Rydberg atomic electric field measurement system and method based on spatial light modulator

Abstract

The invention discloses a Rydberg atomic electric field measurement system and method based on a spatial light modulator, and relates to the technical field of optical measurement and quantum electric field measurement. According to the method, the phase, the frequency and the light intensity of the laser are controlled by controlling the spatial modulator, the laser phase, the frequency and the light intensity required by specific energy level transition of the Rydberg atoms are accurately matched, the electric field can be continuously measured in a large range only by controlling the spatial modulator, the operation is simple, a large amount of time is saved, and the measurement precision is high. And the measurement requirement of a wide-range electric field from low frequency to high frequency can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement and quantum electric field measurement, and in particular to a Rydberg atom electric field measurement system and method based on a spatial light modulator. Background Art

[0002] Electric field strength is one of the seven key quantities of radio metrology defined by the International Committee for Weights and Measures. Precision electric field measurement technology has played an extremely important role in communications, remote sensing, aerospace, and detection radar. Traditional electric field measurement techniques, such as the electric dipole method and the capacitance method, may have insufficient accuracy or damage risks under high-frequency or strong electric field conditions, and cannot provide sufficient measurement range or accuracy. In recent years, electric field measurement technology based on Rydberg atoms has attracted attention due to its high sensitivity and high resolution. However, due to the need to precisely control the laser characteristics to match the specific energy level transitions of the Rydberg atoms, the existing technology of Rydberg atoms has limitations in large-scale continuous measurement, and it is difficult to meet the measurement needs of a wide range of electric fields from low frequency to high frequency. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a Rydberg atom electric field measurement system and method based on a spatial light modulator, which solves the problem that the prior art is limited in large-scale continuous measurement and is difficult to meet the measurement requirements of a wide range of electric fields from low frequency to high frequency.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0005] A method for measuring the electric field of Rydberg atoms based on a spatial light modulator is provided, which comprises the following steps:

[0006] S1, generating a first laser and a second laser respectively by a laser system;

[0007] S2, adjusting the first laser by an adjustment unit to obtain the adjusted first laser and injecting the adjusted first laser into a spatial light modulator;

[0008] S3, modulating the adjusted first laser light by adjusting the structure of the spatial light modulator to obtain a different modulated first laser light;

[0009] S4, injecting the modulated first laser in step S3 and the second laser after passing through the dichroic mirror into the Rydberg atom gas chamber to excite the Rydberg atoms, and obtaining different EIT signals through a photodetector;

[0010] S5, using a signal processing unit to analyze different EIT signals to obtain corresponding electric fields;

[0011] S6. Based on the electric field in step S5, determine the electric field range of the Rydberg atoms.

[0012] Furthermore, the laser system includes a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the adjustment unit includes a spatial filter, a polarization beam splitter PCB, and a four-mirror ring cavity; the four-mirror ring cavity includes two plane mirrors and two concave mirrors.

[0013] Further, step S3 includes the following steps:

[0014] S3-1, adjusting the liquid crystal layer voltage of the spatial light modulator to obtain the refractive index of the corresponding pixel point;

[0015] S3-2, adjusting the phase of the first laser based on each refractive index to obtain a phase delay of the first laser;

[0016] S3-3, setting a phase grating according to the phase delay of the first laser;

[0017] S3-4, adjusting the frequency of the first laser by using a phase grating;

[0018] S3-5, determine whether the frequency of step S3-4 reaches the frequency threshold; if so, proceed to step S3-6; otherwise, return to step S3-1;

[0019] S3-6, setting a polarizer and adjusting the light intensity of the first laser according to the frequency and phase delay of the first laser;

[0020] S3-7, judging whether the light intensity of step S3-6 reaches the light intensity threshold; if so, obtaining the adjusted first laser and proceeding to step S3-8; otherwise, returning to step S3-1;

[0021] S3-8, repeating steps S3-1 to S3-7 until a preset number of times is reached to obtain different adjusted first lasers.

