Ultra-high-precision spectroscopic detection device based on atomic spin precession

Abstract

The present invention discloses an ultra-high-precision spectroscopic detection device based on atomic spin precession, which includes a collimating lens, two polarization beam splitting prisms, a birefringent crystal, a 1 / 4 wave plate, an atomic gas chamber, three reflecting prisms, a 1 / 2 wave plate and three detectors. The device can collimate the chaotic incident light and then pass it through the PBS polarization beam splitting prism to split the incident non-polarized light into two beams of linear polarized light with perpendicular polarization states. The two branches are used to simultaneously perform linear polarization differential detection and circular polarization interference detection, which naturally has higher accuracy and sensitivity. In addition, the device can be easily expanded into an array structure by optical fiber taper to achieve higher accuracy.

Description

Technical Field

[0001] The present invention relates to an optical instrument, in particular to a spectroscopic detection device. Background Art

[0002] Spin is an intrinsic property of atoms, and spin precession is sensitive to magnetic fields or rotation relative to inertial space. Detecting atomic spin precession allows for the measurement of magnetic fields or inertial rotation, leading to the development of atomic magnetometers, atomic gyroscopes, and other atomic sensors. Atomic spins are naturally chaotic. External magnetic fields and pump light can impart macroscopic orientation to these chaotic atomic spins, known as polarization. A polarized atomic gas cell is macroscopically equivalent to a Faraday rotator crystal, whose optical rotation coefficient is related to atomic spin precession. Atomic spin precession detection typically uses linearly polarized light as the probe light. Changes in atomic spin precession are measured by measuring the rotation angle of the polarization plane of linearly polarized light after it passes through an alkali metal gas cell.

[0003] Chinese patent CN 104677508 B discloses a method and device for detecting atomic spin precession based on circularly polarized probe light. This method, based on the optical rotation properties of polarized atoms in an atomic gas chamber, uses a birefringent optical path to generate left-handed and right-handed circularly polarized light. The left-handed and right-handed circularly polarized light are incident on the atomic gas chamber. A phase difference proportional to the atomic spin precession is generated between the left-handed and right-handed circularly polarized light passing through the gas chamber. A reflector is used to return the outgoing circularly polarized light along its original path, exchanging the left and right directions of the two circular polarizations and doubling the phase difference. Circularly polarized light interferometry is then used to cause the left-handed and right-handed circularly polarized light to interfere, achieving phase difference measurement and highly sensitive detection of atomic spin precession. Since two beams must be coupled into the same optical fiber, and their polarization states must be aligned with the fast and slow axes of the polarization-maintaining fiber, respectively, this is challenging. Coupling into the fiber requires precise alignment of the light and matching of the mode fields, which results in low coupling efficiency. This approach presents difficulties and low coupling efficiency. Furthermore, when coupling into the polarization-maintaining fiber, the polarization state cannot be guaranteed, and there is a time delay difference between the fast and slow axes. Furthermore, the input of the polarization-maintaining fiber must be linearly polarized, with the polarization direction along the fast or slow axis, for the output to maintain the original polarization state. If only linearly polarized light is emitted, but not along the fast or slow axis, the output is elliptically polarized light. This elliptically polarized state is affected by temperature and stress variations along the entire length of the fiber, making it unstable and unpredictable. Summary of the Invention

[0004] The object of the present invention is to provide a high-precision spectroscopic detection device that does not use polarization-maintaining optical fiber.

[0005] To achieve the above-mentioned object, the present invention is an ultra-high-precision spectroscopic detection device based on atomic spin precession, which includes a collimating lens, two polarization beam splitting prisms, a birefringent crystal, a quarter-wave plate, an atomic gas chamber, three reflecting prisms, a half-wave plate and three detectors. The collimating lens is arranged on the incident light path, a first polarization beam splitting prism is arranged opposite the collimating lens to split the incident light into two polarized lights, a birefringent crystal is arranged closely on the first polarized light path of the first polarization beam splitting prism to split the first polarized light into two paths, and a quarter-wave plate is arranged on the birefringent crystal to convert the two polarized lights into left and right circularly polarized lights. A plate is provided, and a first reflecting prism is closely arranged on the second polarized light path of the first polarized beam splitter prism, which reflects the linear polarized light in parallel with the first polarized light; an atomic gas chamber is provided opposite to the 1 / 4 wave plate, and a second reflecting prism is attached to the atomic gas chamber, which faces the first reflecting prism and reflects the second polarized light to the atomic gas chamber; a 1 / 2 wave plate and a second polarized beam splitter prism are sequentially provided on the linear polarized light path of the atomic gas chamber, a third reflecting prism is provided on the splitting light path of the second polarized beam splitter prism, and a first and a second detector are respectively provided on the two light paths of the second polarized beam splitter prism; a third detector is provided on the circularly polarized light path of the atomic gas chamber.

