WO2000002033A1 - Dispositif de detection d'un element chimique par photoexcitation - Google Patents
Dispositif de detection d'un element chimique par photoexcitation Download PDFInfo
- Publication number
- WO2000002033A1 WO2000002033A1 PCT/CH1999/000284 CH9900284W WO0002033A1 WO 2000002033 A1 WO2000002033 A1 WO 2000002033A1 CH 9900284 W CH9900284 W CH 9900284W WO 0002033 A1 WO0002033 A1 WO 0002033A1
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- WO
- WIPO (PCT)
- Prior art keywords
- laser
- substance
- host substance
- host
- heating
- Prior art date
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Classifications
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- 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
- G01N21/171—Systems in which incident light is modified in accordance with the properties of the material investigated with calorimetric detection, e.g. with thermal lens detection
Definitions
- the present invention relates to a device for detecting a chemical element by photoexcitation. It relates, more particularly, to a device for measuring the concentration of elements existing in trace amounts in a host substance which may be solid, liquid or gaseous.
- a host substance which may be solid, liquid or gaseous.
- Photoexcitation measurement methods are particularly suitable for this type of detection. Indeed, their relative simplicity and their selectivity allow them to be applied to a very wide range of chemical measurement tasks.
- a solid, liquid or gaseous sample of the substance containing the desired elements is subjected to the action of an optical excitation source emitting a light beam, the spectral distribution of which is chosen so as to correspond to a specific absorption band of the molecules observed.
- the light is partially absorbed by these molecules which take an excited state.
- the de-excitations induced by collisions between the molecules observed and those of the host substance have the effect of heating the latter.
- the wavelength of the light must be chosen so that the radiative de-excitation time is much longer than the non-radiative de-excitation time, responsible for heating the medium through transitions from the rotational modes to translational modes which are induced by collisions.
- the heating produces a pressure wave which is proportional to it.
- a device of this type used for controlling air pollution and working with a CO 2 laser, is described in the article by A. Th ⁇ ny and MW Sigrist “New developments in C0 2 -laser photoacoustic monitoring of trace gases ”published in Infrared Phys. Technol. Vol.36, N ° 2, pp.585-615, 1995.
- the optical source plays an essential role in this regard.
- the light produced by the source has a double action. It excites the molecules sought in the sample but also generates parasitic effects, mainly heating of the mechanical parts placed nearby and heating of molecules of the host substance.
- the heating of the mechanical parts is eliminated by controlling the shape of the beam using lenses or mirrors in order to minimize its impact on these parts. It is clear that this operation is greatly facilitated if the source emits in a small number of modes.
- the heating of molecules other than those sought it is avoided by selecting the emission spectrum of the source so that its overlap with the absorption spectrum of the measured element is maximum and that the overlap with the spectrum of absorption of the host substance is minimal.
- the acoustic noise in the case of a pressure measurement, decreases with frequency and that, if a resonant cavity is used, its size also decreases with frequency.
- the ideal for a photoexcitation source is to be centered on a specific absorption of the molecules observed, to emit in a small number of modes and to be modular.
- the main limiting factor is the availability of suitable excitation sources.
- the majority of specific absorptions of chemical elements with several atoms are found in the middle infrared, a region of the spectrum also called the chemical fingerprint zone.
- a gas laser for example C0 2
- C0 2 has the advantage of high radiance and, in some cases, the possibility of modulating the optical intensity.
- modulation is limited to relatively low frequencies.
- the available wavelengths are limited and do not fully cover the medium infrared.
- a tunable semiconductor laser of the type marketed by the company New Focus, Inc. (USA) has also been proposed, but since such a source is not capable of reaching mid-infrared, it is necessary to use harmonics of the absorption frequency and, therefore, we must be satisfied with a very low cross section despite the high initial radiance.
- the present invention aims to provide a photoexcitation detection device which, thanks to a new type of excitation light source, is very significantly improved, compared to the embodiments existing, both from the point of view of its performance and its field of use.
- the invention relates to a device for photoexcitation detection of a chemical element in a host substance, of the type comprising:
- an optical excitation source consisting of a semiconductor laser emitting, in the direction of a sample of the substance, a beam of light whose wavelength, located in the middle infrared, corresponds to an absorption band item specific;
- This device is characterized in that it uses, as an optical excitation source, is a III / V semiconductor laser.
- the detection and measurement means respond to the pressure wave generated by heating of the host substance, which can be solid, liquid or gaseous, to produce a representation of the concentration of the element in the host substance.
- the detection and measurement means respond to the variation in the refractive index of the host substance, due to the pressure wave generated by heating of this substance, to produce a representation of the element's concentration.
