DE102020212027A1 - NMR gyroscope - Google Patents

Abstract

The invention relates to an NMR gyroscope, the NMR gyroscope (200) comprising a first optical arrangement (211), the first optical arrangement (211) being arranged in the beam path between the illumination source (205) and the vapor cell arrangement (201), and wherein the first optical arrangement (211) is set up to convert the light beam (2001) of the illumination source (205) into a first pump light beam (20110), having a first polarization, for exciting the spin precession movement in the sensing medium (204) of first pump region (2011) with a first sense of circulation,a second pump light beam (20120) having a second polarization for exciting spin precession motion in the sensing medium (204) of the second pump region (2012) with a second sense of circulation, the first sense of circulation and the second sense of rotation are opposite to each other, and a readout light beam (2000) having a third polarization for reading out the spin precession motions of the first pump area (2011) and the second pumping area (2012).

Description

State of the art

MEMS Components for NMR Atomic Sensors (R.M. Noor and A.M. Shkel; Journal of Microelectromechanical Systems, 27(6):1148-1159, Dec. 2018) describes the structure and operation of an NMR gyroscope.

essence and advantages of the invention

The technology of the future requires ever more precise sensors. In the field of navigation, especially after gyroscopes, which can precisely measure the rotation rate. High-precision yaw rate sensors based on optical resonators are already installed in aircraft today. For autonomous driving and flying, as well as for applications that have poor connection to GPS, radar and similar systems, such as underwater navigation, high-precision onboard sensors are required, which places special demands on the size and the required construction volume of the high-precision onboard sensors.

Ensuring safe stopping, based on inertial sensors, in the event of failure of the other systems is essential, especially for applications in the field of autonomous driving. In order to improve the safety and comfort of autonomous vehicles in particular, a significant increase in drift stability and a significant reduction in the noise of yaw rate sensors (= gyroscope) is desirable in order to enable purely inertial navigation even for longer distances such as in tunnels or in urban canyons . Therefore, the focus for these applications is on gyroscopes, known from basic research, which generate nuclear magnetic resonance signals from atomic nuclei with a non-vanishing magnetic moment (spin 1/2 nuclei, spin 3/2 nuclei, spin ((2n+1)/2) nuclei, where n is a natural number). These show increased drift stability and increased accuracy compared to the MEMS yaw rate sensors currently used in the automotive industry. Furthermore, they show reduced interference from vibrations and accelerations.

In nuclear magnetic resonance gyroscopes, also called NMR gyroscopes (NMR=nuclear magnetic resonance), which are based on a vapor cell, the resulting spin-larmor precession ω _larmor is read out in a vapor cell. An outer rotation ω _rot represents an additional rotation, which can be determined by reading out the rotation frequency ω _mess as follows: $${\mathrm{\omega }}_{\text{mess}}={\mathrm{\omega }}_{\text{larmor}}\pm {\mathrm{\omega }}_{\text{Red}}$$

An exemplary structure of an NMR gyroscope and its mode of operation are presented, for example, in “MEMS Components for NMR Atomic Sensors” (R. M. Noor and A. M. Shkel; Journal of Microelectromechanical Systems, 27(6):1148-1159, Dec. 2018).

Interferences such as electrical noise from components of the NMR gyroscope, fluctuations in lasers used in the NMR gyroscope (especially frequency, detuning and power of the laser), and noise of the magnetic fields used in the NMR gyroscope, etc., as well as interfering magnetic fields or temperature gradients major influence on the drift accuracy over time and the sensitivity of the gyroscope.

The terms “light” and “electromagnetic radiation” are used synonymously.

The invention relates to an NMR gyroscope.

An advantage of the invention with the features of the independent patent claim is that the NMR gyroscope has a very compact structure and requires a small number of components (eg lighting sources) without sacrificing performance and measurement accuracy. By reducing the pack size, magnetic field fluctuations can be compensated for, which advantageously results in lower requirements for the coils for magnetic field generation and internal power sources, as well as lower requirements for shielding against external magnetic fields with the same measurement accuracy. The same applies to the requirements for lighting sources (e.g. laser sources) and temperature stabilization. Furthermore, the effects of external interference on the measurement result of the NMR gyroscope can be reduced in a simple manner without complex and costly modifications in order to increase the sensitivity and reliability of the NMR gyroscope and reduce signal drift. Into the In particular, the invention enables interference signals caused by changes in external parameters, such as a magnetic field environment and/or an ambient temperature of the NMR gyroscope, and internal interference signals to be eliminated. A further advantage results from the fact that with the NMR gyroscope according to the invention, in the event that no rotation rate is present, the signal at the output of the NMR gyroscope disappears, which makes highly precise calibration possible, which compensates for the drift (ie the signal when there is no rotation rate applied) significantly reduced. In particular, this advantageously also allows correction of manufacturing deviations through calibration. Furthermore, the vanishing signal for the non-rotating system is advantageous in signal processing and enables higher precision and lower drift.

• • eine Dampfzellenanordnung, wobei die Dampfzellenanordnung ein Sensiermedium umfasst, welches in der Dampfzellenanordnung angeordnet ist,
• • eine Beleuchtungsquelle zum Bereitstellen eines Pump-Lichtstrahls am Ort der Dampfzellenanordnung, wobei der Pump-Lichtstrahl zum Anregen einer Spin-Präzessionsbewegung im Sensiermedium eingerichtet ist, und
• • eine Detektionsanordnung, wobei die Detektionsanordnung zur Bestimmung einer Drehmessgröße des NMR-Gyroskops aus der Spin-Präzessionsbewegung eingerichtet ist.

This is accomplished with an NMR gyroscope, comprehensive

• • a steam cell arrangement, wherein the steam cell arrangement comprises a sensing medium which is arranged in the steam cell arrangement,
• • an illumination source for providing a pump light beam at the location of the vapor cell arrangement, the pump light beam being set up for exciting a spin precession movement in the sensing medium, and
• • a detection arrangement, wherein the detection arrangement is set up to determine a rotational measurement variable of the NMR gyroscope from the spin precession movement.

• • dass die Dampfzellenanordnung einen ersten Pumpbereich und einen zweiten Pumpbereich aufweist,
• • dass das NMR-Gyroskop eine erste optische Anordnung umfasst, wobei die erste optische Anordnung im Strahlengang zwischen der Beleuchtungsquelle und der Dampfzellenanordnung angeordnet ist, und wobei die erste optische Anordnung dazu eingerichtet ist, den Lichtstrahl der Beleuchtungsquelle
  • - in einen ersten Pump-Lichtstrahl, aufweisend eine erste Polarisation, zum Anregen der Spin-Präzessionsbewegung im Sensiermedium des ersten Pumpbereichs mit einem ersten Umlaufsinn,
  • - einen zweiten Pump-Lichtstrahl, aufweisend eine zweite Polarisation, zum Anregen der Spin-Präzessionsbewegung im Sensiermedium des zweiten Pumpbereichs mit einem zweiten Umlaufsinn, wobei der erste Umlaufsinn und der zweite Umlaufsinn gegenläufig zueinander sind, und
  • - einen Auslese-Lichtstrahl, aufweisend eine dritte Polarisation, zum Auslesen der Spin-Präzessionsbewegungen des ersten Pumpbereichs und des zweiten Pumpbereichs,

aufzuteilen.The NMR gyroscope is characterized by

• • that the vapor cell arrangement has a first pumping area and a second pumping area,
• • that the NMR gyroscope comprises a first optical arrangement, the first optical arrangement being arranged in the beam path between the illumination source and the vapor cell arrangement, and the first optical arrangement being arranged to illuminate the light beam of the illumination source
  • - in a first pump light beam, having a first polarization, for exciting the spin precession movement in the sensing medium of the first pump region with a first direction of rotation,
  • - a second pump light beam, having a second polarization, for exciting the spin precession motion in the sensing medium of the second pump region with a second sense of rotation, the first sense of rotation and the second sense of rotation being opposite to one another, and
  • - a readout light beam, having a third polarization, for reading out the spin precession movements of the first pump region and of the second pump region,

split up.

i.e. the precession movement in the first pump region and the precession movement in the second pump region are in opposite directions: if the spins in the first pump region precess clockwise, for example, the nuclear spins in the second pump region precess counterclockwise.

