Low-noise atom modulation spectrum detection system and method based on saturated fluorescence detection

Abstract

The low-noise atom modulation spectrum detection system comprises a signal generator, sine wave signals generated by the signal generator are divided into two paths, one path is output to a laser device, and laser with modulation information is modulated in a current control mode; and the other path provides a reference signal for demodulation of the lock-in amplifier, the output laser is divided into pump light and probe light to ensure generation of saturated fluorescence in the rubidium atom steam chamber, then a low-noise silicon photoelectric detector is used for detecting a saturated fluorescence signal, and the lock-in amplifier demodulates and outputs the modulated saturated fluorescence signal. And meanwhile, a detection path of the saturated absorption spectrum is reserved, so that comparison with a modulated saturated fluorescence spectrum signal is facilitated. According to the invention, the requirement on the size of the atom steam chamber is obviously reduced, and the method is suitable for the application scenes of the Suppler spectrum, such as high-sensitivity, low-noise, anti-interference and miniaturized laser frequency stabilization and atom hyperfine structure detection.

Description

Technical Field

[0001] This invention relates to the field of atomic modulation spectroscopy detection technology, and in particular to a low-noise atomic modulation spectroscopy detection system and method based on saturated fluorescence detection. Background Technology

[0002] In recent years, modulation-transfer spectroscopy has received widespread attention among various frequency stabilization technologies. This method modulates a strong pump light using an electro-optic modulator or an acousto-optic modulator. Four-wave mixing of the pump and probe light occurs in a saturated rubidium vapor chamber, and a lock-in amplifier demodulates the probe light, transferring modulation information from the pump light, to extract a high signal-to-noise ratio error signal. However, this method requires a sufficiently long rubidium vapor chamber to ensure clear visibility of the saturated absorption signal. Furthermore, the electro-optic or acousto-optic modulator occupies a significant amount of space in the optical path, preventing further miniaturization of the equipment.

[0003] Modulation-transfer spectroscopy relies on the interpretation of atomic absorption spectra, which necessitates a sufficient number of atomic absorption photons in the laser path. To ensure the airtightness of the atomic vapor chamber and control costs, the atomic density within the vapor chamber should not be too high. Therefore, an atomic vapor chamber with a length of 5 cm or more is typically required. This vapor chamber is relatively large, and its volume is difficult to further reduce. For space-constrained atomic physics laboratories or atomic clocks on satellites, using a smaller atomic vapor chamber would undoubtedly significantly reduce space requirements. In existing modulation-transfer spectroscopy schemes, due to the optical path originating from a polarizing beam splitter, the unavoidable reflections from the rubidium atomic vapor chamber walls interfere with the probe light, resulting in an inevitable discrepancy between the extracted error signal and the ideal situation. Furthermore, power fluctuations from the laser itself cause phase and intensity fluctuations, affecting the stability of the four-wave mixing within the rubidium atomic vapor chamber, thus leading to higher demodulated signal noise and a lower signal-to-noise ratio. Summary of the Invention

[0004] The present invention aims to provide a low-noise atomic modulation spectroscopy detection system and method based on saturated fluorescence detection, so as to reduce the volume of the atomic vapor chamber used, effectively reduce the cost of atomic spectroscopy detection, and achieve low noise and high signal-to-noise ratio of the demodulated modulated saturated fluorescence signal.

[0005] Therefore, the technical solution adopted by this invention is as follows: a low-noise atomic modulation spectral detection system based on saturated fluorescence detection, comprising an optical path mechanism and a circuit mechanism; the optical path mechanism includes: a laser, a half-wave plate, a first polarizing beam splitter, a first detector mirror, and an atomic vapor chamber; the laser emits a laser beam with modulation information, which passes through the half-wave plate and is split into a detector beam and a pump beam; the detector beam and the pump beam are separated after passing through the first polarizing beam splitter; the detector beam enters the atomic vapor chamber after passing through the first detector mirror; the optical path mechanism further includes a first pump mirror, a second pump mirror, and a first photodetector; the pump beam passes sequentially through the first pump mirror and the second pump mirror. Behind the mirror, the light reaches the atomic vapor chamber, which absorbs the probe light and pump light to generate saturated fluorescence with modulation information. The first photodetector collects the saturated fluorescence. The circuit structure includes a signal generator, a lock-in amplifier, a current amplifier, and an oscilloscope. The first and second output terminals of the signal generator are electrically connected to the input terminal of the laser and the first input terminal of the lock-in amplifier, respectively. The output terminal of the first photodetector is electrically connected to the input terminal of the current amplifier, and the output terminal of the current amplifier is electrically connected to the second input terminal of the lock-in amplifier. The first input terminal of the oscilloscope is electrically connected to the output terminal of the lock-in amplifier, and the second input terminal is electrically connected to the output terminal of the current amplifier.

