Array-type in-situ detection system and method for multi-parameter measurement of alkali metal gas chamber

Abstract

The present invention relates to an array type in-situ detection system and method for multi-parameter measurement of alkali metal gas chamber, comprising: a laser, a beam expansion optical path, a diffuser laser homogenization optical path, a double microlens array homogenization optical path, a polarizer, a measured alkali metal gas chamber, an attenuation plate and a CCD imaging system connected in sequence; the laser output light beam is first expanded by the beam expansion optical path, then the light beam is preliminarily homogenized by the diffuser laser homogenization optical path, and then the output light beam is made into a uniform beam array by the double microlens array homogenization optical path; the output light beam array is polarized by the polarizer to make it a linear polarization laser with a high polarization degree; then it is incident on the measured alkali metal gas chamber, and the output light beam is attenuated by the attenuation plate with a preset attenuation rate to prevent the saturation of the rear end CCD imaging system, and the array light beam enters the rear end CCD imaging system after attenuation. The present invention can realize synchronous in-situ testing of multiple parameters at different positions of the atomic gas chamber, and the test results are more accurate and reliable.

Description

Technical Field

[0001] The present invention belongs to the technical field of key parameter detection of alkali metal gas chambers, and relates to an array type in-situ detection system and method, and in particular to an array type in-situ detection system and method for multi-parameter measurement of alkali metal gas chambers. Background Art

[0002] Alkali metal gas cells are widely used in the fields of atomic magnetometers, atomic spin gyroscopes, atomic clocks, atomic frequency standards, and laser frequency locking. As core components, the measurement technology of some of its key parameters has also always attracted much attention.

[0003] The key parameters of the alkali metal gas cell include atomic density, temperature, temperature gradient, wall thickness and refractive index.

[0004] At present, the more common methods for atomic density detection are optical rotation detection and optical depth detection. The optical rotation method uses the Farady optical rotation effect of linearly polarized light. By applying a strong magnetic field to the alkali metal gas chamber, when the linearly polarized laser passes through the alkali metal gas chamber, different atomic number densities correspond to different rotation angles of the polarization direction of the linearly polarized light, thereby achieving the measurement of the atomic number density. The optical depth method uses the fact that when the linearly polarized laser passes through the alkali metal gas chamber, the atomic number density on the path is different, and the transmission intensity of the laser is also different. The atomic number density can be obtained by measuring the transmittance of the linearly polarized light after passing through the alkali metal gas chamber.

[0005] Since the optical depth detection does not require a strong magnetic field or parameter scanning, its principle is simple and easy to operate, so it is widely used. However, most detection schemes use a laser beam as the input, or use a moving atomic gas cell to let the light beam pass through different positions of the gas cell. The measurement results of these schemes can only reflect the local parameter information of the alkali metal gas cell, or will be affected by time-varying factors, resulting in inaccurate measurement results.

[0006] After searching, no public documents of the prior art identical or similar to the present invention were found. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and to propose an array-type in-situ detection system for multi-parameter measurement of alkali metal gas chambers, which can solve the technical problem of synchronous and in-situ measurement of multiple parameters such as the atomic number density at different positions of the atomic gas chamber.

[0008] The present invention solves the practical problem by adopting the following technical solutions:

[0009] An array type in-situ detection system for multi-parameter measurement of alkali metal gas chambers, comprising: a laser, a beam expansion optical path, a diffuser laser homogenization optical path, a double microlens array homogenization optical path, a polarizer, an alkali metal gas chamber to be measured, an attenuation plate and a CCD imaging system connected in sequence;

[0010] The laser output light beam is first expanded through a beam expansion optical path, then preliminarily homogenized through a diffuser laser homogenization optical path, and then homogenized through a double microlens array optical path, so that the output light beam is a uniform light beam array; the output light beam array is polarized through a polarizer to make it a linearly polarized laser with a high polarization degree; and then it is incident on the alkali metal gas chamber to be measured, and the output light beam is attenuated through an attenuation plate with a preset attenuation rate to prevent the saturation of the rear-end CCD imaging system, and the attenuated array light beam enters the rear-end CCD imaging system.

[0011] Moreover, during the measurement process, the wavelength of the laser is tuned so that the wavelength of the incident laser beam resonates with the alkali metal atomic spectral line in the alkali metal atomic gas cell to be measured.

[0012] Moreover, the beam expansion optical path is composed of two lenses with different focal lengths, and the focal points of the two lenses coincide with each other. The lens with a smaller focal length is the incident lens, and the lens with a larger focal length is the exit lens.

