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WO2017001811A1 - Spectroscopie raman améliorée - Google Patents

Spectroscopie raman améliorée Download PDF

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Publication number
WO2017001811A1
WO2017001811A1 PCT/GB2016/000133 GB2016000133W WO2017001811A1 WO 2017001811 A1 WO2017001811 A1 WO 2017001811A1 GB 2016000133 W GB2016000133 W GB 2016000133W WO 2017001811 A1 WO2017001811 A1 WO 2017001811A1
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WO
WIPO (PCT)
Prior art keywords
raman
raman spectrum
spectrum
wavelength
absorption
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/GB2016/000133
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English (en)
Inventor
Rebecca Joanne HOPKINS
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UK Secretary of State for Defence
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UK Secretary of State for Defence
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Filing date
Publication date
Application filed by UK Secretary of State for Defence filed Critical UK Secretary of State for Defence
Publication of WO2017001811A1 publication Critical patent/WO2017001811A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/90—Investigating the presence of flaws or contamination in a container or its contents

Definitions

  • This invention relates to improved methods for determining the characteristics of surfaces or sub-surfaces (i.e. behind a surface or barrier), particularly plastic surfaces.
  • the method is particularly applicable to determining the characteristics of substances within containers, especially plastic containers.
  • Raman spectroscopy is generally undertaken with light sources of wavelengths in the visible or near infra-red regions, such as 532 nm (visible) or 785 nm (near infra-red). Since the intensity of the returned Raman signal is inversely proportional to the fourth power of the excitation wavelength, shorter wavelengths can provide stronger Raman scattering and better signal-to-noise ratio.
  • irradiation at 532 nm results in a high level of fluorescence from the irradiated surface, which can overwhelm any Raman signal, and although irradiation with 785 nm suppresses the effect of fluorescence from materials in Raman spectra it is not completely eliminated, and can still create difficulties in identifying a material, especially with some plastic and glass materials.
  • the use of a longer wavelength (1064nm) has been demonstrated to mitigate the problem of fluorescence further
  • Spatially offset Raman Spectroscopy is one technique that has been developed to produce spectra for materials behind surfaces or barriers, or contents inside containers, termed subsurface spectra.
  • the technique exploits the fact that many materials are neither completely transparent to light nor completely block it, but that they tend to inelastic scatter light due to the Raman effect.
  • two Raman spectra are recorded which contain different contributions from the surface/container and subsurface/contents.
  • SORS is based on the generation of one spectra from light detected at the point of light irradiation, arid a second spectra from light detected at an offset position from that point.
  • the two spectra are then subtracted using a scaled subtraction to produce a spectrum of the subsurface/contents, and potentially a spectrum of the material at the surface.
  • Materials are identified by comparing the spectra to those of known materials. This approach enables assessment of the characteristics of a material, such as the contents of a container, without physical contact with the material. For instance identification of drugs or dangerous chemicals at security check points such as in airports, allowing identification of the materials without sampling, which could expose those involved to a potentially hazardous substance.
  • This approach to generating subsurface spectra can in particular suffer from the effects of absorption by the surface, in addition to the problems from fluorescence, resulting in generation of incomplete or low quality spectra.
  • the present invention provides a method of producing a Raman spectrum which reduces or omits the effect of surface absorption in the spectrum
  • the surface comprising: irradiating the surface with light of a first wavelength, collecting scattered light, and generating a first Raman spectrum from the light collected; irradiating the surface with light of a second wavelength, collecting scattered light, and generating a second Raman spectrum from the light collected, wherein the first and second wavelength are selected such that the Raman shifted ranges of the first Raman spectrum and second Raman spectrum are adjacent or overlap, and have further been selected such that the first and second Raman spectrum can be combined to reduce or omit the effect of absorption peaks in either spectra resulting from the surface; and combining the first Raman spectrum and second Raman spectrum to produce a third Raman spectrum representative of the surface, which third Spectrum reduces or omits the effect of absorption from the surface.
  • the first and second wavelengths are both greater than 1000 nm.
  • the method is for producing a Raman spectrum of a sub-surface which reduces or omits the effect of absorption from the surface in the spectrum.
  • the surface may for example be a container, and sub-surface may be the contents of a container.
  • the method utilises spatially offset Raman Spectroscopy (SORS).
  • SORS spatially offset Raman Spectroscopy
  • Such a method for producing a sub-surface Raman spectrum using SORS which reduces or omits the effect of absorption from the surface in the spectrum may comprise: a Irradiating the surface with light of a first wavelength at a first position; b. Collecting scattered light from the first position, and a second position spatially offset from the first position; c. Spectrally separating at least a portion of the collected light from each
