Nuclear magnetic resonance gyroscope and methods for using a nuclear magnetic resonance gyroscope as a gyrocompass

Abstract

To provide a nuclear magnetic resonance gyroscope by means of which a north-south direction can be determined, a nuclear magnetic resonance gyroscope (100) comprising a vapor cell (10) containing atoms with nuclei having a non-zero magnetic moment, a first pump laser (11), a second pump laser (12) and a probe laser (13) is proposed, wherein the first pump laser (11) is aligned along a first axis (14), wherein the second pump laser (12) is aligned along a second axis (15), and wherein the probe laser (13) is aligned along a third axis (16).

Description

[0001] The present invention relates to a nuclear magnetic resonance gyroscope. Furthermore, the present invention relates to a method for using a nuclear magnetic resonance gyroscope as a gyrocompass. State of the art

[0002] The needle of a magnetic compass points towards the Earth's magnetic north pole. Magnetic north differs from true north, which is defined by the Earth's rotational axis. A gyrocompass, on the other hand, points towards true north.

[0003] A mechanical gyrocompass consists of a rapidly rotating gyroscope suspended in a gimbal. The gyroscope is also positioned so that it experiences a torque as long as its rotation is not pointing north. When the rotation is north, and thus the gyroscope's axis of rotation aligns with the Earth's rotational direction, the torque disappears. Damping causes the gyroscope to come to rest when the applied force is eliminated.

[0004] Gyrocompasses are used particularly in shipping and aviation. A particular advantage of gyrocompasses over magnetic compasses is that gyrocompasses are not susceptible to interference from ferromagnetic materials, such as ship steel.

[0005] However, mechanical gyrocompasses and their gimbal suspension are mechanically complex, large, and also expensive.

[0006] Furthermore, fiber optic gyrocompasses and gyrocompasses based on laser ring resonators are known. These are also large, expensive, and complex, and additionally require mechanical and temperature stabilization. Moreover, fiber optic gyrocompasses and laser ring resonator gyrocompasses are difficult to miniaturize.

[0007] Atomic nuclear magnetic resonance gyroscopes, also known as NMR rotation rate sensors, are known in the state of the art. These have the advantage of excellent sensitivity and drift stability, as well as a high miniaturization potential.

[0008] To determine rotation rates, nuclear magnetic resonance (NMR) gyroscopes analyze the NMR signals of atomic nuclei with non-zero magnetic moments. State-of-the-art technology includes optically pumped NMR gyroscopes based on a vapor cell. These gyroscopes measure the spin precession ω. messThe data was read out in a steam cell. The spin precession is caused by a superposition of the Larmor precession ω. larmor and an external rotation ω R Given. The external rotation ω R represents an additional rotation, which can be derived from the equation ω mess = ω armor ± ω R can be determined.

[0009] From CN 107063226 A a double air chamber nuclear magnetic resonance gyroscope is known, comprising a first magnetic shield, a first air chamber, a first pump coil, a first main magnetic field coil, a first laser detector, a second magnetic shield, a second air chamber, a second pump coil, a second main magnetic field coil, a second laser detector, a laser device, a magnetic field generator and a signal processor. Disclosure of the invention

[0010] The present invention is based on the objective of providing a nuclear magnetic resonance gyroscope by means of which a north-south direction can be determined. Furthermore, the present invention is based on the objective of providing a method for using a nuclear magnetic resonance gyroscope as a gyrocompass.

[0011] To solve the problem underlying the invention, a nuclear magnetic resonance gyroscope comprising a vapor cell containing atoms with atomic nuclei having a non-zero magnetic moment, a first pump laser, a second pump laser and a probe laser is proposed, wherein the first pump laser is aligned along a first axis, wherein the second pump laser is aligned along a second axis, and wherein the probe laser is aligned along a third axis.

[0012] Preferably, the nuclear pingyroscope comprises exactly one vapor cell. The first pump laser, the second pump laser, and the probe laser are then configured to illuminate exactly one vapor cell with laser light.

