A device for realizing frequency and power synchronous stability in laser sweep process

Abstract

The application discloses a device for realizing frequency and power synchronous stabilization in a laser sweep frequency process, and belongs to the field of light source regulation in precise spectrum measurement technology.The device comprises a reference light source frequency stabilization module, a laser beat frequency sweep frequency module and a probe light power stabilization module.The reference light source frequency stabilization module locks the reference light output by a narrow linewidth laser to an atomic absorption peak in a gas chamber, and uses the reference light as a reference standard frequency in the sweep frequency process.The laser beat frequency sweep frequency module realizes probe light frequency stabilization by means of beat frequency of the probe light and the reference light and by applying feedback control, realizes probe light sweep frequency function by means of segmented sweep and regulation of beat frequency values of the two beams of light, and extracts part of the probe light for power stabilization.The device realizes the sweep frequency process with accurate and controllable sweep frequency range and interval by the cooperation of the three modules of the reference light source frequency stabilization module, the laser beat frequency sweep frequency module and the probe light power stabilization module, and guarantees the synchronous stabilization of the frequency and the power in the sweep frequency process.

Description

Technical Field

[0001] This invention belongs to the field of light source control in precision spectral measurement technology, and involves fields such as optical atomic clocks, gas concentration measurement, and Doppler broadening temperature measurement. Specifically, it relates to an alkali metal atomic absorption spectrum sweeping device for precision measurement of atomic absorption spectra. Background Technology

[0002] The interaction between atoms and lasers contains rich physical information. Tuning the laser within a certain range can yield atomic absorption spectra. Analysis of these spectra enables various applications, including atomic clocks, gas concentration measurement, and Doppler thermometry. In these applications, laser frequency tuning, or frequency sweeping, is a necessary step for achieving precise spectral measurements. For example, in Doppler broadening thermometry, the laser frequency and power must remain stable at each detection frequency point during the frequency sweep, and the interval between adjacent frequency points (the sweep interval) must be equal. Frequency and power instability during the sweep process, as well as the unknown nature of the sweep interval, significantly impact the accuracy of Doppler broadening temperature measurements.

[0003] Currently, laser frequency sweeping is achieved through several methods. First, direct current tuning: This involves directly injecting current into the laser to control the carrier concentration in the active region, thereby shifting the output optical frequency. This method is simple and has a fast response time, with a tunable range of tens of GHz without mode tuning. However, the initial and final scan frequencies and the sweep interval are unknown. This method forms the basis of many other frequency sweeping methods. Second, temperature tuning: Temperature changes also cause the carrier concentration in the active region of the laser to shift the optical frequency. The temperature tuning range is even larger, reaching hundreds of GHz, but the response time is slow, and precise control of the frequency and sweep interval is not possible. Third, using an electro-optic modulator: This involves constructing an optical path structure based on a Mach-Zehnder interferometer and changing the input frequency of the RF source to achieve optical frequency transfer. This method requires high precision and stability of the devices. Fourth, frequency sweeping based on an external reference source: This typically uses an optical frequency comb and an FP cavity as standard reference sources. The probe light is swept by beating the reference source and the probe light. This method achieves high stability of the optical frequency during the sweep process and allows for precise sweep intervals.

[0004] Compared to the methods mentioned above, using an external reference source offers numerous advantages, including precise control of the frequency sweeping source. However, commonly used external reference sources, such as optical frequency combs, FP cavities, and wavelength meters, are typically bulky, complex to use, and expensive, making optical path integration difficult and limiting their development and application in the field of laser frequency sweeping. FP cavities generate multiple transmission peaks based on the principle of interference. Frequency sweeping methods based on FP cavities lock the reference light onto a specific characteristic peak, and then achieve frequency sweeping through the beat frequency difference between the reference and probe light. Frequency sweeping methods based on optical frequency combs beat the probe light with the comb, achieving optical frequency sweeping by locking the frequency difference between the probe light and the two comb teeth. The absorption peak of alkali metal atoms in the gas cell has a characteristic frequency that can be used as a reference frequency. This invention uses the gas cell as an external reference source for optical frequency sweeping, which is more conducive to system integration. Summary of the Invention

[0005] To address the issues of precise control of sweeping light source parameters and optical path integration, the main objective of this invention is to provide a device for achieving synchronous stabilization of frequency and power during laser sweeping, enabling precise and controllable laser sweeping and ensuring synchronous stabilization of frequency and power at a single frequency test point during the sweeping process.

