CN106153575A - A kind of acousto-optic modulation double light path double detector type near infrared spectrometer and method of testing - Google Patents

Abstract

The invention discloses an acousto-optic modulation double optical path double detector type near-infrared spectrometer and a testing method. The instrument includes spectral analysis optics, a radio frequency drive module, a signal acquisition module, a control and processing module, a power supply module, and a cuvette sample testing structure. The invention adopts the design of dual optical paths and dual detectors, combined with the test method of testing reference light and measuring optical signals in sequence when there is no vessel, empty vessel and sample vessel, and can effectively reduce the instability of the light source and the difference between the two detectors through comprehensive data processing. The purpose of test errors caused by environmental interference, sample vessel differences, etc.

Description

An acousto-optic modulation dual optical path dual detector near-infrared spectrometer and testing method

Technical field:

The present invention relates to the improvement of real-time spectral analysis technology, and specifically refers to a light splitting method based on an acousto-optic tunable filter, using a beam splitter to realize monochromatic signal light and reference light with controllable energy splitting ratio, and adopting dual optical paths and dual The detector sequentially tests the reference light when there is no vessel, the empty vessel, and the vessel containing the sample, and a test method for measuring light signals. The test error is effectively reduced through comprehensive data processing, and belongs to the field of optoelectronic technology.

Background technique:

With the advancement of chemometrics, optical fiber and computer technology, spectral analysis technology, as a representative of "green detection technology", has the advantages of effectively improving analysis efficiency and reducing labor and production costs, and has achieved rapid development. At present, spectral analysis technology plays an increasingly important role in the field of analysis and testing, especially in the field of online analysis and testing and industrial control. Generally speaking, due to the advantages of fast analysis speed, wide application range, and non-destructive online detection, spectral analysis instruments occupy an important position in analytical testing instruments, and are widely used in agriculture, animal husbandry, food, chemical, petrochemical, pharmaceutical, tobacco, etc. Many practical fields, etc.

Acousto-optic tunable filter (AOTF) is a narrow-band tunable filter, which is a spectroscopic device made according to the principle of acousto-optic interaction. When a beam of polychromatic light passes through a high-frequency vibrating optically elastic crystal, the monochromatic light of a certain wavelength will be diffracted inside the crystal and transmitted from the crystal at an angle, and the polychromatic light that has not been diffracted will be transmitted along the The original light propagation direction is directly transmitted through the crystal, thereby achieving the purpose of light splitting. Wavelength scanning is achieved by changing the frequency-selective splitting wavelength of the RF drive applied to the crystal. At present, the development of spectral analysis instruments based on acousto-optic tunable filters is still in its infancy in China, and commercial products are rarely reported. There are still some technical bottlenecks in the development of related instrument systems, mainly reflected in spectral resolution, detection sensitivity, acquisition speed and adaptability to multi-sample detection.

Literature research found that the AOTF-based spectroscopic principle solution (patent CN 201210511740) proposed for the above-mentioned technical difficulties provides an AOTF-type near-infrared spectrometer using duty ratio regulation technology, which is realized by controlling the pulse generator and RF drive source. The duty cycle of the radio frequency output signal is set, so that the acousto-optic tunable filter performs scanning and splitting according to the control requirements, so as to achieve the purpose of improving spectral resolution and detection sensitivity. However, this method also has certain limitations, mainly reflected in the fact that the optical path of the instrument's photoelectric signal acquisition can neither eliminate the fluctuation of light intensity caused by the instability of the light source, nor the influence of errors introduced by environmental interference. In addition, the inconsistency of the sample vessel during the actual detection process of this method will also affect the accuracy of the spectral measurement of the sample to be tested.

Invention content:

Aiming at the deficiencies in the prior art, the present invention provides a spectral analysis instrument and testing method with dual optical paths and dual detectors, so as to effectively reduce testing errors caused by unstable light sources, environmental interference, and differences in sample vessels.

The main design idea of this invention is:

1) The acousto-optic tunable filter is selected as the spectroscopic device, and the design of dual optical paths and double detectors is adopted. The monochromatic light split by the acousto-optic tunable filter is divided by the adjustable beam splitter into a controllable beam splitting ratio. The reference light and the measurement light, wherein the reference light signal is received by the reference light path and the corresponding photodetector, the measurement light is first incident on the sample cell, and its transmitted (or reflected) light signal is received by the measurement light path and the corresponding photodetector

2) Adopt the method of sequentially testing the reference light and measuring light signals when there is no vessel, empty vessel, and sample vessel, and comprehensively perform data processing to effectively reduce the instability of the light source, the difference between the two detectors, environmental interference, and the difference in the sample vessel. test error;

3) Before the sample test, according to the optical characteristics of the sample to be tested, adjust the energy and beam splitting ratio of the reference light and the measurement light by combining the adjustable aperture and the adjustable beam splitter, so that the energy of the two is appropriate and the magnitude is close. Improve instrument dynamic range and enhance test data validity.