[0013] In contrast to known magnetic resonance gyroscopes, the magnetic resonance gyroscope according to the invention thus comprises a first pump laser and a second pump laser. Accordingly, the magnetic resonance gyroscope according to the invention has two sensitive axes, wherein the first sensitive axis corresponds to the first axis and the second sensitive axis to the second axis. Such a magnetic resonance gyroscope can be used with particular advantage in a method for using a magnetic resonance gyroscope as a gyrocompass, as explained below.

[0014] It is particularly preferred that the first axis, the second axis and the third axis are mutually orthogonal to each other.

[0015] In other words, the sensitive axes defined by the pump beam of the first pump laser and the pump beam of the second pump laser are arranged at an angle of 90° to each other. The axis of the probe laser, or the third axis, is oriented perpendicular to the first sensitive axis defined by the first pump laser and to the second sensitive axis defined by the second pump laser.

[0016] Preferably, the atoms comprise atoms of an alkali metal, in particular Rb atoms, and atoms of a noble gas, in particular Xe atoms.

[0017] With a further advantage, it can be provided that the first pump laser generates circularly polarized light, that the second pump laser generates circularly polarized laser light, and that the probe laser generates linearly polarized laser light.

[0018] The first and second pump lasers serve, in a known manner, to polarize the spins and thus the magnetic moments of the atomic nuclei in an external bias magnetic field. The spin precession can then be read out using the preferably linearly polarized probe laser beam.

[0019] Furthermore, it may be provided that the nuclear magnetic resonance gyroscope includes a coil system for generating static bias magnetic fields and alternating magnetic fields, wherein the coil system comprises a first coil, a second coil and a third coil.

[0020] With a further advantage, it is provided that the first coil and the second coil are designed to generate a first bias magnetic field parallel to the first axis and a second bias magnetic field parallel to the second axis, and to generate a first alternating magnetic field transverse to the first bias magnetic field and a second alternating magnetic field transverse to the second bias magnetic field, wherein a frequency of the first alternating magnetic field and of the second alternating magnetic field corresponds to a Larmor frequency, in particular a Larmor frequency of Rb.

[0021] Preferably, the third coil for generating a third alternating magnetic field is designed parallel to the probe laser, wherein a frequency of the third alternating magnetic field corresponds to a Larmor frequency, in particular a Larmor frequency of Xe.

[0022] A further advantage is that the first coil, the second coil, and the third coil can be designed to compensate for residual magnetic fields.

[0023] Preferably, the steam cell is arranged centrally and / or in the middle of the coil system.

[0024] Furthermore, the coil system and the steam cell can be arranged in a magnetic shield.

[0025] Furthermore, the nuclear magnetic resonance gyroscope may be provided with a polarizing beam splitter cube and a balanced detector.

[0026] Another solution to the problem underlying the invention consists in providing a method for using a previously described nuclear magnetic resonance gyroscope as a gyrocompass, wherein at least the first rotation rate ω R,1 and a second rotation rate ω R,2 can be determined using the nuclear magnetic resonance gyroscope, where the first rotation rate ω R,1is determined along a first direction parallel to the first axis, where the second rotation rate ω R,2 is determined along a second direction parallel to the second axis, and wherein the first rotation rate ω R,1 and the second rotation rate ω R,2 a north-south direction is determined.

[0027] By procedure, at least one first rotation rate ω is used. R,1 and a second rotation rate ω R,2 Determined using a nuclear magnetic resonance gyroscope. At the first rotation rate ω R,1 and the second rotation rate ω R,2 These are external rotation rates, each of which is determined at a known Larmor frequency ω. larmor the nuclear spin isotopes used from the spin precession ω determined from the nuclear magnetic resonance signal of the probe laser mess according to the equation ω mess = ω larmor ± ω R = γB0 ± ω R be determined. ω R stands for ω R,1 and ω R,2The factor γ indicates the gyromagnetic ratio of the nuclear spin isotope used, preferably Xe. B0 is the bias magnetic field generated by the magnetic field coil at the location of the steam cell.

[0028] Preferably, the first axis and the second axis of the nuclear magnetic resonance gyroscope are aligned parallel to the Earth's surface, and / or the third axis is aligned perpendicular to the Earth's surface.