[0006] The present invention is achieved through the following technical solution.

[0007] The present invention discloses a device for stabilizing frequency and power during laser frequency sweeping, comprising a reference light source frequency stabilization module, a laser frequency sweeping module, and a probe light power stabilization module.

[0008] The reference light source frequency stabilization module includes a reference light source laser, an optical isolator, a half-wave plate, a polarizing beam splitter, a beam splitter, a gas cell, a beam splitter, a reflector, a photodetector, a mixer, a phase adjuster, a low-pass filter, a PI controller, an adder, a phase adjuster, a signal generator, and a triangular wave sweep frequency generator.

[0009] The reference light is locked onto the absorption peak of atoms in the gas cell, thereby stabilizing the frequency of the reference light. A triangular wave generated by a triangular wave sweeper is superimposed on the reference laser source with a modulation signal generated by a signal generator. The output light passes through an optical isolator, a half-wave plate, a polarizing beam splitter, and a beam splitter for reflecting and transmitting light, splitting the optical path into two. One path illuminates a photodetector, and its output signal is mixed with the modulation signal generated by the signal generator by a mixer. The laser light is then demodulated by a low-pass filter. The demodulated electrical signal is input to a PI controller to generate a feedback signal. This feedback control locks the reference light onto the absorption peak of alkali metal atoms, achieving frequency stabilization of the reference light source. Preferably, the reflection-to-transmission ratio of the beam splitter is 3:7.

[0010] The laser frequency sweeping module includes a probe light source laser, an optical isolator, a half-wave plate, a polarizing beam splitter prism, a frequency-stabilized reference beam, a reflector, a beam combiner prism, a GlanTeller prism, a lens, a high-speed detector, a filter amplifier circuit, a frequency divider, a signal shaping unit, a digital frequency measurement unit, a host computer, and a high-precision voltage source.

[0011] The probe light output from the laser source is split into two beams after passing through an optical isolator, a half-wave plate, and a polarizing beam splitter. One beam is combined with the reference light source through a beam combiner prism. The combined beam passes through a Glan Taylor prism and a lens before illuminating the detector, achieving frequency matching between the probe light and the reference light. The beat frequency signal from the photodetector undergoes signal processing, including filtering and shaping circuitry, a frequency divider, and signal shaping, transforming it into a square wave signal which is measured by a digital frequency measurement unit. The measured beat frequency signal is then transmitted to the host computer. The host computer's LabVIEW program includes a digital PID module. The preset value and the actual measured beat frequency value are input into the digital PID module to obtain a feedback voltage. The program controls the output voltage of a high-precision voltage source to control the movement and stabilization of the probe light frequency.

[0012] To achieve applications such as atomic or molecular sensing with the same composition as the gas cell, frequency sweeping is required to generate an absorption spectrum. The frequency sweeping process is based on the gas cell absorption peak of the reference optical path as a reference. However, since the reference source absorption peak is located within the test spectrum of the probe light, the beat frequency signal during the frequency sweeping process cannot reflect the relative position of the probe light and the reference light, which is a challenge in achieving frequency sweeping. For DBR semiconductor lasers, increasing the injection current results in a red shift of the output light frequency, while decreasing the injection current results in a left shift of the output light frequency. An external adder circuit, i.e., an external modulation voltage circuit, is designed to map the external modulation voltage to the DBR laser injection current. Increasing the voltage at the modulation port increases the injection current, thus decreasing the light frequency shift; conversely, decreasing the voltage at the modulation port results in a blue shift of the light frequency. Based on this principle, the relative position of the reference light and the probe light is determined by segmented frequency sweeping, dividing the frequency sweep range into three segments: below the reference frequency, equal to the reference frequency, and above the reference frequency. The frequency sweeping process is implemented as follows.

