• 专利附录
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    • 专利摘要:
    The invention relates to a vector magnetometer (10) comprising a cell (1) filled with an atomic gas subjected to an ambient magnetic field, an optical pump source (2) capable of transmitting towards the cell a light beam (F ) tuned to a pumping wavelength and a parametric resonance detection device (6) receiving the light beam (L) having passed through the cell. The magnetometer further comprises a polarization device (3) capable of conferring, simultaneously or alternatively, a linear polarization and a circular polarization light beam emitted in the direction of the cell. And the detection device (6) comprises an optical assembly configured to separate optical signals respectively carrying information relating to a state of alignment and a state of orientation of the atoms of the atomic gas.
    公开号:FR3077884A1
    申请号:FR1851170
    申请日:2018-02-12
    公开日:2019-08-16
    发明作者:Agustin Palacios-Laloy
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    ELLIPTICAL POLARIZATION VECTOR MAGNETOMETER
    DESCRIPTION
    TECHNICAL AREA
    The field of the invention is that of magnetometers with optical pumping controlled in zero field.
    PRIOR STATE OF THE ART
    Optically pumped magnetometers use atomic gases confined in a cell, typically metastable helium or alkali gases, as the sensitive element. These magnetometers, which can take different configurations, allow you to go back to the magnetic field by exploiting the following three processes which take place either sequentially or concomitantly:
    1) The use of polarized light sources, typically lasers, makes it possible to prepare atomic states characterized by a certain orientation or alignment of their spins. This process is called "optical pumping" in the field.
    2) These atomic states evolve under the effect of the magnetic field, in particular under the Zeeman effect, which corresponds to shifts in energy levels as a function of the magnetic field to which the atoms are subjected.
    3) The optical properties of the atomic medium then undergo modifications which depend on the state of the atoms. It is thus possible by optical measurement, for example by optical absorption measurement, to go back to the Zeeman offset undergone, and to deduce therefrom a measurement of the magnetic field in which the cell is immersed.
    According to the different possible configurations of existing optically pumped magnetometers, there is a measurement of the module, also called standard, of the magnetic field for scalar magnetometers, or a determination of the different components of the magnetic field for vector magnetometers, at the location of the cell.
    The level of sensitivity, also called low noise, and accuracy achievable with such optically pumped magnetometers are very remarkable and clearly more favorable than those of most other magnetic measurement technologies (fluxgate, Hall effect, magnetoresistance, etc.) . Only the SQUID type magnetometer has a similar noise, but it requires cryogenic cooling of the sensitive element, which contains elements which need to be superconductive for its operation, which limits its practical field of application.
    To carry out a vectorial measurement of the magnetic field with a wide bandwidth, there are two well-known configurations: the first known as "Hanle effect" and the second which receives the name of "parametric resonance magnetometer". These configurations are described in particular in the article by J. DupontRoc, Determination by optical methods of the three components of a very weak magnetic field, Review of Applied Physics, vol. 5, no. 6, pp. 853-864, 1970. They operate at very low external magnetic field values, inducing a Zeeman shift smaller than the relaxation rate of the Zeeman sub-levels of the atom, which in the case of helium fixes a limit around 100 nano Tesla, 500 times less intense than the Earth's magnetic field.
    When a weak transverse static magnetic field is applied to the cell and swept around zero, the atoms under subjected to a movement of precession and the number of absorbed photons, coming from the laser of optical pumping, undergoes resonant variations (Hanle effect) . Analogous resonances, called parametric resonances, in the presence of frequency modulated magnetic fields, are observed when a radiofrequency field is applied. Under these conditions, the magnetic moment of each atom undergoes resonant oscillations at frequencies multiple of that of the radiofrequency field. The measurement of the amplitude of these oscillations makes it possible to go back to the module of the component of the collinear magnetic field to the radiofrequency field.
