CN112039523B - Rubidium two-photon transition optical frequency scale based on polarization modulation - Google Patents
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- 230000010287 polarization Effects 0.000 title claims abstract description 78
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 title claims abstract description 57
- 229910052701 rubidium Inorganic materials 0.000 title claims abstract description 54
- 230000007704 transition Effects 0.000 title claims abstract description 54
- 230000003287 optical effect Effects 0.000 title claims abstract description 36
- 230000006641 stabilisation Effects 0.000 claims abstract description 10
- 238000011105 stabilization Methods 0.000 claims abstract description 10
- 239000013307 optical fiber Substances 0.000 claims abstract description 9
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- 230000000087 stabilizing effect Effects 0.000 claims description 3
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- 230000005684 electric field Effects 0.000 description 4
- 238000000034 method Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 229910052792 caesium Inorganic materials 0.000 description 2
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000005283 ground state Effects 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
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- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 238000005040 ion trap Methods 0.000 description 1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
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Abstract
The invention discloses a rubidium two-photon transition light frequency scale based on polarization modulation, which comprises a laser, wherein output laser of the laser sequentially passes through an isolator and a half wave plate and then enters a polarization beam splitter, the polarization beam splitter is used for dividing the output laser into first transmission light and first reflection light, the first reflection light is used for comparing beat frequency with an optical comb and outputting frequency, the first transmission light is coupled into Gaussian light through an optical fiber and enters a laser control module, the laser control module outputs zero-order light, the zero-order light is modulated into circularly polarized light by a polarization modulation module and enters a quantum frequency discrimination module, left-hand circular polarization is arranged in a half period of polarized light, right-hand circular polarization is arranged in the other half period, the quantum frequency discrimination module outputs a two-photon transition signal to a frequency stabilization module, and the frequency stabilization module is respectively connected with a piezoelectric control end and a current port of the laser. The invention can improve the short-term frequency stability of the optical frequency standard.
Description
Technical Field
The invention relates to the technical field of atomic frequency standards, in particular to a rubidium two-photon transition optical frequency standard based on polarization modulation.
Background
The atomic frequency standard is a high-precision time-frequency standard taking an atomic stable transition spectral line as a frequency reference, and is widely applied to the fields of navigation, positioning, communication, traffic electric power, military national defense, scientific research and the like. The atomic frequency standard which is currently commercially used is a microwave frequency standard which takes atomic transition spectral lines of a microwave band as references, and comprises a rubidium atomic frequency standard, a cesium atomic frequency standard and a hydrogen atomic frequency standard. In twenty-first century, the atomic light frequency transition-based light frequency standard entered a rapid development period, and the uncertainty reached the level of E-18, which was nearly two orders of magnitude higher than the current best-performing cesium fountain clock. However, these optical frequency bands based on ion traps and optical lattices generally require complex systems to realize atomic trapping and Zhong Zi transition spectral line search, so that the functions of the optical frequency bands can be realized only in a laboratory environment, and the application range is limited.
In recent years, a bubble type rubidium atomic light frequency standard technology gradually enters the field of view of scientific researchers, a rubidium bubble technology is adopted to avoid an atomic trapping system with a complex optical frequency standard, and optical frequency two-photon transition with higher precision is used as a frequency reference, so that the device has the characteristics of miniaturization and high performance. The principle is shown in figure 1, rubidium atoms generate 5S 1/2 To 5D 5/2 According to the two-photon transition selection rule, the rubidium atom can undergo transition from a ground state F=2 to an excited state F=4, 3, 2 and 1, and the transition probability is calculated to be reduced in sequence. After two-photon transition of rubidium atom, 5D can be generated 5/2 To 6P 3/2 To 5S 1/2 In 6P 3/2 To 5S 1/2 The blue fluorescence of 420nm is released in the process of (2), and a fluorescence signal for observing two-photon transition can be obtained by collecting the blue fluorescence by a photomultiplier and amplifying the blue fluorescence by an amplifier.
In the experiment, only one laser with the center frequency of 778nm can be used, two beams of antiparallel laser are generated through a reflecting mirror or a high-reflection film to excite rubidium atoms to generate two-photon transition, after a two-photon transition signal is obtained, the laser frequency is locked at the center frequency of a two-photon transition spectral line peak value from F=2 to F=4 with the maximum transition probability, and then parameter optimization is carried out, so that a stable two-photon optical frequency scale is obtained.
