阅读说明：本技术 基于光强差分的单光束原子磁强计偏置及噪声抑制装置及方法 (Single-beam atomic magnetometer biasing and noise suppression device and method based on light intensity difference ) 是由 陈瑶 张宁 赵立波 马银涛 郭强 于明智 于 2020-12-28 设计创作，主要内容包括：本发明公开一种基于光强差分的单光束原子磁强计偏置及噪声抑制装置及方法,激光器产生的光依次经过柱面透镜一、二的整形后,经λ/2波片和偏振分光棱镜后进行分束,一束经过滤光片将光强衰减后到达光电探测器一,另一束经起偏器后通过光纤耦合头依次进入位于磁屏蔽桶内的λ/4波片、光阑,然后照射原子气室,透射出气室的光束受到原子自旋进动影响,线偏振光的偏振轴发生偏转；输出后到达光电探测器二；两束光经过光电探测器一和二差分后,由光电二极管放大器进行放大,锁相放大器用于提取放大器输出信号中的频率信息。通过将原子气室前后的光束光强进行差分,从而消除原子无极化状态下背景光强的偏置和检测前后的光强噪声,提高原子磁强计的灵敏度。(The invention discloses a single-beam atomic magnetometer bias and noise suppression device and method based on light intensity difference, wherein light generated by a laser sequentially passes through a first cylindrical lens and a second cylindrical lens for shaping, then passes through a lambda/2 wave plate and a polarization beam splitter prism for beam splitting, one beam of light passes through a light filter for attenuating the light intensity and then reaches a first photoelectric detector, the other beam of light passes through a polarizer and then sequentially enters a lambda/4 wave plate and a diaphragm which are positioned in a magnetic shielding barrel through an optical fiber coupling head, then irradiates an atomic gas chamber, the light beam which transmits the gas chamber is influenced by the self-spinning precession of atoms, and the polarization axis of linearly polarized light deflects; the output signal reaches a second photoelectric detector; the two beams of light are amplified by a photodiode amplifier after being subjected to difference between the first photodetector and the second photodetector, and the phase-locked amplifier is used for extracting frequency information in an output signal of the amplifier. By differentiating the light intensity of the light beams in front of and behind the atomic gas chamber, the bias of the background light intensity in the atomic electrodeless state and the light intensity noise in front of and behind the detection are eliminated, and the sensitivity of the atomic magnetometer is improved.)

1. A single-beam atomic magnetometer biasing and noise suppression device based on light intensity difference is characterized by comprising a pumping laser (1), a first cylindrical lens (2), a second cylindrical lens (3), a lambda/2 wave plate (4), a polarization splitting prism (5), an optical filter (6), a first photoelectric detector (7), a photodiode amplifier (8), a polarizer (9), an optical fiber coupling head (10), a lambda/4 wave plate (11), a magnetic shielding barrel (12), a magnetic compensation and modulation coil (13), a diaphragm (14), an atomic gas chamber (15), a function generator (16), a phase-locked amplifier (17), a heating laser (18) and a second photoelectric detector (19);

the cylindrical lens I (2), the cylindrical lens II (3), the lambda/2 wave plate (4), the polarization splitting prism (5) and the polarizer (9) share the optical axis; the focal length of the cylindrical lens I (2) is larger than that of the cylindrical lens II (3).

The magnetic shielding barrel (12) is used for providing a weak magnetic field environment required by an atomic magnetometer for the atomic gas chamber (15);

the magnetic compensation and modulation coil (13) is used for compensating and controlling residual magnetic fields sensed by atoms in the magnetic shielding barrel (12);

the function generator (16) is arranged outside the magnetic shielding barrel (12), and is connected with a magnetic compensation and modulation coil (13) which generates a direct current and an alternating current magnetic field through a cable to supply power to the magnetic compensation and modulation coil;

the heating laser (18) is used for heating the atomic gas chamber (15);