    In these two configurations, it is advantageous to operate the magnetometer "in closed loop" by constantly subjecting the sensitive element to a zero total magnetic field. This so-called zero-field operation has the advantage of being less sensitive to the variation of experimental parameters (laser powers, density of the sensitive element, etc.).
    The zero total magnetic field is obtained by generating compensating magnetic fields by injecting currents into suitable coils which surround the sensitive element. These compensation fields cancel each of the components of the ambient magnetic field by means of closed-loop regulation of the injected currents. The measurement of the currents flowing in the coils makes it possible to deduce the fields which it is necessary to apply to cancel the various components of the ambient field, and therefore to have the value of these various components.
    The parametric resonance magnetometer thus makes it possible to deduce the three components of the ambient magnetic field independently, which makes vector measurement possible. The two components parallel to the axis of application of two radiofrequency fields are thus obtained by measuring the amplitude of the photo-detection signal at the frequency of oscillation of the corresponding radiofrequency field and in quadrature with the latter. In fact, this amplitude is directly proportional to the magnetic field parallel to the axis of the corresponding radio frequency field. It is also possible to obtain the third component of the magnetic field (perpendicular to the two RF fields) because the first inter-harmonic of the two oscillation frequencies of the radiofrequency fields is proportional to its amplitude. However, the proportionality factors for the measurement of this third axis are strongly unfavorable compared to the first two. Thus, the noise associated with the measurement of the field along this third axis is typically at least an order of magnitude higher than that associated with the other two axes. However, this noise level can prove to be problematic in magnetometer applications where the magnetic field measurement is used to deduce the position of field sources (currents or magnetic materials), this excess noise inducing high uncertainties on the magnitudes of these sources or their location.
    STATEMENT OF THE INVENTION
    The invention aims to overcome this excess noise affecting the measurement on the third axis of the magnetometer to reduce the uncertainty of the vector measurement of the magnetic field. To this end, the invention proposes a vector magnetometer which comprises:
    - a cell intended to be filled with an atomic gas subjected to an ambient magnetic field,
    an optical pumping source arranged to emit towards the cell a beam of light having a pumping wavelength,
    - a parametric resonance detection device arranged to receive the light beam having passed through the cell.
    The vector magnetometer further includes a polarization device configured to impart linear polarization and circular polarization to the beam of light emitted toward the cell. The detection device comprises an optical arrangement arranged so as to separate optical signals carrying respectively information relating to an alignment state and to an orientation state of the atoms of the atomic gas.
    Some preferred but non-limiting aspects of this magnetometer are:
    it includes a source of excitation of parametric resonances configured so that it induces in the cell an excitation radiofrequency field having three components, each of the components of the radiofrequency field oscillating at its own oscillation frequency, and the device detection is configured to perform synchronous detection at one harmonic of each of the oscillation frequencies;
    the detection device is configured to measure the amplitude of the optical signal carrying information relating to the state of orientation of the atoms of the atomic gas at a harmonic of the oscillation frequency of each of the components of the radiofrequency field of excitation orthogonal to the direction of propagation of the light beam, and to measure the amplitude of the optical signal carrying information relating to the state of alignment of the atoms of the atomic gas to a harmonic of the oscillation frequency of each components of the excitation radiofrequency field orthogonal to the direction of the electric field of the light beam;
    the optical assembly comprises a light beam splitter having passed through the cell in a first channel and a second channel, an alignment state analyzer on the first channel and a circular orientation state analyzer on the second channel;
    the alignment status analyzer includes a linear polarizer and a photodetector;
    the orientation state analyzer comprises a circular polarizer and a photodetector;
    the alignment state analyzer comprises a quarter wave plate, a polarization splitter able to separate on a first and a second path the right circular polarization and the left circular polarization of the light beam and a photodetector on each of the first and second paths;
    the orientation state analyzer comprises a polarization splitter capable of separating on a first and a second path the horizontal linear polarization and the vertical linear polarization of the light beam, and a photodetector on each of the first and second paths;
    the optical assembly comprises a temporal separator of the light beam having passed through the cell alternately in a circularly polarized beam and in a linearly polarized beam, and an atomic state analyzer downstream of the separator;
    the polarization device is configured so as to simultaneously confer linear polarization and circular polarization to the beam of light emitted towards the cell;
    the polarization device is configured so as to alternately confer linear polarization and then circular polarization to the beam of light emitted in the direction of the cell.