[0029] The first rotation rate ω R,1 The first direction is thus determined parallel to the Earth's surface, and the second rotation rate ω R,2 is determined along the second direction parallel to the Earth's surface. This means that the determined rotation rates ω R,1 and ω R,2 the projection of the Earth's rotation Ω E to the Earth's surface along the respective axis or direction. The following applies: ωR=ωEh cos α=ΩE cos φ cos α. This is ωEh=ΩE cos φ the horizontal component of the Earth's rotation Ω E along the true north-south direction. The horizontal component ωEh The Earth's rotation depends on the geographical latitude φ. Furthermore, the measured rotation rates ω depend on R,1 and ω R,2 of the azimuth angle α between the horizontal component ωEh the Earth's rotation and the direction or axis used for the measurement, i.e., the first axis and the second axis.

[0030] The horizontal component of the Earth's rotation ωEh Given knowledge of the geographical latitude φ, and using the known Earth's rotation Ω, it is possible to calculate E = 15.041° / h can be determined.

[0031] By procedure, the first rotation rate ω is used. R,1 and the second rotation rate ω R,2A north-south direction is determined. This means, in particular, that the azimuth angle α, preferably the azimuth angle α between the first direction or axis and the north-south direction, is determined. Knowing the azimuth angle α between the first direction or axis and the north-south direction, the north-south direction with respect to the first direction or axis can be determined by taking the azimuth angle α into account.

[0032] Preferably, the first axis or the second axis of the nuclear magnetic resonance gyroscope is aligned along the determined north-south direction.

[0033] The magnetic resonance gyroscope according to the invention is therefore particularly suitable for use as a gyrocompass. For use as a gyrocompass, it is necessary to know the north-south direction precisely. It is particularly advantageous that the magnetic resonance gyroscope according to the invention has two sensitive axes, defined by the direction of the first pump laser along the first axis and the direction of the second pump laser along the second axis. Thus, two external rotation rates ω can be determined. R,1 and ω R,2 Determine along the sensitive axes which can be used to determine the north-south direction.

[0034] It is preferably provided that an azimuth angle α is determined between the first direction and the north-south direction, and that the north-south direction is obtained by applying the azimuth angle α to the first direction.

[0035] In other words, the angle of the first axis of the magnetic resonance gyroscope to the north-south direction is determined. This angle is the azimuth angle α. After determining the azimuth angle α, it can be applied to the first direction given by the orientation of the first axis to determine the actual north-south direction.

[0036] It is preferably provided that the azimuth angle α is given by α = tan -1 (-ω R,2 / ω R,1 ) is determined.

[0037] Due to the orthogonality of the axes, i.e., that an angle of 90° is provided between the second direction and the first direction, or between the first axis and the second axis, it follows, because cos(α + 90°) = - sin(α), that ωR,1=ωEh cos α and that ωR,2=−ωEh sin α.

[0038] Preferably, it is provided that the first rotation rate ω is determined R,1the first pump laser and the probe laser are switched on, such that a bias magnetic field parallel to the first pump laser and / or to the first axis and a first alternating magnetic field transverse to the first bias magnetic field are coupled in by means of the first coil and the second coil, and that a third alternating magnetic field parallel to the probe laser and / or to the third axis is coupled in by means of the third coil, wherein the first rotation rate ω is derived from a signal of the probe laser. R,1 is determined.

[0039] When determining the first rotation rate, the second pump laser is preferably switched off.

[0040] A further advantage is that the second rotation rate ω can be determined using... R,2the second pump laser and the probe laser are switched on, such that a bias magnetic field parallel to the second pump laser and / or to the second axis and a second alternating magnetic field transverse to the second bias magnetic field are coupled in by means of the first coil and the second coil, and that a third alternating magnetic field parallel to the probe laser and / or to the third axis is coupled in by means of the third coil, whereby the second rotation rate ω is derived from a signal of the probe laser. R,2 is determined.

[0041] When determining the second rotation rate, the second pump laser is preferably switched off.

[0042] The determination of the azimuth angle is therefore preferably divided into two steps.

[0043] In a first step, the first pump laser and the probe laser are switched on. The second pump laser is switched off. A first static bias magnetic field is generated in parallel with the first pump laser. Additionally, a first alternating magnetic field, transverse to the first bias magnetic field and preferably resonant with the Rb Larmor frequency, is applied. A third alternating magnetic field, preferably resonant with the Xe nuclear spin Larmor frequency, is applied in parallel with the probe laser. The first rotation rate ω is derived from the probe laser signal. R,1 , i.e., the Earth's rotation along the first axis parallel to the first pump laser was extracted by signal evaluation.