The present invention is specified as follows:

1. The spectrum analysis instrument of the present invention comprises spectrum analysis optics (1), radio frequency drive module (2), signal acquisition module (3), control and processing module (4), power supply module (5), cuvette sample Test structure (6), as shown in Figure 1. The spectrum analysis optics include light source (101), off-axis parabolic converging mirror (102), adjustable aperture (103), off-axis parabolic collimating mirror (104), AOTF (105), converging lens (106), adjustable Beam splitter (107); RF drive module includes DDS chip (201), RF transformer (202), LC low-pass filter (203), low noise amplifier (204), power amplifier (205), SP2T RF switch (206) The signal acquisition module comprises a reference signal detector (301), a reference signal detector preamplifier circuit (302), a test signal detector (303), a test signal detector preamplifier circuit (304), a lock-in amplifier circuit ( 305), A/D data acquisition circuit (306); control and processing module includes FPGA software (401) and upper computer (402); power supply module includes primary power supply (501), secondary power supply (502); cuvette sample The test structure includes a cuvette (601) and a switchable cuvette support (602).

2. The spectrum analysis optics converges, spatially filters and collimates the light from the light source, and then passes through the AOTF (105), the control and processing module (4) controls the radio frequency drive module (2) to drive the light splitting, and forms the required measurement list Chromatic light; after the monochromatic light is converged by the converging lens (106), combined with the optical characteristics of the sample to be measured and the reference light and measurement light detection signal value, the light energy level is controlled and measured by the adjustable diaphragm (103), and the The beam splitter (107) realizes the adjustment of the beam splitting ratio of the reference light and the measurement light, and the combination of the two realizes the energy of the reference light and the measurement light is appropriate and the magnitude is close to control.

3. The cuvette sample test structure, combined with the test method, realizes the switching of the cuvette (601) at A, B, and C positions by the switchable cuvette support (602), and realizes the test without vessels in order , reference light and measurement light signals when the container is empty or contains samples, comprehensive data processing to reduce test errors caused by unstable light sources, differences between the two detectors, environmental interference, and differences in sample containers.

4. In the comprehensive data processing of the present invention, after obtaining reference light and measuring light signals when no vessel, empty vessel and sample vessel are contained in combination with the measuring method, the following processing is carried out:

1) Process the measurement light spectrum I + reference light spectrum I + reference light spectrum I _{+ 1 without the} vessel according to formula 1 to obtain the spectral energy ratio constant vector C of the measurement light and the reference light when there is no vessel, and establish the reference light and the incident measurement light inherent relationship. At this time, the synchronous test value of measuring light and reference light includes the influence of light source, optical device, detector and its circuit, and environmental interference. It can be used for subsequent data processing to reduce the instability of light source, the difference of detector and circuit, and the influence of environmental interference. influences;

2) Process the measurement light spectrum I _{2 space} and the reference light spectrum I _{1 space} of the empty vessel according to formula 2, establish the inherent relationship between the reference light and the measurement light after passing through the vessel, and obtain the spectral transmittance T _space of the vessel itself, which is used for subsequent Data processing to remove the effects of sample vessel variance;

3) Process the measurement light spectrum I ₂ sample containing sample vessel and the reference light spectrum I _{1 sample containing sample} according to formula 3, establish the inherent relationship between the reference light and the measurement light after passing through the sample container, and obtain the transmittance spectrum of the sample container T _{contains samples} .

4) Combining the inherent relationship between the reference light and the measured light passing through the container containing the sample, and the transmittance spectrum, the transmittance spectrum curve and the absorbance of the sample itself can be obtained through formula 4 and formula 5.

By the Lambert-Beer law:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; log</span>}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ,</span>$

Among them, K is the proportional coefficient of light being absorbed, c is the sample concentration, l is the optical path length, T is the transmittance, and A is the absorbance.