    The invention also relates to a method for measuring a magnetic field using a vector magnetometer comprising a cell filled with an atomic gas subjected to an ambient magnetic field, an optical pumping source capable of emitting towards from the cell a beam of light tuned to a pumping wavelength, a device for detecting parametric resonances receiving the beam of light having passed through the cell and a closed-loop servo system of the magnetometer to operate it in the field no. This method comprises the steps consisting in linearly and circularly polarizing the light beam emitted towards the cell, and in separating, by means of an optical arrangement from the detection device, optical signals carrying respectively information relating to a state of alignment and state of orientation of the atoms of the atomic gas.
    Some preferred but non-limiting aspects of this process are as follows:
    it includes the generation in the cell, by means of an excitation source of parametric resonances, an excitation radiofrequency field having three components, each of the components of the radiofrequency field oscillating at its own oscillation frequency, and synchronous detection to a harmonic of each of the oscillation frequencies;
    it includes a measurement of the amplitude of the optical signal carrying information relating to the state of orientation of the atoms of the atomic gas to a harmonic of the oscillation frequency of each of the components of the radiofrequency field of excitation orthogonal to the direction of propagation of the light beam, and a measure of the amplitude of the optical signal carrying information relating to the state of alignment of the atoms of the atomic gas to a harmonic of the oscillation frequency of each of the components the excitation radiofrequency field orthogonal to the direction of the electric field of the light beam;
    it comprises a division of the light beam having passed through the cell into a first channel and a second channel, an alignment state analysis on the first channel and an orientation state analysis on the second channel;
    it comprises a temporal separation of the light beam having passed through the cell alternately into a circularly polarized beam and into a linearly polarized beam, and an atomic state analysis carried out downstream of said separation;
    the light beam emitted towards the cell is simultaneously linearly and circularly polarized;
    the light beam emitted towards the cell is alternately linearly polarized then circularly.
    BRIEF DESCRIPTION OF THE DRAWINGS
    Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings on which ones :
    - Figure 1 is a diagram of a magnetometer according to the invention;
    - Figure 2 is a diagram of an example of arrangement of the radiofrequency fields with respect to the components of the optical pumping;
    - Figures 3, 4 and 5 are diagrams of optical arrangements that can be implemented in the device for detecting parametric resonances of the magnetometer according to the invention.
    DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
    Referring to Figure 1, the invention relates to a vector pumped optical magnetometer 10 which comprises a cell 1 filled with an atomic gas, for example helium-4 or an alkaline gas, subjected to an ambient magnetic field B o whose projection on three axes of rectangular coordinates defines three components. The ambient magnetic field B o is thus broken down into three components Bx, By and Bz each along one of the measurement axes of the magnetometer x, y and z.
    The cell is illuminated by an optical pumping source 2 capable of emitting towards the cell 1 a beam of light F, for example a laser beam, tuned to a pumping wavelength (this beam is thus also designated by beam pump). The pumping wavelength is calibrated on an atomic transition line, for example on the D o line at 1083 nm in the case of helium-4. The light beam is polarized by means of a polarization device 3 interposed between the optical pumping source and the cell or directly integrated into the optical pumping source.
    In the case where the sensitive element is helium-4, the magnetometer 10 also comprises a high frequency discharge (HF) system, comprising an HF generator 4 and overvoltage coils 5, for bringing the atoms of the atomic gas in an energized state where they are able to undergo the atomic transition when they are lit by the laser beam, typically in the metastable state 2 3 Si.
