Pressure broadening real-time measuring device and method based on optical rotation effect

Abstract

The invention relates to an optical rotation effect-based pressure broadening real-time measurement device and method, which can be used for respectively measuring the ellipticity and the optical rotation angle of polarized light by using the phase delay characteristic of a photoelastic modulator, and further realizing the pressure broadening measurement of an atomic gas chamber according to the ratio relationship between the ellipticity and the optical rotation angle of the polarized light. Compared with a conventional method, real-time measurement of pressure broadening is not affected by detection light intensity, pumping light intensity, air chamber temperature and other external factors, and stable, accurate and rapid measurement of pressure broadening of the atomic air chamber can be achieved under the conditions of large detuning measurement and interference of an experimental environment.

Description

Technical Field

[0001] The invention relates to a photoelastic modulation type atomic gas chamber pressure broadening measurement device and method, belonging to the technical field of optical detection. Background Art

[0002] The traditional method for measuring atomic gas chamber pressure broadening is the light absorption method. The test process requires multiple measurements of different light powers before and after the atomic gas chamber and the calibration voltage of the shielding coil. The atomic gas chamber pressure broadening value (Lorentz) is obtained by Lorentz line fitting. The operation process is complicated and the measurement time is long. The test process is easily affected by laser power and wavelength fluctuations and temperature fluctuations. The complexity of the light absorption method and the external influence during the long measurement process make it unable to meet the current ultra-high sensitivity and extremely weak magnetic field measurement needs. Therefore, a fast and stable atomic gas chamber pressure broadening measurement method is needed. By studying the interaction between light and atoms, it can be known that the ratio of the ellipticity of polarized light to the optical rotation angle is only related to the detection light frequency detuning and D 1 The pressure broadening of the line is related to the intensity of the detection light, the intensity of the pumping light, the temperature of the gas chamber, etc. 4 He and quenching gas N 2 The density corresponds to different D 1 The pressure broadens the line, so the ratio of the optical rotation angle and the ellipticity of the polarized light can be used to measure the alkali metal atoms D in the atomic gas cell. 1 The pressure of the line widens.

[0003] After measuring the ellipticity and optical rotation angle of polarized light, the ratio of the two can be fitted to obtain the alkali metal atom D in the atomic gas chamber. 1 Pressure broadening of the line. Since the optical rotation angle and ellipticity of polarized light can still be measured with high accuracy when the detection light frequency is detuned to a large extent, this method can achieve accurate measurement of the pressure broadening of the atomic gas cell under large detuning measurement conditions. Compared with other measurement methods, this measurement method is fast and simple.

[0004] For example, in an atomic magnetometer, the magnetic field is measured by the interaction between polarized light and an atomic ensemble. The optical rotation angle of polarized light reflects the size of the atomic spin precession signal, and the ellipticity of polarized light reflects important parameters such as the optical pumping rate and the light absorption rate. Highly sensitive measurements of the optical rotation angle and ellipticity are required to reflect the interaction strength between polarized light and the atomic ensemble. The measurement and calibration of pressure broadening are key technologies for magnetic field measurement, and are very important for magnetic field measurement. It can be seen that it is of great significance to use the optical rotation angle and ellipticity to quickly and accurately measure pressure broadening. However, it is difficult for conventional pressure broadening measurement techniques to achieve high-precision and fast measurements under large detuning measurement conditions. Therefore, this pressure broadening measurement technology is of great significance in atomic magnetometers. Summary of the invention

[0005] The technical problem solved by the present invention is: to provide a real-time pressure broadening measurement device and method based on the optical rotation effect, to propose an optical element fine-tuning scheme to reduce the optical element installation error angle, to propose a method for calculating the ratio of ellipticity and optical rotation angle to measure the pressure broadening of the atomic gas chamber, thereby improving the stability, accuracy, rapidity and simplicity of the atomic gas chamber pressure broadening measurement.

