Transfer spectrum frequency stabilization device based on atomic beam modulation

Abstract

The invention relates to the technical field of laser frequency stabilization, and discloses a transfer spectrum frequency stabilization device based on atomic beam modulation, which comprises a frequency alignment module, a frequency stabilization module and an electricity module, the frequency alignment module comprises a laser output unit and a beam splitter, and a laser beam output by the laser output unit is divided into first pumping laser and first detection laser through the beam splitter; the frequency stabilization module comprises a phase modulation unit, a beam combiner, a hot atomic beam chamber and a detector; the phase modulation unit performs phase modulation on the first pumping laser to obtain second pumping laser; the first detection laser enters a hot atomic beam cavity, the second pumping laser and the first detection laser reversely and coaxially enter the hot atomic beam cavity through a beam combiner, a nonlinear four-wave mixing effect is generated between the second pumping laser and a hot atomic beam in the atomic beam cavity, and the formed second detection laser is received by a detector; the electrical module is used for obtaining error signals according to detection signals of the detector and feeding back the error signals to the laser output unit. And the high-frequency stability of the laser beam is realized.

Description

Technical Field

[0001] The invention relates to the technical field of laser frequency stabilization, and in particular to a frequency stabilization device based on atomic beam modulation transfer spectrum. Background Art

[0002] Narrow linewidth lasers with high frequency stability are important components of optical clock systems. There are two commonly used methods for laser frequency stabilization. One is to lock the laser frequency to the resonant absorption line of atoms and molecules, and the other is to use the ultra-stable, high-precision FP cavity as a frequency reference to lock the frequency of the laser. The former is based on specific absorption spectra and has the characteristics of good frequency reproducibility, high short-term and long-term stability, strong anti-interference ability, compact and stable structure, etc. It is the most commonly used frequency stabilization method in quantum systems, including saturation absorption spectroscopy, polarization spectroscopy, modulation transfer spectroscopy, etc. Modulation transfer spectroscopy technology is essentially a laser heterodyne detection technology. The phase-modulated pump laser and the unmodulated detection laser pass through the atomic and molecular gas medium to produce saturated absorption four-wave mixing nonlinear effects, thereby generating a process of transferring the modulated signal to the detection light. The error signal demodulated by the modulation transfer method can remove background fluctuations and noise, reduce the interference of residual amplitude modulation, and ultimately achieve stable and reliable, non-unlocking, non-modulated laser output. Traditional modulation transfer spectroscopy frequency stabilization technology generally uses an atomic gas chamber to provide characteristic spectral lines. In order to increase the frequency stability of the stabilized laser, it is necessary to increase the signal-to-noise ratio of the error signal. The gas pressure or the absorption length of the gas is often used to increase the gas absorption rate of the laser. However, increasing the gas pressure means increasing the probability of gas collisions, which causes collision broadening of the characteristic spectral lines and reduces the frequency stability. Increasing the absorption length of the gas means increasing the return optical path, thereby increasing the complexity of the optical path of the modulation transfer spectroscopy.

[0003] Therefore, there is an urgent need for a frequency stabilization device based on atomic beam modulation transfer spectrum to solve the above problems. Summary of the invention

[0004] Based on the above, the purpose of the present invention is to provide a frequency stabilization device based on atomic beam modulation transfer spectrum, which ensures a high signal-to-noise ratio while maintaining a narrow modulation transfer spectrum linewidth, thereby achieving high frequency stability of the laser beam.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A frequency stabilization device based on atomic beam modulation transfer spectrum, comprising a frequency alignment module, a frequency stabilization module and an electrical module;

[0007] The frequency alignment module comprises a laser output unit and a beam splitter, wherein the laser output unit is used to output a laser beam, and the laser beam is divided into a first pump laser and a first detection laser via the beam splitter;

[0008] The frequency stabilization module includes a phase modulation unit, a beam combiner, a thermal atom beam chamber and a detector. The phase modulation unit is used to receive the first pump laser and perform phase modulation on the first pump laser to obtain a second pump laser. The first detection laser enters the thermal atom beam chamber, and the second pump laser enters the thermal atom beam chamber via the beam combiner in a reverse coaxial manner with the first detection laser. The first detection laser, the second pump laser and the thermal atom beam in the atom beam chamber undergo a nonlinear four-wave mixing effect, and the second detection laser formed by the first detection laser passing through the thermal atom beam chamber is received by the detector.