The steam cell assembly may include one steam cell, two steam cells, or more than two steam cells. A vapor cell is designed, for example, as a hollow body made of glass, the interior of which can be hermetically sealed from the environment of the vapor cell, so that gases in particular cannot escape from the interior of the vapor cell during operation and pressures can be generated inside the vapor cell that differ from the ambient pressure of the NMR gyroscope differ. To set a pressure and/or to generate a gas in the steam cell, for example, a heating element can be arranged on the steam cell or in the vicinity of the steam cell. For example, electrically conductive wires can be used as the heating element, with the temperature of the media located in the vapor cell being adjustable via the electric current flowing through the wires. A further embodiment for heating the vapor cell or vapor cells comprises at least one laser, i. H. a heating laser, the laser light of which is directed onto a region of the at least one vapor cell. The laser light is absorbed by the material of the vapor cell, in particular the silicon, and thus heats the vapor cell. In particular, the at least one vapor cell can be made of glass and can be round, cylindrical, cube-shaped, etc., for example.

One advantage is that the illumination source can be used to provide the pump light beams (also called pump laser beams) and to provide the read-out light beam (also called read-out laser beam), as a result of which an illumination source can be saved compared to the prior art. Using a common illumination source for the first and second pump region and for reading also has the advantage of common noise statistics.

An advantage, which results in particular from the use of two pump regions with oppositely precessing spins, is an intrinsic cancellation of internal noise signals, in particular electronic noise signals from lasers, magnetic fields, etc., charge shifts in the shielding, etc., and a higher sensitivity as a result and less drift of the NMR gyroscope. Thus, interfering influences such as noise (common noise), which affect both pump regions, cancel each other out during the measurement and consequently a higher accuracy of the yaw rate of a rotation of the NMR gyroscope determined with the NMR gyroscope can be achieved.

In one embodiment, the NMR gyroscope comprises a magnetic field generating device for providing a magnetic bias field and an oscillating magnetic field at the location of the vapor cell arrangement, wherein the magnetic bias field is set up to determine a direction of a precession movement of the spins of the sensing medium and the oscillating magnetic field is set up to synchronize the precession movements of the spins of the sensing medium . These can be generated, for example, by miniaturized Helmholtz coils. Even more homogeneous fields can be generated by complex coil geometries, for example. In particular, complex coils can be used in defined levels for this purpose, which - as for example in "bfieidtoos - a software package for magnetic field modelling", R. Zetter, J. livanainen, A. Mkinen, L. Parkkonen, Conference Proceedings WOPM, 2019, Mainz described - can be modeled. What is special about such coils is that the different field directions can be generated close together. In addition, it is possible that the steam cells are not located in the middle between the "coils" as with conventional Helmholtz coils. Alternatively or additionally, the magnetic field generating device can comprise three-axis or multi-axis magnetic field coils, for example to compensate for interference fields within the vapor cell arrangement or to provide bias fields with different directions and/or strengths for the vapor cell arrangement.

In one embodiment, the sensing medium includes a second medium. For example, an alkali metal such as rubidium (Rb), in particular rubidium 87 ( ⁸⁷ Rb) or rubidium 85 ( ⁸⁵ Rb), cesium (Cs), potassium (K), etc. or mercury (Hg) can be used as the second medium. The spin precession movement in the sensing medium is understood to mean the precession movement of the electron spins in the second medium.

In a further embodiment, the sensing medium can comprise a first medium in addition to the second medium. The first medium and the second medium can in particular be gaseous or can be converted into a gaseous state by heating the vapor cell. For example, a noble gas such as xenon (Xe), neon (Ne), krypton (Kr) or helium-3 ( ³ He) can be used as the first medium. If the steam cell arrangement includes two steam cells, the steam cells can in particular include sensing media that differ from one another. In particular, the first medium in the first vapor cell and the first medium in the second vapor cell can differ. For example, the first medium in the first vapor cell and the first medium in the second vapor cell can have different gyromagnetic ratios and/or gyromagnetic ratios of different signs. The spin precession movement in the sensing medium is understood to mean the precession movement of the nuclear spins in the first medium.

In all embodiments of the sensing medium, the wavelength of the light that can be emitted by the illumination source is matched to the energy scheme of the second medium, so that the light can be absorbed by the second medium and polarization of the electron spins can be generated (optical pumping). Circularly polarized light is preferably used for the illumination.

In the case of circularly polarized light, a distinction is made between σ ⁺ -polarization ("sigma plus") and σ ^- polarization ("sigma minus"), which causes a change in the magnetic quantum number m of +1 or -1 during atomic transitions between energy levels . Linearly polarized light (Δ m = 0 at the atomic transition) is called π -polarized light. Here, a right-hand circularly polarized light ray counter to the static bias field, ie antiparallel to the bias field, is equal to a left-hand circularly polarized light ray along the bias field, ie parallel to the bias field.

The NMR gyroscope is initialized by optical pumping. During optical pumping of the second medium (e.g. alkali metal atoms) in weak magnetic fields, it becomes right (σ ⁺ ) - or left-hand circular (σ ^- ) polarized light is injected parallel or antiparallel to the bias field B ₀ to selectively excite transitions with a difference in the magnetic quantum number of the Zeemann levels of plus one or minus one. A representative representation of the optical pumping of rubidium 87 can be found in 1 and the associated description. The electron spins of the second medium in the vapor cell arrangement are polarized by optical pumping.

If the sensing medium includes a first medium in addition to the second medium, use is made of the fact that a strong electron-nuclear spin interaction between the first medium, e.g. xenon, and the second medium, e.g. rubidium, causes the electron spin polarization to polarize the nuclear spins of the first medium leads. The bias field dictates a direction about which the polarized nuclear spins of the first medium precess. By applying the oscillating magnetic field (AC magnetic field), which has at least one component orthogonal to the direction of the bias field, the precession motion of the polarized nuclear spins around the direction of the bias field is synchronized, so that all polarized nuclear spins are in phase with each other at the Larmor frequency (if no external rotation rate applied to the NMR gyro) precess around the direction of the bias field. The frequency of the oscillating magnetic field preferably matches the Larmor frequency of the polarized nuclear spins. The magnetic field generating device, which is set up to provide the pre-magnetization field and the oscillating magnetic field at the location of the vapor cell arrangement, can comprise coils, for example, in particular two Helmholtz coils arranged orthogonally to one another.

The electron spins of the second medium act like an "in-situ magnetometer". The electron spins of the second medium are sensitive to the periodic magnetic field change caused by the in-phase nuclear spin precession. It is thus possible to transfer the in-phase nuclear spin precession to the electron spins of the second medium. The precession movement of the polarized nuclear spins can thus be converted into a readable electrical signal. For this purpose, the vapor cell arrangement can be illuminated, for example, with a linearly polarized readout laser beam. When passing through the vapor cell arrangement, the polarization of the readout laser beam is rotated periodically, which is caused by the precession movement of the polarized nuclear spins of the first medium (Faraday effect). The Faraday effect describes the rotation of the plane of polarization of a linearly polarized electromagnetic wave in a medium when there is a magnetic field parallel to the direction of propagation of the wave. The periodic rotation of the polarization of the read-out laser beam can be converted into an electrical signal by a detection arrangement, for example. The detection arrangement can comprise at least one polarizer and at least one detector element, with the polarizer being arranged in the beam path between the vapor cell arrangement and the detector element. A radiation sensor based, for example, on silicon (Si), germanium (Ge), germanium on silicon, indium gallium arsenide (InGaAs), etc. can be used as the detector element. Photodiodes or bolometers, for example, are also suitable as radiation sensors. Depending on a property of the electromagnetic radiation impinging on the radiation sensor, radiation sensors can output an electrical detection signal which is a measure of the radiation property. Radiation sensors can measure, for example, a radiation intensity or an energy flux density of the readout light beam transmitted by the vapor cell arrangement. Because of the polarizer, the detector element can detect the polarization rotation of the read-out laser beam, for example, as a periodically changing radiation intensity.

If the sensing medium only comprises the second medium, the electron spin precession movement of the second medium can be read out directly, analogously to the method described above. The precession movement of the electron spins, which is a measure of the rotation of the NMR gyroscope, can thus be converted into a readable electrical signal.

In one embodiment, the first optical arrangement comprises a first beam splitter and a second beam splitter, the first beam splitter being set up to split the light beam coming from the illumination source into the first pump light beam and a partial beam, the second beam splitter being in the beam path of the partial beam to the Splitting the sub-beam into the second pump light beam and the read-out light beam is arranged. One advantage is that one illumination source is sufficient, and miniaturization of the NMR gyroscope can consequently be made possible. Using a common illumination source for the first and second pump regions also has the advantage of common noise statistics.