[0006] The technical solution of the present invention is as follows: A real-time pressure broadening measurement device based on optical rotation effect comprises a linear polarized light generating module arranged on the detection light incident side of an atomic gas chamber, a polarization characteristic detecting module arranged on the detection light exit side of the atomic gas chamber, and a circular polarized light generating module arranged on the pumping light incident side of the atomic gas chamber, wherein the polarization characteristic detecting module is connected to a pressure broadening measurement module, and the pressure broadening measurement module comprises a phase-locked amplifier respectively connected to an atomic gas chamber pressure broadening solution system, a controller and a photodetector in the polarization characteristic detecting module, wherein the photodetector is connected to a photoelastic modulator through an analyzer in turn, wherein the photoelastic modulator can be selectively connected to the detection light exit side of the atomic gas chamber through or without a second quarter wave plate, wherein the photoelastic modulator is connected to the controller, wherein the modulation frequency of the photoelastic modulator is set by the controller, wherein the controller provides a reference frequency for the phase-locked amplifier, wherein the phase-locked amplifier demodulates the output signal of the photodetector according to the reference frequency, and the atomic gas chamber pressure broadening solution system solves the atomic gas chamber pressure broadening through a single-frequency voltage signal and a double-frequency voltage signal output by the phase-locked amplifier.

[0007] Include the following expressions: , Among them U 1 is the frequency-doubled voltage signal output by the phase-locked amplifier when the detection light passes through the second quarter-wave plate, U 2 is the double frequency voltage signal output by the phase-locked amplifier when the detection light passes through the second quarter-wave plate, U 3 is the frequency-doubled voltage signal output by the lock-in amplifier when the detection light does not pass through the second quarter-wave plate, U 4 is the doubled frequency voltage signal output by the phase-locked amplifier when the detection light does not pass through the second quarter-wave plate, Γ / 2 is the pressure broadening of the atomic gas chamber, and Δv is the frequency detuning of the detection light.

[0008] The atomic gas chamber is located in a heating and magnetic shielding system.

[0009] The circularly polarized light generating module comprises a pumping laser, a pumping laser light intensity control module, a pumping laser beam expansion system, a reflector, a polarizer and a first quarter wave plate which are connected in sequence. After the pumping light passes through the first quarter wave plate, it irradiates the atomic gas chamber from the pumping light incident side of the atomic gas chamber.

[0010] The linear polarized light generating module comprises a detection laser, a detection laser light intensity control module, a detection laser beam expansion system and a polarizer which are connected in sequence. After passing through the polarizer, the detection light irradiates the atomic gas chamber from the detection light incident side of the atomic gas chamber.

[0011] A real-time measurement method for pressure broadening based on optical rotation effect, using the real-time measurement device for pressure broadening based on optical rotation effect, comprises the following steps: Step 1, install the atomic gas chamber, install the linear polarized light generation module, install the polarization characteristic detection module, install the circular polarized light generation module, install the pressure broadening measurement module, rotate the polarizer until the output signal of the photodetector is a minimum value, rotate the second quarter wave plate until the angle between its fast axis and the transmission axis of the polarizer is 0°, rotate the photoelastic modulator until the angle between its fast axis and the transmission axis of the polarizer is 45°, turn on the magnetic shielding system, heat the atomic gas chamber to 200°C and stabilize it for one hour; Step 2, setting the reference frequency of the phase-locked amplifier to the modulation frequency of the photoelastic modulator, so that the phase-locked amplifier outputs the first and second times of the voltage signal of the photodetector, so as to utilize the first-time sensitive ellipticity when the second quarter-wave plate is added to the detection optical path, and the first-time sensitive optical rotation angle when the quarter-wave plate is removed from the detection optical path; Step 3, respectively recording the frequency-doubled voltage output by the phase-locked amplifier after the detection light passes through the atomic gas chamber U 1 and U 3 , double frequency voltage U 2 and U 4 , calculate the ratio of ellipticity and optical rotation angle; Step 4, through the ratio of ellipticity and optical rotation angle, and the calibration of the detuning frequency of the detection light, the pressure broadening expression of the atomic gas chamber is fitted to achieve real-time measurement of pressure broadening based on the optical rotation effect.

[0012] Step 1 includes adjusting the angle between the fast axis of the second quarter wave plate and the transmission axis of the polarizer β QWP The adjustment range varies from -14° to 14°.

[0013] The technical effects of the present invention are as follows: The present invention provides a real-time pressure broadening measurement device and method based on the optical rotation effect, which can respectively measure the polarization light ellipticity and the optical rotation angle by using the phase delay characteristics of the photoelastic modulator, and realize the pressure broadening measurement of the atomic gas chamber according to the ratio relationship between the polarization light ellipticity and the optical rotation angle. Compared with the conventional method, the real-time pressure broadening measurement of the present invention is not affected by other external factors such as the detection light intensity, the pumping light intensity and the gas chamber temperature, and can realize the stable, accurate and rapid measurement of the pressure broadening of the atomic gas chamber under the conditions of large detuning measurement and interference in the experimental environment.

