Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometer

Abstract

The invention relates to a Fabry-Perot cavity locking method for laser detuning frequency stabilization of an SERF magnetometer. According to the method, the resonant frequency of the Fabry-Perot cavity is locked to a beam of frequency-stabilized laser subjected to atomic energy level locking, and the Fabry-Perot cavity with the stable cavity length is obtained. The method designed by the invention comprises the following steps: locking the cavity length of laser according to the transmission peak position of transmission laser of the Fabry-Perot cavity, modulating and demodulating the optical power signal of the transmission laser, and then correcting the cavity length of the Fabry-Perot cavity in a feedback control manner. Namely, the resonant frequency of the Fabry-Perot cavity and the frequency of the laser emitted by the laser are kept in resonance for a long time, so that a stable free spectral range is obtained, and a stable frequency reference and a large detuning amount are provided for the SERF extremely weak magnetic measurement laser.

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

[0003] In a spin-exchange relaxation free (SERF) magnetometer, optical pumping of atomic spins by semiconductor lasers is a prerequisite for ultra-high sensitivity atomic spin magnetic field measurements. In order to achieve highly sensitive SERF extremely weak magnetic field measurements, the laser frequency stability must reach the MHz level. At the same time, in order to avoid ultra-high optical thickness caused by the resonance of the laser with alkali metal atoms, a detuning of up to 100 GHz is often required.

[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 spectrum, 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, in the absence of suitable atomic spectrum lines 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 the traditional laser frequency stabilization method cannot provide a large laser frequency detuning amount for SERF extremely weak magnetic field measurement. The present invention provides a Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometer, which utilizes a Fabry-Perot cavity that can lock the cavity length for a long time to provide a fixed free spectral range as a reference frequency for the stabilized laser, thereby achieving detuning of the laser frequency.

[0006] The technical solution of the present invention is as follows:

[0007] The Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometer is characterized by comprising the following steps:

[0008] Step 1, scanning the Fabry-Perot cavity in the laser detuning frequency stabilization device of the SERF magnetometer to obtain multiple longitudinal modes of the incident laser, where the longitudinal mode is the transmission peak 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, using a lock-in amplifier to demodulate the optical power signal according to the modulation signal to obtain an error signal describing the degree of frequency error;

[0012] Step 5, determine whether the error signal is zero, if yes, proceed to step 6, if no, determine whether it is greater than zero or less than zero, if greater than zero, return to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity, if less than zero, return to step 2 to reduce 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 stabilization laser, a piezoelectric converter, a Fabry-Perot cavity, a photodetector, a phase-locked 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 instructions to the Fabry-Perot cavity driver to make the Fabry-Perot cavity driver work 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 are 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 the detuning and frequency stabilization of the laser.

[0023] The technical effects of the present invention are as follows: the Fabry-Perot cavity locking method for laser detuning and frequency stabilization of SERF magnetometers of the present invention can utilize the wide amplitude range of the triangular wave output by the Fabry-Perot cavity driver to scan out multiple laser longitudinal modes, that is, laser transmission peaks, and can lock the cavity length on any scanned transmission peak. After the cavity length of the Fabry-Perot cavity is locked, its free spectrum range is also locked accordingly, so that a stable frequency reference source can be provided for a laser that needs detuning and frequency stabilization, and its cavity length is sufficient for the laser to achieve a large 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 diagram of the structure of a laser detuning frequency stabilization device involved in the Fabry-Perot cavity locking method for laser detuning frequency stabilization of a SERF magnetometer.

[0025] Figure 2 The present invention is a schematic flow chart of a Fabry-Perot cavity lock method for laser detuning and frequency stabilization of a SERF magnetometer. Figure 2The method comprises the steps of: scanning the Fabry-Perot cavity in the laser detuning frequency stabilization device of the SERF magnetometer to obtain a plurality of longitudinal modes of the incident laser, which are the transmission peaks of the transmitted laser; selecting one of the transmission peaks and applying a corresponding DC voltage to the piezoelectric converter to preliminarily lock the cavity length of the Fabry-Perot cavity; superimposing a modulation signal on the DC voltage to modulate the cavity length, thereby tuning the optical power signal of the transmitted laser; 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; judging whether the error signal is zero, if yes, proceeding to step 6, if not, judging 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 reduce the DC voltage to correct the cavity length of the Fabry-Perot cavity; and 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- phase-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 diagram of the structure of a laser detuning frequency stabilization device involved in the Fabry-Perot cavity locking method for laser detuning frequency stabilization of a SERF magnetometer. Figure 2 The figure 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. Figure 1 to Figure 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 a plurality of longitudinal modes of an incident laser, wherein the longitudinal modes are transmission peaks of a transmitted laser; step 2, selecting one of the transmission peaks, 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; Step 5, determine whether the error signal is zero, if yes, proceed to Step 6, if not, determine whether it is greater than zero or less than zero, if greater than zero, return to Step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity, if less than zero, return to Step 2 to reduce 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, and provide a stable frequency reference source for the laser detuning frequency stabilization of the SERF magnetometer.