[0022] Further, step S5 includes the following steps:

[0023] S5-1. Select any EIT signal;

[0024] S5-2, obtaining a spectrum of the selected EIT signal;

[0025] S5-3. Obtain the corresponding frequency shift Δ according to the spectrum of the selected EIT signal stark ;

[0026] S5-4, frequency shift Δ stark Calculate and obtain the corresponding electric field;

[0027] S5-5, judging whether the electric field in step S5-4 is greater than the electric field E avoid; If yes, discard the electric field; otherwise, keep the electric field;

[0028] S5-6. Repeat steps S5-3 to S5-5 until all EIT signals are processed.

[0029] Furthermore, the calculation formula of step S5-4 is:

[0030]

[0031] Here, |E| represents the absolute value of the electric field, and α represents the atomic polarizability of the Rydberg state.

[0032] A Rydberg atom electric field measurement system based on a spatial light modulator comprises a Rydberg atom gas chamber, a laser system, an adjustment unit, a photodetector, a signal processing unit and a control unit; wherein:

[0033] Rydberg atomic gas cell, used to provide Rydberg atoms;

[0034] A laser system for generating laser light;

[0035] A photodetector for detecting the laser light after it has passed through the Rydberg atomic gas cell and interacted with the Rydberg atoms and detecting the EIT signal;

[0036] An adjustment unit, used to adjust the direction and beam size of the laser;

[0037] A control unit, used to adjust the phase, intensity and frequency of the laser to obtain different EIT signals and transmit them to the signal processing unit;

[0038] The signal processing unit is used to analyze the EIT signal and calculate the electric field strength.

[0039] Furthermore, the laser system includes a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the adjustment unit includes a spatial filter, a polarization beam splitter PCB, and a four-mirror ring cavity; the four-mirror ring cavity includes two plane mirrors and two concave mirrors; and the control unit includes a spatial light modulator.

[0040] The beneficial effects of the present invention are as follows: the method controls the phase, frequency and light intensity of the laser by controlling the spatial modulator, accurately matching the laser phase, frequency and light intensity required for the Rydberg atom to perform a specific energy level transition. Only the spatial modulator needs to be controlled to achieve continuous measurement of the electric field over a large range. The operation is simple, a lot of time is saved, and the measurement requirements of a wide range of electric fields from low frequency to high frequency can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a method flow chart;

[0042] Figure 2 Schematic diagram of adjusting the laser phase for a spatial light modulator;

[0043] Figure 3 An optical path configuration diagram for modulating light intensity by a spatial light modulator;

[0044] Figure 4 It is the transmission spectrum amplitude diagram corresponding to different laser powers;

[0045] Figure 5 It is the system structure diagram;

[0046] Figure 6 For 35S 1 / 2 The Stark spectrum of the state and E avoid Schematic diagram;

[0047] Figure 7 For 18S 1 / 2 The Stark spectrum of the state and E avoid Schematic diagram;

[0048] Figure 8 25S 1 / 2 The Stark spectrum of the state and E avoid Schematic diagram. DETAILED DESCRIPTION

[0049] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0050] like Figure 1 As shown, a method for measuring the electric field of Rydberg atoms based on a spatial light modulator comprises the following steps:

[0051] S1, generating a first laser and a second laser respectively by a laser system;

[0052] The laser system includes a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the pump light is coupled into the laser crystal to generate fundamental frequency light to oscillate in the cavity.

[0053] S2, adjusting the first laser by an adjustment unit to obtain the adjusted first laser and injecting the adjusted first laser into a spatial light modulator;

[0054] The adjustment unit includes a spatial filter, a polarization beam splitter PCB, and a four-mirror annular cavity; the four-mirror annular cavity includes two plane reflectors and two concave mirrors, that is, an optical isolator and a frequency selection device are used. Due to the unidirectional operation of the four-mirror annular cavity, the gain medium is uniformly widened inside the crystal, thereby suppressing the hole burning effect and outputting a good single-frequency laser with a line width of less than 200khz. Taking into account the thermal insensitivity effect of the crystal, the astigmatism elimination of the resonant cavity, the working stable area, the good mode matching, the high-precision and high-stability integrated cavity design of current drive and temperature control, it can output a single-frequency laser with high stability, high single frequency, narrow line width and high beam quality.

