Tunable laser frequency stabilization system and method based on Rydberg atom direct current Stark

Abstract

The invention relates to a tunable laser frequency stabilization system and method based on Rydberg atom direct current stark, and belongs to the technical field of laser frequency stabilization. The tuned frequency is determined by the atomic state and the voltage at the two ends of the polar plate and can be calculated through a theoretical model, the locked laser frequency has high precision and long-term stability, and the precision and the long-term stability are within MHz. In the invention, the atomic gas chamber with the built-in electrode plate is adopted to avoid the problem that a traditional gas chamber can shield a direct-current electric field, a direct-current electric field can be generated in the atomic gas chamber by applying a voltage to the two ends of the electrode plate, and an atomic energy level moves due to a direct-current stark effect, so that the tuning of the frequency of the coupled laser can be completed; the applied voltage is generally below 10V, the tuning range is between GHz and dozens of GHz according to different selected Rydberg states, and the operation is relatively convenient and simple.

Description

Technical Field

[0001] This invention relates to a tunable laser frequency stabilization system and method based on Rydberg atom DC Stark, belonging to the field of laser frequency stabilization technology. Background Technology

[0002] Electric field measurement based on Rydberg atoms has become a cutting-edge research area in quantum precision measurement in recent years. Due to the high polarizability of Rydberg atoms and their extreme sensitivity to applied electric fields, they have been extensively studied in applications such as electric field strength measurement, electromagnetic spectrum monitoring, and communication reception. Particularly in the field of electromagnetic spectrum monitoring, it is a crucial technique for accurately acquiring ultra-wideband electromagnetic space situational awareness and gaining electromagnetic spectrum advantages. By monitoring over an ultra-wide spectrum, we can efficiently utilize electromagnetic spectrum resources and implement precise electromagnetic interference, providing strong technical support for communication security and electronic countermeasures.

[0003] A frequency-locked coupled light source with a large tuning range is fundamental for realizing ultra-wideband microwave detection. Currently used frequency stabilization methods for coupled light include PDH (Programmable High-Degree Hybridization) and EIT (Extremely Stable In-Process) frequency stabilization. PDH locks the laser onto an ultra-stable optical cavity, resulting in a laser frequency with good short-term stability. Furthermore, by changing the cavity length using piezoelectric ceramics, the laser frequency can be adjusted within a certain range. However, due to the lack of an absolute reference at atomic energy levels, the length of the ultra-stable optical cavity is subject to long-term drift caused by factors such as temperature and mechanical deformation. Therefore, the long-term stability of the laser frequency stabilized using this method is uncontrollable. EIT, another frequency stabilization method, locks the coupled laser frequency onto the transition line from the excited state to the Rydberg level. While it offers the advantage of frequency stability, the laser frequency is not adjustable because the atomic energy levels remain constant in the absence of an external field. Summary of the Invention

[0004] In view of this, the present invention provides a tunable laser frequency stabilization system and method based on Rydberg atom DC Stark, which can combine tunability and long-term stability.

[0005] To achieve the objectives of this invention, the following technical solutions are provided.

[0006] A tunable laser frequency stabilization system based on the DC Stark effect of Rydberg atoms, comprising a frequency stabilization optical path system and a processing system; The frequency-stabilized optical path system includes: a coupling laser for generating coupling light; a probe laser for generating probe light; a gas chamber with an internal electrode plate for containing an atomic sample, wherein the probe light and the coupling light overlap in the gas chamber to excite the atoms in a stepwise manner to produce an electromagnetically induced transparency effect; an optical component for guiding and combining the coupling light and the probe light so that they enter the gas chamber collinearly; and a photodetector for detecting the probe light signal after passing through the gas chamber. The processing system is electrically connected to the coupled laser, the electrode plate of the gas chamber, and the photodetector; the processing system is configured to: apply a corresponding voltage to the electrode plate according to the target frequency to generate a DC electric field in the gas chamber, thereby moving the atomic energy levels through the DC Stark effect; control the coupled laser to perform frequency scanning and modulation; receive the signal from the photodetector and demodulate it to generate an error signal; The error signal is processed by proportional-integral method and then fed back to the coupled laser, locking its frequency at the shifted electromagnetic induction transparent peak.

[0007] The coupled laser is a tunable semiconductor laser or a tunable fiber laser.

[0008] The gas chamber containing the built-in electrode plate has the electrode plate connected by leads to apply voltage to generate a uniform DC electric field inside the gas chamber, thus avoiding shielding of the electric field by the inner wall of the gas chamber.

