Time-multiplexed dual atomic magnetometry
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Publication Number
US-11639976-B2
Publication Date
2023-05-02
Expiration Date
Abstract
Time-multiplexed atomic magnetometry uses first and second atomic vapor cells to measure an external magnetic field. Each vapor cell operates according to a sequence of alternating pumping and probing stages. However, the sequences are temporally offset from each other such that the second vapor cell is pumped while the first vapor cell is probed, and the first vapor cell is pumped while the second vapor cell is probed. With this time-multiplexed operation, the external magnetic field can be measured without any time gaps. The Hilbert transform of the signals may be taken to obtain their instantaneous phases, which may then be interleaved to form a single gapless time sequence that represents the external magnetic field over a time window that lasts for several continuous pumping/probing stages.
Core Innovation
The invention provides a time-multiplexed dual atomic magnetometer that uses first and second vapor cells positioned so an external magnetic field induces Larmor precession of atoms within each cell. A first polarimeter measures a first polarization of a first probe beam after the first probe beam propagates through the first vapor cell, and outputs a first polarization signal. A second polarimeter measures a second polarization of a second probe beam after the second probe beam propagates through the second vapor cell, and outputs a second polarization signal.
A signal processor processes the first polarization signal to obtain a first data block representing the first polarization signal during a first measurement stage. The signal processor processes the second polarization signal to obtain a second data block representing the second polarization signal during a second measurement stage that starts when the first measurement stage ends. The signal processor appends the second data block to the first data block to obtain a temporal sequence representing the external magnetic field during the first and second measurement stages.
In the disclosed implementation, polarization data from each cell are processed to derive an instantaneous Larmor frequency and corresponding magnetic-field sequences, and then concatenated or interleaved into a gapless temporal sequence. Instantaneous-phase retrieval using an analytic signal and Hilbert transform is used to obtain instantaneous-phase information, and the resulting magnetic-field sequences are appended into a single temporal sequence.
Claims Coverage
The partial content includes two independent claims: a system claim for a time-multiplexed dual atomic magnetometer and a method claim for time-multiplexed dual atomic magnetometry. Across the dependent claims referenced, inventive features mainly refine how probe and polarimeter data are converted into data blocks, appended into a temporal sequence, and how timing and magnetic-bias geometry are controlled.
Time-multiplexed dual atomic magnetometer with two vapor cells and appended temporal sequence
The apparatus has first and second vapor cells induced by an external magnetic field to undergo Larmor precession of atoms in each vapor cell, a first polarimeter measuring a first polarization signal from a first probe beam through the first vapor cell during a first measurement stage, a second polarimeter measuring a second polarization signal from a second probe beam through the second vapor cell during a second measurement stage that starts when the first measurement stage ends, and a signal processor that processes the polarization signals to obtain first and second data blocks and appends the second data block to the first data block to obtain a temporal sequence representing the external magnetic field during the first and second measurement stages.
Time-multiplexed dual atomic magnetometry with inducing, measuring, processing into data blocks, and appending into a temporal sequence
The method induces Larmor precession of atoms located within first and second vapor cells with an external magnetic field, measures with a first polarimeter a first polarization of a first probe beam after it propagates through the first vapor cell to obtain a first polarization signal, measures with a second polarimeter a second polarization of a second probe beam after it propagates through the second vapor cell to obtain a second polarization signal, processes the first polarization signal to obtain a first data block during a first measurement stage, processes the second polarization signal to obtain a second data block during a second measurement stage starting when the first measurement stage ends, and appends the second data block to the first data block to obtain a temporal sequence representing the external magnetic field during the first and second measurement stages.
Instantaneous-phase retrieval for deriving magnetic-field sequences for appending
The signal or method processing performs instantaneous-phase retrieval on the first and second data blocks to obtain first and second magnetic-field sequences, then appends the second magnetic-field sequence to the first magnetic-field sequence.
Gating to restrict probe propagation to designated vapor cells during stages
A controller gates first and second probe beams so each beam propagates only through its respective vapor cell during its designated measurement stage.
Gating to restrict pump propagation to designated vapor cells during pumping stage
The controller gates a first pump beam and a second pump beam so each propagates only through its respective vapor cell during a pumping stage prior to the corresponding measurement stage, spin-polarizing the atoms in that cell.
Magnetic bias field oriented perpendicular to common probe propagation direction
The first and second probe beams propagate along a common propagation direction, and the magnetic bias field is perpendicular to the common propagation direction based on the placement of a magnetic field coil.
Equal measurement stage duration
The first and second measurement stages have the same duration.
Magnetic bias field oriented parallel to common probe propagation direction
The method applies the magnetic bias field such that a direction of the magnetic bias field is parallel to a common propagation direction of the first and second probe beams.
Overall claim coverage centers on measuring polarization from two vapor cells in time-multiplexed stages and forming a temporal sequence by processing polarization signals into data blocks and appending them. Dependent features explicitly include instantaneous-phase retrieval for magnetic-field sequence derivation, gating of probe and pump beams to associate beams with designated cells and stages, constraints on measurement stage duration, and geometric constraints on magnetic bias field orientation relative to probe propagation direction.
Stated Advantages
Gapless temporal sequence representing the external magnetic field across the first and second measurement stages.
Instantaneous Larmor frequency and corresponding magnetic-field sequences derived from instantaneous-phase retrieval.
Bandwidth advantage expected to exceed 10 kHz.
Preferential measurement of field components using magnetic bias-field orientation.
Documented Applications
Geosciences.
Magnetic communication.
Threat detection.
Magnetoencephalography (MEG).
NMR.
MRI.
Therapeutic repurposing via time-varying magnetic fields including siRNA/mRNA therapy.
Optional multi-cell expansion and system component/controller configurations for the time-multiplexed dual atomic magnetometer.
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