A laser frequency stabilization method based on the optically polarized atomic dichroism

Abstract

A laser frequency stabilization method based on the dichroism of optically polarized atoms utilizes the dichroism of alkali metal atoms polarized by the optical pump effect for frequency stabilization. This overcomes the difficulty of achieving atomic resonance in high-pressure gas chambers in traditional frequency stabilization methods, optimizes the complexity of the frequency stabilization system, reduces costs, and shrinks the size. The method is characterized by defining one side of the alkali metal gas chamber as a first incident side and the opposite side as a second incident side, forming a counter-incident relationship with the first incident side. The laser light input to the first incident side is circularly polarized to pump and polarize the alkali metal atoms. The laser light input to the second incident side is linearly polarized. After the linearly polarized light passes through the alkali metal atoms with dichroism due to optical polarization and counter-incident with the circularly polarized light, the polarization plane of the linearly polarized light rotates. The long-term in-situ stability of the laser frequency is controlled based on the correspondence between the polarization plane rotation angle of the linearly polarized light and the laser frequency.

Description

Technical Field

[0001] This invention belongs to the field of laser frequency stabilization technology and is applicable to atomic spin inertial / magnetic field measurement systems, particularly a laser frequency stabilization method based on the dichroism of optically polarized atoms. Background Technology

[0002] With the rapid development of scientific and technological fields such as atomic spectroscopy, optical fiber communication, and quantum sensing, more complex requirements have been placed on laser frequency stabilization technology.

[0003] Currently, common laser frequency stabilization methods include spectral absorption lines, spectral cavities, and gratings. However, in systems such as atomic spin inertial / magnetic field measurements where optical pumping of atoms within a high-pressure chamber is required, existing laser frequency stabilization methods, such as spectral absorption curve methods, struggle to achieve in-situ frequency stability. Using optical cavities or gratings for frequency stabilization can increase size and cost.

[0004] In summary, there is an urgent need to design a low-cost method for long-term in-situ stable control of pump light frequency for application in systems such as atomic spin inertial / magnetic field measurement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a laser frequency stabilization method based on the dichroism of optically polarized atoms. The method utilizes the dichroism of optically pumped polarized atoms, and the polarization plane rotation angle of linearly polarized light after passing through polarized alkali metal atoms is related to the laser frequency, so as to achieve long-term in-situ stable control of the pump light frequency.

[0006] The technical solution of the present invention is as follows:

[0007] A laser frequency stabilization method based on the dichroism of optically polarized atoms is characterized by comprising: setting one side of an alkali metal gas cell as a first incident side, and setting the other side opposite to the first incident side as a second incident side that forms a counter-incidence with the first incident side; the laser input to the first incident side is circularly polarized light to pump alkali metal atoms, thereby polarizing the alkali metal atoms; the laser input to the second incident side is linearly polarized light; after the linearly polarized light passes through the alkali metal atoms that have dichroism due to optical polarization and is counter-incidence with the circularly polarized light, the polarization plane of the linearly polarized light rotates; and the long-term in-situ stability of the laser frequency is controlled according to the correspondence between the polarization plane rotation angle of the linearly polarized light and the laser frequency.

[0008] The polarizability expression for the alkali metal atom is as follows:

[0009]

[0010] Where P e Rp is the polarizability of alkali metal atoms, Rsd is the optical pumping rate, and Rsd is the relaxation rate of alkali metal atoms.

[0011] The expression relating the polarization plane rotation angle of the linearly polarized light to the laser frequency is as follows:

[0012]

[0013]

[0014] Where φ is the rotation angle of the polarization plane of linearly polarized light, l is the length of the light path within the gas chamber, and r e Let n be the classical electron radius, c be the speed of light, f be the oscillator strength, and n be the oscillator strength. a P is the atomic number density. e is the polarizability of alkali metal atoms, D(v) is a term related to the laser emission frequency v, v0 is the resonant frequency of alkali metal atoms, and Δv is the pressure broadening of the alkali metal gas chamber.

[0015] When v = v0, then φ = 0. By controlling φ = 0, long-term in-situ stable control of the laser frequency can be achieved.

