RU2395900C1 - Atomic beam frequency standard - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: frequency standard comprises atomic beam tube with source of atomic bundle, microwave resonator, photodetector of optical pumping and output photodetector device. Atomic beam tube includes window of optical detection and window of optical pumping, which are optically joined to outlet of laser module. Besides the second joint is realised via modulator. Outlet of output photodetector device is connected via the first photodetection device and the first unit of automatic frequency tuning with the first control inlet of tuned quartz generator, outlet of which via unit of radio frequency excitation signal generation is connected to radio frequency inlet of microwave resonator. Outlet of photodetector of optical pumping is connected via the second photodetection device, and the second unit of automatic frequency tuning to the first control inlet of controlled current stabiliser, outlet of which is connected to control inlet of laser module. Support inlets of the first automatic frequency tuning unit and unit of radio frequency excitation signal generation are connected to outlet of the first low-frequency generator, besides the second of these joints is realised via the first electronic switch. Support inlets of the second automatic frequency tuning unit and unit of controlled current stabiliser are connected to outlet of the second low-frequency generator, besides, the second of these joints is realised via the second electronic switch. Control inlet of modulator is connected via the third electronic switch to outlet of frequency synthesiser, inlet of which is connected to outlet of tuned quartz generator. The second outlet of the first photodetection device is connected to the second control inlet of tuned quartz generator via the first device of automatic frequency searching, the second outlet of which is connected to control inlet of the first electronic switch. The second outlet of the second photodetection device is connected to the second control inlet of controlled current stabiliser via the second device of automatic frequency searching, the second outlet of which is connected to control inlets of the first automatic frequency searching device and second and third electronic switches.

EFFECT: creation of atomic beam frequency standard, which operates according to double-frequency scheme realised with the help of single laser module, where initial values of frequencies in tuned quartz generator and laser module are automatically set in compliance with frequencies of used atomic transitions.

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Description

The claimed invention relates to a frequency stabilization technique and can be used in passive-type quantum frequency standards with a quantum discriminator based on an atomic beam tube with laser pumping and laser detection of a beam of working atoms.

The principle of operation of the atomic beam frequency standard is based on the stabilization of the frequency of the tunable quartz oscillator relative to the resonant frequency of the spectral line corresponding to a certain quantum transition of the working substance of the atomic beam of the atomic beam tube that performs the function of a quantum discriminator, see, for example, [1] - A.I. .Pikhtelev, A.A. Ulyanov, B.P. Fateev et al. Frequency and time standards based on quantum generators and discriminators. // M., Sov. radio. 1978, p. 5.

The generalized block diagram of the atomic-beam frequency standard contains a tunable quartz oscillator, a radio frequency excitation signal generating unit, an atomic ray tube quantum discriminator and an automatic frequency adjusting block generating a control voltage for the tunable crystal oscillator, connected in series in a closed ring of automatic frequency tuning, and also a block for generating reference signals connected by its outputs to the corresponding inputs of the block automatically Coy loop, and a radio frequency unit for generating a drive signal input and - a yield of a crystal oscillator being adjusted, for example, see RF patent [2] -. RU 2220499 C2, H03L 7/16, H01S 3/10, 27.12.2003. The RF excitation signal generating unit generates, based on the output signal of the tunable crystal oscillator (a harmonic signal with a frequency f ₁ ) and the corresponding output signal of the reference signal generating unit, a phase-frequency (frequency) microwave RF signal, the nominal value of the carrier frequency f _{2 of} which corresponds to the peak the contour of the spectral line of the atomic beam tube (the Ramsey or Rabi line contour) determined by the resonant frequency f _{0 of the} contour of the spectral line the interaction of the working substance of an atomic beam with a radio frequency excitation signal. The frequency f _{0 is} stable and is therefore used as a reference for tuning the frequency of the tunable crystal oscillator. At the output of the atomic beam tube, a signal is generated that carries information about the deviation of the current value of the frequency f ₂ from the frequency f ₀ . The automatic frequency control unit, based on the output signal of the atomic ray tube and the corresponding output signal of the reference signal generation unit, generates, for example, synchronously detecting an error signal, and then, by integrating the error signal, generates a control voltage for the tunable crystal oscillator. Under the influence of the control voltage, the frequency f _{1 of the} output signal of the tunable crystal oscillator and the associated carrier frequency f _{2 of} the RF excitation signal are changed in the direction of decreasing the error signal, thereby stabilizing the frequency of the output signal of the tunable crystal oscillator relative to the frequency f ₀ .

Known atomic beam frequency standard presented in US patent [3] - US 4943955, H03L 7/26, 07.24.1990, containing a tunable crystal oscillator, a radio frequency excitation signal generating unit, an atomic beam tube connected in series in a closed ring of automatic frequency control with a deflecting magnetic system and an automatic frequency control device that generates a control voltage for a tunable crystal oscillator.

The RF excitation signal generating unit comprises a frequency converter and an associated programmable frequency synthesizer. The signal input of the frequency converter, forming the signal input of the RF signal generation unit, is connected to the output of the tunable crystal oscillator. The signal output of the frequency converter, forming the signal output of the RF signal generating unit, is connected to the radio frequency input of the atomic beam tube. The high-frequency output of a programmable frequency synthesizer (the output of a phase-modulated high-frequency signal) is connected to the reference input of the frequency converter. The low-frequency output of a programmable frequency synthesizer (the output of a low-frequency signal with a frequency corresponding to the modulation frequency) forms the reference output of the RF excitation signal generating unit, connected to the reference input of the automatic frequency adjustment device.

As a cathode ray tube, a traditional design cesium tube with a deflecting magnetic system is used, examples of which are presented in US patents: [4] - US 4425653, H01S 3/091, 01/10/1984; [5] - US 4354108, H01S 1/00, 10/12/1982: [6] - US 3967115, H01S 1/00, 06/29/1976; [7] - US 3397310, U.S. Cl. 250-41.3. 08/13/1968; [8] - US 3323008, U.S. Cl. 315-111. 05/30/1967. Such an atomic beam tube contains a source of an atomic beam placed on one axis, the first deflecting magnet. A microwave resonator, a second deflecting magnet and a photoelectronic multiplier, wherein the radio frequency input of the microwave resonator forms the radio frequency input of the atomic beam tube, and the output of the photoelectronic multiplier forms the output of the atomic beam tube.

The automatic frequency control device includes an input unit that performs the functions of amplification and analog-to-digital signal conversion, a central unit that performs the function of digital synchronous detection, and an output unit that performs the functions of digital-to-analog signal conversion and integrates the converted signal. The signal input of the input unit is the signal input of the automatic frequency control device connected to the output of the atomic beam tube. The output of the output unit is the output of the automatic frequency control device connected to the control input of the tunable crystal oscillator.

The work of the atomic beam frequency standard presented in [3] occurs as follows. Block forming a radio frequency excitation signal generation from being adjusted quartz oscillator output signal (a harmonic signal with a frequency f ₁₎ modulated in phase with the frequency of the low-frequency modulation F _m1 microwave signal rf excitation, the nominal value of the carrier frequency f ₂ which corresponds to the resonant frequency f ₀ of the spectral line atomic beam tube, determined by the interaction of the working substance of the atomic beam with a radio frequency excitation signal, and the value of the low-frequency frequency modulation F _m1 corresponds to the half-width of this circuit.