[0013] The method for implementing the frequency sweep function includes the following steps:

[0014] Step 1: The host computer LabVIEW program generates a sweep frequency array based on the set sweep frequency range and sweep frequency interval, and divides the sweep frequency array into a low frequency array, a reference frequency array, and a high frequency array;

[0015] Step 2: Lock the laser output from the probe light source laser onto the reference light. At this time, the beat frequency value is zero, and obtain the feedback voltage value when it is stable.

[0016] Step 3: Low-frequency sweep; First, set the feedback voltage value obtained in Step 2 as the lower limit of the output voltage of the digital PID module in the LabVIEW program on the host computer; Second, compare the first value in the low-frequency array with the beat frequency value, and stabilize the beat frequency value through feedback control using the digital PID module and high-precision voltage source in the LabVIEW program on the host computer, thus completing the frequency stabilization of the first point in the low-frequency array; Subsequently, with the lower limit of the output voltage of the digital PID module unchanged, the same feedback control is repeated in sequence according to the order in the low-frequency array to stabilize the frequency of each point in the low-frequency array until the last point in the low-frequency array is completed, thus achieving low-frequency sweep;

[0017] Step 4: Stabilize the reference frequency point; lock the probe light source onto the reference light, i.e., the beat frequency is zero, record the feedback voltage value when it is stable, and use it as the upper limit of the output of the digital PID module in the high-frequency scanning segment;

[0018] Step 5: High-frequency band sweep is the same as low-frequency band sweep in Step 3, except that the feedback voltage value obtained in Step 4 is set as the upper limit of the output voltage of the digital PID module in the LabVIEW program on the host computer; the high-frequency band sweep is achieved by feedback control between the digital PID module on the host computer and the hardware module to stabilize the frequency from the first to the last point in the high-frequency array.

[0019] By splicing together the three processes of below the reference frequency, equal to the reference frequency, and above the reference frequency, a frequency sweep function covering the atomic absorption spectrum of alkali metals can be achieved, and the frequency stability of a single measurement point can be guaranteed.

[0020] The probe light power stabilization module is used to stabilize the power of the probe light, thereby improving the signal-to-noise ratio of the measurement signal. The probe light power stabilization module includes a lens, an acousto-optic modulator, a polarizing beam splitter, a photodetector, a PI controller, an RF source, and a power amplifier.

[0021] The probe light is reduced to a laser beam through two lenses, and then split into two beams after passing through an acousto-optic modulator and a polarizing beam splitter. One beam is used for subsequent detection, and the other is used for laser power stabilization. The electrical signal from the photodetector is used to achieve closed-loop feedback control of the laser power through a PI controller, an RF source, and a power amplifier.

[0022] The absorption spectrum data used for sensing measurements is obtained through the following process: the frequency sweep process and power stabilization are performed simultaneously. After the host computer LabVIEW program determines that a single frequency point is stable during the frequency sweep process, it enters the sensing measurement module based on the absorption spectrum to perform data testing. The entire absorption spectrum is obtained after the frequency sweep process is completed.

[0023] Preferably, the beat frequency signal is processed by a filtering and shaping circuit, a signal frequency division circuit, and a signal shaping circuit module to convert it into a low-frequency square wave signal. This signal is then transmitted to a digital frequency measurement unit to obtain the beat frequency value and uploaded to the host computer LabVIEW program for processing.

[0024] Preferably, the laser beat frequency sweep module completes the optical frequency sweep process based on a gas chamber. By setting the sweep frequency range and sweep frequency interval in the LabVIEW program on the host computer, a sweep frequency array, also known as a beat frequency array, is generated. The sweep frequency data is divided into a low-frequency array, a reference frequency array, and a high-frequency array, and the sweep frequency is performed in this order during the experiment. The preset value in the sweep frequency array is compared with the beat frequency value obtained by the digital frequency measurement unit and transmitted to the digital PID module in the LabVIEW program. Through feedback control, the beat frequency value is made consistent with the preset value. This process is repeated until the sweep frequency of the three arrays is completed, and finally the optical frequency scan within the preset range is completed, ensuring the frequency stability and power stability at each optical frequency point.

