A method for improving the signal-to-noise ratio of NMOR atomic magnetometer based on polarization moment manipulation

Abstract

A method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation, wherein an optical modulator is first used to modulate a beam of linearly polarized pump light, and the modulated pump light is applied to an alkali metal gas chamber; then, under the action of the modulated pump light, the atomic polarization in the alkali metal gas chamber is mainly composed of two parts: a quadrupole moment and a hexadecapole moment; then, a controller is used to control the optical modulator so that the modulation phase of the pump light is reversed, thereby eliminating the hexadecapole moment while retaining the quadrupole moment; finally, the response amplitude of the magnetic resonance signal is increased without changing the magnetic resonance linewidth, thereby improving the signal-to-noise ratio of the NMOR atomic magnetometer and improving the magnetic field measurement sensitivity of the NMOR atomic magnetometer.

Description

Technical Field

[0001] The present invention relates to a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation, which can be applied to an atomic magnetometer whose pump light is linearly polarized light, can meet the requirements of precise magnetic field measurement under high ambient magnetic fields, and is particularly suitable for improving the signal-to-noise ratio of an NMOR atomic magnetometer under geomagnetic conditions, and belongs to the technical field of atomic magnetometers. Background Art

[0002] NMOR atomic magnetometer is a magnetometer based on nonlinear magneto-optical rotation (NMOR, Nonlinearmagneto-optical rotation, nonlinear magneto-optical rotation effect), which has the characteristics of high sensitivity and miniaturization. Different from traditional atomic magnetometers, NMOR atomic magnetometer can work in a large magnetic field environment, so it has broad application prospects in the fields of biological health monitoring, mineral exploration, magnetic anomaly detection, etc. Therefore, it is of great significance to improve its measurement sensitivity.

[0003] At present, the improvement of the sensitivity of the NMOR atomic magnetometer mainly relies on hardware improvements. The sensitivity can be improved by using better quality semiconductor lasers, increasing the area of ​​interaction between light and atoms, using coated gas chambers, etc., but all of these increase the measurement cost and have certain limitations. The present invention is based on optical pumping technology. Without adding other equipment, the method of directly controlling the modulation phase of the pumping light through an optical modulator can purify the polarization information, which can effectively improve the signal-to-noise ratio of the system and contribute to the high-precision measurement of the magnetic field. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the problems that the existing methods for improving the signal-to-noise ratio of NMOR atomic magnetometers are complex to implement, large in size, and lack of optical control, a method for improving the signal-to-noise ratio of NMOR atomic magnetometers based on polarization moment manipulation is proposed. By periodically flipping the modulation phase of the pumping light, the polarization signal is purified without increasing the complexity of the system, ultimately achieving precise measurement of the magnetic field and improving the signal-to-noise ratio of the system.

[0005] The technical solution of the present invention is as follows:

[0006] A method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation, characterized in that it comprises the following steps:

[0007] Step A, driving the optical modulator to modulate the amplitude of the pumping laser and align it with the alkali metal gas chamber;

[0008] Step B, tuning the pump laser to the resonance frequency, generating quadrupole atomic polarization and hexadecapole atomic polarization in the alkali metal gas chamber;

[0009] Step C, controlling the optical modulator through a controller so that the modulation phase of the pumping laser is flipped to eliminate the hexadecanopole moment and retain the quadrupole moment, thereby achieving polarization moment purification;

[0010] Step D: outputting the magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment through a data acquisition device.

[0011] The step A includes the following steps to achieve amplitude modulation of the pumping laser:

[0012] Step A1, turning on the pump laser and using a controller to drive the optical modulation device;

[0013] Step A2, modulating the light intensity of the pumping laser by an optical modulation device;

[0014] Step A3, aligning the pumping laser with the alkali metal gas chamber.

[0015] The step B includes the following steps to realize the polarization of the atomic ensemble:

[0016] Step B1, tuning the pump laser to a resonance frequency;

[0017] Step B2, generating standard linear polarized light through a polarizing device, and transmitting the standard linear polarized light through an alkali metal gas cell, thereby generating quadrupole atomic polarization and hexadecapole atomic polarization in the alkali metal gas cell.

