An apparatus and method for achieving high-contrast CPT resonance signals

Abstract

This invention discloses an apparatus and method for achieving a high-contrast CPT resonance signal. The apparatus includes a coherent light source generation module, a beam quality optimization module, a beam parameter optimization module, an atomic gas cell module, an optical detection and acquisition module, a laser frequency stabilization module, and a signal generator. The coherent light source generation module generates coherent two-color light with an energy distribution satisfying a Gaussian distribution. The beam quality optimization module converts the Gaussian beam into a flat-top beam. The beam parameter optimization module optimizes the parameters of the flat-top beam. The atomic gas cell module enables the beam to interact with atoms, obtaining an atomic superposition absorption spectrum. The optical detection and acquisition module detects the optical signal and converts it into an electrical signal. The laser frequency stabilization module locks the laser frequency to the lowest point of the atomic superposition absorption spectrum. The signal generator linearly scans the radio frequency signal, causing the frequency difference of the coherent two-color light to change linearly, outputting a high-contrast CPT resonance signal. This invention can effectively improve the contrast of the CPT resonance signal.

Description

Technical Field

[0001] This invention belongs to the field of coherent optics and atomic physics, and specifically relates to an apparatus and method for realizing a high-contrast CPT resonance signal. Background Technology

[0002] The interaction between a coherent light field and atoms couples previously unrelated energy levels, forming a coherent superposition state, thus producing the atomic coherence effect. Coherent Population Trapping (CPT) is one such atomic coherence effect. It utilizes the Λ-type three-level structure formed by the hyperfine energy level of the atomic ground state and the excited state energy level. By interacting with atoms using coherent two-color light, when the frequency difference of the coherent two-color light equals the hyperfine energy level spacing of the atomic ground state, the atoms are prepared into a coherent superposition state, resulting in a phenomenon where they neither absorb laser light nor emit fluorescence. The CPT effect can be used to realize atomic clocks, magnetometers, and frequency stabilization systems, offering advantages in miniaturization and integration, and playing an important role in various fields such as navigation satellites and magnetic anomaly detection.

[0003] Traditional CPT resonance signals are prepared by the interaction of a beam of circularly polarized coherent two-color light with atoms. This method has the advantages of simple optical path structure and can be miniaturized and integrated, but it suffers from the problem of a low contrast ratio (the ratio of the amplitude of the CPT resonance signal to the background amplitude). Summary of the Invention

[0004] The purpose of this invention is to provide an apparatus and method for achieving high-contrast CPT resonance signals, which can effectively improve the contrast of CPT resonance signals.

[0005] To achieve the above objectives, one aspect of the present invention provides an apparatus for realizing a high-contrast CPT resonance signal, comprising a coherent light source generation module, a beam quality optimization module, a beam parameter optimization module, an atomic gas cell module, an optical detection acquisition module, a laser frequency stabilization module, and a signal generator;

[0006] The coherent light source generation module is used to generate coherent two-color light with an energy distribution that satisfies a Gaussian distribution. The coherent light source generation module includes a current source, a microwave source, a biaser, and a laser. The current signal output by the current source and the radio frequency signal output by the microwave source are coupled through the biaser and injected into the laser, so that the output laser of the laser is modulated. The light field energy distribution of the output laser satisfies the Bessel function and generates multiple sidebands, of which the ±1st order sidebands serve as coherent two-color light and the output laser serves as the carrier of coherent two-color light.

[0007] The beam quality optimization module is used to convert the Gaussian beam into a flat-top beam. The beam quality optimization module includes a first plano-convex lens, a second plano-convex lens, and a third plano-convex lens. The coherent dichromatic light passes through the first plano-convex lens, the second plano-convex lens, and the third plano-convex lens in sequence. The first plano-convex lens is used to collimate the coherent dichromatic light and reduce the divergence angle of the coherent dichromatic light. The second plano-convex lens and the third plano-convex lens work together to make the light intensity transmitted through the third plano-convex lens conform to a circular flat-top distribution.