[0016] The first incident side is sequentially connected to a depolarizing beam splitter, a first quarter-wave plate, a third polarizing beam splitter, a second half-wave plate, a second polarizing beam splitter, a liquid crystal phase retarder, a first polarizing beam splitter, a first half-wave plate, an optical isolator, and a laser. The liquid crystal phase retarder is sequentially connected to a light intensity control system, a first photodetector, and the third polarizing beam splitter. The second incident side is sequentially connected to a fifth polarizing beam splitter, a second reflector, a second quarter-wave plate, and a first reflector. The first reflector is connected to the pump light reflection side of the depolarizing beam splitter. The linearly polarized light reflection side of the depolarizing beam splitter is connected to the input side of a fourth polarizing beam splitter via the third half-wave plate. The reflection side of the fourth polarizing beam splitter is connected to a second photodetector, and the transmission side of the fourth polarizing beam splitter is connected to a third photodetector. The second and third photodetectors are respectively connected to a frequency control system, and the frequency control system is connected to the laser.

[0017] The alkali metal chamber is located inside the oven.

[0018] The second half-wave plate is used to adjust the splitting ratio of the reflected and transmitted light of the third polarizing beam splitter.

[0019] The circularly polarized light reflected from the depolarizing beam splitter passes sequentially through the first reflecting mirror, the second quarter-wave plate, and the second reflecting mirror, and is then reflected by the fifth polarizing beam splitter to become linearly polarized light. The linearly polarized light then faces the circularly polarized pump beam transmitted through the depolarizing beam splitter.

[0020] The transmission side of the first polarizing beam splitter is connected to the liquid crystal phase retarder, and the reflected light from the first polarizing beam splitter is used as the main light in other systems.

[0021] The technical effects of this invention are as follows: Compared with the prior art, the laser frequency stabilization method based on the dichroism of optically polarized atoms has the advantage that it utilizes the dichroism of alkali metal atoms polarized by the optical pump effect for frequency stabilization, overcoming the difficulty of achieving atomic resonance in high-pressure gas chambers in traditional frequency stabilization methods, optimizing the complexity of the frequency stabilization system, reducing the cost of laser frequency stabilization, and shrinking the size of the frequency stabilization system, thus providing a new solution for laser frequency stabilization. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the structural principle of a laser frequency stabilization method based on the dichroism of photopolarized atoms, which implements the present invention.

[0023] The reference numerals in the attached figures are explained as follows: 1-Laser; 2-Optical isolator; 3-First half-wave plate; 4-First polarizing beam splitter; 5-Liquid crystal phase retarder; 6-Second polarizing beam splitter; 7-Second half-wave plate; 8-Third polarizing beam splitter; 9-First quarter-wave plate; 10-Depolarizing beam splitter; 11-First photodetector; 12-First reflector; 13-Third half-wave plate; 14-Second photodetector; 15-Fourth polarizing beam splitter; 16-Third photodetector; 17-Second quarter-wave plate; 18-Second reflector; 19-Oven; 20-Alkali metal gas chamber; 21-Fifth polarizing beam splitter; 22-Frequency control system; 23-Light intensity control system. Detailed Implementation

[0024] The following is in conjunction with the attached diagram ( Figure 1 The invention will be described in the following sections and examples.

[0025] Figure 1 This is a schematic diagram illustrating the structural principle of a laser frequency stabilization method based on the optically polarized atomic dichroism of the present invention. (Reference) Figure 1 As shown, a laser frequency stabilization method based on the dichroism of optically polarized atoms includes setting one side of an alkali metal gas chamber 20 as a first incident side and the other side opposite to the first incident side as a second incident side that forms a counter-incidence with the first incident side. The laser light input to the first incident side is circularly polarized light to pump alkali metal atoms, thereby polarizing the alkali metal atoms. The laser light input to the second incident side is linearly polarized light. After the linearly polarized light passes through the alkali metal atoms that have dichroism due to optical polarization and is counter-incidence with the circularly polarized light, the polarization plane of the linearly polarized light will rotate. The long-term in-situ stability of the laser frequency is controlled according to the correspondence between the polarization plane rotation angle of the linearly polarized light and the laser frequency.

[0026] The polarizability expression for the alkali metal atom is as follows:

[0027]

[0028] Where P e Rp is the polarizability of alkali metal atoms, Rsd is the optical pumping rate, and Rsd is the relaxation rate of alkali metal atoms.

