Industries, Ltd. Element optique a infrarouge et appareil de mesure
US5440126A (en) * 1991-04-26 1995-08-08 British Technology Group Ltd. Optical probe heads
US5773825A (en) * 1995-09-22 1998-06-30 Axiom Analytical, Inc. Bi-layer attenuated total reflectance device providing optimized absorbance linearity

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5440126A (en) * 1991-04-26 1995-08-08 British Technology Group Ltd. Optical probe heads
EP0624785A1 (fr) * 1992-10-07 1994-11-17 Sumitomo Electric Industries, Ltd. Element optique a infrarouge et appareil de mesure
US5773825A (en) * 1995-09-22 1998-06-30 Axiom Analytical, Inc. Bi-layer attenuated total reflectance device providing optimized absorbance linearity

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9080913B2 (en) 2011-03-29 2015-07-14 Hamamatsu Photonics K.K Terahertz-wave spectrometer and prism member
EP2693200A1 (fr) * 2011-03-29 2014-02-05 Hamamatsu Photonics K.K. Spectromètre à ondes térahertz
EP2693200A4 (fr) * 2011-03-29 2014-09-17 Hamamatsu Photonics Kk Spectromètre à ondes térahertz
US9696206B2 (en) 2011-03-29 2017-07-04 Hamamatsu Photonics K.K. Terahertz-wave spectrometer
US9417182B2 (en) * 2012-05-29 2016-08-16 Hamamatsu Photonics K.K. Prism member, terahertz-wave spectroscopic measurement device, and terahertz-wave spectroscopic measurement method
US20150136986A1 (en) * 2012-05-29 2015-05-21 Hamamatsu Photonics K.K. Prism member, terahertz-wave spectroscopic measurement device, and terahertz-wave spectroscopic measurement method
CN103398948B (zh) * 2013-08-14 2015-09-16 武汉大学 一种用于傅里叶变换红外光谱仪的atr探头
CN103398948A (zh) * 2013-08-14 2013-11-20 武汉大学 一种用于傅里叶变换红外光谱仪的atr探头
WO2017045998A1 (fr) * 2015-09-14 2017-03-23 Lorenz Sykora Élément de réflexion atr et procédé de spectroscopie atr
US10585040B2 (en) 2015-09-14 2020-03-10 Lorenz Sykora ATR reflection element and ATR spectroscopy method
FR3117214A1 (fr) * 2020-12-07 2022-06-10 Seb S.A. Element optique pour un dispositif de determination de la brillance relative d’une pluralite de fibres capillaires
WO2022123150A1 (fr) * 2020-12-07 2022-06-16 Seb S.A. Elément optique pour un dispositif de détermination de la brillance relative d'une pluralité de fibres capillaires
WO2024011021A1 (fr) * 2022-07-08 2024-01-11 Daylight Solutions, Inc. Ensemble de cellules de test comprenant un réflecteur total atténué

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GB0021502D0 (en) 2000-10-18
AU2001248511A1 (en) 2002-03-13

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