one ends of the first photoelectric detector (7), the second photoelectric detector (19) and the photodiode amplifier (8) are electrically connected, and the other end of the first photoelectric detector (7) is grounded through a first grounding resistor (20); the other end of the second photoelectric detector (19) is grounded through a second grounding resistor (21); the other end of the photodiode amplifier (8) is electrically connected with the phase-locked amplifier (17);

the pump light generated by the pump laser (1) is shaped by a cylindrical lens I (2) and a cylindrical lens II (3) in sequence, and then is split by the combination of a lambda/2 wave plate (4) and a polarization beam splitter prism (5), wherein one beam is attenuated by a light filter (6) and then reaches a photoelectric detector I (7), the other beam is polarized by a polarizer (9) and then sequentially enters a lambda/4 wave plate (11) and a diaphragm (14) which are positioned in the magnetic shielding barrel (12) through an optical fiber coupling head (10), and then irradiates an atomic gas chamber (15), the beam transmitted out of the atomic gas chamber (15) is influenced by atomic spin precession, and the polarization axis of linearly polarized light is deflected; the output reaches a second photoelectric detector (19); the two beams of light are subjected to difference through the first photoelectric detector (7) and the second photoelectric detector (19) and then amplified through the photodiode amplifier (8), and the phase-locked amplifier (17) is used for extracting frequency information in an output signal of the photodiode amplifier (8).

2. The single beam atomic magnetometer biasing and noise suppression device based on light intensity differential according to claim 1, wherein the filter (6) is preferably a neutral density filter.

3. Single beam atomic magnetometer biasing and noise suppression means according to claim 1, characterised in that said polarizer (9) is preferably a Glan Taylor prism.

4. A bias and noise suppression method of a single-beam SERF state atomic magnetometer based on light intensity differential detection is characterized in that the method is realized based on the device of claim 1, and the method specifically comprises the following steps:

s1: firstly, a magnetic field generated by a magnetic compensation and modulation coil (13) is controlled by a function generator (16) to compensate the magnetic field felt by atoms in the atom gas chamber (15), so that the magnetic field felt by the atom gas chamber (15) is zero;

s2: adjusting the power of the pump laser (1) to enable the spin polarization rate of electrons to reach 50%, under the condition, shielding light entering a second photoelectric detector (19), measuring photocurrent transmitted by the first photoelectric detector (7), and at the moment, obtaining the detected photocurrent which is system bias;

s3: and turning on the light entering the second photodetector (19), and selecting a proper attenuation coefficient to enable the total current entering the photodiode amplifier (8) to be 0, namely eliminating the bias of the detection system and simultaneously realizing the suppression of the common-mode power noise of the pumping light system.

Technical Field

The invention belongs to the field of magnetic sensors, and particularly relates to a single-beam atomic magnetometer biasing and noise suppression device and method based on light intensity difference.

Background

With the deep development of the technical fields of biology, medical treatment and the like, people put higher requirements on the measurement of a very weak magnetic field, and the magnetic sensor is expected to have higher sensitivity, lower noise and lower power and can realize the chip formation. At present, a magnetic sensor for measuring a weak magnetic field which has been commercially used is a superconducting quantum interferometer (SQUID), but since it is expensive to manufacture and requires low-temperature refrigeration, its application in a wider field is limited. While atomic magnetometers applying quantum technology are receiving more and more attention, especially SERF (Spin-Exchange-Relaxation-Free) state atomic magnetometers are greatly developed, theoretically, the sensitivity can reach aT/Hz^1/2Magnitude.

