RU2567119C1 - Method for remote wireless detection and identification of chemical substances and organic objects and device therefor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method includes obtaining Raman and fluorescence spectra of a substance, dividing said spectra into Raman scattering and fluorescence components, analysing the Raman scattering and fluorescence components and identifying the substance using spectral processing techniques. Fluorescence is excited using UV LEDs and Raman scattering is excited using radiation of a laser source. As the recording device a static Fourier spectrometer is used, which forms a two-dimensional spectrum from a fringe pattern, which is recorded and stored in digital form. The resultant fringe pattern is converted into the resultant spectrum via fast Fourier transform. A final decision on detection and identification of substances is made based on the results of comparing the spectrum with a spectral database.

EFFECT: high sensitivity and smaller size of the device.

4 cl, 8 dwg

Description

Technical field

The invention relates to the field of optical-physical methods for determining the composition of chemicals and objects of organic origin.

State of the art

The most informative and effective methods of remote non-sampling determination of the composition of various substances are Raman spectroscopy and photoluminescence (PL). Raman methods are based on inelastic (Raman) scattering of light by molecules illuminated by a source of exciting radiation, and allow one to determine the composition of substances with high selectivity from the Raman spectra. To form the PL spectra, various types of exciting radiation sources are used, ranging from halogen lamps to numerous semiconductor LEDs and lasers. When molecules of the analyte undergo transition from the excited state to the ground state, secondary radiation is formed, which is the PL spectrum.

A fairly large number of technical solutions are known, based both on Raman spectroscopy and PL methods. The PL methods have a higher sensitivity compared to Raman spectroscopy, but are less selective. When using only Raman methods, sufficient sensitivity is not achieved, providing the possibility of remote analysis. When using only PL methods, the required selectivity is not achieved.

Known methods for the remote detection of toxic substances (OB), in particular the method (RF Patent No. 2155954, IPC G01N 21/64, published March 12, 1997), based on remote sensing of the atmosphere by laser radiation with a wavelength of 266 nm and registration as background characteristics the atmosphere, and the intensities of the luminescence signals of OB aerosols in the range from 300 to 440 nm, which allows you to determine the presence or absence of OB aerosols on the sounding path.

However, this method does not provide the ability to selectively detect and identify various types of OBs.

A known method of remote detection and identification of objects of organic origin (RF Patent 2233438, IPC G01N 21/64, publ. July 27, 2004). The proposed method includes remote pulsed sounding of the test object with laser radiation, registration and recording of secondary radiation spectra, comparing the characteristics of the radiation spectra of the test sample with the spectrum of the reference sample included in the device database immediately before the laser sounding of the test object. Two independent observation and recording channels are formed for remote sensing, while the first channel uses pulsed laser radiation in the range of 0.8 ... 1.6 μm, and in the second - in the range of 0.26 ... 0.38 μm. The required divergence of the laser radiation, as well as the spatial scanning of the object under investigation, is formed and carried out independently for each channel. High reliability of correct recognition is achieved through the use of a pre-recorded frequency-time passport of a reference sample that includes the Raman and LIF spectra (laser-induced fluorescence) proposed by the authors.

The disadvantage of the proposed method is the need to use a sufficiently large and energy-intensive sources of exciting radiation, which does not allow the use of this technical solution to create small portable devices.

Methods and devices for detecting and identifying various substances based on the simultaneous use of Raman and PL are also known.

In the application US 20080084555 (IPC G01J 3/36, publ. 10.04.2008) describes methods and devices designed for the simultaneous formation and registration of Raman and PL spectra. The devices contain interchangeable laser sources: a multiwave laser or a laser with a fixed wavelength; replaceable filters that cut out the wavelength of the exciting radiation (458 nm, 488 nm, 515 nm); a monochromator or spectrograph with a detector unit containing two detectors, one of which is designed to record Raman spectra in the spectral range of 480 ... 580 nm, and the second - PL spectra in the range of 950 ... 1200 nm.

The disadvantage of the proposed method is that the intensity of the recorded secondary radiation is divided between two detectors, which reduces the threshold sensitivity values of each channel separately. The lack of fiber optic bundles prevents the use of the proposed device in natural conditions.