The radio frequency excitation signal is fed to the radio frequency input of the atomic beam tube, i.e. to the RF input of the microwave cavity. The processes occurring in this case in an atomic beam tube are described on the basis of a two-level energy model of the atoms of the working substance with a frequency of the radio frequency atomic transition equal to f ₀ . The essence of these processes is as follows. The initial energy distribution of the beam atoms at the output of the source of the atomic beam obeys the Boltzmann distribution and, to a first approximation, is equally probable. Further, in the region where the first deflecting magnet is located, energetic sorting of atoms occurs due to differences in dipole magnetic moments. As a result of such sorting, atoms in the first (lower) energy state fly into the microwave cavity. The interaction of these atoms with the radio frequency excitation signal of an atomic beam tube is resonant and is described by the contour of the Ramsey spectral line with a central frequency of the radio frequency atomic transition equal to f ₀ . As a result of this interaction, the atoms of the beam at the output of the microwave cavity are predominantly in the second (upper) energy state, i.e. the population is inverted in the energy structure of atoms. The number of beam atoms that have transitioned to the second energy state characterizes the effectiveness of this interaction and, ultimately, determines the value of the signal received at the output of the atomic beam tube (i.e., a value proportional to the number of beam atoms fed to the input of the photoelectron multiplier). To maximize the output signal of the atomic beam tube, the atoms of the beam with the help of a second deflecting magnet are focused on the input of the photomultiplier tube, the output of which is the output of the atomic beam tube.

The output signal of an atomic beam tube thus obtained contains a constant component and harmonics with frequencies that are multiples of the modulation frequency F _m1 . These harmonics carry in their amplitudes and phases information about the deviation of the current value of the frequency f ₂ from the frequency f ₀ . The first of these harmonics is used as a useful component of the output of the atomic ray tube to obtain information about the deviation of the current value of the frequency f ₂ from the frequency f ₀ , i.e. to receive an error signal.

An error signal is obtained in the automatic frequency control device as a result of synchronous detection of the output signal of the atomic ray tube relative to the reference signal with a frequency of F _m1 , which is fed to the reference input of the automatic frequency control device from the reference output of the RF signal generating unit. The resulting error signal is further integrated to obtain a control voltage for the tunable crystal oscillator, which is the output signal of the automatic frequency control device.

Under the influence of the control voltage supplied to the control input of the tunable crystal oscillator from the output of the automatic frequency control device, the frequency f _{1 of the} output signal of the tunable crystal oscillator and the associated carrier frequency f _{2 of} the radio frequency excitation signal are changed to reduce the error signal, thereby stabilizing the frequency the output signal of the tunable crystal oscillator relative to the frequency f ₀ .

The advantage of the considered atomic beam frequency standard is the simplicity of implementation, and the disadvantage is the significant instability of the frequency of the output signal due to the low signal-to-noise ratio at the output of the atomic beam tube, which is associated with the low efficiency of atom sorting and focusing of the atomic beam using deflecting magnets.

The solution to the problem of improving the signal-to-noise ratio at the output of an atomic beam tube and correspondingly increasing the frequency stability of the atomic beam frequency standard is provided in more complicated schemes for implementing atomic beam frequency standards using laser optical pumping and laser optical detection of the atomic beam instead of magnetic sorting and focusing.

Among atomic beam frequency standards using laser optical pumping and laser optical detection of the atomic beam, there are known solutions in which laser optical pumping and laser optical detection are carried out at two different frequencies, see, for example, article [9] - C. Sallot, M. Baldy, D. Gin, R. Petit. 3 · 10 ^-12 · τ ^-1/2 on industrial optically pumped cesium beam frequency standard. // 2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointy with the 17 ^th European Frequency and Time Forum. 2003, pp. 100-104, as well as US patent [10] - US 4684900, H03L 7/26, 08/04/1987.

The essence of the two-frequency scheme of laser optical pumping and laser optical detection of an atomic beam is as follows. Laser optical pumping is performed by single-mode laser radiation with a first frequency ν ₁ in the path section before the beam atoms enter the microwave cavity, and the frequency ν ₁ corresponds to the resonant frequency of the absorbing optical atomic transition between the energy levels of atoms. Laser optical detection is performed by single-mode laser radiation with a second frequency ν ₂ in the trajectory after the beam atoms leave the microwave cavity, while the frequency ν ₂ corresponds to the resonant frequency of the circular optical atomic transition used between the energy levels of atoms. For example, as indicated in [9], in the Cs ¹³³ atomic beam, the transition between the sublevels 6S _1/2 F = 4 and 6Р _3/2 F = 4 can be used as the absorbing optical atomic transition corresponding to the frequency ν ₁ , and as A circular optical atomic transition corresponding to a frequency of ν ₂ can use a transition between the sublevels 6S _1/2 F = 4 and 6Р _3/2 F = 5, in this case the frequency difference is ν ₁ -ν ₂ = 251.4 MHz. Other optical atomic transitions may be used, and it should be noted that the total number of usable optical atomic transitions is limited and is determined by a single number. So, in cesium Cs ^{133 the} number of optical atomic transitions suitable for use for the purposes under consideration is limited by the number of sublevels in the 6P _3/2 state and equal to five, and in rubidium Rb ^{87 it} is limited by the number of sublevels in the 5P _3/2 state and equal to four.

The resonance of the interaction between the working substance of the atomic beam and the radio frequency excitation signal of the microwave cavity is detected by a photo detector using the fluorescence radiation of the atoms of the beam irradiated with the aforementioned laser radiation of detection. The RF excitation signal is a phase (frequency) modulated microwave signal whose carrier frequency f ₂ corresponds to the resonant frequency f _{0 of the} radio frequency atomic transition used, excited by the RF excitation signal. The low-frequency component of the signal taken from the photodetector output, corresponding to the modulation frequency of the RF excitation signal, carries information about the deviation of the current value of the carrier frequency f ₂ from the resonant frequency f ₀ . This signal is then used in a standard way to adjust the frequency of the output signal of the tunable crystal oscillator.

The use of laser optical pumping and laser optical detection leads to an increase in the signal-to-noise ratio at the output of the atomic beam tube, which ultimately makes it possible to reduce the frequency instability of the output signal of the atomic beam frequency standard. Moreover, to achieve this result, it is necessary to ensure the stability of the frequencies of laser optical pumping and laser optical detection.

As a prototype, the rubidium atomic beam frequency standard described in [11] was adopted by A. Besedina, A. Gevorkyan, V. Zholnerov. Two-frequency Pumping in ⁸⁷ Rb Atomic Beam Frequency Standard with Laser Pumping / Detection for Space Application. EFTF '07 // European Frequency and Time Forum, 2007, pp. 623-628, Fig. 6, in which the frequencies of laser optical pumping and laser optical detection are generated using two separate laser modules, the radiation stability of which is ensured by individual automatic tuning circuits frequencies whose structure is considered in the same work.

The atomic beam frequency standard, adopted as a prototype, contains a tunable quartz oscillator connected in series in a closed ring of automatic frequency control, the output of which is the output of the atomic beam frequency standard, an RF signal generation unit, an atomic beam tube, a first photodetector and a first an automatic frequency control unit generating a control voltage for the tunable crystal oscillator, as well as the first low-frequency generator generating a reference signal with a frequency of F _m1 (modulation frequency of the RF excitation signal), the output of which is connected to the reference input of the RF excitation signal generating unit and the reference input of the first automatic frequency control unit.

