Magnetic induction intensity detection device and method based on laser self-mixing interference

Abstract

The invention discloses a magnetic induction intensity detection device based on laser self-mixing interference, which is characterized in that laser emitted by a laser is divided into two light paths after being split by an optical splitter; wherein a polarizing film, a magneto-optical crystal and a transducer are sequentially arranged on one optical path; the transducer is electrically connected with the control module, and the control module generates a continuous sine wave signal to continuously control the transducer; a detector is arranged on the other light path; the detector is electrically connected with the Fourier transform module, and the Fourier transform module analyzes a laser self-mixing interference signal acquired by the detector; the magneto-optical crystal is located in the magnetic field; laser emitted by the laser device is reflected for multiple times between the laser device and the transducer, and laser self-mixing interference is formed under the action of the polaroid. The laser is reflected for multiple times between the laser and the transducer, the Faraday optical rotation effect can be enhanced, the polaroid serves as the polarizer and the polarization analyzer, and the advantages that an external polarization analyzer is not needed, the measurement cost is reduced, and the sensitivity is improved are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser precision measurement, and in particular to a magnetic induction intensity detection device and method based on laser self-mixing interference. Background Art

[0002] Magnetic field detection technology is of great significance in basic scientific research, application technology development and practical engineering applications. It is not only a key tool for understanding basic physical phenomena in nature, but also plays an important role in many application technology fields such as medical imaging, data storage, navigation and positioning, industrial detection, energy management, biomedical engineering, etc.

[0003] One of the traditional methods of magnetic field detection is to use the Faraday rotation effect, which indirectly measures the magnetic induction intensity by measuring the rotation angle of the polarization direction of linearly polarized light when it passes through a medium placed in a magnetic field. This method has the characteristics of high sensitivity, non-invasiveness and remote detection.

[0004] However, the traditional Faraday rotation effect measurement method has some limitations. When two polarizers are used as polarizers and analyzers, the attenuation of light will be aggravated, which directly affects the accuracy and reliability of the detection results. In addition, this configuration usually requires a complex optical system and multiple optical components, which increases the complexity and cost of the system. Therefore, it is an urgent technical need to develop a new magnetic field detection technology that can maintain the advantages of high sensitivity and non-invasiveness while simplifying the system configuration, reducing costs and improving the accuracy and reliability of measurements. Summary of the invention

[0005] The present invention aims to solve one of the technical problems existing in the related art at least to a certain extent.

[0006] One object of the present invention is to provide a magnetic induction intensity detection device based on laser self-mixing interference, which reduces the optical elements in the optical path, reduces light attenuation, and realizes more accurate, more reliable and more cost-effective magnetic induction intensity detection.

[0007] Another object of the present invention is to provide a method for detecting magnetic induction intensity based on laser self-mixing interference using the above-mentioned device, which uses laser self-mixing interference technology and Fourier transform analysis technology to effectively filter out background noise and improve the stability and reliability of measurement results.

[0008] In order to achieve the above-mentioned object, the present invention provides a magnetic induction intensity detection device based on laser self-mixing interference, comprising a laser for emitting laser light, wherein the laser light emitted by the laser light is split by a spectrometer into two optical paths;

[0009] A polarizer, a magneto-optical crystal and a transducer are sequentially arranged on one optical path; the transducer is electrically connected to a control module, and the control module generates a continuous sine wave signal to continuously control the transducer;

[0010] A detector is arranged on the other optical path; the detector is electrically connected to the Fourier transform module, and the Fourier transform module analyzes the laser self-mixing interference signal acquired by the detector;

[0011] The magneto-optical crystal is located inside the magnetic field to form a Faraday effect; the laser light emitted by the laser is reflected multiple times between the laser and the transducer, and under the action of the polarizer, laser self-mixing interference is formed.

[0012] A further preferred technical solution of the present invention is that the axis of the magneto-optical crystal is coaxial with the laser light emitted by the laser, and the axis of the magneto-optical crystal is coaxial with the normal line of the transducer surface.