[0006] As a preferred embodiment of the above scheme, the first detection mirror and the second pump mirror are respectively disposed on the left and right sides of the atomic vapor chamber, so that the detection light and the pump light enter the atomic vapor chamber from the left and right sides respectively.

[0007] More preferably, the lock-in amplifier includes a preamplifier, a phase shifter, a mixer, and a low-pass filter. The input terminal of the phase shifter is electrically connected to the second output terminal of the signal generator. The input terminal of the preamplifier is electrically connected to the output terminal of the current amplifier. The first input terminal of the mixer is electrically connected to the output terminal of the phase shifter. The second input terminal is electrically connected to the output terminal of the preamplifier. The input terminal of the low-pass filter is electrically connected to the output terminal of the mixer. The first input terminal of the oscilloscope is electrically connected to the output terminal of the low-pass filter.

[0008] A further preferred embodiment includes a fluorescent reflector, wherein the first photodetector and the fluorescent reflector are respectively disposed on the front and rear sides of the atomic vapor chamber, so that the fluorescent reflector reflects saturated fluorescence onto the first photodetector.

[0009] More preferably, the first photodetector is a Solvay SM05PD3A photodetector with a responsivity of 0.60 A / W.

[0010] More preferably, the current amplifier and the lock-in amplifier are respectively a Stanford SR570 preamplifier and a Stanford SR865A lock-in amplifier.

[0011] A low-noise atomic modulation spectroscopic detection method based on saturated fluorescence detection includes the following steps:

[0012] S1. Use the signal generator to output a modulation signal to the laser for current control, so that the laser emits laser light with modulation information;

[0013] S2. The laser beam is split into probe beam and pump beam by the half-wave plate, and the probe beam and pump beam are separated by the first polarizing beam splitter.

[0014] S3. The probe light is reflected by the first probe reflector and enters the atomic vapor chamber from the left side. The pump light is reflected by the first pump reflector and the second pump reflector in sequence and enters the atomic vapor chamber from the right side.

[0015] S4. The probe light and pump light are absorbed through the atomic vapor chamber, and saturated fluorescence with modulation information is generated. The saturated fluorescence is collected using the first photodetector.

[0016] S5. The original saturated fluorescence signal generated by the first photodetector is amplified using the current amplifier and transmitted to the lock-in amplifier and oscilloscope.

[0017] S6. Use the signal generator to output a reference signal with the same frequency and phase as the modulation signal to the lock-in amplifier, and use the lock-in amplifier to demodulate the original saturated fluorescence signal;

[0018] S7. The demodulated modulated saturated fluorescence signal is transmitted to the oscilloscope through the lock-in amplifier;

[0019] S8. Use a mobile storage device to record the modulated saturated fluorescence signal and the original saturated fluorescence signal data of the oscilloscope, and plot the modulated saturated fluorescence spectrum using the modulated saturated fluorescence signal data to obtain a low-noise atomic modulation spectrum based on saturated fluorescence detection.

[0020] As a preferred embodiment of the above scheme, the optical path mechanism further includes a second polarizing beam splitter, a second probe mirror, and a second photodetector. The output of the second photodetector is electrically connected to the second input of the oscilloscope. After passing through the atomic vapor chamber, the probe light passes sequentially through the second polarizing beam splitter and the second probe mirror, and is then reflected to the second photodetector. The second photodetector outputs a saturated absorption signal to the oscilloscope. The original saturated fluorescence signal and the saturated absorption signal serve as a reference for modulating the saturated fluorescence signal. The pump light is reflected by the second pump mirror, then passes through the second polarizing beam splitter, and then enters the atomic vapor chamber.

[0021] More preferably, the output terminal of the laser is electrically connected to the third input terminal of the oscilloscope, so that the laser outputs a sweep frequency signal to the oscilloscope as a reference trigger signal for the sweep frequency period.