[0029] The expression relating the polarization plane rotation angle of the linearly polarized light to the laser frequency is as follows:

[0030]

[0031]

[0032] Where φ is the rotation angle of the polarization plane of linearly polarized light, l is the length of the light path within the gas chamber, and r e Let n be the classical electron radius, c be the speed of light, f be the oscillator strength, and n be the oscillator strength. a P is the atomic number density. e is the polarizability of alkali metal atoms, D(v) is a term related to the laser emission frequency v, v0 is the resonant frequency of alkali metal atoms, and Δv is the pressure broadening of the alkali metal gas chamber.

[0033] When v = v0, then φ = 0. By controlling φ = 0, long-term in-situ stable control of the laser frequency can be achieved.

[0034] The first incident side is sequentially connected to a depolarizing beam splitter 10, a first quarter-wave plate 9, a third polarizing beam splitter 8, a second half-wave plate 7, a second polarizing beam splitter 6, a liquid crystal phase retarder 5, a first polarizing beam splitter 4, a first half-wave plate 3, an optical isolator 2, and a laser 1. The liquid crystal phase retarder 5 is sequentially connected to a light intensity control system 23, a first photodetector 11, and the third polarizing beam splitter 8. The second incident side is sequentially connected to a fifth polarizing beam splitter 21, a second reflector 18, a second quarter-wave plate 17, and a first reflector. 12. The first reflector 12 is connected to the pump light reflection side of the depolarizing beam splitter 10. The linearly polarized light reflection side of the depolarizing beam splitter 10 is connected to the input side of the fourth polarizing beam splitter 15 via a third half-wave plate 13. The reflection side of the fourth polarizing beam splitter 15 is connected to the second photodetector 14, and the transmission side of the fourth polarizing beam splitter 15 is connected to the third photodetector 16. The second photodetector 14 and the third photodetector 16 are respectively connected to the frequency control system 22, which is connected to the laser 1. The alkali metal gas chamber 20 is located inside the oven 19.

[0035] The second half-wave plate 7 is used to adjust the splitting ratio of the reflected and transmitted light of the third polarizing beam splitter 8.

[0036] The circularly polarized light reflected from the depolarizing beam splitter 10 passes sequentially through the first reflecting mirror 12, the second quarter-wave plate 17, and the second reflecting mirror 18, and is then reflected by the fifth polarizing beam splitter 21 to become linearly polarized light. This linearly polarized light then opposes the circularly polarized pump beam transmitted through the depolarizing beam splitter 10. The transmission side of the first polarizing beam splitter 4 is connected to the liquid crystal phase retarder 5, and the reflected light from the first polarizing beam splitter 4 serves as the main light in other systems.

[0037] This invention discloses a laser frequency stabilization method based on the dichroism of optically polarized atoms. Taking atomic spin inertial / magnetic field measurement systems as the research object, this method addresses the difficulty of in-situ control of pump light frequency. After circularly polarized light pumps atoms to polarize them, the polarized atoms exhibit dichroism towards left-handed and right-handed circularly polarized light. Linearly polarized light is used to oppose the pumped circularly polarized light. Based on the correspondence between the polarization plane rotation angle of the linearly polarized light and the laser frequency, an in-situ laser frequency stabilization scheme based on the dichroism of optically polarized atoms is established. This invention, while meeting the design requirements for stable pump light frequency control, improves the polarization efficiency of alkali metal atoms, suppresses longitudinal optical frequency shift, and enhances the anti-interference capability of pump light frequency stability control. It features volume saving and ease of engineering implementation, and is suitable for products such as atomic spin inertial / magnetic field measurement, showing a very broad application prospect.