[0014] The characteristics of the present invention are as follows: (1) The present invention uses a single photoelastic modulator to realize polarized light modulation, which fully suppresses the low-frequency technical noise interference in the signal to be measured and effectively realizes noise suppression.

[0015] (2) The optical element installation error angle is reduced by fine-tuning the optical element, and the measurement error is suppressed by using the calibration scheme and the ellipticity and optical rotation angle calculation method. In the present invention, the quarter-wave plate is fine-tuned based on the first and second frequencies of the output voltage signal of the phase-locked amplifier, and a calibration scheme and the ellipticity and optical rotation angle calculation method are proposed to reduce the optical element error, improve the measurement accuracy of the ellipticity and optical rotation angle, and ensure a more accurate measurement of the atomic gas chamber pressure broadening.

[0016] (3) The precise value of pressure broadening is obtained from the experimental data by fitting. The measurement method itself has few sources of error and the fitting method eliminates other errors in the experiment, thus ensuring the accuracy of the measurement results.

[0017] (4) Stable, accurate and rapid measurement of atomic gas chamber pressure broadening can be performed under conditions such as large detuning. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a schematic structural diagram of a real-time pressure broadening measurement device based on optical rotation effect.

[0019] The description of the accompanying drawings is as follows: 1-pumping laser; 2-pumping laser intensity control module; 3-pumping laser beam expansion system; 4-reflector; 5-polarizer; 6-first quarter wave plate; 7-detection laser; 8-detection laser intensity control module; 9-detection laser beam expansion system; 10-polarizer; 11-second quarter wave plate; 12-photoelastic modulator; 13-polarizer; 14-photodetector; 15-phase-locked amplifier; 16-controller; 17-atomic gas chamber pressure broadening solution system. DETAILED DESCRIPTION

[0020] Below is the attached figure ( Figure 1 ) and examples illustrate the present invention.

[0021] Figure 1 Schematic diagram of the structure of a real-time pressure broadening measurement device based on optical rotation effect according to the present invention. Figure 1 As shown, a real-time pressure broadening measurement device based on optical rotation effect includes a linear polarized light generation module arranged on the detection light incident side of the atomic gas chamber, a polarization characteristic detection module arranged on the detection light exit side of the atomic gas chamber, and a circular polarized light generation module arranged on the pumping light incident side of the atomic gas chamber, wherein the polarization characteristic detection module is connected to the pressure broadening measurement module, and the pressure broadening measurement module includes a phase-locked amplifier 15 respectively connected to the atomic gas chamber pressure broadening solution system 17, a controller 16 and a photodetector 14 in the polarization characteristic detection module, wherein the photodetector 14 is connected to the photoelastic modulator 12 in turn through the polarizer 13. The photoelastic modulator 12 can be selectively connected to the detection light output side of the atomic gas chamber through or without the second quarter-wave plate 11. The photoelastic modulator 12 is connected to the controller 16. The modulation frequency of the photoelastic modulator 12 is set by the controller 16. The controller 16 provides a reference frequency for the phase-locked amplifier 15. The phase-locked amplifier 15 demodulates the output signal of the photodetector 14 according to the reference frequency. The atomic gas chamber pressure broadening solution system 17 solves the atomic gas chamber pressure broadening through the first-frequency voltage signal and the second-frequency voltage signal output by the phase-locked amplifier 15.

[0022] Include the following expressions: , in U 1 is the frequency-doubled voltage signal output by the lock-in amplifier 15 when the detection light passes through the second quarter-wave plate 11, U 2 is the double frequency voltage signal output by the lock-in amplifier 15 when the detection light passes through the second quarter wave plate 11, U 3 is the frequency-doubled voltage signal output by the lock-in amplifier 15 when the detection light does not pass through the second quarter-wave plate 11, U 4 is the doubled frequency voltage signal output by the phase-locked amplifier 15 when the detection light does not pass through the second quarter-wave plate 11, Γ / 2 is the pressure broadening of the atomic gas chamber, and Δv is the frequency detuning of the detection light.

[0023] The atomic gas chamber is located in the heating and magnetic shielding system. The circularly polarized light generation module includes a pumping laser 1, a pumping laser light intensity control module 2, a pumping laser beam expansion system 3, a reflector 4, a polarizer 5 and a first quarter wave plate 6 connected in sequence. The pumping light irradiates the atomic gas chamber from the pumping light incident side of the atomic gas chamber after passing through the first quarter wave plate 6. The linearly polarized light generation module includes a detection laser 7, a detection laser light intensity control module 8, a detection laser beam expansion system 9 and a polarizer 10 connected in sequence. The detection light irradiates the atomic gas chamber from the detection light incident side of the atomic gas chamber after passing through the polarizer 10.