[0055] S3, modulating the phase, frequency and light intensity of the adjusted first laser by adjusting the structure of the spatial light modulator to obtain different modulated first lasers; Figure 2 As shown, the spatial light modulator is SLM, including a glass substrate, a transparent ITO electrode, a liquid crystal layer, a reflective layer, a pixel electrode (aluminum film) and a silicon-based COMS chip;

[0056] A spatial light modulator (LCOS-SLM) is a programmable device that can modulate the phase of light, such as Figure 3 As shown in the figure, from the perspective of wave optics, optical elements such as lenses, gratings, and pyramidal prisms all change the phase of light in a certain way to achieve the desired effect, so these effects can be achieved by spatial light modulators. In addition, due to its programmability, spatial light modulators can also achieve phase modulation functions that are difficult, costly, and impossible to achieve with traditional optical elements.

[0057] The incident laser beam passes through the transparent glass substrate layer and ITO electrode layer of the spatial light modulator, reaches the liquid crystal layer to complete the phase modulation (voltage → liquid crystal molecule arrangement direction → refractive index → ​​optical path → phase), and then is reflected by the reflective surface for output. The laser at this time is modulated laser. Then step S3 includes the following steps:

[0058] S3-1, adjusting the liquid crystal layer voltage of the spatial light modulator to obtain the refractive index of the corresponding pixel point;

[0059] S3-2, adjusting the phase of the first laser based on each refractive index to obtain a phase delay of the first laser;

[0060] By changing the voltage of the liquid crystal layer of the spatial light modulator to control the refractive index of each pixel, the phase of the light wave passing through the pixel can be changed. Phase modulation can be described by the following formula:

[0061] φ(x,y)=(2π / λ)Δn(x,y)d

[0062] Among them, π represents pi, λ represents the laser wavelength, φ(x, y) represents the phase delay at the coordinate (x, y) on the SLM, Δn(x, y) represents the refractive index change at the coordinate (x, y) on the SLM, and d represents the thickness of the liquid crystal layer.

[0063] S3-3, setting a phase grating according to the phase delay of the first laser;

[0064] S3-4, adjusting the frequency of the first laser by using a phase grating;

[0065] The phase gradient generated by the SLM can create a phase grating that can diffract the light waves passing through, thereby producing a change in frequency. The frequency change of the diffracted light can indirectly adjust the laser frequency:

[0066]

[0067] Among them, Δν represents the change in laser frequency, c represents the speed of light, and Δφ represents the phase difference introduced by the SLM. By adjusting the voltage on the SLM, the refractive index of the liquid crystal layer can be changed, thereby changing the optical path and the phase change rate, and then adjusting the frequency to match the energy level difference of the Rydberg atoms.

[0068] S3-5, determine whether the frequency of step S3-4 reaches the frequency threshold; if so, proceed to step S3-6; otherwise, return to step S3-1; the frequency threshold is set according to the frequency that can match the energy level difference of the Rydberg atom;

[0069] S3-6, setting a polarizer and adjusting the light intensity of the first laser according to the frequency and phase delay of the first laser;

[0070] Although SLM is a phase modulator, light intensity modulation and polarization modulation can be achieved through proper configuration, for example, by adding corresponding 1 / 4 glass plates, polarizers, etc. in the front and back.