[0006] The collimating lens, two polarization beam splitting prisms, birefringent crystal, 1 / 4 wave plate, atomic gas chamber, three reflecting prisms, 1 / 2 wave plate and three detectors are respectively arranged on the splitting optical path of the optical fiber tapered extension array. The optical path of the optical fiber tapered extension array is sequentially provided with an input collimator, multiple groups of 50:50 beam splitting prism groups, and an attenuation adjuster, a receiving collimator and an output collimator on each group of beams.

[0007] After adopting the above scheme, the incident light from the conventional optical fiber with chaotic polarization state can be collimated and then passed through the PBS polarization splitter prism to split the incident non-polarized light into two beams of linear polarized light with perpendicular polarization states. The two branches are used to perform linear polarization differential detection and circular polarization interference detection at the same time, which naturally has higher accuracy and sensitivity. In addition, the fiber tapering can be easily expanded into an array structure to achieve higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Schematic diagram of the spectroscopic detection structure of the present invention;

[0009] Figure 2 This is the optical fiber tapered expansion array of the present invention.

[0010] Description of labels:

[0011] 1. Collimating lens, 2. First 9-polarization beam splitter prism, 3. Birefringent crystal; 4. 1 / 4 wave plate; 5. Atomic gas chamber; 6. First reflecting prism; 7. Second reflecting prism; 8. 1 / 2 wave plate; 9. Second polarization beam splitter prism; 10. Third reflecting prism; 11. Third detector; 12. First detector; 13. Second detector; 14. Input collimator; 15. 50:50 beam splitter prism group; 16. Attenuation adjuster; 17. Receiving collimator; 18. Output collimator. DETAILED DESCRIPTION

[0012] In order to explain the technical content, structural features, achieved objectives and effects of the present invention in detail, the following is a detailed description in conjunction with the embodiments and the accompanying drawings.

[0013] See also Figure 2 As shown, the present invention conveniently expands the incident light of conventional optical fiber with disordered polarization state into an array through optical fiber taper. The incident light is irradiated by the input collimator 14 to the 50:50 splitting prism group 15 and is divided into 8 light paths. Each light path is provided with an attenuation adjuster 16, a receiving collimator 17 and an output collimator 18.

[0014] like Figure 1 As shown, through Figure 2 The incident light of the middle output collimator 18 is collimated by the collimating lens 1, and the first polarization beam splitter prism 2 (polarization beam splitter prism is PBS) splits the light beam into two polarized lights. The first polarized light is split into two beams by the birefringent crystal 3 and then passes through the 1 / 4 wave plate 4 to become two beams of left and right circularly polarized light, which then pass through the atomic gas chamber 5 and reach the third detector 11.

[0015] When a beam of circularly polarized light is incident on an atomic gas cell along the z-axis, the photons' angular momentum is transferred to the alkali metal atoms, causing them to form consistent spins and precessions along the direction of the transmitted light. This allows the atomic gas cell, with a high atomic density, to be placed in a low magnetic field. Pumping with circularly polarized light allows the atomic spin exchange frequency to be far greater than the Larmor precession frequency. Spin exchange collisions within the gas cell result in no spin exchange relaxation, manifesting as polarized atoms returning to their initial polarization state before they have time to depolarize. This state is known as the atomic SERF state. Alkali metal gas cells (SERF atomic magnetometers use alkali metal atoms (K, Rb, Cs, etc.) as atomic sources. Alkali metal gas cells typically include alkali metal atoms, a buffer gas (4He), and a quenching gas (N2)). These cells exhibit not only an optical rotation effect on linearly polarized light but also a phase delay characteristic for left- and right-handed circularly polarized light.

