GB2240172A - A spectroscopy sensing method and apparatus for the measurement or detection of a material - Google Patents
A spectroscopy sensing method and apparatus for the measurement or detection of a material Download PDFInfo
- Publication number
- GB2240172A GB2240172A GB9001224A GB9001224A GB2240172A GB 2240172 A GB2240172 A GB 2240172A GB 9001224 A GB9001224 A GB 9001224A GB 9001224 A GB9001224 A GB 9001224A GB 2240172 A GB2240172 A GB 2240172A
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- sensing
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- 239000000463 material Substances 0.000 title claims abstract description 82
- 238000001514 detection method Methods 0.000 title claims abstract description 43
- 238000005259 measurement Methods 0.000 title claims abstract description 23
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000004611 spectroscopical analysis Methods 0.000 title description 2
- 230000003287 optical effect Effects 0.000 claims abstract description 138
- 238000010521 absorption reaction Methods 0.000 claims abstract description 20
- 238000001228 spectrum Methods 0.000 claims abstract description 16
- 230000003595 spectral effect Effects 0.000 claims description 24
- 230000005540 biological transmission Effects 0.000 claims description 8
- 230000000694 effects Effects 0.000 claims description 7
- 239000013307 optical fiber Substances 0.000 claims description 5
- 230000001419 dependent effect Effects 0.000 claims description 4
- 230000000704 physical effect Effects 0.000 claims description 4
- 239000012925 reference material Substances 0.000 claims description 4
- 238000012887 quadratic function Methods 0.000 claims description 2
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- 239000000523 sample Substances 0.000 description 15
- 239000000835 fiber Substances 0.000 description 3
- 229910052761 rare earth metal Inorganic materials 0.000 description 3
- 230000003466 anti-cipated effect Effects 0.000 description 2
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- 150000002910 rare earth metals Chemical class 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000010183 spectrum analysis Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 238000005100 correlation spectroscopy Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
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- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
Classifications
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- 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
- G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
- G01J3/433—Modulation spectrometry; Derivative 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
- G01J3/12—Generating the spectrum; Monochromators
- G01J3/1256—Generating the spectrum; Monochromators using acousto-optic tunable filter
-
- 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
- G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
- G01J3/433—Modulation spectrometry; Derivative spectrometry
- G01J3/4338—Frequency modulated 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
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/0014—Radiation pyrometry, e.g. infrared or optical thermometry for sensing the radiation from gases, flames
-
- 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
- G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
- G01N2021/3531—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis without instrumental source, i.e. radiometric
-
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/061—Sources
- G01N2201/0616—Ambient light is used
Abstract
A spectroscopic sensing method for the measurement or detection of at least one material in a sensing region 6, the method being one in which the material either emits light in one or more narrow emission lines or absorbs light from a light source 4 in one or more narrow absorption lines, and in which the light existing from the material is directed through optical modulator means 8 capable of modulating the optical phase or frequency of the light such that its optical spectrum varies as a function of time, before being directed through a reference region 12 containing a known sample of the material to be detected, before in turn being directed to optical detection means 14. Spectroscopic sensing apparatus is also disclosed. <IMAGE>
Description
A SPECTROSCOPY SENSING METHOD AND
APPARATUS FOR THE MEASUREMENT OR DETECTION
OF A MATERIAL
It is well known to perform spectral analysis using the technique of correlation spectroscopy, where a material having a complex absorption spectrum is analysed, detected or otherwise recognised by comparing its measured spectrum with one already known from previous measurement or theory.
In our co-pending United Kingdom patent application
Nos. 8912446.5, 8916777.9 and 8924620.1 there is described the detection of a material by spectral analysis, using a light source (which covers the region corresponding to spectral lines of, for example, absorption within the material to be analysed), an optical system for directing light from the light source along a path through a cell containing the material to be analysed and also through a further cell containing a known sample of the material to be analysed, and finally a light detection means in which the cell containing the known sample of the material is capable of being modulated to vary the absorption lines of the material in the cell. This enables the combined transmission of the cell and the further cell to be varied and this in turn causes a detectable variation in the signal detected by the detector means.The extent of the variation is dependent upon the quantity of material in the measurement cell. In patent application No.