[0038] A laser frequency stabilization method based on the optically polarized atomic dichroism includes a laser (1), an optical isolator (2), a first half-wave plate (3), a first polarizing beam splitter (4), a liquid crystal phase retarder (5), a second polarizing beam splitter (6), a second half-wave plate (7), a third polarizing beam splitter (8), a first quarter-wave plate (9), an anti-polarizing beam splitter (10), a first photodetector (11), a first mirror (12), a third half-wave plate (13), a second photodetector (14), and a fourth polarizing beam splitter. Beam splitter (15), third photodetector (16), second quarter-wave plate (17), second mirror (18), oven (19), alkali metal chamber (20), fifth polarizing beam splitter (21), frequency control system (22), light intensity control system (23); a beam of linearly polarized light output from laser (1) passes sequentially through optical isolator (2), first half-wave plate (3), first polarizing beam splitter (4), liquid crystal phase retarder (5), second polarizing beam splitter (6), second half-wave plate (7), third After passing through the polarization beam splitter (8), the light is split into two beams with orthogonal polarization directions. The first beam passes through the first photodetector (11), and the light signal is converted into a current signal and fed back to the light intensity control system (23). The second beam passes through the first quarter-wave plate (9) and the depolarization beam splitter (10) in sequence, and is split into two beams of equal size and the same polarization direction. The first beam enters the alkali metal gas chamber (20) to pump polarize the alkali metal. The second beam passes through the first reflector (12), the second quarter-wave plate (17), and the second reflector (18) in sequence. 18) After being reflected by the fifth polarizing beam splitter (21), the light enters the gas chamber, and then is reflected by the depolarizing beam splitter (10) and then passes through the third half-wave plate and the fourth polarizing beam splitter (15) in sequence. The light is then split into two beams of linearly polarized light with perpendicular polarization directions, and is detected by the second photodetector (14) and the third photodetector (16) respectively. The signals converted by the second photodetector (14) and the third photodetector (16) are differentially divided and then controlled by the frequency control system (22) to generate control signals to control the frequency of the laser (1).

[0039] The second half-wave plate (7) is used to adjust the splitting ratio of the reflected and transmitted light of the third polarizing beam splitter. The light intensity stabilization system consists of the first polarizing beam splitter (4), the second polarizing beam splitter (6), the third polarizing beam splitter (8), the first photodetector (11), and the liquid crystal phase retarder (5), which together form a light intensity stabilization module to stabilize the intensity of the transmitted light passing through the third polarizing beam splitter (8).

[0040] The oven (19) is used to heat the alkali metal chamber (20).

[0041] The circularly polarized light reflected from the depolarizing beam splitter (10) passes sequentially through the first reflecting mirror (12), the second quarter-wave plate (17), and the second reflecting mirror (18), and is then reflected by the fifth polarizing beam splitter to become linearly polarized light. The linearly polarized light then interacts with the circularly polarized pump beam transmitted through the depolarizing beam splitter (10).

[0042] Due to the pumping of circularly polarized light, alkali metal atoms are polarized. The polarized atoms have dichroism. After passing through the polarized alkali metal atoms, the polarization plane of the frequency-detuned linearly polarized light will rotate. By controlling the frequency of the laser (1), the polarization plane rotation angle of the linearly polarized light is made zero, thus achieving stable control of the laser (1).

[0043] This frequency stabilization method is particularly applicable to, but not limited to, systems such as atomic spin inertial / magnetic field measurement. When this method is used for frequency stabilization in other systems, the reflected light from the first polarizing beam splitter (4) can be used as the main light in other systems.

[0044] The laser frequency stabilization method based on the dichroism of optically polarized atoms utilizes the dichroism of polarized atoms. Due to the dichroism, the polarization plane of frequency-detuned linearly polarized light rotates after passing through polarized alkali metal atoms. Stable control of the laser (1) is achieved by controlling the frequency of the laser (1) to make the polarization plane rotation angle of the linearly polarized light zero. Specifically, the method is as follows:

[0045] The circularly polarized light transmitted through the depolarizing beam splitter (10) pumps alkali metal atoms, and the polarizability P of the alkali metal atoms... e for:

[0046]

[0047] Among them, R p R is the optical pump rate. sd The relaxation rate of alkali metal atoms. The signals from the second photodetector (14) and the third photodetector (16) are differentially processed in the frequency control system (22) to obtain the linearly polarized light reflected from the fifth polarization beam splitter (21) after passing through the alkali metal gas chamber (20) and rotating at the linear polarization plane angle φ.