[0071] SLM can precisely modulate the phase of incident light by controlling the liquid crystal layer through voltage. Each pixel on the SLM is independently controlled to produce different phase delays. A quarter wave plate is added before and after the SLM, and the phase change of the light wave passing through the quarter wave plate is π / 2. The quarter wave plate is usually used to convert linear polarized light into circular polarized light or change the phase of polarized light. The angle of the fast axis of the wave plate relative to the x-axis (45 degrees or 135 degrees) determines the phase change of the polarized light passing through the wave plate, which affects the amplitude of the light when it passes through the analyzer. The light intensity is proportional to the square of the laser amplitude, so the light intensity will also be affected. Finally, the analyzer (polarizer) controls the intensity of light passing through a specific polarization direction.

[0072] By adjusting the phase pattern generated by the SLM and the configuration of the 1 / 4 wave plate, the intensity of light passing through the analyzer can be controlled. When the polarization direction of the analyzer is consistent with the polarization direction of the light, the light intensity is maximum; when they are perpendicular, the light intensity is minimum. By precisely controlling the laser intensity, it is ensured that the Rydberg atoms are effectively excited to a high energy level, which is conducive to observing the Stark effect. At the same time, the characteristics of the EIT window can be optimized, thereby improving the resolution and sensitivity of the electric field measurement.

[0073] S3-7, judging whether the light intensity of step S3-6 reaches the light intensity threshold; if so, obtaining the adjusted first laser and entering step S3-8; otherwise, returning to step S3-1; the light intensity threshold is set according to the Rydberg atoms being effectively excited to a high energy level;

[0074] S3-8, repeating steps S3-1 to S3-7 until a preset number of times is reached to obtain different adjusted first lasers.

[0075] S4, injecting the modulated first laser in step S3 and the second laser after passing through the dichroic mirror into the Rydberg atom gas chamber to excite the Rydberg atoms, and obtaining different EIT signals through a photodetector;

[0076] S5, using a signal processing unit to analyze different EIT signals to obtain corresponding electric fields;

[0077] Step S5 includes the following steps:

[0078] S5-1. Select any EIT signal;

[0079] S5-2, obtaining a spectrum of the selected EIT signal;

[0080] S5-3. Obtain the corresponding frequency shift Δ according to the spectrum of the selected EIT signal stark ;

[0081] S5-4, frequency shift Δ stark Calculate and obtain the corresponding electric field;

[0082] The electric field causes the frequency shift of the EIT spectrum, which is reflected in the movement of the spectrum on the x-axis. The frequency shift Δ stark The size is defined as the peak position Δ at zero field c0 and the peak position under external field Δ c1 The difference, Δ stark =Δ c0 -Δ c1 .like Figure 4 As shown in the figure, the blue dotted lines correspond to the peak positions when E = 0 and E = 5 V / cm, and the corresponding frequency shift Δ stark is about 50MHz, it can be seen that by measuring Δstark And theoretically calculate the atomic polarizability α of the Rydberg state, and the calculation formula of the final step S5-4 is:

[0083]

[0084] Here, |E| represents the absolute value of the electric field, and α represents the atomic polarizability of the Rydberg state.

[0085] exist Figure 4 In the process, since the light in the horizontal polarization direction will be fully modulated by the SLM, the light in the vertical polarization direction will not be modulated by the SLM at all. Therefore, while adjusting the polarizer, observe the light spot effect after modulation. The polarizer position with the strongest and best modulation effect is the horizontal polarization direction. The polarization direction is changed to control the laser power, and the laser interacts with another laser in the air chamber to obtain the EIT spectrum. The amplitude of the EIT spectrum changes with the laser power.

[0086] S5-5, judging whether the electric field in step S5-4 is greater than the electric field E avoid ; If yes, discard the electric field; otherwise, keep the electric field;

[0087] S5-6. Repeat steps S5-3 to S5-5 until all EIT signals are processed.

[0088] S6. Based on the electric field in step S5, determine the electric field range of the Rydberg atoms.

