Method and device for detecting longitudinal field component of light field in real time

Abstract

The invention relates to a method and device for detecting longitudinal field components of a light field in real time, and the method comprises the following steps: S1, obtaining pump light, coupling light and detection light, carrying out the resonant coupling of three beams of laser and a cesium atom medium, and achieving the frequency locking through frequency locking light; s2, the propagation directions of the three laser beams are perpendicular to one another; s3, linear polarization processing is carried out on the three beams of laser, the polarization direction of the pump light is the same as the polarization direction of the transverse field component of the coupling light, and the polarization direction of the probe light is the same as the polarization direction of the longitudinal field component of the coupling light; s4, the three laser beams enter the cesium atom medium, the absorptivity of the cesium atom medium is modulated in space through the saturated absorption effect, and therefore longitudinal field component information is mapped to spatial distribution of the absorptivity of the cesium atom medium; and S5, realizing the real-time detection of the longitudinal field component of the coupled light by measuring the light intensity distribution of the transmission detection light in real time. The system has the advantages of reasonable design, real-time detection, simple operation, high stability, low cost, simple maintenance and the like, and is easy to popularize and apply.

Description

Technical Field:

[0001] The present invention relates to the technical field of the interaction between light and atoms in quantum optics, and particularly relates to a method and device for real-time detecting the longitudinal field component of an optical field. Background Art:

[0002] Light, as an electromagnetic wave existing in three-dimensional space, its electric and magnetic field components can propagate along any direction in space. For an optical field propagating along a specific direction, the electric and magnetic field components perpendicular and parallel to the propagation direction are respectively called transverse field components and longitudinal field components. In the past, the paraxial approximation method was usually adopted in the study of many optical problems, that is, mainly focusing on the transverse field components of the optical field, while the influence of the longitudinal field components was often ignored. With the development of modern optics such as photonics, micro-nano optics, and surface plasmon optics, relevant researchers have begun to pay attention to the physical properties and related novel phenomena that occur within the wavelength scale range of the optical field. At this time, the optical field confined in an extremely small space will simultaneously exhibit transverse field components and longitudinal field components. When the optical field is highly localized in a photonic crystal structure, a strong longitudinal field component will be generated. In addition, in a high numerical aperture focusing system, the strongly focused optical field will also generate a non-negligible longitudinal field component. The research on the longitudinal field component of the optical field not only promotes the development of emerging fields such as topological photonics and chiral quantum optics, but also shows great application potential in many frontier fields such as super-resolution imaging, near-field microscopy, and multi-dimensional optical field control.

[0003] However, in the related research on the longitudinal field component of the optical field, how to detect the longitudinal field component of the optical field experimentally has always been a major technical problem. Traditional optical elements such as polarizers and wave plates can only be used to analyze the transverse field components of the optical field of paraxial beams. For the longitudinal field component of the optical field that only exists within an extremely small space range, its experimental measurement generally involves near-field nano-detection technology. Currently, all the schemes for measuring the longitudinal field component of the optical field worldwide are based on scanning near-field microscopes and are mainly divided into two categories: one is near-field detection based on a nano-fiber probe, that is, a nano-fiber probe with a very small tip is brought close to the sample surface to detect the near-field light distribution near the surface. By analyzing the optical signals collected by the fiber probe, the information of the longitudinal field component of the optical field can be obtained. This method has extremely high spatial resolution (on the order of dozens of nanometers) and can accurately measure the distribution of the longitudinal field component of the optical field in a small area. The other is near-field detection based on nano-particles, that is, the optical field to be measured is incident on nano-particles with a very small volume. By analyzing the optical signals scattered by the nano-particles, the information of the longitudinal field component of the optical field can be obtained. Through different post-processing algorithms, this scheme can not only directly obtain the distribution of the longitudinal field component of the optical field, but also reconstruct the distribution of all components of the optical field in three-dimensional space.

[0004] Although the above two methods can both achieve the detection of the longitudinal field component of the optical field, the above two types of schemes both involve the precise manipulation and calibration of nanofiber probes or nanoparticles at the nanoscale, and require extremely precise and complex control and measurement systems. Therefore, they have the disadvantages of complicated measurement processes and slow response speeds. In addition, both of these two types of schemes are realized based on a scanning near-field microscope system, which is expensive and complex to maintain. Especially, it needs to be used on a high-precision active vibration isolation platform, which greatly limits its popularization and application. With the rapid development of modern optics, there is an urgent need for a fast, simple, and low-cost technology for detecting the longitudinal field component of the optical field.