[0009] The processing system includes an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), and a microcontroller. One of the DAC modules outputs scanning and modulation signals to the coupled laser, and the other DAC outputs a control voltage to the electrode plate. The ADC module is used to acquire signals from the photodetector. The microcontroller executes signal demodulation and proportional-integral (PI) control algorithms.

[0010] The processing system pre-stores data on the relationship between atomic level shift and applied electric field strength, which is used to calculate and apply the corresponding voltage based on the target frequency.

[0011] This invention also provides a tunable laser frequency stabilization method based on the DC Stark effect of Rydberg atoms. Using the system described in this invention, the method includes the following steps: According to the target frequency, the corresponding voltage is applied to the electrode plates of the gas chamber through the processing system, and the atomic energy level is moved by the DC Stark effect; By controlling the coupled laser to perform frequency scanning, the electromagnetically induced transparent spectrum after the movement is obtained; In the obtained spectrum, select the electromagnetic induction transparent peak that corresponds to the target frequency; A sinusoidal modulation is applied to the coupled laser, and the signal detected by the photodetector is demodulated to generate an error signal; The error signal is processed by proportional-integral conversion and then fed back to control the frequency of the coupled laser, locking it onto the selected electromagnetic induction transparency peak.

[0012] Specifically, the step of applying the corresponding voltage according to the target frequency involves: calling the pre-stored relationship data between atomic energy level shift and electric field strength, calculating the required electric field strength according to the target frequency, and converting it into a voltage applied to both ends of the electrode plate.

[0013] When the angular momentum of the Rydberg state of an atom is 2, the electromagnetically induced transparent spectrum will split after an electric field is applied. The step of selecting the electromagnetically induced transparent peak is to select the peak that corresponds to the theoretically calculated energy level shift relationship.

[0014] The frequency of the locked coupled laser is determined by the intrinsic energy levels of the atoms and the applied DC electric field, with the relationship being f = f0 + Δ, where f0 is the resonant frequency without an applied electric field and Δ is the energy level shift caused by the DC Stark effect.

[0015] In the weak field approximation, the energy level shift Δ is proportional to the square of the applied electric field strength E, i.e., Δ = α / 2 · E², where α is the polarizability of the atom.

[0016] Beneficial effects (1) The frequency of the system after tuning is determined by the atomic state and the voltage at both ends of the electrode plate. It can be calculated by theoretical model. The locked laser frequency has high precision and long-term stability, and its accuracy and long-term stability are within MHz.

[0017] (2) The system of the present invention uses an atomic gas cell with built-in electrode plates to avoid the problem of shielding DC electric field in traditional gas cells. Applying a voltage to both ends of the electrode plates can generate a DC electric field inside the atomic gas cell. The atomic energy level moves due to the DC Stark effect, thereby completing the tuning of the frequency of the coupled laser. The applied voltage is generally below 10V. Depending on the selected Rydberg state, the tuning range is between GHz and tens of GHz. The operation is relatively convenient and simple.

[0018] (3) Traditional methods lock the coupled laser at this transition peak, but the frequency of the coupled laser cannot be tuned due to the fixed atomic energy levels. This invention utilizes the DC Stark effect to achieve tunable coupled laser locking by shifting the atomic energy levels. Under the weak field approximation, the magnitude of the energy level shift is proportional to the square of the applied electric field. When the field strength is large, a numerical method of multi-level coupling can be used to calculate the relationship between the magnitude of the energy level shift and the electric field strength.

[0019] (4) In this invention, the laser frequency is stabilized at the shifted EIT peak. The characteristic of this method is that the frequency can be tuned by changing the voltage across the electrode plate; the tuned frequency is determined by the atomic state and the voltage across the electrode plate, and has long-term stability, which can be obtained by precise theoretical calculation.

[0020] (5) In this invention, a small sinusoidal modulation signal is applied to the laser by the control system, which generates a modulation signal of the same frequency in the probe light. By mixing the sinusoidal signal of the same frequency with the photodetector signal in the processing system, an error signal reflecting the spectral slope can be obtained. The error signal is output to the coupled laser for locking after passing through the proportional-integral section inside the control system.

[0021] (6) In the method of the present invention, the tuned frequency is determined by the atomic state and the voltage at both ends of the electrode plate, which can be calculated by theoretical model. The locked laser frequency has high precision and long-term stability, and its precision and long-term stability are within MHz. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the system of the present invention.

[0023] Figure 2 This is a schematic diagram showing the relationship between the DC Stark effect energy and the electric field strength of the Rydberg state in the system of this invention.

[0024] Figure 3 These are the EIT diagrams of the system of this invention with and without an electric field.

