Fabry-Perot cavity-locked method for laser detuning frequency stabilization in SERF magnetometers

Abstract

The present invention relates to a Fabry-Perot cavity locking method for laser detuning and frequency stabilization of a SERF magnetometer. The method obtains a Fabry-Perot cavity with a stable cavity length by locking the resonant frequency of the Fabry-Perot cavity to a beam of frequency-stabilized laser light that has been locked at the atomic energy level. The method designed by the present invention is to lock the cavity length of the laser according to the transmission peak position of the transmitted laser of the Fabry-Perot cavity, modulate and demodulate the transmitted laser light power signal, and then correct the cavity length of the Fabry-Perot cavity by feedback control, that is, to keep the resonant frequency of the Fabry-Perot cavity and the frequency of the laser emitted by the laser in resonance for a long time, thereby obtaining a stable free spectral range, and providing a stable frequency reference and a large detuning amount for the laser used for SERF extremely weak magnetic measurement.

Description

Technical Field

[0001] The invention relates to a Fabry-Perot cavity locking method for laser detuning frequency stabilization of a SERF magnetometer, belonging to the technical field of laser frequency stabilization. Background Art

[0002] Semiconductor lasers, with their advantages of small size, high efficiency, and narrow linewidth, have been recognized as ideal light sources for atomic physics experiments. With the rapid development of semiconductor laser technology and the continuous improvement of semiconductor laser performance, semiconductor lasers are widely used in experimental systems for quantum optics, quantum sensing, high-precision metrology, laser spectroscopy, and high-precision measurement, such as laser cooling and trapping, atom interferometry, and atomic or optical clocks. Stable laser frequency is one of the most important requirements for these experimental systems. In these systems, to minimize frequency drift in the semiconductor laser output, the semiconductor laser frequency is typically locked to a stable reference frequency standard in order to obtain a laser source with long-term frequency stability.

[0003] In spin-exchange relaxation-free (SERF) magnetometers, optical pumping of atomic spins by semiconductor lasers is a prerequisite for ultra-sensitive atomic spin magnetic field measurements. To achieve highly sensitive SERF measurements of extremely weak magnetic fields, laser frequency stability must reach the MHz level. Furthermore, to avoid ultra-high optical depths caused by laser resonance with alkali metal atoms, detuning of up to 100 GHz is often necessary.

[0004] Therefore, a frequency stabilization method is needed to lock the frequency of the laser to a position far from the resonance line. The most common laser frequency stabilization technology is to directly lock the laser frequency to the atomic reference spectral line, such as saturation absorption method and dichroic atomic vapor laser locking. The short-term frequency stability achieved by these frequency stabilization methods can reach the kHz level. However, if there is no suitable atomic spectral line corresponding to the required laser frequency, these frequency stabilization methods are no longer applicable. Detuned laser frequency stabilization often uses acousto-optic modulators and electro-optic modulators, but these two methods are difficult to achieve such a large range of detuning, so they are not suitable for large detuning laser frequency stabilization. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the problem that traditional laser frequency stabilization methods cannot provide a large laser frequency detuning amount for SERF extremely weak magnetic field measurements. The present invention provides a Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometers. The Fabry-Perot cavity, which can lock the cavity length for a long time, provides a fixed free spectral range as a reference frequency for the stabilized laser, thereby achieving detuning of the laser frequency.

[0006] The technical solutions of the present invention are as follows:

[0007] A Fabry-Perot cavity-locked method for laser detuning frequency stabilization in a SERF magnetometer is characterized by comprising the following steps:

[0008] Step 1: Scan the Fabry-Perot cavity in the laser detuning frequency stabilization device of the SERF magnetometer to obtain multiple longitudinal modes of the incident laser, which are the transmission peaks of the transmitted laser.