[0005] It should be noted that the above content belongs to the technical cognition scope of the inventor and does not necessarily constitute the prior art. Summary of the Invention:

[0006] The purpose of the present invention is to solve the problems existing in the prior art, and provide a method and device for real-time detecting the longitudinal field component of the optical field, subverting the technical idea of detecting the longitudinal field component of the optical field based on a scanning near-field microscope. An innovative design is proposed to realize the detection of the longitudinal field component of the optical field based on the interaction between cesium atomic medium and laser, which has the advantages of reasonable design, real-time detection, simple operation, high stability, low cost, and easy maintenance, and is easy to be popularized and applied.

[0007] A method for real-time detecting the longitudinal field component of the optical field includes the following steps:

[0008] S1. Obtain three laser beams, namely a pump laser, a coupling laser, and a probe laser. The coupling laser is the optical field to be measured, and the frequencies of the three laser beams are all locked at the resonance frequency of the 6S 1 / 2 (F = 4) → 6P 1 / 2 (F = 3) hyperfine level transition of cesium atoms;

[0009] S2. Design the propagation directions of the pump laser, the coupling laser, and the probe laser to be perpendicular to each other and intersect at the cesium atomic medium;

[0010] S3. Perform linear polarization processing on the pump laser, the coupling laser, and the probe laser respectively. The polarization direction of the pump laser is the same as the polarization direction of the transverse field component of the coupling laser, and the polarization direction of the probe laser is the same as the polarization direction of the longitudinal field component of the coupling laser;

[0011] S4. The pump laser enters the cesium atomic medium and acts on the 6S 1 / 2 (F = 4, mF = ±0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = ±0, ±1, ±2, ±3) hyperfine level transition of cesium atoms, and prepare the cesium atoms into the ground state 6S 1 / 2On the Zeeman sub-levels (F = 4, mF = ±4); the coupling light enters the cesium atomic medium, and the transverse field component of the coupling light acts on the 6S of cesium atoms 1 / 2 (F = 4, mF = ±0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = ±0, ±1, ±2, ±3) hyperfine level transition, and the longitudinal field component acts on the 6S of cesium atoms 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition; the probe light enters the cesium atomic medium and acts on the 6S of cesium atoms 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition;

[0012] S5. Real-time detection of the longitudinal field component of the coupling light is achieved by measuring the light intensity distribution of the transmitted probe light in real time.

[0013] The light intensities of the pump light and the coupling light are greater than the saturation light intensity of the cesium atomic medium, and the light intensity of the probe light is less than the saturation light intensity of the cesium atomic medium.

[0014] The light spot of the pump light at the cesium atomic medium covers the cesium atomic medium.

[0015] The cesium atomic medium is composed of cesium atomic vapor enclosed in a square glass container, and an antireflection film is provided on the end face of the glass container.

[0016] In step S1, a laser is used to emit a laser with a wavelength of 895 nm. The laser is divided into four beams of laser by a fiber optic coupler. Three of the laser beams are used as the pump light, the coupling light, and the probe light respectively, and the other laser beam is used as the frequency-locking light for frequency locking of the laser.

[0017] In step S3, after the coupling light is linearly polarized, it is expanded and focused to form a strongly focused coupling light carrying a longitudinal field component.

[0018] In step S5, since the longitudinal field component of the coupling light and the probe light act on the same hyperfine transition, it will cause a saturation effect on the absorption of the probe light by the cesium atomic medium. The absorption rate of the cesium atomic medium is spatially modulated through the saturation absorption effect, so that the longitudinal field component information is mapped onto the spatial distribution of the absorption rate of the cesium atomic medium. The probe light is used to measure the spatial distribution of the absorption rate of the cesium atomic medium, and thus real-time detection of the longitudinal field component of the coupling light is achieved.

[0019] A device for real-time detecting the longitudinal field component of an optical field, comprising a laser, wherein the laser is connected to an optical fiber coupler, and the optical fiber coupler divides the laser into four beams of laser, namely pump light, coupled light, detection light and frequency-locked light. Among them, the pump light, coupled light and detection light are respectively connected to the optical field longitudinal field component detection system through optical fibers, and the frequency-locked light is used for locking the frequency of the laser.