[0018] The step C comprises the following steps to purify the polarization moment:

[0019] Step C1, applying periodic pulse modulation with a phase change of π / 4 to the optical modulator through a controller;

[0020] Step C2, the optical modulator performs a periodic flip of the phase of the pumping laser at π / 4 to eliminate the hexadecapole moment, retain the quadrupole moment, and achieve polarization moment purification.

[0021] The step D comprises the following steps to implement magnetic field measurement of the NMOR atomic magnetometer:

[0022] Step D1, using a photodetector to form a differential detection system;

[0023] Step D2, outputting in real time the magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment alone through the data acquisition module;

[0024] Step D3, by calculating the calibration coefficient of the magnetometer to compare the signal-to-noise ratio of the magnetometer before and after phase manipulation, K=A / γ, where K is the calibration coefficient, A is the signal response amplitude, and γ is the line width. After eliminating the hexadecanoe moment and retaining the quadrupole moment, the signal response amplitude A of the magnetometer increases, while the line width γ remains unchanged, so the calibration coefficient increases significantly. When the calibration coefficient increases, the magnetometer has a stronger ability to sense magnetic fields and its signal-to-noise ratio is significantly improved.

[0025] The NMOR atomic magnetometer comprises a semiconductor laser, an optical modulator, a collimator, a Glan prism, an alkali metal gas chamber and a polarization beam splitter prism connected in sequence, the reflection side of the polarization beam splitter prism is connected to the negative input end of the differential amplifier through a first photodetector, the transmission side of the polarization beam splitter prism is connected to the positive input end of the differential amplifier through a second photodetector, the output end of the differential amplifier is connected to the input end of a phase-locked amplifier, the output end of the phase-locked amplifier is connected to a computer, the computer is connected to a controller, and the controller is connected to the optical modulator.

[0026] The technical effects of the present invention are as follows: the present invention provides a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation, which first uses an optical modulator to modulate a beam of linearly polarized pump light, and allows the modulated pump light to act on an alkali metal gas chamber; then, under the action of the modulated pump light, the atomic polarization in the alkali metal gas chamber is mainly composed of two parts: a quadrupole moment and a hexadecanopole moment; then, the optical modulator is controlled by a controller to flip the modulation phase of the pump light, thereby eliminating the hexadecanopole moment while retaining the quadrupole moment; finally, the response amplitude of the magnetic resonance signal is improved without changing the magnetic resonance linewidth, thereby improving the signal-to-noise ratio of the NMOR atomic magnetometer and improving the magnetic field measurement sensitivity of the NMOR atomic magnetometer.

[0027] The present invention discloses a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation. The method takes the NMOR atomic magnetometer as a research object, and aims at improving the signal-to-noise ratio of the NMOR atomic magnetometer. Based on a fine pump light modulation technology, the pump light modulation phase is periodically flipped by a controller to eliminate the hexadecane moment, retain the quadrupole moment, and enhance the magnetic field response signal, thereby improving the sensitivity of the system. The present invention is simple to operate, improves the signal-to-noise ratio of the system without increasing the volume and cost of the system, and is applicable to other linearly polarized light pumped atomic magnetometers, and has broad application prospects.

[0028] The advantages of the present invention over the prior art are as follows: (1) Based on the basic principle of the NMOR atomic magnetometer, the present invention separates the quadrupole moment and the hexadecapole moment by finely controlling the pumping laser, which can clarify and evaluate the contribution of different polarization moments to the magnetic field response signal, and has certain guiding significance for the design and operation of related experiments. (2) The present invention is simple to operate, and the polarization moment is purified by periodically flipping the modulation phase of the pumping light, which improves the system signal-to-noise ratio without increasing the system volume and cost, and has certain reference value for improving the sensitivity of atomic magnetometers under other linear polarization effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The schematic diagram of the structure of the NMOR atomic magnetometer involved in the method for improving the signal-to-noise ratio of the NMOR atomic magnetometer based on polarization moment manipulation of the present invention. NMOR (Nonlinear magneto-optical rotation) refers to the nonlinear magneto-optical rotation effect.