It is easy to know that A _{containing sample} = A _empty + A _sample

Therefore, it can be deduced that:

Test procedure of the present invention is as shown in accompanying drawing 2, is specifically described as follows:

1. Adjust the energy and beam splitting ratio of the reference light and the measurement light: the test structure is in the state of containing the sample vessel (only for adjustment), and the energy and beam splitter of the reference light and the measurement light are adjusted by using the adjustable aperture and the adjustable beam splitter. The beam splitting ratio is adjusted to make the two signals appropriate and close in magnitude;

2. Vessel-free reference light and measurement light test: remove the cuvette on the cuvette holder, test the reference light and measurement light signals, and store them for processing;

3. Empty vessel reference light and measurement light test: put the empty vessel into the cuvette holder, test the reference light and measurement light signals, and store them for processing;

4. Test of reference light and measurement light of the sample vessel: put the empty vessel measured in the above step into the sample to be tested, put it into the cuvette holder, test the reference light and measurement light signal, and store it for processing;

5. Data processing;

6. Complete the test experiment.

The advantage of this patent is:

1) Adopt the design of double optical path and double detectors, test the reference light and measurement light signals in sequence when there is no vessel, empty vessel and sample vessel, comprehensive data processing, effectively reduce the instability of light source, the difference between the two detectors, environmental interference, sample Test errors caused by differences in containers, etc.;

2) Before the test, according to the optical characteristics of the sample to be tested, the adjustable diaphragm and adjustable beam splitter are used to adjust the energy and beam splitting ratio of the reference light and the measurement light, so that the signals of the two are appropriate and close in magnitude, and the test data can be improved. effectiveness.

Description of drawings:

Fig. 1 is the principle block diagram of spectral analysis instrument of the present invention,

Among them, 1-spectral analysis optics, 2-radio frequency drive module, 3-signal acquisition module, 4-control and processing module, 5-power supply module, 6-cuvette sample test structure.

Figure 2 is a flow chart of the testing steps.

detailed description:

Below is a preferred embodiment of this patent according to Fig. 1, in order to illustrate the structural features and implementation methods of this patent, but not to limit the scope of this patent.

The dual optical path dual detector near-infrared spectrometer based on the acousto-optic tunable filter includes the following parts:

(1) Broad-spectrum halogen light source 101: In this embodiment, the Halogen Display/Optic Lamp of Germany Osram Lighting Co., Ltd. is selected, with a rated power of 20W and a rated voltage of 12V.

(2) Off-axis parabolic mirrors 102 and 104: In this embodiment, the OQALM76.2-002 and OQALM25.4-001 off-axis parabolic mirrors of Beijing Maofeng Photoelectric Technology Co., Ltd. are selected, and the single focal lengths are 38.1 mm and 12.7 mm. mm.

(3) Adjustable aperture diaphragm 103 : In this embodiment, the D5S adjustable aperture diaphragm of Thorlabs Company is selected, and the aperture diameter is 0.7mm-5mm.

(4) Acousto-optic tunable filter 105: In this embodiment, a short-wave near-infrared acousto-optic tunable filter developed by the 26 Research Institute of China Electronics Technology Group is selected.

Its specific indicators are:

(5) Adjustable beam splitter 107: In this embodiment, the device is self-made by a one-dimensional manual precision translation stage and a light cutting mirror.

(6) Photodetectors 301 , 303 : In this embodiment, J23TE3-66C-R01M-2.6 detectors from Judson Company of the United States are selected, and the diameter of the photosensitive surface is 1 mm.

(7) Cuvette sample test The cuvette in structure 6: the selected material is JGS2 quartz glass cuvette, and the cuvette support is a self-made part.

(8) RF driver module 2 is a self-made circuit board, mainly including FPGA controller, DDS-based RF signal generator, RF transformer, LC low-pass filter, low-noise amplifier, power amplifier, SP2T RF switch, etc.

(9) The power module 5 is a self-made circuit board, in which the secondary power supply 502 uses a DC-DC module, the models are DF20-24D12, DF20-24S15, DFB10-24S5, and the DC-DC conversion of the main control power module uses LT company The integrated voltage regulator chip, the maximum output current can reach 3A.

(10) The signal acquisition module is a self-made circuit board, including two detectors and pre-amplification, lock-in amplification, A/D data acquisition, and FPGA.

(11) The computer used for the upper computer is a desktop computer produced by Lenovo Company, and the upper computer software is self-programmed software.