[0044] In a second step, the second pump laser and the probe laser are switched on. The first pump laser is switched off. A second static bias magnetic field is generated in parallel with the second pump laser. Additionally, a second alternating magnetic field, transverse to the second bias magnetic field and preferably resonant with the Rb Larmor frequency, is applied. A third alternating magnetic field, preferably resonant with the Xe nuclear spin Larmor frequency, is applied in parallel with the probe laser. The second rotation rate ω is derived from the probe laser signal. R,2 , i.e., the Earth's rotation along the second axis parallel to the second pump laser was extracted by signal evaluation.

[0045] The azimuth angle α, and thus the north-south direction, can then be determined by α = tan -1 (-ω R,2 / ω R,1 ) can be determined.

[0046] Furthermore, it may be provided that the determined azimuth angle α is used to determine an offset.s , preferably a temporal change of the offset, and / or a sensitivity sens s , preferably used for temporal changes in the sensitivity of the nuclear magnetic resonance gyroscope.

[0047] Thus, the information about the azimuth angle α can be used to compensate for deficiencies of the magnetic resonance gyroscope. Known deficiencies of such magnetic resonance gyroscopes concern the offset or its change over time (offset drift) and the sensitivity or its change over time (sensitivity drift).

[0048] Preferably, the offset is provided that s , and / or the sensitivity sens s , by solving the equation, preferably numerically ∫t1(sig(t)−offsets) / senssdt=α(t1) be appreciated.

[0049] The real time-dependent sensor signal sig(t) of the nuclear magnetic resonance gyroscope is determined by sig(t)=sensr(t)⋅dα(t)dt+offsetr(t) given and depends on the change over time dα(t)dt of the azimuth angle α, the actual sensitivity sens r (t) and the real offset offset r (t) from. Integration of the real time-dependent sensor signal sig(t) yields the above integral. This can be solved numerically to obtain an estimate offset s for the offset and an estimate sens s to maintain sensitivity.

[0050] Advantageously, it is provided that a signal from the nuclear magnetic resonance gyroscope, in particular a signal from the probe laser, is corrected using the determined azimuth angle α, whereby the corrected signal sig corr (t) from the equation sig corr (t) = (sig(t) - offset s ) / (sens s / sens n ) is determined.

[0051] The factor sens n This corresponds to the nominal sensitivity of the nuclear magnetic resonance gyroscope.

[0052] The invention is explained in more detail below with reference to the accompanying figures. These show Fig. 1 a magnetic resonance gyroscope, Fig. 2a a view of the Earth, Fig. 2b a section of a side view of the Earth, Fig. 2c a view of the Earth's surface, Fig. 3 a magnetic resonance gyroscope, and Fig. 4 a flowchart for a procedure for using a nuclear magnetic resonance gyroscope as a gyrocompass.

[0053] Fig. Figure 1 shows a nuclear magnetic resonance gyroscope 100 in accordance with the invention. The nuclear magnetic resonance gyroscope 100 comprises a vapor cell 10 containing atoms with nuclei having a non-zero magnetic moment, a first pump laser 11, a second pump laser 12, and a probe laser 13. The first pump laser 11 is aligned along a first axis 14, and the second pump laser 12 is aligned along a second axis 15. The probe laser 13 is aligned along a third axis 16. The vapor cell 10 is arranged within a coil system 17 comprising a first coil 18, a second coil 19, and a third coil 20. The vapor cell 10 and the coil system 17 are located within a magnetic shield 21. Outside the shield 21, a measuring device 22 is provided for detecting the probe laser signal. The measuring device 22 comprises a polarizing beam splitter cube 23 and photodetectors 24.The first axis 14, the second axis 15, and the third axis 16 are mutually orthogonal. The first pump laser 11 and the second pump laser 12 each generate circularly polarized laser light. The probe laser 13, on the other hand, is configured to generate linearly polarized laser light. The first coil 18 and the second coil 19 are configured to generate a first bias magnetic field parallel to the first axis 14 and a second bias magnetic field parallel to the second axis 15, as well as a first alternating magnetic field transverse to the first bias magnetic field and a second alternating magnetic field transverse to the second bias magnetic field. The third coil 20 serves to generate a third alternating magnetic field parallel to the probe laser 13, i.e., parallel to the third axis 16.