[0020] The optical field longitudinal field component detection system includes a base, on which a support frame is provided. A cesium atom medium is provided on the support frame, and a Cartesian coordinate system is established with the center of the cesium atom medium as the origin. In the x-axis direction, an optical fiber collimator A, a polarizer A and a light collector A are sequentially arranged, and the optical fiber collimator A is connected to the pump light. In the z-axis direction, an optical fiber collimator B, a polarizer B, a lens A, a lens B, a microscope objective and a light collector B are sequentially arranged, and the optical fiber collimator B is connected to the coupled light. In the y-axis direction, an optical fiber collimator C, a polarizer C and a camera are sequentially arranged, and the optical fiber collimator C is connected to the detection light.

[0021] The support frame includes four columns spaced on the base, and a holder is provided on the columns, and the cesium atom medium is arranged on the holder.

[0022] On the two columns on the right side, a bracket A is provided, and the optical fiber collimator A and the polarizer A are provided on the bracket A. On the two columns on the left side, a bracket B is provided, and the light collector A is provided on the bracket B. On the two columns on the front side, a bracket C is provided, and the optical fiber collimator C and the polarizer C are provided on the bracket C. On the two columns on the rear side, a bracket D is provided, and the camera is provided on the bracket D. Four columns are sequentially designed with mounting seats A, B, C, D and E from top to bottom. The mounting seat A is provided with the optical fiber collimator B and the polarizer B, the mounting seat B is provided with the lens A, the mounting seat C is provided with the lens D, the mounting seat D is provided with the microscope objective, and the mounting seat E is provided with the light collector B.

[0023] The optical fiber collimator A is connected to the optical fiber coupler through an optical fiber A, the optical fiber collimator B is connected to the optical fiber coupler through an optical fiber B, and the optical fiber collimator C is connected to the optical fiber coupler through an optical fiber C.

[0024] The frequency-locked light is connected to the laser frequency locking system through an optical fiber. The laser frequency locking system includes an optical fiber collimator. The optical fiber collimator accesses the frequency-locked light, and the frequency-locked light is collimated into a spatial light beam by the optical fiber collimator and then divided into two beams of reflected light A and transmitted light A by a half-wave plate A and a polarization beam splitter prism A; the reflected light A enters the cesium atomic vapor cell A after being reflected by a beam splitter; the transmitted light A enters the cesium atomic vapor cell A after passing through a quarter-wave plate, a mirror A and a mirror B; the light emerging from the cesium atomic vapor cell A enters the polarization beam splitter prism B after passing through a beam splitter and a half-wave plate B and is divided into two beams of reflected light B and transmitted light B; the reflected light B is connected to a subtractor through a photodetector A, and the transmitted light B is connected to the subtractor through a photodetector B. The electrical signals output by the photodetector A and the photodetector B are subtracted by the subtractor to obtain a polarization spectrum signal. The PID lock receives the polarization spectrum signal as a feedback signal and outputs a control signal to achieve frequency locking of the laser.

[0025] The present invention adopts the above method and can bring the following beneficial effects:

[0026] (1) By making full use of the characteristic that the response speed of cesium atomic medium to the light field is very fast (in the order of microseconds), real-time detection of the longitudinal component of the light field can be achieved; (2) The detection device has no movable parts and does not involve a precision displacement control system, is simple to operate, has high stability and strong environmental adaptability; (3) The detection device does not involve a nanoscale precision scanning control system and signal acquisition and analysis software, has a low cost and is simple to maintain, and is easy to promote and apply. Description of the drawings:

[0027] Figure 1 It is a schematic structural diagram of the light field longitudinal component detection system of the present invention;

[0028] Figure 2 It is a side rear view of the light field longitudinal component detection system of the present invention;

[0029] Figure 3 It is a spatial position relationship diagram of the pump light, the coupling light and the detection light of the present invention;

[0030] Figure 4 It is a schematic installation diagram of the cesium atomic medium of the present invention;

[0031] Figure 5 It is a schematic structural diagram of the laser frequency locking system of the present invention;

[0032] Figure 6 It is a schematic diagram of the energy levels of the cesium atomic D1 line of the present invention;

[0033] Figure 7 It is a light intensity distribution diagram of the detection light passing through the cesium atomic medium of the present invention;