A known method and device described in the application US 20060232781 (IPC G01B 9/02, G01J 3/45, publ. 10/19/2006), based on the use of a fast static Fourier spectrometer for recording transmission spectra in order to determine liquids and gases placed in specialized camera with fiber optic input and output. The device comprises an optical source coupled to an optical fiber; chamber for test samples; fiber optic bundle with a micro-optical nozzle; a lens matching the optical output of the optical fiber probe with the input of a static Fourier spectrometer, which is a Michelson interferometer with a beam splitting cube with two mirror faces, one of which is a step mirror, providing the necessary modulation of the travel difference; a detector whose photosensitive elements are optically aligned with the position of the steps of one of the mirrors of the beam splitting cube; a controller and a signal processor for converting the analog signals of the detector and an electronics unit with a graphical interface to display the results of the analysis.

The device is intended for recording transmission spectra of samples of studied liquid and gaseous media and cannot be used for sampling-free and, even more so, remote analysis. In addition, one of the mirrors of the beam splitter cube is a synthesized step structure coated with a reflective coating, which requires rigid attachment of the photosensitive elements of the detector with the position of the beam splitter, which limits the aperture of the beam splitter (0.45 × 0.45 mm at the output of the beam splitter) and , respectively, the aperture of the receiving path of the recording device.

The closest in technical essence to the patented invention is a method for determining a substance by Raman scattering and photoluminescence and a device that implements it (Application US 20110292376, IPC G01J 1/58, G01J 3/02, publ. 01.12.2011). The method includes obtaining Raman and PL spectra, dividing said spectra into Raman and PL components, analyzing Raman and PL components, and identifying a substance using a set of spectral processing methods. A device that implements the method includes a replaceable laser source, a collimation system, a connector for changing lasers, a backlight system for simultaneously obtaining Raman and PL spectra of a substance, a detector, a signal processing unit.

The disadvantages of the proposed method include low sensitivity, and the disadvantages of the device are the bulkiness of the structure.

Disclosure of invention

The technical result of the invention is a significant increase in the sensitivity of detection and identification of chemicals while reducing the dimensions of the fiber probe.

The technical result is achieved by the fact that the proposed method for remote non-sampling detection and identification of chemicals and objects of organic origin includes obtaining Raman spectra and photoluminescence (PL) of a substance, dividing these spectra into components of the Raman and PL, analysis of the components of the Raman and PL and identification substances using spectral processing methods. Moreover, to register the spectra of secondary radiation, the PL and Raman form one common receiving channel. For the excitation of photoluminescence, probing radiation of ultraviolet LED sources of two different wavelengths is formed; for excitation of Raman radiation, radiation from a laser source is generated. As a recording device, a fast static Fourier spectrometer is used, which forms a two-dimensional spectrum at the output, which is obtained by the fast Fourier transform from the interferogram, which is recorded and stored in digital form using an array photodetector. To exclude the influence of background illumination, the secondary radiation spectra are recorded during sequential excitation by radiation sources with different wavelengths, while the background spectra are also periodically recorded with the excitation radiation sources turned off, and background spectra are subtracted from the secondary radiation spectra. When registering interferograms of secondary radiation, the exposure is automatically set, determined by the actual time of detection and identification of substances, in the range from the minimum value determined by the speed of the matrix photodetector and signal processing unit to the maximum programmable value; to increase the signal-to-noise ratio, the interferograms stored in the static Fourier spectrometer are accumulated to produce the resulting interferogram. This resulting interferogram is corrected using an optical mask, which is a two-dimensional function that takes into account geometric distortions of the optical elements of the recording device, which is pre-recorded using coherent radiation from a laser source with a known wavelength and stored in the device's memory for subsequent use. The resulting interferogram is converted to the resulting spectrum using a fast Fourier transform. The final decision on the detection and identification of substances is made by comparing the resulting spectrum with spectra that make up the working base of the spectral data, are pre-recorded, stored in the device's memory and include the spectra of the detected substances recorded using all of these sources of exciting radiation.

A device that implements this method contains a removable laser source, a connector for changing laser sources, a collimation system, a backlight system for simultaneously obtaining Raman and PL spectra of substances, a detector, a signal processing unit. In this case, it includes both LED and laser sources of exciting radiation, optically coupled using standard SMA optical connectors with a fiber optic bundle containing radiation transmitting channels and one receiving channel, combined and optically coupled to the lens of the collimation system. The receiving channel of a fiber optic bundle through an SMA optical connector and a blocking filter for cutting the wavelength of a laser source of exciting radiation is coupled to the optical path of a static Fourier spectrometer. The specified optical path consists of a beam splitting cube, which is a hypotenuse gluing of two prisms with beveled reflecting mirror faces made of optical material having a maximum transmittance in a given spectral range, and intended for the formation of two-dimensional interference patterns, and from a lens projecting an interference pattern onto matrix photodetector forming a measuring signal proportional to the intensity of interference a new picture, for its transmission to a computer unit for signal processing, control of the operating modes of the sources of exciting radiation and indications.