[0029] The laser detuning frequency stabilization device of the SERF magnetometer in step 1 comprises a frequency stabilization laser 1, a piezoelectric converter 2, a Fabry-Perot cavity 3, a photodetector 4, a phase-locked amplifier 5, a Fabry-Perot cavity driver 6 and a host computer 7 connected in sequence, wherein 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 instructions 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 the detuning and frequency stabilization of the laser.

[0037] 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 frequency-stabilized laser beam 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 optical 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 resonant with the frequency of the laser emitted by the laser for a long time, thereby obtaining a stable free spectrum range, and providing a stable frequency reference and a large detuning amount for the laser used for SERF extremely weak magnetic measurement.

[0038] A Fabry-Perot cavity lock system for laser detuning and frequency stabilization of a SERF magnetometer comprises a frequency stabilization laser (1), a piezoelectric ceramic (2), a Fabry-Perot cavity (3), a photodetector (4), a phase-locked 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 photoelectric detector can convert the detected optical power signal into a voltage signal and has a multi-level voltage amplification function, thereby enabling the collection 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 through serial communication and display waveforms on the host computer; the host computer can issue instructions to the driver to make the driver work 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 the scanning mode, and 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 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.

[0045] The Fabry-Perot cavity driver adjusts the output DC signal according to the error signal demodulated by the phase-locked 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 SERF magnetometer of the present invention comprises the following steps:

[0047] Step 1: In the device, the frequency-stabilized laser (1) stabilizes the laser frequency through the frequency-stabilized optical path, emits a 780nm laser, and is incident from the side of the Fabry-Perot cavity (3) coupled with the piezoelectric ceramic (2). The transmitted laser output from the Fabry-Perot cavity (3) enters the photodetector (4), and the photodetector (4) converts the detected optical power signal into a voltage signal, which is then transmitted to the phase-locked amplifier (5) and the Fabry-Perot cavity driver (6). The Fabry-Perot cavity driver (6) then converts the analog signal into a digital signal and sends it to the host computer (7). The host computer (7) uses the 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), and 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 the 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 frequency-stabilized laser (1). The principle of this phenomenon is shown in the following formula, L is the cavity length, N is an integer, λ is the incident laser wavelength, n is the refractive index, and the condition that the Fabry-Perot cavity (3) and the frequency-stabilized laser (1) need to meet for the resonance is that the cavity length is an integer multiple of the laser half wavelength.

[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 a command to the Fabry-Perot cavity driver (6) to superimpose a modulation signal on the DC voltage, so that the cavity length produces a small jitter within a certain range, and 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 phase-locked amplifier (5) demodulates the voltage signal input by the photodetector (4) with the modulation signal received from the Fabry-Perot cavity driver (6) 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 frequency-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 keeps the Fabry-Perot cavity (3) and the frequency-stabilized laser (1) in resonance. 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, 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 the detuning and frequency stabilization of the laser.

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

Claims

1. A Fabry-Perot cavity lock method for laser detuning frequency stabilization in SERF magnetometers, characterized in that: The following steps are involved: Step 1, scanning the Fabry-Perot cavity in the laser detuning frequency stabilization device of the SERF magnetometer to obtain multiple longitudinal modes of the incident laser, where the longitudinal mode is the transmission peak 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, using a lock-in amplifier to demodulate the optical power signal according to the modulation signal to obtain an error signal describing the degree of frequency error; Step 5, determine whether the error signal is zero, if yes, proceed to step 6, if no, determine whether it is greater than zero or less than zero, if greater than zero, return to step 2 to increase the DC voltage to correct the cavity length of the Fabry-Perot cavity, if less than zero, return to step 2 to reduce 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.

2. The Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometer according to claim 1, characterized in that: The SERF magnetometer laser detuning frequency stabilization device in step 1 includes a frequency stabilization laser, a piezoelectric converter, a Fabry-Perot cavity, a photodetector, a phase-locked 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.

3. The Fabry-Perot cavity lock 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.

4. The Fabry-Perot cavity locking method for laser detuning frequency stabilization of SERF magnetometer according to claim 2, characterized in that: The host computer issues instructions to the Fabry-Perot cavity driver to make the Fabry-Perot cavity driver work 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 are 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.

5. The Fabry-Perot cavity locking 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.

6. The Fabry-Perot cavity locking 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 the detuning and frequency stabilization of the laser.

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