[0009] The electrical module is used to obtain an error signal according to the detection signal of the detector, and feed back the error signal to the laser output unit to stabilize the frequency of the output laser beam. The electrical module is also used to transmit a modulation signal to the phase modulation unit.

[0010] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the laser output unit includes a laser and a frequency shifter, the laser is used to emit the laser beam, and the frequency shifter is used to shift the frequency of the laser beam to the transition spectrum of the hot atoms.

[0011] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the laser output unit further includes a first light intensity regulator, which is used to adjust the light intensity of the laser beam after frequency shifting by the frequency shifter.

[0012] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the phase modulation unit includes a first reflector, an electro-optical modulator and a second reflector, the first pump laser is reflected into the electro-optical modulator via the first reflector, the electro-optical modulator adjusts the phase of the first pump laser to obtain the second pump laser, and the second pump laser is reflected via the second reflector to reach the combiner.

[0013] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the phase modulation unit includes a second light intensity regulator, which is arranged between the beam combiner and the second reflector along the optical path of the second pump laser and is used to adjust the light intensity of the second pump laser.

[0014] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, a calcium furnace is provided at one end of the hot atom chamber, and the calcium furnace is used to heat calcium atoms to form a calcium hot atom beam, and to spray the calcium hot atom beam into the hot atom chamber along a direction perpendicular to the first detection light.

[0015] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the electrical module includes a local oscillator source, a mixer and a servo feedback circuit. The local oscillator source is used to provide the modulation signal to the phase modulation unit, the mixer is used to receive the detection signal of the detector and generate the error signal, and the servo feedback circuit controls the current or voltage of the laser according to the error signal to achieve frequency stability of the laser beam output by the laser.

[0016] As a preferred solution of a frequency stabilization device based on atomic beam modulation transfer spectrum, the laser changes the frequency of the output laser beam through current tuning or piezoelectric ceramic tuning.

[0017] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the first reflector and the second reflector are both plane mirrors.

[0018] As a preferred solution of the frequency stabilization device based on atomic beam modulation transfer spectrum, the beam splitter is a polarization beam splitter prism.

[0019] The beneficial effects of the present invention are:

[0020] The present invention provides a frequency stabilization device based on atomic beam modulation transfer spectrum. The nonlinear four-wave mixing effect occurs between a first detection laser, a second pump laser and a hot atom beam in an atomic beam chamber, so that the second pump laser signal is transferred to the first detection laser. The error signal obtained thereby can effectively remove background fluctuations and noise, thereby ensuring a high signal-to-noise ratio. At the same time, the hot atom beam provides a reference spectrum line with a stable frequency. Compared with a traditional atomic gas chamber, the hot atom beam is more stable, and the spectrum line broadening introduced by the collision between hot atoms in the hot atom beam is smaller. The high signal-to-noise ratio of the error signal can be ensured while maintaining a narrower modulation transfer spectrum line width, thereby improving the frequency stability of the laser beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the contents of the embodiments of the present invention and these drawings without paying any creative work.

[0022] Figure 1 It is a structural schematic diagram of a frequency stabilization device based on atomic beam modulation transfer spectrum provided by an embodiment of the present invention;

[0023] Figure 2 It is an optical path diagram of a frequency stabilization device based on atomic beam modulation transfer spectrum provided by an embodiment of the present invention.