8916777.9, there is also discussed the detection of hot gases from their emission spectra, by an essentially similar method in which the light source is composed of the hot gases themselves, without the need for a further light source.
The present invention is a variation of the disclosures in our above mentioned United Kingdom patent applications in that, although a material-cell is used as a reference region in an optical system using a separate measurement region, the absorption in this reference cell is not subjected to a direct modulation.
Instead an optical modulator means is employed.
Accordingly, this invention provides a spectroscopic sensing method for the measurement or detection of at least one material in a sensing region, the method being one in which the material either emits light in one or more narrow emission lines or absorbs light from a light source in one or more narrow absorption lines, and in which the light existing from the material is directed through optical modulator means capable of modulating the optical phase or frequency of the light such that its optical spectrum varies as a function of time, before being directed through a reference region containing a known sample of the material to be detected, before in turn being directed to optical detection means where the detected variations in the received optical signal intensity, in response to variations in the modulation caused by the optical modulator means, are dependent upon the concentration of the material to be detected which is present in the sensing region, provided the concentration of the same or similar material in the reference region is known, and where the detected signal variations are processed to measure or detect the material in the sensing region.
The material to be detected will normally be one having one or more relatively narrow absorption lines, for example a gas or a vapour, although certain solids or liquids having narrow absorption lines may also be detected. Such solids or liquids may be, for example, rare earth element containing crystals, glasses or solutions.
The invention is also applicable to hot gases or flames, certain regions of which, for example incandescent carbon particles, give rise to relatively broadband emission of light. This emission acts as the above mentioned light source so that the material to be measured or monitored then absorbs a proportion of this light on passage through further parts of the hot gas or flame.
The invention is also applicable to cases where the sensing region contains a hot gas or gas plasma, and where the spectral lines are gas emission lines characteristic of the material to be detected, and where the combination of a frequency or phase shifting element and a sensing region containing the known sample of gas forms a device of variable transmission which is selective to the particular gas to be detected.
Hence variations may be caused in the detected signal received by detector means. The detected signal will normally be such that it increases when the optical modulator means, for example an optical phase or frequency shifter, is operated.
The invention may also be applied to the detection of gases in a free-air or space environment, in which the light source is a naturally occurring one.
Thus, for example, the light source may be direct or diffuse sunlight, background infrared light, starlight, moonlight. The light may pass through a region or regions containing gas of the type to be detected, and then subsequently through optical modulator means such for example as through a frequency or phase shifting element, and then through a reference region containing a known sample of the gas or gases of the type to be detected, before finally impinging on the detector means.
In the method of the invention, the relative positions of-the sensing region and the reference region may be interchanged.
The method may be one in which the variation of the detected response to the applied optical modulation is observed in order to derive more detailed spectral information on the absorption or emission lines of the material. This may be effected, for example, by changing the optical frequency shift of a Bragg cell iodulator to derive the linewidth of the spectral lines of the material from the functional variation of the received optical intensity, as the frequency is shifted and as the overlap integral of the spectral lines is changed. The information on the spectral lines may be used to deduce further information regarding the temperature and/or the flow rate of the gas by comparison with anticipated Doppler broadening of the lines by well known physical gas laws, taking into account where necessary the expected pressure-broadening of the lines.The information on the spectral lines may alternatively be used to deduce further information regarding the pressure of the gas by comparison with the anticipated pressure-broadening of the lines by well known physical gas laws, taking into account where necessary, the expected Doppler broadening of the lines.
The method of the present invention may be one in which a proportion of light is directed from the light source through an optical modulator via a separate optical path but through the same optical modulator on to a separate detector, and in which the resulting detected signal is used to correct the signal from the first optical detection means, in order to compensate for any undesirable detected signal changes on the first optical detection means which might occur even in the absence of any material to be detected in'the sensing region. The proportion of the light directed from the source through the optical modulator on to the separate detector will usually be directed via an optical path not including the sensing region. This embodiment of the invention will usually not be employed in cases where emission lines are involved.