[0024] A real-time measurement method for pressure broadening based on optical rotation effect, using the above-mentioned real-time measurement device for pressure broadening based on optical rotation effect, comprising the following steps: Step 1, installing an atomic gas chamber, installing a linear polarized light generation module, installing a polarization characteristic detection module, installing a circular polarized light generation module, installing a pressure broadening measurement module, rotating the polarizer until the output signal of the photodetector is a minimum value, rotating the second quarter wave plate until the angle between its fast axis and the transmission axis of the polarizer is 0°, rotating the photoelastic modulator until the angle between its fast axis and the transmission axis of the polarizer is 45°, turning on the magnetic shielding system, heating the atomic gas chamber to 200°C and stabilizing it for one hour; Step 2, setting the reference frequency of the phase-locked amplifier to the modulation frequency of the photoelastic modulator, so that the phase-locked amplifier outputs the first and second harmonics of the photodetector voltage signal, so as to utilize the first harmonic sensitive ellipticity when the second quarter wave plate is added to the detection light path, and the first harmonic sensitive optical rotation angle when the quarter wave plate is removed from the detection light path; Step 3, respectively recording the first harmonic voltage output by the phase-locked amplifier after the detection light passes through the atomic gas chamber U 1 and U 3 , double frequency voltage U 2 and U 4 , calculate the ratio of ellipticity and optical rotation angle; step 4, through the ratio of ellipticity and optical rotation angle, and calibrate the detuning frequency of the detection light, fit the pressure broadening expression of the atomic gas chamber, and realize the real-time measurement of pressure broadening based on optical rotation effect.

[0025] Step 1 includes adjusting the angle between the fast axis of the second quarter wave plate and the transmission axis of the polarizer β QWP The adjustment range varies from -14° to 14°.

[0026] The present invention relates to a real-time pressure broadening measurement device and method based on the optical rotation effect. The method uses the phase delay characteristics of a photoelastic modulator to respectively measure the ellipticity of polarized light and the optical rotation angle, and then realizes the pressure broadening measurement of an atomic gas chamber according to the ratio relationship between the ellipticity of polarized light and the optical rotation angle. Compared with conventional methods, the measurement method proposed by the present invention is not affected by other external factors such as detection light intensity, pumping light intensity and gas chamber temperature, and can realize stable, accurate and rapid measurement of atomic gas chamber pressure broadening under conditions of large detuning measurement and interference in the experimental environment.

[0027] A real-time pressure broadening measurement device based on optical rotation effect, the optical rotation effect includes circular birefringence effect and circular dichroism effect, and can realize rapid and anti-interference measurement of atomic gas chamber pressure broadening, the device comprises a pumping laser, a pumping laser light intensity control module, a pumping laser beam expansion system, a reflector, a polarizer, a quarter wave plate, a detection laser, a detection laser beam expansion system, a detection laser light intensity control module, a quarter wave plate, a photoelastic modulator, a photodetector, a phase-locked amplifier, a controller, an atomic gas chamber pressure broadening solution system, an atomic gas chamber, and a heating and magnetic shielding system; the pumping laser, the pumping laser light intensity control module, the pumping laser beam expansion system, the reflector, the polarizer and the quarter wave plate constitute a standard parameter pumping polarized light generation module; the polarization state of the standard parameter pumping polarized light changes after interacting with the atomic gas chamber; the detection laser The optical device, the detection laser beam expansion system, the detection laser intensity control module and the polarizer constitute a standard parameter detection polarized light generation module; in the atomic gas chamber and the heating and magnetic shielding system, the atomic gas chamber is heated to 200°C and stabilized for one hour to fully polarize the atoms in the gas chamber, and the magnetic shielding shields the external magnetic field to place the atomic gas chamber in an extremely weak magnetic environment; the polarization state of the standard parameter detection polarized light changes after the interaction with the atomic gas chamber; the detection light carries the circular birefringence effect and circular dichroism effect information of the interaction between light and atoms, based on which the pressure broadening of the atomic gas chamber is measured, wherein the information of the circular birefringence effect is reflected by the optical rotation angle parameter, and the information of the circular dichroism effect is reflected by the ellipticity parameter; the detection light enters the photodetector after passing through the quarter wave plate and the photoelastic modulator, and the ellipticity information is realized by using the phase delay characteristics of the photoelastic modulator. The detection light passes through the photoelastic modulator and then enters the photodetector, and the phase delay characteristic of the photoelastic modulator is used to realize the optical rotation angle information The modulation frequency of the photoelastic modulator is set by the photoelastic modulator controller, and the photoelastic modulator controller provides a reference frequency for the phase-locked amplifier, and the phase-locked amplifier demodulates the signal according to the reference frequency, and solves the ratio of the calibration results of the ellipticity and the optical rotation angle measurement when stable through the atomic gas chamber pressure broadening solution system. , the precise value of the pressure broadening of the atomic gas chamber can be quickly solved.