In the literature, two-photon transitions of rubidium are excited by linearly polarized light. As shown in fig. 2, a linearly polarized light excites two-photon transition (Δm F =0) is 0 (which can be obtained from all two-photon transition paths and corresponding transition probabilities under linear polarization). The circularly polarized light also excites two-photon transitions (Δm) F The sign of the light source is corresponding to left and right rotation of the light source, and theoretical calculation shows that the transition probability of two photons excited by circular polarization is about 1.5 times that of linear polarization, and the corresponding transition signal intensity is also enhanced to be 1.5 times that of the original oneUnder the action of circularly polarized light, the comprehensive first-order Zeeman frequency shift corresponding to two-photon transition is not 0, which is unfavorable for obtaining an optical frequency scale with high frequency stability. If the signal to noise ratio is improved by using circular polarization, the first-order Zeeman frequency shift can be eliminated, and the short-term frequency stability of the rubidium atom two-photon optical frequency scale can be improved.
Disclosure of Invention
The present invention aims to solve the above problems by providing a rubidium two-photon transition optical frequency scale based on polarization modulation, and solving the problem of first-order zeeman frequency shift.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the rubidium two-photon transition light frequency scale comprises a laser, output laser of the laser sequentially passes through an isolator and a half wave plate and then enters a polarization beam splitter, the polarization beam splitter is used for dividing the output laser into first transmission light and first reflection light, the first reflection light is used for comparing with an optical comb beat frequency and outputting frequency, the first transmission light is coupled into Gaussian light through an optical fiber and enters a laser control module, the laser control module outputs zero-order light, the zero-order light is modulated into circularly polarized light by a polarization modulation module and enters a quantum frequency discrimination module, left-hand circular polarization is arranged in a half period of the polarized light, right-hand circular polarization is arranged in the other half period, the quantum frequency discrimination module outputs a two-photon transition signal to a frequency stabilization module, and the frequency stabilization module is respectively connected with a piezoelectric control end and a current port of the laser.
The laser control module comprises a zoom optical fiber collimator, wherein first transmitted light enters the zoom optical fiber collimator to be converted into collimated light and then enters the acousto-optic modulator, first-order diffracted light and zero-order light which are output by the acousto-optic modulator are reflected by a voltage-controlled reflecting mirror group after passing through a diaphragm, the rest zero-order light is reflected by the first-order diffracted light and then enters a beam splitter through a lens, the beam splitter is used for dividing the reflected light into second transmitted light and second reflected light, the second transmitted light generates circularly polarized light through a polarization modulation module, the second reflected light is detected by a photoelectric detector and is converted into a voltage signal to be output to a first proportional integral differential amplifier, a first error voltage which is generated by the first proportional integral differential amplifier according to the input voltage signal is fed back to a first signal generator, the power of a radio frequency signal which is output by the first signal generator is adjusted according to the first error voltage, and the radio frequency signal which is generated by the first signal generator is amplified by a radio frequency signal amplifier and then loaded on an acousto-optic crystal in the acousto-optic modulator.
The polarization modulation module as described above includes a ferroelectric polarization rotator, a gram taylor prism and a second signal generator,
the second transmitted light is changed into linear polarized light through a gram Taylor prism and then enters a ferroelectric polarization rotator, a square wave modulation signal is provided for the ferroelectric polarization rotator by a second signal generator, circularly polarized light output by the ferroelectric polarization rotator enters a quantum frequency discrimination module and is reflected back on the rear surface of rubidium bubbles of the quantum frequency discrimination module to form rubidium bubble reflected light, the rubidium bubble reflected light sequentially passes through the ferroelectric polarization rotator and the gram Taylor prism and then enters a beam splitter, and third reflected light and third transmitted light are formed through beam splitting of the beam splitter.
The beam coincidence module as described above includes a four-quadrant position sensor, a beam position aligner and a piezoelectric controller,
the third reflected light is incident to the four-quadrant position sensor to generate an optical power signal, the beam position aligner calculates the spot coordinates of the optical power signal and a second error signal after receiving the optical power signal transmitted by the four-quadrant position sensor, the piezoelectric controller converts the second error signal into a correction voltage, and the voltage-controlled reflector group receives the correction voltage output by the piezoelectric controller and adjusts the reflection direction and position of zero-order light, so that circularly polarized light output by the polarization modulation module and rubidium bubble reflected light are always antiparallel and coincide.
