METHOD AND DEVICE FOR DETECTION AND/OR MEASUREMENT OF IMPURITIES IN DROPLETS

Abstract

The present relates to a measurement device (1) for the detection and/or measurement of particles in a fluid, the measurement device comprising a fluid source (11) for producing a flow of fluid (111) along a fluid flow path, a first laser source (12) positioned for emitting a first laser beam (120) of laser light in a measurement volume of the fluid flow path for light scattering; a scattered light detecting means (13) for detecting a presence of a particle in the fluid flow path through detection and measurement of laser beam light scattered on different angles by said particle, wherein it further comprises a second laser source (14) positioned for emitting a second laser beam (140) of laser light in said measurement volume of the fluid flow path for Raman and fluorescence excitation; a Raman and fluorescence detecting means (15) for detecting a Raman scattering signal emitted by the fluid and a Fluorescence signal emitted by said particle upon excitation by said second laser beam (140).

Claims

1. Measurement device (1) for the detection and/or measurement of particles in a fluid, the measurement device comprising: a fluid source (11) for producing a flow of fluid (111) along a fluid flow path, a laser source (12) positioned for emitting a laser beam (120) of laser light in a measurement volume of the fluid flow path; a scattered light detecting means (13) for detecting a presence of a particle in the fluid flow path through detection and measurement of laser beam light scattered on different angles by said particle, characterized in that it further comprises a Raman and fluorescence detecting means (15) for detecting a Raman scattering signal emitted by the fluid and a Fluorescence signal emitted by said particle upon excitation by said laser beam (120, 140).

2. Measurement device according to claim 1, wherein said fluid source (11) is a nozzle for producing a flow of water droplets with a flow path beyond the nozzle.

3. Measurement device according to claim 1, wherein said fluid source (11) comprises a tube for producing a flow of water droplets with a flow path along said tube.

4. Measurement device according to any of the preceding claims, further comprising a first lens set (16) for collecting a first laser light (121) scattered in the measurement volume by particles contained in the flow of fluid (111).

5. Measurement device according to claim 4, wherein said first lens set (16) is configured for focusing the scattered light (121) in a line at a focal distance (f2) of the lens set (16), said line being transverse to a flow direction of the flow of fluid in said measurement volume.

6. Measurement device according to claim 5, wherein said first lens set (16) is configured for focusing said scattered light in a line by focusing said scattered light in a direction parallel to said flow direction (y) and for making the rays of scattered light parallel to each other in a plane perpendicular to said flow direction.

7. Measurement device according to any of the preceding claims, wherein the scattered light detecting means (13) is a multipixel light scattering detector.

8. Measurement device according to any of the preceding claims, further comprising a second lens set (17) for collecting the Raman signal emitted by the fluid molecule and fluorescence signal emitted by the particle upon excitation by said laser beam (120, 140).

9. Measurement device according to any of the preceding claims, wherein the Raman and fluorescence detecting means (15) is a photo-detector positioned for the detection of laser light (141) collected by the second lens set (17).

10. Measurement device according to claim 9, wherein the photo-detector (15) is a linear multipixel detector for capturing the laser light focused by the lens set (17), wherein said linear multipixel detector (4) is positioned at a distance from the focal distance (f2) of the lens set (17) and oriented with its longitudinal axis parallel to said line.

11. Measurement device according to one of the preceding claims, wherein said laser source (12) is configured for emitting a continuous laser beam (120).

12. Measurement device according to one of the preceding claims, wherein said laser source is configured for emitting a laser beam (120) having a wave length of 200 to 800 nm

13. Measurement device according to one of the preceding claims, wherein said laser source (12) is configured for emitting a laser beam (120) having an emission spectrum up to tens of nm.

14. Measurement device according to one of the preceding claims, wherein said laser source (12) is configured for emitting a laser beam (120) having an output optical power range from few mW up to few W

15. Measurement device according to one of the preceding claims, further comprising a second laser source (14) positioned for emitting a second laser beam (140) of laser light in said measurement volume of the fluid flow path for Raman and fluorescence excitation while the laser source (12) is for light scattering only.

16. Measurement device according to claim 15, wherein said second laser source (14) is triggered only upon detection of light scattering by the scattered light detecting means (13).