An atomic beam tube contains an atomic beam source (Rb ⁸⁷ ) located on the same axis and a microwave resonator, the radio frequency input of which forms the radio frequency input of the atomic beam tube connected to the output of the radio frequency excitation signal generating unit. The atomic beam tube has an optical pumping window located in the region of the passage of the atomic beam from the source of the atomic beam to the microwave cavity, which serves to input into the atomic beam the optical pumping signal generated by the laser pump module, and an optical detection window located in the exit region an atomic beam from a microwave cavity, which is used to input an optical detection signal generated by a laser detection module into the atomic beam tube. In the region where the atomic beam leaves the microwave cavity, there is an output photodetecting device, the output of which forms the first output of the atomic beam tube, to which the input of the first photodetector is connected, and in the region of the passage of the atomic beam from the beam source to the microwave cavity there is an optical pump photodetector, the output of which forms the second output of the atomic beam tube.

The second output of the atomic beam tube is connected through a second photodetector to the signal input of the second automatic frequency control unit. The output of the second automatic frequency control unit is connected to the first control input of the first controlled current stabilizer, the output of which is connected to the control input of the laser pump module. The reference input of the second automatic frequency control unit and the reference input of the first controlled current stabilizer are connected to the output of the second low-frequency generator, which forms the reference signal with a frequency of F _m2 (modulation frequency of the radiation of the laser pump module).

The first output of the atomic beam tube, in addition to the above connection with the input of the first photodetector, is also connected to the input of the third photodetector, the output of which through the third block of automatic frequency control is connected to the first control input of the second controlled current stabilizer, the output of which is connected to the control input of the laser detection module . The reference input of the third block of automatic frequency control and the reference input of the second controlled current stabilizer are connected to the output of the third low-frequency generator, which forms the reference signal with a frequency of F _m3 (modulation frequency of the radiation of the laser detection module).

The laser pump module and the laser detection module are made on the basis of semiconductor laser diodes with close laser wavelengths located in the region λ = 780, ... nm, corresponding to the D ₂ absorption line in rubidium Rb ⁸⁷ .

The blocks of automatic frequency control are made according to the traditional scheme, usually used in quantum frequency standards for frequency auto-tuning. The structure of this circuit includes an input amplifier, a synchronous detector and an output integrator, while the reference input of the synchronous detector forms the reference input of the automatic frequency control unit, and the input of the amplifier and the output of the integrator form the signal input and output of the automatic frequency control unit, respectively.

The RF excitation signal generating unit is a step-up modulating frequency converter that generates a phase modulated low-frequency modulated frequency signal from the output signal of a tunable crystal oscillator (harmonic signal with a frequency f ₁ ) and the output signal of the first low-frequency generator (with a frequency F _{m1 of the} order of several tens of hertz) f _m1 microwave radio frequency excitation signal, the nominal value of the carrier frequency f ₂ which corresponds to the resonant frequency f ₀ contour Spectral lines atomic beam tube, determined by the interaction of the working substance of the atomic beam with radio-frequency excitation signal and characterized by contour lines Ramsey, the value of the low-frequency modulation frequency F _m1 corresponds to the half-width of the circuit.

The RF excitation signal taken from the output of the RF excitation signal generating unit is supplied to the radio frequency input of the atomic beam tube (to the radio frequency input of the microwave resonator), through which the atomic beam from the source of the atomic beam, subjected to laser optical pumping, passes.

Laser optical pumping of an atomic beam is carried out by an optical pumping signal, i.e., frequency-modulated radiation of a laser pumping module, introduced into an atomic beam tube through an optical pumping window in the section of passage of an atomic beam from the source of the atomic beam to the microwave cavity. The carrier frequency of the laser pump module corresponds to the resonant frequency ν _{1 of the} absorbing optical atomic transition used, and the modulation frequency F _m2 (of the order of ten kilohertz) is less than the half-width of the spectral line of this transition. Schematically, an optical atomic transition between energy levels corresponding to a resonant frequency ν ₁ is shown in the energy diagram of atoms of a beam of a working substance of an atomic beam tube by a transition between energy levels “2” and “3” (Fig. 1). In the real rubidium atomic beam frequency standard, this optical atomic transition can correspond, for example, to the transition between the sublevels 5S _1/2 F = 2 and 5Р _3/2 F = 2.

As a result of laser optical pumping, the atoms fly into the microwave cavity, being mainly in the energy state of the first (lower) level, designated in Fig. 1 as level “1”. In a microwave resonator, the beam atoms interact with a radio frequency excitation signal - phase-modulated with a frequency of F _{m1 a} microwave signal with a carrier frequency f ₂ corresponding to the resonant frequency f _{0 of the} used radio frequency atomic transition (i.e., the resonant frequency f _{0 of the} spectral line a beam tube determined by the interaction of the working substance of an atomic beam with a radio frequency excitation signal). In the case under consideration, the rubidium atomic beam frequency standard is f ₀ = 6834.682 ... MHz. As a result of the interaction of the working substance of the atomic beam with the radio frequency excitation signal, the atoms of the beam fly out of the microwave cavity, being mainly in the energy state of the second level (level "2", figure 1).

The atomic beam emerging from the microwave cavity undergoes laser optical detection. Laser optical detection is carried out by an optical detection signal — frequency-modulated radiation of a laser detection module, introduced into an atomic beam tube through an optical detection window at the exit site of an atomic beam from a microwave cavity. The carrier frequency of the radiation of the laser detection module corresponds to the resonant frequency ν _{2 of the} used circular optical atomic transition between the energy levels “2” and “3 '” (Fig. 1), and the modulation frequency F _m3 (of the order of ten kilohertz) is less than the half-width of the spectral line of this transition. In a real rubidium atomic beam frequency standard, this optical atomic transition can correspond, for example, to the transition between the sublevels 5S _1/2 F = 2 and 5Р _3/2 F = 3 at a frequency ν ₂ , which differs from the frequency ν ₁ by Δν = ν ₂ -ν ₁ = 267 MHz.

The result of laser optical detection is controlled by the fluorescence light reradiated by the atoms of the beam, which is detected by the output photodetecting device. The spectral components of the signal of the output photodetecting device, corresponding to the frequency F _m1 modulation of the RF signal and the frequency F _m3 modulation of the radiation of the laser detection module, carry information about the deviation of the carrier frequency f _{2 of} the RF signal from the resonant frequency f ₀ and the deviation of the carrier frequency of the radiation of the laser detection module from resonant frequency ν ₂ . These spectral components are extracted from the output signal of the output photodetecting device, respectively, by the first and third photodetector devices.

The spectral component of the output signal of the output photodetecting device, corresponding to the frequency F _{m1 of} modulation of the RF excitation signal, allocated by the first photodetector, is fed to the signal input of the first automatic frequency control unit, which generates a control voltage to adjust the frequency f _{1 of the} tunable crystal oscillator (and, accordingly, associated with it carrier frequency f _{2 of} the radio frequency excitation signal), setting it in accordance with the resonant frequency f _0.

The spectral component of the output signal of the output photodetecting device, corresponding to the frequency F _{m3 of} modulation of the radiation of the laser detection module, allocated by the third photodetector, is fed to the signal input of the third block of automatic frequency control, which generates a control voltage to adjust the second controlled current stabilizer, the constant component of the output current of which determines value of the carrier frequency of the radiation of the laser detection module, setting it in accordance with the resonant frequency ν ₂ .