The double-beam atomic magnetometer has the main principle that a beam of circularly polarized light is used for pumping alkali metal atoms, the larmor precession of the atoms under a magnetic field is detected by linearly polarized light, the linearly polarized light can generate the deflection of a linear polarization surface after passing through an alkali metal air chamber, and the measurement of the external magnetic field is realized by detecting the rotation angle of the linearly polarized light; different from a double-beam magnetometer, the single-beam atomic magnetometer only uses one beam of circularly polarized pumping light to pass through an alkali metal atom air chamber, realizes the modulation of the power of the pumping light by modulating the direction of atomic spin through a magnetic field, and performs frequency demodulation on an optical intensity signal through a phase-locked amplifier to obtain magnetic field information. This method is susceptible to light intensity fluctuations and presents a large output photo-electric signal offset, so that a strong background offset signal exists before the signal enters the photo-electric amplifier, affecting the amplification capability of the photo-electric amplifier.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a single-beam atomic magnetometer bias and noise suppression device based on light intensity difference, which can be used for differentiating the light intensity in front of and behind an alkali metal gas chamber, eliminating the bias of background light intensity and enabling an output signal to be near a zero point; the differential method is simple and feasible, two ends of the two light intensity signals are grounded after being connected in series, the differential signal is led out from the middle point, and noise is reduced.

The purpose of the invention is realized by the following technical scheme:

a single beam atomic magnetometer biasing and noise suppression device based on light intensity difference comprises a pumping laser, a first cylindrical lens, a second cylindrical lens, a lambda/2 wave plate, a polarization beam splitter prism, an optical filter, a first photoelectric detector, a photodiode amplifier, a polarizer, an optical fiber coupling head, a lambda/4 wave plate, a magnetic shielding barrel, a magnetic compensation and modulation coil, a diaphragm, an atomic gas chamber, a function generator, a phase-locked amplifier, a heating laser and a second photoelectric detector;

the first cylindrical lens, the second cylindrical lens, the lambda/2 wave plate, the polarization beam splitter prism and the polarizer share the optical axis; the focal length of the first cylindrical lens is larger than that of the second cylindrical lens;

the magnetic shielding barrel is used for providing a weak magnetic field environment required by the atomic magnetometer for the atomic gas chamber;

the magnetic compensation and modulation coil is used for compensating and controlling a residual magnetic field sensed by atoms in the magnetic shielding barrel;

the function generator is arranged outside the magnetic shielding barrel, and is connected with a magnetic compensation and modulation coil which generates a direct current and an alternating current magnetic field through a cable to supply power to the magnetic compensation and modulation coil;

the heating laser is used for heating the atomic gas chamber;

one end of the first photoelectric detector, one end of the second photoelectric detector and one end of the photodiode amplifier are electrically connected, and the other end of the first photoelectric detector is grounded through a grounding resistor I; the other end of the second photoelectric detector is grounded through a second grounding resistor; the other end of the photodiode amplifier is electrically connected with the phase-locked amplifier;

the pump light generated by the pump laser is shaped by a first cylindrical lens and a second cylindrical lens in sequence, and then is split by the combination of a lambda/2 wave plate and a polarization beam splitter prism, wherein one beam of the pump light is attenuated by a light filter and then reaches a first photoelectric detector, the other beam of the pump light is polarized by a polarizer and then sequentially enters a lambda/4 wave plate and a diaphragm which are positioned in the magnetic shielding barrel through the optical fiber coupling head, then an atomic gas chamber is irradiated, the light beam transmitted out of the atomic gas chamber is influenced by atomic spin precession, and the polarization axis of linearly polarized light is deflected; the output signal reaches a second photoelectric detector; and the two beams of light are amplified by a photodiode amplifier after being subjected to difference between the first photoelectric detector and the second photoelectric detector, and the phase-locked amplifier is used for extracting frequency information in an output signal of the photodiode amplifier.

Further, the filter is preferably a neutral density filter.

Further, the polarizer is preferably a Glan Taylor prism.

A bias and noise suppression method of a single-beam SERF state atomic magnetometer based on light intensity differential detection is realized based on the device, and the method specifically comprises the following steps:

s1: firstly, a magnetic field generated by a function generator control magnetic compensation and modulation coil compensates a magnetic field felt by atoms in an atom gas chamber, so that the magnetic field felt by the atom gas chamber is zero;

s2: adjusting the power of the pump laser to enable the electron spin polarizability to reach 50%, under the condition, shielding light entering the second photoelectric detector, measuring photocurrent transmitted by the first photoelectric detector, and at the moment, obtaining the detected photocurrent which is system bias;

s3: and opening the light entering the second photoelectric detector, and selecting a proper attenuation coefficient to enable the total current entering the photodiode amplifier to be 0, namely eliminating the bias of the detection system and simultaneously inhibiting the common-mode power noise of the pumping light system.