In one embodiment, the first beam splitter and/or the second beam splitter are designed as polarizing beam splitters. Polarizing beam splitters are advantageously characterized in that Splitting ratio is determined by the polarization angle of the incoming light and precise splitting ratios can be set by means of polarizing beam splitters. Thus, in particular the intensity of the electromagnetic radiation for the first pump region and the second pump region can advantageously be adjusted. This can be used, for example, to correct production fluctuations. An example of this is a slight difference in the gas density of the vapor cells, which is corrected by the laser intensity in such a way that the polarization and thus the magnetization and thus also the signal of the two vapor cells are the same. In particular, the transmission of the polarizing beam splitter can be adjusted by arranging optical filters in the beam path.

In one embodiment, at least one optical filter for adjusting the light transmission of the first beam splitter is arranged in the beam path between the illumination source and the first beam splitter, and/or at least one optical filter for adjusting the light transmission of the second beam splitter is arranged in the beam path between the first beam splitter and the second beam splitter. Advantageously, the pump intensity for the two pump regions can thus be set in each case. In particular, retardation plates can be used as optical filters to adjust the intensities of the pump light beams and/or the read-out light beam.

Retarder plates are optical components that change the polarization and phase of electromagnetic waves (usually light) passing through. An example of a retardation plate is a λ/4 plate, which retards light polarized parallel to a component-specific axis by a quarter wavelength compared to light polarized perpendicular thereto. It can turn linearly polarized light into circularly polarized light and circularly polarized light back into linearly polarized light. Another example of a retardation plate is a λ/2 plate. This delays light that is polarized parallel to a component-specific axis by half a wavelength compared to light that is polarized perpendicularly to it. It can rotate the direction of polarization of linearly polarized light by a selectable angle. In the case of circularly polarized light, a λ/2 plate reverses the helicity, i. H. left polarized light becomes right polarized light and vice versa. The polarization changes occur because the light is broken down into two mutually perpendicular polarization directions, which pass through the retardation plate at different speeds, i.e. their phases are shifted in relation to one another. Retardation plates include, for example, birefringent media such as birefringent crystals.

The use of delay plates can consequently result in the pump regions being illuminated with mutually oppositely circularly polarized electromagnetic radiation, which makes it possible for the spins in the first pump region and in the second pump region to precess in opposite directions to one another. This leads to the aforementioned advantages with regard to calibration and measurement accuracy.

In one embodiment, the pump beams are oppositely circularly polarized and/or the readout light beam is linearly polarized, i. H. the first polarization and the second polarization are opposite circular polarizations and/or the third polarization is a linear polarization.

In one embodiment, the NMR gyroscope comprises a second optical arrangement in the optical path of the readout light beam. In particular, the second optical arrangement comprises at least one optical element for beam guidance and/or beam shaping. Optical elements for beam guidance and/or beam shaping can include, for example, mirrors, micromirrors, lenses, optical diaphragms, delay plates, etc. Alternatively or additionally, the at least one optical element can be set up to adjust the polarization of the light (for example polarizers).

In particular, the second optical arrangement comprises two mirrors, in particular micromirrors, the two mirrors being arranged in such a way that the readout light beam is guided through the vapor cell arrangement to the detection arrangement, and the second optical arrangement has an optical aperture for adjusting a beam cross section of the readout light beam includes. An advantage is that the illumination source and the detection arrangement can advantageously be arranged on a common side of the NMR gyroscope, and no separate illumination source is required for reading.

In one embodiment, the detection arrangement comprises a first detection unit for detecting the first pump light beam after passing through the first pump region, a second detection unit for detecting the second pump light beam after passing through the second pump region, and a main De tection unit for detecting the read-out light beam after passing through the vapor cell arrangement. One advantage is that a transmission intensity of the first pump light beam and of the second pump light beam can be detected in each case. The measurement results can be used for illuminating source stabilization (in particular laser stabilization) or for temperature stabilization, in particular for stabilizing the vapor cell temperature. In particular, the latter can be effected by a control circuit which includes the heating element or heating elements. In particular, this embodiment advantageously enables a distinction to be made between laser variations and temperature variations in the cell. Balanced detection enables the signal to be measured and the "offset" to be detected by calculating the difference and the sum of the signals. If this is not constant, it represents the fluctuations of the laser. Since this is the same laser as for the pump regions, the noise behavior of this laser is also known.

The transmission of the vapor cell depends on the absorption, and therefore on the particle density, and therefore on the temperature. If we detect this and know the noise behavior of the laser and thus correct it, we can determine the temperature of the vapor cells. This can be corrected independently of each other and thus also temperature drifts (due to temperature gradients).

In one embodiment, the main detection unit comprises a polarizing beam splitter and a first detector element for detecting a first portion of the light transmitted by the vapor cell assembly and a second detector element for detecting a second portion of the light transmitted by the vapor cell assembly. The main detection unit is designed as a so-called "balanced detector". One advantage is that the measurement accuracy can be increased in this way, because any existing signal offset is corrected by means of “balanced detection”; only the difference in the signals of the two detector elements is taken into account in the evaluation. In particular, the illumination source can be readjusted in such a way that this difference in the signals is constant.

In one embodiment, the NMR gyroscope includes a magnetic shield assembly, wherein the vapor cell assembly is located in an area shielded by the magnetic shield assembly. An advantage is that the vapor cell arrangement is thus shielded from surrounding magnetic fields, such as the earth's magnetic field, in order to increase the measurement accuracy and reliability of the NMR gyroscope.

In one embodiment, the illumination source and/or the first optical arrangement are arranged outside the shielded area. Alternatively or additionally, the detection arrangement is arranged at least partially outside the shielded area.

Alternatively or additionally, at least one optical element of the second optical arrangement is arranged outside of the shielded area.

An advantage of locating components outside of the magnetic shield assembly is that it enables miniaturization of the NMR gyroscope since the shielded area can be reduced and thus the magnetic shield assembly can be made more compact than if the shield assembly encloses all components. In particular, material for forming the magnetic shield, in particular mu-metal, can be saved, making the NMR gyroscope lighter, more compact and less expensive. A further advantage is that the vapor cell assembly can thus be shielded from fields emanating from the electronic components (such as fields from the illumination source) by the magnetic shielding arrangement, which further improves the reliability and performance of the NMR gyroscope. Alternatively, these influences can also be corrected, at least in part, electronically during the evaluation. In particular, if the components are not located outside the magnetic shielding arrangement, electronic correction is recommended to improve measurement accuracy and reliability.

In one embodiment, the vapor cell arrangement comprises a vapor cell, with a buffer gas being arranged in the vapor cell, which, by spatially restricting the electron-nuclear spin interaction in the sensing medium in the vapor cell, realizes the first pump region and the second pump region. An advantage is that only one vapor cell is required, allowing for a reduction in size and hence miniaturization of the NMR gyroscope without sacrificing sensitivity and reliability. Furthermore, the manufacturing cost can be reduced and the manufacture of the NMR gyroscope can be simplified.

Nitrogen (N) can be used as a buffer gas, for example. Alternatively or in addition, argon (Ar) can be used as a buffer gas.

According to one embodiment, the vapor cell arrangement comprises a first vapor cell and a second vapor cell, wherein the first vapor cell comprises the first pumping region and the second vapor cell comprises the second pumping region. Advantageously, vapor cells can be manufactured in a MEMS process in a very small pack size. The production in large quantities is therefore possible. As a result, the use of two vapor cells is advantageous in terms of miniaturization and cost reduction compared to the use of complex coils and/or shields. Because there are two identical elements (two steam cells), they can be manufactured in the same process and used in one process step.

Since both vapor cells are read out by a laser beam, the correction in this embodiment is advantageously carried out very quickly.

Since external interference, provided that it is the same for both cells, cancels out each other during detection (see above), it is advantageous to place the first vapor cell and the second vapor cell close together, in particular the distance between the vapor cells should be less than one centimeter (<1 cm). This ensures that external interference is as homogeneous as possible over the area of the vapor cells and thus has the same effect, or that the homogeneous and thus intrinsically corrected proportion is as large as possible.

According to one embodiment, the NMR gyroscope comprises a magnetic field generating device for providing a magnetic bias field and an oscillating magnetic field at the location of the vapor cell arrangement, wherein the magnetic bias field is set up to define a direction of the spin precession movement and the oscillating magnetic field is set up to synchronize the spin precession movement.

The illumination source can include, for example, a laser or a laser diode, in particular a surface emitter (VCSEL) for illumination. An irradiation direction of the light used for illumination has at least one component parallel or antiparallel to the magnetic field direction of the bias field, in particular the irradiation direction is parallel or antiparallel to the magnetic field direction of the bias field (M _z mode).

The spin precession of two states, which have magnetic quantum numbers Δm _f of the same magnitude but opposite signs, Larmor precesses in exactly opposite directions. Subject to the same bias field B ₀ , they also rotate at the same Larmor frequency |ω _larmor |=|γ B ₀ |, where γ denotes the gyromagnetic ratio. If they are also initialized by the same resonant alternating magnetic field, they precess in phase.