[0054] The nuclear magnetic resonance gyroscope 100 after Fig. 1 can be used in a method 200 for the use of a nuclear magnetic resonance gyroscope 100 as a gyrocompass. Within the framework of the method 200, at least one first rotation rate ω is used. R,1 and a second rotation rate ω R,2 determined using the nuclear magnetic resonance gyroscope 100, where the first rotation rate ω R,1 is determined along a first direction 25 parallel to the first axis 14, where the second rotation rate ω R,2 along a second direction 26 parallel to the second axis 15, and wherein the first rotation rate ω R,1 and the second rotation rate ω R,2 A north-south direction of 30 is determined.

[0055] Fig. 2a shows a schematic view of the Earth 27. Fig. Figure 2b shows a side view and Fig. Figure 2c shows a top view of the Earth's surface 28. The Earth 27 rotates with a known rotation frequency Ω. Eabout its axis of rotation 29. A previously described nuclear magnetic resonance gyroscope 100 is arranged on the Earth's surface 28 at a geographical latitude φ. If the first axis 14 of the nuclear magnetic resonance gyroscope 100 is aligned parallel to the north-south direction 30, then the first rotation rate ω determined parallel to the first axis 14 is R,1 given by ωR,1=ωEh=ΩE cos φ, where ωEh=ΩE cos φ the horizontal component of the Earth's rotation Ω E along the north-south direction is 30.

[0056] At the beginning of the procedure 200, the north-south direction 30 is not exactly known. The first axis 14 of the nuclear magnetic resonance gyroscope 100 is therefore generally not aligned exactly along the north-south direction 30, but rather along a first direction 25. In this case, as in Fig. Figure 3 shows schematically the nuclear magnetic resonance gyroscope 100 arranged on the Earth's surface 28, and the determined external rotation rate ω.R,1 = Ω E cos φ cos α along the first direction 25 parallel to the first axis 14 additionally depends on the azimuth angle α, which is determined by the angle between the horizontal component ωEh The Earth's rotation and the first direction 25 are given. For a rotation rate ω measured along a second direction 26 parallel to the second axis 15. R,2 ω applies R,2 = Ω E cos φ cos(α + 90°) = - Ω E cos φ sin(α). Thus, from the rotation rates ω R,1 and ω R,2 the azimuth angle α by α = tan -1 (-ω R,2 / ω R,1 ) are determined.

[0057] For this purpose, in a first step the first pump laser 11 and the probe laser 13 are switched on. The second pump laser 12 is switched off. A first static bias magnetic field is generated parallel to the first pump laser 11. In addition, a first alternating magnetic field transverse to the first bias magnetic field is applied. A third alternating magnetic field is applied parallel to the probe laser 13. The first rotation rate ω is derived from the probe laser signal. R,1 , i.e., the Earth's rotation along the first axis 14 parallel to the first pump laser 11, extracted by signal evaluation.

[0058] In a second step, the second pump laser 12 and the probe laser 13 are switched on. The first pump laser 11 is switched off. A second static bias magnetic field is generated parallel to the second pump laser 12. In addition, a second alternating magnetic field transverse to the second bias magnetic field is applied. A third alternating magnetic field is applied parallel to the probe laser 13. The second rotation rate ω is derived from the probe laser signal. R,2 , i.e., the Earth's rotation along the second axis 15 parallel to the second pump laser 12, extracted by signal evaluation.