[0089] like Figure 5 As shown, a Rydberg atom electric field measurement system based on a spatial light modulator includes a Rydberg atom gas chamber, a laser system, an adjustment unit, a photodetector, a signal processing unit and a control unit; wherein:

[0090] Rydberg atomic gas cell, used to provide Rydberg atoms;

[0091] A laser system for generating laser light;

[0092] A photodetector for detecting the laser light after it has passed through the Rydberg atomic gas cell and interacted with the Rydberg atoms and detecting the EIT signal;

[0093] An adjustment unit, used to adjust the direction and beam size of the laser;

[0094] A control unit, used to adjust the phase, intensity and frequency of the laser to obtain different EIT signals and transmit them to the signal processing unit;

[0095] The signal processing unit is used to analyze the EIT signal and calculate the electric field strength.

[0096] The laser system includes a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the adjustment unit includes a spatial filter, a polarization beam splitter PCB, and a four-mirror ring cavity; the four-mirror ring cavity includes two plane reflectors and two concave mirrors; and the control unit includes a spatial light modulator.

[0097] In one embodiment of the present invention, the laser frequency is adjusted by the SLM to ensure that the laser frequency is consistent with the transition frequency of the Rydberg atoms, which is the basis for achieving electromagnetic induced transparency (EIT) and observing the Stark effect. Infer the electric field strength E acting on the atom;

[0098] In the Rydberg atom at 35S 1 / 2 In the case of the state, the electric field avoids the crossing position E avoid Part of the Stark structure diagram is enlarged, such as Figure 4 As shown. avoid Before, the EIT spectrum frequency shift Δ stark (The difference between the Stark energy under external field and the Stark energy under zero field) is still in a square relationship with the electric field. avoid After, 35S1 / The Stark energy of the 2-state Rydberg atom no longer satisfies the square relationship with the electric field. Therefore, when measuring the electric field, E should be taken into account. avoid The impact brought about by this is that when the field strength to be measured exceeds this range, other appropriate Rydberg states should be selected.

[0099] By adjusting the Rydberg atomic transition frequency through SLM and selecting the appropriate Rydberg state, it is theoretically possible to measure the electric field in a very large range of power systems. When the Rydberg state is fixed, the minimum measurable field strength E min The expression is as follows:

[0100]

[0101] Among them, the minimum spectral frequency shift Δ stark min The typical line width in the experiment is 10 MHz. To leave a certain margin, the minimum spectral frequency shift Δ stark min Set it to 15MHz.

[0102] For Rydberg S and D states, the total angular quantum number J and the total magnetic quantum number M have different atomic polarizabilities α. The relationship between the total angular quantum number J, the total magnetic quantum number M and the atomic polarizability α is:

[0103]

[0104] Among them, α0 and α2 represent the scalar polarizability and tensor polarizability respectively, α S、D represents the atomic polarizability in the Rydberg S and D states.

[0105] According to the relationship between the total angular quantum number J, the total magnetic quantum number M and the atomic polarizability α, 18S 1 / 2 State and 25S 1 / 2 E min , combining the two Rydberg states of E avoid ,like Figure 7 and Figure 8 As shown, the measurable field strength ranges are 35.14 to 318.0 V / cm and 9.64 to 38.52 V / cm respectively.

[0106] In summary, the present invention controls the phase, frequency and light intensity of the laser by controlling the spatial modulator, and accurately matches the laser phase, frequency and light intensity required for the Rydberg atom to perform a specific energy level transition. Only by controlling the spatial modulator can the electric field be continuously measured over a large range. The operation is simple, and a lot of time is saved. It can meet the measurement requirements of a wide range of electric fields from low frequency to high frequency.