The quantum frequency discrimination module comprises rubidium bubble, a fluorescence collection lens group, a photomultiplier tube and a preamplifier,
the circularly polarized light output by the polarization modulation module enters the rubidium bubble, the rubidium source absorbs the circularly polarized light output by the polarization modulation module and the circularly polarized light reflected by the rear surface of the rubidium bubble at the same time to generate fluorescent signals,
the fluorescence signal is collected by the fluorescence collection lens group and then converted into a photocurrent signal by the photomultiplier and transmitted to the preamplifier, and the preamplifier converts the photocurrent signal into a two-photon transition signal.
The beam waist position of the circularly polarized light output by the polarization modulation module is overlapped with the center position of the rubidium bubble.
The frequency stabilization module as described above includes a lock-in amplifier, a second pid amplifier, a third pid amplifier and an adder,
the lock-in amplifier receives the two-photon transition signal and outputs a third error signal to the second and third pid amplifiers, the lock-in amplifier also outputs a sinusoidal signal to the adder,
the second pid amplifier receives the third error signal and outputs a piezoelectric control signal to the piezoelectric control end of the laser,
the third pid amplifier receives the third error signal and outputs a frequency adjustment signal to the adder,
the adder adds the frequency adjustment signal and the sinusoidal signal to output a frequency modulated signal to a current port of the laser.
Compared with the prior art, the invention has the following beneficial effects:
after the polar modulation scheme is adopted, the first-order zeeman frequency shift of the rubidium atom two-photon transition frequency is counteracted, which is the same as a two-photon frequency scale excited by linearly polarized light. Meanwhile, under the same condition, the signal to noise ratio of the two-photon signal generated by the circularly polarized excited atoms is 1.5 times of the corresponding signal to noise ratio of the linearly polarized light, and the short-term frequency stability of the two-photon optical frequency scale is expected to be improved.
Drawings
FIG. 1 is a schematic representation of the energy level of a 778nm two-photon transition of rubidium;
FIG. 2 is a schematic diagram of Zeeman splitting induced by differently polarized light;
FIG. 3 is a block diagram of a rubidium two-photon transition optical frequency scale based on polar modulation;
FIG. 4 is a diagram of the structural relationship of the laser control module, the beam superposition module, and the polarization modulation module;
FIG. 5 is a block diagram of a quantum frequency discrimination module;
FIG. 6 is a block diagram of a frequency stabilization module;
fig. 7 is a timing diagram of a polar modulation scheme.
Detailed Description
The present invention is described in further detail below in conjunction with the following examples, which are provided to illustrate and explain the present invention and are not intended to limit the present invention.
As shown in fig. 3, the rubidium two-photon transition optical frequency scale based on polarization modulation comprises a 778nm laser 1, an isolator 2, a polarization beam splitter 3, a laser control module 4, a polarization modulation module 5, a light beam superposition module 6, a quantum frequency discrimination module 7 and a frequency stabilization module 8.
The output end of the 778nm laser 1 is connected with the input end of the isolator 2, so that reflected light is prevented from entering the laser 1, and the laser 1 is prevented from being damaged.
As shown in fig. 4, the light passes through the output end of the isolator 2, enters the polarizing beam splitter 3 after passing through a half-wave plate (not shown in the figure), is split into a first transmitted light and a first reflected light by the polarizing beam splitter 3, the proportion of the first transmitted light to the first reflected light can be controlled by rotating the half-wave plate, and the first reflected light is used for beat frequency comparison with an optical comb and Zhong Yueqian frequency output after closed loop. The first transmitted light is coupled through an optical fiber to become Gaussian light with better mode and enters the laser control module 4.
The first transmitted light entering the laser control module 4 enters the zoom optical fiber collimator 41 to become collimated light and then enters the acousto-optic modulator 42, meanwhile, the first signal generator 48 generates a high-frequency sinusoidal radio frequency signal, the power of the radio frequency signal is amplified by the radio frequency signal amplifier 49 and then loaded on an acousto-optic crystal in the acousto-optic modulator 42, the light passing through the beam splitter is partially diffracted to generate first-order diffracted light and direct transmitted zero-order light, the first-order diffracted light and the zero-order light output by the acousto-optic modulator 42 are removed by a diaphragm (not shown in the figure), the remaining zero-order light is reflected by the voltage-controlled mirror group 43 and then enters the beam splitter 45 through the lens 44, the second transmitted light and the second reflected light are separated into a second transmitted light through the beam splitter 45, the second transmitted light is generated by the polarization modulation module 5, the beam waist position of the circularly polarized light coincides with the center position of the rubidium bubble 71, the second reflected light after the beam splitting of the beam splitter 45 is detected by the photoelectric detector 46 and converted into a voltage signal and then output to the first-proportion integral differential amplifier 47, the first-proportion differential amplifier 47 converts the voltage signal into a first circularly polarized light signal, the first-polarized light is successfully amplified by the polarization modulation module 48, the first-frequency signal is successfully amplified by the first-modulated amplifier 48, the first-proportion error signal is successfully generated by the radio frequency amplifier 48, and the first error signal is finally, the first error signal is output, and the radio frequency signal is stabilized by the first-modulated function is generated, and the radio frequency signal is output, and the radio frequency signal is stable.