[0022] The beneficial effects of this invention are:

[0023] 1. Since this invention collects the saturated fluorescence of atoms, there is no strong background light noise interfering with waveform collection. Therefore, as long as the excited atomic saturated fluorescence exists, a clearly visible waveform can be collected, which greatly reduces the volume requirement of the atomic vapor chamber, thereby reducing the volume of the atomic vapor chamber.

[0024] 2. This invention does not require the use of an electro-optic modulator or an acousto-optic modulator, thereby reducing the footprint and miniaturizing the system.

[0025] 3. This invention demodulates the original saturated fluorescence signal without demodulating the probe light that causes interference, thus achieving low noise and high signal-to-noise ratio in the demodulated saturated fluorescence signal.

[0026] 4. The present invention uses a first photodetector to absorb saturated fluorescence. The number of atoms excited per unit time is almost unaffected by power fluctuations and there is no power intensity noise. Therefore, the phase fluctuations and intensity fluctuations caused by the power fluctuations of the laser itself will not affect the modulated saturated fluorescence signal. The modulated saturated fluorescence signal of the present invention has strong anti-interference ability.

[0027] 5. This invention reduces the volume of the atomic vapor chamber required for atomic spectroscopy detection and reduces the amount of atoms used, thereby reducing the procurement cost of the atomic vapor chamber. In addition, it eliminates the cost of using electro-optic modulators or acousto-optic modulators, thus effectively reducing the detection cost of atomic spectroscopy. Attached Figure Description

[0028] Figure 1 These are modulation saturated fluorescence spectral signals of the D2 line position of the large rubidium atomic vapor chamber in this invention, with modulation frequencies of 10 kHz, 15 kHz, and 20 kHz.

[0029] Figure 2 yes Figure 1 Enlarged view of the first two characteristic peaks.

[0030] Figure 3 This is the original saturated fluorescence spectrum signal of the D2 line position of the large rubidium atomic vapor cell in this invention.

[0031] Figure 4 yes Figure 3 A magnified view of the larger peaks in the middle.

[0032] Figure 5 The above are modulation saturated fluorescence spectral signals at the D2 line position of the small rubidium-87 atomic vapor cell in this invention, with modulation frequencies of 10 kHz, 15 kHz and 20 kHz respectively.

[0033] Figure 6 These are the original saturated fluorescence spectra of the D2 line position of the small rubidium-87 atomic vapor cell in this invention, with modulation frequencies of 10 kHz, 15 kHz, and 20 kHz, respectively.

[0034] Figure 7 This is a saturated absorption spectrum signal of the probe light passing through the D2 line of the large rubidium atomic vapor chamber in this invention.

[0035] Figure 8 This is a saturated absorption spectrum signal of the probe light passing through the D2 line of the small rubidium-87 atomic vapor cell in this invention.

[0036] Figure 9 This is a schematic diagram of the low-noise atomic modulation spectroscopy detection system based on saturated fluorescence detection in this invention. Detailed Implementation

[0037] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0038] like Figure 9As shown, a low-noise atomic modulation spectral detection system based on saturated fluorescence detection includes an optical path mechanism and a circuit mechanism. The optical path mechanism includes: a laser 1, a half-wave plate 2, a first polarizing beam splitter 3, a first detector mirror 5, and an atomic vapor chamber 6. The optical path mechanism also includes a first pump mirror 4, a second pump mirror 11, and a first photodetector 7. The circuit mechanism includes: a signal generator 20, a lock-in amplifier 17, a current amplifier 8, and an oscilloscope 14. The first and second output terminals of the signal generator 20 are electrically connected to the input terminals of the laser 1 and the first input terminal of the lock-in amplifier 17, respectively. The output terminal of the first photodetector 7 is electrically connected to the input terminal of the current amplifier 8, and the output terminal of the current amplifier 8 is electrically connected to the second input terminal of the lock-in amplifier 17. The first input terminal of the oscilloscope 14 is electrically connected to the output terminal of the lock-in amplifier 17, and the second input terminal is electrically connected to the output terminal of the current amplifier 8. The laser 1 is a DFB laser, and the atomic vapor chamber 6 is a rubidium atomic vapor chamber. The first photodetector 7 and the second photodetector 13 employ a Solvay SM05PD3A photodetector and a PDA36A2 integrated photodetector, respectively, with a responsivity of 0.60 A / W. The PDA36A2 integrated photodetector has built-in gain functionality and can directly convert photocurrent into a voltage signal. The current amplifier 8 and the lock-in amplifier 17 employ a Stanford SR570 preamplifier current amplifier and a Stanford SR865A lock-in amplifier, respectively.