[0025] Beneficial effects:

[0026] 1. This invention discloses a device for synchronizing and stabilizing frequency and power during laser frequency sweeping. It uses a gas cell as a reference source to achieve optical frequency sweeping, enabling dual stabilization of both the probe light frequency and power during the sweeping process. Compared to reference sources such as optical frequency combs and wavelength meters, the gas cell-based optical frequency sweeping method is simple, low-cost, and facilitates the miniaturization and integration of the optical path.

[0027] 2. This invention discloses a device for stabilizing frequency and power during laser frequency sweeping. The optical frequency sweeping range and optical frequency sweeping interval can be precisely controlled according to actual needs. In addition to achieving equidistant linear frequency sweeping, non-equidistant linear frequency sweeping can also be achieved through feedback control via a LabVIEW program on a host computer, enabling precise measurement of local absorption spectrum regions.

[0028] 3. The frequency sweep range is usually limited by the bandwidth of the beat frequency detector. This invention discloses a device for stabilizing frequency and power during laser frequency sweeping. The frequency sweeping function is achieved by adjusting the beat frequency signal between the detector light source and the reference optical path's alkali metal atom absorption peak. When probing the absorption spectrum of the alkali metal atom gas cell using the detector optical path, the bandwidth of the photodetector is not required to be greater than the frequency sweep range; rather, it is less than or even half of it. That is, a smaller bandwidth detector can achieve a larger frequency sweep range, reducing the bandwidth requirements of the detector during laser frequency sweeping.

[0029] 4. The present invention discloses a device for stabilizing frequency and power during laser frequency sweeping. The frequency sweeping method based on gas cells is easier to integrate optical paths than the frequency sweeping method based on FP cavities and optical frequency combs, and can reduce the bandwidth requirements of the detector for the frequency sweeping range. Attached Figure Description

[0030] Figure 1 A device for stabilizing frequency and power during laser frequency sweeping;

[0031] Among them, 1-reference light source frequency stabilization module, 2-laser frequency sweeping module, 3-probe light power stabilization module;

[0032] Figure 2 It is the reference light source frequency stabilization module in the device of this invention.

[0033] Among them, 100-reference light source laser, 101-optical isolator, 102-half-wave plate, 103-polarizing beam splitter, 104-beam splitter, 105-gas cell, 106-beam splitter, 107-reflector, 108-reflector, 109-photodetector, 110-mixer, 111-phase adjuster, 112-low-pass filter, 113-PI controller, 114-adder, 115-signal generator, and 116-triangular wave sweep frequency generator.

[0034] Figure 3 It is the laser frequency sweeping module in the device of this invention.

[0035] Among them, 200-detection light source laser, 201-optical isolator, 202-half-wave plate, 203-polarizing beam splitter prism, 204-frequency stabilized reference light, 205-reflector, 206-beam combiner prism, 207-Glan Taylor prism, 208-lens, 209-high-speed detector, 210-filtering and shaping circuit, 211-frequency divider, 212-signal shaping, 213-digital frequency measurement unit, 214-host computer, and 215-high-precision voltage source.

[0036] Figure 4 It is the detection light power stabilization module in the device of this invention.

[0037] Among them, 301-lens, 302-lens, 303-acoustic-optic modulator, 304-polarizing beam splitter, 305-photodetector, 306-PI controller, 307-RF source, and 308-power amplifier. Detailed Implementation

[0038] The invention will now be described in detail with reference to the accompanying drawings and examples:

[0039] Example 1:

[0040] This embodiment describes a frequency sweep aimed at obtaining the D1 line of the cesium atomic absorption spectrum. The sweep range is 7 GHz, which means scanning 3 GHz below the reference frequency and 4 GHz above the reference frequency, with a sweep interval of 20 MHz.

[0041] like Figure 1As shown in the figure, this embodiment discloses a synchronization device that can stabilize frequency and power during laser frequency sweeping, including: a reference light source frequency stabilization module 1, a laser frequency sweeping module 2, and a probe light power stabilization module 3.