[0013] Moreover, the diffuser laser homogenization light path is composed of a diffuser and two focusing lenses with the same parameters. The focal points of the two focusing lenses coincide, and the diffuser is located at the focal position between the two lenses. After the laser beam is incident, it is focused on the first focusing lens, and the diffuser is on the focal plane of the focusing lens. After the light beam is homogenized by the diffuser, it is collimated and output through the rear-end focusing lens.

[0014] Moreover, the double microlens array uniform light path is composed of two microlens arrays with similar specifications and parameters; after the laser beam is expanded, collimated, and initially homogenized, it is parallelly incident on the double microlens array uniform light path, and the output beam is a uniform beam array.

[0015] Moreover, the attenuation ratio of the attenuation plate at the rear end of the alkali metal gas chamber should be selected according to the actual incident beam power and the temperature of the alkali metal gas chamber, and it is necessary to ensure that the rear end CCD acquisition system is not saturated. The greater the incident power, the greater the attenuation ratio of the attenuation plate. The higher the temperature of the alkali metal gas chamber, the higher the attenuation ratio of the attenuation plate.

[0016] Furthermore, the CCD imaging system adopts a full-frame large-array CCD, which is convenient for receiving the transmission information of the light beam in all directions.

[0017] Furthermore, the center of the photosensitive surface of the CCD imaging system and the center of the detected surface of the atomic gas cell should be aligned as much as possible, and the photosensitive surface and the detected surface of the alkali metal gas cell should be kept parallel.

[0018] An array-type in-situ detection method for multi-parameter measurement of an alkali metal gas chamber comprises the following steps:

[0019] Step 1: First test the corresponding relationship between the image grayscale and the light intensity received by the CCD imaging system;

[0020] Step 2: When there is no alkali metal atom gas chamber, by selecting an attenuation plate with an attenuation coefficient of α, the CCD imaging system is made unsaturated. According to the linear relationship between grayscale and incident light intensity, the intensity of each beam in the array beam can be obtained by the grayscale sum within the imaged spot area, which is the incident intensity:

[0021] I ki =k(∑p n ) ki / α

[0022] Step 3, placing the alkali metal gas chamber in the corresponding position, and adjusting the azimuth through the precision azimuth adjuster, so that the center of the measured surface of the atomic gas chamber is substantially coincident with the center of the CCD photosensitive surface, and the two surfaces are substantially parallel;

[0023] Step 4: Select a suitable attenuation coefficient β to make the CCD imaging grayscale moderate, and calculate the beam intensity as the emission intensity at each position in the same way as step 2:

[0024] I ji =k(Σp n ) ji / β

[0025] Step 5: Calculate the transmittance at each position:

[0026]

[0027] Step 6: Using the principle of optical depth method and the empirical formula of saturated vapor pressure, calculate the atomic number density and temperature at each position. The corresponding temperature gradient can be obtained based on the calculated temperature.

[0028] Moreover, the specific method of step 1 is: using a single laser beam with different light powers to respectively incident on the CCD imaging system, and recording the grayscale and within the beam spot area of ​​the CCD imaging system. The linear relationship coefficient between the grayscale and the incident light power is obtained by fitting, that is:

[0029] I=k∑p i .

[0030] Advantages and beneficial effects of the present invention:

[0031] 1. The present invention proposes an array-type in-situ detection system and method for multi-parameter measurement of alkali metal gas chambers. A light beam array is generated through a diffuser laser homogenization optical path and a double microlens array optical path, and is incident on the alkali metal gas chamber to interact with the alkali metal atoms. Then, an information acquisition system composed of an attenuation plate and a full-frame large-area array CCD is used to synchronously obtain the transmission information of each position of the alkali metal atom gas chamber. According to the principle of optical depth method, the atomic number density, temperature, temperature gradient and thermal equilibrium state information of each position are obtained using the transmission information. The structure of the present invention is simpler and can realize the synchronous measurement of parameters at multiple positions.

[0032] 2. The present invention uses a diffuser laser homogenization optical path to perform preliminary homogenization on the laser beam, which can greatly improve the light intensity uniformity of the laser beam and is beneficial to the generation of the rear-end beam array.

[0033] 3. The present invention uses a double microlens array to generate an array beam, which is simpler in structure than a conventional solution of using a splitter to generate an array beam.

[0034] 4. The present invention adopts a full-frame large-array CCD acquisition system, which has a large photosensitive area and can meet the measurement of alkali metal gas chambers of most sizes.