[0024] In the figure:

[0025] 100. frequency alignment module; 200. frequency stabilization module; 300. electrical module;

[0026] 1. Laser; 2. Frequency shifter; 3. First light intensity regulator; 4. Beam splitter; 5. First reflector; 6. Electro-optic modulator; 7. Second reflector; 8. Beam combiner; 9. Thermal atom beam chamber; 10. Detector; 11. Second light intensity regulator; 12. Calcium furnace; 13. Local oscillator source; 14. Mixer; 15. Servo feedback circuit. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0028] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0030] In the description of the present embodiment, the terms "upper", "lower", "left", "right" and other directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation of the present invention. In the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0031] like Figure 1 and Figure 2 As shown, this embodiment provides a frequency stabilization device based on atomic beam modulation transfer spectrum, which includes a frequency alignment module 100, a frequency stabilization module 200 and an electrical module 300. The frequency alignment module 100 includes a laser output unit and a beam splitter 4. The laser output unit is used to output a laser beam, and the laser beam is divided into a first pump laser and a first detection laser via the beam splitter 4; the frequency stabilization module 200 includes a phase modulation unit, a beam combiner 8, a thermal atom beam chamber 9 and a detector 10. The phase modulation unit is used to receive the first pump laser and perform phase modulation on the first pump laser to obtain a second pump laser; the first detection laser enters the thermal atom beam chamber 9, and the second pump laser enters the thermal atom beam chamber 9 in the opposite direction and coaxially with the first detection laser via the beam combiner 8, that is, the beam combiner 8 plays a role of spatial beam combining the first detection laser and the second pump laser; the first detection laser, the second pump laser and the thermal atom beam in the atomic beam chamber undergo a nonlinear four-wave mixing effect, and the second detection laser formed after the first detection laser passes through the thermal atom beam chamber 9 is received by the detector 10. The nonlinear four-wave mixing effect occurs through the first detection laser, the second pump laser and the hot atom beam in the atomic beam chamber, so that the second pump laser signal is transferred to the first detection laser. The error signal obtained in this way can effectively remove background fluctuations and noise, and ensure a high signal-to-noise ratio. At the same time, the hot atom beam provides a frequency-stable reference spectrum line. Compared with the traditional atomic gas chamber, the hot atom beam is more stable, and the spectral line broadening introduced by the collision between hot atoms in the hot atom beam is smaller, which can maintain a narrower modulation transfer spectrum line width while ensuring a high signal-to-noise ratio of the error signal, thereby improving the frequency stability of the laser beam.

[0032] In the present embodiment, a calcium furnace 12 is provided at one end of the hot atom chamber, and the calcium furnace 12 is used to heat calcium atoms to form a calcium hot atom beam, and is used to spray the calcium hot atom beam into the hot atom chamber in a direction perpendicular to the first detection light. The calcium furnace 12 provides a stable and sufficient calcium atom beam flow rate, and the calcium atoms are sprayed to the atomic beam chamber clock at a high speed, so that the spectral line broadening introduced by the collision between calcium atoms is negligible, thereby improving the frequency stability of the laser beam. Of course, in other embodiments, other atomic furnaces, such as strontium furnaces, ytterbium furnaces, etc., can also be provided at one end of the hot atom chamber to generate a strontium hot atom beam or an ytterbium hot atom beam in the hot atom chamber, which is specifically set according to actual needs.

[0033] Specifically, the laser output unit includes a laser 1 and a frequency shifter 2, wherein the laser 1 is used to emit a laser beam, and the frequency shifter 2 is used to shift the frequency of the laser beam to the transition spectrum of the hot atom, for example, to the transition spectrum of the calcium hot atom. Wherein, the laser 1 is, for example, a 657nm laser 1, and the frequency shifter 2 is, for example, an acousto-optic modulator, which shifts the frequency of the 657nm laser 1 by the acousto-optic diffraction effect, and the frequency shift amount is, for example, 40-200MHz. Since the acousto-optic modulator is a relatively mature prior art, its structure and principle are not described one by one here.

[0034] Optionally, the 657nm laser 1 is a fiber laser 1 or a semiconductor laser 1, and the frequency of the output laser beam is changed by current tuning or piezoelectric ceramic tuning.

[0035] The laser beam after frequency shifting by the frequency shifter 2 is split into two laser beams by the beam splitter 4, one beam is used as the first pump laser, and the other beam is used as the first detection laser. The beam splitter 4 is, for example, a polarization beam splitter prism.