[0034] Among them, 1. Laser, 2. Fiber optic coupler, 3. Pump light, 4. Coupled light, 5. Probe light, 6. Frequency-locked light, 7. Detection system for longitudinal field component of optical field, 701. Base, 702. Column, 703. Cage, 704. Cesium atom medium, 705. Fiber optic collimator A, 706. Polarizer A, 707. Light collector A, 708. Fiber optic collimator B, 709. Polarizer B, 710. Lens A, 711. Lens B, 712. Microscopic objective lens, 713. Light collector B, 714. Fiber optic collimator C, 715. Polarizer C, 716. Camera, 717. Bracket A, 718. Bracket B, 719. Bracket C, 720. Bracket D, 721. Mounting seat A, 722. Mounting seat B, 723. Mounting seat C, 724. Mounting seat D, 725. Mounting seat E, 8. Laser frequency locking system, 801. Fiber optic collimator, 802. Half-wave plate A, 803. Polarizing beam splitter prism A, 804. Reflected light A, 805. Transmitted light A, 806. Beam splitter, 807. Cesium atom medium A, 808. Quarter-wave plate A, 809. Mirror A, 810. Mirror B, 811. Half-wave plate B, 812. Reflected light B, 813. Transmitted light B, 815. Photoelectric detector A, 816. Photoelectric detector B, 817. Subtractor, 818. PID controller, 9. Fiber optic A, 10. Fiber optic B, 11. Fiber optic C. Specific implementation manner:

[0035] In order to more clearly explain the overall concept of the present invention, the following will be described in detail by way of examples in conjunction with the accompanying drawings of the specification.

[0036] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0037] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the key points of each embodiment are to illustrate the differences from other embodiments.

[0038] As Figure 1-7 shown, a method for real-time detecting the longitudinal field component of an optical field includes the following steps:

[0039] S1. Obtain three laser beams of pump light 3, coupled light 4 and probe light 5. The coupled light 4 is the optical field to be measured, and the frequencies of the three laser beams are all locked at the resonance frequency of the hyperfine level transition of cesium atom D1 line 6S 1 / 2 (F = 4) → 6P 1 / 2 (F = 3); the wavelengths of the pump light 3, coupled light 4 and probe light 5 are 895 nm;

[0040] S2. Design the propagation directions of the pump light 3, the coupling light 4, and the probe light 5 to be perpendicular to each other and intersect at the cesium atomic medium 704;

[0041] S3. Perform linear polarization processing on the pump light 3, the coupling light 4, and the probe light 5 respectively. The polarization direction of the pump light 3 is the same as the polarization direction of the transverse field component of the coupling light 4, and the polarization direction of the probe light 5 is the same as the polarization direction of the longitudinal field component of the coupling light 4;

[0042] S4. The pump light 3 enters the cesium atomic medium 704 and acts on the cesium atoms 6S 1 / 2 (F = 4, mF = 0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = 0, ±1, ±2, ±3) hyperfine level transition (π transition), and prepare the cesium atoms to the ground state 6S 1 / 2 (F = 4, mF = ±4) Zeeman sublevels; the coupling light 4 enters the cesium atomic medium 704, and the transverse field component of the coupling light 4 acts on the cesium atoms 6S 1 / 2 (F = 4, mF = 0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = 0, ±1, ±2, ±3) hyperfine level transition (π transition), and the longitudinal field component acts on the cesium atoms 6S 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition (σ transition); the probe light 5 enters the cesium atomic medium 704 and acts on the cesium atoms 6S 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition (σ transition);

[0043] S5. Realize the real-time detection of the longitudinal field component of the coupling light 4 by measuring the light intensity distribution of the transmitted probe light 5 in real time. The system realizes the resonant coupling of the cesium atomic medium 704 with the pump light 3, the coupling light 4, and the probe light 5, and realizes the real-time detection of the longitudinal field component of the coupling light 4 by measuring the light intensity distribution of the probe light 5 after passing through the cesium atomic medium 704.

[0044] The light intensities of the pump light 3 and the coupling light 4 are greater than the saturation light intensity of the cesium atomic medium 704, and the light intensity of the probe light 5 is less than the saturation light intensity of the cesium atomic medium 704.

[0045] The light spot of the pump light 3 at the cesium atomic medium 704 covers the cesium atomic medium 704 (i.e., the diameter of the light spot of the pump light 3 at the cesium atomic medium 704 is greater than the side length of the cesium atomic medium 704), so as to prepare all the cesium atoms in the cesium atomic medium 704 to the 6S 1 / 2 (F = 4, mF = ±4) energy levels.

[0046] In step S1, a laser 1 emits a laser beam with a wavelength of 895 nm. The laser beam is divided into four laser beams by a 1×4 fiber coupler 2. Among them, three laser beams are used as pump light 3, coupling light 4, and probe light 5 respectively, and the other laser beam is used as frequency-locking light 6 for frequency locking of the laser 1.