    The magnetometer also includes a parametric resonance excitation circuit which comprises a radio frequency generator 8 which supplies helmhoItz coils 7 of orthogonal axes which surround the cell in order to generate a magnetic field for the excitation of parametric resonances, also designated by excitation radiofrequency field. The magnetometer also comprises a device for detecting parametric resonances 6 receiving the beam of light having passed through the cell.
    The magnetometer can also include a closed loop servo system of the magnetometer to constantly subject the sensitive element to a zero total magnetic field. The servo system comprises a regulator 9 coupled to the detection device 6 and which injects a current into the Helmholtz coils 7 in order to generate a magnetic compensation field Bc such that the sum Bc + B 0 is kept at zero permanently.
    Alternatively, the magnetometer can be operated in an open loop, without compensation for the ambient field.
    It is usual to carry out pumping with circularly polarized light, which induces so-called "oriented" atomic states which are characterized by the fact that the mean value of their magnetic moment of spin is different from zero in the direction corresponding to the propagation. of the pump harness. For example if this direction corresponds to the z axis, the magnetic moment of spin Sz will have a nonzero mean value.
    It is also possible to perform pumping with linearly polarized light, which induces so-called "aligned" atomic states which are characterized by the fact that the mean value of a second-order observable on the magnetic spin moment is different from zero. For example, a state aligned along the z axis is characterized by the fact that the observable 3S 2 - S 2 is different from zero. The alignment axis is then fixed by the direction of the electric field of the light used for pumping, a light with an electric field parallel to z creating an alignment along z.
    The invention proposes to carry out pumping differently by adopting for polarization device 3 a device configured to confer linear polarization and circular polarization to the beam of light emitted in the direction of the cell. In particular, this device is configured to give the atoms of atomic gas in the cell a state that is both aligned and oriented.
    The polarization device 3 can be configured to confer linear polarization and circular polarization simultaneously, the beam emitted towards the cell therefore being elliptically polarized. Such a device 3 can comprise a linear polarizer and a quarter-wave plate whose neutral axes are rotated at an angle different from 45 ° relative to those of the linear polarizer, for example 22.5 °.
    The effect of such an elliptical polarization is to prepare the atomic states according to an orientation and an alignment resulting from both a linear polarization and a circular polarization. Thus, the state that the atoms of atomic gas in the cell acquire, is both aligned and oriented, in proportion to the degree of ellipticity of the polarization. The state of the atoms is more particularly broken down into an orientation along the propagation of the pump beam and an alignment mainly oriented along the axis of the linear polarization of the pump beam (with a small longitudinal component to the propagation of light resulting from a residual term from pumping in circular polarization).
    Alternatively, the polarization device 3 can be configured to alternately confer linear polarization and then circular polarization. Such a polarizer 3 can include a linear polarizer and an electrically controllable delay plate. This blade is modulated with a square wave so that during the half-periods when its output level is high (noted SH), it behaves like a quarter-wave blade, while during the level half-periods low (noted SL) it behaves like a blade without delay or like a half-wave blade. Thus, during the SH half-periods, the beam emitted towards the cell is circularly polarized and the atomic states in the cell are oriented. And during the SH half-periods, the beam emitted towards the cell is linearly polarized and the atomic states in the cell are oriented. The dynamics of the atoms being dominated by a relaxation time of the order of 1 ms, if the SL / SH modulation is faster (which is the case in the example presented below), the atoms are placed in a superposition of aligned and oriented states. It is therefore not a question of a successive passage through these two states but of the concomitance of the two properties.
    It will be noted that in order to limit the impact of nonlinear magneto-optical effects, the light power of the pump beam is preferably limited so that it is typically lower or of the order of the saturation intensity. These effects, described for example in the article by D. Budker et al. Resonant nonlinear magnetooptical effects in atoms, Rev. Mod. Phys., Vol. 74, no. 4, pp. 1153-1201, Nov. 2002, can indeed induce couplings between the evolutions of the components in orientation and in alignment which make the evolution of the state of the atoms considerably more complex and harm the proper functioning of the invention.