In a similar way, the radiation frequency of the laser pump module is automatically tuned. In this case, the control of laser optical pumping is performed by the fluorescence light reradiated by the atoms, detected by an optical pump photodetector, the spectral component of the output signal of which corresponds to the frequency F _{m2 of the} radiation modulation of the laser pump module, carries information about the deviation of the carrier frequency of the laser pump module from the resonant frequency ν ₁ . The output signal of the optical pump photodetector is fed through the second photodetector to the signal input of the second automatic frequency control unit, which generates a control voltage to adjust the first controlled current stabilizer, the constant component of the output current of which determines the carrier frequency of the radiation of the laser pump module, setting it in accordance with the resonant frequency ν ₁ .

All three blocks of automatic frequency control work on the same principle, first performing synchronous detection of the signal coming from the output of the corresponding photodetector relative to the reference signal generated by the corresponding low-frequency generator, and then integrating the error signal obtained as a result of synchronous detection to obtain the necessary control voltage.

Thus, in the atomic-beam frequency standard adopted as a prototype, three automatic frequency control rings work simultaneously: the main ring is the automatic frequency control ring of the tunable crystal oscillator, and two additional rings are the automatic frequency control ring of the laser pump module radiation and the ring automatic adjustment of the radiation frequency of the laser detection module. The joint work of these three rings of automatic frequency control provides the ability to achieve the required stability characteristics of the output signal of the atomic beam frequency standard in the steady state.

The achievement of the required stability characteristics is due, among other factors, to the narrow bandwidth of the automatic frequency adjustment rings determined by the width of the spectral lines of the atomic transitions used. As a result of this, the problem arises of forcing the initial (“coarse”) frequency setting of the output signal of the tunable crystal oscillator, which determines the frequency of the RF excitation signal, in accordance with the resonant frequency f ₀ , and also the radiation frequencies of the laser modules in accordance with the resonant frequencies ν ₁ and ν ₂ , which is necessary to ensure the possibility of their subsequent "capture" and "tracking" in the corresponding rings of automatic frequency control.

The obvious solution to this problem, which is implemented in practice, is to “manually” initial configure the tunable crystal oscillator and laser modules using external instrumentation and manually controlled auxiliary voltage sources connected to the second control inputs of the tunable crystal oscillator and controlled current stabilizers. This initial “manual” tuning of the tunable crystal oscillator and laser modules is performed independently for each tuning object and in random order.

The lack of means for automatic initial tuning of the tunable crystal oscillator and laser modules, which necessitates the use of "manual" initial tuning, narrows the scope of the possible practical application of the prototype, limiting it to the class of equipment serviced by technical personnel. This is a disadvantage that impedes the use of the prototype at maintenance-free facilities that operate fully automatically. In addition, the presence of two laser modules, which ensures the implementation of a dual-frequency laser optical pumping and laser optical detection of an atomic beam in an atomic beam tube, complicates the atomic-beam frequency standard, increases energy consumption, and reduces reliability.

The technical result, to which the claimed invention is directed, is to create an atomic-beam frequency standard that operates on a dual-frequency circuit implemented using a single laser module, and in which the initial frequencies of the tunable crystal oscillator and laser module are automatically set in accordance with the frequencies used atomic transitions. Such an atomic beam frequency standard has expanded, in comparison with the prototype, practical applications, including as part of maintenance-free on-board equipment.

The essence of the claimed invention is as follows. The atomic-beam frequency standard contains a tunable quartz oscillator connected in series in a closed loop of automatic frequency control, the output of which is the output of the atomic-beam frequency standard, an RF excitation signal generating unit, an atomic beam tube, a first photodetector and a first automatic frequency control unit, an output which is connected to the first control input of the tunable crystal oscillator, as well as the first low-frequency generator, the output of which of the connections to the reference input of the first block and the automatic frequency reference input unit for generating a radio frequency excitation signal. An atomic beam tube contains an atomic beam source and a microwave resonator located on the same axis, the radio frequency input of which forms the radio frequency input of the atomic beam tube connected to the output of the radio frequency excitation signal generating unit, an optical pump window located in the region of the passage of the atomic beam from the atomic source beam to the microwave cavity, designed to enter into the atomic beam tube an optical pump signal, and an optical detection window located in the output region of the atomic beam and h microwave resonator, designed to enter into the atomic beam tube of the optical detection signal. In addition, in the region of the exit of the atomic beam from the microwave cavity there is an output photodetecting device, the output of which forms the first exit of the atomic beam tube connected to the input of the first photodetector, and in the region of the passage of the atomic beam from the source of the atomic beam to the microwave cavity is an optical photodetector pumping, the output of which forms the second output of the atomic beam tube. The second output of the atomic beam tube is connected through a second photodetector and a second automatic frequency control unit connected in series to the first control input of the controlled current stabilizer, the output of which is connected to the control input of the laser module, the output of which is optically connected to the optical pump window, while the reference input of the second the automatic frequency control unit and the reference input of a controlled current stabilizer are connected to the output of the second low-frequency generator. Unlike the prototype, the output of the first low-frequency generator is connected to the reference input of the RF excitation signal generating unit through the first electronic key, the output of the second low-frequency generator and the reference input of the controlled current stabilizer are connected via the second electronic key, and the optical output of the laser module is connected to the optical window pumping is carried out through a modulator, the electrical control input of which is connected through a third electronic key to the synth output frequency jam, the input of which is connected to the output of the tunable crystal oscillator. The output of the laser module is also optically connected to the optical detection window, the second output of the first photodetector is connected to the signal input of the first automatic frequency search device, the first and second outputs of which are connected respectively to the second control input of the tunable crystal oscillator and the control input of the first electronic key, and the second output the second photodetector is connected to the signal input of the second automatic frequency search device, the first output of which is dinene with the second control input of the controlled current stabilizer, and the second output with the control input of the first automatic frequency search device and with the control inputs of the second and third electronic keys.

The invention and the possibility of its implementation are illustrated by illustrative materials presented in figures 1 and 2, where:

figure 1 schematically shows the transitions used between the energy levels of the atoms of the working substance of the atomic beam tube;

figure 2 presents the structural diagram of the inventive atomic beam frequency standard.

The inventive atomic beam frequency standard contains, see FIG. 2, a tunable crystal oscillator 1, the output of which is the output of the atomic beam frequency standard, a radio frequency excitation signal generating unit 2, an atomic beam tube 3, connected in series in a closed ring of automatic frequency tuning, the first photodetector 4 and the first automatic frequency control unit 5, the output of which is connected to the first control input of the tunable crystal oscillator 1. The reference input of the forming unit the RF excitation signal 2 is connected through the first electronic switch 6 to the output of the first low-frequency generator 7, which forms a reference signal with a frequency of F _m1 (modulation frequency of the RF excitation signal is of the order of several tens of hertz). The output of the first low-frequency generator 7 is also connected to the reference input of the first block of automatic frequency control 5.

The atomic ray tube 3 contains an atomic beam source 8 and a microwave resonator 9 located on the same axis, the radio frequency input of which forms the radio frequency input of the atomic ray tube 3 connected to the output of the RF signal generation unit 2. The atomic ray tube 3 has an optical window pump 10, located in the region of the passage of the atomic beam from the source of the atomic beam 8 to the microwave cavity 9, for inputting an optical pump signal into the atomic beam tube 3, and the optical detection window 11, positioned This is a signal in the region of the exit of the atomic beam from the microwave cavity 9, intended for inputting an optical detection signal into the atomic beam tube 3. In addition, in the region of the exit of the atomic beam from the microwave cavity 9, there is an output photodetecting device 12, the output of which forms the first exit of the atomic beam tube 3 connected to the input of the first photodetector 4, and in the region of the passage of the atomic beam from the source of the atomic beam 8 to the microwave -resonator 9 is an optical pump photodetector 13, the output of which forms the second output of the atomic beam tube 3.