The invention has the following beneficial effects:

the light intensity difference between the front and the back of the alkali metal air chamber can be realized, the bias of the background light intensity is eliminated, the output signal is close to the zero point, the influence of the light intensity fluctuation on the magnetic field measurement result is reduced, and the condition is created for the miniaturization of the magnetometer. The differential method is simple and feasible, two ends of the two light intensity signals are grounded after being connected in series, the differential signal is led out from the middle point, and noise is reduced.

Drawings

FIG. 1 is a schematic diagram of a single beam atomic magnetometer biasing and noise suppression device based on light intensity differential in accordance with the present invention;

fig. 2 is a schematic diagram of the differential method and signal acquisition of the present invention.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the objects and effects of the present invention will become more apparent, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

As shown in FIG. 1, the single-beam atomic magnetometer biasing and noise suppression device based on light intensity difference comprises a pumping laser 1, a first cylindrical lens 2, a second cylindrical lens 3, a lambda/2 wave plate 4, a polarization splitting prism 5, a filter 6, a first photodetector 7, a photodiode amplifier 8, a polarizer 9, an optical fiber coupling head 10, a lambda/4 wave plate 11, a magnetic shielding barrel 12, a magnetic compensation and modulation coil 13, a diaphragm 14, an atomic gas chamber 15, a function generator 16, a phase-locked amplifier 17, a heating laser 18 and a second photodetector 19;

the first cylindrical lens 2, the second cylindrical lens 3, the lambda/2 wave plate 4, the polarization beam splitter prism 5 and the polarizer 9 share the optical axis; the focal length of the first cylindrical lens 2 is greater than that of the second cylindrical lens 3;

the magnetic shielding barrel 12 is used for providing a weak magnetic field environment required by an atomic magnetometer for the atomic gas chamber 15;

the magnetic compensation and modulation coil 13 is used for compensating and controlling residual magnetic fields sensed by atoms in the magnetic shielding barrel 12;

the function generator 16 is arranged outside the magnetic shielding barrel 12, and the modulation coil 13 which generates direct current and alternating current magnetic fields is connected through a cable to supply power to the coil 13.

The heating laser 18 is used for heating the atomic gas chamber 15;

as shown in fig. 2, one end of the first photodetector 7, the second photodetector 19, and one end of the photodiode amplifier 8 are electrically connected, and the other end of the first photodetector 7 is grounded through a first grounding resistor 20; the other end of the second photoelectric detector 19 is grounded through a second grounding resistor 21; the other end of the photodiode amplifier 8 is electrically connected with the phase-locked amplifier 17;

the pumping light generated by the pumping laser 1 is shaped by a first cylindrical lens 2 and a second cylindrical lens 3 in sequence, and then is split by the combination of a lambda/2 wave plate 4 and a polarization beam splitter prism 5, wherein one beam is attenuated by a light filter 6 and then reaches a first photoelectric detector 7, the other beam is polarized by a polarizer 9 and then sequentially enters a lambda/4 wave plate 11 and a diaphragm 14 which are positioned in a magnetic shielding barrel 12 through a fiber coupling head 10, then irradiates an atom air chamber 15, the light beam transmitted out of the atom air chamber 15 is influenced by the precession of atom spin, and the polarization axis of linearly polarized light is deflected; the output reaches a second photoelectric detector 19; the two beams of light are amplified by the photodiode amplifier 8 after being differentiated by the first photodetector 7 and the second photodetector 19, and then frequency information in the output signal of the photodiode amplifier 8 is extracted by the phase-locked amplifier 17, so that the external magnetic field information is calculated.