The present invention also provides spectroscopic sensing apparatus for the detection or measurement of at least one material, which apparatus comprises a light source, a sensing region containing a sample of at least one material to be measured or detected, optical modulator means, a reference region containing a known sample of the material to be detected, and light detection means responsive to light intensity variations resulting from variations in the light level after transmission from the light source to the light detection means, as the optical modulator means changes the optical spectrum of the light exiting from the sensing region with the exiting light arising from light transmitted from the light source through the material to be detected or measured, and the apparatus being one in which the intensity of light transmitted from the light source to the light detection means is modulated as a result of the spectral modulation of the exiting light from the sensing region, relative to the absorption lines of the reference material, and in which the resulting modulation of the detected signal is processed by a post-detection processor to derive a measure of the concentration or physical properties of the material in the sensing region.
The optical modulator means may be a frequency or phase modulation device, the extent of modulation being changed as a function of time.
In both the method and apparatus of the invention, the sensing region may be a free space or a cell. The reference region may be a sample in a cell.
The light source may be direct light or diffused ambient light as indicated above.
The light source may be an incandescent light source such for example as a tungsten filament lamp. Alternatively the light source may be a luminescent or super luminescent light emitting diode. Still further, the light source may be a broadband laser light source.
Alternatively, the light source may be a fluorescent or superfluorescent optical fibre light source, for example one containing a rare earth dopant material and pumped with a laser source.
The present invention also provides spectroscopic sensing apparatus for the detection or measurement of at least one material, which apparatus comprises a hot region containing an unknown sample of the material to be measured or detected, optical modulator means, a reference region containing a known sample of the material to be measured or detected, and light detection means responsive to light intensity variations resulting from variations in light transmission changes as the optical modulator means changes the optical spectrum of the light exiting from the sensing region, and the apparatus being one in which the exiting light arises from spectral emission lines from the hot material to be detected or measured, in which the intensity of light transmitted from the hot sample of material is modulated as a result of the spectral modulation of the exiting light, relative to the absorption lines of the reference material, and in which the resulting modulation of the detected signal is processed by a post-detection processor to derive a measure of the concentration or physical properties of the material in the sensing region.
In the apparatus of the invention, the position of the sensing region and the reference region may be interchanged.
The optical modulator means may be an optical
Bragg cell as mentioned above, which translates the frequency of the light by an acousto-optic effect in response to an alternating electronic drive signal applied to the optical Bragg cell.
The optical modulator means may alternatively be an optical Pockels' cell, which translates the optical phase of the light by a linear electro-optic effect in response to an applied electrical signal. In such an arrangement, for example, an applied voltage may rise linearly with time for a certain period, causing an effective translation of optical frequency for that period.
In further alternative apparatus of the invention, the optical modulator means for the optical signal may be an optical Kerr cell which operates in a similar manner to the Pockels' cell, except that with the optical Kerr cell, the phase modulation of the light caused by the cell is a quadratic function of applied voltage, unlike the
Pockels' cell which behaves in a linear manner.
In a further embodiment of the apparatus of the invention, the modulation means may be a section of optical fibre waveguide, the optical path length of which is modulated by mechanically straining the waveguide in a manner variable with time, thereby causing variations in the optical phase as a function of time, and hence a change in the optical spectrum exiting from the waveguide relative to that entering the waveguide.
The detector means employed in the apparatus of the invention may be an optical intensity detector responsive to optical power received. Thus, for example, the optical intensity detector may be a junction photodiode, an avalanche photo-diode or a photo-conductive detector
The apparatus may be one in which one or more of the optical paths between the optical components is a guided path via an optical waveguide, for example an optical fibre.
If desired, the light exiting from the optical modulator means may be divided into two or more optical paths, before passage through separate reference samples on to separate detection systems, in order to enable essentially separate measurement of different materials.
Alternatively, the apparatus may be one in which the light exiting from the optical modulator means is divided into two or more optical paths, before passage through separate reference samples on to separate detection systems, each optical path having a different spectral detection response in order to enable essentiallyseparate measurement of the same material in different regions of the optical spectrum.
The optical Bragg cell is an acousto-optic device which effects optical frequency shifting. The
Pockels' and Kerr cells are electro-optic devices which effect optical phase shifting. The phase of the light is modulated in a time-dependent manner in order to change its optical frequency spectrum. By using the frequency or phase shifting, the light having passed through the sensing region is shifted in optical wavelength such that the spectral overlap between the spectral lines of the material in the sensing region and the measurement region is reduced, thereby increasing the total absorption which takes place during the sequential passage through the sensing region and the measurement region, in turn causing a reduction in the final detected optical signal.