[0009] Step 2: selecting one of the transmission peaks and applying a preset DC voltage to a piezoelectric converter connected to the Fabry-Perot cavity to preliminarily lock the cavity length of the Fabry-Perot cavity;

[0010] Step 3, superimposing a modulation signal on the DC voltage to modulate the cavity length, thereby tuning the optical power signal of the transmitted laser;

[0011] Step 4: Demodulate the optical power signal according to the modulation signal using a lock-in amplifier to obtain an error signal describing the degree of frequency error;

[0012] Step 5, determining whether the error signal is zero. If so, proceeding to step 6. If not, determining whether the error signal is greater than zero or less than zero. If greater than zero, returning to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity. If less than zero, returning to step 2 to decrease the DC voltage to correct the cavity length of the Fabry-Perot cavity.

[0013] Step 6: Continuously lock the cavity length to obtain a stable free spectrum range, providing a stable frequency reference source for the SERF magnetometer laser detuning frequency stabilization.

[0014] The SERF magnetometer laser detuning frequency stabilization device in step 1 includes a frequency-stabilized laser, a piezoelectric converter, a Fabry-Perot cavity, a photodetector, a lock-in amplifier, a Fabry-Perot cavity driver and a host computer connected in sequence, and the Fabry-Perot cavity driver is connected to the piezoelectric converter.

[0015] The piezoelectric converter is a piezoelectric ceramic, and the piezoelectric ceramic is rigidly coupled to the laser incident surface of the Fabry-Perot cavity.

[0016] The host computer issues an instruction to the Fabry-Perot cavity driver to make the Fabry-Perot cavity driver operate in a scanning mode or a locking mode. In the scanning mode, the Fabry-Perot cavity driver outputs a triangular wave to scan the cavity length of the Fabry-Perot cavity. The laser transmitted from the Fabry-Perot cavity has multiple laser transmission peaks formed by interference resonance in the cavity and is displayed by the host computer. In the locking mode, the Fabry-Perot cavity driver outputs a DC voltage to lock the cavity length of the Fabry-Perot cavity, and superimposes a modulation signal on the DC voltage to modulate the cavity length. The modulation signal is sent to a phase-locked amplifier to demodulate the optical power signal to obtain an error signal representing the difference between the resonant frequency of the Fabry-Perot cavity and the laser frequency.

[0017] Step 2 includes the following relational expressions:

[0018]

[0019] Where L is the cavity length, N is a positive integer, λ is the incident laser wavelength, and n is the refractive index.

[0020] Step 6 includes the following relational expressions:

[0021]

[0022] where v FSR is the free spectral range, c is the speed of light, n is the refractive index, and L is the cavity length. When the cavity length is locked, the free spectral range is also locked, which can provide a stable frequency reference for laser detuning and frequency stabilization.

[0023] The technical effects of the present invention are as follows: The present invention provides a Fabry-Perot cavity locking method for laser detuning and frequency stabilization in a SERF magnetometer. The method utilizes the wide amplitude range of the triangular wave output by the Fabry-Perot cavity driver to scan out multiple laser longitudinal modes, i.e., laser transmission peaks, and lock the cavity length to any of the scanned transmission peaks. Once the Fabry-Perot cavity length is locked, its free spectral range is also locked, providing a stable frequency reference source for lasers requiring detuning and frequency stabilization. Furthermore, the cavity length is sufficient for the laser to achieve a wide range of frequency detuning, and the Fabry-Perot cavity can be more conveniently scanned or locked using a host computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic structural diagram of a laser detuning frequency stabilization device involved in the Fabry-Perot cavity locked cavity method for laser detuning frequency stabilization of a SERF magnetometer.