[0008] The beam parameter optimization module is used to control the polarization, power and spot size of the flat-top beam to obtain circularly polarized coherent two-color light with uniform energy distribution; the atomic gas cell module includes an atomic gas cell, which is used to make the circularly polarized coherent two-color light entering the atomic gas cell interact with the atoms in the atomic gas cell, thereby generating atomic transitions and CPT effects, and obtaining atomic superposition absorption spectra and CPT resonance signals respectively.

[0009] The optical detection and acquisition module is used to focus the light beam passing through the atomic gas cell, detect the optical signal and convert it into an electrical signal; the laser frequency stabilization module is used to lock the carrier frequency of the coherent two-color light to the lowest point of the atomic superposition absorption spectrum; the signal generator is used to linearly scan the frequency of the radio frequency signal, so that the frequency difference of the coherent two-color light changes linearly, thereby outputting a high-contrast CPT resonance signal through the optical detection and acquisition module.

[0010] Another aspect of the present invention provides a method for realizing a high-contrast CPT resonance signal, wherein the high-contrast CPT resonance signal is realized using the above-described apparatus, the method comprising:

[0011] Using a coherent light source generation module, coherent two-color light is obtained, the energy distribution of which conforms to a Gaussian distribution;

[0012] By using a beam quality optimization module, the beam energy distribution of coherent two-color light is optimized, thereby converting a Gaussian beam into a flat-top beam.

[0013] The beam parameter optimization module is used to adjust the polarization, power, and spot size of the flat-top beam to achieve beam parameter optimization.

[0014] The optimized beam enters the atomic gas chamber module and interacts with atoms to produce an atomic superposition absorption spectrum.

[0015] Based on the obtained atomic superposition absorption spectrum, a coherent dual-color optical carrier frequency lock is achieved using a laser frequency stabilization module;

[0016] By using a signal generator to linearly scan the frequency of the radio frequency signal, the frequency difference of the coherent two-color light changes linearly, thus realizing the preparation of a high-contrast CPT resonant signal.

[0017] According to the apparatus and method for realizing a high-contrast CPT resonance signal according to the above aspects of the present invention, the laser entering the atomic gas cell is converted from a Gaussian beam to a flat-top beam, thereby improving the uniformity of laser intensity distribution and increasing the number density of atoms interacting with the light, thereby improving the contrast of the CPT resonance signal. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort:

[0019] Figure 1 This is a schematic diagram of the structure of a device for realizing a high-contrast CPT resonance signal according to an embodiment of the present invention;

[0020] Figure 2 This is a comparison chart of beam quality test results between a traditional Gaussian beam and the flat-top beam of this invention embodiment;

[0021] Figure 3 This is a comparison chart of test results for CPT resonance signals achieved using a traditional CPT resonance signal device and the device described in this embodiment of the invention;

[0022] Figure 4 This is a flowchart of a method for realizing a high-contrast CPT resonance signal according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] One embodiment of the present invention provides an apparatus for realizing a high-contrast CPT resonance signal. The atoms used to generate the CPT effect can be rubidium, cesium, etc.; in this embodiment, [the atom is used]. 87Taking the D1 line level structure of Rb atoms as an example, this invention will be described in detail. First, the principle of the CPT effect will be explained. A Λ-type three-level structure consists of two ground-state energy levels and one excited-state energy level. When coherent two-color light interacts with Λ-type three-level atoms, the two coherent light fields excite the ground-state atoms to the same excited state. When the frequency difference of the coherent two-color light is equal to the interval between the ground-state energy levels of the Λ-type three-level atoms, approximately 6.834 GHz, some ground-state atoms are pumped to a coherent superposition state of the two ground-state energy levels, resulting in a phenomenon where neither light is absorbed nor fluorescence is emitted. This manifests as enhanced transmitted light in the transmission spectrum of the emitted light from the atomic gas cell, known as the CPT effect.