[0025] Figure 4 This is a flowchart of the tunable frequency-stabilized laser method based on the Rydberg atom DC Stark of this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a tunable laser frequency stabilization system based on Rydberg atom DC Stark, the system as follows: Figure 1 As shown, it includes a frequency-stabilized optical path system and a processing system.

[0028] The frequency-stabilized optical path system includes a coupled laser, a half-glass slide, a polarizing beam splitter, a reflector, a dichroic mirror, a locked probe laser, and a gas cell with built-in electrode plates. The coupled laser can be a tunable semiconductor laser or a tunable fiber laser, and it has a frequency tuning interface for subsequent scanning and modulation of the laser frequency. The laser generated by the coupled laser passes through the half-glass slide to change its polarization direction; part of the light is used as the laser beam, and the other part is reflected to the frequency-stabilized optical path system for laser frequency stabilization. It then passes through the reflector and dichroic mirror into the gas cell. The probe light is output after passing through the laser coupler, and then enters the gas cell through the reflector and dichroic mirror. The probe light and coupled light coincide in the gas cell, where they excite atoms to transition from the ground state to the Rydberg state in a stepwise manner. When the frequency of the coupled light resonates with the atomic energy level, a transmission peak is generated due to the electromagnetic induction transparency effect (EIT). Traditional methods lock the coupled laser onto this transition peak. However, due to the fixed atomic energy levels, the frequency of the coupled laser cannot be tuned. This invention utilizes the DC Stark effect to achieve tunable coupled laser locking by shifting the atomic energy levels. Under the weak field approximation, the magnitude of the energy level shift is proportional to the square of the applied electric field.

[0029]

[0030] When the electric field strength is large, a numerical method using multi-level coupling can be used to calculate the relationship between the magnitude of the energy level shift and the electric field strength.

[0031] A conductive layer is formed inside the gas chamber due to the adsorption of cesium atoms on its inner wall. This conductive layer has a shielding effect against a DC electric field. To apply a DC electric field to the atoms, an atomic gas chamber with built-in electrode plates is used, which are connected by leads. By applying a voltage across the electrodes, a uniform electric field is generated in the gas chamber. Under this uniform electric field, the atomic energy levels shift due to the DC Stark effect. The photoelectric signal from the photodetector enters the processing system.

[0032] The processing system includes one ADC module, two DAC modules, and a microcontroller. One DAC module is connected to the modulation port of the coupled laser, and the other DAC module is connected to the electrode plate in the gas chamber. The ADC module is connected to the photodetector. The main functions of the processing system are: 1. Controlling the voltage across the electrode plate according to the set frequency; 2. Performing triangular wave scanning and sine wave modulation on the laser; 3. Acquiring the signal from the photodetector; 4. Demodulating the signal from the photodetector to obtain the error signal; 5. Performing PI processing on the error signal and outputting it.

[0033] In this invention, the principle of laser frequency stabilization is to change the voltage across the electrode plates in the gas chamber. This causes a corresponding shift in the atomic energy levels under the DC Stark effect, which in turn changes the position of the EIT peak. Therefore, the laser frequency is stabilized at the shifted EIT peak, and the locked coupling light frequency is... , The frequency of the coupled light without electric field locking is denoted as .

[0034] The features of this invention are: 1. Frequency tuning can be achieved by changing the voltage across the electrode plates; 2. The tuned frequency is determined by the atomic state and the voltage across the electrode plates, has long-term stability, and can be calculated by a theoretical model.

[0035] This invention also provides a tunable laser frequency stabilization method based on Rydberg atom DC Stark, implemented using the system of this invention, comprising: 1. First, select the frequency to be shifted near the atomic transition energy level, and process the pre-calculated relationship between the atomic energy level and the applied electric field stored in the system, such as... Figure 2 As shown, the processing system finds the corresponding electric field magnitude based on the selected frequency. The electric field multiplied by the electrode spacing gives the applicable voltage. This voltage is output by the control system and applied across the electrodes.

[0036] 2. By scanning the laser frequency through the control system, the transmission spectrum after Stark shift can be observed, such as... Figure 3 As shown.

[0037] 3. Select the shifted EIT transmission peak. For a Rydberg state with angular momentum of 2, the EIT transmission spectrum will split into multiple segments after an electric field is applied. In this case, it is necessary to select the EIT transmission peak that corresponds to the calculated electric field relationship of the energy level.