[0028] The fast axis of the quarter wave plate and the transmission axis of the polarizer have an included angle of 0°, and the fast axis of the photoelastic modulator and the transmission axis of the polarizer have an included angle of 45°.

[0029] The atomic gas cell pressure broadening measurement is realized by using an atomic gas cell pressure broadening measurement device, comprising the following steps: a. Install the atomic gas chamber and the heating and magnetic shielding system; install the pumping laser, the pumping laser light intensity control module, the pumping laser beam expansion system, the reflector, the polarizer and the quarter-wave plate; install the detection laser, the detection laser beam expansion system, the detection laser light intensity control module, the polarizer and the photodetector, and rotate the polarizer until the output of the photodetector is a minimum. Install the quarter-wave plate and the photoelastic modulator, rotate the quarter-wave plate until the angle between its fast axis and the polarizer transmission axis is 0°, and rotate the photoelastic modulator until the angle between its fast axis and the polarizer transmission axis is 45°; turn on the magnetic shielding system, heat the atomic gas chamber to 200°C and stabilize it for one hour; b. setting the reference frequency of the lock-in amplifier to the modulation frequency of the photoelastic modulator so that the lock-in amplifier outputs the first and second times of the voltage signal of the photodetector; c. Record the one-fold voltage output by the lock-in amplifier U 1 and double frequency voltage U 2 After removing the half wave plate, repeat the fine adjustment operation of the quarter wave plate in step a, and repeat the steps described in step b to perform the ellipticity signal one-fold frequency voltage U 3 and double frequency voltage U 4 Measurement of d. Record the frequency-doubled voltage output by the phase-locked amplifier after passing through the atomic gas chamber U 1 and U 3 , double frequency voltage U 2 and U 4 , solve the ratio of ellipticity and optical rotation angle; e. Calculate the ratio of ellipticity and optical rotation angle The frequency detuning amount Δv of the detection light is calibrated, and then the pressure broadening value is obtained through fitting.

[0030] In step b, the quarter wave plate is finely adjusted to a minimum value of the first harmonic frequency of the demodulated signal to achieve fine adjustment of the quarter wave plate.

[0031] In step c, the quarter wave plate is rotated so that the angle between its fast axis and the transmission axis of the polarizer is in the range of -14° to 14°.

[0032] In step e, the experimentally measured single-frequency and double-frequency signals and the calibrated detection light frequency detuning amount are used as independent variables, the pressure broadening value is used as the dependent variable, and the pressure broadening value is used as the proportional scale coefficient for fitting.

[0033] The present invention discloses a real-time pressure broadening measurement device based on the optical rotation effect, the core of the optical path includes a quarter wave plate, a photoelastic modulator, a polarizer and a photodetector. The quarter wave plate and the photoelastic modulator realize polarized light modulation under a specific phase, and the modulated detection light enters the photodetector after passing through the polarizer. The circuit includes a phase-locked amplifier, a controller and an atomic gas chamber pressure broadening solution system, and the reference frequency of the phase-locked amplifier is provided by the photoelastic modulator controller. The phase-locked amplifier demodulates the light intensity signal, and the ratio information of the optical rotation angle and ellipticity of the polarized light can be obtained by demodulating the first and second harmonics of the signal when a quarter wave plate is present and when no quarter wave plate is present in the optical path.

[0034] The optical rotation angle is obtained by solving the density matrix method α and ellipticity e The expression can be expressed as: , Where n is the number density of alkali metal atoms in the atomic chamber, l is the propagation length of the detection light in the alkali metal atomic ensemble in the chamber, and r e is the classical electron radius, c is the classical light speed, S x is the polarizability of the alkali metal atom ensemble in the gas chamber in the x-axis direction, f D1 Alkali metal atom D 1 Line oscillation intensity factor, is the complex Lorentz line shape, represents the part of the Lorentz line shape, represents the imaginary part of the Lorentz line shape.