[0016] Polarized alkali metal atoms exhibit circular dichroism. Using a birefringent optical path, left- and right-handed circularly polarized light is generated. Passing through the alkali metal gas cell, the resulting phase delays are different, producing a phase difference φ. High-sensitivity detection of atomic spin precession is achieved by measuring this phase difference. The specific relationship between the phase difference φ generated by left- and right-handed circularly polarized light passing through the polarized alkali metal gas cell and the spin precession signal Px of the atom to be measured is:

[0017]

[0018] Among them, l is the length of the gas chamber, c is the speed of light, re is the electron radius, n is the number density of alkali metal atoms, f is the interaction intensity between atoms and light, ν is the light frequency, ν0 is the optical resonance transition frequency of alkali metal atoms, D(ν-ν0) is the dispersion function of the atom to the laser, and Px is the projection of the atomic polarizability vector along the x direction, that is, the measurement axis direction, that is, the atomic spin precession signal.

[0019] Phase difference information Δφ can be extracted through coherent detection technology (a well-known technology). Interference between left-handed and right-handed circularly polarized light can achieve phase difference measurement and high-sensitivity detection of atomic spin precession.

[0020] The second polarized light is totally reflected by the reflecting prisms 6 and 7 and enters the atomic gas chamber 5. The 1 / 2 wave plate 8 is adjusted so that the light beam is split into two paths when passing through the second polarization splitting prism 9 and enters the first and second detectors 12 and 13 respectively.

[0021] When the linearly polarized probe light passes through the SERF state atomic gas cell, it will be deflected. The rotation angle of the polarization plane is defined as the light rotation angle θ. Its relationship with the projection Pxe of the atomic spin precession signal on the detection direction (x-axis) can be expressed as

[0022]

[0023] Where: n is the saturated vapor density of alkali metal atoms; l is the length of the gas cell, c is the speed of light in vacuum, and re is the electron radius; fD1≈1 / 3, fD2≈2 / 3; v is the frequency of the probe light, vD1 and vD2 are the transition frequencies of alkali metal atoms on the D1 and D2 lines; ΓL is the pressure broadening coefficient. The SERF state atomic gas cell can be macroscopically equivalent to an optically active crystal, and its optical rotation characteristics can be described by the equivalent Faraday rotation equation:

[0024]

[0025] Where: K V is the equivalent optical rotation coefficient of the polarized SERF atomic gas cell. For the set gas cell, K V and l are both fixed values, θ is proportional to Pxe, and accurate measurement of θ can obtain accurate spin precession information, thereby realizing the measurement of the magnetic field. KV can be expressed as

[0026]

[0027] The atomic spin precession signal can be measured by detecting the first and second detectors 12 and 13, and the spin precession information can be extracted by measuring the difference between the light intensities I1 and I2 of the two detectors (refer to Chinese patent 201811209041.6 or 201510679672.4).

[0028] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An ultra-high-precision spectroscopic detection device based on atomic spin precession, characterized by: The invention comprises a collimating lens, two polarization beam splitting prisms, a birefringent crystal, a quarter wave plate, an atomic gas chamber, three reflecting prisms, a half wave plate and three detectors. The collimating lens is arranged on the incident light path. A first polarization beam splitting prism for splitting the incident light into two polarized lights is arranged directly on the collimating lens. A birefringent crystal for splitting the first polarized light into two paths is arranged closely on the first polarized light path of the first polarization beam splitting prism. A quarter wave plate for converting the two polarized lights into left and right circularly polarized lights is arranged on the birefringent crystal. A first polarization beam splitting prism for splitting the first polarized light into two paths is arranged close to the first polarized light path of the first polarization beam splitting prism. A first reflecting prism is closely arranged on the polarization light path and reflects the linear polarized light in parallel with the first route polarized light; an atomic gas chamber is arranged opposite to the 1 / 4 wave plate, and a second reflecting prism is attached to the atomic gas chamber and faces the first reflecting prism and reflects the second route polarized light to the atomic gas chamber; a 1 / 2 wave plate and a second polarization splitter prism are arranged in sequence on the linear polarization light path of the atomic gas chamber, a third reflecting prism is arranged on the splitting light path of the second polarization splitter prism, and a first and a second detector are respectively arranged on the two light paths of the second polarization splitter prism; a third detector is arranged on the circularly polarized light path of the atomic gas chamber.

2. The ultra-high-precision spectroscopic detection device based on atomic spin precession according to claim 1, characterized in that: The collimating lens, two polarization beam splitting prisms, birefringent crystal, 1 / 4 wave plate, atomic gas chamber, three reflecting prisms, 1 / 2 wave plate and three detectors are respectively arranged on the splitting optical path of the optical fiber tapered extension array. The optical path of the optical fiber tapered extension array is sequentially provided with an input collimator, multiple groups of 50:50 beam splitting prism groups, and an attenuation adjuster, a receiving collimator and an output collimator on each group of beams.

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