The second transmitted light (zero-order light) enters the polarization modulation module 5, is changed into linear polarized light with high extinction ratio through the gram taylor prism 52, then enters the ferroelectric polarization rotator 51, meanwhile, square wave modulation signals with the duty ratio of 50% are added to the ferroelectric polarization rotator 51 through the second signal generator 53, so that the polarized state of circularly polarized light output by the ferroelectric polarization rotator 51 is left-handed circular polarization in half period, the other half period is right-handed circular polarization, the circularly polarized light output by the ferroelectric polarization rotator 51 is used as output light of the polarization modulation module 5, the circularly polarized light enters the quantum frequency discrimination module 7 and is reflected on the rear surface of the rubidium bubble 71 to form rubidium bubble reflected light, the rubidium bubble reflected light sequentially enters the ferroelectric polarization rotator 51 and the gram taylor prism 52, then enters the ferroelectric polarization rotator 45, and is split into third reflected light and third transmitted light through the beam splitter 45, and the third reflected light enters the beam superposition module 6. Only the third reflected light will be utilized here and the third transmitted light will not be utilized.
The four-quadrant position sensor 61 in the beam superposition module 6 receives the third reflected light and then automatically measures the optical power distributed on the photocells in four quadrants to generate an optical power signal, the beam position aligner 62 receives the optical power signal transmitted by the four-quadrant position sensor 61 and then calculates the spot coordinates of the optical power signal and a second error signal, the piezoelectric controller 63 converts the second error signal into a correction voltage signal, the voltage-controlled mirror group 43 receives the correction voltage transmitted by the piezoelectric controller 63, the voltage-controlled mirror group 43 automatically adjusts the horizontal and pitching directions according to the magnitude and positive and negative of the correction voltage, and then adjusts the reflection direction and position of zero-order light output by the acousto-optic modulator 42, so that the spot of the optical power signal is always stable at a reference position, that is, the light (output light of the polarization modulation module 5) entering the rubidium bubble 71 is always antiparallel and coincides with the light (rubidium bubble reflected light) reflected from the rear surface (shown as a mirror in fig. 5).
The zero-order light with the direction and position regulated by the light beam superposition module 6 is transmitted by the beam splitter 45 to form second transmission light, the second transmission light generates circularly polarized light by the polarization modulation module 5 and enters the rubidium bubble 71 of the quantum frequency discrimination module 7, and the rubidium source simultaneously absorbs the circularly polarized light and one photon of circularly polarized light reflected by the rear surface of the rubidium bubble 71, and the generation of 5S is shown in figure 1 1/2 -5D 5/2 Is followed by last state 5D 5/2 Cascaded transition 5D due to spontaneous radiation 5/2 -6P 3/2 -5S 1/2 Return to ground state 5S 1/2 Wherein 6P 3/2 -5S 1/2 Blue fluorescence of 420nm is released in the process, and the fluorescence signal is collected by the fluorescence collection lens group 72, converted into a photocurrent signal by the photomultiplier 73, transmitted to the preamplifier 74, and amplified and converted into a voltage signal, namely a two-photon transition signal.