The second output of the atomic beam tube 3 is connected through a second photodetector 14 and a second automatic frequency control unit 15 connected in series with the first control input of the controlled current stabilizer 16, the output of which is connected to the control input of the laser module 17. The reference input of the controlled current stabilizer 16 is connected through the second an electronic key 18 with the output of the second low-frequency generator 19, forming a reference signal with a frequency of F _m2 (the frequency of low-frequency modulation of laser radiation is about ten and kilohertz). The output of the second low-frequency generator 19 is also connected to the reference input of the second block of automatic frequency control 15.

The output of the laser module 17 is optically connected to the optical detection window 11, and also through the modulator 20 to the optical pumping window 10. In this example, the optical output of the modulator 20 is optically connected to the optical pumping window 10 using a reflecting mirror 21, and the optical input of the modulator 20 is optically coupled to the output of the laser module 17 by means of a translucent mirror 22, branching off part of the radiation of the laser module 17 into the optical detection window 11. Another possible implementation of these optical connections is possible, in of fiber optic fibers (not shown in FIG. 2). The electrical control input of the modulator 20 is connected through a third electronic key 23 to the output of the frequency synthesizer 24, the input of which is connected to the output of the tunable crystal oscillator 1.

The second output of the first photodetector 4 is connected to the signal input of the first automatic frequency search device 25, the first output of which is connected to the second control input of the tunable crystal oscillator 1, and the second output is connected to the control input of the first electronic key 6.

The second output of the second photodetector 14 is connected to the signal input of the second automatic frequency search device 26, the first output of which is connected to the second control input of the controlled current stabilizer 16, and the second output is connected to the control input of the first automatic frequency search device 25 and with the control inputs of the second 18 and third 23 electronic keys.

As a modulator 20, known electro-optical or acousto-optical modulators with an electric control input can be used that realize angular (phase, frequency) or amplitude modulation of light, examples of which are presented, in particular, in the book [12] - G.P. Katys, N.V. .Kravtsov, L.E. Chirkov, S.M.Konovalov. Modulation and deviation of optical radiation. // M., Nauka, 1967, p.12, 23-30, 110-118, and also in the patents of the Russian Federation: [13] - RU 2029977 C1, G02F 1/03, 02.27.1995; [14] RU 2225631 C2, G02F 1/00, G02F 1/29, 03/10/2004; [15] - RU 2248601 C1, G02F 1/03, 03.20.2005.

The first automatic frequency search device 25 in this example contains the first analog-to-digital converter 27, the first microcontroller 28 and the first digital-to-analog converter 29 connected in series. The signal input of the analog-to-digital converter 27 and the control input of the microcontroller 28 are respectively the signal and control inputs of the first automatic search device frequency 25, and the output of the digital-to-analog converter 29 and the control output of the microcontroller 28 are respectively the first and second outputs of the first automatic frequency search device 25.

The second automatic frequency search device 26 in this example contains a second analog-to-digital converter 30, a second microcontroller 31 and a second digital-to-analog converter 32 connected in series. The signal input of the analog-to-digital converter 30, the output of the digital-to-analog converter 32 and the control output of the microcontroller 31 are respectively a signal input and the first and second outputs of the second automatic frequency search device 26.

As microcontrollers 28 and 31 in practical circuits, for example, single-chip microcontrollers with internal memory PIC17C4x, PIC17C75x, M3820 and others similar to them can be used. As a control output in such microcontrollers, one of the outputs of the bits of the data input-output port can be used, and as a control input, one of the outputs of the other data input-output port or one of the interrupt inputs.

Adjustable crystal oscillator 1 and controlled current stabilizer 16 are made as in the prototype, while their second control inputs used in the prototype for connecting manually controlled auxiliary voltage sources, in the inventive atomic beam frequency standard, are used to connect automatic frequency search devices 25 and 26, respectively .

Photodetectors 4 and 14 are two-channel amplifiers-converters of current to voltage with filtering elements that implement frequency separation of channels. At the same time, in the photodetector 4, a variable component of the input signal at a frequency of F _m1 passes through the first channel to the first output, and a constant component of the input signal passes through the second channel to the second output. In the photodetector 14, a variable component of the input signal at a frequency of F _m2 passes through the first channel to the first output, and a constant component of the input signal passes through the second channel to the second output.

The automatic frequency control units 5 and 15 contain, as in the prototype, an input amplifier, a synchronous detector and an integrator at the output, while the input of the input amplifier, the reference input of the synchronous detector and the output of the integrator form respectively a signal input, a reference input and an output of the automatic frequency control unit. Each of the automatic frequency adjustment blocks 5, 15 synchronously detects the useful signal coming from the first output of the corresponding photodetector 4, 14, relative to the reference signal coming from the output of the corresponding low-frequency generator 7, 19, and subsequent integration of the error signal resulting from synchronous detection with obtaining the necessary control voltage. In practical implementations, the integrator can be made in the form of an integrator, nullified in the absence of a useful signal at the input of the automatic frequency control unit, for example, in the form of an integrator with zeroing, presented in the patent of the Russian Federation [16] - RU 2015556 C1, G06G 7/186, 06/30/1994 whose control input (zeroing input) is connected through a threshold element to the output of the input amplifier of the automatic frequency control unit (not shown in Fig. 2).

The signal generating unit of the RF excitation signal 2 is made as in the prototype in the form of a step-up modulating frequency converter, which generates on the basis of the output signal of the tunable crystal oscillator 1 (harmonic signal with frequency f ₁ ) and the output signal of the first low-frequency generator 7 (with frequency F _m1 ) modulated by phase with a frequency of low-frequency modulation F _m1 microwave signal of radio frequency excitation, the nominal value of the carrier frequency f ₂ which corresponds to the resonant frequency f _{0 of the} radio frequency atomic transition, i.e. the resonance frequency f _{0 of the} spectral line contour of the atomic beam tube 3, determined by the interaction of the working substance of the atomic beam with a radio frequency excitation signal (in this case, the Ramsey line contour), while the value of the low-frequency modulation frequency F _m1 corresponds to the half-width of this contour.

The atomic beam tube 3 can be made as in the prototype in the form of a rubidium atomic beam tube with the same used frequencies ν ₁ and ν _{2 of} optical atomic transitions and the same frequency f _{0 of the} radio frequency atomic transition as in the prototype.

The operation of the inventive atomic beam frequency standard in the part corresponding to the steady state operation mode, i.e. upon completion of the initial setup of the tunable crystal oscillator 1 and the laser module 17, considered later, is as follows.

Adjustable crystal oscillator 1 generates a harmonic signal with a frequency f ₁ , which is the output signal of the atomic beam frequency standard. The current value of the frequency f ₁ is determined by the sum of the control voltages supplied to the first and second control inputs of the tunable crystal oscillator 1. In this case, the control voltage at the first control input of the tunable crystal oscillator 1 is determined by the current output voltage of the automatic frequency control unit 5, and the control voltage at the second control the input of the tunable crystal oscillator 1 is determined by the output voltage of the automatic frequency search device 25, fixed at a constant level according to the results of the initial ("rough") tuning of the frequency of the tunable crystal oscillator 1.