The testing and data processing steps are:

1. Adjust the energy and beam splitting ratio of reference light and measurement light

The test structure is in the state of containing the sample vessel (only for initial adjustment), and the adjustable aperture and adjustable beam splitter are used to adjust the energy and beam splitting ratio of the reference light and the measurement light so that the signals of the two are appropriate and close in magnitude ;

2. Sample test

Turn on the wide-spectrum halogen light source 101, pass through the off-axis parabolic reflector 102, the adjustable aperture stop 103, and the off-axis parabolic reflector 104 to collimate and parallelize the polychromatic light incident on the acousto-optic tunable filter 105; The sample is placed in the cuvette sample cell 6, the control and processing module 4 outputs a modulated radio frequency drive signal, and the drive signal drives the acousto-optic tunable filter 105; the modulated monochromatic light obtained after light splitting passes through the converging collimating lens group After 106, the beam splitter 107 is divided into two optical signals of reference light and measuring light, the reference optical signal is received by the reference optical path photodetector 301, the measuring light is incident on the cuvette sample cell 6, and the transmitted (or reflected) optical signal is measured The optical path photodetector 303 receives; the signal acquisition module extracts two photoelectric signals by phase-locked amplification correlation demodulation technology, and uploads them to the computer, thereby completing the acquisition and processing of spectral information.

3. Data processing

Using the aforementioned formula 2, formula 3, and formula 4, the required transmittance spectrum of the measured sample can be obtained:

The data measured for a series of samples are processed as above through the host computer, and then saved. Reserved for subsequent quantitative analysis and other applications.

The test method is simple, the light path is simple, and the operability is strong. The design of double light paths and double detectors, combined with the test method of testing reference light and measuring optical signals when there are no vessels, empty vessels and sample vessels in sequence, can effectively reduce the light source. It is an ideal near-infrared spectral analysis instrument to improve the test accuracy due to test errors caused by instability, differences between the two detectors, environmental interference, and sample vessel differences.

Claims (2)

1. an acousto-optic modulation double light path double detector type near infrared spectrometer, including spectrum analysis optical module, radio-frequency driven Module, signal acquisition module, control and processing module, power module, cuvette sample test structure, it is characterised in that:

Described spectrum analysis optical module include light source (101), off axis paraboloid mirror convergent mirror (102), adjustable diaphragm (103), Off axis paraboloid mirror collimating mirror (104), AOTF (105), collecting lens (106), adjustable beam splitter (107)；Light source (101) sends Light is through off axis paraboloid mirror convergent mirror (102) convergence, adjustable diaphragm (103) space filtering and off axis paraboloid mirror collimating mirror (104) After collimation, by AOTF (105), by controlling and processing module (4) control radio-frequency driven module (2) driving light splitting, formed required Measurement monochromatic light by collecting lens (106) assemble after, by adjustable beam splitter (107) press reference light and measurement light energy suitable And magnitude is close to determining that splitting ratio is distributed, forming reference light and measure light, reference light enters cuvette sample test structure (6), Two-way light is the most corresponding afterwards is detected by reference signal detector (301) and test signal sensor (303), forms double light path double Detector optical system for testing；Reference light and measure light and combine the optical characteristics of testing sample and reference light and measurement light detecting signal Value, is realized luminous energy magnitude by adjustable diaphragm (103) and controls, adjustable beam splitter (107) realize reference light and measure light splitting ratio Adjust, finally make reference light and to measure the energy of light suitable and magnitude is close；Each module is powered respectively by power module (5)；

Described cuvette sample test structure (6) includes cuvette (601), changeable cuvette support (602), in conjunction with test Method, is realized cuvette (601) in A, B, the switching of location of C by changeable cuvette support (602), and spectrogrph is accordingly Reference light when realizing without vessel, pocket ware and contain sample vessel and the test of measurement optical signal.

2. a test side based on acousto-optic modulation double light path double detector type near infrared spectrometer a kind of described in claims 1 Method, it is characterised in that method step is as follows:

Near infrared spectrometer obtain without vessel, pocket ware and containing sample vessel time reference light and measurement optical signal after, carry out as Lower process:

1) by the measurement light spectrum I without vessel_{2 nothings}With reference light spectrum I_{1 nothing}Process by formula 1, obtain without measurement light during vessel and Spectral energy proportionate relationship constant vector C of reference light, sets up reference light and the incident intrinsic relation measuring light；

2) by the measurement light spectrum I of pocket ware_{2 is empty}With reference light spectrum I_{1 is empty}Process by formula 2, set up reference light with by vessel after The intrinsic relation of measurement light, obtain spectral-transmission favtor T of vessel itself_Empty；

3) by the measurement light spectrum I containing sample vessel_{2 contain sample}With reference light spectrum I_{1 contains sample}Process by formula 3, set up reference light and pass through Containing the intrinsic relation of measurement light after sample vessel, obtain Optical transmission spectrum T containing sample vessel_{Containing sample}；

4) combining reference light with by containing the intrinsic relation of measurement light after sample vessel, and Optical transmission spectrum, through formula 4, public Formula 5 processes, available sample self Optical transmission spectrum curve and absorbance；