[0035] 5. The present invention uses a beam array to synchronously irradiate the alkali metal gas chamber to perform multi-position synchronous real-time measurement, thereby avoiding the influence of some time-varying factors on the parameter measurement results during the measurement process. For example, the randomness of atomic movement, the thermal equilibrium state of the gas chamber, and the instability of external heating cause the difference in parameters such as the atomic number density at the same position at different times.

[0036] 6. The present invention uses a beam array to interact with alkali metal atoms, and based on the light depth theory and saturated vapor pressure theory, can measure multiple parameters such as atomic number density, temperature, and temperature gradient at each position inside the alkali metal gas chamber, without the need for multiple measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is an overall schematic diagram of an array-type in-situ detection system for multi-parameter measurement of an alkali metal gas chamber according to the present invention;

[0038] Figure 2 is an overall schematic diagram of a system without an alkali metal atom gas cell;

[0039] Figure 3 Schematic diagram of the beam expansion optical path in the present invention;

[0040] Figure 4 This is a schematic diagram of the laser homogenization light path of the diffuser in the present invention;

[0041] Figure 5 Schematic diagram of the light path of the double microlens array in the present invention;

[0042] Figure 6 It is a schematic diagram of the cross section of an ideal 9-beam array and the position of the beam incident surface of the alkali metal atom gas chamber in the present invention;

[0043] Description of reference numerals:

[0044] 1-laser; 2-beam expansion optical path; 3-diffusion plate laser homogenization optical path; 4-double microlens array homogenization optical path; 5-polarizer; 6-tested alkali metal gas chamber; 7-attenuation plate; 8-CCD imaging system. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

[0046] An array type in-situ detection system for multi-parameter measurement of alkali metal gas chambers, such as Figures 1 to 5 As shown, it comprises: a laser (1), a beam expansion optical path (2), a diffuser laser homogenization optical path (3), a double microlens array homogenization optical path (4), a polarizer (5), an alkali metal gas chamber to be measured (6), an attenuation plate (7), and a CCD imaging system (8) connected in sequence;

[0047] The laser output light beam is first expanded through a beam expansion optical path, then preliminarily homogenized through a diffuser laser homogenization optical path, and then homogenized through a double microlens array optical path, so that the output light beam is a uniform light beam array; the output light beam array is polarized through a polarizer to make it a linearly polarized laser with a high polarization degree; and then it is incident on the alkali metal gas chamber to be measured, and the output light beam is attenuated through an attenuation plate with a preset attenuation rate to prevent the saturation of the rear-end CCD imaging system, and the attenuated array light beam enters the rear-end CCD imaging system.

[0048] In this embodiment, during the measurement process, the wavelength of the laser is tuned so that the wavelength of the incident laser beam resonates with the alkali metal atomic spectral line in the alkali metal atomic gas cell to be measured.

[0049] In this embodiment, the beam expansion optical path (2) is composed of two lenses with different focal lengths, and the focal points of the two lenses coincide. The lens with a smaller focal length is the incident lens, and the lens with a larger focal length is the exit lens, that is, the lens with a smaller focal length is at the incident end, and the lens with a larger focal length is at the exit end.

[0050] The focal lengths of the two lenses in the beam expansion optical path can be selected according to actual beam expansion requirements.

[0051] In this embodiment, the diffuser laser homogenization light path is composed of a diffuser and two focusing lenses with the same parameters. The focal points of the two focusing lenses coincide, and the diffuser is located at the focal position between the two lenses. After the laser beam is incident, it is focused on the first focusing lens, and the diffuser is on the focal plane of the focusing lens. After the light beam is homogenized by the diffuser, it is collimated and output through the rear focusing lens.

[0052] In this embodiment, the dual microlens array homogenization optical path is composed of two microlens arrays with similar specifications and parameters; after the laser beam is expanded and collimated, and initially homogenized, it is parallelly incident on the dual microlens array homogenization optical path, and the output beam is a uniform beam array;

[0053] The number and size of the microlens units of the microlens array should be designed and processed according to the required number and size of light beams.

[0054] In this embodiment, the attenuation ratio of the attenuation plate at the rear end of the alkali metal gas chamber should be selected according to the actual incident light beam power and the temperature of the alkali metal gas chamber, and it is necessary to ensure that the rear end CCD acquisition system is not saturated. The greater the incident power, the greater the attenuation ratio of the attenuation plate. The higher the temperature of the alkali metal gas chamber, the higher the attenuation ratio of the attenuation plate.

[0055] In this embodiment, the CCD imaging system adopts a full-frame large-array CCD, which is convenient for receiving the transmission information of the light beam in all directions. Its advantages of large dynamic range and large photosensitive area can well meet the needs of this detection system.