[0025] Based on the above CPT effect principle, such as Figure 1 As shown, the apparatus for realizing a high-contrast CPT resonance signal in this embodiment of the invention includes a coherent light source generation module, a beam quality optimization module, a beam parameter optimization module, an atomic gas cell module 12, an optical detection and acquisition module, a laser frequency stabilization module 15, and a signal generator 16. The coherent light source generation module includes a current source 1, a microwave source 2, a bias device 3, and a laser 4. The beam quality optimization module includes a first plano-convex lens 5, a second plano-convex lens 6, and a third plano-convex lens 7. The beam parameter optimization module includes a half-wave plate 8, a polarizer 9, a quarter-wave plate 10, and a precision pinhole 11. The optical detection and acquisition module includes a fourth plano-convex lens 13 and a photodetector 14. The first plano-convex lens 5, the second plano-convex lens 6, the third plano-convex lens 7, and the fourth plano-convex lens 13 are all aspherical lenses.

[0026] The coherent light source generation module is used to generate coherent two-color light with an energy distribution that follows a Gaussian distribution. The current source 1 of the coherent light source generation module outputs a current signal of approximately 100 mA, and the microwave source 2 outputs a radio frequency signal of approximately 3.417 GHz. These signals are coupled into a 795 nm VCSEL laser 4 via a bias converter 3. The energy distribution of the output laser field follows a Bessel function, generating multiple sidebands (coherent multicolor light). The ±1st order sidebands constitute the coherent two-color light, used for CPT preparation. The output laser serves as the carrier wave for the coherent two-color light.

[0027]

[0028] in, i 0 indicates the current source output signal. ω 0 indicates the output laser carrier frequency. ω m The modulation frequency, i.e., the output signal frequency of the RF source, is approximately 3.417 GHz, and m represents the modulation coefficient. The modulated laser contains a carrier wave and sidebands. Due to the high energy of the ±1st order sidebands, they are used as coherent two-color light to prepare the CPT resonance signal, with a frequency difference of 2. ω mIt is approximately 6.834 GHz, and the output laser energy follows a Gaussian distribution.

[0029] The beam quality optimization module optimizes the beam energy distribution of coherent bicolor light, converting the Gaussian beam into a flat-top beam. The laser output from laser 4 passes sequentially through the first plano-convex lens 5, the second plano-convex lens 6, and the third plano-convex lens 7 of the beam parameter optimization module. The first plano-convex lens 5 collimates the coherent bicolor light field, reducing the laser divergence angle and making the light incident on the second plano-convex lens 6 approximately parallel. The second plano-convex lens 6 and the third plano-convex lens 7 combine to convert the Gaussian beam into a flat-top beam. The second plano-convex lens 6 distributes the beam intensity within the aperture, achieving a uniform beam intensity distribution at specific locations, while the third plano-convex lens 7 collimates the exit direction of each ray, making the exit light approximately parallel.

[0030] In one embodiment, coherent dichromatic light passes through a first plano-convex lens 5 with a focal length of 15 mm. Using a shearing interferometer, the position of the first plano-convex lens 5 is adjusted to narrow the divergence angle of the coherent dichromatic light, converting it into parallel light. Further, the coherent dichromatic light is sequentially incident on a second plano-convex lens 6 with a focal length of 15 mm and a third plano-convex lens 7 with a focal length of 30 mm. Using a beam quality analyzer and a shearing interferometer, the positions of the second plano-convex lens 6 and the third plano-convex lens 7 are adjusted so that the light intensity distribution transmitted through the third plano-convex lens 7 is approximately a circular flat-top, such as... Figure 2 The image on the right shows parallel light. For comparison, Figure 2 The left image shows the Gaussian beam of a traditional CPT resonant signal device.

[0031] The beam parameter optimization module is used to control the polarization, power, and spot size of the flat-top beam. The optimized beam sequentially passes through a half-wave plate 8, a polarizer 9, a quarter-wave plate 10, and a precision pinhole 11 within the beam parameter optimization module. The half-wave plate 8 and polarizer 9 are combined to achieve optical power control; polarizer 9 has a high extinction ratio. The half-wave plate 8, in conjunction with polarizer 9, enables optical power control. The quarter-wave plate 10 converts linearly polarized light into circularly polarized light. The precision pinhole 11 controls the spot size and filters out stray light.