Claims

1. A method for measuring the electric field of Rydberg atoms based on a spatial light modulator, characterized in that: The following steps are involved: S1, generating a first laser and a second laser respectively by a laser system; S2, adjusting the first laser by an adjustment unit to obtain the adjusted first laser and injecting the adjusted first laser into a spatial light modulator; S3, modulating the adjusted first laser light by adjusting the structure of the spatial light modulator to obtain a different modulated first laser light; S4, injecting the modulated first laser in step S3 and the second laser after passing through the dichroic mirror into the Rydberg atom gas chamber to excite the Rydberg atoms, and obtaining different EIT signals through a photodetector; S5, using a signal processing unit to analyze different EIT signals to obtain corresponding electric fields; S6. Based on the electric field in step S5, determine the electric field range of the Rydberg atoms.

2. The Rydberg atom electric field measurement method based on a spatial light modulator according to claim 1, characterized in that: The laser system comprises a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the adjustment unit comprises a spatial filter, a polarization beam splitter PCB, and a four-mirror ring cavity; the four-mirror ring cavity comprises two plane reflectors and two concave mirrors.

3. The Rydberg atom electric field measurement method based on a spatial light modulator according to claim 1, characterized in that: The step S3 comprises the following steps: S3-1, adjusting the liquid crystal layer voltage of the spatial light modulator to obtain the refractive index of the corresponding pixel point; S3-2, adjusting the phase of the first laser based on each refractive index to obtain a phase delay of the first laser; S3-3, setting a phase grating according to the phase delay of the first laser; S3-4, adjusting the frequency of the first laser by using a phase grating; S3-5, determine whether the frequency of step S3-4 reaches the frequency threshold; if so, proceed to step S3-6; otherwise, return to step S3-1; S3-6, setting a polarizer and adjusting the light intensity of the first laser according to the frequency and phase delay of the first laser; S3-7, judging whether the light intensity of step S3-6 reaches the light intensity threshold; if so, obtaining the adjusted first laser and proceeding to step S3-8; otherwise, returning to step S3-1; S3-8, repeating steps S3-1 to S3-7 until a preset number of times is reached to obtain different adjusted first lasers.

4. The method for measuring the electric field of Rydberg atoms based on a spatial light modulator according to claim 3, characterized in that: The step S5 comprises the following steps: S5-1. Select any EIT signal; S5-2, obtaining a spectrum of the selected EIT signal; S5-3, obtaining a corresponding frequency shift Δstark according to the spectrum of the selected EIT signal; S5-4, calculating the frequency shift Δstark to obtain the corresponding electric field; S5-5, determining whether the electric field in step S5-4 is greater than the electric field Eavoid; if so, discarding the electric field; otherwise, retaining the electric field; S5-6. Repeat steps S5-3 to S5-5 until all EIT signals are processed.

5. The method for measuring the electric field of Rydberg atoms based on a spatial light modulator according to claim 4, characterized in that: The calculation formula of step S5-4 is: Here, |E| represents the absolute value of the electric field, and α represents the atomic polarizability of the Rydberg state.

6. A measurement system for the Rydberg atom electric field measurement method based on a spatial light modulator according to any one of claims 1 to 5, characterized in that: It includes a Rydberg atomic gas chamber, a laser system, an adjustment unit, a photoelectric detector, a signal processing unit and a control unit; wherein: Rydberg atomic gas cell, used to provide Rydberg atoms; A laser system for generating laser light; A photodetector for detecting the laser light after it has passed through the Rydberg atomic gas cell and interacted with the Rydberg atoms and detecting the EIT signal; An adjustment unit, used to adjust the direction and beam size of the laser; A control unit, used to adjust the phase, intensity and frequency of the laser to obtain different EIT signals and transmit them to the signal processing unit; The signal processing unit is used to analyze the EIT signal and calculate the electric field strength.

7. The Rydberg atom electric field measurement system based on a spatial light modulator according to claim 6, characterized in that: The laser system includes a first laser and a second laser; the first laser adopts an 852nm laser; the second laser adopts a 510nm laser; the adjustment unit includes a spatial filter, a polarization beam splitter PCB, and a four-mirror ring cavity; the four-mirror ring cavity includes two plane reflectors and two concave mirrors; the control unit includes a spatial light modulator.

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