Variations in the drive level of the optical frequency or phase shifting means may be employed to vary the extent of the resulting change of the optical spectrum transmitted as a function of time so as to result in a time varying signal on the detector means. The amplitude of the signal changes are, for a given concentration of the material in the reference region and for a given modulation, dependent on the concentration of the similar material in the sensing region.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:
Figure 1 shows first spectroscopic sensing apparatus; and
Figure 2 shows second spectroscopic sensing apparatus.
Referring to Figure 1, there is shown spectroscopic sensing apparatus 2 comprising a light source 4 and a sensing region 6 which may take the form of a measurement cell or a measurement region. The sensing region 6 contains an unknown sample of a material or materials. The apparatus 2 further comprises optical modulator means 8 which may be in the form of an optical frequency/phase shifter. The optical modulator means 8 receives a drive signal along line 10. Signals from the optical modulator means 8 pass to a reference region 12 which may be in the form of a reference cell. The reference region 12 contains a known sample of the material or materials. Light from the light source 4 then passes through optical detector means 14.
Signals from the optical detector means 14 may be passed through a processor (not shown) via line 16.
In the apparatus 2 shown in Figure 1, the optical paths may be free-path or guided. Where the optical paths are guided, they may be guided in fibre optic guides.
Additional optical elements, for example lenses or mirrors may be used to guide or direct the light.
Figure 2 shows alternative spectroscopic sensing apparatus 2 which is for use with a hot gas where there is no need for a separate light source 4.
Similar parts as in Figure 1 have been given the same reference numerals for ease of comparison and understanding.
In Figure 2, the hot gas may alternatively be a flame and it is indicated by reference numerals 4, 6. This is because the hot gas or flames will basically contain an unknown gas sample and thus equate to the light source 4 and the unknown material sample in the sensing region 6 of
Figure 1.
In the apparatus 2 shown in Figures 1 and 2, it is possible to change the order of the passage of light through certain of the illustrated optical elements, without essentially changing the resultant principle of operation of the apparatus 2. Thus, for example, the relative positions of the sensing region 6 and the reference region 12 in Figure 1 may be interchanged.
As the optical modulator means 8 is operated, the optical spectrum which has exited from the sensing region 6 is translated in optical frequency (if a Bragg cell modulator is employed) or in optical frequency varying rapidly with time (if an optical phase modulator is employed), such that the optical spectra of the material or materials in the sensing region 6 and the reference region 14 no longer overlap. Hence the effective absorption level in the reference region 12 changes. The effective absorption level in the reference region 12 increases in the case of absorption lines in the sensing region 6 but decreases when the sensing region 6 contains a hot gas which emits light in the same lines. The change in the effective absorption level in the reference region 12 results in changes in the detected signal which are detected by the optical detector 14.
If the frequency or phase change in the optical modulator means 8 is caused to change in a controlled manner with time, it is also possible to cause the mathematical overlap integral of the spectral lines to change in a controlled manner with time. Then from the measured variation of the detected optical signal with time, it is possible to derive quantitative information regarding the spectral linewidth of the material in the sensing region 6. This spectral linewidth of the material can,in the case of certain materials such for example as gases, theoretically be processed to derive further useful information on the physical state of the gas. Thus, for example, knowing the pressure of a gas, the temperature and/or flow rate of the gas may be calculated using known physical gas laws.
Conversely, knowing the temperature of the gas, its pressure may be calculated.
It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the light source 4 may be an incandescent light source, a filament lamp, an arc lamp, a light emitting diode, a fluorescent or superfluorescent fibre, a gas plasma light source, or a narrow-line low-pressure gas discharge lamp. The optical transmission media may be free-space open air paths, optically-directed paths via lenses or mirrors, optically guided paths such for example as optical fibres, or combinations of the stated optical transmission media. The optical modulator means 8 may be an acousto-optic Bragg cell, an electrooptic Pockels' cell, a Kerr cell, or an optical fibre stretching device such for example as a fibre wound on a piezo-electric transducer.