The principle of the single-beam atomic magnetometer bias and noise suppression device based on the light intensity difference is as follows;

the motion process of alkali metal atoms in a magnetic field after being pumped by a single-beam laser can be described by a Block equation, and the steady state solution of the polarization rate along the pumping direction is as follows:

wherein p is₀Is the steady state polarizability; sigma B_x，ΣB_yAnd sigma B_zRespectively the size of a three-axis magnetic field; r is the sum of the pumping rate and the relaxation rate of alkali metal atoms, namely the total relaxation rate, and gamma is the electron gyromagnetic ratio.

In the unmodulated state, after the circular polarization passes through the gas cell, at the position of the atomic absorption peak, the output of the second photodetector can be written as:

U＝U₀+ΔU≈U₀+k·I₀·OD·ΔP_z·Exp(-OD(1-P_z)) (2)

wherein, U₀The voltage value after the light intensity signal is amplified for the constant bias after passing through the air chamber, OD is the optical depth, k is the proportionality coefficient of the light intensity signal amplified into the voltage signal, I₀For the intensity of incident light, Δ P_zIs the change of polarizability in the z direction under the action of an external magnetic field. The pumping light output and the change of the atomic polarizability are in a linear relation, and magnetic field information can be obtained by resolving the polarizability.

Under the action of the external x-direction or y-direction modulation magnetic field, frequency doubling demodulation is carried out by the phase-locked amplifier 17, and then the polarization rate change delta P in the z direction_zAnd a constant magnetic field in the x-direction exhibits the following relationship:

ΔP_z＝k·P_z·γ·B_x/R (3)

the voltage value of the output signal and the externally input magnetic field B can be combined with the formulas (2) to (3)_xAre related and exhibit a proportional relationship. If the two photodetectors are differentiated, U can be eliminated₀Biasing the signal while rejecting common mode noise signals.

Therefore, the single-beam SERF state atomic magnetometer bias and noise suppression method based on light intensity differential detection provided by the invention specifically comprises the following steps:

s1: firstly, the magnetic field generated by the magnetic compensation and modulation coil 13 is controlled by the function generator 16 to compensate the magnetic field felt by atoms in the atom gas chamber 15, so that the magnetic field felt by the atom gas chamber 15 is zero;

s2: and adjusting the power of the pump laser 1 to enable the electron spin polarizability to reach 50%, under the condition, shielding light entering the second photoelectric detector 19, and measuring the photocurrent transmitted by the first photoelectric detector 7, wherein the detected photocurrent is the system bias.

S3: and opening light entering the second photoelectric detector 19, and selecting a proper attenuation coefficient to enable the total current entering the photoelectric detection diode amplifier 8 after being filtered by the optical filter 6 to be 0, namely eliminating the bias of the detection system and simultaneously inhibiting the common mode power noise of the pumping light system.

After the bias and the noise suppression are carried out by the method, the magnetic field measurement is carried out, and the precision of the magnetic field measurement can be improved. The specific measurement process is as follows:

selecting a proper conversion coefficient from photocurrent to output voltage according to the current entering the photodiode amplifier 8, inputting an output signal synchronous signal of the function generator 16 to a reference signal end of the lock-in amplifier 17, accessing an output voltage signal of the photodiode amplifier 8 to an input signal of the lock-in amplifier 17, and adjusting the phase of the lock-in amplifier 17 to enable the x output of the lock-in amplifier 17 to be maximum. And inputting a measuring magnetic field, measuring the x output voltage of the lock-in amplifier 17 to obtain the coefficient of the input magnetic field and the output voltage, namely the scale coefficient, and finally realizing the measurement of the magnetic field.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and although the invention has been described in detail with reference to the foregoing examples, it will be apparent to those skilled in the art that various changes in the form and details of the embodiments may be made and equivalents may be substituted for elements thereof. All modifications, equivalents and the like which come within the spirit and principle of the invention are intended to be included within the scope of the invention.