[0039] The first detector reflector 5 and the second pump reflector 11 are respectively disposed on the left and right sides of the atomic vapor chamber 6, so that the detector light and pump light enter the atomic vapor chamber 6 from the left and right sides respectively. The lock-in amplifier 17 includes a preamplifier 15, a phase shifter 19, a mixer 18, and a low-pass filter 16. The input terminal of the phase shifter 19 is electrically connected to the second output terminal of the signal generator 20, the input terminal of the preamplifier 15 is electrically connected to the output terminal of the current amplifier 8, the first input terminal of the mixer 18 is electrically connected to the output terminal of the phase shifter 19, the second input terminal is electrically connected to the output terminal of the preamplifier 15, the input terminal of the low-pass filter 16 is electrically connected to the output terminal of the mixer 18, and the first input terminal of the oscilloscope 14 is electrically connected to the output terminal of the low-pass filter 16. It also includes a fluorescent reflector 9. The first photodetector 7 and the fluorescent reflector 9 are respectively disposed on the front and rear sides of the atomic vapor chamber 6, so that the fluorescent reflector 9 reflects saturated fluorescence onto the first photodetector 7.

[0040] A low-noise atomic modulation spectroscopic detection method based on saturated fluorescence detection includes the following steps:

[0041] S1. The signal generator 20 outputs a modulation signal to the laser 1 for current control, thereby causing the laser 1 to emit laser light with modulation information.

[0042] Before conducting atomic modulation spectroscopy detection, laser 1 is first started, and the current control and power control functions are turned on. Then, signal generator 20 is connected to the current control port of laser 1 and oscilloscope 14 simultaneously to start frequency sweep, perform detection, and adjust the frequency sweep range. Then, lock-in amplifier 17, current amplifier 8, oscilloscope 14, first photodetector 7, and second photodetector 13 are started. Then, the signal modulation half-wave plate 2 of oscilloscope 14 is observed to adjust the splitting ratio. The splitting power is measured with a power meter at any time. Then, signal generator 20 is connected to the current control port of laser 1 and lock-in amplifier 17 simultaneously, and the modulation signal is started to be output. During atomic modulation spectroscopy detection, the input voltage range, sensitivity, gain, and phase of lock-in amplifier 17 are adjusted to obtain a clearly visible characteristic peak signal. The laser is modulated by the modulation signal generated by reference signal generator 20 through the current control function built into laser 1, so that it carries modulation information when it is emitted.

[0043] S2. The laser beam is split into probe beam and pump beam by half-wave plate 2, and the probe beam and pump beam are separated by first polarization beam splitter 3.

[0044] S3. The probe light is reflected by the first probe reflector 5 and enters the atomic vapor chamber 6 from the left. The pump light is reflected by the first pump reflector 4 and the second pump reflector 11 in sequence and enters the atomic vapor chamber 6 from the right.

[0045] The intensity of the pump light is greater than that of the probe light. The probe light and the pump light enter the rubidium atom vapor chamber 6 from the left and right sides, respectively. This ensures that the probe light and the pump light excite the rubidium atoms to produce saturated fluorescence. It also facilitates the recording and comparison of the saturated absorption signals of the rubidium atom vapor chamber 6 with different sizes.

[0046] S4. The probe light and pump light are absorbed through the atomic vapor chamber 6, and saturated fluorescence with modulation information is generated. The saturated fluorescence is collected using the first photodetector 7.

[0047] The probe light and pump light converge within the rubidium atom vapor chamber 6, causing the transition frequencies of the rubidium atoms in chamber 6 to saturate, resulting in saturated fluorescence. The modulation information from the laser is transferred to the saturated fluorescence through the saturated absorption and fluorescence emission of the atoms. Because fluorescence generation is isotropic—meaning the emission probability is equal in all directions—and the number of photons emitted by a single atom per unit time is finite, the intensity of saturated fluorescence is several orders of magnitude lower than that of a laser. Therefore, a specific optical system and a high signal-to-noise ratio, high-sensitivity photodetector are typically used to collect the fluorescence.