- These means advantageously include a light source emitting a probe beam which passes through the sample and means for measuring the deflection of this beam which results from the variation of the refractive index of the substance.
- the detection and measurement means respond to the variation in the refractive index of the host substance, due to its heating, to produce a representation of the concentration of the element.
- These means advantageously include a light source emitting a probe beam which crosses the sample collinearly with the excitation beam and means for measuring the widening of the probe beam which results from the variation of the refractive index of the substance.
- the device may also include an enclosure intended to receive the sample.
- This enclosure can be smaller than the acoustic wavelength at the excitation frequency or dimensioned so as to include acoustic modes resonating at the excitation frequency.
- FIG. 1 shows schematically the main components of a device for detecting chemical elements by photoexcitation
- FIG. 2 shows a first embodiment of the device according to the invention, in which heating is detected by the pressure wave it generates;
- - Figure 3 shows a second embodiment, in which overheating is detected by the variation in the refractive index of the host substance caused by the pressure wave; and - Figure 4 shows a third embodiment, in which heating is detected by the variation in the refractive index that it causes.
- Figure 1 shows, very schematically, the constitution of a device for detecting chemical elements by photoexcitation. It essentially comprises: - An excitation optical source 1 emitting a light beam whose wavelength corresponds to a specific absorption band of the molecules of the element sought, which is present in the trace state; - A sealed measurement enclosure 2 arranged on the path of the light beam and containing a sample of the substance, solid, liquid or gaseous, which serves as the host for the element sought;
- the device can detect heating of the host substance either directly by the pressure wave which it generates, or by the variation of the refractive index of the host substance that causes the pressure wave, or again by the variation in the refractive index that causes heating.
- the light source 1 is a III / V semiconductor laser emitting in the medium infrared, that is to say capable of working in a band of wavelengths substantially between 2 and 12 microns. More specifically, and by way of nonlimiting example, five different types of medium infrared semiconductor laser can be used, namely:
- QCL Quantum Cascade Laser
- Such a type of laser makes it possible to obtain all the advantages of the sources presented above and to avoid the disadvantages thereof. It can also be manufactured in such a way as to emit chemical fingerprints in the region, emits in a small number of modes and is modular. It also has the advantage of being small and having low power consumption. This second characteristic is particularly crucial since the electrical control of the laser emits much less stray radiation than that of a high-voltage discharge laser.
- the spectral width of the QCL is very small.
- multi-mode QCLs fitted with internal Bragg reflectors have typical widths of 5 cm “1 and 1 cm “ 1 . Therefore, the proportion of optical energy absorbable by the molecules sought is significantly greater than in the case of a thermal source, for example.
- QCLs can be made at any wavelength between 3.5 and 12 microns. Such a spectrum makes it possible to illuminate a vast sampling of the fundamental absorption lines of the organic components involved in usual chemistry.
- the QCL operates at temperatures close to room temperature and consumes small amounts of electricity (typically a few Watts). It is thus possible to place it in an enclosure of very small volume (20 cm 3 approximately), which constitutes a notable advantage compared to devices with lasers with lead salts, requiring cooling at cryogenic temperatures, or OPO (Optical Parametric Oscillators), requiring powerful gas lasers.
- OPO Optical Parametric Oscillators
- QCLs are very independent of their emission wavelength as a function of temperature, which is a very important characteristic when a system must be able to operate stably under a wide variety of climatic circumstances.
- QCL offers a much greater capacity for excitation of the molecules sought at comparable volume and energy consumption.
- the sensitivity of the device is significantly improved.
- the excitation cross section of the . molecule sought being much larger when using a photon exciting a fundamental absorption rather than a harmonic and the available powers of bipolar lasers in the near infrared being, moreover, comparable to those of QCL, the photo-excitation effect obtained is more important with a QCL.
- the semiconductor laser 1 is placed in an insulating enclosure 5 protecting it from the ambient atmosphere.
- a transparent window 6 is provided in one of the faces of the enclosure, on the path of the laser beam, in order to allow it to leave it.
- the laser 1 is placed on a metal plate 7 made of copper, beryllium or any other metal with high conductivity, itself based on a cooling device 8, for example of the thermoelectric type.
- the emitted laser beam enters the measurement enclosure 2 through an opening 9, possibly closed by a transparent window.
- a second opening 10, possibly closed by a transparent window, is formed in the wall opposite that of the inlet opening 9.
- FIG. 2 shows a first embodiment of a device according to the invention, usable in solid, liquid or gaseous medium.
- the pressure wave resulting from the heating of the host substance is detected directly using a microphone 11 placed right next to the measurement enclosure 2.