[0047] In step S3, after the coupling light 4 undergoes linear polarization processing, beam expansion and focusing processing are performed to form a strongly focused coupling light carrying a longitudinal field component.

[0048] In step S5, since the longitudinal field component of the coupling light 4 and the probe light 5 act on the same hyperfine transition, it will cause the absorption of the probe light 5 by the cesium atom medium 704 to undergo a saturation effect. The absorption rate of the cesium atom medium 704 is spatially modulated through the saturation absorption effect, so that the longitudinal field component information is mapped onto the spatial distribution of the absorption rate of the cesium atom medium 704. The probe light 5 is used to measure the spatial distribution of the absorption rate of the cesium atom medium 704, and thus the real-time detection of the longitudinal field component of the coupling light 4 is realized.

[0049] A device for real-time detecting the longitudinal field component of an optical field includes a laser 1. The laser 1 emits a laser beam with a wavelength of 895 nm. The laser 1 is connected to a fiber coupler 2. The fiber coupler 2 divides the laser beam into four laser beams: pump light 3, coupling light 4, probe light 5, and frequency-locking light 6. Among them, the pump light 3, coupling light 4, and probe light 5 are respectively connected to an optical field longitudinal field component detection system 7 through optical fibers. The optical field longitudinal field component detection system 7 realizes the resonant coupling of the cesium atom medium 704 with the pump light 3, coupling light 4, and probe light 5, and realizes the real-time detection of the longitudinal field component of the coupling light 4 by measuring the light intensity distribution of the probe light 5 after passing through the cesium atom medium 704. The frequency-locking light 6 is used for frequency locking of the laser 1. The frequency-locking light 6 can be connected to a laser frequency locking system 8. This system provides a frequency locking scheme based on polarization spectroscopy. Other laser frequency locking schemes can also be adopted according to the actual situation, such as saturation absorption spectrum, two-photon absorption spectrum, etc. There are also some laser products that integrate a frequency locking module, which can also be directly and adaptively applied to the solution of the present invention for laser frequency locking.

[0050] The optical field longitudinal field component detection system 7 includes a base 701. A support frame is provided on the base 701, and a cesium atom medium 704 is provided on the support frame. Here, the cesium atom medium 704 is a square cesium atom vapor cell with a side length of 1 mm (that is, composed of cesium atom vapor enclosed in a square glass container with a side length of 1 mm). An antireflection film covering the resonance wavelength (895 nm) of the cesium atom D1 line is plated on the end face of the glass container. A Cartesian coordinate system is established with the center of the cesium atom medium 704 as the origin;

[0051] In the x-axis direction, there are successively an optical fiber collimator A705, a polarizer A706, and a light collector A707. The optical fiber collimator A705 is connected to the pump light 3. The optical fiber collimator A705 collimates the pump light 3 into a parallel light beam propagating along the x-axis direction. The polarizer A706 is used to prepare the pump light 3 into linearly polarized light along the y-axis direction. The pump light 3 enters the cesium atom medium 704 and acts on the cesium atoms 6S 1 / 2 (F = 4, mF = 0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = 0, ±1, ±2, ±3) hyperfine level transition (π transition), preparing the cesium atoms into the ground state 6S 1 / 2 (F = 4, mF = ±4) Zeeman sub-level, and the light collector A707 is used to block the pump light 3 transmitted from the cesium atom medium 704;

[0052] In the z-axis direction, there are successively an optical fiber collimator B708, a polarizer B709, a lens A710, a lens B711, a microscope objective 712, and a light collector B713. The optical fiber collimator B708 is connected to the coupled light 4. The optical fiber collimator B708 collimates the coupled light 4 into a parallel light beam propagating along the z-axis direction. The polarizer B709 is used to prepare the coupled light 4 into a parallel light beam propagating along the y-axis direction. The parallel coupled light 4 enters the high numerical aperture microscope objective 712 fixed on the RMS threaded cage plate after being expanded by the lens A710 and the lens B711. The coupled light 4 forms a strongly focused coupled light carrying a longitudinal field component through the microscope objective 712. After the coupled light 4 acts on the cesium atom medium 704, it enters the light collector B713 fixed on the base 701 (that is, the light collector B713 is used to block the coupled light 4 transmitted from the cesium atom medium 704). The strongly focused coupled light can be expressed as follows:

[0053] E = E T +E L

[0054] In the formula, E T is the transverse field component along the y-axis direction, and E L is the longitudinal field component along the z-axis direction. The transverse field component E T of the coupled light 4 acts on the 6S of the cesium atoms 1 / 2 (F = 4, mF = 0, ±1, ±2, ±3) → 6P 1 / 2 (F = 3, mF = 0, ±1, ±2, ±3) hyperfine level transition (π transition), and the longitudinal field component E L acts on the 6S of the cesium atoms 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition (σ transition). Since the cesium atoms are prepared to 6S by the pump light 3 1 / 2At the energy level (F = 4, mF = ±4), the cesium atom medium 704 only responds strongly to the longitudinal field component E of the coupling light 4 L and hardly responds to the transverse field component E of the coupling light 4 T .