17. Measurement device according to one of claims 15 or 16, wherein said second laser source (14) is configured for emitting a pulsed laser beam (140).

18. Measurement device according to one of claims 15 to 17, wherein said second laser source (14) is configured for emitting a laser beam (140) having a wave length of 200 to 450 nm.

19. Measurement device according to one of claims 15 to 18, wherein said second laser source (14) is configured for emitting a laser beam (140) having an optical peak power per pulse of more than few kW.

20. Measurement device according to one of claims 15 to 19, wherein said second laser source (14) is configured for emitting a laser beam (140) having an emission spectrum of less than few nm.

21. Measurement device according to any of claims 15 to 20, further comprising a diffraction grating (18) for wavelength separation.

22. Measurement method for the detection and/or analysis of fluid-borne particles, comprising the steps of: producing a flow of fluid (111) along a fluid flow path, said flow of fluid potentially containing fluid-borne particles to be detected; emitting a beam (120) of laser light in a measurement volume of the fluid flow path; collecting said laser light (121) scattered in the measurement volume by fluid-borne particles contained in the flow of fluid and focusing said scattered light in a line; detecting said scattered laser light (121) with a scattered light detecting means (13) and acquiring a of light scattering pattern; collecting said laser light (141) scattered in the measurement volume by particles contained in the flow of fluid and focusing said scattered light in a line; detecting said scattered laser light (141) with a Raman and fluorescence detecting means (15) and acquiring Raman signal intensities and fluorescence signal intensities; calculating the measured number of impurities particles.

23. Measurement method according to claim 21, further comprising a correction factor calculation step by taking ratios between measured and expected number of Stocks photons.

24. Measurement method according to claim 21, further comprising an impurity mass concentration calculation step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further particular advantages and features of the invention will become more apparent from the following non-limitative description of at least one embodiment of the invention which will refer to the accompanying drawings, wherein

[0041] FIG. 1 represents a measurement device according to a first embodiment of the present invention

[0042] FIG. 2 represents a measurement device according to a second embodiment of the present invention

[0043] FIG. 3 represents an example of expected light scattering pattern from spherical particles of 0.5, 1, and 2 um diameters, refractive index of water is 1.331.

[0044] FIG. 4 schematically represents a typical Raman emission spectrum of distilled water.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The present detailed description is intended to illustrate the invention in a non-limitative manner since any feature of an embodiment may be combined with any other feature of a different embodiment in an advantageous manner.

[0046] As mentioned earlier, the described method and device of the present invention are intended for on-the-fly and instantaneous detection of presence and concentration measurement of organic molecules or mixture of organic molecules, preferably in aerosols of water droplets.

[0047] Basically, the method and the device of the present invention uses simultaneously three basic physical effects: [0048] Angularly resolved light Mie scattering also known as elastic light scattering; [0049] Raman scattering of water molecules also know is inelastic light scattering; [0050] Laser induced fluorescence.

[0051] More particularly, the method uses elastic light scattering and fluorescence emission to estimate the quantity of impurities molecules present inside water droplet. On the other hand, the Raman scattering is used as a reference signal to correct eventual error due to particle position in a laser beam, nonhomogeneous laser beam intensity, or any other factors influencing light collection efficiency.

[0052] FIG. 1 with single laser shows a schematic view of an implementation of the device 1 according to a first embodiment of the present invention which is a measurement device 1 for the detection and/or measurement of particles in a fluid, and comprising a fluid source 11 for producing a flow of fluid 111 along a fluid flow path which can be a nozzle for producing a flow of water droplets with a flow path beyond the nozzle, or which can comprise a tube for producing a flow of water droplets with a flow path along said tube. More particularly, the measurement device 1 preferably comprises a single laser source 12, preferably a continuous laser source, which is used for light scattering, Raman and fluorescence excitation.

[0053] The first laser source 12 is positioned for emitting a, preferably continuous, laser beam 120 of laser light having a wave length of 200 to 450 nm, preferably 200 to 400 nm, a narrow emission spectrum up to tens of nm and the output optical power ranges from hundreds mW up to tens of W in a measurement volume of the fluid flow path. A short, UV-region, central emission wavelength of this laser is necessary since it efficiently induce a fluorescence response from organic molecules. Moreover, shorter wavelengths are much more efficient for Raman scattering excitation (˜λ.sup.4) as well. The laser source 12 preferably also has a narrow emission spectrum, e.g. less than few nm.