If there is no yaw rate at the NMR gyroscope, ie the system (the NMR gyroscope) is not rotated from the outside, the detection signal, which is detected by the detection arrangement, consequently disappears, since this is due to the nuclear spins precessing in phase in the first pump region and cancel the periodically changing magnetic field caused by the in-phase nuclear spins in the second pump region, which precess in the opposite direction to the nuclear spins in the first pump region. Furthermore, all disturbance terms ω _s also disappear if they affect the two pump regions to the same extent. This enables a highly precise calibration, which significantly reduces the drift (signal when there is no yaw rate). This is also an advantage in signal processing. Furthermore, a correction of manufacturing deviations by calibration is also advantageously possible.

If there is now an external yaw rate ω _rot , this is the same for both cells and does not cancel out, but adds up. In this way, a signal is obtained that is “free” of interference terms that have the same effect on both pump ranges. $${\mathrm{\omega }}_{\text{mess}}=\left(-\left|{\mathrm{\omega }}_{\text{larmor}}+{\mathrm{\omega }}_{\text{S}}\right|+{\mathrm{\omega }}_{\text{Red}}\right)+\left(\left|{\mathrm{\omega }}_{\text{larmor}}+{\mathrm{\omega }}_{\text{s}}\right|+{\mathrm{\omega }}_{\text{Red}}\right)=2{\mathrm{\omega }}_{\text{Red}}$$

Here the expressions in round brackets stand for the first and the second pump region. It is important that the signal disappears without an external rate of turn / rotation. This offers the previously mentioned advantages.

• • Das Vormagnetisierungsfeld am Ort des ersten Pumpbereichs und das Vormagnetisierungsfeld am Ort des zweiten Pumpbereichs sind antiparallel zueinander oder weisen zumindest eine Komponente auf, die antiparallel zu einer Komponente des jeweils anderen Pumpbereichs ist; oder
• • Optisches Pumpen mit zirkular polarisierten Lichtstrahlen, welche in ihrer Polarisation voneinander abweichen (beispielsweise optisches Pumpen des ersten Pumpbereichs mit σ⁺-polarisiertem Licht und des zweiten Pumpbereichs mit σ^--polarisiertem Licht).

Possibilities for generating the counter-rotating precession movements of the nuclear spins of the sensing medium in the vapor cells are, for example:

• • The magnetic bias field at the location of the first pump region and the magnetic bias field at the location of the second pump region are antiparallel to one another or have at least one component which is antiparallel to a component of the other pump region; or
• • Optical pumping with circularly polarized light beams which differ from one another in their polarization (for example optical pumping of the first pumping region with σ ⁺ -polarized light and the second pumping region with σ ^- -polarized light).

Each of these possibilities is suitable for generating opposing precession movements of the nuclear spins in the vapor cells. If both options are used simultaneously, however, a precession movement results again in the same direction, since the original direction of the precession movement is restored as a result of the double reversal of the precession movement.

• • Aufteilen des von der Beleuchtungsquelle kommenden Lichtstrahls in einen ersten Pump-Lichtstrahl, einen zweiten Pump-Lichtstrahl und einen Auslese-Lichtstrahl,
• • Erzeugen einer synchronisierten Spin-Präzessionsbewegung im Sensiermedium des ersten Pumpbereichs mit dem ersten Umlaufsinn mittels des ersten Pump-Lichtstrahls und Erzeugen einer synchronisierten Spin-Präzessionsbewegung im Sensiermedium des zweiten Pumpbereichs mit dem zweiten Umlaufsinn mittels des zweiten Pump-Lichtstrahls, wobei der erste Umlaufsinn und der zweite Umlaufsinn gegenläufig zueinander sind,
• • Optisches Auslesen der Spin-Präzessionsbewegungen im ersten Pumpbereich und im zweiten Pumpbereich, wobei der Auslese-Lichtstrahl den ersten Pumpbereich und den zweiten Pumpbereich durchläuft hat den Vorteil, dass Auswirkungen äußerer Störeinflüsse auf das Messergebnis des NMR-Gyroskops auf einfache Weise ohne aufwendige und kostenintensive Modifikationen reduziert werden können, um die Sensitivität und Zuverlässigkeit des NMR-Gyroskops zu erhöhen und Signaldrifts zu reduzieren.

A method of operating the NMR gyroscope, comprising the steps of:

• • Splitting the light beam coming from the illumination source into a first pumping light beam, a second pumping light beam and a readout light beam,
• • Generating a synchronized spin precession movement in the sensing medium of the first pump region with the first direction of rotation by means of the first pump light beam and generating a synchronized spin precession movement in the sensing medium of the second pump region with the second direction of rotation by means of the second pump light beam, the first sense of rotation and the second direction of rotation are opposite to each other,
• • Optical reading of the spin precession movements in the first pumping area and in the second pumping area, with the readout light beam passing through the first pumping area and the second pumping area, has the advantage that the effects of external interference on the measurement result of the NMR gyroscope can be easily removed without complex and costly Modifications can be reduced to increase the sensitivity and reliability of the NMR gyroscope and to reduce signal drift.

During optical reading, the vapor cell arrangement can be irradiated with linearly polarized light and the light transmitted by the vapor cell arrangement can be detected.

Alternatively or additionally, the sum of the spin precession movements of the polarized nuclear spins in the first pump region and in the second pump region can be detected during optical readout. In particular, the sum of the spin precession movements is recorded, whereby if there is no external rotation rate applied to the NMR gyroscope, the detection signal disappears, since the nuclear spins precessing in phase in the first pump region and the nuclear spins precessing in phase in the second pump region, which precess in the opposite direction to the nuclear spins in the first pump region, cancel out the periodically changing magnetic field. Furthermore, all disturbance terms ω _s also disappear if they affect the two pump regions to the same extent.

character list

Embodiments of the invention are shown in the drawings and are explained in more detail in the following description. The same reference symbols in the figures denote the same or equivalent elements.

• 1 eine Skizze des Energieschemas eines zweiten Mediums, hier Rubidium 87,
• 2 zeigt eine Skizze zur Illustration der Präzessionsbewegungen der polarisierten Elektronenspins im ersten Pumpbereich und im zweiten Pumpbereich,
• 3 zeigt einen beispielhaften Aufbau eines NMR-Gyroskops,
• 4 zeigt einen Querschnitt eines Ausschnitts des NMR-Gyroskops gemäß einem ersten Ausführungsbeispiel,
• 5 zeigt einen Querschnitt eines Ausschnitts des NMR-Gyroskops gemäß einem zweiten Ausführungsbeispiel,
• 6 zeigt einen Querschnitt eines Ausschnitts des NMR-Gyroskops gemäß einem dritten Ausführungsbeispiel,
• 7A-7D zeigen Querschnitte der magnetischen Abschirmung und der Magnetfelderzeugungseinrichtung des NMR-Gyroskops, und
• 8 zeigt einen Querschnitt eines Ausschnitts des NMR-Gyroskops gemäß einem vierten Ausführungsbeispiel,

Show it

• 1 a sketch of the energy scheme of a second medium, here Rubidium 87,
• 2 shows a sketch to illustrate the precession movements of the polarized electron spins in the first pump region and in the second pump region,
• 3 shows an exemplary structure of an NMR gyroscope,
• 4 shows a cross section of a section of the NMR gyroscope according to a first embodiment,
• 5 shows a cross section of a section of the NMR gyroscope according to a second embodiment,
• 6 shows a cross section of a section of the NMR gyroscope according to a third embodiment,
• 7A-7D Fig. 12 show cross-sections of the magnetic shield and magnetic field generating means of the NMR gyroscope, and Figs
• 8th shows a cross section of a detail of the NMR gyroscope according to a fourth embodiment,

Embodiments of the invention

1 shows the term scheme 100 of rubidium 87, which can be used, for example, as a medium for optical pumping, in particular as a second medium in an NMR gyroscope 200, on the basis of which the optical pumping is explained below. An exemplary structure of the NMR gyroscope 200 is shown in 3 shown. The energy scheme 100 of rubidium 87 shows a fine structure splitting, which results from the spin-orbit coupling between electron spin (S=±1/2) and orbital angular momentum. The first excited state exhibits a fine structure splitting into a first substate 117 (5 ² P _1/2 ) and a second substate 118 (5 ² P _3/2 ). For an excitation of the rubidium 87 atom from its ground state 116 (5 ² S _1/2 ) into the first sub-state 117 (5 ² P _1/2 ), irradiation of light 120 with a wavelength of 794.98 nanometers (nm) is required. For excitation of the rubidium 87 atom from its ground state 116 (5 ² S _1/2 ) into the second sub-state 118, irradiation with light 119 with a wavelength of 780.24 nm is required. Furthermore, there is a hyperfine structure splitting, which results from the nuclear angular momentum. The hyperfine structure splitting is caused by the coupling of the total angular momentum of the electron shell with the angular momentum of the nucleus. The ground state 116 has a hyperfine structure splitting into an F=1 state (110) and an F=2 state (111), the distance 115 between the two energy levels 110, 111 being 6.8 GHz (gigahertz). The first sub-state 117 splits into a first energy level 112 with F=1 and a second energy level 113 with F=2, a distance 114 between the two energy levels 112, 113 being 0.8 GHz.