[0042] The reference light source frequency stabilization module 1 is used to lock the reference light source onto the absorption peak of the D1 line of cesium atoms to form a frequency-stabilized reference light source. The laser beat frequency sweep module 2 performs beat frequency processing on the probe light source and the frequency-stabilized reference light source to realize the frequency sweep of the probe light and the single-point frequency stabilization during the frequency sweep process. The probe light then passes through the probe light power stabilization module 3 to achieve power stabilization. The combination of the three modules realizes the frequency sweep function and the synchronous stabilization of frequency and power during the frequency sweep process.

[0043] The purpose of the reference light source frequency stabilization module 1 is to provide a standard reference source for the swept frequency light source.

[0044] like Figure 2 As shown, the reference light source frequency stabilization module includes: a reference light source laser 100, an optical isolator 101, a half-wave plate 102, a polarizing beam splitter 103, a beam splitter 104, a gas cell 105, a beam splitter 106, a reflector 107, a reflector 108, a photodetector 109, a mixer 110, a phase adjuster 111, a low-pass filter 112, a PI controller 113, an adder 114, a signal generator 115, and a triangular wave sweep frequency generator 116.

[0045] The reference laser 100 is a semiconductor laser with a wide tuning range, covering the D1 absorption line of cesium atoms, and has an output power of 30mW. The triangular wave sweep signal generated by the triangular wave sweeper 116, along with the modulation signal generated by the signal generator 115, is superimposed by the adder 114 to modulate the light source. An optical isolator 101 prevents backlight reflection, and a half-wave plate 102 and a polarizing beam splitter 103 are used to adjust the reference light power used for beat frequency. Two beam splitters 104 and 106 with a 7:3 transmittance ratio, along with two mirrors 107 and 108, split the beam passing through the cesium atom gas cell 105 into two beams with overlapping paths but opposite propagation directions to form a saturated absorption spectrum. The photodetector 109 converts the received optical signal into an electrical signal. The modulated signal is then mixed by the phase adjuster 111 and the mixer 110. The high-frequency signal is filtered out by the low-pass filter 112 to generate an error signal. The PI controller 113 then performs feedback control on the reference light source, thereby stabilizing the frequency of the reference light source.

[0046] The purpose of the laser frequency sweep module 2 is to realize the frequency sweep function and maintain the frequency stability of a single measurement point during the frequency sweep process.

[0047] like Figure 3As shown, the laser frequency sweeping module includes: a laser source 200, an optical isolator 201, a half-wave plate 202, a polarizing beam splitter 203, a frequency-stabilized reference beam 204, a reflector 205, a beam combiner 206, a Glan Taylor prism 207, a lens 208, a high-speed detector 209, a filtering and shaping circuit 210, a frequency divider 211, a signal shaping circuit 212, a digital frequency measurement unit 213, a host computer 214, and a high-precision voltage source 215.

[0048] The probe laser 200 is also a semiconductor laser with a wide tuning range. Its emitted light is split into two beams after passing through an optical isolator 201, a half-wave plate 202, and a polarizing beam splitter prism 203. One beam is used for subsequent cesium atom D1 line measurement, and the other is used for beat frequency with the reference light source. The frequency-stabilized reference light 204 is combined with part of the probe light source through a reflector 205 and then beat frequency with a beam combiner prism 206. The combined laser beam is kept in the same polarization direction by a Glan Taylor prism 207 and collected by a high-speed detector 209 through a lens 208. The beat frequency signal generated by the detector 209 is filtered and amplified by a filter amplifier 210 to remove high-frequency signals. The digital frequency measurement unit 213 usually has difficulty detecting large signals such as GHz signals, so it uses a frequency divider 211 to divide the frequency. Using a frequency divider makes it easier to monitor the beat frequency signal. The signal shaping circuit 212 converts the beat frequency signal into a square wave signal that is easier to measure by the digital frequency measurement unit 213. The digital frequency measurement unit 213 transmits the measured beat frequency signal to the host computer 214 to obtain the frequency difference between the two beams of light.