[0054] It also comprises a scattered light detecting means 13, which is preferably a multipixel light scattering detector, for detecting a presence of a particle in the fluid flow path through detection and measurement of laser beam light scattered on different angles by said particle and a Raman and fluorescence detecting means 15 for detecting a Raman scattering signal emitted by the fluid and a Fluorescence signal emitted by said particle upon excitation by said laser beam 120.

[0055] Also, it further comprises a first lens set 16 for collecting a first laser light 121 scattered in the measurement volume by particles contained in the flow of fluid 111 which is preferably configured for focusing the scattered light 121 in a line at a focal distance f2 of the lens set 16, where the line is transverse to a flow direction of the flow of fluid in said measurement volume.

[0056] Also, the first lens set 16 is configured for focusing said scattered light in a line by focusing said scattered light in a direction parallel to said flow direction y and for making the rays of scattered light parallel to each other in a plane perpendicular to the flow direction.

[0057] Further, it comprises a second lens set 17 for collecting the Raman signal emitted by the fluid molecule and fluorescence signal emitted by the particle upon excitation by the laser beam 120. Preferably, the Raman and fluorescence detecting means 15 is a photo-detector positioned for the detection of laser light 141 collected by the second lens set 17.

[0058] FIG. 2 shows a schematic view of an implementation of the device 1 according to a second embodiment of the present invention, based on method of the present invention where 11 is an injection nozzle, 13 is a multipixel light scattering detector, 16 is a collection lens for light scattering signal; 17 is a collection lens for Raman and fluorescence signals, 18 is a diffraction grating for wavelength separation, 15 is a multipixel Raman and fluorescence signal detector, 12 is a laser for light scattering, 14 is a laser for Raman and fluorescence excitation.

[0059] More particularly, the measurement device 1 of the present invention preferably comprises a first laser source 12, preferably a continuous laser source, which is used for light scattering and a second laser source 14, preferably a pulsed laser source, for Raman and fluorescence excitation.

[0060] The first laser source 12 can have any central wavelength such as from 300 to 800 nm, for example, and a relatively broad emission spectrum, e.g. up to tens of nm, since it is only used for the light scattering. The output optical power preferably ranges from few mW up to hundreds of mW.

[0061] The second laser source 14 preferably presents UV or deep-UV wavelength such as from 200 up to 450 nm, for example, and a high optical peak power per pulse, preferably more than few kW. The second laser source 14 preferably presents a short wavelength which is necessary since it efficiently induce a fluorescence response from organic molecules. Moreover, shorter wavelengths are much more efficient for Raman scattering excitation (˜λ.sup.4) as well. The second laser source 14 preferably also has a narrow emission spectrum, e.g. less than few nm.

[0062] The measurement device 13 of the present invention also preferably comprises a detector for detecting the presence of an individual particle in the beam of the first laser source 12 and measures the light scattered on different angles. At the same moment, when a particle is detected, the second laser source 14 shots with a single pulse, or multiple pulses, on the particle, which induces Raman scattering on water molecules and fluorescence emission organic impurities if there are present in the droplet.

[0063] The following paragraphs will now more precisely describe the measurement method carried out by the above described device. In addition to the control of the laser sources of the device, the measurement method of the present invention comprises a light scattering measurement step, a Raman scattering detection step and a fluorescence measurement step.

[0064] The light scattering measurement preferably consists in a Mie light scattering. Mie light scattering is a commonly used and very powerful tool for precise measurement of microparticle. The light scattering measurement of the method preferably uses a multipixel detector D1 to measure scattered light, preferably in the range of angles of 60 deg to 120 deg (side scattering) with respect to the laser direction, with unpolarized, or circularly polarized laser source S1 with resolution of 2 deg/pixel, then the expected scattering patterns will look like on the graph shown in FIG. 3, which shows an example of expected light scattering pattern from spherical particles of 0.5, 1, and 2 um diameters, refractive index of water is 1.331.

[0065] In addition, this step preferably uses advanced pattern recognition algorithms such as gradient boosting trees or support vector machine, where one can extract very precise size estimation (+/−0.1 μm).