If the rubidium 87 atom is in an external magnetic field, e.g 1 has sublevels. For example, the F=1 energy level 110 of the ground state 116 has three Zeemann levels, the lowest Zeemann level 109 with the magnetic quantum number m _f = -1, the middle Zeemann level with the magnetic quantum number m _f = 0 and the upper Zeemann level 108 are denoted by the magnetic quantum number m _f = +1. The F=2 energy level 111 of the ground state 116 has five Zeemann levels, the lowest Zeemann level 107 being denoted by the magnetic quantum number m _f = -2 and the highest Zeemann level 105 being denoted by m _f = +2. The distance 106 between two adjacent Zeemann levels is ħω _Larmor , where ω _Larmor corresponds to the frequency of the Larmor precession of the electron spins in the magnetic field caused by the applied magnetic field (in the case of the NMR gyroscope: in the bias field 300).

Analogously, the F=1 of the first excited state 112 has three Zeemann levels, the lowest Zeemann level 104 with the magnetic quantum number m _f = -1, the middle Zeemann level with the magnetic quantum number m _f = 0 and the upper Zeemann level 103 are denoted by the magnetic quantum number m _f = +1. The F=2 energy level 113 of the first excited state 112 has five Zeemann levels, the lowest Zeemann level 102 being denoted by the quantum number _mf =−2 and the uppermost Zeemann level 101 being denoted by _mf =+2.

For optical transitions, the selection rule Δ m _f =±1.0 applies, where Δ m _f describes the difference in the magnetic quantum numbers of the initial and final states. The transitions with Δ m _f =±1 can be excited by irradiation with circularly polarized σ ^± polarized light. This polarizes the rubidium. An atom that is in the Zeemann level 105 of the ground state 116 with m _f =2 (m _f =-2) cannot absorb a σ ⁺ photon (σ ^- photon) because in the first excited state 117 there is no Zeemann -level with m _f = 3 (m _f = -3), which would be necessary for the absorption due to conservation of angular momentum. This means that after a certain pumping time all atoms are in the top (bottom) Zeemann level 105 of the ground state 116 with m _f =2 (m _f = -2). This corresponds to an alignment of the total spin in the direction of the external magnetic field (in the case of the NMR gyroscope: the bias field). In other words, by irradiating σ ⁺ light 120 with a wavelength of 794.98 nm, a large part of Rubi dium can be pumped in an ensemble into the Zeemann levels of the F=2 state 113 since, by a strong pump laser, the population can be quickly pumped out of all states except the m _f =2 state, since there is no state with Δ m _f =1 is within range. The same for m _f = -2 for σ ^- -polarized light and Δ m _f = -1.

2 shows a sketch to illustrate the precession movements of the polarized electron spins 3021, 3022 in the first pump region 2011 and in the second pump region 2012. The following statements regarding the precession movement apply analogously to the polarized nuclear spins, provided that the sensing medium comprises a first medium in addition to the second medium, the Precession motion of nuclear spins is only indirectly caused by optical pumping. This is because the precession movement of the nuclear spins is transferred from the optically pumped electron spins of the second medium, such as Rubidium 87 in this example, to the nuclear spins of the first medium of the NMR gyroscope by means of a strong electron-nuclear spin interaction. In 2 a magnetic field direction of a bias field 300 and a magnetic field direction of an oscillating magnetic field 301 (the oscillation being indicated by a double arrow) are shown, which are orthogonal to one another in this exemplary embodiment. A first arrow 3021 represents a polarized electron spin, for example from rubidium, with the magnetic quantum number m _f =2, a second arrow 3022 represents a polarized electron spin, for example from rubidium, with the magnetic quantum number m _f =−2. A precession motion 304 of the electron spin 3021 around the bias field 200 with the magnetic quantum number _mf =2 is opposite to a precession motion 303 of the electron spin 3022 with the magnetic quantum number _mf =−2. The polarized electron spins 3021, 3022 with a magnetic quantum number of opposite sign can be generated by optical pumping with reverse circularly polarized light, ie σ ⁺ -polarized light for m _f =2 and σ ^- polarized light for m _f =−2. The oscillating magnetic field 301 synchronizes the precession movements so that they are in phase with one another but have an opposite sense of rotation, as is indicated in the sketch by the two circles 303, 304 with the arrows pointing in the opposite direction. If the precession movements are read out optically with a laser using the magneto-optical Faraday effect, the direction that is normal to the image plane disappears due to the opposite, synchronized precession movements.

3 12 shows an exemplary structure of the NMR gyroscope 200. The NMR gyroscope 200 comprises a vapor cell arrangement 201 which is arranged on a heating element 209. FIG. A sensing medium 204 is arranged in the vapor cell arrangement 201 . In this exemplary structure, a buffer gas 203 is further arranged in the vapor cell assembly. In particular, the sensing medium can comprise a second medium, in particular an alkali metal, and a first medium, in particular an inert gas, with the heating element 209 enabling the alkali metal to evaporate. The vapor cell arrangement 201 is surrounded by a magnetic field generating device 206, which provides a static magnetic field, which serves as a bias field 300, and an oscillating magnetic field 301, which has at least one component orthogonal to the bias field 300, at the location of the vapor cell arrangement 201. in the in 3 In the NMR gyroscope 200 shown, the magnetic field generating device 206 comprises a two-axis pair of Helmholtz coils. A magnetic shield 207 is positioned around the vapor cell assembly 201 to shield the vapor cell assembly 201 from ambient magnetic fields, such as the earth's magnetic field. For this as well as for all other exemplary embodiments, the geometry of the magnetic shielding 207, the number of shielding layers and the positions provided for the coils 206 can be varied as desired. A higher number of shielding layers makes the NMR gyroscope 200 more stable and sensitive, but also larger and more expensive. The NMR gyroscope 200 can thus be precisely tailored to the application. The same applies to the magnetic field generating device 206: complex, multi-layered geometries of the coils increase the sensitivity and reduce the drift through increased homogeneity and stability of the generated magnetic fields. However, such coils also increase the costs and from a certain level more space is also required. Furthermore, the NMR gyroscope 200 comprises a pump illumination source 2051 for illuminating the sensing medium 204 in the vapor cell assembly 201. The illumination source 2052 emits electromagnetic radiation 2001 for providing the pump light beams for the vapor cell assembly 201. The pump illumination source 2051 in this example, in which the sensing medium 204 comprises a first medium and a second medium, is set up to polarize electron spins 3021, 3022 of the second medium by optical pumping, with this electron spin polarization being caused by a strong electron-nuclear spin interaction between the second medium and the first medium, the nuclear spins of the first medium are polarizable. The bias field 300 defines a direction of a precession movement of the polarizable nuclear spins of the first medium and the oscillating magnetic field 301 enables the precession movements of the polarizable nuclear spins of the first medium to be synchronized.

The NMR gyroscope 200 includes a detection arrangement 208 which is set up to detect a rotation of the NMR gyroscope 200 about a direction of the bias field 300 from a change in the precession movement of the polarizable nuclear spins. A readout illumination source 2050 emits electromagnetic radiation 2000, in particular linearly polarized electromagnetic radiation.

Here and analogously also in the following exemplary embodiments 4 until 6 and 8th the readout light beam 2000 is in each case transmitted by the vapor cell arrangement 201, with the electromagnetic radiation 2002 transmitted by the vapor cell arrangement 201 utilizing the magneto-optical Faraday effect measuring the precession movements of the polarized nuclear spins of the first medium in the vapor cell arrangement 201 as a measurement signal 2003, for example in the form of a electrical signal, which is a measure of the periodically changing radiation intensity, can be detected. The measurement signal 2003 is transmitted to a signal processing device 2085 which determines a detection signal 2086 (for example a yaw rate or a rotation frequency) of the NMR gyroscope 200 from the measurement signal 2003 . Furthermore, the signal processing device 2085 can be set up to control the fields of the NMR gyroscope 200 . For example, the signal processing device 2085 can be used to calibrate the NMR gyroscope by adapting the fields, in particular the magnetic fields 300, 301 or the temperature, by means of the heating element 209 or a heating laser (as in 6 ), takes place so that, for example, if the NMR gyroscope 200 is not rotated, the measurement signal 2003 disappears (see above). Furthermore, the signal processing device 2085 can be set up for an electronic calibration or correction of the measurement signal 2003 . The signal processing device 2085 can be embodied as part of the NMR gyroscope 200 or can be arranged outside the NMR gyroscope, with the NMR gyroscope 200 having communication interfaces in this case, which in particular transmit the measurement signals 2003 of the NMR gyroscope 200 to the signal processing device 2085 enabled.