The apparatus may be employed to effect measurements such for example as for material detection, or for material characterisation temperature or pressure measurement. Typical examples of materials that may be sensed are gases and especially those gases with narrow absorption or emission lines. Rare-earth metals with narrow spectral lines may also be sensed.
The optical detector means 14 may be, for example, a photomultiplier, a junction photo-diode or a photoconductive type. The main requirement of the optical detector means is that it should have a good responsivity at the wavelength region required.
Various multiplexing options may be employed if desired. Thus, splitting of power, after the optical modulator means, may be employed to enable more than one reference sample to be used with separate optical detection means but sharing the light source and the optical modulator means.
Claims (19)
1. A spectroscopic sensing method for the measurement or detection of at least one material in a sensing region, the method being one in which the material either emits light in one or more narrow emission lines or absorbs light from a light source in one or more narrow absorption lines, and in which the light exiting from the material is directed through optical modulator means capable of modulating the optical phase or frequency of the light such that its optical spectrum varies as a function of time, before being directed through a reference region containing a known sample of the material to be detected, before in turn being directed to optical detection means where the detected variations in the received optical signal intensity, in response to variations in the modulation caused by the optical modulator means, are dependent upon the concentration of the material to be detetected which is present in the sensing region, provided the concentration of the same or similar material in the reference region is known, and where the detected signal variations are processed to measure or detect the material in the sensing region.
2. A spectroscopic sensing method according to claim 1 in which the relative positions of the sensing region and the reference region are interchangeable.
3. A spectroscopic sensing method according to claim 1 or claim 2 in which the variation of the detected response to the applied optical modulation is observed in order to derive more detailed spectral information on the absorption or emission lines of the material.
4. A spectroscopic sensing method according to claim 3 in which the variation of the detected response to the applied optical modulation is observed by changing the optical frequency shift of a Bragg cell modulator to derive the linewidth of the spectral lines of the material from the functional variation of- the received optical intensity, as the frequency is shifted and as the overlap integral of the spectral lines is changed.
5. A spectroscopic sensing method according to any one of the preceding claims in which a proportion of light is directed from the light source through an optical modulator via a separate optical path but through the same optical modulator on to a separate detector, and in which the resulting detected signal is used.to correct the signal from the first optical detection means, in order to compensate for any undesirable detected signal changes on the first optical detection means which might occur even in the absence of any material to be detected in the sensing region.
6. A spectroscopic sensing method for the measurement or detection of at least one material in a sensing region, substantially as herein described with reference to the accompanying drawings.
7. Spectroscopic sensing apparatus for the detection or measurement of at least one material, which apparatus
comprises a light source, a sensing region containing a sample of at least one material to be measured or detected, optical modulator means, a reference region containing a known sample of the material to be detected, and light detection means responsive to light intensity variations resulting from variations in the light level after transmission from the light source to the light detection means, as the optical modulator means changes the optical spectrum of the light exiting from the sensing region with the exiting light arising from light transmitted from the light source through the material to be detected or measured, and the apparatus being one in which the intensity of light transmitted from the light source to the light detection means is modulated as a result of the spectral modulation of the exiting light from the sensing region, relative to the absorption lines of the reference material, and in which the resulting modulation of the detected signal is processed by a post-detection processor to derive a measure of the concentration or physical properties of the material in the sensing region.
8. Spectroscopic sensing apparatus according to claim 7 in which the optical modulator means is a frequency or phase modulation device, the extent of modulation being changed as a function of time.
9. Spectroscopic sensing apparatus according to claim 7 or claim 8 in which the sensing region is a free space or a cell.
10. Spectroscopic sensing apparatus according to any one of claims 7 to 9 in which the reference region is a sample in a cell.
11. Spectroscopic sensing apparatus for the detection or measurement of at least one material, which apparatus comprises a hot region containing an unknown sampleof the material to be measured or detected, optical modulator means, a reference region containing a known sample of the material to be measured or detected, and light detection means responsive to light intensity variations resulting from variations in light transmission changes as the optical modulator means changes the optical spectrum of the light exiting from the sensing region, and the apparatus being one in which the exiting light arises from spectral emission lines from the hot material to be detected or measured, in which the intensity of light transmitted from the hot sample of material is modulated as a result of the spectral modulation of the exiting light, relative to the absorption lines of the reference material, and in which the resulting modulation of the detected signal is processed by a post-detection processor to derive a measure of the concentration or physical properties of the material in the sensing region.