[0032] In one embodiment, coherent bicolor light with a flat-top distribution of intensity passes sequentially through a half-wave plate 8, a polarizer 9 with an extinction ratio greater than 1000:1, a quarter-wave plate 10, and a precision pinhole 11 with a diameter of 3 mm. Using an optical power meter, the angle of the half-wave plate 8 is adjusted so that the power of the beam passing through the precision pinhole 11 is approximately 35 μW. Using a polarization analyzer, the degree of polarization of the output light is measured, and the angle of the quarter-wave plate 10 is adjusted to produce circularly polarized light with a polarization degree close to 100%.

[0033] The laser beam, after parameter optimization, enters the atomic gas chamber module 12 to achieve interaction between the beam and atoms, generating atomic transitions and coherent population trapping effects. The atomic gas chamber module includes an atomic gas chamber filled with alkali metal atoms and a buffer gas, a heating device, and a magnetic shielding container. The alkali metal atoms include, but are not limited to, rubidium and cesium; the buffer gas includes, but is not limited to, helium, argon, and neon, and may contain one or more of these; the heating device can be a heating film or heating wire, covering the outer surface of the atomic gas chamber; the entire atomic gas chamber and heating device are placed inside the magnetic shielding container to achieve the purpose of shielding against external stray magnetic fields.

[0034] In one embodiment, the gas chamber parameters in the atomic gas chamber module are: a diameter of 25 mm, a length of 25 mm, and filled with... 87 Rb atoms and Ne and Ar gases. The atomic gas chamber is heated to 60°C using a non-magnetic heating film. The entire atomic gas chamber module is placed inside a magnetically shielded barrel made of 5 layers of permalloy.

[0035] The optical detection and acquisition module includes a fourth plano-convex lens 13 and a photodetector 14. The fourth plano-convex lens 13 is used to focus the light beam passing through the atomic gas cell, and the photodetector 14 is used to detect the optical signal and convert it into an electrical signal. The laser frequency stabilization module 15 is used to lock the coherent two-color optical carrier frequency to the lowest point of the atomic superposition absorption spectrum (atomic transition frequency). The laser frequency stabilization module 15 includes a lock-in amplifier and a servo controller. The lock-in amplifier is used to perform phase-sensitive detection to obtain an error signal, and the servo controller is used to generate a locking signal, which is fed back to the laser to control the laser frequency.

[0036] In one embodiment, the light beam passing through the atomic gas cell is focused by a fourth plano-convex lens 13 with a focal length of 15 mm and incident on a photodetector 14 to obtain an atomic superposition absorption spectrum. The coherent two-color light carrier frequency is locked to the atomic energy level transition by the laser frequency stabilization module 15.

[0037] Signal generator 16 is used to linearly scan the frequency of the radio frequency signal output from microwave source 2, causing a linear change in the frequency difference of the coherent two-color light, and outputting a high-contrast CPT resonance signal. In one embodiment, signal generator 16 generates a sawtooth wave signal with a frequency of 10 Hz, linearly scans the frequency of the radio frequency signal output from microwave source 2, and the scan width is 6 kHz, causing a linear change in the frequency difference of the coherent two-color light. A high-contrast CPT resonance signal can be observed from the output signal of the photodetector, such as... Figure 3 As shown in the right image, the contrast is 5.67%.

[0038] In comparison, a comparative experiment was conducted using the same parameters as in this embodiment, and the CPT resonance signal obtained using a traditional CPT resonance signal device was used, such as... Figure 3 The left image shows a contrast of 1.63%.

[0039] Embodiments of the present invention also provide a method for achieving a high-contrast CPT resonance signal, such as... Figure 4 As shown, it includes the following steps:

[0040] Step 1: Using a coherent light source generation module, coherent two-color light is obtained with a frequency difference of approximately 6.834 GHz and an energy distribution that conforms to a Gaussian distribution.