[0036] Preferably, the laser output unit further includes a first light intensity regulator 3, which is used to adjust the light intensity of the laser beam after the frequency shifter 2, so that the light intensity of the laser beam can be adjusted according to demand to meet the effect of the subsequent nonlinear four-wave mixing effect. For example, the first light intensity regulator 3 includes a half glass slide, and the half glass slide is arranged between the frequency shifter 2 and the polarization beam splitter prism along the optical path of the laser beam. The half glass slide and the polarization beam splitter prism work together to achieve the light intensity regulation of the laser beam. The light intensity of the laser beam can be adjusted to different degrees according to demand by rotating the angle of the half glass slide. The laser beam is divided into a first pump laser and a first detection laser, for example, at an energy ratio of 1:1 or 2:1 by the half glass slide and the polarization beam splitter prism, and the angle of the half glass slide is adjusted according to the signal-to-noise ratio of the spectral line to achieve the optimal energy ratio. Of course, in other embodiments, the first light intensity regulator 3 can also be other structures, such as an attenuator or a liquid crystal, etc., which are specifically set according to actual needs.

[0037] Furthermore, the phase modulation unit includes a first reflector 5, an electro-optic modulator 6, and a second reflector 7. The first pump laser is reflected into the electro-optic modulator 6 via the first reflector 5. The electro-optic modulator 6 adjusts the phase of the first pump laser to obtain the second pump laser. The second pump laser is reflected via the second reflector 7 to reach the beam combiner 8. Among them, the first reflector 5 and the second reflector 7 are both plane reflectors, which are simple and easy to obtain. For example, they are full reflectors in the 657nm band, so that all lasers in this band can be reflected. The first reflector 5 and the second reflector 7 enable the first pump laser and the second pump laser to reach a preset position, which is convenient for the placement of various components. The electro-optic modulator 6 generates phase modulation on the 657nm first pump laser through the photoelectric effect, thereby generating modulation sidebands on both sides of its center frequency, that is, obtaining a second pump laser with sidebands. Since the electro-optic modulator 6 is a relatively mature existing device, its structure and principle will not be described one by one here.

[0038] Specifically, the second pump laser is reflected by the second reflector 7 to reach the beam combiner 8. The beam combiner 8 is, for example, a polarization beam splitter prism. This polarization beam splitter prism is directly opposite to the beam splitter 4 located on the other side of the atomic beam chamber. The second pump laser passing through the polarization beam splitter prism enters the atomic beam chamber in a direction coaxially opposite to the first detection laser, so as to produce a nonlinear four-wave mixing effect with the first detection laser entering the atomic beam chamber in the opposite direction and the hot atoms in the atomic beam chamber, so that sidebands are also generated on both sides of the center frequency of the first detection laser, and a second detection laser is obtained, which is received by the detector 10. The detector 10 receives the second detection laser, that is, a modulation transfer spectrum is obtained, which is convenient for subsequent analysis and feedback, and finally realizes the stable frequency locking of the laser 1. It should be noted that the second pump laser will partially pass through the polarization beam splitter prism in a straight line, and the other part will be reflected and enter the atomic beam chamber. The part of the laser that passes in a straight line is not used here, so it is not described. Among them, the high-speed and stable calcium thermal atomic beam can provide a stable reference spectrum with a narrow spectral line, so that the modulation transfer spectrum maintains a narrow linewidth, so as to finally obtain a laser beam with high frequency stability and narrow linewidth.

[0039] Preferably, the phase modulation unit includes a second light intensity regulator 11, which is arranged between the beam combiner 8 and the second reflector 7 along the optical path of the second pump laser, and is used to adjust the light intensity of the second pump laser, so that the light intensity of the second pump laser can be adjusted according to demand to meet the effect of the subsequent nonlinear four-wave mixing effect. For example, the second light intensity regulator 11 includes a half glass slide, and the adjacent half glass slides and the polarization beam splitter prism work together to achieve the light intensity regulation of the second pump laser. The angle of the half glass slide can be rotated to adjust the light intensity of the second pump laser to different degrees according to demand. Of course, in other embodiments, the second light intensity regulator 11 can also be other structures, such as an attenuator or liquid crystal, etc., which are specifically set according to actual needs.