4 12 shows a cross section of the NMR gyroscope 200 according to one embodiment. The NMR gyroscope 200 comprises an electronics arrangement 213 which provides control and/or regulation electronics and/or a power supply for the electronic components, such as the illumination source 205, the detection arrangement 208, the heating elements 209, etc.

Furthermore, the NMR gyroscope 200 includes a magnetic shield 207, the components located in an area shielded by the magnetic shield 207 (ie the area enclosed by the magnetic shield 207) being protected from external magnetic fields, such as the earth's magnetic field, and the fields of the electronic components, shielded, d. H. unaffected by these. In this exemplary embodiment, the magnetic shielding 207 comprises three layers which enclose the shielded area. The layers are each spaced apart by spacers 202 . The spacers 202 can be made of a ceramic or other insulating material, for example. A gas such as air may be introduced between the layers or a vacuum may be established between the layers.

The electronics arrangement 213, the illumination source 205 and a main detection unit 2080 are arranged on a first side of the magnetic shielding 207 in this exemplary embodiment. Here, in particular, the illumination source 205 and the main detection unit 2080 are arranged outside the shielded area. The magnetic shielding 207 is open to the illumination source 205 and the main detection unit 2080, so that the electromagnetic radiation 2001 emitted by the illumination source 205 can penetrate into the shielded area and so that the electromagnetic radiation 2002 transmitted by the vapor cell arrangement 201 arranged in the shielded area can exit the shielded area to be detected by the main detection unit 2080 . The openings can optionally be closed with windows, through which the rays 2001, 2002 can enter or exit, so that the gas or the vacuum can be maintained between the shielding layers.

A magnetic field generating device 206 is arranged in the shielded area within the magnetic shielding 207 . In this exemplary embodiment, the magnetic field generating device 206 is arranged around the vapor cell arrangement 201 and is set up to generate a static magnetic field, which serves as a bias field 300, and an oscillating magnetic field 301, which has at least one component orthogonal to the bias field 300, at the location of the vapor cell arrangement 201 to provide. in the in 4 In the cross-section shown, only the Z-coil for generating the static magnetic field can be seen above and below the vapor cell assembly. The vertical to it The coil plane of the magnetic field generating device 206 cannot be seen in the cross section. In particular, the magnetic field generating device 206 can include complex coils in defined planes, which - such as in "bfieldtoos - a software package for magnetic field modeling", R. Zetter, J. Livanainen, A. Mkinen, L. Parkkonen, Conference Proceedings WOPM, 2019 , Mainz described - can be modeled.

The vapor cell arrangement 201 comprises a first vapor cell 2011a, which comprises the first pumping region 2011, and a second vapor cell 2012a, which comprises the second pumping region 2012. The sensing medium 204 is arranged within the vapor cells 2011a, 2012a in each case. In particular, the sensing medium 204 can comprise a second medium, in particular an alkali metal. In addition to the second medium, the sensing medium preferably also includes a first medium, in particular an inert gas. Heating elements 209 are arranged on the vapor cells 2011a, 2012a, with the heating element 209 enabling the sensing medium 204 to be heated, in particular evaporating the alkali metal Medium firmly and by means of the oscillating magnetic field 301 a synchronization of the precession movements of the polarizable nuclear spins of the first medium and the electron spins of the second medium is made possible. The bias field 300 in the first pump region 2011 is in 4 for example, parallel to the bias field 300 in the second pump region 2012 and points out of the plane of the drawing. In particular, the first pump region 2011 and the second pump region 2012 can also be located in the same pre-magnetization field 300 that is preferably homogeneous in the region of the vapor cell arrangement 201 .

• • einen ersten Pump-Lichtstrahl 20110, aufweisend eine erste Polarisation, zum Anregen der Spin-Präzessionsbewegung im Sensiermedium 204 des ersten Pumpbereichs 2011 mit einem ersten Umlaufsinn,
• • einen zweiten Pump-Lichtstrahl 20120, aufweisend eine zweite Polarisation, zum Anregen der Spin-Präzessionsbewegung im Sensiermedium 204 des zweiten Pumpbereichs 2012 mit einem zweiten Umlaufsinn, wobei der erste Umlaufsinn und der zweite Umlaufsinn gegenläufig zueinander sind, und
• • einen Auslese-Lichtstrahl 2000, aufweisend eine dritte Polarisation, zum Auslesen der Spin-Präzessionsbewegungen des ersten Pumpbereichs 2011 und des zweiten Pumpbereichs 2012,

aufzuteilen.A first optical arrangement 211 is arranged in the shielded area, which is set up to focus the light beam 2001 emitted by the illumination source 205 in

• • a first pump light beam 20110, having a first polarization, for exciting the spin precession motion in the sensing medium 204 of the first pump region 2011 with a first sense of rotation,
• • a second pump light beam 20120, having a second polarization, for exciting the spin precession motion in the sensing medium 204 of the second pump region 2012 with a second sense of rotation, the first sense of rotation and the second sense of rotation being opposite to one another, and
• • a read-out light beam 2000, having a third polarization, for reading out the spin precession movements of the first pump region 2011 and of the second pump region 2012,

split up.

In this exemplary embodiment, the first optical arrangement 211 comprises five optical filters and a first beam splitter 2101 and a second beam splitter 2102. The first beam splitter 2101 and the second beam splitter 2102 can be designed as polarizing beam splitters. The electromagnetic radiation 2001 emitted by the illumination source 205, which is unpolarized in this embodiment, enters the shielded area through an opening in the magnetic shield 207 and passes through a first optical filter 2111 and a second optical filter 2112 before arriving at the first beam splitter 2101 occurs. A light transmission of the first beam splitter 2101 can be defined by means of the optical filters. In particular, the optical filters 2111, 2112 can be designed as delay plates and can thus be used to adjust the intensities of the first pump light beam 20110 and the partial beam 2004. The first beam splitter 2101 is set up to split the light beam 2001 coming from the illumination source 205 into the first pump light beam 20110 and the partial beam 2004 after passing through the optical filters 2111, 2112.

The first pump light beam 20110 passes through a third optical filter 2113, here a circular polarizer, as a result of which the first pump light beam 20110 is given a first polarization. The circularly polarized first pump light beam illuminates the first pump region 2011. The sensing medium 204, in particular the second medium, is excited by optical pumping in order to generate a spin precession movement with a first direction of rotation. After passing through the first vapor cell 2011a, the first pump light beam 20110 is detected by a first detection unit 2081. In this exemplary embodiment, the first detection unit 2081 comprises a detector element 2083. A radiation sensor can be used as the detector element 2083, for example. The detector element can detect the radiation intensity or an energy flux density of the first pump light beam 20110 after passing through the first vapor cell 2011a.

The partial beam 2004 passes through a fourth optical filter 2114, preferably a retardation plate, in order to adjust the intensities of the second pump light beam 20120 and the readout light beam 2000. The partial beam 2004 then strikes the second beam splitter, which splits the partial beam 2004 into the second pump light beam 20120 and the read-out light beam 2000 . The second pump light beam 20120 passes through a fifth optical filter 2113, here a circular polarizer, as a result of which the second pump light beam 20120 is given a second polarization. The circularly polarized second pump light beam 20120 illuminates the second pump region 2012. A possible combination of optical filters 2111, 2112, 2113, 2114, 2115 according to an embodiment is: the first optical filter 2111 is a linear polarizer, the second optical filter 2112 is a λ /2 plate, the third optical filter 2113 and the fifth optical filter 2115 are each designed as a λ/4 plate and the fourth optical filter 2114 is designed as a λ/2 plate. In this case, the sensing medium 204, in particular the second medium, is excited by optical pumping in order to generate a spin precession movement with a second direction of rotation, the second direction of rotation and the first direction of rotation being opposite to one another. After passing through the second vapor cell 2012a, the second pump light beam 20120 is detected by a second detection unit 2082. In this exemplary embodiment, the second detection unit 2082 comprises a detector element 2083. A radiation sensor can be used as the detector element 2083, for example. The detector element can detect the radiation intensity or an energy flux density of the second pump light beam 20120 after passing through the second vapor cell 2012a. Alternatively, the first detection unit 2081 and/or the second detection unit 2082 can be arranged outside the magnetic shielding, ie outside the shielded area in which the vapor cell arrangement 201 and the magnetic field generating device 206 are arranged (not shown). This also applies to the other exemplary embodiments. As a result, material, in particular mu-metal, which can be used for magnetic shielding, can advantageously be saved, making the NMR gyroscope 200 lighter and less expensive.