  • Raman spectrum representative of the sub-surface wherein both the first and second wavelength are greater than 1000 nm, and the two wavelengths are selected such that the Raman shifted ranges of the first Raman spectrum and .
  • second Raman spectrum are adjacent or overlap, and have further been selected such that the first and second Raman spectrum can be combined to reduce or omit the effect of absorption peaks in either spectra resulting from the surface; and f.
  • the method is in particular directed to producing a Raman spectrum of the contents (subsurface) of a container (surface) which reduces or omits the effect of absorption from the container material in the spectrum, thus providing an improved SORS method for generating a Raman spectrum of a substance, through a barrier or container, which comprises supplying incident light of two or more different wavelengths to the surface of the container.
  • a barrier or container which comprises supplying incident light of two or more different wavelengths to the surface of the container.
  • Combining Raman spectra from incident light of different wavelengths preferably requires the output wavelength ranges to overlap to enable the baselines to be matched and the intensity of the spectral features to be scaled.
  • Spectral matching algorithms used to identify materials use peak position and relative peak intensity.
  • Raman Spectroscopy that provides an output in the stokes shifted Raman region 500- 2300cm "1 is preferred as many key features which allow for identification of materials occur in this range.
  • the Raman region of 0-3000cm "1 is however desirable as it contains additional features.
  • Wavelengths of 1000nm or greater have been shown to mitigate the effect of fluorescence from the surface and sub-surface which occurs at shorter wavelengths.
  • the selection of suitable wavelengths is also likely to depend on the intensity of the Raman effect available, since the intensity of the Raman effect decreases with longer wavelengths.
  • One suitable range may be 1000 nm to about 1750 nm.
  • the Applicant has found that irradiation of a surface with incident light sources of two wavelengths ⁇ 1000 nm, can be used to produce two Raman spectra of a sub-surface, which when combined can reduce or omit the effects of absorption in the final spectrum, and thus consequently produce a more representative, sharper or more complete spectrum of the sub surface.
  • the reduction of the effect of absorption in the spectrum should improve the likelihood of matching the spectrum of the contents with comparative spectra in libraries, such as those using matching algorithms.
  • Suitable wavelengths can be identified through interrogation of the absorption
  • the wavelengths may be selected by identifying and avoiding absorption peaks that occur in the Raman shifted region of the surface (container) transmission spectra.
  • the present invention provides a method for selecting two wavelengths for the method of the first aspect to reduce or omit the effect of absorption from a surface in a Raman spectrum, preferably of the subsurface, comprising; a. Irradiating the surface at a plurality of wavelengths, b. Collecting scattered light for each wavelength; c. Spectrally separating the collected scattered light to produce a transmission spectrum for the surface at each wavelength; and d. Selecting two wavelengths, preferably above 1000 nm, which display
  • Raman spectrum preferably of the subsurface, which reduces or omits the effect of absorption from the surface, as compared to separate Raman spectra, preferably for the subsurface, at the two separate wavelengths.
  • the method is in particular directed to selecting two wavelengths to reduce or omit the effect of absorption from the material of a container in a Raman spectrum of the contents of that container.
  • the Applicant has in particular identified and selected wavelengths suitable for overcoming problems of absorption when interrogating containers produced from high-density poly ethylene (HDPE), a common household plastic.
  • HDPE high-density poly ethylene
  • the transmission spectra profiles of HDPE have been interrogated to select ranges of excitation wavelengths suitable for producing spectra of container contents that can be combined to reduce or omit the effects of the absorption of the HDPE container. Essentially to enable any areas of absorption interference in the two spectra to be reduced or preferably omitted, and the two resulting spectra combined due to the adjacency or preferably overlap of the spectral regions.
  • Two Raman excitation wavelengths suitable for use with HDPE containers are 1118 nm and 1180 nm, chosen such that the resulting Stokes shifted Raman spectrum occurs within the spectral ranges 1255 nm - 1362 nm and 1500 - 1700 nm where there are no HDPE absorption features, resulting in absorption free Stokes shifted Raman spectrum from 506.- 1602 cm 1 and 1808 - 3062 cm “1 .
  • Raman excitation wavelengths can be selected to produce incomplete Stokes shifted Raman spectra within absorption free spectral windows. These multiple Raman spectra can then be fused together to produce a more complete Raman spectrum, such as one with greater spectral coverage.
  • Table 2 demonstrates that use of multiple excitation laser wavelengths between 1000 nm - 1255 nm can be used to produce Stokes shifted Raman spectra from 0 - 4117 cm "1 for HDPE by accessing the absorption free spectral windows.
  • ⁇ is the Raman shift expressed in wavenumbers
  • ⁇ 0 is the excitation wavelength
  • ⁇ is the Raman spectrum wavelength
  • the technical benefit of an improved method (method of the first aspect) of identifying substances in HDPE containers improves the time and efficiency of systems for identifying substances in common containers.