    In the context of the invention, a pair of coils 7 is provided on each of the axes of the magnetometer so as to generate an excitation radiofrequency field having three orthogonal components. The excitation source of parametric resonances is more particularly controlled so that it induces in the cell an excitation radiofrequency field having three components, each of these components oscillating at its own oscillation frequency. We thus find an RFx component, an RFy component and an RFz component on the x, y and z axes of respective pulses ξ, Ω and ω.
    Under these conditions, the magnetic moment of each atom in the cell undergoes resonant oscillations at frequencies multiple of that of the components of the excitation radiofrequency field. This then results in modulation of the transmitted light, in particular at pulsations ξ, Ω and ω. The amplitude of the oscillations at one of these pulses thus makes it possible to measure the modulus of the collinear magnetic field with the corresponding component of the RF field.
    FIG. 2 shows an example of the arrangement of the components of the radiofrequency field with respect to the components of the pumping. In this figure, k denotes the vector of propagation of the light beam oriented in the direction zetE denotes the electric field, oriented in the direction x, corresponding to the linear direction of the elliptical polarization. The coils 7 make it possible to generate a component of the excitation radiofrequency field per axis of the magnetometer, namely a component B RF1 oriented along the axis z, a component B RF2 oriented along the axis y and a component B RF3 oriented according to l 'x axis, of respective pulses ω, Ω and ξ.
    In an exemplary embodiment, the component B RF2 orthogonal to the two preferred pumping directions has the highest frequency, for example 50 kHz. The two other components of the radiofrequency field have much lower frequencies, although much higher than the relaxation rate of the atoms, and in a non-integer relationship between them and compared to the frequency of the component B RF2 . For example, for helium where the relaxation rate of the atoms is of the order of 1 kHz, the frequencies of the components B RF1 and B RF3 can be fixed at 7 kHz and 9 kHz respectively.
    The components B RF2 and B RF3 are strictly orthogonal to the direction of the orientation. The atomic orientation therefore undergoes an evolution dependent on these components, while the component B RF1 which is parallel to the pumping direction has only a second order effect on the evolution of this orientation. The evolution of the atomic orientation is therefore essentially reduced to that which would exist in the absence of B RF1 . Thus, the orientation presents components at the frequencies (as well as their harmonics and inter-harmonics) of the components B RF2 and B RF3 of respective pulsations Ω and ξ. The amplitude of a photo-detection signal at one of these frequencies is proportional to the component of the ambient magnetic field parallel to the corresponding component of the radio frequency field. We can thus go back in particular to the components By and Bx of the ambient field. And the first interharmonic at Ω ± ξ allows to go back to the Bz component of the ambient field with however a significantly higher noise level. However, this noise level is compensated for by the measurement of Bz described below via the alignment given to the atoms.
    The components B RF1 and B RF2 are orthogonal to the direction of the electric field E. The evolution of the atomic alignment is therefore mainly controlled by these two components, while the component B RF3 parallel to this alignment has a weak impact on that -this. This impact is nevertheless a little more important than that which the component B RF1 has on the orientation due to a residue of longitudinal alignment coming from the alignment induced by circular polarization (whereas there is no of components oriented by any residue induced by linear polarization). The evolution of the alignment is nevertheless substantially similar to that which would exist in the absence of B RF3 , in a similar manner to what is observed in magnetometers with optical pumping pumped in alignment as described for example in S. Morales et al., Magnetocardiography measurements with 4 He vector optically pumped magnetometers at room temperature, Phys. Med. Biol., 2017. Thus the alignment presents components at the frequencies (as well as their harmonics and inter-harmonics) of the components B RF1 and B RF2 of respective pulsation ω and Ω. The amplitude of a photo-detection signal at one of these frequencies is proportional to the component of the ambient magnetic field parallel to the corresponding component of the RF field. In particular, we can go back to the Bz and By components of the ambient field. And the first inter-harmonic at ω ± Ω allows to go up to the component Bx of the ambient field with a noise level clearly less favorable than for the two other components. However, this noise level is compensated for by the measurement of Bx previously described via the orientation given to the atoms.