[0030] Figure 2 It is a schematic flow chart of a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to the present invention. Figure 2 The method includes step 1, using an optical modulator to modulate the pump laser; step 2, using the modulated laser to generate atomic polarization - quadrupole moment and hexadecapole moment; step 3, using a controller to flip the pump laser modulation phase; step 4, using a data acquisition device to output a magnetic field measurement signal.

[0031] Figure 3 The present invention is a polarization moment manipulation diagram for implementing a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation technology. Figure 3 The left side of the box is the polarization moment (coordinate points are -0.04, -0.03, ···, 0.04), the right side of the box is the modulation signal (coordinate points are 0, 5, ···, 25), and the bottom of the box is time (s, coordinates are 0, 2, ···, 20). Figure 3 At 15 seconds, the controller 11 applies a phase reversal (a periodic reversal of phase π / 4), and the modulation signal changes to 15. After 15 seconds, the quadrupole moment 12 remains almost unchanged (the quadrupole moment is Figure 3 The middle dotted waveform), the hexadecanopole moment 13 decays rapidly (the hexadecanopole moment is Figure 3 The middle solid line waveform) realizes the purification of the polarization moment.

[0032] The description of the accompanying drawings is as follows: 1-semiconductor laser; 2-optical modulator (such as fiber electro-optic modulator, acousto-optic modulator, etc.); 3-collimation head; 4-alkali metal gas chamber supporting shell; 5-photodetector; 6-polarization splitter prism; 7-alkali metal gas chamber; 8-Glan prism; 9-PC (computer); 10-phase-locked amplifier; 11-controller; 12-quadrupole; 13-hexadecanoe; 14-pumping light square wave modulation signal; 15-square wave modulation signal after phase change. DETAILED DESCRIPTION

[0033] Below is the attached figure ( Figure 1-Figure 3 ) and Examples illustrate the present invention.

[0034] Figure 1 The present invention is a schematic diagram of the structure of an NMOR atomic magnetometer involved in a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation. Figure 2 It is a schematic flow chart of a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to the present invention. Figure 3 This is a polarization moment manipulation diagram for implementing a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation technology of the present invention. Figures 1 to 3 As shown, a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation includes the following steps: step A, driving an optical modulator to modulate the amplitude of a pumping laser and align it with an alkali metal gas chamber; step B, tuning the pumping laser to a resonant frequency to generate quadrupole atomic polarization and hexadecanopole atomic polarization in the alkali metal gas chamber; step C, controlling the optical modulator through a controller to flip the modulation phase of the pumping laser to eliminate the hexadecanopole moment and retain the quadrupole moment, thereby achieving polarization moment purification; step D, outputting a magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment through a data acquisition device.

[0035] The step A includes the following steps to achieve amplitude modulation of the pumping laser: step A1, turning on the pumping laser and using a controller to drive the optical modulation device; step A2, modulating the light intensity of the pumping laser through the optical modulation device; step A3, aligning the pumping laser with the alkali metal gas chamber.

[0036] The step B includes the following steps to realize the polarization of the atomic ensemble: step B1, tuning the pumping laser to the resonance frequency; step B2, generating standard linear polarized light through a polarization device, and transmitting the light through an alkali metal gas chamber, thereby generating quadrupole atomic polarization and hexadecanopole atomic polarization in the alkali metal gas chamber.

[0037] The step C comprises the following steps to purify the polarization moment: step C1, applying periodic pulse modulation with a phase change of π / 4 to the optical modulator through a controller; step C2, the optical modulator periodically flips the phase of the pumping laser by π / 4 to eliminate the hexadecapole moment and retain the quadrupole moment to purify the polarization moment.

[0038] The step D comprises the following steps to realize the magnetic field measurement of the NMOR atomic magnetometer: step D1, using a photoelectric detector to form a differential detection system; step D2, outputting the NMOR atomic magnetometer magnetic field measurement signal under the action of the quadrupole moment alone in real time through a data acquisition module; step D3, comparing the signal-to-noise ratio of the magnetometer before and after phase manipulation by calculating the scale factor of the magnetometer, K=A / γ, where K is the scale factor, A is the signal response amplitude, and γ is the line width. After eliminating the hexadecanoe moment and retaining the quadrupole moment, the signal response amplitude A of the magnetometer increases, while the line width γ remains unchanged, so the scale factor increases significantly. When the scale factor increases, the magnetometer has a stronger ability to sense the magnetic field, and its signal-to-noise ratio is significantly improved.