[0056] In this embodiment, for the accuracy of detection, this detection system requires that the center of the photosensitive surface of the CCD imaging system and the center of the detected surface of the atomic gas chamber be aligned as much as possible, and the photosensitive surface and the detected surface of the alkali metal gas chamber be kept parallel. Before the alkali metal gas chamber detection, it is required to perform precise azimuth adjustment so that the center of the CCD photosensitive surface and the center of the detected surface of the atomic gas chamber are aligned as much as possible and the two surfaces are kept parallel.

[0057] Before testing, it is necessary to determine the image of the incident light beam on the CCD after passing through the attenuation plate when there is no alkali metal gas chamber in the system, as the intensity of the incident light beam. When there is an alkali metal gas chamber to be tested, there will also be a corresponding image. By comparing the grayscale of the two images, the transmittance of the alkali metal gas chamber to be tested can be obtained. Then, using the principle of optical depth method and the empirical formula of saturated vapor pressure, the atomic number density, temperature, and temperature gradient of the corresponding position are calculated, and the temperature is measured at different times. By calculating the temperature gradient at each position, it can be determined whether the system has reached thermal equilibrium and the time required for the entire process.

[0058] When a linearly polarized laser passes through an alkali metal atom gas chamber, the intensity attenuation of the beam satisfies the following relationship:

[0059] I(z)=I(0)exp(-nσ(v)l)

[0060] After conversion, the following relationship can be obtained. It can be seen from the following formula that the optical depth is exponentially related to the transmittance of the laser.

[0061]

[0062] When resonant laser is used for incidence, the spectral absorption cross section is

[0063]

[0064] By combining the above formulas, the atomic number density can be calculated as

[0065]

[0066] Then, based on the above empirical formula for saturated vapor pressure, the temperature at the corresponding position can be obtained.

[0067]

[0068] Where I(z) is the laser intensity at z, I(0) is the incident light intensity, n is the atomic number density, σ(v) is the spectral absorption cross-section of the alkali metal atom, l is the distance the light beam travels in the gas chamber, c is the speed of light, and r e is the electron radius, f is the resonance intensity, Γ is the broadening of the alkali metal atomic absorption line, v is the beam frequency, v0 is the resonance frequency, A K , B K is the empirical coefficient of saturated vapor pressure, and T is the temperature.

[0069] An array-type in-situ detection method for multi-parameter measurement of an alkali metal gas chamber comprises the following steps:

[0070] Step 1: First test the corresponding relationship between the image grayscale and the light intensity received by the CCD imaging system;

[0071] The specific method of step 1 is: use a single laser beam with different light powers to respectively incident on the CCD imaging system, and record the grayscale and within the area of ​​the beam spot of the CCD imaging system. The linear relationship coefficient between the grayscale and the incident light power is obtained by fitting, that is:

[0072] I=k∑p i

[0073] Step 2: When there is no alkali metal atom gas chamber, by selecting an attenuation plate with an attenuation coefficient of α, the CCD imaging system is made unsaturated. According to the linear relationship between grayscale and incident light intensity, the intensity of each beam in the array beam can be obtained by the grayscale sum within the imaged spot area, which is the incident intensity:

[0074] I ki =k(∑p n ) ki / α

[0075] Step 3, placing the alkali metal gas chamber in the corresponding position, and adjusting the azimuth through the precision azimuth adjuster, so that the center of the measured surface of the atomic gas chamber is substantially coincident with the center of the CCD photosensitive surface, and the two surfaces are substantially parallel;

[0076] Step 4: Select a suitable attenuation coefficient β to make the CCD imaging grayscale moderate, and calculate the beam intensity as the emission intensity at each position in the same way as step 2:

[0077] I ji =k(∑p n ) ji / β

[0078] Step 5: Calculate the transmittance at each position:

[0079]

[0080] Step 6: Using the principle of optical depth method and the empirical formula of saturated vapor pressure, calculate the atomic number density and temperature at each position. The corresponding temperature gradient can be obtained based on the calculated temperature.

[0081] In this embodiment, by measuring at different times, when the transmittance at different positions no longer changes significantly, it indicates that the alkali metal atomic gas chamber has reached an equilibrium state, thereby determining whether the atomic gas chamber has reached thermal equilibrium and obtaining the time required for the entire process.

[0082] In the present invention, the beam expansion ratio of the beam expansion optical path, the number of microlenses in the dual microlens array, the aperture of the microlens unit, and the attenuation coefficient of the attenuation sheet all need to be adjusted according to actual measurement needs.