  • Two collection points for example at the point of incidence and at one point spatially offset from the point of incidence, are sufficient to produce spectral data for SORS. In other cases more collection points spatially offset from each other may be used and the spectral data combined to yield more accurate or more complete data to determine the characteristics of the sub-surface and/or surface.
  • Two wavelengths of incident light are sufficient to produce spectral data that can be combined to reduce or omit the effects of absorption. More wavelengths may however be used and the spectral data combined to yield more accurate or more complete data to determine the characteristics of the sub-surface and/or surface.
  • the method may further comprise steps of identifying the material using a processor and library matching algorithms.
  • spectroscopic information can be obtained that can be interpreted to establish the contents of a container without exposure to the contained substance.
  • the present invention uses multiple wavelengths in the longer SWIR range to allow Raman features of the contained substances to be obtained which could otherwise be unavailable due to reabsorption of scattered light.
  • the power density of the light source/laser is maintained in a range to optimise scattering without melting/damaging the container/barrier.
  • the spatially offset measurement point in SORS is preferably at an optimum distance from the point of incidence of the light source, which for these wavelengths is typically between 2 - 5 mm.
  • the collection of Raman spectra from points spatially offset from the point of incidence of the probe laser results in a series of spectra (2 or more).
  • the series of spectra taken contain different relative contributions of the Raman signals generated from the container material and the substance contained.
  • a different set of data is produced. This enables more representative spectra of the contained substance to be obtained by applying numerical processing to the two resulting spectra to produce a spectrum representative of the substance which can be matched to data to identify the substance.
  • the present invention provides an apparatus suitable for performing the method of the first aspect comprising means for providing two wavelengths of light, preferably of greater than 1000 nm.
  • the means for providing the two wavelengths of light may be two separate light sources, such as two lasers.
  • the wavelengths of light may be 1 1 18 nm and 1 180 nm, though numerous other wavelengths are possible.
  • the apparatus may comprise a processor for undertaking scaled subtraction of spectra, and/or for combining spectra to reduce or omit the effect of absorption from the surface, or container.
  • Figure 1 illustrates transmission spectra of a number of coloured HDPE containers from household products in which Raman shifted regions from excitation at 785 nm, 1064 nm and 1240 nm are overlaid for comparison;
  • Figure 2 illustrates transmission spectra of coloured HDPE containers from household products in which Raman shifted regions from excitation at 11 18 nm and 1 180 nm are overlaid for comparison.
  • SORS is one method that has been demonstrated as providing a solution to this technical challenge for some contents and container combinations.
  • SORS allows through-barrier detection, fluorescence from the container and/or contents can still be problematic. This fluorescence can mask at least the weaker Raman chemical fingerprint signals of the contents, thereby preventing detection.
  • Using a longer excitation wavelength that falls outside (or on the tail) of the fluorescence absorption band can help to mitigate against fluorescence from the container and/or contents, and the Applicant has shown that a single wavelength of 1064 nm can be used to overcome or reduce sample fluorescence in the Raman spectra, as opposed to shorter wavelengths typically used in commercial Raman devices (e.g. 785 nm).
  • Absorptions peaks present in the container absorption spectra that occur in the Raman shifted region can affect the completeness or quality of any spectrum, and especially can affect scaled subtraction and result in unrepresentative sample spectra being obtained. These unrepresentative spectra can cause problems for identification, such as through library matching algorithms. The Applicant has considered these problems.
  • a dual wavelength system can however overcome these problems, using at least two wavelengths ⁇ 1000 nm, targeted at parts of the transmission spectra where no absorption features occur (e.g. 1255 - 1362 nm and 1500 - 1700 nm for HDPE containers), and as a good example use of the excitation wavelengths of 1 1 18 nm and 1 180 nm to cover the Raman shifted ranges 506 - 1602 cm “1 and 1808 - 3062 cm “1 for HDPE, and produce a more complete spectra free of interference from absorption.
  • This approach overcomes the issues of container and/or contents fluorescence, and avoids absorption peaks present in the transmission spectra of the barriers/containers of interest, which lead to unrepresentative spectra being obtained.
  • the Applicant has identified that an apparatus having two excitation wavelengths ⁇ 1000 nm can be used to generate more representative or complete sub-surface spectra and especially overcome fluorescence from the contents/container and absorption of Raman scattered light by the container, which problems have been shown to result in the production of incomplete or unrepresentative spectra, that in particular can cause problems for library matching algorithms.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Physics & Mathematics (AREA)
  • General Health & Medical Sciences (AREA)
  • Biochemistry (AREA)
  • Analytical Chemistry (AREA)
  • Chemical & Material Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Abstract