[0035] From equations (1) and (2), we can see that the ratio of ellipticity to optical rotation angle is expressed as: , Where Γ / 2 is the pressure broadening of the alkali metal atoms in the gas chamber, and Δv is the frequency detuning of the detection light.

[0036] From formula (3), we can see that the ratio of ellipticity to optical rotation angle is only related to the pressure broadening of alkali metal atoms and the detuning of the detection light frequency, and has nothing to do with any other external factors. If any two of the three terms, the ratio of ellipticity to optical rotation angle, the pressure broadening of alkali metal atoms, and the detuning of the detection light frequency, are known, the remaining unknown terms can be obtained. Therefore, we can calibrate the detuning of the detection light frequency with the experimentally measured optical rotation angle and ellipticity, and then obtain the pressure broadening of alkali metal atoms in the atomic gas chamber.

[0037] The theory of this method is accurate and complete, and there are no other error terms in theory. It is an in-situ measurement method. This method is simple and easy to implement experimentally, and the measurement process takes very little time, which reduces the impact of other experimental methods on subsequent experiments. At the same time, the error source of this method is also small in the experiment.

[0038] The experimental principle of this method is that the optical rotation angle obtained after passing through the atomic gas chamber is α , the ellipticity is e The Jones vector E of the elliptically polarized light is 0 ' can be expressed as: , Among them, E 0 is the amplitude of the elliptically polarized light, i is the imaginary unit, the Jones matrix of the quarter-wave plate G 1 / 4 It can be expressed as: , The phase delay δ of the photoelastic modulator can be expressed as: , in, d 0 is the peak phase delay of the photoelastic modulator, ω is the modulation frequency of the photoelastic modulator, t is the modulation time of the photoelastic modulator, d s is the static phase delay of the photoelastic modulator. Therefore, the Jones matrix of the photoelastic modulator is G PEM It can be expressed as: , in, i PEM is the installation error angle of the photoelastic modulator. The Jones vector of the light emitted by the photoelastic modulator can be expressed as E= G PEM G 1 / 4 E 0 ', then the light intensity I received by the photodetector is: , Among them, E * represents the complex conjugate of the Jones vector of the light emitted by the photoelastic modulator. d s and i PEM Finally, when there is a quarter-wave plate in the detection light path, the photodetector converts the received light intensity I into an electrical signal, which is then converted into a double frequency voltage signal output by the phase-locked amplifier. U 1 and double frequency voltage signal U 2 for: , in, or is a coefficient related to the amplification of the balanced photodetector and the lock-in amplifier, J 1 ( d 0 )and J 2 ( d 0 ) are first-order and second-order Bessel functions.

[0039] Similarly, when there is no quarter-wave plate in the detection optical path, the doubled frequency voltage signal U 3 and double frequency voltage signal U 4 It can be expressed as: , It is easy to know that when the half wave plate exists in the detection optical path, the frequency is doubled. U 1 Sensitive ellipticity e , when the half wave plate does not exist in the detection light path, the frequency is doubled U 3 Sensitive optical rotation angle α .

[0040] It can be seen that the experimental fitting formula for experimentally measuring the pressure broadening of the atomic gas chamber can be expressed as: , Among them, the pressure broadening of alkali metal atoms in the gas chamber Γ / 2 is fitted as the dependent variable of the fitting function, and the rest are experimental measurement data, which serve as the independent variables of the fitting function.

[0041] like Figure 1As shown, the present invention is a real-time pressure broadening measurement device based on the optical rotation effect, comprising: a polarized light generation module, an atomic gas chamber, a polarization characteristic detection module and a pressure broadening measurement module. The polarized light generation module is composed of a pumping laser 1, a pumping laser light intensity control module 2, a pumping laser beam expansion system 3, a reflector 4, a polarizer 5, and a quarter wave plate 6. The polarization state of the generated polarized light changes after interacting with the atomic gas chamber. The polarization characteristic detection module is composed of a detection laser 7, a detection laser light intensity control module 8, a detection laser beam expansion system 9, a polarizer 10, a quarter wave plate 11, a photoelastic modulator 12, an analyzer 13, and a photodetector 14. The pressure broadening measurement module is composed of a phase-locked amplifier 15, a controller 16, and an atomic gas chamber pressure broadening solution system 17. The device is described as follows. The pumping laser 1 emits laser light, and after passing through the pumping laser light intensity control module 2, the pumping laser beam expansion system 3, the reflector 4, the polarizer 5, and the quarter wave plate 6, circularly polarized light is generated. The polarization characteristics of the circularly polarized light change after interacting with the atomic gas cell.