- the electrical output signal from the microphone 11 is applied to an electronic amplification circuit 12 associated with a display system 13.
- the pressure wave generated in the enclosure 2 is proportional to the heating of the host substance, which is proportional to the energy absorbed by the molecules of the element sought. This being present in the form of traces only, the energy absorbed is proportional to its concentration. Consequently, the intensity of the signal delivered by the circuit 12 is proportional to the concentration of the element sought in the host substance.
- the system 13 displays the value of the concentration measured in digital or analog form.
- the measurement enclosure 2 is smaller than the acoustic wavelength at the working frequency. Then excited, in general, the entire contents of the enclosure and cooling takes place against its walls.
- the enclosure 2 is dimensioned so as to include acoustic modes resonating at the frequency of job.
- This configuration makes it possible to accumulate acoustic energy inside the cavity and, therefore, to improve detectivity by a more intense signal.
- the acoustic noise which decreases with frequency, can be significantly reduced. The excitation of the molecules taking place over a small proportion of the volume, the cooling is therefore done first by conduction and convection in the host substance, then by conduction against the walls of the enclosure.
- the excitation beam can then be sent directly to the sample, near which the microphone is placed.
- FIG. 3 represents another embodiment of the device according to the invention.
- the pressure wave resulting from the heating of the host substance is optically detected.
- a second light source 14 is then available, chosen so as to emit at a wavelength for which the host substance is transparent. It can be a Helium-Neon laser.
- the beam emitted by this source, called the probe beam is injected into the enclosure 2, through the opening 9, parallel to the excitation beam coming from the main source 1.
- the pressure wave caused by heating compresses the host substance whose refractive index is modified in proportion to the concentration of the element sought.
- the beam of the probe thus undergoes, by crossing the enclosure 2, a deflection representative of the desired concentration.
- the probe beam is, at its exit from the enclosure 2 through the opening 10, received by an optical position detector 15, advantageously consisting of a line of CCD cells (Charge Coupled Device), connected to an analysis circuit 16 associated with a display system 17.
- Circuit 16 identifies the CCD cell affected by the probe beam, translates its address into a deflection angle and then into a concentration of the element sought in the substance host and provides a representative output signal of this concentration.
- the system 17 displays the value of the concentration measured in digital or analog form.
- FIG. 4 represents another embodiment of the device according to the invention.
- warming of the host substance is also detected by an optical measurement.
- a second light source 18 chosen so as to emit at a wavelength for which the host substance is transparent. It can be a Helium-Neon laser.
- the probe beam thus emitted is injected into the enclosure 2, through the opening 9, collinearly with the excitation beam coming from the main source 1, by means of a dichroic beam splitter 19.
- the heating of the host substance , liquid or solid causes a proportional change in its refractive index. This variation generates a divergent index gradient lens.
- the beam of the probe thus undergoes, by crossing the enclosure 2, an enlargement representative of the desired concentration.
- the probe beam is, at its exit from the enclosure 2 through the opening 10, received by an optical beam widening detector 20, advantageously consisting of a line or a matrix of cells CCD, connected to an analysis circuit 21 associated with a display system 22.
- Circuit 21 identifies the CCD cells affected by the probe beam, translates their address into a widening angle and then into a concentration of the element sought in the host substance and provides an output signal representative of this concentration.
- the system 22 displays the value of the concentration measured in digital or analog form.
- the device of FIG. 3 can be used according to the principle of the device of FIG. 4.