[0049] Since the reference light source is locked onto the absorption peak, the beat frequency signal measured by the digital frequency measurement unit 213, i.e., the difference between the two frequencies, cannot distinguish the relative positions of the probe light and the reference frequency-stabilized light. To obtain the absorption peak of the cesium atom D1 line, frequency sweeping is required on both sides of the stable reference frequency. An external modulation voltage circuit is designed to create a mapping relationship between the external modulation circuit and the injection current. When a positive voltage is applied to the voltage modulation port of the semiconductor laser, the light frequency decreases, while when a negative voltage is applied, the light frequency increases. Based on this phenomenon, unidirectional scanning can be achieved by setting the voltage limit range of the PID controller. The frequency sweeping process covering the cesium atom D1 line is divided into three segments: sweeping the frequency range where the optical frequency is lower than the reference frequency; sweeping the frequency range at the reference frequency; and sweeping the frequency range where the optical frequency is higher than the reference frequency. Combining these three segments can achieve the frequency sweeping process covering the cesium atom D1 line. The specific steps are as follows:

[0050] Step 1: Using the 214LabVIEW program on the host computer, set the sweep frequency range and sweep frequency interval (here, we take linear equal interval as an example). Generate a sweep frequency array based on the input parameters. The values ​​in the sweep frequency array correspond to the beat frequency values, that is, the difference between the detected frequency and the reference frequency. If the sweep frequency range is set to 7GHz and the sweep frequency interval is set to 20MHz, then the low-frequency sweep frequency array is {20, 40, 60…3000}, the reference frequency is {0}, and the high-frequency array is {20, 40, 60…4000}.

[0051] Step 2: When the program runs, the probe light source is first locked onto the reference light source, that is, the beat frequency signal is zero at this time. The purpose of this step is to move the probe light onto the reference standard light and obtain the feedback voltage value when the probe light source is stable.

[0052] Step 3: Low-frequency sweep. The feedback voltage value recorded in Step 2 is used as the lower limit of the PID output voltage. The beat frequency signal received in the host computer 214 program is compared with the first value of 20MHz in the sweep frequency array. This value is then input into the digital PID control module to obtain the feedback voltage. Through precise voltage source control, the beat frequency signal of the two beams is consistently maintained at 20MHz. At this point, frequency stabilization at that frequency point is achieved. After completing the test at this sweep point, the next beat frequency point of 40MHz is sequentially extracted, stabilized, and tested. This process is repeated until all frequency points in the sweep frequency array are scanned.

[0053] Step 4: Then lock the probe light onto the stable reference light, i.e., the beat frequency is zero, and record the feedback voltage value at this time through the program.

[0054] Step 5: High-frequency sweep. Set the feedback voltage recorded in Step 4 to the upper limit of the voltage in the digital PID module of the host computer 214 program. In the same way as the low-frequency sweep, after the host computer 214 acquires the beat frequency signal, it compares it with the first value of 20MHz in the high-frequency array. The feedback obtained through the digital PID module stabilizes the frequency point. Repeat the operation until the beat frequency value of the two beams is stabilized at 4GHz, and then the high-frequency sweep is completed.

[0055] Combining the three frequency sweeping processes allows for a frequency sweeping function with a sweeping range of 7GHz and an interval of 20MHz, while ensuring frequency stability at each frequency point during the sweeping process.

[0056] The probe optical power stabilization module 3 provides a stable power probe optical path for the subsequent probe optical path.

[0057] like Figure 4 As shown, the detection light power stabilization module includes: lens 301, lens 302, acousto-optic modulator 303, polarization beam splitter 304, photodetector 305, PI controller 306, radio frequency source 307, and power amplifier 308.

[0058] Laser beam contraction is achieved by using a lens group consisting of two lenses 301 and 302 with focal lengths of 100mm and 30mm respectively. After passing through an acousto-optic modulator 303 and a polarizing beam splitter 304, the laser beam is split into two. One beam is used for subsequent detection, and the other beam is used for feedback control of laser power through a photodetector, a PI controller, an RF source, and a power amplifier to achieve power stability.