La présente invention concerne des procédés et un appareil fondés sur la spectroscopie Raman améliorée qui permettent de déterminer les caractéristiques de surfaces ou de sous-surfaces (c'est-à-dire derrière une surface ou une barrière), en particulier des surfaces en matière plastique. Le procédé peut être utilisé de manière spécifique pour déterminer les caractéristiques de substances présentes à l'intérieur de contenants, notamment des contenants en matière plastique.
PCT/GB2016/000133 2015-06-29 2016-06-29 Spectroscopie raman améliorée Ceased WO2017001811A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB1511318.6A GB201511318D0 (en) 2015-06-29 2015-06-29 Improved spatially-offset raman spectroscopy
GB1511318.6 2015-06-29

Publications (1)

Publication Number Publication Date
WO2017001811A1 true WO2017001811A1 (fr) 2017-01-05

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PCT/GB2016/000133 Ceased WO2017001811A1 (fr) 2015-06-29 2016-06-29 Spectroscopie raman améliorée

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GB (2) GB201511318D0 (fr)
WO (1) WO2017001811A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114486853A (zh) * 2022-02-09 2022-05-13 西南大学 一种能够抵抗干扰的食品拉曼光谱检测放大仪器

Citations (2)

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WO2006061565A1 (fr) * 2004-12-09 2006-06-15 The Science And Technology Facilities Council Analyse spectrale raman de tissus et de fluides situes sous une surface
WO2014060983A1 (fr) * 2012-10-18 2014-04-24 Koninklijke Philips N.V. Dispositif pour un système d'analyse, système d'analyse comprenant ce dispositif et procédé d'utilisation du dispositif

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Publication number Priority date Publication date Assignee Title
WO2014192007A1 (fr) * 2013-05-27 2014-12-04 Indian Institute Of Science Procédé et appareil permettant d'obtenir des signatures spécifiques d'échantillon
US20160103073A1 (en) * 2014-10-14 2016-04-14 Alakai Defense Systems, Inc. Fluorescence removal from raman spectra by polarization subtraction

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006061565A1 (fr) * 2004-12-09 2006-06-15 The Science And Technology Facilities Council Analyse spectrale raman de tissus et de fluides situes sous une surface
WO2014060983A1 (fr) * 2012-10-18 2014-04-24 Koninklijke Philips N.V. Dispositif pour un système d'analyse, système d'analyse comprenant ce dispositif et procédé d'utilisation du dispositif

Non-Patent Citations (2)

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Title
BELL S E J ET AL: "Analysis of luminescent samples using subtracted shifted Raman spectroscopy", THE ANALYST, R S C PUBLICATIONS, GB, vol. 123, no. 8, 1 August 1998 (1998-08-01), pages 1729 - 1734, XP007916533, ISSN: 0003-2654, DOI: 10.1039/A802802H *
SHREVE A P ET AL: "EFFECTIVE REJECTION OF FLUORESCENCE INTERFERENCE IN RAMAN SPECTROSCOPY USING A SHIFTED EXCITATION DIFFERENCE TECHNIQUE", APPLIED SPECTROSCOPY, THE SOCIETY FOR APPLIED SPECTROSCOPY. BALTIMORE, US, vol. 46, no. 4, 1 April 1992 (1992-04-01), pages 707 - 711, XP000264023, ISSN: 0003-7028, DOI: 10.1366/0003702924125122 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114486853A (zh) * 2022-02-09 2022-05-13 西南大学 一种能够抵抗干扰的食品拉曼光谱检测放大仪器

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GB201611103D0 (en) 2016-08-10
GB2541515B (en) 2019-06-12
GB201511318D0 (en) 2015-08-12
GB2541515A (en) 2017-02-22

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