[0083] It should be emphasized that the embodiments of the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific implementation modes. Any other implementation modes derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. An array-type in-situ detection system for multi-parameter measurement of alkali metal gas chambers, characterized in that: include: A laser, a beam expansion optical path, a diffuser laser homogenization optical path, a double microlens array homogenization optical path, a polarizer, an alkali metal gas chamber to be measured, an attenuation plate and a CCD imaging system are connected in sequence; The laser output light beam is first expanded through a beam expansion optical path, then preliminarily homogenized through a diffuser laser homogenization optical path, and then homogenized through a double microlens array optical path, so that the output light beam is a uniform light beam array; the output light beam array is polarized through a polarizer to make it a linearly polarized laser with a high polarization degree; then it is incident on the alkali metal gas chamber to be measured, and the output light beam is attenuated through an attenuation plate with a preset attenuation rate to prevent the saturation of the rear CCD imaging system, and the attenuated array light beam enters the rear CCD imaging system; During the measurement process, the wavelength of the laser is tuned so that the wavelength of the incident laser beam resonates with the alkali metal atomic spectral line in the alkali metal atomic gas chamber to be measured; The beam expansion optical path is composed of two lenses with different focal lengths, and the focal points of the two lenses coincide, the lens with a smaller focal length is the incident lens, and the lens with a larger focal length is the exit lens; The diffuser laser homogenization optical path is composed of a diffuser and two focusing lenses with the same parameters. The focal points of the two focusing lenses coincide with each other, and the diffuser is located at the focal position between the two lenses. After the laser beam is incident, it is focused on the first focusing lens, and the diffuser is on the focal plane of the focusing lens. After the light beam is homogenized by the diffuser, it is collimated and output by the rear focusing lens. The double microlens array uniform light path is composed of two microlens array light beams with similar specifications and parameters; after the laser is expanded and collimated, and initially homogenized, it is parallelly incident on the double microlens array uniform light path, and the output light beam is a uniform light beam array.

2. The array-type in-situ detection system for multi-parameter measurement of alkali metal gas chamber according to claim 1, characterized in that: The attenuation ratio of the attenuation plate at the rear end of the alkali metal gas chamber should be selected based on the actual incident light beam power and the temperature of the alkali metal gas chamber, and it is necessary to ensure that the rear end CCD acquisition system is not saturated; the greater the incident power, the greater the attenuation ratio of the attenuation plate; the higher the temperature of the alkali metal gas chamber, the higher the attenuation ratio of the attenuation plate.

3. The array-type in-situ detection system for multi-parameter measurement of alkali metal gas chamber according to claim 1, characterized in that: The CCD imaging system adopts a full-frame large-array CCD, which is convenient for receiving the transmission information of the light beam in all directions.

4. The array-type in-situ detection system for multi-parameter measurement of alkali metal gas chamber according to claim 1, characterized in that: The center of the photosensitive surface of the CCD imaging system and the center of the detected surface of the atomic gas chamber should be aligned as much as possible, and the photosensitive surface and the detected surface of the alkali metal gas chamber should be kept parallel.

5. A detection method of an array-type in-situ detection system for multi-parameter measurement of alkali metal gas chambers based on any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: First test the corresponding relationship between the image grayscale and the light intensity received by the CCD imaging system; Step 2: When there is no alkali metal atom gas chamber, by selecting an attenuation plate with an attenuation coefficient of α, the CCD imaging system is made unsaturated. According to the linear relationship between grayscale and incident light intensity, the intensity of each beam in the array beam can be obtained by the grayscale sum within the imaged spot area, which is the incident intensity: I ki =k(∑p n ) ki / a Step 3, placing the alkali metal gas chamber in the corresponding position, and adjusting the azimuth through the precision azimuth adjuster, so that the center of the measured surface of the atomic gas chamber is substantially coincident with the center of the CCD photosensitive surface, and the two surfaces are substantially parallel; Step 4: Select a suitable attenuation coefficient β to make the CCD imaging grayscale moderate, and calculate the beam intensity as the emission intensity at each position in the same way as step 2: I ji =k(∑p n ) ji / β Step 5: Calculate the transmittance at each position: Step 6: Calculate the atomic number density and temperature at each position using the principle of optical depth method and the empirical formula for saturated vapor pressure; and obtain the corresponding temperature gradient based on the calculated temperature.

6. The detection method according to claim 5, characterized in that: The specific method of step 1 is: using a single laser beam with different light powers to respectively incident on the CCD imaging system, and recording the grayscale and within the beam spot area of ​​the CCD imaging system; and obtaining the linear relationship coefficient between the grayscale and the incident light power by fitting, that is: I=k∑p i 。

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