[0059] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for stabilizing frequency and power during laser frequency sweeping, characterized in that: Includes a reference light source frequency stabilization module (1), a laser beat frequency sweep module (2), and a probe light power stabilization module (3); The reference light source frequency stabilization module (1) includes a reference light source laser (100), an optical isolator (101), a half-wave plate (102), a polarizing beam splitter (103), a beam splitter (104), a gas cell (105), a beam splitter (106), a mirror (107), a mirror (108), a photodetector (109), a mixer (110), a phase adjuster (111), a low-pass filter (112), a PI controller (113), an adder (114), a signal generator (115), and a triangular wave sweeper (116). The reference light is locked onto the absorption peak of the atoms in the gas cell, thereby stabilizing the frequency of the reference light. The triangular wave generated by the triangular wave sweeper (116) and the modulation signal generated by the signal generator (115) are superimposed on the reference light source laser (100). The output light passes through the optical isolator (101), half-wave plate (102), polarizing beam splitter (103), and beam splitter (104) for reflecting and transmitting light, and the optical path is split into two paths. One path of light illuminates the photodetector (109). The output signal and the modulation signal generated by the signal generator (115) are mixed by the phase adjuster (111) and the mixer (110). The laser is then demodulated by the low-pass filter (112). The demodulated electrical signal is input to the PI controller (113) to generate a feedback signal. The reference light is locked onto the absorption peak of the alkali metal atom through feedback control, thereby stabilizing the frequency of the reference light source. The laser beat frequency sweep module (2) includes a probe light source laser (200), an optical isolator (201), a half-wave plate (202), a polarizing beam splitter (203), a frequency-stabilized reference beam (204), a reflector (205), a beam combiner prism (206), a Glan Taylor prism (207), a lens (208), a high-speed detector (209), a filter amplifier circuit (210), a frequency divider (211), a signal shaping unit (212), a digital frequency measurement unit (213), a host computer (214), and a high-precision voltage source (215). The probe light output from the probe light source laser (200) is split into two beams after passing through an optical isolator (201), a half-wave plate (202), and a polarizing beam splitter (203). One of the beams is combined with the reference light source (204) through a beam combining prism (206). The combined beam passes through a Glan Taylor prism (207) and a lens (208) before illuminating the detector (209) to achieve the beat frequency between the probe light and the reference light. The beat frequency signal from the photodetector (209) undergoes signal processing, including a filtering and shaping circuit (210). The frequency divider (211) and signal shaping (212) convert the signal into a square wave signal, which is then measured by the digital frequency measurement unit (213). The measured beat frequency signal is then transmitted to the host computer (214). The LabVIEW program of the host computer (214) contains a digital PID module. The preset value and the actual measured beat frequency value are input into the digital PID module to obtain the feedback voltage. The LabVIEW program of the host computer (214) controls the output voltage of the high-precision voltage source (215) to control the movement and stabilization of the probe optical frequency. The frequency sweep process is achieved by using the absorption peak of the gas cell in the reference optical path as a reference. However, since the absorption peak of the reference source is located in the test spectrum of the probe light, the beat signal during the frequency sweep process cannot reflect the relative position of the probe light and the reference light. For DBR semiconductor lasers, increasing the injection current decreases the output optical frequency, and decreasing the injection current increases the output optical frequency. Through an external adder circuit, i.e., an external modulation voltage circuit, the external modulation voltage is mapped to the injection current of the DBR laser. That is, increasing the voltage modulation port voltage increases the injection current, resulting in a red shift of the optical frequency; conversely, decreasing the voltage modulation port voltage results in a blue shift of the optical frequency. Based on this principle, the relative position of the reference light and the probe light can be determined, and the frequency sweep process can be achieved by segmenting the frequency range: below the reference frequency range, at the reference frequency point, and above the reference frequency range. The detection optical power stabilization module (3) includes a lens (301), a lens (302), an acousto-optic modulator (303), a polarization beam splitter (304), a photodetector (305), a PI controller (306), an RF source (307), and a power amplifier (308). The probe light is beam-constricted by two lenses (301) and (302), and then split into two beams after passing through an acousto-optic modulator (303) and a polarization beam splitter (304). One beam is used for subsequent detection, and the other is used for laser power stabilization. The electrical signal from the photodetector (305) is used to achieve closed-loop feedback control of the laser power through a PI controller (306), an RF source (307), and a power amplifier (308). The absorption spectrum data used for sensing measurement is obtained through the following process: the frequency sweep process and power stabilization are carried out simultaneously. After the host computer (214) LabVIEW program determines that the single frequency point is stable during the frequency sweep process, it enters the sensing measurement module based on the absorption spectrum to perform data testing. The entire absorption spectrum is obtained after the frequency sweep process is completed.