[0041] Step 2: Using the beam quality optimization module, the beam energy distribution of the coherent dichromatic light is optimized to transform the Gaussian beam into a flat-top beam. Specifically, the coherent dichromatic light with Gaussian energy distribution passes through a first plano-convex lens, narrowing its divergence angle and converting it into parallel light, which is then incident on a second plano-convex lens. After passing through the second plano-convex lens, a uniform beam intensity distribution is achieved at a specific location, and the light is then incident on a third plano-convex lens. The third plano-convex lens collimates the incident light, converting the outgoing light into parallel light.

[0042] Step 3: Using the beam parameter optimization module, the polarization, power, and spot size of the flat-top beam are adjusted to optimize the beam parameters, achieving a circular flat-top beam output with an optical power of approximately 35 μW and a polarization degree close to 100%. Specifically, coherent bicolor light with energy conforming to the flat-top distribution passes sequentially through a half-wave plate, a polarizer, a quarter-wave plate, and a precision pinhole. By adjusting the half-wave plate, the power of the output light from the polarizer can be controlled; by adjusting the quarter-wave plate, the output light can be converted from linearly polarized light to circularly polarized light. By combining the half-wave plate, polarizer, and quarter-wave plate, independent control of the power and polarization state of the coherent bicolor light can be achieved. Passing the coherent bicolor light through the precision pinhole allows for control of the spot size of the output light and filters out stray light at the edge of the spot, obtaining circularly polarized coherent bicolor light with uniform energy distribution.

[0043] Step 4: The optimized light beam enters the atomic gas chamber module. The coherent two-color light enters the atomic gas chamber module and interacts with the atoms inside. The outgoing light is focused by the fourth plano-convex lens and incident on the photodetector, obtaining the atomic superposition absorption spectrum. The energy density distribution of the light beam entering the atomic gas chamber module is uniform, and the intensity distribution of its beam spot cross-section is approximately a circular flat-top distribution.

[0044] Step 5: Based on the obtained atomic superposition absorption spectrum, the error signal is extracted using the lock-in amplifier in the laser frequency stabilization module, and the laser frequency is locked using the servo controller, thereby locking the coherent two-color light carrier frequency to the atomic energy level transition.

[0045] Step Six: After achieving laser frequency locking, the frequency of the radio frequency signal output from the microwave source is linearly scanned by adjusting the signal generator, causing the frequency difference of the coherent two-color light to change linearly, thus outputting a high-contrast CPT resonant signal. In one embodiment, a sawtooth wave signal with a frequency of 10 Hz is generated by the signal generator to sweep the radio frequency signal output from the microwave source, with a sweep width of approximately 6 kHz, thereby preparing a high-contrast CPT resonant signal and obtaining a CPT resonant signal with a contrast ratio of 5.67%.

[0046] In summary, the apparatus and method for realizing high-contrast CPT resonance signals in this embodiment of the invention utilizes a coherent light source generation module to obtain coherent two-color light with energy conforming to a Gaussian distribution. Then, a beam quality optimization module is used to convert the Gaussian beam into a flat-top beam, and a beam parameter optimization module is used to control parameters such as polarization, power, and spot size. The optimized coherent two-color light enters an atomic gas cell module, interacts with atoms to generate a superimposed absorption spectrum, and a frequency stabilization module is used to lock the laser frequency. Based on this, a signal generator is used to sweep the microwave signal to realize the preparation of a high-contrast CPT resonance signal.

[0047] The apparatus and method for realizing high-contrast CPT resonance signals according to embodiments of the present invention have the following beneficial effects:

[0048] 1. This invention uses a beam quality optimization module to convert Gaussian-distributed coherent two-color light into a flat-top beam, further increasing the atomic number density that interacts with light, thereby improving the contrast of the CPT resonance signal.