[0013] Preferably, both end surfaces of the magneto-optical crystal along the axial direction are smooth surfaces, and the surface of the transducer facing the laser has mirror reflection characteristics.

[0014] Preferably, the polarization direction of the polarizer is the same as the polarization direction of the laser light emitted by the laser, and the polarizer serves as a polarizer and an analyzer.

[0015] Another aspect of the present invention provides a method for detecting magnetic induction intensity based on laser self-mixing interference using the above detection device, comprising the steps of:

[0016] S1. The collimated laser generated by the laser is divided into two beams by a beam splitter, one of which passes through a polarizer, a magneto-optical crystal and a transducer, and the other is received by a detector;

[0017] The laser passes through the polarizer and becomes polarized light; the magneto-optical crystal is located inside the magnetic field, and the polarization direction of the polarized light passing through the magneto-optical crystal is rotated; the polarized light after optical rotation is irradiated on the surface of the transducer, and after being reflected by the transducer, it passes through the magneto-optical crystal again, and the polarization direction of the polarized light is rotated a second time; the polarized light after the second optical rotation passes through the polarizer and the beam splitter and returns to the laser; the laser is reflected multiple times between the laser and the transducer surface, forming laser self-mixing interference;

[0018] S2, the control module generates a continuous sine wave signal to drive the transducer, so that the phase of the polarized light irradiated on the surface of the transducer changes continuously, and at the same time the laser self-mixing interference signal is monitored by the Fourier transform module to obtain the power spectrum of the laser self-mixing interference;

[0019] S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted to obtain the power spectrum attenuation coefficient.

[0020] S4, changing the magnetic induction intensity, repeating steps S1-S3, recording the power spectrum attenuation coefficients of different magnetic induction intensities, and fitting the power spectrum attenuation coefficients of different magnetic induction intensities to obtain the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient;

[0021] S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity according to the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

[0022] Preferably, in step S2, the method for acquiring the power spectrum of laser self-mixing interference is:

[0023] The laser self-mixing interference signal after i reflections is expressed as:

[0024]

[0025] Among them, ε is the coupling coefficient of the laser returning to the inside of the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser respectively, and r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser;

[0026] The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as:

[0027] P(f)=|∫[P(t)·exp(-jft)]dt| 2 ;

[0028] Wherein, P is power, f is frequency, t is time, dt represents the unit time of laser passing through the magneto-optical crystal, and j is the complex number symbol.

[0029] Preferably, the power spectrum attenuation coefficient in step S3 is expressed as:

[0030] P(f)=a1·exp(-f / f / )+b1;

[0031] Among them, a1 and b1 are fitting coefficients.

[0032] Preferably, the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient obtained in S4 is expressed as:

[0033] f / =a2·exp(-B / b2)+c2;

[0034] Among them, a2, b2, and c2 are fitting coefficients.

[0035] Beneficial effects: The present invention uses a single polarizer to act as both a polarizer and an analyzer, thereby reducing optical components in the optical path, reducing light attenuation, simplifying system configuration, and achieving more accurate, more reliable, and more cost-effective magnetic induction intensity detection;

[0036] The present invention utilizes laser self-mixing interference technology to enhance the detection capability of magnetic field changes, especially under low magnetic induction intensity. At the same time, Fourier transform analysis technology is adopted to obtain the power spectrum of laser self-mixing interference, and the power spectrum under different magnetic induction intensities is fitted and analyzed to effectively filter out background noise and improve the stability and reliability of measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of a magnetic induction intensity detection device based on laser self-mixing interference of the present invention;

[0038] Figure 2 A frequency-power relationship curve obtained by a magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention;

[0039] Figure 3 This is a power spectrum attenuation coefficient fitting curve diagram obtained by the magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention;

[0040] Figure 4 A fitting curve diagram of the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient obtained by the magnetic induction intensity detection method based on laser self-mixing interference in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments, and they should not be understood as limitations on the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the description of the present invention, it should be understood that the terms used are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0042] Combine the following Figure 1-Figure 4 The present invention describes a magnetic induction intensity detection device and method based on laser self-mixing interference.