[0025] Figure 2 The present invention is a flow chart of a Fabry-Perot cavity locked cavity method for laser detuning and frequency stabilization in a SERF magnetometer. Figure 2The method includes the following steps: 1, scanning a Fabry-Perot cavity in a laser detuning frequency stabilization device of a SERF magnetometer to obtain multiple longitudinal modes of an incident laser, which are transmission peaks of a transmitted laser; 2, selecting one of the transmission peaks and applying a corresponding DC voltage to a piezoelectric converter to preliminarily lock the cavity length of the Fabry-Perot cavity; 3, superimposing a modulation signal on the DC voltage to modulate the cavity length, thereby tuning the optical power signal of the transmitted laser; 4, demodulating the optical power signal according to the modulation signal by a phase-locked amplifier to obtain an error signal describing the degree of frequency error; 5, determining whether the error signal is zero; if so, proceeding to step 6; if not, determining whether it is greater than zero or less than zero; if greater than zero, returning to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity; if less than zero, returning to step 2 to decrease the DC voltage to correct the cavity length of the Fabry-Perot cavity; and 6, continuously locking the cavity length to obtain a stable free spectrum range, thereby providing a stable frequency reference source for the laser detuning frequency stabilization of the SERF magnetometer.

[0026] The reference numerals are explained as follows: 1-frequency-stabilized laser; 2-piezoelectric converter or piezoelectric ceramic; 3-Fabry-Perot cavity; 4-photodetector; 5-locked amplifier; 6-Fabry-Perot cavity driver; 7-host computer. DETAILED DESCRIPTION

[0027] Below is the attached figure ( Figure 1-Figure 2 ) and Examples illustrate the present invention.

[0028] Figure 1 The present invention is a schematic structural diagram of a laser detuning frequency stabilization device involved in the Fabry-Perot cavity locked cavity method for laser detuning frequency stabilization of a SERF magnetometer. Figure 2 This is a flow chart of the Fabry-Perot cavity lock method for laser detuning and frequency stabilization of SERF magnetometers according to the present invention. Figures 1 to 2As shown, a Fabry-Perot cavity locking method for laser detuning and frequency stabilization of a SERF magnetometer comprises the following steps: Step 1, scanning a Fabry-Perot cavity in a laser detuning and frequency stabilization device of a SERF magnetometer to obtain multiple longitudinal modes of an incident laser, where the longitudinal modes are transmission peaks of a transmitted laser; Step 2, selecting one of the transmission peaks and applying a preset DC voltage to a piezoelectric converter connected to the Fabry-Perot cavity to preliminarily lock the cavity length of the Fabry-Perot cavity; Step 3, superimposing a modulation signal on the DC voltage to modulate the cavity length, thereby tuning the optical power signal of the transmitted laser; Step 4, A phase-locked amplifier is used to demodulate the optical power signal according to the modulation signal to obtain an error signal describing the degree of frequency error. In step 5, it is determined whether the error signal is zero. If so, the process proceeds to step 6. If not, it is determined whether it is greater than zero or less than zero. If it is greater than zero, the process returns to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity. If it is less than zero, the process returns to step 2 to decrease the DC voltage to correct the cavity length of the Fabry-Perot cavity. In step 6, the cavity length is continuously locked to obtain a stable free spectrum range, thereby providing a stable frequency reference source for laser detuning and frequency stabilization of the SERF magnetometer.

[0029] The SERF magnetometer laser detuning frequency stabilization device in step 1 includes a frequency-stabilized laser 1, a piezoelectric converter 2, a Fabry-Perot cavity 3, a photodetector 4, a lock-in amplifier 5, a Fabry-Perot cavity driver 6, and a host computer 7, which are connected in sequence. The Fabry-Perot cavity driver 6 is connected to the piezoelectric converter 2. The piezoelectric converter 2 is a piezoelectric ceramic, which is rigidly coupled to the laser incident surface of the Fabry-Perot cavity 3.