[0042] The detection laser 7 emits a laser, and generates linearly polarized light after passing through the detection laser intensity control module 8, the detection laser beam expansion system 9 and the polarizer 10. The polarization characteristics of the linearly polarized light change after interacting with the atomic gas chamber. When the polarized light passes through the quarter-wave plate 11, it is converted into modulated polarized light by the photoelastic modulator 12. The modulated polarized light passes through the analyzer 13 and directly enters the photodetector 14, and then the photodetector 14 outputs a voltage signal. The phase-locked amplifier 15, whose reference frequency is the modulation frequency of the photoelastic modulator, extracts the first-harmonic frequency and second-harmonic frequency components in the voltage signal, and then processes them through the photoelastic modulator controller 16. The photoelastic modulator controller 16 is used to set the modulation frequency of the photoelastic modulator on the one hand, and to provide a reference frequency for the phase-locked amplifier on the other hand.

[0043] The fast axis of the quarter wave plate and the transmission axis of the polarizer have an included angle of 0°, and the fast axis of the photoelastic modulator and the transmission axis of the polarizer have an included angle of 45°.

[0044] The specific implementation process of the present invention is as follows: a. Install the pumping laser, pumping laser intensity control module, pumping laser beam expansion system, reflector, polarizer, quarter wave plate, detection laser, detection laser intensity control module, detection laser beam expansion system, polarizer, quarter wave plate, photoelastic modulator, analyzer, photodetector, lock-in amplifier, controller, atomic gas chamber pressure broadening solution system, and first block the reflected light of the reflector, and adjust the polarizer until the output of the photodetector is a minimum. The spot size must be determined by the size of the optical element and the detection area of ​​the photodetector. According to the fast axis position marked on the device, rotate the quarter wave plate until the angle between its fast axis and the polarizer transmission axis is 0°, and rotate the photoelastic modulator until the angle between its fast axis and the polarizer transmission axis is 45°. It should be noted that the laser wavelength of the laser needs to match the optical element, especially to be consistent with the setting of the photoelastic modulator.

[0045] b. Set the reference frequency of the phase-locked amplifier to the modulation frequency of the photoelastic modulator, so that the phase-locked amplifier outputs the first and second frequencies of the voltage signal of the photodetector. Fine-tune the quarter-wave plate until the first frequency is the minimum value to achieve fine adjustment of the quarter-wave plate. Since the presence of the quarter-wave plate in the detection optical path determines the measurement method of the optical rotation angle and ellipticity of polarized light, it needs to be finely adjusted to reduce the measurement error caused by optical components.

[0046] c. Record the frequency-doubled voltage output by the phase-locked amplifier when there is a quarter-wave plate in the detection light path and when there is no quarter-wave plate after the detection light passes through the atomic gas chamber. U 1 and U 3 , double frequency voltage U 2 and U 4 , solve for the ratio of the ellipticity and the optical rotation angle caused by the atomic gas cell.

[0047] d. The detuning amount of the detection light frequency is calibrated by the ratio of the calculated ellipticity and the optical rotation angle. When the system is stable, the pressure broadening of the atomic gas chamber can be obtained by fitting the ratio of the calculated ellipticity and the optical rotation angle.

[0048] At this point, the pressure broadening measurement of the atomic gas chamber has been realized.

[0049] The present invention realizes the measurement of atomic gas chamber pressure broadening based on the functional relationship between the output voltage first harmonic frequency, second harmonic frequency and optical rotation angle, ellipticity, and the calibration of the detection light frequency detuning amount. An optical element fine-tuning scheme is proposed to reduce the optical element installation error angle, and an optical rotation angle and ellipticity solution method is proposed to reduce the error of pressure broadening measurement and improve the measurement accuracy. The application of the modulation detection method improves the sensitivity of the device. The applied fitting method eliminates other error factors in the experimental process. Rapid and accurate measurement of atomic gas chamber pressure broadening under large detuning conditions is achieved.