[0048]

[0049] Where l is the length of the light path within the air chamber; n a The atomic number density; r e Where c is the classical electron radius; f is the speed of light; f is the oscillator strength; D(v) is a term related to the laser emission frequency v of the laser (1), which is:

[0050]

[0051] Where v0 is the resonant frequency of alkali metal atoms, and Δν is the pressure broadening of the alkali metal gas chamber (20). It can be seen from the formula that when the laser frequency ν emitted by the laser (1) is equal to the resonant frequency v0 of alkali metal atoms, the rotation angle of the linearly polarized light is zero. By controlling the rotation angle of the polarization plane of the linearly polarized light to be zero, long-term in-situ stable control of the pump light frequency can be achieved.

[0052] The advantages of this invention compared with the prior art are as follows: This invention utilizes the dichroism of alkali metal atoms polarized by the optical pump effect for frequency stabilization, overcoming the difficulty of achieving atomic resonance in high-pressure gas chambers in traditional frequency stabilization methods, optimizing the complexity of the frequency stabilization system, reducing the cost of laser frequency stabilization, and shrinking the size of the frequency stabilization system, thus providing a new solution for laser frequency stabilization.

[0053] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, and / or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A laser frequency stabilization method based on the optically polarized atomic dichroism, characterized in that, The method includes setting one side of the alkali metal gas chamber as the first incident side and the other side opposite to the first incident side as the second incident side. The laser light input to the first incident side is circularly polarized light to pump alkali metal atoms, thereby polarizing the alkali metal atoms. The laser light input to the second incident side is linearly polarized light. After the linearly polarized light passes through the alkali metal atoms, which have dichroism due to optical polarization, it will rotate. The long-term in-situ stability of the laser frequency can be controlled according to the correspondence between the rotation angle of the linearly polarized light's polarization plane and the laser frequency. The first incident side is sequentially connected to a depolarizing beam splitter, a first quarter-wave plate, a third polarizing beam splitter, a second half-wave plate, a second polarizing beam splitter, a liquid crystal phase retarder, a first polarizing beam splitter, a first half-wave plate, an optical isolator, and a laser. The liquid crystal phase retarder is sequentially connected to a light intensity control system, a first photodetector, and the third polarizing beam splitter. The second incident side is sequentially connected to a fifth polarizing beam splitter, a second reflector, a second quarter-wave plate, and a first reflector. The first reflector is connected to the pump light reflection side of the depolarizing beam splitter. The linearly polarized light reflection side of the depolarizing beam splitter is connected to the input side of a fourth polarizing beam splitter via the third half-wave plate. The reflection side of the fourth polarizing beam splitter is connected to a second photodetector. The transmission side of the fourth polarizing beam splitter is connected to a third photodetector. The second and third photodetectors are respectively connected to a frequency control system, and the frequency control system is connected to the laser. The expression relating the polarization plane rotation angle of the linearly polarized light to the laser frequency is as follows: ， ， Where φ is the rotation angle of the polarization plane of linearly polarized light, l is the length of the light path within the gas chamber, and r e Let n be the classical electron radius, c be the speed of light, f be the oscillator strength, and n be the oscillator strength. a P is the atomic number density. e is the polarizability of alkali metal atoms, D(v) is a term related to the laser emission frequency v, v0 is the resonant frequency of alkali metal atoms, and Δv is the pressure broadening of the alkali metal gas chamber.

2. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, The polarizability expression for the alkali metal atom is as follows: ， Where P e Rp is the polarizability of alkali metal atoms, Rsd is the optical pumping rate, and Rsd is the relaxation rate of alkali metal atoms.

3. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, When v = v0, then φ = 0. By controlling φ = 0, long-term in-situ stable control of the laser frequency can be achieved.

4. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, The alkali metal chamber is located inside the oven.

5. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, The second half-wave plate is used to adjust the splitting ratio of the reflected and transmitted light of the third polarizing beam splitter.

6. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, The circularly polarized light reflected from the depolarizing beam splitter passes sequentially through the first reflecting mirror, the second quarter-wave plate, and the second reflecting mirror, and is then reflected by the fifth polarizing beam splitter to become linearly polarized light. The linearly polarized light then faces the circularly polarized pump beam transmitted through the depolarizing beam splitter.

7. The laser frequency stabilization method based on the optically polarized atomic dichroism according to claim 1, characterized in that, The transmission side of the first polarizing beam splitter is connected to the liquid crystal phase retarder, and the reflected light from the first polarizing beam splitter is used as the main light in other systems.

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