[0030] The host computer 7 issues an instruction to the Fabry-Perot cavity driver 6 to make the Fabry-Perot cavity driver 6 work in a scanning mode or a locking mode. In the scanning mode, the Fabry-Perot cavity driver 6 outputs a triangular wave to scan the cavity length of the Fabry-Perot cavity 3. The laser transmitted from the Fabry-Perot cavity 3 has multiple laser transmission peaks formed by interference resonance in the cavity and is displayed by the host computer 7; in the locking mode, the Fabry-Perot cavity driver 6 outputs a DC voltage to lock the cavity length of the Fabry-Perot cavity 3, and superimposes a modulation signal on the DC voltage to modulate the cavity length. The modulation signal is sent to the phase-locked amplifier 5 to demodulate the optical power signal to obtain an error signal representing the difference between the resonant frequency of the Fabry-Perot cavity 3 and the laser frequency.

[0031] Step 2 includes the following relational expressions:

[0032]

[0033] Where L is the cavity length, N is a positive integer, λ is the incident laser wavelength, and n is the refractive index.

[0034] Step 6 includes the following relational expressions:

[0035]

[0036] where v FSR is the free spectral range, c is the speed of light, n is the refractive index, and L is the cavity length. When the cavity length is locked, the free spectral range is also locked, which can provide a stable frequency reference for laser detuning and frequency stabilization.

[0037] The present invention relates to a Fabry-Perot cavity locking method for laser detuning and frequency stabilization in a SERF magnetometer. This method achieves a Fabry-Perot cavity with a stable cavity length by locking the resonant frequency of the Fabry-Perot cavity to a frequency-stabilized laser beam that has been atomically locked at the energy level. The method devised by the present invention locks the cavity length of the laser according to the transmission peak position of the laser transmitted through the Fabry-Perot cavity, modulates and demodulates the transmitted laser optical power signal, and then corrects the cavity length of the Fabry-Perot cavity through feedback control. This ensures that the resonant frequency of the Fabry-Perot cavity remains resonant with the frequency of the laser emitted by the laser for a long period of time, thereby achieving a stable free spectral range. This provides a stable frequency reference and a large detuning amount for the laser used in SERF extremely weak magnetic field measurements.

[0038] A Fabry-Perot cavity lock system for laser detuning and frequency stabilization of a SERF magnetometer comprises a frequency-stabilized laser (1), a piezoelectric ceramic (2), a Fabry-Perot cavity (3), a photodetector (4), a lock-in amplifier (5), a Fabry-Perot cavity driver (6), and a host computer (7).

[0039] The frequency-stabilized laser is a laser that has been frequency-stabilized by a laser frequency stabilization method and can output a stable laser frequency to provide a frequency reference for the Fabry-Perot cavity.

[0040] The piezoelectric ceramic is rigidly coupled to the laser incident surface of the Fabry-Perot cavity.

[0041] The photodetector can convert the detected optical power signal into a voltage signal and has a multi-level voltage amplification function, thereby enabling the acquisition of the transmitted laser optical power signal of the Fabry-Perot cavity.

[0042] The Fabry-Perot cavity driver can transmit data to a host computer via serial communication and display waveforms on the host computer; the host computer can issue instructions to the driver to enable the driver to operate in a scanning mode or a locking mode.

[0043] Among them, the Fabry-Perot cavity driver can output a triangular wave to scan the cavity length of the Fabry-Perot cavity in scanning mode. Multiple laser transmission peaks can be observed on the host computer. This is because the laser undergoes interference resonance in the cavity, and the intensity of the transmitted laser will be significantly enhanced.

[0044] Among them, the Fabry-Perot cavity driver can output a DC voltage to lock the cavity length of the Fabry-Perot cavity in the locking mode, and superimpose a modulation signal on the DC voltage to modulate the cavity length. The modulation signal is sent to the phase-locked amplifier to demodulate the optical power signal to obtain an error signal representing the difference between the resonant frequency of the Fabry-Perot cavity and the laser frequency.

[0045] The Fabry-Perot cavity driver adjusts the output DC signal according to the error signal demodulated by the lock-in amplifier, corrects the cavity length of the Fabry-Perot cavity, and keeps the cavity length locked.