[0038] 4. Locking is performed by obtaining an error signal through modulation and demodulation after receiving the transmission spectrum. This error signal is then fed back via a PI controller to lock the coupled laser frequency at the maximum value of the transmission spectrum. Specifically, a small sinusoidal modulation signal is applied to the laser by the control system. This generates a modulation signal of the same frequency in the probe light. By mixing this sinusoidal signal with the photodetector signal in the processing system, an error signal reflecting the spectral slope is obtained. This error signal is then passed through the proportional-integral (PI) section of the control system and output to the coupled laser for locking. The frequency stabilization flowchart is shown below. Figure 4 As shown.

[0039] This invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered within the scope of protection of this invention.

Claims

1. A tunable laser frequency stabilization system based on the DC Stark effect of Rydberg atoms, characterized in that, Including frequency-stabilized optical path system and processing system; The frequency-stabilized optical path system includes: a coupling laser for generating coupling light; a probe laser for generating probe light; a gas chamber with an internal electrode plate for containing an atomic sample, wherein the probe light and the coupling light overlap in the gas chamber to excite the atoms in a stepwise manner to produce an electromagnetically induced transparency effect; an optical component for guiding and combining the coupling light and the probe light so that they enter the gas chamber collinearly; and a photodetector for detecting the probe light signal after passing through the gas chamber. The processing system is electrically connected to the coupled laser, the electrode plate of the gas chamber, and the photodetector; the processing system is configured to: apply a corresponding voltage to the electrode plate according to the target frequency to generate a DC electric field in the gas chamber, thereby moving the atomic energy levels through the DC Stark effect; control the coupled laser to perform frequency scanning and modulation; receive the signal from the photodetector and demodulate it to generate an error signal; The error signal is processed by proportional-integral method and then fed back to the coupled laser, locking its frequency at the shifted electromagnetic induction transparent peak.

2. The system according to claim 1, characterized in that, The coupled laser is a tunable semiconductor laser or a tunable fiber laser.

3. The system according to claim 1, characterized in that, The gas chamber with built-in electrode plates has the electrode plates connected by leads to apply voltage to generate a uniform DC electric field inside the gas chamber, thus avoiding shielding of the electric field by the inner wall of the gas chamber.

4. The system according to claim 1, characterized in that, The processing system includes an analog-to-digital converter module, a digital-to-analog converter module, and a microcontroller; one of the digital-to-analog converter modules is used to output scanning and modulation signals to the coupled laser, and the other digital-to-analog converter module is used to output control voltage to the electrode plate; The analog-to-digital converter module is used to acquire the signal from the photodetector; the microcontroller is used to execute the signal demodulation and proportional-integral control algorithm.

5. The system according to any one of claims 1-4, characterized in that, The processing system pre-stores data on the relationship between atomic level shift and the applied electric field strength, which is used to calculate and apply the corresponding voltage based on the target frequency.

6. A method for frequency stabilization of tunable laser based on the DC Stark effect of Rydberg atoms, characterized in that, The method using the system as described in any one of claims 1 to 5 includes the following steps: According to the target frequency, the corresponding voltage is applied to the electrode plates of the gas chamber through the processing system, and the atomic energy level is moved by the DC Stark effect; By controlling the coupled laser to perform frequency scanning, the electromagnetically induced transparent spectrum after the movement is obtained; In the obtained spectrum, select the electromagnetic induction transparent peak that corresponds to the target frequency; A sinusoidal modulation is applied to the coupled laser, and the signal detected by the photodetector is demodulated to generate an error signal; The error signal is processed by proportional-integral conversion and then fed back to control the frequency of the coupled laser, locking it onto the selected electromagnetic induction transparency peak.

7. The method according to claim 6, characterized in that, The specific steps for applying the corresponding voltage according to the target frequency are as follows: calling the pre-stored relationship data between atomic energy level shift and electric field strength, calculating the required electric field strength according to the target frequency, and converting it into a voltage applied to both ends of the electrode plate.

8. The method according to claim 6 or 7, characterized in that, When the angular momentum of the Rydberg state of an atom is 2, the electromagnetically induced transparent spectrum will split after an electric field is applied. The step of selecting the electromagnetically induced transparent peak is to select the peak that corresponds to the theoretically calculated energy level shift relationship.

9. The method according to claim 8, characterized in that, The frequency of the locked coupled laser is determined by the intrinsic energy levels of the atoms and the applied DC electric field, with the relationship being f = f0 + Δ, where f0 is the resonant frequency without an applied electric field and Δ is the energy level shift caused by the DC Stark effect.

10. The method according to claim 9, characterized in that, Under the weak field approximation, the energy level shift Δ is proportional to the square of the applied electric field strength E, i.e., Δ = α / 2 · E², where α is the polarizability of the atom.

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