[0040] Furthermore, the electrical module 300 includes a local oscillator source 13, a mixer 14 and a servo feedback circuit 15. The local oscillator source 13 is used to provide a modulation signal to the phase modulation unit, specifically to provide a radio frequency signal to the electro-optical modulator 6, so that the electro-optical modulator 6 realizes phase modulation of the first pump laser according to the radio frequency signal; the mixer 14 is used to receive the detection signal of the detector 10 and generate an error signal, specifically to obtain the error signal through phase detection, and the servo feedback circuit 15 controls the current or voltage of the laser 1 according to the error signal, that is, to lock the frequency of the output laser beam of the laser 1, thereby realizing the frequency stability of the laser beam output by the laser 1.

[0041] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A frequency stabilization device based on atomic beam modulation transfer spectrum, characterized in that: It includes frequency alignment module, frequency stabilization module and electrical module; The frequency alignment module comprises a laser output unit and a beam splitter, wherein the laser output unit is used to output a laser beam, and the laser beam is divided into a first pump laser and a first detection laser via the beam splitter; The frequency stabilization module includes a phase modulation unit, a beam combiner, a thermal atom beam chamber and a detector. The phase modulation unit is used to receive the first pump laser and perform phase modulation on the first pump laser to obtain a second pump laser. The first detection laser enters the thermal atom beam chamber, and the second pump laser enters the thermal atom beam chamber via the beam combiner in a reverse coaxial manner with the first detection laser. The first detection laser, the second pump laser and the thermal atom beam in the atom beam chamber undergo a nonlinear four-wave mixing effect, and the second detection laser formed by the first detection laser passing through the thermal atom beam chamber is received by the detector. The electrical module is used to obtain an error signal according to the detection signal of the detector, and feed back the error signal to the laser output unit to stabilize the frequency of the output laser beam. The electrical module is also used to transmit a modulation signal to the phase modulation unit.

2. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 1, characterized in that: The laser output unit comprises a laser and a frequency shifter, wherein the laser is used to emit the laser beam, and the frequency shifter is used to shift the frequency of the laser beam to the transition spectrum of the hot atoms.

3. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 2, characterized in that: The laser output unit further includes a first light intensity regulator, which is used to adjust the light intensity of the laser beam after frequency shifting by the frequency shifter.

4. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 1, characterized in that: The phase modulation unit includes a first reflector, an electro-optical modulator and a second reflector. The first pump laser is reflected into the electro-optical modulator via the first reflector. The electro-optical modulator adjusts the phase of the first pump laser to obtain the second pump laser. The second pump laser is reflected via the second reflector to reach the beam combiner.

5. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 4, characterized in that: The phase modulation unit includes a second light intensity regulator, which is arranged between the beam combiner and the second reflector along the optical path of the second pump laser and is used to adjust the light intensity of the second pump laser.

6. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 1, characterized in that: A calcium furnace is provided at one end of the hot atom chamber, and the calcium furnace is used to heat calcium atoms to form a calcium hot atom beam, and is used to spray the calcium hot atom beam into the hot atom chamber along a direction perpendicular to the first detection light.

7. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 2, characterized in that: The electrical module includes a local oscillator source, a mixer and a servo feedback circuit. The local oscillator source is used to provide the modulation signal to the phase modulation unit. The mixer is used to receive the detection signal of the detector and generate the error signal. The servo feedback circuit controls the current or voltage of the laser according to the error signal to achieve frequency stability of the laser beam output by the laser.

8. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 2, characterized in that: The laser changes the frequency of outputting the laser beam by current tuning or piezoelectric ceramic tuning.

9. The frequency stabilization device based on atomic beam modulation transfer spectrum according to claim 4, characterized in that: The first reflector and the second reflector are both plane reflectors.

10. The frequency stabilization device based on atomic beam modulation transfer spectroscopy according to claim 1, characterized in that: The beam splitter is a polarization beam splitter prism.

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