[0046] The Fabry-Perot cavity locking method for laser detuning and frequency stabilization of a SERF magnetometer according to the present invention comprises the following steps:

[0047] Step 1: In the device, a frequency-stabilized laser (1) stabilizes the laser frequency through a frequency-stabilizing optical path, emits a 780nm laser, and is incident from the side of the Fabry-Perot cavity (3) coupled to the piezoelectric ceramic (2). The transmitted laser output from the Fabry-Perot cavity (3) enters the photodetector (4), which converts the detected optical power signal into a voltage signal, which is then transmitted to a lock-in amplifier (5) and a Fabry-Perot cavity driver (6). The Fabry-Perot cavity driver (6) then converts the analog signal into a digital signal and sends it to a host computer (7). The host computer (7) uses its internal oscilloscope function to convert the digital signal into a waveform for display.

[0048] Step 2: The host computer (7) sends a scanning mode instruction to the Fabry-Perot cavity driver (6). The Fabry-Perot cavity driver (6) outputs a triangular wave and applies it to the piezoelectric ceramic (2) to scan the cavity length of the Fabry-Perot cavity (3). The host computer (7) sends an instruction to adjust the voltage amplitude and voltage bias of the triangular wave until a transmission peak can be observed through the oscilloscope function of the host computer (7). The appearance of the transmission peak indicates that the cavity length at this time meets the conditions for the resonance of the Fabry-Perot cavity (3) and the stabilized laser (1). The principle of this phenomenon is shown in the following formula, where L is the cavity length, N is an integer, λ is the wavelength of the incident laser, and n is the refractive index. The condition that the Fabry-Perot cavity (3) and the stabilized laser (1) need to meet for the resonance is that the cavity length is an integer multiple of half the wavelength of the laser.

[0049]

[0050] Step 3: Select a transmission peak to lock the cavity length on the host computer (7), and send a locking mode instruction to the Fabry-Perot cavity driver (6). The Fabry-Perot cavity driver (6) outputs a DC voltage to lock the cavity length. The voltage corresponds to the voltage value applied by the Fabry-Perot cavity driver (6) to the piezoelectric ceramic (2) when the transmission peak appears.

[0051] Step 4: The host computer (7) sends an instruction to the Fabry-Perot cavity driver (6) to superimpose a modulation signal on the DC voltage, causing the cavity length to produce a small jitter within a certain range. At the same time, the transmitted laser light power signal of the Fabry-Perot cavity (3) also produces a small signal fluctuation. The photodetector (4) converts the signal into a voltage signal and sends it to the phase-locked amplifier (5).

[0052] Step 5: The lock-in amplifier (5) uses the modulation signal received from the Fabry-Perot cavity driver (6) to demodulate the voltage signal input by the photodetector (4) to obtain an error signal, which is then sent to the Fabry-Perot cavity driver (6). The error signal represents the difference between the resonant frequency of the Fabry-Perot cavity (3) and the frequency of the laser emitted by the stabilized laser (1).

[0053] Step 6: The Fabry-Perot cavity driver (6) adjusts the output DC voltage value according to the error signal, corrects the cavity length of the Fabry-Perot cavity (3), and maintains resonance between the Fabry-Perot cavity (3) and the frequency-stabilized laser (1). If the error signal is greater than zero, the DC voltage is increased to increase the transmitted laser light power; if the error signal is equal to zero, the DC voltage is kept unchanged; if the error signal is less than zero, the DC voltage is reduced to increase the transmitted laser light power.

[0054] Step 7: Keep the modulation signal unchanged, continue to superimpose it on the DC voltage, and repeat steps 4 to 7 to achieve continuous locking of the Fabry-Perot cavity, obtain a stable free spectrum range, and provide a stable frequency reference source for the SERF magnetometer laser detuning frequency stabilization. The relationship between the free spectrum range of the Fabry-Perot cavity and the cavity length is shown in the following formula: FSR is the free spectral range, c is the speed of light, n is the refractive index, and L is the cavity length. When the cavity length is locked, the free spectral range is also locked, which can provide a stable frequency reference for laser detuning and frequency stabilization.