[0055] In the y-axis direction, there are successively an optical fiber collimator C714, a polarizer C715, and a camera 716. The optical fiber collimator C714 is connected to the probe light 5. The optical fiber collimator C714 collimates the probe light 5 into a parallel light beam propagating along the y-axis direction. The polarizer C715 is used to prepare the probe light 5 into linearly polarized light along the z-axis direction. After the probe light 5 passes through the cesium atom medium 704, it enters the camera 716. The camera 716 is used to measure the light intensity distribution of the transmitted probe light 5 (as Figure 7 shown). The probe light 5 acts on the cesium atom 6S 1 / 2 (F = 4, mF = ±4) → 6P 1 / 2 (F = 3, mF = ±3) hyperfine level transition (σ transition). Since the longitudinal field component E of the coupling light 4 L also acts on the same hyperfine level transition, it will further cause the absorption of the cesium atom medium 704 to the probe light 5 to have a saturation effect. The absorption coefficient of the cesium atom medium 704 to the probe light 5 is:

[0056]

[0057] In the formula, α is the absorption system, is the Planck constant, d is the dipole matrix element, Γ is the spontaneous emission rate, N is the atomic number density, λ is the probe light wavelength, ε0 is the vacuum permittivity, and x, y, and z are spatial coordinates;

[0058] After being absorbed by the cesium atom medium 704, the probe light 5 evolves into:

[0059]

[0060] In the formula, E p (x, y = 0, z) is the optical field distribution of the probe light before entering the cesium atom medium 704, L is the side length of the cesium atom medium, and i is the imaginary unit.

[0061] After passing through free space diffraction, the transmitted probe light 5 reaches the camera 716. The probe light field distribution at the camera 716 is:

[0062]

[0063] In the formula, represents the Fourier transform.

[0064] What the camera 716 measures is the light intensity distribution of the probe light 5:

[0065] I p (x,y→∞,z) ∝ |E p (,y→∞,z)| 2

[0066] The longitudinal field component E of the coupled light 4 L spatially modulates the absorption coefficient of the cesium atomic medium 704 for the probe light 5, and further spatially modulates the light intensity distribution of the probe light 5 after passing through the cesium atomic medium 704. Therefore, the longitudinal field component E of the coupled light 4 can be detected in real time by measuring the light intensity distribution of the transmitted probe light 5 with the camera 716 in real time L .

[0067] The support frame includes four columns 702 spaced apart on the base 701. A cage 703 is provided on the columns 702, and the cesium atomic medium 704 is provided on the cage 702

[0068] On the two columns 702 on the right side, there are brackets A717. A fiber collimator A705 and a polarizer A706 are provided on the brackets A717. On the two columns 702 on the left side, there are brackets B718. A light collector A707 is provided on the brackets B718. On the two columns 702 on the front side, there are brackets C719. A fiber collimator C714 and a polarizer C715 are provided on the brackets C719. On the two columns 702 on the rear side, there are brackets D720. A camera 716 is provided on the brackets D720. Four columns 702 are successively provided with mounting seats A721, mounting seats B722, mounting seats C723, mounting seats D724 and mounting seats E725 from top to bottom. A fiber collimator B708 and a polarizer B709 are provided on the mounting seat A721. A lens A710 is provided on the mounting seat B722. A lens D711 is provided on the mounting seat C723. A microscope objective 712 (a high numerical aperture microscope objective) is provided on the mounting seat D724 (which can use an RMS threaded cage plate). A light collector B713 is provided on the mounting seat E725

[0069] The fiber collimator A705 is connected to the fiber coupler 2 through the fiber A9. The fiber collimator B708 is connected to the fiber coupler 2 through the fiber B10. The fiber collimator C714 is connected to the fiber coupler 2 through the fiber C11

