U.S. patent application number 15/372201 was filed with the patent office on 2017-07-27 for magneto-optical defect sensor with common rf and magnetic fields generator.
This patent application is currently assigned to Lockheed Martin Corporation. The applicant listed for this patent is Lockheed Martin Corporation. Invention is credited to Gregory S. Bruce, Joseph W. Hahn, Duc Huynh, Wilbur Lew.
Application Number | 20170212187 15/372201 |
Document ID | / |
Family ID | 57795122 |
Filed Date | 2017-07-27 |
United States Patent
Application |
20170212187 |
Kind Code |
A1 |
Hahn; Joseph W. ; et
al. |
July 27, 2017 |
MAGNETO-OPTICAL DEFECT SENSOR WITH COMMON RF AND MAGNETIC FIELDS
GENERATOR
Abstract
Systems and apparatuses are disclosed for providing a uniform RF
field and magnetic bias field to a nitrogen vacancy center
diamond.
Inventors: |
Hahn; Joseph W.; (Erial,
NJ) ; Bruce; Gregory S.; (Abington, NJ) ;
Huynh; Duc; (Princeton Junction, NJ) ; Lew;
Wilbur; (Mount Laurel, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lockheed Martin Corporation |
Bethesda |
MD |
US |
|
|
Assignee: |
Lockheed Martin Corporation
Bethesda
MD
|
Family ID: |
57795122 |
Appl. No.: |
15/372201 |
Filed: |
December 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15003298 |
Jan 21, 2016 |
9551763 |
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15372201 |
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PCT/US16/14392 |
Jan 21, 2016 |
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15003298 |
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PCT/US16/14403 |
Jan 21, 2016 |
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PCT/US16/14392 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/032 20130101;
G01R 33/0017 20130101 |
International
Class: |
G01R 33/032 20060101
G01R033/032; G01R 33/00 20060101 G01R033/00 |
Claims
1. A magnetometer comprising: a magneto-optical defect center
material with a plurality of magneto-optical defect centers; a
first optical excitation source that transmits excitation light
that excites at least a portion of the magneto-optical defect
centers of the magneto-optical defect center material; a first
photo sensor that receives generated light that is generated by the
portion of the magneto-optical defect centers; a plurality of radio
frequency (RF) elements spaced around the magneto-optical defect
center material, wherein the plurality of RF elements generate a
microwave signal that is substantially uniform over the
magneto-optical defect center material and generate a magnetic bias
field to the magneto-optical defect center material; and a
processor operatively coupled to the first photo sensor, wherein
the processor is configured to determine a magnitude of an external
magnetic field based on a signal received from the first photo
sensor.
2. The magnetometer of claim 1, wherein the plurality of RF
elements are spaced about the magneto-optical defect center
material to form a cuboid shape, and wherein the magneto-optical
defect center material is within the cuboid shape.
3. The magnetometer of claim 1, wherein the plurality of RF
elements is six RF elements.
4. The magnetometer of claim 3, wherein the plurality of RF
elements are arranged in a cube formation, and wherein the
magneto-optical defect center material is within the cube
formation.
5. The magnetometer of claim 1, wherein a first RF element of the
plurality of RF elements comprises an ingress hole through which
the excitation light passes, and wherein a second RF element of the
plurality of RF elements comprises an egress hole through which the
generated light passes.
6. The magnetometer of claim 5, wherein the excitation light passes
through a first side of the magneto-optical defect center material,
and wherein the generated light passes through a second side of the
magneto-optical defect center material.
7. The magnetometer of claim 6, wherein the first side of the
magneto-optical defect center material and the second side of the
magneto-optical defect center material are opposite sides of the
magneto-optical defect center material.
8. The magnetometer of claim 1, wherein a first RF element of the
plurality of RF elements comprises a first ingress hole through
which the excitation light passes, wherein a second RF element of
the plurality of RF elements comprises a second ingress hole
through which the excitation light passes, wherein a third RF
element of the plurality of RF elements comprises a first egress
hole through which at least a first portion of generated light
passes.
9. The magnetometer of claim 8, further comprising a second optical
excitation source, wherein the first optical excitation source
transmits a first portion of the excitation light and the second
optical excitation source transmits a second portion of the
excitation light.
10. The magnetometer of claim 8, wherein a fourth RF element of the
plurality of RF elements comprises a second egress hole through
which at least a second portion of the generated light passes.
11. The magnetometer of claim 10, wherein the excitation light
passes through a first side of the magneto-optical defect center
material and through a second side of the magneto-optical defect
center material, and wherein the generated light passes through a
third side of the magneto-optical defect center material and
through a fourth side of the magneto-optical defect center
material.
12. The magnetometer of claim 11, wherein the first side of the
magneto-optical defect center material and the third side of the
magneto-optical defect center material are opposite sides of the
magneto-optical defect center material, and wherein the second side
of the magneto-optical defect center material and the fourth side
of the magneto-optical defect center material are opposite sides of
the magneto-optical defect center material.
13. The magnetometer of claim 1, wherein each of the RF elements
comprises an RF connection that is configured to receive a feed
signal, and wherein the feed signal generates the microwave
signal.
14. The magnetometer of claim 13, wherein the feed signal further
generates the magnetic field bias.
15. The magnetometer of claim 14, wherein the feed signal for each
of the RF elements is a different RF feed signal.
16. The magnetometer of claim 1, wherein the magneto-optical defect
center material is diamond material.