    The parametric resonance detection device 6 is thus configured to follow the evolution of atomic alignments and orientations and to obtain, by synchronous demodulation at the three frequencies of the components of the radiofrequency field, the amplitudes of the three components of the ambient magnetic field. The detection device 6 comprises for this purpose an optical arrangement configured to separate, temporally or spatially, optical signals carrying respectively information relating to an alignment state and to an orientation state of the atoms of the atomic gas.
    The detection device can in particular be configured to measure the amplitude of the optical signal carrying information relating to the state of orientation of the atoms of the atomic gas to a harmonic of each of the components of the excitation radiofrequency field orthogonal to the propagation direction k of the laser beam, namely the components B RF2 and B RF3 , this amplitude being respectively proportional to the component By and Bx of the ambient field.
    The detection device is further configured to measure the amplitude of the optical signal carrying information relating to the alignment state of the atoms of the atomic gas to a harmonic of each of the components of the excitation radiofrequency field, orthogonal to the direction of the electric field E, namely the components B RF1 and B RF2 , this amplitude being respectively proportional to the component Bz and By of the ambient field.
    As described below, the analysis of the optical signal carrying information relating to an alignment state, respectively to an orientation state of the atoms of the atomic gas, can be an analysis relating to the absorption of the component linear, respectively circular, when crossing the cell, or can be an analysis relating to the relative proportion of the right and left circular polarizations, respectively of the horizontal and vertical linear polarizations, in the beam having crossed the cell.
    In a first embodiment illustrated in FIGS. 3 and 4, the optical assembly comprises a divider 11 of the light beam L having passed through the cell in a first channel VI and a second channel V2, an alignment status analyzer on the first channel and an orientation state analyzer on the second channel. It is indeed not possible to position such analyzers in series, because the information on the circular / linear polarization is completely lost at the output of such an analyzer. We therefore proceed to a spatial separation of the light into two parts using the divider 11, these two parts having an equal or similar energy, which in particular makes it possible to be able to measure concomitantly the alignment and the orientation. According to a particular exemplary embodiment, the divider 11 is a non-polarizing separating plate which separates the power of the beam on the two channels VI, V2, each having 50% of the incident power of the light beam L.
    When the light beam used for pumping is also used as the probe beam for detection, the information on alignment and orientation is contained in the absorption of the linear and circular components respectively. As shown in FIG. 3, the alignment state analyzer on one of the channels comprises a linear polarizer 12 and a photodetector 13 which supplies a photo-detection signal carrying information relating to the state of d alignment of the atoms, and the orientation state analyzer on the other of the channels comprises a circular polarizer 22 (a quarter wave plate 14 associated with a linear polarizer 15) and a photodetector 16 which provides a signal photo-detection carrying information relating to the state of orientation of the atoms.
    To gain sensitivity, it is advantageous to use a probe beam separate from the pump beam. In such a case, it is useful to offset the frequency of the probe light with respect to the frequency of the atomic transition used so as not to induce residual pumping with the probe beam. This offset makes that an absorption measurement is not very effective. It is therefore preferable to carry out a birefringence measurement consisting in measuring the relative proportion of the left and right circular polarizations or of the linear horizontal and vertical polarizations.
    To do this, as shown in FIG. 4, the alignment state analyzer on the first channel VI comprises a quarter-wave plate 19, a polarization splitter 17 able to separate on a first and a second path the right circular polarization and left circular polarization of the laser beam, and a photodetector 18 on each of the first and second paths to allow the light intensity ratio between the two circular polarizations to be measured and thus to provide a photo-detection signal carrying information relating to the alignment of atoms. And the orientation state analyzer on the second channel V2 comprises a polarization splitter 20 able to separate on a first and a second path the horizontal linear polarization and the vertical linear polarization of the laser beam, and a photodetector 21 on each first and second paths to enable the light intensity ratio between the two linear polarizations to be measured and thus to provide a photo-detection signal carrying information relating to the orientation of the atoms.