The output signal of the tunable crystal oscillator 1 is fed to the signal input of the RF signal generating unit 2, to the reference input of which a reference signal with a frequency of F _m1 (of the order of several tens of hertz) is supplied from the output of the low-frequency generator 7 through a closed electronic key 6. Based on these input signals, a radio frequency excitation signal modulated in phase with a low frequency modulation frequency F _{m1 is} generated in the RF excitation signal generating unit 2, the microwave frequency RF excitation signal, whose nominal value of the carrier frequency f _2, which is uniquely associated with the current frequency value f ₁ , corresponds to the resonant frequency f ₀ radio frequency atomic transition, i.e. the resonant frequency of the contour of the spectral line of the atomic beam tube 3, determined by the interaction of the working substance of the atomic beam with a radio frequency excitation signal and corresponding to the transition between energy levels "1" and "2" (figure 1), and the value of the low-frequency modulation frequency F _m1 corresponds to the spectral half-width lines of this transition.

The RF excitation signal taken from the output of the RF excitation signal generating unit 2 is supplied to the radio frequency input of the atomic beam tube 3, i.e. to the radio frequency input of the microwave resonator 9. Also in the atomic beam tube 3 through the optical pumping window 10 and the optical detection window 11 receives optical pumping signals and optical detection.

The optical detection signal is part of the radiation of the laser module 17, branched into the optical detection window 11 using a translucent mirror 22. The radiation of the laser module 17 is a frequency modulated optical signal whose carrier frequency corresponds to the resonant frequency ν ₂ used in the detection of a circular optical atomic transition between the energy levels "2" and "3 '" (figure 1), and the frequency F _{m2 of} modulation (of the order of ten kilohertz) is less than the spectral half-width the lines of this transition, as well as the absorbing optical atomic transition used in optical pumping, characterized by the frequency ν ₁ . The radiation parameters of the laser module 17 are determined by the parameters of the amplitude-modulated current supplied to its control input from the output of the controlled current stabilizer 16. The constant component of this current, which determines the carrier frequency of the radiation of the laser module 17, is determined by the sum of the control voltages supplied to the first and second control inputs of controllable current stabilizer 16, and the frequency of this current is determined by the modulation frequency F _m2 low-frequency oscillator 19, the output signal behaving go to the reference input of the controlled current stabilizer 16 through a closed electronic key 18. In this case, the control voltage at the first control input of the controlled current stabilizer 16 is determined by the current output voltage of the automatic frequency control unit 15, and the control voltage at the second control input is determined by the output voltage of the automatic frequency search device 26, fixed at a constant level according to the results of the initial ("rough") tuning of the radiation frequency of the laser module 1 7.

The optical pump signal is generated as a result of additional high-frequency modulation with a frequency Δν = ν ₂ -ν ₁ of the radiation of the laser module 17, which is transmitted through the translucent mirror 22 to the optical input of the modulator 20. The signal that sets the modulation frequency Δν is the signal fed to the electrical control input modulator 20 through a closed electronic key 23 from the output of the frequency synthesizer 24, where it is formed on the basis of the output signal of the tunable crystal oscillator 1. As a result of an additional high-frequency modulation in the spectrum of radiation taken from the optical output of the modulator 20, additional spectral components appear, determined by the frequency difference ν ₂ -Δν. In fact, there is a transformation of the spectrum of the input laser radiation with the appearance of components shifted by the frequency Δν relative to the components of the original spectrum, where the value of Δν, as mentioned above, for the rubidium atomic beam frequency standard is 267 MHz. This method of converting the spectrum of laser radiation is known, in particular, it is the basis for the method of converting the spectrum of laser radiation described in the patent of the Russian Federation [17] - RU 2071159 C1, H01S 3/10, 12/27/1996.

The output signal of the modulator 20 with the help of a reflecting mirror 21 is supplied to the optical pump window 10. Useful spectral components of this signal are components determined by the carrier frequency ν ₁ , where ν ₁ = ν ₂ -Δν, and the lateral frequency F _m2 . These components fall into the spectral band of the used absorbing optical atomic transition between the energy levels “2” and “3” (Fig. 1), under the influence of these components, the atomic beam is pumped optically in the section of its passage from the source of atomic beam 8 to the microwave resonator 9, which leads to the enrichment of the energy level "1" and the depletion of the energy level "2" (figure 1).

The effect of other spectral components present in the output signal of the modulator 20 is not significant. Thus, spectral components whose frequencies do not coincide with the resonant frequencies of optical atomic transitions do not affect the energy state of atoms of an atomic beam at all. The result of the action of a spectral component with a frequency of ν ₂ (the frequency of a circular optical atomic transition) on a part of the atoms remaining in the energy state “2” has a short-term character (of the order of 10 ^-8 s, determined by the lifetime of atoms in the excited state “3 '”) and ends before the atomic beam enters the microwave cavity 9.

Thus, as a result of laser optical pumping, the atoms of the atomic beam fly into the microwave cavity 9, being mainly in the energy state of the first level "1" (figure 1). In the microwave cavity 9, the beam atoms interact with a radio frequency excitation signal - phase-modulated with a frequency F _m1 microwave signal with a carrier frequency f ₂ corresponding to the resonant frequency f _{0 of the} radio frequency atomic transition excited by the interaction of the working substance of the atomic beam with the radio frequency excitation signal. As a result of the interaction of the atomic beam with the RF excitation signal, the atoms of the beam fly out of the microwave cavity 9, being mainly in the energy state of the second level “2” (Fig. 1), which makes it possible to perform subsequent laser optical detection at a frequency corresponding to the resonant frequency ν ₂ circular optical atomic transition between the energy levels "2" and "3 '" (figure 1).

The result of laser optical detection is controlled by the fluorescence light reradiated by the atoms of the beam, detected by the output photodetecting device 12. The spectral component of the signal of the output photodetecting device 12, corresponding to the modulation frequency F _{m1 of} the radio frequency excitation signal, carries information about the deviation of the carrier frequency f _{2 of} the radio frequency excitation signal from the resonant ₀ . This component is extracted in the photodetector 4 and, as a feedback signal, comes from its first output to the signal input of the automatic frequency adjustment unit 5, where it is synchronously detected (relative to the frequency F _m1 ) with the allocation of an error signal, which is then integrated to obtain a control voltage, under the action of which the frequency f _{1 of the} output signal of the tunable crystal oscillator 1 is set in accordance with the resonant frequency f ₀ (taking into account the frequency conversion, located in the block for generating a radio frequency excitation signal 2). Thus, as a result of the operation of this automatic frequency control ring, the current frequency value of the output signal of the tunable crystal oscillator 1 is stabilized relative to the resonant frequency f ₀ .

The result of laser optical pumping is controlled in a similar way, using fluorescence light reradiated by the atoms of the beam detected by the optical pump photodetector 13. The spectral component of the output signal of the optical pump photodetector 13, corresponding to the frequency F _{m2 of the} low-frequency modulation of the radiation of the laser module 17, carries information about the frequency deviation of the optical signal pump, determined by the difference between the carrier frequency of the radiation of the laser module 17 (ν ₂ ) and the frequency of the output synthesis signal a torus of frequency 24 (Δν), from the resonant frequency ν _{1 of the} absorbing optical atomic transition. This component is extracted in the photodetector 14 and, as a feedback signal, comes from its first output to the signal input of the automatic frequency control unit 15, where it is synchronously detected (relative to the frequency F _m2 ) with the allocation of an error signal, which is then integrated to obtain a control voltage, under the action of which the constant component of the output current of the controlled current stabilizer 16 is set at a level that determines the value of the frequency of the optical pump signal in tvetstvii with the resonance frequency ν _1, wherein the radiation of the laser module carrier frequency 17 corresponds to the resonance frequency ν ₂ of the circular optical atomic transition used in the detection. Thus, as a result of the operation of this automatic frequency control ring, the value of the carrier frequency of the radiation of the laser module 17 is stabilized relative to the resonant frequency ν ₁ (taking into account the conversion of the spectrum carried out in the modulator 20).