A computer unit for signal processing, control of the operating modes of the sources of exciting radiation and indications, a static Fourier spectrometer with a matrix photodetector unit, and a removable trap filter can be placed in a single housing and are electrically coupled to the secondary power supply system.

The device can also be configured to connect additional external sources of exciting radiation using the provided additional transmission channels in the fiber optic bundle and the corresponding power circuits in the secondary power supply system of the device.

List of figures

FIG. 1 - an algorithm for a non-sampling remote detection and identification of chemicals and objects of organic origin;

FIG. 2 is a block diagram of a device that implements the claimed method;

FIG. 3 is a diagram of a specialized fiber optic probe;

FIG. 4 is a block diagram of a static Fourier spectrometer (SFS);

FIG. 5 is a diagram of a beam splitting cube SPS;

FIG. 6 is an example of recorded interferograms for λ ₁ and λ ₂ ;

FIG. 7 is an example of corrected interferograms for λ ₁ and λ ₂ ;

FIG. 8 is an example of decision making during detection and identification (table 1).

The implementation of the invention

The algorithm of the method for remote non-sampling detection and identification of chemicals and objects of organic origin is presented in FIG. one.

To exclude the influence of background light, the secondary radiation spectra are periodically recorded with the excitation radiation sources turned off 1. First, a two-dimensional interference pattern 1.1 is formed, which is converted to spectrum 1.2.

In accordance with the claimed method, for the excitation of PL, the radiation of semiconductor LEDs of the UV range of two different wavelengths is used, and for the excitation of Raman radiation, the radiation of a UV laser source is used, while the probing of the test surface is carried out when the LEDs of one wavelength 2, then another wavelength 3 , then laser 4. First, a two-dimensional interference pattern is formed (2.1, 3.1, 4.1), then the registered interferogram is corrected using optical masks (2.2, 3.2, 4.2), the corrected interferogram is converted into a range of (2.3, 3.3, 4.3) and switches off the radiation source (2.4, 3.4, 4.4).

To increase the signal-to-noise ratio, the method of accumulating interferograms is additionally applied, while the exposure (accumulation) time is set automatically by the actual recognition and identification time from the minimum level determined by the speed of the photodetector (FPU) and microprocessor processing and control unit (BOUM) 7 to the maximum software level. The accumulation process (exposure) is terminated automatically when recognition and identification are carried out 8 or non-recognition and non-identification 9.

To eliminate the influence of geometric distortions, the registered interferogram is corrected using an optical mask (a two-dimensional hardware function that takes into account all geometric defects of the optical paths and elements of the recording equipment) (example in Figs. 6 and 7). The optical mask is pre-recorded using radiation of a coherent source with a known wavelength and recorded in the memory of the BOUM.

The corrected interferograms are processed by the fast Fourier transform in adder 5 and get the resulting spectra, which are correlatively compared with the spectra that make up the working base of spectral data 6, previously recorded using various sources of exciting radiation, and recorded in the memory of the BOUM.

An example embodiment of the invention

To recognize substances, use the method of simultaneous illumination of the studied object with two sources of exciting radiation with wavelengths λ ₁ and λ ₂ and the implementation of a joint recognition procedure for two spectral ranges (λ ₁ and λ ₂ ) for seven substances (see table of Fig. 8). The decision on detection and identification is made by the method of joint processing of recognition results for each of the LEDs and laser sources used to excite.

A device for remote non-sampling detection and identification of chemicals contains (Fig. 2) a block of interchangeable lenses 10, while each of the interchangeable lenses is designed for its value of the distance to the surface under study and is optically coupled to an optical probe of a fiber optic bundle 12, through which the exciting radiation of UV LEDs grouped in blocks of wavelengths λ ₁ and λ ₂ (blocks 14 and 15 respectively) and selectable from a range of wavelengths depending on a predetermined list of detectable substances enters transmitting channels of the fiber optic harness 12 in the optical probe and through the lens block 10 is projected onto the test surface. The optical coupling of the transmitting channels of the fiber optic bundle 12 with the LED blocks 14 and 15 is carried out using standard optical connectors 23. The secondary radiation (PL) scattered by the test surface is collected by the same lens of the block 10 and through the receiving fiber channel 22 of the optical probe (Fig. 3 ) arrives at the optical input of a fast static Fourier spectrometer (SFS) 18 also through a standard optical connector 23 (the SPS device 18 is shown in Fig. 4). Blocks of LED emitters 14 and 15 can be structurally combined with SPS 18 or taken out in a separate lighting unit. The measuring signal from the output of the SFS 18 enters BOUM 7, which, in addition to processing the measurement information, controls the operation of all sources of exciting radiation 11, 14, 15 and 16. The source 11 is a illuminator, in the housing of which there are two groups of multi-plate LEDs with wavelengths similar to used in blocks 14 and 15.