[0050] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A real-time measurement device for pressure broadening based on optical rotation effect, characterized in that: The invention comprises a linear polarized light generating module arranged on the detection light incident side of the atomic gas chamber, a polarization characteristic detecting module arranged on the detection light exiting side of the atomic gas chamber, and a circular polarized light generating module arranged on the pumping light incident side of the atomic gas chamber, wherein the polarization characteristic detecting module is connected to a pressure broadening measuring module, and the pressure broadening measuring module comprises a phase-locked amplifier respectively connected to an atomic gas chamber pressure broadening solution system, a controller and a photodetector in the polarization characteristic detecting module, wherein the photodetector is connected to a photoelastic modulator through an analyzer in turn, and the photoelastic modulator can be selectively connected to the detection light exiting side of the atomic gas chamber through or without a second quarter wave plate, the photoelastic modulator is connected to the controller, and the modulation frequency of the photoelastic modulator is set by the controller, the controller provides a reference frequency for the phase-locked amplifier, and the phase-locked amplifier demodulates the output signal of the photodetector according to the reference frequency, and the atomic gas chamber pressure broadening solution system solves the atomic gas chamber pressure broadening through the first-time voltage signal and the second-time voltage signal output by the phase-locked amplifier.

2. The real-time pressure broadening measurement device based on optical rotation effect according to claim 1 is characterized in that: Include the following expressions: ， Among them, U1 is the first-frequency voltage signal output by the phase-locked amplifier when the detection light passes through the second quarter-wave plate, U2 is the second-frequency voltage signal output by the phase-locked amplifier when the detection light passes through the second quarter-wave plate, U3 is the first-frequency voltage signal output by the phase-locked amplifier when the detection light does not pass through the second quarter-wave plate, U4 is the second-frequency voltage signal output by the phase-locked amplifier when the detection light does not pass through the second quarter-wave plate, Γ / 2 is the pressure broadening of the atomic gas chamber, and Δv is the frequency detuning of the detection light.

3. The real-time pressure broadening measurement device based on optical rotation effect according to claim 1 is characterized in that: The atomic gas chamber is located in a heating and magnetic shielding system.

4. The real-time pressure broadening measurement device based on optical rotation effect according to claim 1, characterized in that: The circularly polarized light generating module comprises a pumping laser, a pumping laser light intensity control module, a pumping laser beam expansion system, a reflector, a polarizer and a first quarter wave plate which are connected in sequence. After the pumping light passes through the first quarter wave plate, it irradiates the atomic gas chamber from the pumping light incident side of the atomic gas chamber.

5. The real-time pressure broadening measurement device based on optical rotation effect according to claim 1, characterized in that: The linear polarized light generating module comprises a detection laser, a detection laser light intensity control module, a detection laser beam expansion system and a polarizer which are connected in sequence. After passing through the polarizer, the detection light irradiates the atomic gas chamber from the detection light incident side of the atomic gas chamber.

6. A real-time measurement method of pressure broadening based on optical rotation effect, characterized in that: The real-time pressure broadening measurement device based on the optical rotation effect according to any one of claims 1 to 5 comprises the following steps: Step 1, install the atomic gas chamber, install the linear polarized light generation module, install the polarization characteristic detection module, install the circular polarized light generation module, install the pressure broadening measurement module, rotate the polarizer until the output signal of the photodetector is a minimum value, rotate the second quarter wave plate until the angle between its fast axis and the transmission axis of the polarizer is 0°, rotate the photoelastic modulator until the angle between its fast axis and the transmission axis of the polarizer is 45°, turn on the magnetic shielding system, heat the atomic gas chamber to 200°C and stabilize it for one hour; Step 2, setting the reference frequency of the phase-locked amplifier to the modulation frequency of the photoelastic modulator, so that the phase-locked amplifier outputs the first and second times of the voltage signal of the photodetector, so as to utilize the first-time sensitive ellipticity when the second quarter-wave plate is added to the detection optical path, and the first-time sensitive optical rotation angle when the quarter-wave plate is removed from the detection optical path; Step 3, respectively recording the frequency-doubled voltage output by the phase-locked amplifier after the detection light passes through the atomic gas chamber U 1 and U 3. Double frequency voltage U 2 and U 4. Calculate the ratio of ellipticity to optical rotation angle; Step 4, through the ratio of ellipticity and optical rotation angle, and the calibration of the detuning frequency of the detection light, the pressure broadening expression of the atomic gas chamber is fitted to achieve real-time measurement of pressure broadening based on the optical rotation effect.

7. The real-time measurement method of pressure broadening based on optical rotation effect according to claim 6, characterized in that: Step 1 includes adjusting the angle between the fast axis of the second quarter wave plate and the transmission axis of the polarizer β QWP The adjustment range varies from -14° to 14°.

Images