The joint work of both rings of the automatic frequency control - the ring of the automatic frequency control of the tunable crystal oscillator 1 and the ring of the automatic frequency control of the radiation of the laser module 17 - ensures the achievement of the required stability characteristics of the output signal of the inventive atomic beam frequency standard in the steady state operation mode. Moreover, due to the use of one laser module (and not two, as in the prototype), the atomic-beam frequency standard scheme is simplified, energy consumption is reduced, and reliability is increased.

As in the prototype, the inventive atomic beam frequency standard requires a forced initial (“rough”) setting of the frequency of the output signal of the tunable crystal oscillator 1 and the radiation frequency of the laser module 17 in accordance with the frequencies of the atomic transitions used to enable their subsequent “capture” and "Tracking" in the corresponding rings of automatic frequency control. This initial setting of the frequency of the output signal of the tunable crystal oscillator 1 and the radiation frequency of the laser module 17 is carried out automatically after turning on the power and occurs as follows.

In accordance with the programs of the microcontrollers 28 and 31, which are started when the power is turned on, the automatic frequency search devices 25 and 26 generate control signals at their second outputs (control outputs of the microcontrollers 28, 31), under which the electronic keys 6, 18 and 23 open. the first outputs of the automatic frequency search devices 25 and 26 (outputs of the digital-to-analog converters 29, 32) generate signals, under the influence of which the frequency of the output signal of the tunable crystal oscillator 1 and the frequency of radiation of the laser module 17 are installed at the extreme point of the tuning range.

The frequency of the output signal of the tunable crystal oscillator 1 is set to the extreme point of the tuning range under the action of a signal supplied to its second control input from the output of the digital-analog converter 29. In this case, the signal does not arrive at the first control input of the tunable crystal oscillator 1, since under conditions of open key 6 the operation of the automatic frequency control ring of the tunable crystal oscillator 1 is blocked: there is no signal at the reference input of the signal generation unit RF excitation 2, respectively, there is no modulation of the RF excitation signal, there is no useful signal at the first output of the photodetector 4 and, accordingly, there is no signal at the output of the automatic frequency adjustment unit 5 connected to the first control input of the tunable crystal oscillator 1. Under these conditions, the frequency of the output signal of the tunable crystal oscillator 1 is determined only by the voltage present at its second control input.

The radiation frequency of the laser module 17 is set to the extreme point of the tuning range under the influence of the output signal of the controlled current stabilizer 16 generated by the signal supplied to its second control input from the output of the digital-analog converter 32. In this case, the control signal does not go to the first input of the controlled current stabilizer 16 arrives, because in the conditions of an open electronic key 18, the operation of the automatic frequency adjustment ring of the laser module 17 is blocked: there is no signal and the reference input of the controlled current stabilizer 16, respectively, there is no radiation modulation of the laser module 17, there is no useful signal at the first output of the photodetector 14 and, accordingly, there is no signal at the output of the automatic frequency control unit 15 connected to the first control input of the controlled current stabilizer 16. Under these conditions the output signal of the controlled current stabilizer 16, which sets the radiation frequency of the laser module 17, is determined only by the voltage present at its second control input.

The unmodulated radiation of the laser module 17 thus formed is fed to the optical input of the modulator 20, which, under the conditions of an open electronic key 23, transmits this radiation without modulation to its optical output, from which the radiation then enters the optical pump window 10.

Then, the automatic frequency search device 26 starts software tuning of the radiation frequency of the laser module 17, the purpose of which is to “crudely” search for the frequency corresponding to the resonant frequency ν ₂ used in detecting a circular optical atomic transition. This frequency is found by detecting a certain (in the sequence) peak of the output signal of the optical pump photodetector 13 coming through the photodetector 14 (from its second output) to the signal input of the frequency automatic search device 26. In this case, the fact that each detected peak is used corresponds to a specific optical atomic transition between the energy levels of the atoms of the working substance of the atomic beam, the number of which and the location on the frequency axis for each ochego substances known. In the case under consideration, when the atomic beam of rubidium Rb ⁸⁷ is used as the working substance, the number of optical atomic transitions is four, which is determined by four sublevels in the 5P _3/2 state (see, for example, [18] - A. Besedina, A. Gevorkyan, G .Mileti, V.Zholnerov, A. Bassevich. Preliminary result of investigation of the high-stable Rubidium atomic beam frequency standard with laser pumping / detection for space application. EFTF '06 // European Frequency and Time Forum, 2006, pp. 270 -276, Fig.2), while the desired circular optical atomic transition corresponding to the frequency ν ₂ is the third (in the order of increasing frequency) optical atomic transition underway.

The search for frequency ν ₂ (search for a specific peak of the signal taken from the second output of the photodetector 14) is performed according to the program embedded in the microprocessor 31. In accordance with this program, a step-by-step voltage (varying in clocks) is generated at the output of the digital-to-analog converter 32, by which of the controlled current stabilizer 16, the radiation frequency of the laser module 17 accordingly changes. The radiation of the laser module 17 is controlled by a fluorescent beam reradiated by the atoms mu light that is reflected by the photodetector 13. The optical pump output signal of the photodetector 13 of the optical pump passes to the second output of photodetector 14 and further supplied to the signal input device 26, an automatic search frequency (signal input of an analog-digital converter 30). The signal converted into a digital form then goes to the microcontroller 31, where the current signal is stored and compared with the signal received at the previous clock, which allows us to identify the frequencies corresponding to the peak values of the output signal of the optical pump photodetector 13, and thereby find the desired frequency ν ₂ corresponding to the desired peak.

Upon completion of the search for the frequency ν _{2, the} microcontroller 31 fixes the state of the digital-to-analog converter 32 corresponding to the found frequency ν ₂ , i.e. fixes the output signal from the first output of the automatic frequency search device 26 to the second control input of the controlled current stabilizer 16. This fixes the set initial ("rough") value of the frequency of the laser module 17 corresponding to the resonant frequency ν ₂ .

In addition, upon completion of the search for frequency ν ₂ at the second output of the automatic frequency search device 26 (at the control output of the microcontroller 31), a control signal appears at the control inputs of electronic keys 18, 23 and at the control input of the automatic frequency search device 25 (control input of the microcontroller 28 )

Under the influence of this control signal, the electronic keys 18 and 23 are closed, including the ring for automatically adjusting the radiation frequency of the laser module 17. In this case, as described above, low-frequency (in the controlled current stabilizer 16) and high-frequency (in the modulator 20) modulation of laser radiation module 17, an optical pump signal enters the optical pump window 10, which falls into the spectral band of the absorbing optical atomic transition used, and 11 p an optical detection signal falls into the spectral line of the used circular optical atomic transition.

Under the action of the specified control signal, the automatic frequency search device 25 starts to programmatically adjust the frequency of the output signal of the tunable crystal oscillator 1, the purpose of which is to “crudely” search for the frequency corresponding to (taking into account the conversion carried out in the RF signal generation unit 2) the frequency f _{0 of the} radio frequency atomic transition. In this case, the peak of the signal at the output of the output photodetecting device 12 is searched for, which corresponds to the peak of the Ramsey line contour ([18, Fig.6]) obtained as a result of the interaction of laser atoms pumped in the microwave cavity 9 with an unmodulated radio frequency excitation signal arriving at the radio frequency input of the atomic beam tube 3 from the output of the signal generating unit of the radio frequency excitation 2.