[0043] Embodiment 1: This embodiment provides a magnetic induction intensity detection device based on laser self-mixing interference.

[0044] The device, such as Figure 1As shown, it includes a laser, a spectrometer, a polarizer, a magneto-optical crystal, a transducer, a control module, a detector and a Fourier transform module.

[0045] In this embodiment, the laser is a pure solid-state laser; the magneto-optical crystal is made of highly transparent material to reduce the optical loss of the laser during the reflection process and ensure the accuracy of signal transmission. In this embodiment, scandium gallium garnet (TGG) is selected to make the magneto-optical crystal; the transducer is a piezoelectric ceramic crystal. The polarization direction of the polarizer is the same as the polarization direction of the laser emitted by the laser, and it serves as a polarizer and analyzer.

[0046] The output end of the driving power supply is connected to the input end of the laser to drive the laser emitted by the laser. After the laser is split by the beam splitter, it is divided into two optical paths. A polarizer, a magneto-optical crystal and a transducer are arranged on the first optical path. The input end of the transducer is connected to the input end of the control module. The control module generates a continuous sine wave signal to continuously control the transducer, which can control the length of the transducer to change periodically, thereby changing the phase of the laser and generating laser self-mixing interference. The normal of the transducer is coaxial with the laser emitted by the laser, and the coaxiality is used to ensure the accuracy of signal transmission.

[0047] A detector is set on the second optical path, and the laser is irradiated on the input end of the detector. The output end of the detector is connected to the input end of the Fourier transform module, and the Fourier transform module is used to analyze the laser self-mixing interference signal. The Fourier transform can directly display the power spectrum of the laser self-mixing interference signal, which is convenient for operators to observe the influence of changes in magnetic induction intensity.

[0048] The design principle of the device of this embodiment is that the laser is reflected multiple times between the laser and the transducer, and the polarization direction is deflected. The intensity of the deflected laser is weakened after passing through the polarizer, causing the self-mixing interference characteristics of the laser to change. This change is used to detect the magnetic induction intensity.

[0049] The laser emitted by the laser can be reflected multiple times between the transducer and the output end face of the laser, and during the multiple reflections, the laser passes through the magneto-optical crystal multiple times, which has the effect of enhancing the rotation of the laser polarization direction and is suitable for low magnetic induction intensity detection.

[0050] Embodiment 2: This embodiment provides a method for detecting magnetic induction intensity based on laser self-mixing interference, which uses the detection device of embodiment 1.

[0051] The specific steps of this detection method are:

[0052] S1. The collimated laser generated by the pure solid-state laser is divided into two beams by the beam splitter. One beam of light passes through the polarizer, magneto-optical crystal and transducer and then returns to the laser to form laser self-mixing interference; the other beam of light is received by the detector to monitor the laser self-mixing interference signal;

[0053] The laser passes through the polarizer to become polarized light, and then passes through the magneto-optical crystal. When the magnetic induction intensity of the environment in which the magneto-optical crystal is located changes, the Faraday rotation effect is generated, causing the polarization direction of the polarized light to rotate; the polarized light after optical rotation is irradiated on the surface of the transducer, and after being reflected by the transducer, it passes through the magneto-optical crystal again, and the polarization direction of the polarized light undergoes a second rotation; the polarized light after the second optical rotation passes through the polarizer and the spectrometer and returns to the laser, and is reflected multiple times between the laser and the piezoelectric ceramic surface, forming laser self-mixing interference;

[0054] S2, the control module generates a continuous sine function with a frequency of 100HZ and an amplitude of 600mVpp to drive the transducer, so that the phase of the polarized light irradiated on the transducer surface changes continuously. At the same time, the power spectrum of the laser self-mixing interference is observed through the Fourier transform module, such as Figure 2 As shown; the method for obtaining the power spectrum of laser self-mixing interference is:

[0055] The first reflection of laser light between the laser and the transducer is expressed as:

[0056] E1=ζ·r1(1-r2) 2 r3·cos(2·Δθ)·exp[-j·4π(L+l) / λ+gL]·E / ;

[0057] Where g is the gain coefficient of the laser cavity, ζ is the coupling coefficient of the laser returning to the inside of the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser respectively, r3 is the reflectivity of the transducer, and E / is the initial laser, j is the complex number symbol;

[0058] -4π(L+l) is the phase change of the laser caused by the external cavity and the laser cavity, L is the distance between the laser and the transducer, and l is the length of the laser cavity;

[0059] Δθ is the rotation angle of the laser polarization direction, calculated as:

[0060] Δθ=V·B·d;

[0061] Where, d is the length of the magneto-optical crystal, B is the magnetic induction intensity, and V is the Verdet constant of the magneto-optical crystal;

[0062] The light wave that returns to the laser cavity after i reflections is expressed as:

[0063]

[0064] All reflected light between the laser and the transducer is expressed as:

[0065]

[0066] The light inside the laser is represented by:

[0067] E ＝ =r1r2·exp[-j·4πL / λ+gL]·E / ;

[0068] For a stable laser, the light field should reach E+E L =E0; and:

[0069]

[0070] The self-mixing interference of the laser after i reflections is expressed as:

[0071]

[0072] Among them, ζ is the coupling coefficient of the laser returning to the inside of the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser respectively, r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser;

[0073] The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as:

[0074] P(f)=|∫[P(t)·exp(-jft)]d| 2 ;

[0075] Wherein, P is power, f is frequency, t is time, dt represents the unit time of laser passing through the magneto-optical crystal, and j is the complex number symbol.

[0076] S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted, such as Figure 3 As shown, the power spectrum attenuation coefficient is f0 = 10.35kHz; expressed as:

[0077] P(f)=42.34·exp(-f / 10.35)-87.22;

[0078] S4, change the magnetic induction intensity to 0-36.11mT, repeat steps S1-S3, record the power spectrum attenuation coefficients of different magnetic induction intensities, and fit the power spectrum attenuation coefficients of different magnetic induction intensities, such as Figure 4 As shown, the relationship between magnetic induction intensity and power spectrum attenuation coefficient is obtained; it is expressed as:

[0079] f / =4.04·exp(-B / 7.70)-10.52.

[0080] S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity according to the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

[0081] The principle of the detection method of this embodiment is that the power spectrum of laser self-mixing interference shows an attenuation trend, and its attenuation coefficient is related to the magnetic induction intensity, the length of the magneto-optical crystal, and the Verdet coefficient; since the change of the magnetic induction intensity in the environment of the magneto-optical crystal causes the attenuation rate of the power spectrum to change, it further causes the fitting coefficient f0 of the laser self-mixing interference power spectrum to change, so the magnetic induction intensity B can be written as an expression of the power spectrum attenuation coefficient f0.

[0082] In this embodiment, the power spectrum of laser self-mixing interference shows an attenuation trend, and its attenuation coefficient is related to the magnetic induction intensity and the magneto-optical crystal. The change of the magnetic induction intensity of the magneto-optical crystal in the environment causes the change of the attenuation rate of the power spectrum. The power spectrum under different magnetic induction intensities is fitted and analyzed to eliminate the influence of background noise.

[0083] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnetic induction intensity detection device based on laser self-mixing interference, comprising a laser for emitting laser light, characterized in that: The laser light emitted by the laser is split by the beam splitter into two optical paths; A polarizer, a magneto-optical crystal and a transducer are sequentially arranged on one optical path; the transducer is electrically connected to a control module, and the control module generates a continuous sine wave signal to continuously control the transducer; A detector is provided on the other optical path; the detector is electrically connected to the Fourier transform module, and the Fourier transform module analyzes the laser self-mixing interference signal obtained by the detector; The magneto-optical crystal is located inside the magnetic field to form a Faraday effect; the laser light emitted by the laser is reflected multiple times between the laser and the transducer, and under the action of the polarizer, laser self-mixing interference is formed.