2. The device for stabilizing frequency and power during laser frequency sweeping as described in claim 1, characterized in that: The method for implementing the frequency sweep function includes the following steps. Step 1: The host computer (214) LabVIEW program generates a sweep frequency array according to the set sweep frequency range and sweep frequency interval, and divides the sweep frequency array into a low frequency array, a reference frequency, and a high frequency array; Step 2: Lock the laser output from the probe light source laser (200) onto the reference light. At this time, the beat frequency value is zero, and obtain the feedback voltage value when it is stable. Step 3: Low-frequency band sweep; First, set the feedback voltage value obtained in Step 2 as the lower limit of the output voltage of the digital PID in the LabVIEW program of the host computer (214); Second, compare the first value in the low-frequency array with the beat frequency value, and stabilize the beat frequency value through feedback control using the digital PID module and high-precision voltage source in the LabVIEW program of the host computer (214), that is, complete the frequency stabilization of the first point in the low-frequency array; Subsequently, the lower limit of the output voltage of the digital PID module remains unchanged, and the frequency stabilization of each point in the low-frequency array is achieved by repeating the same feedback control according to the order in the low-frequency array until the last point in the low-frequency array is completed, and finally the low-frequency band sweep is achieved; Step 4: Stabilize the reference frequency point; lock the probe light source onto the reference light, i.e., the beat frequency is zero, record the feedback voltage value when it is stable, and use it as the upper limit of the output of the digital PID module in the high-frequency scanning segment; Step 5: High-frequency band sweep is the same as low-frequency band sweep in Step 3, except that the feedback voltage value obtained in Step 4 is set as the upper limit of the output voltage of the digital PID module. By using a digital PID module and a hardware module for feedback control, the frequency stabilization of the first to the last point in the high-frequency array is achieved sequentially, and the high-frequency band sweep is finally completed. By splicing the three processes together, a frequency sweep function covering the atomic absorption spectrum of alkali metals can be achieved, while ensuring the frequency stability of a single measurement point.

3. A device for stabilizing frequency and power during laser frequency sweeping as described in claim 1 or 2, characterized in that: The laser beat frequency sweep module (2) processes the beat frequency signal through the filter shaping circuit (210), signal frequency division (211), and signal shaping (212) circuit modules, converts it into a low-frequency square wave signal, transmits it to the digital frequency measurement unit (213) to obtain the beat frequency value, and uploads it to the host computer (214) for processing.

4. A device for stabilizing frequency and power during laser frequency sweeping as described in claim 1 or 2, characterized in that: The laser beat frequency sweep module (2) completes the optical frequency sweep process based on the gas chamber. By setting the sweep frequency range and sweep frequency interval in the LabVIEW program of the host computer (214), a sweep frequency array, also known as a beat frequency array, is generated. The sweep frequency data is divided into a low frequency array, a reference frequency array, and a high frequency array. The sweep frequency is performed in this order during the experiment. The preset value in the sweep frequency array is compared with the beat frequency value obtained by the digital frequency measurement unit (213), and transmitted to the digital PID module in the LabVIEW program of the host computer (214). The beat frequency value is consistent with the preset value through feedback control. This process is repeated until the sweep frequency of the three arrays is completed, and finally the optical frequency scan of the preset range is completed, ensuring the frequency stability and power stability at each optical frequency point.

5. A device for stabilizing frequency and power during laser frequency sweeping as described in claim 1 or 2, characterized in that: The reflectance-to-transmission ratio of the beam splitter (104) is 3:7.

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