If the magnetic field direction of the magnetic bias field 300 at the location of the first vapor cell 2011a is parallel to the magnetic field direction of the magnetic bias field 300 at the location of the second vapor cell 2012a, the circular polarizers 2113, 2115 are selected in such a way that the first polarization of the first pump light beam 20110 and the second Polarization of the second pump light beam 20120 are circularly polarized in opposite directions, ie, for example, the first pump light beam 20110 is σ ⁺ -polarized and the second pump light beam 20120 σ ^- is polarized. As a result, the spins in the first pump region 2011 and in the second pump region 2012 precess with mutually opposite directions of rotation.

If the magnetic field direction of the magnetic bias field 300 at the location of the first vapor cell 2011a is antiparallel to the magnetic field direction of the magnetic bias field 300 at the location of the second vapor cell 2012a, the circular polarizers 2113, 2115 are selected in such a way that the first polarization of the first pump light beam 20110 and the second Polarization of the second pump light beam 20120 are circularly polarized in the same way, ie that, for example, the first pump light beam 20110 is σ ⁺ polarized and the second pump light beam 20120 is also σ ⁺ -polarized. As a result, the spins in the first pump region 2011 and in the second pump region 2012 precess with mutually opposite directions of rotation.

The NMR gyroscope 200 includes a second optical arrangement 212, which includes at least one optical element for beam guidance and/or beam shaping, in the beam path of the readout light beam 2000. In this exemplary embodiment, the second optical arrangement 212 includes a first mirror 2121 and a second Mirror 2122, the two mirrors 2121, 2122 being arranged in such a way that the read-out light beam 2000 is guided through the vapor cell arrangement 201 to the main detection unit 2080. The first mirror 2121 reflects the readout light beam 2000, the second mirror 2122 being arranged relative to the first mirror 2122 such that the readout light beam 2000 reflected by the first mirror 2121 is reflected by the second mirror in the direction of the vapor cell arrangement 201. An optical diaphragm 2123 for adjusting a beam cross-section of the read-out light beam 2000 is arranged in the beam path of the read-out light beam 2000 between the second mirror 2122 and the second vapor cell 2012a. The optical aperture 2123 is part of the second optical arrangement 212. After passing through the optical aperture 2123, the read-out light beam 2000 first passes through the second vapor cell 2012a and then through the first vapor cell 2011a. The readout light beam 2002 transmitted by the vapor cell arrangement 201 enters the main detection unit 2080 from the shielded area through an opening in the magnetic shielding 207 . In 4 a so-called balanced detector for offset correction is used as the main detection unit 2080, which has a polarizing beam splitter 2103 and a first detector element 2083 for detecting a first portion of the light 2002 transmitted by the vapor cell arrangement 201 and a second detector element 2083 for detecting a second portion of the light 2002 transmitted by the vapor cell assembly 201. Alternatively, instead of a balanced detector, a single detector element 2083 with an upstream polarizer can be used Main detection unit 2080 can be used (not shown). The signals (precession frequency) of the vapor cells 2011a, 2012a are usually detected via a magneto-optical rotation of the laser polarization (Faraday effect), which is proportional to the magnetization of the nuclear spins of the first medium (which oscillates at the prevailing frequencies) in the laser direction. The Larmor precession resulting from the statically applied bias field 300, as well as the change in precession caused by any interference that is uniform for both vapor cells 2011a, 2012a, thus results in a rotation of the polarization by a certain angle in the first vapor cell 2011a. In the second vapor cell 2012a, the polarization is then rotated in the opposite direction. The measurement signal 2003, which results from the uniform interference, is canceled out and disappears. If a rotation rate is present, this is the same for both vapor cells 2011a, 2012b and a rotation proportional to twice the rotation rate is measured. If there is a drift, the signals from the vapor cells will not be identical if the NMR gyroscope 200 is not rotated (if there is no temperature gradient, you will see the same difference in the intensities that are transmitted). drift-free (or to the same intensity) using the optical filters 2112 and 2114. (One of the optical filters would be sufficient for this, but you need both if the ratio between the pump and readout light beam is also to be kept at the selected value .)

The read-out light beam 200 has a third polarization, in particular a linear polarization. The light beams 2001, 2000, 20110, 20120, 2002 run in recesses which are formed in a carrier structure 214. The recesses can be filled with a gas, such as air, or there is a vacuum in the recesses. The support structure 214, which is a main body of the NMR gyroscope 200, is arranged inside the magnetic shield 207. FIG. In particular, the base body carries the vapor cell arrangement 201 and the magnetic field generating device 206. In this exemplary embodiment, the carrier structure 214 also carries the first optical arrangement 211 and the second optical arrangement 212 as well as the first detection unit 2081 and the second detection unit 2082.

in the in 5 The embodiment shown was different from that in 4 In the exemplary embodiment shown, the first optical arrangement 211 and part of the second optical arrangement 212 are arranged outside the area shielded by the magnetic shielding 207 . The main detection unit 2080 is, as in the in 4 illustrated embodiment arranged on a first side of the magnetic shielding 207, on which the electronics assembly 213 is arranged. The first optical assembly 211 is disposed on a portion of the support structure 214 that is outside the shielded area on a second side of the magnetic shield 207, the second side of the magnetic shield 207 being adjacent to the first side. The magnetic shielding 207 has passage openings from the shielded area to the first beam splitter 2101 and to the second beam splitter 2102, which allow the first pumping light beam 20110 and the second pumping light beam 20120 to enter the shielded area for illuminating the first pumping area 2011 and the allow second pumping area. The passage openings are closed by the third optical filter 2113 and the fifth optical filter 2115 . These are arranged in or on the shielding layer of the magnetic shielding 207 adjoining the part of the carrier structure 214 lying on the outside, which carries the first optical arrangement 211 . In particular, this prevents the gas from escaping from the cutouts and between the shielding layers, or it is made possible to maintain the vacuum in the cutouts and between the shielding layers.

The first mirror 2121 of the second optical arrangement 2122 is also arranged on the outer part of the support structure 214 . A passage opening in the magnetic shielding 207, through which the reflected readout light beam 2000 can enter the shielded area through the magnetic shielding 207, is closed by a window 215 that is transparent to the readout light beam 2000. This window 215 is arranged in or on the shielding layer of the magnetic shielding 207 adjoining the part of the carrier structure 214 lying on the outside. The second mirror 2122 of the second optical arrangement 212 and the optical diaphragm 2123 are as in FIG 4 located within the magnetic shield 207 in the shielded area.

In a variant not shown here, the second mirror 2122 of the second optical arrangement 212 and/or the optical diaphragm 2123 can also be arranged outside the shielded area. For this purpose, for example, a passage opening closed by a window can be formed on a third side of the magnetic shielding 207, through which the readout light beam 2000 reflected by the second mirror 2122 in the direction of the vapor cell arrangement 201 can enter the shielded area. In this case, the third side is adjacent to the second side of the magnetic shielding 207 .

In the event that the magnetic shield 207 does not have corners delimiting the first, second and third sides from one another, the sides are to be understood as contiguous surface sections of any shape.

In 6 the steam cells 2011a, 2012b are equipped with heating elements 209 instead of as shown in 4 and 5 be used, heated with heating lasers 2090. There is a heating laser 2090 on the first side of the magnetic shield 207 for heating the first vapor cell 2011a and a heating laser 2090 on the third side, which is opposite the first side, for heating the second vapor cell 2012a. The heating lasers 2090 are set up to provide heating laser beams 2091 at the location of the vapor cells 2011a, 2012a. In 6 the heating lasers 2090 are arranged outside the shielded area, with the heating laser beams 2091 being able to enter the shielded area through passage openings in the magnetic shielding 207 in each case.

Alternatively, the heating lasers 2090 can also be arranged within the shielded area.

The arrangement of the heating laser 2090 is not limited to that in 6 geometry shown. In particular, in an exemplary embodiment not shown here, a single heating laser can be used to heat both steam cells 2011a, 2012a, with the heating laser beam 2091 hitting the second steam cell 2012a, for example after passing through the first steam cell 2011a, and thus both steam cells 2011a, 2012a being heated with the same heating laser beam 2091 will. In particular, optical elements for beam guidance, such as mirrors, lenses, micromirrors, etc., can be used for this purpose. Alternatively, the heating laser beam 2091 can be divided into two partial beams, for example by a beam splitter, with the heating laser partial beams each heating one of the vapor cells 2011a, 2012a.