12. Spectroscopic sensing apparatus according to any one of claims 7 to 11 in which the optical modulator means is an optical Bragg cell which translates the frequency of the light by an acousto-optic effect in response to an alternating electronic drive signal applied to the optical Bragg cell.
13. Spectroscopic sensing apparatus according to any one of claims 7 to 11 in which the optical modulator means is an optical Pockels' cell which translates the optical phase of the light by a linear electro-optic effect in response to an applied electrical signal.
14. Spectroscopic sensing apparatus according to any one of claims 7 to 11 in which the optical modulator means is an optical Kerr cell which operates such that the phase modulation of the light caused by the optical
Kerr cell is a quadratic function of applied voltage.
15. Spectroscopic sensing apparatus according to any one of claims 7 to 11 in which the optical modulator means is a section of optical fibre waveguide, the optical path length of which is modulated by mechanically straining the waveguide in a manner variable with time, thereby causing variations in the optical phase as a function of time, and hence a change in the optical spectrum exiting from the waveguide relative to that entering the waveguide.
16. Spectroscopic sensing apparatus according to any one of claims 7 to 15 in which the light detection means is an optical intensity detector responsive to optical power received.
17. Spectroscopic sensing apparatus according to any one of claims 7 to 16 in which the light exiting from the optical modulator means is divided into two or more optical paths, before passage through separate reference samples on to separate detection systems, in order to enable essentially separate measurement of different materials.
18. pectroscopic sensing apparatus according to any one of claims 7 to 16 in which the light exiting from the optical modulator means is divided into two or more optical paths, before passage through separate reference samples on to separate detection systems, each optical path having a different spectral detection response in order to enable essentially separate measurement of the same material in different regions of the optical spectrum.
19. pectroscopic sensing apparatus for the detection or measurement of at least one material, substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9001224A GB2240172B (en) | 1990-01-19 | 1990-01-19 | A spectroscopy sensing method and apparatus for the measurement or detection of a material |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9001224A GB2240172B (en) | 1990-01-19 | 1990-01-19 | A spectroscopy sensing method and apparatus for the measurement or detection of a material |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9001224D0 GB9001224D0 (en) | 1990-03-21 |
| GB2240172A true GB2240172A (en) | 1991-07-24 |
| GB2240172B GB2240172B (en) | 1993-11-17 |
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ID=10669560
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9001224A Expired - Fee Related GB2240172B (en) | 1990-01-19 | 1990-01-19 | A spectroscopy sensing method and apparatus for the measurement or detection of a material |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2240172B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU689822B2 (en) * | 1994-01-11 | 1998-04-09 | Varian Australia Pty Ltd | Method and means for carrying out atomic spectroscopy |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0076886A1 (en) * | 1981-09-22 | 1983-04-20 | H. Maihak Ag | Method and device for the measurement of the concentration ratio of 2 components in a mixture, absorbing infrared, near infrared, visible or ultraviolet radiation |
| US4818705A (en) * | 1986-03-12 | 1989-04-04 | Pierburg Gmbh | Method and apparatus for analyzing the composition of the exhaust gas of any internal combustion engine |
-
1990
- 1990-01-19 GB GB9001224A patent/GB2240172B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0076886A1 (en) * | 1981-09-22 | 1983-04-20 | H. Maihak Ag | Method and device for the measurement of the concentration ratio of 2 components in a mixture, absorbing infrared, near infrared, visible or ultraviolet radiation |
| US4818705A (en) * | 1986-03-12 | 1989-04-04 | Pierburg Gmbh | Method and apparatus for analyzing the composition of the exhaust gas of any internal combustion engine |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU689822B2 (en) * | 1994-01-11 | 1998-04-09 | Varian Australia Pty Ltd | Method and means for carrying out atomic spectroscopy |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9001224D0 (en) | 1990-03-21 |
| GB2240172B (en) | 1993-11-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19970119 |