[0059] Fig. Figure 4 shows a flowchart for a procedure 200 for using a nuclear magnetic resonance gyroscope 100 as a gyrocompass. In a first procedure step S1, a first rotation rate ω is determined. R,1 determined using the nuclear magnetic resonance gyroscope 100, where the first rotation rate ω R,1The rotation rate ω is determined along a first direction 25 parallel to the first axis 14. In a second process step S2, a second rotation rate ω is determined. R,2 determined using the nuclear magnetic resonance gyroscope 100, where the second rotation rate ω R,2 along a second direction 26 parallel to the second axis 15. In a third process step S3, the rotation rate ω is determined from the first rotation rate. R,1 and the second rotation rate ω R,2 a north-south direction of 30 is determined. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 107063226 A

[0009]

Claims

[1] Nuclear magnetic resonance gyroscope (100) comprising a vapor cell (10) containing atoms with nuclei having a non-zero magnetic moment, a first pump laser (11), a second pump laser (12) and a probe laser (13), wherein the first pump laser (11) is aligned along a first axis (14), wherein the second pump laser (12) is aligned along a second axis (15), and wherein the probe laser (13) is aligned along a third axis (16). [2] Nuclear magnetic resonance gyroscope (100) according to claim 1, characterized by , that the first axis (14), the second axis (15) and the third axis (16) are mutually orthogonal to each other. [3] Nuclear magnetic resonance gyroscope (100), according to claim 1 or 2, characterized by, that the nuclear magnetic resonance gyroscope (100) comprises a coil system (17) for generating static bias magnetic fields and alternating magnetic fields, wherein the coil system (17) comprises a first coil (18), a second coil (19) and a third coil (20). [4] Method (200) for using a nuclear magnetic resonance gyroscope (100) according to one of the preceding claims as a gyrocompass, wherein at least the first rotation rate ω R,1 and a second rotation rate ω R,2 determined by means of the nuclear magnetic resonance gyroscope (100), where the first rotation rate ω R,1 is determined along a first direction (25) parallel to the first axis (14), where the second rotation rate ω R,2 is determined along a second direction (26) parallel to the second axis (15), and wherein the first rotation rate ω R,1 and the second rotation rate ω R,2 a north-south direction (30) is determined. [5] Method (200) according to claim 4, characterized by, that the first axis (14) and the second axis (15) of the nuclear magnetic resonance gyroscope (100) are aligned parallel to the Earth's surface (28), and / or that the third axis (16) is aligned perpendicular to the Earth's surface (28). [6] Method (200) according to claim 4 or 5, characterized by , that an azimuth angle α is determined between the first direction (25) and the north-south direction (30), and that the north-south direction (30) is obtained by applying the azimuth angle α to the first direction (25), and that preferably the azimuth angle α is determined by α = tan -1 (-ω R,2 / ω R,1 ) is determined. [7] Method (200) according to any one of claims 4 to 6, characterized by , that to determine the first rotation rate ω R,1the first pump laser (11) and the probe laser (13) are switched on, that a bias magnetic field and an alternating magnetic field are coupled parallel to the first pump laser (11) and / or to the first axis (14) by means of the first coil (18) and the second coil (19), that an alternating magnetic field is coupled parallel to the probe laser (13) and / or to the third axis (16) by means of the third coil (20), wherein the first rotation rate ω is derived from a signal of the probe laser (13). R,1 is determined. [8] Method (200) according to any one of claims 4 to 7, characterized by , that to determine the second rotation rate ω R,2the second pump laser (12) and the probe laser (13) are switched on, a bias magnetic field and an alternating magnetic field are coupled in parallel to the second pump laser (12) and / or to the second axis (15) by means of the first coil (18) and the second coil (19), and an alternating magnetic field is coupled in parallel to the probe laser (13) and / or to the third axis (16) by means of the third coil (20), whereby the second rotation rate ω is derived from a signal of the probe laser (13). R,2 is determined. [9] Method (200) according to any one of claims 6 to 8, characterized by , that the determined azimuth angle α is used to determine an offset s , preferably a temporal change of the offset, and / or a sensitivity sens s , preferably a temporal change in the sensitivity of the nuclear magnetic resonance gyroscope (100) is used, and that preferably the offset offset s , and / or the sensitivity sens s, by, preferably numerical, solving the equation ∫t1(sig(t)−offsets) / senssdt=α(t1) be appreciated. [10] Method (200) according to claim 6, characterized by , that a signal from the nuclear magnetic resonance gyroscope (100), in particular a signal from the probe laser (13), is corrected using the determined azimuth angle α, wherein the corrected signal from the equation sig corr (t) = (sig(t) - offset s ) / (sens s / sens n ) is determined.

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