The illuminator 11 can be used instead of a fiber optic bundle 12 with a block of interchangeable lenses 10 for more efficient excitation of the PL. In this case, open channels for exciting radiation are formed, and the scattered secondary radiation is projected by the receiving lens onto the input section of the optical probe, which has the same aperture as the optical probe of the fiber optic bundle 12, except that in the fiber optic bundle 13 of the illuminator 11 all the fibers are receiving what achieves a greater aperture of the fiber optic receiving channel compared to the bundle 12.

To excite Raman scattering in the device, a UV laser source is used 16. To ensure efficient recording of Raman spectra generated when using source 16, a block of replaceable cut-out filters 17 is introduced into the receiving optical channel of SPS 18. The filter is selected depending on the wavelength of the laser source 16 and it is designed for cutting radiation at a wavelength of excitation from the spectrum of secondary radiation.

Structurally, the laser source 16 is a separate unit controlled by a single unit 7. The result of the processing of the measurement information is displayed on the means of indication of the device, implemented in block 20. The secondary power supply system 21 enables the device to operate from both an industrial and an on-board network.

In FIG. 3 shows a diagram of a fiber optic probe 10 and an approximate cross-sectional view (A-A) of the synthesized aperture of the fiber optic probe 10. Fiber optic bundle 12 is assembled into the probe:

- receiving fiber channel 22 (white circles) with a standard SMA optical connector 23;

- transmitting fiber channels 24, 25, 26 (shaded circles in Fig. 3).

This design of the cross section 27 of the probe 10 provides a more efficient use of the aperture of the probe for collecting and transmitting secondary radiation of the studied samples and the possibility of remote analysis using only one projection lens.

In FIG. 4 is a block diagram of a static Fourier spectrometer (SPS) 18. Excitation radiation is generated by a unit of emitters with two UV LED sources with different wavelengths and a laser 18.6. Through the transmitting channels 24, 25, 26 through the lens 19 of the probe 10, the exciting radiation enters the surface under study. Secondary radiation is generated by the same lens 19 of the probe 10 and transmitted to the optical input of the SPS unit 18 through the receiving channel 22.

The lens matching 18.1 provides uniform illumination of the beam splitting element 18.2. The beam splitting element 18.2 is a gluing of two prisms with beveled mirror faces and is designed to form a two-dimensional interference pattern, which is projected using the projection small-sized lens 18.3 into the plane of the FPU (matrix CCD camera) 18.4. The beam splitting cube (Fig. 5) of the SPS optical path is made of two prisms by gluing. Prisms should be made of quartz, transparent in the ultraviolet region of the spectrum without absorption bands, non-luminescent. The geometric dimensions of the prisms must be provided with an accuracy of 1 μm, angles with an accuracy of not more than ± 30 arc seconds. An antireflection coating is applied to one of the planes (leg) of each prism, and a mirror coating is applied to the other plane (leg). A beam splitting coating should be applied to the plane of the hypotenuse of one of the prisms, providing a beam splitting ratio of 1/1. In the manufacture, it is necessary to ensure the equality of the distances (the segments marked in Fig. 5 by two lines) from the center of the beam splitter to the reflecting faces of the prisms with an accuracy of 1 μm to ensure a symmetric divergence of the rays forming the two-dimensional interferogram.

To provide power to all functional units and blocks of the SPS, the power and control board 18.7 is designed, which also provides the ability to recharge the batteries 18.8 when working from external power sources from the secondary power supply system 21. The secondary power supply system 21 includes secondary power sources (IVP- 1) designed for operation from an industrial network and IVP-2 - from an onboard network. In addition to them, a charger is also included.

The signal from the FPU 18.4 arrives for processing in the microprocessor unit 18.5. The processing result then goes to the block of indicating means 18.9 and to the control units 7 and indication 20, providing light and sound indication. The control units 7 and display 20 are also designed to provide convenience in controlling the operation of the device, on / off the device, as well as to switch operating modes.