[0066] Such measurement allows instantaneous and precise estimation of equivalent optical diameter. Considering that water droplets have always perfect spherical shape due to the surface tension, this measurement provides direct droplet size and volume estimation. Using standard water density 1000 kg/m.sup.3 and molecular mass around 3×10.sup.−26 kg/molecule, one can also estimate the droplet mass and approximate number of H.sub.2O molecules thanks to the following equation:

[00001]$N_{\mathrm{mol}}=\frac{\frac{4}{3}*\pi *D^3*{\rho }_w}{3*10^{-26}}$

[0067] Where D is the measured particle diameter and ρ.sub.w is the water mass density.

[0068] The second step of the method is a Raman scattering detection. In this step, the second laser source S2 is a pulsed laser which emits laser pulsed which hit the droplet to induce Raman scattering. The number of Stocks photons (photons resulted from Raman scattering) detected on the detector D2 can be estimated according following equation:

[00002]$N_{\mathrm{St}}={\sigma }_R\left(3m-6\right)N_{\mathrm{mol}}\frac{E}{\mathrm{Ahv}}{\sigma }_D$

[0069] Where σ.sub.R is the Raman scattering cross section, typically 10.sup.−29 for resonant scattering and 10.sup.−33 for non-resonant scattering, m is the number of atoms in molecule, N.sub.mol is the number of H.sub.2O molecules, E is the laser (S2) pulse energy, A is the cross section of the laser (S2), h is the Plank constant, ν is the frequency of electromagnetic field of the laser (S2) and σ.sub.D is the detection efficiency of the optical system (L2+G1+D2).

[0070] To give a rough estimation of number of expected photons from a water droplet of 1 μm in diameter, one does the following assumptions:

[0071] The main contribution into Raman spectrum of water comes from valent band at 3400 cm.sup.−1. A typical spectrum presented in FIG. 4, which is a typical Raman emission spectrum of distilled water.

[0072] Preferably, the measurement is done with nitrogen laser source with, for example, an emission wavelength of 337 nm, in such a case most of the Stocks photons resulted from Raman scattering by a 1 μm water droplet will have wavelength around 380 nm, which is easily resolved by a diffraction grating G1 from the excitation wavelength of the laser.

[0073] As an example, this Raman emission is resonant so

[00003]${\sigma }_R\approx 10^{-29},m=3,N_{\mathrm{mol}}=\frac{\frac{4}{3}*\pi *{0.000001}^3*1000}{3*{10}^{-26}}\approx 8*{10}^{10},$

[0074] laser pulse energy is taken 100 μJ, laser cross section is 8*10.sup.−9 m.sup.2 (corresponds to a focused beam of 100 μm in diameter), detection efficiency is taken as 10%. The result is around 5000 Stocks photons detected around 380 nm wavelength, which is a very significant number for modern detectors like vacuum tube photomultipliers and silicon photomultipliers (matrixes of avalanche photodiodes).

[0075] It is important to mention at this point that distilled water does not exhibit any fluorescence emission while excited in a wavelength range of 200-400 nm since water molecules do not have any π- or σ-electron orbitals that could absorb such photons.

[0076] So, if the water droplet does not contain any organic or other complex impurities, the only signal observed will be Raman scattering while excited with UV light.

[0077] The third measurement step is therefore a fluorescence measurement. Fluorescence emission is preferably estimated from the following equation:

[00004]$N_{fl}={\sigma }_{A}Q{N}_{mol}\frac{E}{\mathrm{Ahv}}{\sigma }_D$

[0078] Where σ.sub.A is the Photon absorption cross section, typically 10.sup.−20 for endogenous fluorophores, N.sub.mol is the number of fluorophore molecules (organic impurities), Q is the quantum efficiency of radioactive deexcitation of fluorophore, typically 10%, E is the laser (S2) pulse energy, A is the cross section of the laser (S2, h is the Plank constant, and ν is the frequency of electromagnetic field of the laser (S2), σ.sub.D is the detection efficiency of the optical system (L2+G1+D2).

[0079] Compared with Raman scattering, the fluorescence efficiency is much higher if measured under the same conditions. For example, if water droplet contains only 10.sup.5 fluorophore molecules, it would already emit around 2*10.sup.5 fluorescence photons spread over large rage of wavelengths (at the room temperature).