[0049] 2. The beam parameter optimization module of the present invention achieves independent control of optical power and polarization state by combining 1 / 2 waveplate, polarizer and 1 / 4 waveplate. Through precision pinhole, it realizes the adjustment of beam spot size and the filtering of stray light at the edge. It has the advantages of simplifying the beam parameter adjustment process and improving the ease of system debugging.

[0050] 3. This invention has the advantages of a simple optical path system, miniaturization, and integration. It can be applied to CPT atomic clocks, CPT magnetometers, frequency stabilization systems, etc., effectively improving frequency stability and magnetic field measurement sensitivity.

[0051] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An apparatus for achieving high contrast CPT resonance signals, characterized by, The coherent light source generating module, the light beam quality optimizing module, the light beam parameter optimizing module, the atomic gas chamber module, the light detection and collection module, the laser frequency stabilizing module and the signal generator are included. The coherent light source generating module is used for generating coherent double-color light with energy distribution satisfying Gaussian distribution, and includes a current source, a microwave source, a biasing device and a laser. The light beam quality optimizing module is used for converting a Gaussian light beam into a flat-top light beam, and includes a first plano-convex lens, a second plano-convex lens and a third plano-convex lens. The light beam parameter optimizing module is used for regulating the polarization, power and spot size of the flat-top light beam to obtain circularly polarized coherent double-color light with uniform energy distribution. The light detection and collection module is used for focusing the light beam passing through the atomic gas chamber, detecting the light signal and converting it into an electric signal.

2. The apparatus of claim 1, wherein, The laser frequency stabilizing module is used for locking the carrier frequency of the coherent double-color light to the lowest point of the atomic superposition absorption spectrum.

3. The apparatus of claim 1 or 2, wherein, The signal generator is used for linearly scanning the frequency of the radio frequency signal, so that the frequency difference of the coherent double-color light linearly changes, thereby outputting a high-contrast CPT resonance signal through the light detection and collection module.

4. The apparatus of claim 1 or 2, wherein, The second plano-convex lens is used for distributing the light beam intensity within the aperture to achieve uniform distribution of the light beam intensity at specific positions.

5. The apparatus of claim 4, wherein: The light beam parameter optimizing module includes a 1 / 2 wave plate, a polarizer, a 1 / 4 wave plate and a precision pinhole. The light detection and collection module includes a fourth plano-convex lens and a photodetector. The first plano-convex lens, the second plano-convex lens, the third plano-convex lens and the fourth plano-convex lens are all aspherical lenses.

6. The apparatus of claim 1 or 2, wherein, The atomic cell module further comprises a heating device and a magnetic shielding barrel, the atomic cell is filled with alkali metal atoms and buffer gas, the heating device covers the outer surface of the atomic cell, and the whole atomic cell and the heating device are placed in the magnetic shielding barrel.

7. The apparatus of claim 6, wherein, The alkali metal atoms are rubidium or cesium, the buffer gas comprises one or more of helium, argon and neon, the heating device is a heating film or a heating wire, and the magnetic shielding barrel is made of five layers of permalloy.

8. A method of achieving high contrast CPT resonance signals, characterized by, The device of any one of claims 1-7 is used to realize high-contrast CPT resonance signals, and the method comprises: A coherent light source generation module is used to obtain coherent bichromatic light with a Gaussian energy distribution; An optical beam quality optimization module is used to optimize the optical beam energy distribution of the coherent bichromatic light, so as to convert the Gaussian light beam into a flat-top light beam; An optical beam parameter optimization module is used to regulate the polarization, power and spot size of the flat-top light beam, so as to realize optical beam parameter optimization; The optimized optical beam enters the atomic cell module and interacts with atoms to generate atomic superposition absorption spectrum; According to the obtained atomic superposition absorption spectrum, a laser frequency stabilization module is used to realize coherent bichromatic light carrier frequency locking; A signal generator is used to linearly scan the frequency of the radio frequency signal, so that the frequency difference of the coherent bichromatic light linearly changes, and high-contrast CPT resonance signal preparation is realized.

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