[0048] S5. The original saturated fluorescence signal generated by the first photodetector 7 is amplified by the current amplifier 8 and transmitted to the lock-in amplifier 17 and the oscilloscope 14.

[0049] S6. The signal generator 20 outputs a reference signal with the same frequency and phase as the modulation signal to the lock-in amplifier 17, and the original saturated fluorescence signal is demodulated by the lock-in amplifier 17.

[0050] Signal generator 20 generates a frequency of The sinusoidal signal is divided into two paths: one is the modulation signal and the other is the reference signal. Since the signal generated by the signal generator 20 is transmitted to the laser 1 and the lock-in amplifier 17 at different times, we need to use the phase shifter 19 to adjust the phase of the reference signal to be in phase with the modulation signal each time we detect it.

[0051] S7. The demodulated modulated saturated fluorescence signal is transmitted to the oscilloscope 14 through the lock-in amplifier 17.

[0052] S8. The modulated saturated fluorescence signal and the original saturated fluorescence signal data of the oscilloscope 14 are recorded using a mobile storage device, and the modulated saturated fluorescence spectrum is plotted using the modulated saturated fluorescence signal data, thereby obtaining a low-noise atomic modulation spectrum based on saturated fluorescence detection. The modulated saturated fluorescence spectrum of the present invention is a low-noise atomic modulation spectrum based on saturated fluorescence detection.

[0053] The optical path mechanism also includes a second polarizing beam splitter 10, a second probe mirror 12, and a second photodetector 13. The output of the second photodetector 13 is electrically connected to the second input of the oscilloscope 14. After the probe light passes through the atomic vapor chamber 6, it passes sequentially through the second polarizing beam splitter 10 and the second probe mirror 12, and is then reflected to the second photodetector 13. The second photodetector 13 outputs a saturated absorption signal to the oscilloscope 14. The original saturated fluorescence signal and the saturated absorption signal serve as a reference for modulating the saturated fluorescence signal. The pump light is reflected by the second pump mirror 11, then passes through the second polarizing beam splitter 10, and then enters the atomic vapor chamber 6. The output of the laser 1 is electrically connected to the third input of the oscilloscope 14 so that the laser 1 outputs a sweep frequency signal to the oscilloscope 14 as a reference trigger signal for the sweep frequency period.

[0054] To verify the technical effect of the present invention, we used a conventional large rubidium atomic vapor cell 6 with a diameter of 25 mm and a thickness of 75 mm and a small rubidium atomic vapor cell 6 with a diameter of 15 mm and a thickness of 4 mm containing only rubidium-87 to measure the rubidium D2 line position modulation saturated fluorescence spectrum, and simultaneously monitored the saturated absorption signal of the probe light, thereby confirming the feasibility of its miniaturization.

[0055] Figure 1The image shows the modulation saturation fluorescence spectra of a large rubidium atomic vapor cell (25 mm in diameter and 75 mm in thickness) at modulation frequencies of 10 kHz, 15 kHz, and 20 kHz. The horizontal axis represents coordinate points, and the vertical axis represents signal intensity (unit: volts). It can be seen that... Figure 1 The image shows four distinct main characteristic peaks, from left to right: 87 Rb F g =2→F e =2, 85 Rb F g =3→F e =2, 85 Rb F g =2→F e =2, 87 Rb F g =1→F e =0, and Figure 2 This amplifies the first two characteristic peaks. The signal-to-noise ratio is estimated to reach 9.7 dB. It can be seen that... Figure 1 The modulation frequency of 10 kHz shown in the figure has the best signal-to-noise ratio, followed by modulation frequencies of 15 kHz and 20 kHz.

[0056] Figure 3 This is the original saturated fluorescence spectrum signal at the 6D2 line position of the large rubidium atomic vapor cell. Figure 3 and Figure 4 The original saturated fluorescence spectrum signal without demodulation is shown. By comparing the fluorescence signals before and after demodulation, it can be seen that the lock-in amplifier 17 demodulates sharp characteristic peaks, and its broadening is roughly the same as the original fluorescence spectrum. Therefore, the effectiveness of its demodulation effect can be proven.