The frequency of the output signal of the tunable crystal oscillator 1 is tuned according to the program embedded in the microprocessor 28. In accordance with this program, a step-by-step voltage (varying in clock cycles) is generated at the output of the digital-to-analog converter 29, under the influence of which the frequency f _{1 of the} output signal of the tunable crystal oscillator changes accordingly 1 and the associated frequency f _{2 of} the RF excitation signal. The peak of the Ramsey line contour is searched by the fluorescence light reradiated by the atoms of the beam, detected by the output photodetector 12. The signal taken from the output of the output photodetector 12 passes to the second output of the photodetector 4 and then goes to the signal input of the automatic frequency search device 25 (signal input analog-to-digital converter 27). The signal converted to digital form is then fed to the microcontroller 28, where the current signal is stored and compared with the signal received at the previous clock, which allows us to identify the frequency of the output signal of the tuned crystal oscillator 1, corresponding to the peak of the Ramsey line contour.

Upon completion of the search for the frequency of the output signal of the tunable crystal oscillator 1 corresponding to the peak of the Ramsey line contour, the microcontroller 28 captures the state of the digital-to-analog converter 29 corresponding to the found frequency, i.e. fixes the output signal coming from the first output of the automatic frequency search device 25 to the second control input of the tunable crystal oscillator 1. This fixes the set initial (“rough”) value of the frequency of the output signal of the tunable crystal oscillator 1, corresponding to (taking into account the conversion performed in the block generating a radio frequency excitation signal 2) a resonant frequency f _{0 of the} radio frequency atomic transition.

At the same time, a control signal appears on the second output of the automatic frequency search device 25 (at the control output of the microcontroller 28), by means of which the electronic key 6 closes, turning on the ring for automatically adjusting the frequency of the tuned crystal oscillator 1. From this moment, the current work discussed above begins atomic-beam frequency standard - when both rings of automatic frequency control work simultaneously in the "tracking" mode - the ring of automatic frequency tuning from the tunable quartz oscillator 1 and the ring for automatically adjusting the radiation frequency of the laser module 17, providing stabilization of the frequency of the tunable quartz generator 1 and the radiation frequency of the laser module 17 relative to the resonant frequencies of the atomic transitions used.

The above shows that the claimed invention is feasible and ensures the achievement of a technical result consisting in the creation of an atomic beam frequency standard operating according to a two-frequency scheme implemented using a single laser module, and in which the initial frequencies of the tunable crystal oscillator and the laser module are automatically set to compliance with the resonant frequencies of the atomic transitions used.

Information sources

1. A.I. Pikhtelev, A. A. Ulyanov, B. P. Fateev et al. Frequency and time standards based on quantum generators and discriminators. // M., Sov. radio, 1978.

2. RU 2220499 C2, H03L 7/16, H01S 3/10, publ. 12/27/2003.

3. US 4943955, H03L 7/26, publ. 07.24.1990.

4. US 4425653, H01S 3/091, publ. 01/10/1984.

5. US 4354108, H01S 1/00, publ. 10/12/1982.

6. US 3967115, H01S 1/00, publ. 06/29/1976.

7. US 3397310, U.S. Cl. 250-41.3, publ. 08/13/1968.

8. US 3323008, U.S. Cl. 315-111, publ. 05/30/1967.

9. C. Sallot, M. Balcly, D. Gin, R. Petit. 3 · 10 ^-12 · τ ^-1/2 on industrial optically pumped cesium beam frequency standard. // 2003 IEEE International Frequency Control Symposium and PDA Exhibition Jointy with the 17 ^th European Frequency and Time Forum. 2003, pp. 100-104.

10. US 4684900, H03L 7/26, publ. 08/04/1987.

11. A. Besedina, A. Gevorkyan, V. Zholnerov. Two-frequency Pumping in ⁸⁷ Rb Atomic Beam Frequency Standard with Laser Pumping / Detection for Space Application. EFTF 07 // European Frequency and Time Forum, 2007, pp. 623-628.

12. G.P. Katys, N.V. Kravtsov, L.E. Chirkov, S.M. Konovalov. Modulation and deviation of optical radiation. // M., Science. 1967, p.12, 23-30, 110-118.

13. RU 2029977 C1, G02F 1/03, publ. 02/27/1995.

14. RU 2225631 C2, G02F 1/00, G02F 1/29, publ. 03/10/2004.

15. RU 2248601 C1, G02F 1/03, publ. 03/20/2005.

16. RU 2015556 C1, G06G 7/186, publ. 06/30/1994.

17. RU 2071159 C1, H01S 3/10, publ. 12/27/1996

18. A. Besedina, A. Gevorkyan, G. Mileti, V. Zholnerov, A. Bassevich. Preliminary result of investigation of the high-stable Rubidium atomic beam frequency standard with laser pumping / detection for space application. EFTF 06 // European Frequency and Time Forum. 2006, pp. 270-276, Fig. 2, Fig. 6.

Claims (1)

An atomic beam frequency standard, comprising a tunable quartz oscillator connected in series to a closed loop of automatic frequency control, the output of which is the output of the atomic beam frequency standard, an RF excitation signal generating unit, an atomic beam tube, a first photodetector and a first automatic frequency adjustment unit, the output of which is connected to the first control input of the tunable crystal oscillator, as well as the first low-frequency generator, the output of which connected to the reference input of the first block of automatic frequency control and the reference input of the block for generating a radio frequency excitation signal, the atomic beam tube comprising an atomic beam source and a microwave resonator located on the same axis, the radio frequency input of which forms the radio frequency input of the atomic beam tube connected to by the output of the radio frequency excitation signal generating unit, an optical pump window located in the region of the passage of the atomic beam from the source of the atomic beam to the microwave cavity intended for inputting an optical pump signal into the atomic beam tube and an optical detection window located in the region of the exit of the atomic beam from the microwave cavity, intended for introducing the optical detection signal into the atomic beam tube, while in the region of the exit of the atomic beam the resonator is an output photodetecting device, the output of which forms the first output of the atomic beam tube, connected to the input of the first photodetector, and in the area of the passage of the atomic beam from the source atomically of the first beam to the microwave cavity is an optical pump photodetector, the output of which forms the second output of the atomic beam tube, connected through a second photodetector and a second automatic frequency control unit connected in series with the first control input of the controlled current stabilizer, the output of which is connected to the control input of the laser module the output of which is optically coupled to the optical pump window, while the reference input of the second block of automatic frequency control and the reference input of the controlled the current tabulator is connected to the output of the second low-frequency generator, characterized in that the output of the first low-frequency generator is connected to the reference input of the RF excitation signal generating unit through the first electronic key, the output of the second low-frequency generator and the reference input of the controlled current stabilizer are connected through the second electronic key, and the optical connection of the output of the laser module with the optical pumping window is carried out through a modulator, electric control the input input of which is connected through the third electronic key to the output of the frequency synthesizer, the input of which is connected to the output of the tunable crystal oscillator, while the output of the laser module is also optically coupled to the optical detection window, the second output of the first photodetector is connected to the signal input of the first automatic frequency search device, the first and second outputs of which are connected respectively to the second control input of the tunable crystal oscillator and the control input of the first ele throne key, and the second output of the second photodetector is connected to the signal input of the second automatic frequency search device, the first output of which is connected to the second control input of the controlled current stabilizer, and the second output is connected to the control input of the first automatic frequency search device and with control inputs of the second and third electronic keys.

Images