[0055]

[0056] This method can more conveniently lock the cavity length of the Fabry-Perot cavity (3), that is, lock the free spectrum range of the Fabry-Perot cavity (3), and provide a stable frequency reference and a large frequency detuning amount for the laser used for SERF extremely weak magnetic field measurement.

[0057] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A Fabry-Perot cavity-locked method for laser detuning frequency stabilization in SERF magnetometers, characterized in that: The following steps are involved: Step 1: Scan the Fabry-Perot cavity in the laser detuning frequency stabilization device of the SERF magnetometer to obtain multiple longitudinal modes of the incident laser, which are the transmission peaks of the transmitted laser. Step 2: selecting one of the transmission peaks and applying a preset DC voltage to a piezoelectric converter connected to the Fabry-Perot cavity to preliminarily lock the cavity length of the Fabry-Perot cavity; Step 3, superimposing a modulation signal on the DC voltage to modulate the cavity length, thereby tuning the optical power signal of the transmitted laser; Step 4: Demodulate the optical power signal according to the modulation signal using a lock-in amplifier to obtain an error signal describing the degree of frequency error; Step 5, determining whether the error signal is zero. If so, proceeding to step 6. If not, determining whether the error signal is greater than zero or less than zero. If greater than zero, returning to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity. If less than zero, returning to step 2 to decrease the DC voltage to correct the cavity length of the Fabry-Perot cavity. Step 6: Continuously lock the cavity length to obtain a stable free spectrum range, providing a stable frequency reference source for the SERF magnetometer laser detuning frequency stabilization; The SERF magnetometer laser detuning frequency stabilization device in step 1 includes a frequency-stabilized laser, a piezoelectric converter, a Fabry-Perot cavity, a photodetector, a lock-in amplifier, a Fabry-Perot cavity driver, and a host computer connected in sequence, wherein the Fabry-Perot cavity driver is connected to the piezoelectric converter; The host computer issues an instruction to the Fabry-Perot cavity driver to make the Fabry-Perot cavity driver operate in a scanning mode or a locking mode. In the scanning mode, the Fabry-Perot cavity driver outputs a triangular wave to scan the cavity length of the Fabry-Perot cavity. The laser transmitted from the Fabry-Perot cavity has multiple laser transmission peaks formed by interference resonance in the cavity and is displayed by the host computer. In the locking mode, the Fabry-Perot cavity driver outputs a DC voltage to lock the cavity length of the Fabry-Perot cavity, and superimposes a modulation signal on the DC voltage to modulate the cavity length. The modulation signal is sent to a phase-locked amplifier to demodulate the optical power signal to obtain an error signal representing the difference between the resonant frequency of the Fabry-Perot cavity and the laser frequency.

2. The Fabry-Perot cavity locked method for laser detuning frequency stabilization of SERF magnetometer according to claim 1, characterized in that: The piezoelectric converter is a piezoelectric ceramic, and the piezoelectric ceramic is rigidly coupled to the laser incident surface of the Fabry-Perot cavity.

3. The Fabry-Perot cavity locked method for laser detuning frequency stabilization of SERF magnetometer according to claim 1, characterized in that: Step 2 includes the following relational expressions: Where L is the cavity length, N is a positive integer, λ is the incident laser wavelength, and n is the refractive index.

4. The Fabry-Perot cavity locked method for laser detuning frequency stabilization of SERF magnetometer according to claim 1, characterized in that: Step 6 includes the following relational expressions: where v FSR is the free spectral range, c is the speed of light, n is the refractive index, and L is the cavity length. When the cavity length is locked, the free spectral range is also locked, which can provide a stable frequency reference for laser detuning and frequency stabilization.

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