[0057] Figures 1-4 The effectiveness of modulated saturated fluorescence spectroscopy (MSFS) in applying rubidium atom D2 spectroscopy has been confirmed. We further tested its performance in a small rubidium atom vapor chamber (6) containing only rubidium-87, with a diameter of 15 mm and a thickness of 4 mm. Although the volume of this small rubidium atom vapor chamber (6) is significantly reduced compared to the larger rubidium atom vapor chamber (6), resulting in a significantly smaller excitation range and reduced fluorescence intensity, the signal-to-noise ratio (SNR) is noticeably lower. While the SNR of the MSFS signal is poor at modulation frequencies of 15 kHz and 20 kHz, it remains clearly visible at 10 kHz, fully capable of laser frequency locking, thus confirming the feasibility of applying this technique to the small rubidium atom vapor chamber (6).

[0058] Figure 5 and Figure 6Schematic diagrams of the modulated saturated fluorescence spectrum and the original saturated fluorescence spectrum using the small rubidium-87 atomic vapor cell 6 are shown. Similarly, we compared the saturated absorption signals passing through the large and small rubidium atomic vapor cells 6, such as... Figure 7 As can be seen, the saturated absorption spectral signal is clearly visible, and the broadening after absorption is small. Figure 8 The saturated absorption spectrum signal is weak with no obvious characteristic peaks, and most of its spectral variations are due to laser frequency fluctuations caused by frequency sweeping. Therefore, the comparison reveals the limitation of saturated absorption spectroscopy in further miniaturizing the rubidium atomic vapor chamber 6, thus further confirming the necessity of developing modulated saturated fluorescence spectroscopy.

[0059] In summary, we can see that modulated saturated fluorescence spectroscopy has irreplaceable advantages for miniaturized, high signal-to-noise ratio, high sensitivity, and interference-resistant laser stabilization systems. When detecting rubidium atoms, the signal generator 20 can produce a significantly clear error signal (i.e., a reference signal) at a modulation frequency of 10 kHz, which can be used for laser frequency stabilization.

[0060] In terms of fluorescence collection, the efficiency of fluorescence collection can be improved and the original fluorescence photocurrent enhanced by adjusting the position and orientation of the photodetector, the position and orientation of the rubidium atomic vapor cell 6, and the application of optical devices such as mirrors and lenses, thereby generating a saturated fluorescence signal with a high signal-to-noise ratio. Improving fluorescence collection efficiency is particularly important for the small rubidium atomic vapor cell 6.

[0061] In formal applications, there is no need to consider the optical path design for monitoring saturated absorption spectral signals. The emitted laser can be directly injected into the rubidium atom vapor chamber 6, and then the saturated absorption of rubidium atoms can be achieved through a reflector, which can further reduce the space occupied by the device.

[0062] The device of the present invention was placed in a purer, light-free, low-magnetic-field environment for the experiment to avoid interference from ambient light on the sensitive photodetector.

[0063] By replacing the photomultiplier tube or avalanche amplifier with one of higher sensitivity and higher signal-to-noise ratio, the signal-to-noise ratio of the acquired fluorescence signal can be further improved. Furthermore, by adjusting the parameters of current amplifier 8 and lock-in amplifier 17, more clutter and noise can be filtered out, further improving the overall system signal-to-noise ratio without significant attenuation of the error signal. Finding the optimal modulation frequency by gradually adjusting it can achieve the best possible signal-to-noise ratio for the extracted error signal.

[0064] Besides using the internal modulation method of this invention, external modulation schemes can still be used in this invention. It is feasible to perform external modulation after laser 1 using kHz-level electro-optic modulators and acousto-optic modulators.

[0065] Besides rubidium atoms, cesium atoms, potassium atoms, calcium atoms, sodium atoms, and ytterbium atoms are also common atoms with stable laser frequencies. These atoms are also applicable to this invention; only the atomic vapor chamber 6 and a photodetector of suitable frequency need to be replaced.

[0066] In addition to the present invention, it is also feasible to directly excite rubidium atoms to transition using a laser of the corresponding frequency, or to achieve atomic excitation using a two-photon transition method.