[0070] The frequency-locked light 6 is connected to the laser frequency locking system 8 through an optical fiber. The laser frequency locking system 8 includes an optical fiber collimator 801. The optical fiber collimator 801 accesses the frequency-locked light 6. The frequency-locked light 6 is collimated into a spatial light beam by the optical fiber collimator 801, and then is divided into two beams, a reflected light A804 and a transmitted light A805, by a half-wave plate A802 and a polarization beam splitter prism A803. The intensity ratio of the reflected light A804 and the transmitted light A805 is adjusted by rotating the half-wave plate A802, so that the intensity of the reflected light A804 is much greater than that of the transmitted light A805. The reflected light A804 enters the cesium atomic vapor cell A807 after being reflected by a beam splitter 806. The transmitted light A805 enters the cesium atomic vapor cell A807 after passing through a quarter-wave plate 808, a mirror A809 and a mirror B810. The light emitted from the cesium atomic vapor cell A807 enters a polarization beam splitter prism B812 through the beam splitter 806 and a half-wave plate B811 and is divided into two beams, a reflected light B813 and a transmitted light B814. The reflected light B813 is connected to a subtractor 817 through a photodetector A815, and the transmitted light B814 is connected to the subtractor 817 through a photodetector B816. The electrical signals output by the photodetector A815 and the photodetector B816 are subtracted by the subtractor 817 to obtain a polarization spectrum signal. The PID lock 818 receives the polarization spectrum signal as a feedback signal and outputs a control signal to achieve frequency locking of the laser 1.

[0071] The above specific embodiments cannot be used to limit the protection scope of the present invention. For those skilled in the art of this technology, any alternative improvement or transformation made to the embodiments of the present invention falls within the protection scope of the present invention.

[0072] Those parts not detailed in the present invention are all well-known technologies to those skilled in the art of this technology.

Claims

1. A method for real-time detection of longitudinal field components of a light field, characterized in that: The following steps are involved: S1. Obtain three laser beams: pump light, coupling light and detection light. The coupling light is the light field to be measured. The frequencies of the three laser beams are all locked to the 6S line of the cesium atom D1 line. 1 / 2 (F=4)→6P 1 / 2 (F=3) The resonant frequency of the hyperfine level transition; S2. Design the propagation directions of the pump light, coupling light and detection light to be perpendicular to each other and intersect on the cesium atomic medium; S3, performing linear polarization processing on the pump light, the coupling light and the detection light respectively, wherein the polarization direction of the pump light is the same as the polarization direction of the transverse field component of the coupling light, and the polarization direction of the detection light is the same as the polarization direction of the longitudinal field component of the coupling light; S4, pump light enters the cesium atom medium and acts on the cesium atom 6S 1 / 2 (F=4, mF=±0, ±1, ±2, ±3)→6P 1 / 2 (F=3,mF=±0,±1,±2,±3) hyperfine energy level transition, preparing cesium atoms to the ground state 6S 1 / 2 (F = 4, mF = ± 4) Zeeman sub-level; the coupled light enters the cesium atom medium, and the transverse field component of the coupled light acts on the cesium atom 6S 1 / 2 (F=4, mF=±0, ±1, ±2, ±3)→6P 1 / 2 (F=3,mF=±0,±1,±2,±3) hyperfine level transition, longitudinal field component acts on cesium atom 6S 1 / 2 (F=4,mF=±4)→6P 1 / 2 (F=3,mF=±3) hyperfine energy level transition; the detection light enters the cesium atom medium and acts on the cesium atom 6S 1 / 2 (F=4,mF=±4)→6P 1 / 2 (F=3,mF=±3) hyperfine level transition; S5. Real-time detection of the longitudinal field component of the coupled light is achieved by real-time measurement of the light intensity distribution of the transmitted detection light.

2. The method for real-time detection of longitudinal field components of a light field according to claim 1, characterized in that: The light intensity of the pump light and the coupling light is greater than the saturation light intensity of the cesium atomic medium, and the light intensity of the detection light is less than the saturation light intensity of the cesium atomic medium; the light spot of the pump light at the cesium atomic medium covers the cesium atomic medium.

3. The method for real-time detection of longitudinal field components of a light field according to claim 2, characterized in that: The cesium atom medium is composed of cesium atom vapor enclosed in a square glass container, and an anti-reflection film covering the resonance wavelength of the cesium atom D1 line is plated on the end surface of the glass container.

4. The method for real-time detection of longitudinal field components of a light field according to claim 3, characterized in that: In step S1, a laser with a wavelength of 895 nm is emitted by a laser, which is divided into four laser beams through a fiber coupler, three of which are used as pump light, coupling light and detection light respectively, and the other laser beam is used as frequency locking light for frequency locking of the laser.