2. The magnetic induction intensity detection device based on laser self-mixing interference according to claim 1 is characterized in that: The axis of the magneto-optical crystal is coaxial with the laser light emitted by the laser, and the axis of the magneto-optical crystal is coaxial with the normal line of the transducer surface.

3. The magnetic induction intensity detection device based on laser self-mixing interference according to claim 1 is characterized in that: The two end surfaces of the magneto-optical crystal along the axis direction are smooth surfaces, and the surface of the transducer facing the laser has a mirror reflection characteristic.

4. The magnetic induction intensity detection device based on laser self-mixing interference according to claim 1 is characterized in that: The polarization direction of the polarizer is the same as the polarization direction of the laser light emitted by the laser, and the polarizer serves as a polarizer and an analyzer.

5. A method for detecting magnetic induction intensity based on laser self-mixing interference using the detection device according to any one of claims 1 to 4, characterized in that: Includes steps: S1. The collimated laser generated by the laser is divided into two beams by a beam splitter, one of which passes through a polarizer, a magneto-optical crystal and a transducer, and the other is received by a detector; The laser passes through the polarizer and becomes polarized light; the magneto-optical crystal is located inside the magnetic field, and the polarization direction of the polarized light passing through the magneto-optical crystal is rotated; the polarized light after optical rotation is irradiated on the surface of the transducer, and after being reflected by the transducer, it passes through the magneto-optical crystal again, and the polarization direction of the polarized light is rotated a second time; the polarized light after the second optical rotation passes through the polarizer and the beam splitter and returns to the laser; the laser is reflected multiple times between the laser and the transducer surface, forming laser self-mixing interference; S2, the control module generates a continuous sine wave signal to drive the transducer, so that the phase of the polarized light irradiated on the surface of the transducer changes continuously, and at the same time the laser self-mixing interference signal is monitored by the Fourier transform module to obtain the power spectrum of the laser self-mixing interference; S3. The power spectrum of laser self-mixing interference shows a peak attenuation phenomenon. The peak of the power spectrum is fitted to obtain the power spectrum attenuation coefficient. S4, changing the magnetic induction intensity, repeating steps S1-S3, recording the power spectrum attenuation coefficients of different magnetic induction intensities, and fitting the power spectrum attenuation coefficients of different magnetic induction intensities to obtain the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient; S5. Obtain the power spectrum of laser self-mixing interference under different magnetic induction intensities, calculate the attenuation coefficient of the power spectrum, and obtain the magnetic induction intensity according to the relationship between the magnetic induction intensity and the power spectrum attenuation coefficient in step S4.

6. The detection method according to claim 5, characterized in that: In step S2, the method for obtaining the power spectrum of laser self-mixing interference is: The self-mixing interference of the laser after i reflections is expressed as: in, is the coupling coefficient of the laser returning to the inside of the laser; r1 and r2 are the reflectivity of the front and rear end faces of the laser respectively, and r3 is the reflectivity of the transducer; n is the total number of reflections; Δθ is the rotation angle of the laser polarization direction; is the phase of the i-th reflected laser; The power spectrum is obtained by Fourier transforming the laser self-mixing interference signal, which is expressed as: P(f)=|∫[P(t)·exp(-jft)]dt| 2 ; Where P is power, f is frequency, t is time, ft is the product of frequency and time, dt represents unit time, and j is the complex number symbol.

7. The detection method according to claim 6, characterized in that: The power spectrum attenuation coefficient in step S3 is expressed as: P(f)=a1·exp(-f / f0)+b1; Among them, a1 and b1 are fitting coefficients.

8. The detection method according to claim 7, characterized in that: The relationship between the magnetic induction intensity and the power spectrum attenuation coefficient is obtained in S4 and is expressed as: f0=a2·exp(-B / b2)+c2; Among them, a2, b2, and c2 are fitting coefficients.

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