[0067] Currently, the embodiments of this invention mainly focus on atomic laser frequency stabilization and the measurement of atomic hyperfine structures. For atomic laser frequency stabilization, the laser 1 frequency should first be adjusted to near the target frequency. The spectral line positions are then located and adjusted to approximate positions through frequency sweeping. Next, the modulated saturated fluorescence signal is processed using proportional-integral-differential methods, and this signal is used to fine-tune laser 1, ensuring that the laser frequency generated by laser 1 remains stable within a very small range. Similarly, by controlling the frequency sweep speed and range, physicists can observe the modulated saturated fluorescence spectrum to observe the hyperfine structure of atoms, including some more finely detailed characteristic spectral lines. They can also investigate the influence of the Zeeman effect of magnetic fields on atomic energy levels.

[0068] The innovations of this invention mainly include three points. First, it employs a modulation signal transfer based on fluorescence detection. Instead of detecting the fluorescence generated by excited atoms, it uses the detection light carrying modulation information through four-wave mixing in the modulation transfer spectrum, thereby capturing the modulation information in the atomic spectrum. Second, it utilizes a smaller atomic vapor chamber 6. By using a significantly smaller atomic vapor chamber 6, it achieves an error signal extraction effect (i.e., demodulation effect on the modulation saturated fluorescence signal) similar to that of the original large-volume atomic vapor chamber 6. Third, this invention provides a novel atomic spectral detection method, offering researchers a new option for studying the hyperfine structure of atoms.

[0069] Compared to modulation-transfer spectroscopy and saturation absorption spectroscopy, which require more rubidium atoms to absorb, this invention utilizes purer modulation fluorescence, allowing for the detection of a significant spectral signal even with a smaller rubidium atom vapor chamber 6. This provides a new solution for the miniaturization of laser frequency stabilization devices. Simultaneously, the saturation fluorescence signal is unaffected by laser power fluctuations, further enhancing the anti-interference capability of the laser frequency stabilization system. This invention can produce integrated, miniaturized laser frequency stabilization systems and can also be used to probe the ultrafine structures of various atoms. Its primary market serves various atomic physics laboratories and atomic clocks, with particularly high demand from atomic physics laboratories working on laser cooling and magneto-optical traps.

[0070] Currently available related products mainly include polarization spectral stabilization, saturated absorption spectral stabilization, dual-color laser stabilization, frequency modulation spectral stabilization, modulation-transfer spectral stabilization, and frequency-voltage conversion stabilization technologies. However, these solutions generally suffer from problems such as complex structure, weak anti-interference capability, low signal-to-noise ratio, or large footprint. In contrast, this invention detects modulated saturated fluorescence, possessing advantages such as simple structure, high signal-to-noise ratio, strong anti-interference capability, and small footprint, thus exhibiting greater practicality and commercialization potential.

[0071] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection, characterized in that: Including optical path mechanisms and circuit mechanisms; The optical path mechanism includes: a laser (1), a half-wave plate (2), a first polarizing beam splitter (3), a first probe mirror (5), and an atomic vapor chamber (6); the laser (1) emits a laser beam with modulation information, which passes through the half-wave plate (2) and is split into a probe beam and a pump beam. The probe beam and the pump beam are separated after passing through the first polarizing beam splitter (3). The probe beam enters the atomic vapor chamber (6) after passing through the first probe mirror (5). The optical path mechanism also includes a first pump reflector (4), a second pump reflector (11), and a first photodetector (7); the pump light passes through the first pump reflector (4) and the second pump reflector (11) in sequence and then reaches the atomic vapor chamber (6). The atomic vapor chamber (6) absorbs the probe light and the pump light and generates saturated fluorescence with modulation information. The first photodetector (7) collects the saturated fluorescence. The circuit structure includes: a signal generator (20), a lock-in amplifier (17), a current amplifier (8), and an oscilloscope (14); the first and second output terminals of the signal generator (20) are electrically connected to the input terminal of the laser (1) and the first input terminal of the lock-in amplifier (17), respectively; the output terminal of the first photodetector (7) is electrically connected to the input terminal of the current amplifier (8); the output terminal of the current amplifier (8) is electrically connected to the second input terminal of the lock-in amplifier (17); the first input terminal of the oscilloscope (14) is electrically connected to the output terminal of the lock-in amplifier (17), and the second input terminal is electrically connected to the output terminal of the current amplifier (8).

2. The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection according to claim 1, characterized in that: The first detection mirror (5) and the second pump mirror (11) are respectively arranged on the left and right sides of the atomic vapor chamber (6) so that the detection light and the pump light enter the atomic vapor chamber (6) from the left and right sides respectively.