    In a second embodiment which can be used whether the probe beam is distinct or not from the pump beam (when the probe beam is identical to the probe beam, the polarization is of the alternating type of linear polarization and circular polarization ), a time separation is carried out on the same channel of the optical signals carrying the alignment and orientation information. This temporal separation is carried out at a frequency faster than the relaxation time of the atoms and not commensurable at the frequencies of the components of the RF field, for example at a frequency of 1 MHz.
    As shown in FIG. 5, the optical assembly can for this purpose comprise an electrically controllable delay blade 23. This blade is modulated with a square wave so that during the half-periods when its output level is high (noted SH ), it behaves like a quarter-wave plate, whereas during low-level half-periods (noted SL) it behaves like a blade without delay or like a half-wave blade. Following this slide, the optical assembly comprises an atomic state analyzer performing an absorption measurement or a birefringence measurement with a polarization splitter 24 and two photodetectors 24. Taking the example of a birefringence measurement, during the phases SL, the output of the atomic state analyzer is proportional to the difference between the two linear polarizations, which corresponds to a rotation of the plane of polarization of the probe and makes it possible to measure the orientation according to the axis of propagation of it, according to a measurement scheme known in the field under the name of "Faraday scheme", as explained for example in the article F. Laloë, M. Leduc, and P. Minguzzi, Relations between the angular state of an atomic vapor subjected to optical pumping and its absorption and dispersion properties.,
    Journal of Physics, vol. 30, no. 2-3, pp. 277-288, 1969. During the SH phases, the output of the atomic state analyzer is proportional to the difference in intensity between the two circular polarizations, which makes it possible to obtain information on the atomic alignment transverse to the direction of propagation of the probe beam according to what is reported in this same article.
    The invention is not limited to the vectorial magnetometer described above, and also extends to a method of measuring a magnetic field using such a magnetometer, and in particular to a method comprising the steps consisting in polarizing linearly and circularly the light beam emitted towards the cell, and to be separated, by means of an optical arrangement of the detection device, optical signals carrying respectively information relating to an alignment state and to a state of atomic gas atoms orientation.
    权利要求:
    Claims (12)
    [1" id="c-fr-0001]
    1. Vector magnetometer (10) comprising:
    - a cell (1) intended to be filled with an atomic gas subjected to an ambient magnetic field (B o ),
    - an optical pumping source (2) arranged to emit a beam of light (F) having a pumping wavelength towards the cell (1),
    - a parametric resonance detection device (6) arranged to receive the light beam (L) having passed through the cell, characterized in that it further comprises a polarization device (3) configured so as to confer linear polarization and a circular polarization with the light beam emitted in the direction of the cell (1), and in that the detection device (6) comprises an optical arrangement arranged so as to separate optical signals carrying respectively information relating to a alignment state and an orientation state of the atoms of the atomic gas, said information making it possible to measure the ambient magnetic field (B o ).
    [2" id="c-fr-0002]
    2. Vector magnetometer according to claim 1, comprising an excitation source of parametric resonances (7, 8) configured so that it induces in the cell an excitation radiofrequency field (B RF1 , B RF2 , B RF3 ) having three components each oscillating at its own oscillation frequency, and in which the detection device (6) is configured to perform synchronous detection at a harmonic of each of the oscillation frequencies.
    [3" id="c-fr-0003]
    3. Vector magnetometer according to claim 2, in which the detection device (6) is configured to measure the amplitude of the optical signal carrying information relating to the orientation state of the atoms of the atomic gas at a harmonic of the oscillation frequency of each of the components of the excitation radiofrequency field (B RF2 , B RF3 ) orthogonal to the direction of propagation (k) of the light beam, and to measure the amplitude of the optical signal carrying the information relating to the alignment state of the atoms of the atomic gas to a harmonic of the oscillation frequency of each of the components of the excitation radiofrequency field (B RF1 , B RF2 ) orthogonal to the direction of the electric field (E) of the beam of light.