[0080] The last step of the method consists in a measurement of the concentration of the organic impurities in the droplet.

[0081] As mentioned before, the described method is intended for instantaneous measurement of organic impurities in water droplets. The whole process can therefore be split over following steps of producing a flow of fluid 111 along a fluid flow path, the flow of fluid potentially containing fluid-borne particles to be detected; emitting a first beam 120 of laser light in a measurement volume of the fluid flow path; collecting the laser light 121 scattered in the measurement volume by fluid-borne particles contained in the flow of fluid and focusing the scattered light in a line; detecting the scattered laser light 121 with a scattered light detecting means 13 and acquiring a of light scattering pattern; emitting a second beam 140 of laser light in a measurement volume of the fluid flow path; collecting the laser light 141 scattered in the measurement volume by particles contained in the flow of fluid and focusing the scattered light in a line; detecting the scattered laser light 141 with a Raman and fluorescence detecting means (15) and acquiring Raman signal intensities and fluorescence signal intensities; calculating the measured number of impurities particles.

[0082] The measured number of impurities molecules is preferably given by the following equation:

[00005]$N_{im}=\frac{N_{\mathrm{St}}^{\exp }{N}_{\mathrm{fl}}^{\mathrm{mes}}}{N_{St}^{\mathrm{mes}}{\sigma }_{A}Q\frac{E}{\mathrm{Ahv}}{\sigma }_D}=\frac{{\sigma }_R\left(3m-6\right)N_{\mathrm{mol}}\frac{E}{Ahv}{\sigma }_D{N}_{\mathrm{fl}}^{\mathrm{mes}}}{N_{St}^{\mathrm{mes}}{\sigma }_{A}Q\frac{E}{Ahv}{\sigma }_D}$

[0083] Where N.sub.St.sup.exp is the expected number of Stocks photons coming from Raman scattering, calculated by Error! Reference source not found., N.sub.St.sup.mes is the number of Stocks photons coming from Raman scattering, detected by the device, N.sub.fl.sup.mes is the number of fluorescence photons detected by the device.

[0084] By inserting this equation with the first one above, the expression becomes:

[00006]$N_{im}=\frac{{\sigma }_R\left(3m-6\right)N_{\mathrm{mol}}\frac{E}{Ahv}{\sigma }_D{N}_{\mathrm{fl}}^{\mathrm{mes}}}{N_{St}^{\mathrm{mes}}{\sigma }_{A}Q\frac{E}{Ahv}{\sigma }_D}$

[0085] By simplifying this equation and applying the constants for H.sub.2O, the expression takes the following form:

[00007]$N_{im}=\frac{4{\sigma }_R\pi D^3{\rho }_w{N}_{\mathrm{fl}}^{\mathrm{mes}}}{M_w{\sigma }_{A}Q{N}_{St}^{\mathrm{mes}}}$

[0086] When the molecular mass of impurity is known, then the mass concentration can be estimated as well with the following equation:

[00008]$m_{im}=N_{\mathrm{im}}{M}_{im}\frac{4{\sigma }_R\pi D^3{\rho }_w{M}_{\mathrm{im}}{N}_{fl}^{\mathrm{mes}}}{{\sigma }_A{\mathrm{QN}}_{\mathrm{St}}^{\mathrm{mes}}{M}_w}$

[0087] It can be noted that the result depends only on the number of measured photons from fluorescence emission and Raman scattering, and measured optical size in third power. It does not depend on the second laser energy or detection efficiency of the system. If one groups all the constants in this equation the expression becomes:

[00009]$m_{im}=A\frac{D^3{N}_{fl}^{\mathrm{mes}}}{N_{\mathrm{St}}^{\mathrm{mes}}}$

[0088] The resulting expression allows for simple and straightforward mass estimation of impurity molecules in each water droplet detected by the described device.

[0089] While the embodiments have been described in conjunction with a number of embodiments, it is evident that many alternatives, modifications and variations would be or are apparent to those of ordinary skill in the applicable arts. Accordingly, this disclosure is intended to embrace all such alternatives, modifications, equivalents and variations that are within the scope of this disclosure. This for example particularly the case regarding the different apparatuses which can be used.