As shown in fig. 6, the lock-in amplifier 81 in the frequency stabilizing module 8 receives the two-photon transition signal from the preamplifier 74 and performs differential processing on the two-photon transition signal to obtain a third error signal, and the second pid amplifier 82 receives the third error signal sent by the lock-in amplifier 81 and feeds back the third error signal to a piezoelectric control signal (voltage signal) at the piezoelectric control end of the laser 1 to form a frequency stabilizing loop. The laser 1 is usually frequency locked at the peak corresponding to rubidium two-photon transition f=2-f=4, and when the laser frequency deviates from the frequency corresponding to this peak, the third error voltage generated by the above process changes the frequency by adjusting the laser cavity length of the 778nm laser 1, so as to compensate the frequency fluctuation (route (a)). Route (b) is the same as route (a), the third pid amplifier 83 receives the third error signal and outputs a frequency adjustment signal to the adder 84, and the frequency adjustment signal and the sinusoidal signal output by the lock-in amplifier 81 are added by the adder 84 to generate a frequency modulation signal, and fed back to the current port of the laser to adjust the frequency. By combining the route (a) and the route (b), the parameters of the corresponding proportional-integral-differential amplifier are regulated by two-way feedback compensation of the piezoelectric control end and the current end of the laser, and the laser frequency output by the laser 1 can be stabilized at the appointed position of the rubidium two-photon transition spectral line. Route (c) provides a sinusoidal signal to the laser 1 for the lock-in amplifier 81 to modulate the laser output frequency, and adds the sinusoidal signal and the third error voltage by the adder 84 and finally outputs the sum to the current port of the laser to adjust the frequency. Route (d) shows that the laser 1 obtains a fluorescence signal by other modules.
The polarization modulation scheme is shown in fig. 6, in which the second transmitted light (zero-order light) passes through the gratehler prism 52 in the polarization modulation module (5) and becomes high-purity linear polarized light, the phase difference between the electric field component Ey and Ex of the laser is 0, the linear polarized light passes through the ferroelectric polarization rotator 51, and the second signal generator 53 outputs a square wave modulation signal to the ferroelectric polarization rotator 51, so that the electric field phase difference of the linear polarized light passing through the ferroelectric polarization rotator 51 changes with the square wave modulation signal, namely, phase modulation is performed, the phase difference between the electric field component Ex and the electric field component Ey of the generated circularly polarized light becomes-pi/2 in the first half period and becomes pi/2 in the second half period, and the corresponding sigma respectively - Left-hand circular polarized light and sigma + Right-handed circularly polarized light. The circularly-varying circularly-polarized light output from the ferroelectric polarization rotator 51 enters the rubidium bubble 71 in the quantum frequency discrimination module 7 to act with rubidium atoms to generate a stronger two-photon transition signal (as described above, the transition probability becomes 1.5 times of the linearly polarized light excitation). Sigma (sigma) - Left-hand circular polarization and sigma + The two-photon transition excited by the right-hand circular polarized light has first-order zeeman frequency shift, and the two frequency shift amounts are equal and opposite, and cancel each other in a period, which shows that the total frequency shift amount is zero. By utilizing the characteristic that the frequency shift amount in one modulation period is 0, in the frequency stabilization link, the laser frequency is locked by an error signal generated by an integral number of modulation periods, and the rubidium two-photon optical frequency scale with higher signal to noise ratio and no first-order Zeeman frequency shift can be realized.
The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.
Claims (6)
1. The rubidium two-photon transition light frequency scale based on polarization modulation comprises a laser (1), and is characterized in that output laser of the laser (1) sequentially passes through an isolator (2) and a half-wave plate and then enters a polarization beam splitter (3), the polarization beam splitter (3) divides the first transmission light into first reflection light, the first reflection light is used for being compared with an optical comb beat frequency and outputting frequency, the first transmission light is coupled into Gaussian light through an optical fiber and enters a laser control module (4), the laser control module (4) outputs zero-order light, the zero-order light is modulated into a circularly polarized light incident quantum frequency discrimination module (7) through a polarization modulation module (5), left-hand circular polarization is adopted in a half-period of the polarization state of the circularly polarized light, the other half-period is right-hand circular polarization, the quantum frequency discrimination module (7) outputs two-photon transition signals to a frequency stabilization module (8), the frequency stabilization module (8) is respectively connected with a piezoelectric control end and a current port of the laser (1),
the laser control module (4) comprises a zoom optical fiber collimator (41), first transmitted light enters the zoom optical fiber collimator (41) to be converted into collimated light and then enters the acousto-optic modulator (42), first-order diffracted light and zero-order light which are output by the acousto-optic modulator (42) are reflected by a voltage-controlled reflecting mirror group (43) after passing through a diaphragm, the rest zero-order light is incident to a beam splitter (45) through a lens (44), the second transmitted light and second reflected light are separated into second transmitted light by the beam splitter (45), the second transmitted light generates circularly polarized light through a polarization modulation module (5), the second reflected light is detected by a photoelectric detector (46) and converted into a voltage signal to be output to a first proportional integral derivative amplifier (47), a first error voltage which is generated by the first proportional integral derivative amplifier (47) according to the input voltage signal is fed back to a first signal generator (48), and a radio frequency signal which is generated by the first signal generator (48) is subjected to power adjustment of an output radio frequency signal according to the first error voltage, and the radio frequency signal which is loaded on the acousto-optic modulator (42) after passing through a radio frequency signal amplifier (49).