[0039] The NMOR atomic magnetometer includes a semiconductor laser 1, an optical modulator 2, a collimator head 3, a Glan prism 8, an alkali metal gas chamber 7 (the alkali metal gas chamber is located in an alkali metal gas chamber supporting shell 4) and a polarization beam splitter prism 6 connected in sequence. The reflection side of the polarization beam splitter prism 6 is connected to the negative input terminal (-) of the differential amplifier through a first photodetector (photodetector 5), the transmission side of the polarization beam splitter prism 6 is connected to the positive input terminal (+) of the differential amplifier through a second photodetector, the output terminal of the differential amplifier is connected to the input terminal (in) of a phase-locked amplifier 10, the output terminal (out) of the phase-locked amplifier 10 is connected to a computer 9 (PC), the computer 9 is connected to a controller 11, and the controller 11 is connected to the optical modulator 2.

[0040] Figure 1 The present invention is a schematic diagram of the structure of an NMOR atomic magnetometer involved in a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation. Figure 1 Under the action of the optical modulator 2, the emitted light of the semiconductor laser 1 passes through the collimator 3 and the Glan prism 8 in sequence, and then generates two polarizations, the quadrupole moment and the hexadecapole moment, in the alkali metal gas chamber 7. The polarization beam splitter prism 6 and two photodetectors 5 form a differential detection system to detect the rotation angle of the polarization plane of the laser passing through the gas chamber. The data acquisition system composed of the phase-locked amplifier 10 and the computer 9 processes in real time to achieve the measurement of the magnetic field. In addition, the phase-locked amplifier 10 and the controller 11 respectively apply frequency and phase control to the optical modulator 2 to achieve the purification of the polarization moment, and finally achieve the improvement of the signal-to-noise ratio of the magnetometer.

[0041] Figure 2This is a schematic flow chart of a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to the present invention. Figure 1 to Figure 2 As shown, a method for improving the signal-to-noise ratio of an NMOR atomic magnetometer based on polarization moment manipulation technology includes the following steps: step A, driving an optical modulator to modulate the amplitude of a pumping laser so that the pumping laser is aligned with an alkali metal gas chamber; step B, tuning the pumping laser to a resonant frequency to generate two different types of atomic polarizations, quadrupole moment and hexadecanole moment, in the alkali metal gas chamber; step C, controlling the optical modulator through a controller to flip the modulation phase of the pumping laser and eliminate the hexadecanole moment; step D, outputting a magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment through a data acquisition device.

[0042] The step A comprises: performing amplitude modulation on the pumping laser, turning on the semiconductor laser, driving the optical modulator through the controller, periodically modulating the light intensity of the pumping laser, and aligning the pumping laser with the alkali metal gas chamber;

[0043] The step B comprises: finely tuning the pumping laser frequency to the alkali metal resonance frequency, the pumping laser passing through the optical modulator and then passing through the polarization device to generate a beam of standard linear polarized light acting on the alkali metal gas chamber, and generating two kinds of atomic polarizations, quadrupole moment and hexadecapole moment, therein;

[0044] The step C comprises: applying a periodic phase reversal signal to the optical modulator through a controller, wherein the phase reversal value is π / 4, and after the pumping laser passes through the optical modulator, its phase will also be periodically reversed, thereby achieving fine adjustment of the pumping light phase;

[0045] The step D comprises: forming a differential detection system through a photoelectric detector to detect the optical rotation angle, and using a data acquisition module to output the magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment to improve the signal-to-noise ratio of the NMOR atomic magnetometer.

[0046] Figure 3 The present invention is a polarization moment manipulation diagram for implementing a method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation technology. Figure 3 The figure shows the changing states of the quadrupole moment and the hexadecanopole moment in the atomic ensemble before and after the phase manipulation of the pumping light modulation. From 0 to 15 seconds, the light intensity of the pumping laser is modulated by a square wave 14 through an optical modulator, and two atomic polarizations, quadrupole moment 12 and hexadecanopole moment 13, are generated in the alkali metal gas chamber. At 15 seconds, the phase flip is applied by the controller 11, and the modulation signal changes to 15. After 15 seconds, the quadrupole moment 12 remains almost unchanged, and the hexadecanopole moment 13 decays rapidly, realizing the purification of the polarization moment.