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99959124A EP1093573A1 (fr) | 1998-07-06 | 1999-06-30 | Dispositif de detection d'un element chimique par photoexcitation |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9808711A FR2780788B1 (fr) | 1998-07-06 | 1998-07-06 | Dispositif de detection d'un element chimique par photoexcitation |
FR98/08711 | 1998-07-06 |
Publications (1)
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WO2000002033A1 true WO2000002033A1 (fr) | 2000-01-13 |
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Application Number | Title | Priority Date | Filing Date |
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PCT/CH1999/000284 WO2000002033A1 (fr) | 1998-07-06 | 1999-06-30 | Dispositif de detection d'un element chimique par photoexcitation |
Country Status (3)
Country | Link |
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EP (1) | EP1093573A1 (fr) |
FR (1) | FR2780788B1 (fr) |
WO (1) | WO2000002033A1 (fr) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7152007B2 (en) | 2000-02-28 | 2006-12-19 | Tera View Limited | Imaging apparatus and method |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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GB2409026B (en) * | 2003-12-09 | 2007-09-12 | Teraview Ltd | An investigation system,a receiver and a method of investigating a sample |
Citations (4)
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US4243327A (en) * | 1979-01-31 | 1981-01-06 | Nasa | Double-beam optical method and apparatus for measuring thermal diffusivity and other molecular dynamic processes in utilizing the transient thermal lens effect |
US4938593A (en) * | 1987-01-30 | 1990-07-03 | The Regents Of The University Of Michigan | Photothermal densitometer for reading electrophoresis gels |
US5457709A (en) * | 1994-04-04 | 1995-10-10 | At&T Ipm Corp. | Unipolar semiconductor laser |
US5513006A (en) * | 1992-09-18 | 1996-04-30 | Kernforschungszentrum Karlsruhe Gmbh | Photo-thermal sensor including an expansion lens in a light beam path through a sample for determining the concentration of a compound in the sample |
-
1998
- 1998-07-06 FR FR9808711A patent/FR2780788B1/fr not_active Expired - Lifetime
-
1999
- 1999-06-30 EP EP99959124A patent/EP1093573A1/fr not_active Ceased
- 1999-06-30 WO PCT/CH1999/000284 patent/WO2000002033A1/fr not_active Application Discontinuation
Patent Citations (4)
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US4243327A (en) * | 1979-01-31 | 1981-01-06 | Nasa | Double-beam optical method and apparatus for measuring thermal diffusivity and other molecular dynamic processes in utilizing the transient thermal lens effect |
US4938593A (en) * | 1987-01-30 | 1990-07-03 | The Regents Of The University Of Michigan | Photothermal densitometer for reading electrophoresis gels |
US5513006A (en) * | 1992-09-18 | 1996-04-30 | Kernforschungszentrum Karlsruhe Gmbh | Photo-thermal sensor including an expansion lens in a light beam path through a sample for determining the concentration of a compound in the sample |
US5457709A (en) * | 1994-04-04 | 1995-10-10 | At&T Ipm Corp. | Unipolar semiconductor laser |
Non-Patent Citations (7)
Title |
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A.RYBALTOWSKI, Y.XIAO, D.WU, B.LNE, H.YI, H.FENG, J.DIAZ, M.RAZEGHI: "High power InAsSb/InPasSb/InAs mid-infrared lasers", APPLIED PHYSICS LETTERS, vol. 71, no. 17, 27 October 1997 (1997-10-27), pages 2430 - 2432, XP002096097 * |
J.W.CHEY, P. SULTAN, H.J. GERRITSEN: "Resonant photoacoustic detection of methane in nitrogen using a room temperature infrared light emitting diode", APPLIED OPTICS, vol. 26, no. 6, 15 August 1987 (1987-08-15), pages 3192 - 3193, XP002096094 * |
K.STEPHAN, W.HURDELBRINK: "Die photoakustische Infrarot-Laser-Spektroskopie zur Konzentrationsmessung in Gasen", CHEM.ING.TECH., vol. 58, no. 6, 1986, pages 485 - 487, XP002096095 * |
LIN C -H ET AL: "LOW-THRESHOLD QUASI-CW TYPE-II QUANTUM WELL LASERS AT WAVELENGTHS BEYOND 4 MUM", APPLIED PHYSICS LETTERS, vol. 71, no. 22, 1 December 1997 (1997-12-01), pages 3281 - 3283, XP000730290 * |
OLSSON B E R ET AL: "OPTOACOUSTIC LEAD-SALT DIODE LASER DETECTION OF TRACE SPECIES IN A FLOW SYSTEM", APPLIED SPECTROSCOPY, vol. 49, no. 8, 1 August 1995 (1995-08-01), pages 1103 - 1106, XP000523731 * |
R.Q.YANG, B.H.YANG, D.ZHANG, C.H.LIN, S.J.MURRY, H.WU, S.S.PEI: "High power mid-infrared interband cascade lasers based on type-II quantum wells", APPLIED PHYSICS LETTERS, vol. 71, no. 17, 27 October 1997 (1997-10-27), pages 2409 - 2411, XP002096096 * |
T.H.VANSTEENKISTE, F.R. FAXVG, D.M.ROESSLER: "Photoacoustic Measurement of Carbon Monoxide Using a Semiconductor Diode Laser", APPLIED SPECTROSCOPY, vol. 35, no. 2, 1981, pages 194 - 196, XP002096093 * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7152007B2 (en) | 2000-02-28 | 2006-12-19 | Tera View Limited | Imaging apparatus and method |
Also Published As
Publication number | Publication date |
---|---|
FR2780788B1 (fr) | 2000-09-22 |
EP1093573A1 (fr) | 2001-04-25 |
FR2780788A1 (fr) | 2000-01-07 |
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