3. The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection according to claim 1, characterized in that: The lock-in amplifier (17) includes a preamplifier (15), a phase shifter (19), a mixer (18), and a low-pass filter (16). The input of the phase shifter (19) is electrically connected to the second output of the signal generator (20). The input of the preamplifier (15) is electrically connected to the output of the current amplifier (8). The first input of the mixer (18) is electrically connected to the output of the phase shifter (19), and the second input is electrically connected to the output of the preamplifier (15). The input of the low-pass filter (16) is electrically connected to the output of the mixer (18). The first input of the oscilloscope (14) is electrically connected to the output of the low-pass filter (16).

4. The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection according to claim 1, characterized in that: It also includes a fluorescent reflector (9), with the first photodetector (7) and the fluorescent reflector (9) respectively positioned on the front and rear sides of the atomic vapor chamber (6) so that the fluorescent reflector (9) reflects saturated fluorescence onto the first photodetector (7).

5. The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection according to claim 1, characterized in that: The first photodetector (7) is a Soleb SM05PD3A photodetector with a responsivity of 0.60 A / W.

6. The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection according to claim 1, characterized in that: The current amplifier (8) and the lock-in amplifier (17) are respectively Stanford SR570 preamplifier (8) and Stanford SR865A lock-in amplifier (17).

7. A low-noise atomic modulation spectroscopic detection method based on saturated fluorescence detection, characterized in that, The low-noise atomic modulation spectroscopic detection system based on saturated fluorescence detection as described in any one of claims 1-6 includes the following steps: S1. The signal generator (20) outputs a modulation signal to the laser (1) for current control, thereby causing the laser (1) to emit laser light with modulation information; S2. The laser beam is split into probe beam and pump beam by the half-wave plate (2), and the probe beam and pump beam are separated by the first polarizing beam splitter (3). S3. The probe light is reflected by the first probe reflector (5) and enters the atomic vapor chamber (6) from the left. The pump light is reflected by the first pump reflector (4) and the second pump reflector (11) in sequence and enters the atomic vapor chamber (6) from the right. S4. The probe light and pump light are absorbed through the atomic vapor chamber (6) and saturated fluorescence with modulation information is generated. The saturated fluorescence is collected using the first photodetector (7). S5. The original saturated fluorescence signal generated by the first photodetector (7) is amplified using the current amplifier (8) and transmitted to the lock-in amplifier (17) and the oscilloscope (14). S6. The signal generator (20) outputs a reference signal with the same frequency and phase as the modulation signal to the lock-in amplifier (17), and the original saturated fluorescence signal is demodulated by the lock-in amplifier (17). S7. The demodulated modulated saturated fluorescence signal is transmitted to the oscilloscope (14) through the lock-in amplifier (17); S8. Use a mobile storage device to record the modulated saturated fluorescence signal and the original saturated fluorescence signal data of the oscilloscope (14), and draw the modulated saturated fluorescence spectrum through the modulated saturated fluorescence signal data, thereby obtaining a low-noise atomic modulation spectrum based on saturated fluorescence detection.

8. The low-noise atomic modulation spectroscopic detection method based on saturated fluorescence detection according to claim 7, characterized in that: The optical path mechanism also includes a second polarizing beam splitter (10), a second probe mirror (12), and a second photodetector (13). The output of the second photodetector (13) is electrically connected to the second input of the oscilloscope (14). The probe light passes through the atomic vapor chamber (6) and then passes through the second polarizing beam splitter (10) and the second probe mirror (12) in sequence. It is then reflected to the second photodetector (13). The second photodetector (13) outputs a saturated absorption signal to the oscilloscope (14). The original saturated fluorescence signal and the saturated absorption signal serve as a reference for modulating the saturated fluorescence signal. The pump light is reflected by the second pump mirror (11), then passes through the second polarizing beam splitter (10), and then enters the atomic vapor chamber (6).

9. The low-noise atomic modulation spectroscopic detection method based on saturated fluorescence detection according to claim 7, characterized in that: The output terminal of the laser (1) is electrically connected to the third input terminal of the oscilloscope (14) so ​​that the laser (1) outputs a sweep frequency signal to the oscilloscope (14) as a reference trigger signal for the sweep frequency period.

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