[0047] The sensitivity of the NMOR atomic magnetometer is related to its calibration coefficient, and its measurement process is K = A / γ. Among them, K is the calibration coefficient, A is the response amplitude, and γ is the line width. When the calibration coefficient increases, the signal-to-noise ratio of the magnetometer increases and the sensitivity is improved. After manipulating the phase of the pump light modulation, the line width remains almost unchanged, while the response amplitude is enhanced due to the purification of the polarization moment signal. Therefore, the calibration coefficient of the NMOR atomic magnetometer can be enhanced by phase manipulation, thereby improving the signal-to-noise ratio of the NMOR atomic magnetometer, and ultimately achieving an improvement in the sensitivity of magnetic field measurement.

[0048] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation, characterized in that: The following steps are involved: Step A, driving the optical modulator to modulate the amplitude of the pumping laser and align it with the alkali metal gas chamber; Step B, tuning the pump laser to the resonance frequency, generating quadrupole atomic polarization and hexadecapole atomic polarization in the alkali metal gas chamber; Step C, controlling the optical modulator through a controller so that the modulation phase of the pumping laser is flipped to eliminate the hexadecanopole moment and retain the quadrupole moment, thereby achieving polarization moment purification; Step D, outputting the NMOR atomic magnetometer magnetic field measurement signal under the action of quadrupole moment through a data acquisition device; The step C comprises the following steps to purify the polarization moment: Step C1, applying periodic pulse modulation with a phase change of π / 4 to the optical modulator through a controller; Step C2, the optical modulator performs a periodic flip of the phase of the pumping laser at π / 4 to eliminate the hexadecapole moment, retain the quadrupole moment, and achieve polarization moment purification.

2. The method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to claim 1, characterized in that: The step A includes the following steps to achieve amplitude modulation of the pumping laser: Step A1, turning on the pump laser and using a controller to drive the optical modulation device; Step A2, modulating the light intensity of the pumping laser by an optical modulation device; Step A3, aligning the pumping laser with the alkali metal gas chamber.

3. The method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to claim 1, characterized in that: The step B includes the following steps to realize the polarization of the atomic ensemble: Step B1, tuning the pump laser to a resonance frequency; Step B2, generating standard linear polarized light through a polarizing device, and transmitting the standard linear polarized light through an alkali metal gas cell, thereby generating quadrupole atomic polarization and hexadecapole atomic polarization in the alkali metal gas cell.

4. The method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to claim 1, characterized in that: The step D comprises the following steps to implement magnetic field measurement of the NMOR atomic magnetometer: Step D1, using a photodetector to form a differential detection system; Step D2, outputting in real time the magnetic field measurement signal of the NMOR atomic magnetometer under the action of the quadrupole moment alone through the data acquisition module; Step D3, by calculating the calibration coefficient of the magnetometer to compare the signal-to-noise ratio of the magnetometer before and after phase manipulation, K=A / γ, where K is the calibration coefficient, A is the signal response amplitude, and γ is the line width. After eliminating the hexadecanoe moment and retaining the quadrupole moment, the signal response amplitude A of the magnetometer increases, while the line width γ remains unchanged, so the calibration coefficient increases significantly. When the calibration coefficient increases, the magnetometer has a stronger ability to sense magnetic fields and its signal-to-noise ratio is significantly improved.

5. The method for improving the signal-to-noise ratio of a NMOR atomic magnetometer based on polarization moment manipulation according to claim 1, characterized in that: The NMOR atomic magnetometer comprises a semiconductor laser, an optical modulator, a collimator, a Glan prism, an alkali metal gas chamber and a polarization beam splitter prism connected in sequence, the reflection side of the polarization beam splitter prism is connected to the negative input end of the differential amplifier through a first photodetector, the transmission side of the polarization beam splitter prism is connected to the positive input end of the differential amplifier through a second photodetector, the output end of the differential amplifier is connected to the input end of a phase-locked amplifier, the output end of the phase-locked amplifier is connected to a computer, the computer is connected to a controller, and the controller is connected to the optical modulator.

Images