5. The method for real-time detection of longitudinal field components of a light field according to claim 4, characterized in that: In step S3, after the coupled light is processed by linear polarization, it is expanded and focused to form a strongly focused coupled light carrying a longitudinal field component.

6. The method for real-time detection of longitudinal field components of a light field according to claim 5, characterized in that: In step S5, since the longitudinal field component of the coupled light and the detection light act on the same hyperfine transition, the absorption of the detection light by the cesium atomic medium will be saturated. The absorptivity of the cesium atomic medium is modulated spatially through the saturated absorption effect, thereby mapping the longitudinal field component information to the spatial distribution of the absorptivity of the cesium atomic medium. The detection light is used to measure the spatial distribution of the absorptivity of the cesium atomic medium, thereby realizing real-time detection of the longitudinal field component of the coupled light.

7. A device for real-time detection of longitudinal field components of a light field, characterized in that: The invention comprises a laser, wherein the laser is connected to an optical fiber coupler, wherein the optical fiber coupler divides the laser into four laser beams, namely, a pump light, a coupling light, a detection light and a frequency-locking light, wherein the pump light, the coupling light and the detection light are respectively connected to a light field longitudinal field component detection system through optical fibers, and the frequency-locking light is used for locking the laser frequency; The optical field longitudinal field component detection system comprises a base, a support frame is arranged on the base, a cesium atomic medium is arranged on the support frame, and a Cartesian coordinate system is established with the center of the cesium atomic medium as the origin; In the x-axis direction, a fiber collimator A, a polarizer A and a light collector A are arranged in sequence, and the fiber collimator A is connected to the pump light; In the z-axis direction, a fiber collimator B, a polarizer B, a lens A, a lens B, a microscope objective lens and a light collector B are arranged in sequence, and the fiber collimator B is connected to the coupled light; In the y-axis direction, a fiber collimator C, a polarizer C and a camera are arranged in sequence, and the fiber collimator C is connected to the detection light.

8. The device for real-time detection of longitudinal field components of a light field according to claim 7, characterized in that: The support frame comprises four columns which are arranged at intervals on a base, a retaining frame is arranged on the columns, and the cesium atomic medium is arranged on the retaining frame.

9. The device for real-time detection of longitudinal field components of a light field according to claim 8, characterized in that: The two upright posts on the right side are provided with a bracket A, on which a fiber collimator A and a polarizer A are provided; the two upright posts on the left side are provided with a bracket B, on which a light collector A is provided; the two upright posts on the front side are provided with a bracket C, on which a fiber collimator C and a polarizer C are provided; the two upright posts on the rear side are provided with a bracket D, on which a camera is provided; the four upright posts are sequentially designed with mounting seats A, mounting seats B, mounting seats C, mounting seats D and mounting seats E from top to bottom, on which a fiber collimator B and a polarizer B are provided, on which a lens A is provided, on which a lens D is provided, on which a microscope objective lens is provided, and on which a light collector B is provided; the fiber collimator A is connected to a fiber coupler via an optical fiber A, the fiber collimator B is connected to a fiber coupler via an optical fiber B, and the fiber collimator C is connected to a fiber coupler via an optical fiber C.

10. The device for real-time detection of longitudinal field components of a light field according to claim 9, characterized in that: The frequency-locking light is connected to a laser frequency locking system through an optical fiber. The laser frequency locking system comprises an optical fiber collimator. The optical fiber collimator is connected to the frequency-locking light. The frequency-locking light is collimated into a spatial light beam through the optical fiber collimator, and then divided into two beams of reflected light A and transmitted light A through a half-wave plate A and a polarization beam splitter prism A; the reflected light A enters a cesium atom vapor chamber A after being reflected by a beam splitter; the transmitted light A enters a cesium atom vapor chamber A after passing through a quarter-wave plate, a reflector A and a reflector B; the light emitted from the cesium atom vapor chamber A enters a polarization beam splitter prism B after passing through a beam splitter and a half-wave plate B, and is divided into two beams of reflected light B and transmitted light B; the reflected light B is connected to a subtractor through a photodetector A, and the transmitted light B is connected to a subtractor through a photodetector B. The electrical signals output by the photodetector A and the photodetector B are subtracted by the subtractor to obtain a polarization spectrum signal, and the PID locker receives the polarization spectrum signal as a feedback signal, and outputs a control signal to achieve frequency locking of the laser.

Images