After accumulating the recorded interferograms in digital form using a photodetector array device and obtaining the resulting interferograms (resulting but not corrected interferograms for different radiation wavelengths λ ₁ and λ ₂ are shown in Fig. 6), these resulting interferograms are corrected using an optical mask (corrected interferograms are shown in Fig. 7), then spectra are obtained from the corrected interferograms using the fast Fourier transform (FFT) and then the coefficients are calculated correlations of the spectra of the investigated substance with the spectra of individual substances that make up the working base of spectral data in the memory of the BOUM.

Table 1 (Fig. 8) shows the results (when irradiated at wavelengths λ ₁ and λ ₂ ) of detection and identification by arithmetic mean values of the correlation coefficients of the spectra of the experimental substance with the spectra of individual substances that make up the working base of spectral data. The threshold value of the arithmetic mean of the correlation coefficients for the detection and identification of substances was taken to a generally accepted value of 80%. As a result of processing the experimental data of an example embodiment of the method, only one of the seven correlation-significant (with correlation coefficients of at least 50%) substances was found and identified.

The claimed method for remote non-sampling detection and identification of chemicals and objects of organic origin and a device for its implementation are implemented in the device, which is currently undergoing tests, the results of which confirm the correctness of the technical solutions.

Claims (4)

1. A method for remote non-sampling detection and identification of chemicals and objects of organic origin, including obtaining Raman spectra (CR) and photoluminescence (PL) of a substance, dividing these spectra into components of Raman and PL, analyzing components of Raman and photoluminescence, and identifying substances using spectral processing methods, characterized in that for registration of the spectra of secondary radiation, the PL and Raman form one common receiving channel; for excitation of photoluminescence, probing radiation of ultraviolet LED sources of two different wavelengths is formed; for excitation of Raman radiation, radiation of a laser source; as a recording device, a static Fourier spectrometer is used that generates a two-dimensional spectrum at the output, which is obtained by the fast Fourier transform of the interferogram, which is recorded and stored in digital form using an array photodetector; in order to exclude the influence of background illumination, the secondary radiation spectra are recorded upon sequential excitation by radiation sources with different wavelengths, while the background spectra are also periodically recorded when the excitation radiation sources are turned off and the background spectra are subtracted from the secondary radiation spectra; when registering interferograms of secondary radiation, the exposure is automatically set, determined by the actual time of detection and identification of substances, in the range from the minimum value determined by the speed of the matrix photodetector and signal processing unit to the maximum programmable value; to increase the signal-to-noise ratio, interferograms stored in the static Fourier spectrometer are accumulated to produce the resulting interferogram; correcting this resulting interferogram using an optical mask, which is a two-dimensional function that takes into account the geometric distortions of the optical elements of the recording device, which is pre-recorded using coherent radiation from a laser source with a known wavelength and stored in the device memory for subsequent use; the resulting interferogram is converted to the resulting spectrum using a fast Fourier transform; the final decision on the detection and identification of substances is made by comparing the resulting spectrum with the spectra that make up the working base of the spectral data, previously recorded, stored in the device and including the spectra of the detected substances recorded using all of these sources of exciting radiation. 2. A device that implements the method according to claim 1, comprising a replaceable laser source, a connector for changing laser sources, a collimation system, a backlight system for simultaneously obtaining Raman and PL spectra of substances, a detector, a signal processing unit, characterized in that it includes simultaneously LED and laser sources of exciting radiation, optically coupled using standard SMA optical connectors with a fiber optic bundle containing radiation transmitting channels and one receiving channel, are combined and optically coupled to the lens collimation system; the receiving channel of the optical fiber through an SMA optical connector and a blocking filter for cutting the wavelength of the laser source of exciting radiation is coupled to the optical path of a static Fourier spectrometer; said optical path consists of a beam splitting cube, which is a hypotenuse gluing of two prisms with beveled reflecting mirror faces made of optical material having a maximum transmittance in a given spectral range, and intended for the formation of two-dimensional interference patterns, and from a lens projecting an interference pattern onto matrix photodetector forming a measuring signal proportional to the intensity of interference a new picture, for its transmission to a computer unit for signal processing, control of the operating modes of the sources of exciting radiation and indications. 3. The device according to claim 2, characterized in that the computer unit for processing signals, controlling the operating modes of the sources of exciting radiation and indications, a static Fourier spectrometer with a matrix photodetector unit, and a removable blocking filter are placed in a single housing and are electrically coupled to the secondary power supply system. 4. The device according to p. 2, characterized in that it is configured to connect additional external sources of exciting radiation using the provided additional transmission channels in the fiber optic bundle and the corresponding power circuits in the secondary power supply system of the device.

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