The geometry of the magnetic shielding 207, the number of shielding layers and the positions provided for coils can be varied as desired in all the exemplary embodiments. Improving magnetic shielding 207, for example by increasing the number of shielding layers, makes NMR gyroscope 200 more stable and sensitive, but also larger and more expensive. The magnetic field generating device 206 includes coils, with complex, multi-layered coil geometries increasing the sensitivity and reducing the drift due to increased homogeneity and stability of the magnetic fields generated. The NMR gyroscope 200 can be tailored precisely to the application through the choice of the magnetic shielding 207 and/or the magnetic field generating device 206 .

7A-7D show exemplary cross sections of the magnetic shielding 207 and the magnetic field generating device 206 of the NMR gyroscope 200. The magnetic shielding is made of mu-metal in particular. The coils of the magnetic field generating device 206 can lie on different surfaces. To improve the field homogeneity, any additional planes containing coil layers can also be inserted. Alternatively, Helmholtz coils or those with correction coils can also be used. The second coil 217 in this case corresponds to the Z-coil for generating the static magnetic field (pre-magnetization field), which is also shown in FIGS 4 , 5 , 6 and 8th is shown in cross section. The first coil 216 is the coil plane that is vertical thereto.

In 7A For example, the magnetic shield 207 comprises two shield layers, the shield layers of the magnetic shield 207 each having a circular cross-section with different radii. In particular, the shielding layers can be in the form of hollow cylinders, so that the inner hollow cylinder is encased by the outer hollow cylinder. The carrier structure 214 is arranged inside the hollow cylinder with the smallest radius, on which the magnetic field generating device 206, here in the form of a first coil 216 and a second coil 216, is arranged. The top and bottom surfaces of the hollow cylinders can be closed by plates.

In 7B was compared to the in 7A shown arrangement added another shielding layer, which from the two shielding layers 7A encased.

In 7C the magnetic shielding 207 comprises two shielding layers, the shielding layers of the magnetic shielding 207 each having a rectangular, in particular square, cross section. In particular, the shielding layers may be in the form of hollow cuboids or hollow cubes nested within one another. The outer shielding layer encloses the inner shielding layer, with the inner shielding layer enclosing the support structure 214 on which the Magnetic field generating device 206, here in the form of a first coil 216 and a second coil 216, is arranged.

In 7D was compared to the in 7C shown arrangement added another shielding layer, which from the two shielding layers 7C encased.

The shielding layers can - as for example in the 4 , 5 , 6 and 8th shown - spaced apart.

In 8th the vapor cell arrangement comprises only one vapor cell 2013, with a buffer gas 203 also being arranged in the vapor cell 2013 in addition to the sensing medium 204, which comprises, for example, the first medium and the second medium first pump region 2011 and the second pump region 2012 are realized. Two heating elements 209 are arranged on the steam cell 2013 here for heating the steam cell 2013 . Heating with a 2090 heating laser is of course also possible.

Analogous to 8th can in 4 , 5 and 6 instead of two vapor cells 2011a, 2012a, only one vapor cell 2013, which is filled with the sensing medium 204 and the buffer gas for the spatial limitation of the electron-nuclear spin interaction, can be used.

Claims (15)

NMR gyroscope (200), comprising • a vapor cell arrangement (201) comprising a sensing medium (204) which is arranged in the vapor cell arrangement (201), • an illumination source (205) for providing a pump light beam (20110, 20120) at Location of the vapor cell arrangement (201), wherein the pump light beam (20110, 20120) is set up to excite a spin precession movement in the sensing medium (204), and • a detection arrangement (208), the detection arrangement (208) for determining a rotational measurement variable of the NMR gyroscope (200) is set up from the spin precession movement, characterized in that • that the vapor cell arrangement (201) has a first pumping region (2011) and a second pumping region (2012), • that the NMR gyroscope (200) has a first optical arrangement (211), wherein the first optical arrangement (211) is arranged in the beam path between the illumination source (205) and the vapor cell arrangement (201), and wherein the first optical arrangement (2 11) is set up to convert the light beam (2001) from the illumination source (205) into a first pump light beam (20110), having a first polarization, for exciting the spin precession movement in the sensing medium (204) of the first pump region (2011). a first sense of rotation, - a second pump light beam (20120), having a second polarization, for exciting the spin precession motion in the sensing medium (204) of the second pump region (2012) with a second sense of rotation, the first sense of rotation and the second sense of rotation being opposite to each other, and - splitting a readout light beam (2000) having a third polarization for reading out the spin precession movements of the first pump region (2011) and the second pump region (2012). NMR gyroscope (200) after claim 1 , characterized in that the first optical arrangement (211) comprises a first beam splitter (2101) and a second beam splitter (2102), wherein the first beam splitter (2101) is set up to the from the illumination source (205) coming light beam (2001) into the first pump light beam (20110) and a partial beam (2004), the second beam splitter (2102) in the beam path of the partial beam (2004) for splitting the partial beam (2004) into the second pump light beam (20120) and the readout -Light beam (2000) is arranged. NMR gyroscope (200) after claim 2 , characterized in that the first beam splitter (2101) and/or the second beam splitter (2102) are designed as polarizing beam splitters. NMR gyroscope (200) according to one of claims 2 or 3 , characterized in that at least one optical filter (2111, 2112) for adjusting the light transmission of the first beam splitter (2101) and/or in the beam path between the first beam splitter (2101 ) and the second beam splitter (2102) at least one optical filter (2114) for adjusting the light transmission of the second beam splitter (2102) are arranged. NMR gyroscope (200) according to any one of the preceding claims, characterized in that the first polarization and the second polarization are mutually opposite circular polarizations and/or the third polarization is a linear polarization. NMR gyroscope (200) according to one of the preceding claims, characterized in that the NMR gyroscope (200) comprises a second optical arrangement (212) in the optical path of the readout light beam (2000). NMR gyroscope (200) according to one of the preceding claims, characterized in that the second optical arrangement (212) comprises at least one optical element for beam guidance and/or for beam shaping. NMR gyroscope (200) according to one of the preceding claims, characterized in that - the second optical arrangement (212) comprises two mirrors (2121, 2122), the two mirrors (2121, 2122) being arranged in such a way that the readout light beam (2000) is guided through the vapor cell arrangement (201) to the detection arrangement (208) and - the second optical arrangement (212) comprises an optical diaphragm (2123) for adjusting a beam cross section of the readout light beam (2000). NMR gyroscope (200) according to any one of the preceding claims, characterized in that the detection arrangement (208) - a first detection unit (2081) for detecting the first pump light beam (20110) after passing the first pump region (2011), - a second detection unit (2082) for detecting the second pumping light beam (20120) after passing through the second pumping region (2012) and - a main detection unit (2080) for detecting the readout light beam (2000) after passing through the vapor cell arrangement (201). The NMR gyroscope (200) of any preceding claim characterized in that the NMR gyroscope (200) includes a magnetic shield assembly (207), the vapor cell assembly (201) being located in an area shielded by the magnetic shield assembly (207). . NMR gyroscope (200) after claim 10 , characterized in that the illumination source (205) and/or the first optical arrangement (211) are arranged outside the shielded area. NMR gyroscope (200) according to one of Claims 10 or 11 , characterized in that the detection arrangement (208) is arranged at least partially outside the shielded area. NMR gyroscope (200) according to any one of the preceding claims, characterized in that the vapor cell arrangement (201) comprises a vapor cell (2013), wherein a buffer gas (203) is arranged in the vapor cell (2013), which by spatial restriction of an electron Nuclear spin interaction in the sensing medium (204) in the vapor cell (2013) realized the first pump area (2011) and the second pump area (2012). NMR gyroscope (200) according to one of Claims 1 until 13 , characterized in that the vapor cell arrangement (201) comprises a first vapor cell (2011a) and a second vapor cell (2012a), wherein the first (2011a) vapor cell comprises the first pumping region (2011) and the second vapor cell (2012a) comprises the second pumping region ( 2012). NMR gyroscope (200) according to one of the preceding claims, characterized in that the NMR gyroscope (200) has a magnetic field generating device (206) for providing a bias field (300) and an oscillating magnetic field (301) at the location of the vapor cell arrangement (201), wherein the bias field (300) for defining a direction of spin precession motion and the oscillating magnetic field (301) are set up to synchronize the spin precession movement.

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