    [4" id="c-fr-0004]
    4. Vector magnetometer according to one of claims 1 to 3, in which the optical assembly comprises a divider (11) of the light beam (L) having passed through the cell in a first channel (VI) and a second channel (V2, an alignment state analyzer on the first channel (VI) and an orientation state analyzer on the second channel (V2).
    [5" id="c-fr-0005]
    5. A vector magnetometer according to claim 4, wherein the alignment state analyzer comprises a linear polarizer (12) and a photodetector (13).
    [6" id="c-fr-0006]
    6. Vector magnetometer according to one of claims 4 and 5, wherein the circular orientation state analyzer comprises a circular polarizer (14, 15) and a photodetector (16).
    [7" id="c-fr-0007]
    7. Vector magnetometer according to claim 4, in which the alignment state analyzer comprises a quarter wave plate (19), a polarization splitter (17) able to separate the polarization on a first and a second path. right circular and left circular polarization of the light beam and a photodetector (18) on each of the first and second paths.
    [8" id="c-fr-0008]
    8. Vector magnetometer according to one of claims 4 and 7, wherein the orientation state analyzer comprises a polarization splitter (20) able to separate on a first and a second path the horizontal linear polarization and the polarization vertical line of the light beam, and a photodetector (21) on each of the first and second paths.
    [9" id="c-fr-0009]
    9. Vector magnetometer according to one of claims 1 to 3, in which the optical assembly comprises a temporal separator of the light beam having passed through the cell alternately into a circularly polarized beam and into a linearly polarized beam, and a state analyzer atomic (24, 25) downstream of the separator.
    [10" id="c-fr-0010]
    10. Vector magnetometer according to one of claims 1 to 9, wherein the polarization device (3) is configured so as to confer simultaneously linear polarization and circular polarization to the beam of light emitted towards the cell.
    [11" id="c-fr-0011]
    11. Vector magnetometer according to one of claims 1 to 9, in which the polarization device (3) is configured so as to confer alternately linear polarization and then circular polarization to the beam of light emitted in the direction of the cell.
    [12" id="c-fr-0012]
    12. Method for measuring a magnetic field using a vector magnetometer (10) comprising a cell (1) filled with an atomic gas subjected to an ambient magnetic field, an optical pumping source (2) capable emitting towards the cell a beam of light tuned to a pumping wavelength, a device for detecting parametric resonances (6) receiving the beam of light (L) having passed through the cell and a servo system ( 7, 8, 9) in a closed loop of the magnetometer to operate it in zero field, characterized in that it comprises the steps consisting in linearly and circularly polarizing the beam of light emitted towards the cell, and in separating, at by means of an optical assembly of the detection device, optical signals respectively carrying information relating to an alignment state and to an orientation state of the atoms of the atomic gas.
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    同族专利:
    公开号 | 公开日
    FR3077884B1|2021-01-01|
    EP3524990A1|2019-08-14|
    US10845438B2|2020-11-24|
    US20190250223A1|2019-08-15|
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    法律状态:
    2019-02-28| PLFP| Fee payment|Year of fee payment: 2 |
    2019-08-16| PLSC| Search report ready|Effective date: 20190816 |
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1851170|2018-02-12|
    FR1851170A|FR3077884B1|2018-02-12|2018-02-12|ELLIPTICAL POLARIZATION VECTOR MAGNETOMETER|FR1851170A| FR3077884B1|2018-02-12|2018-02-12|ELLIPTICAL POLARIZATION VECTOR MAGNETOMETER|
    US16/272,103| US10845438B2|2018-02-12|2019-02-11|Vector magnetometer with elliptical polarisation|
    EP19156325.3A| EP3524990A1|2018-02-12|2019-02-11|Vector magnetometer with elliptic polarisation|
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