2. The rubidium two-photon transition optical frequency scale based on polarization modulation according to claim 1, wherein the polarization modulation module (5) comprises a ferroelectric polarization rotator (51), a gram taylor prism (52) and a second signal generator (53),
the second transmitted light is changed into linear polarized light through a gram Taylor prism (52) and then enters a ferroelectric polarization rotator (51), a square wave modulation signal is provided for the ferroelectric polarization rotator (51) by a second signal generator (53), circularly polarized light output by the ferroelectric polarization rotator (51) enters a quantum frequency discrimination module (7) and is reflected back on the rear surface of a rubidium bubble (71) of the quantum frequency discrimination module (7) to form rubidium bubble reflected light, the rubidium bubble reflected light sequentially passes through the ferroelectric polarization rotator (51) and the gram Taylor prism (52) and then enters a beam splitter (45), and third reflected light and third transmitted light are formed through beam splitting of the beam splitter (45).
3. The rubidium two-photon transition optical standard based on polarization modulation according to claim 2, further comprising a beam coincidence module (6), wherein the beam coincidence module (6) comprises a four-quadrant position sensor (61), a beam position aligner (62) and a piezoelectric controller (63),
the third reflected light is incident to the four-quadrant position sensor (61) to generate an optical power signal, the beam position aligner (62) receives the optical power signal transmitted by the four-quadrant position sensor (61) and calculates the spot coordinates of the optical power signal and a second error signal, the piezoelectric controller (63) converts the second error signal into a correction voltage, and the voltage-controlled reflector group (43) receives the correction voltage output by the piezoelectric controller (63) and adjusts the reflection direction and position of zero-order light, so that circularly polarized light output by the polarization modulation module (5) and rubidium bubble reflected light are always antiparallel and coincide.
4. The rubidium two-photon transition optical frequency scale based on polarization modulation according to claim 3, wherein the quantum frequency discrimination module (7) comprises a rubidium bubble (71), a fluorescence collection lens group (72), a photomultiplier tube (73) and a preamplifier (74),
circularly polarized light output by the polarization modulation module (5) enters the rubidium bubble (71), and the rubidium source absorbs the circularly polarized light output by the polarization modulation module (5) and circularly polarized light reflected by the rear surface of the rubidium bubble (71) simultaneously to generate fluorescent signals,
the fluorescence signal is collected by a fluorescence collection lens group (72), and then converted into a photocurrent signal by a photomultiplier tube (73) and transmitted to a preamplifier (74), and the preamplifier (74) converts the photocurrent signal into a two-photon transition signal.
5. The rubidium two-photon transition light frequency scale based on polarization modulation according to claim 4, wherein the beam waist position of the circularly polarized light output by the polarization modulation module (5) coincides with the center position of the rubidium bubble (71).
6. The rubidium two-photon transition optical frequency scale based on polarization modulation according to claim 4, wherein the frequency stabilizing module (8) comprises a phase-locked amplifier (81), a second proportional-integral-differential amplifier (82), a third proportional-integral-differential amplifier (83) and an adder (84),
the phase-locked amplifier (81) receives the two-photon transition signal and outputs a third error signal to the second proportional-integral-differential amplifier (82) and the third proportional-integral-differential amplifier (83), the phase-locked amplifier (81) also outputs a sinusoidal signal to the adder (84),
the second proportional-integral-differential amplifier (82) receives the third error signal and outputs a piezoelectric control signal to the piezoelectric control end of the laser (1),
the third pid amplifier (83) receives the third error signal and outputs a frequency adjustment signal to an adder (84),
an adder (84) adds the frequency adjustment signal and the sinusoidal signal to output a frequency modulated signal to a current port of the laser (1).
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| CN115173858B (en) * | 2022-06-13 | 2023-10-20 | 中国科学院精密测量科学与技术创新研究院 | Laser power frequency shift suppression device for rubidium two-photon laser frequency standard |
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