17. The magnetometer of claim 1, wherein the magneto-optical defect
centers are nitrogen vacancy centers.
18. A device comprising: a magneto-optical defect center material
with a plurality of magneto-optical defect centers; and a plurality
of radio frequency (RF) elements spaced around the magneto-optical
defect center material, wherein the plurality of RF elements
generate a microwave signal that is substantially uniform over the
magneto-optical defect center material and generate a magnetic bias
field to the magneto-optical defect center material.
19. The device of claim 18, wherein the plurality of RF elements
are spaced about the magneto-optical defect center material to form
a cuboid shape, and wherein the magneto-optical defect center
material is within the cuboid shape.
20. The device of claim 18, wherein the plurality of RF elements is
six RF elements.
21. The device of claim 20, wherein the plurality of RF elements
are arranged in a cube formation, and wherein the magneto-optical
defect center material is within the cube formation.
22. The device of claim 18, wherein a first RF element of the
plurality of RF elements comprises an ingress hole through which
excitation light passes, wherein the excitation light excites at
least a portion of the plurality of magneto-optical defect centers,
and wherein a second RF element of the plurality of RF elements
comprises an egress hole through which generated light passes,
wherein the generated light is generated by the portion of the
plurality of magneto-optical defect centers.
23. The device of claim 22, wherein the excitation light passes
through a first side of the magneto-optical defect center material,
and wherein the generated light passes through a second side of the
magneto-optical defect center material.
24. The device of claim 23, wherein the first side of the
magneto-optical defect center material and the second side of the
magneto-optical defect center material are opposite sides of the
magneto-optical defect center material.
25. The device of claim 22, further comprising a photo sensor that
receives at least a portion of the generated light.
26. The device of claim 18, wherein a first RF element of the
plurality of RF elements comprises a first ingress hole through
which excitation light passes, wherein a second RF element of the
plurality of RF elements comprises a second ingress hole through
which excitation light passes, wherein the excitation light excites
at least a portion of the plurality of magneto-optical defect
centers, wherein a third RF element of the plurality of RF elements
comprises a first egress hole through which at least a first
portion of generated light passes, and wherein the generated light
is generated by the portion of the plurality of magneto-optical
defect centers.
27. The device of claim 26, wherein a fourth RF element of the
plurality of RF elements comprises a second egress hole through
which at least a second portion of the generated light passes.
28. The device of claim 27, wherein the excitation light passes
through a first side of the magneto-optical defect center material
and through a second side of the magneto-optical defect center
material, and wherein the generated light passes through a third
side of the magneto-optical defect center material and through a
fourth side of the magneto-optical defect center material.
29. The device of claim 28, wherein the first side of the
magneto-optical defect center material and the third side of the
magneto-optical defect center material are opposite sides of the
magneto-optical defect center material, and wherein the second side
of the magneto-optical defect center material and the fourth side
of the magneto-optical defect center material are opposite sides of
the magneto-optical defect center material.
30. The device of claim 18, wherein each of the RF elements
comprises an RF connection that is configured to receive a feed
signal, and wherein the feed signal generates the microwave
signal.
31. The device of claim 30, wherein the feed signal further
generates the magnetic field bias.
32. The device of claim 31, wherein the feed signal for each of the
RF elements is a different RF feed signal.
33. The device of claim 18, wherein the magneto-optical defect
center material is diamond material.
34. The device of claim 18, wherein the magneto-optical defect
centers are nitrogen vacancy centers.
35. A method comprising: receiving, at each of a plurality of radio
frequency (RF) elements, a feed signal; generating, by the
plurality of RF elements, a microwave signal that is substantially
uniform over a magneto-optical defect center material that has a
plurality of magneto-optical defect centers; and generating, by the
plurality of RF elements, a magnetic bias field that is applied to
the magneto-optical defect center material.
36. The method of claim 35, further comprising: passing excitation
light though a hole of a first RF element of the plurality of RF
elements, wherein the excitation light excites at least a portion
of the magneto-optical defect centers; and transmitting generated
light through a hole of a second RF element of the plurality of RF
elements, wherein the generated light is generated by the portion
of the magneto-optical defect centers.
37. The method of claim 36, further comprising receiving, at a
photo sensor, at least a portion of the generated light.
38. The method of claim 35, wherein the receiving the feed signal
comprises receiving a unique feed signal at each of the plurality
of RF elements.
39. The method of claim 35, further comprising: passing excitation
light though a hole of a first RF element of the plurality of RF
elements and through a hole of a second RF element of the plurality
of RF elements, wherein the excitation light excites at least a
portion of the magneto-optical defect centers; and transmitting at
least a first portion of generated light through a hole of a third
RF element of the plurality of RF elements, wherein the generated
light is generated by the portion of the magneto-optical defect
centers.
40. The method of claim 39, further comprising transmitting a
second portion of the generated light through a hole of a fourth RF
element of the plurality of elements.
41. The method of claim 39, further comprising receiving, at a
photo sensor, the first portion of the generated light.
42. The method of claim 41, further comprising: receiving, at a
first photo sensor, the first portion of the generated light; and
receiving, at a second photo sensor, the second portion of the
generated light.
43. The method of claim 35, wherein the magneto-optical defect
center material is diamond material.
44. The method of claim 35, wherein the magneto-optical defect
centers are nitrogen vacancy centers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation of U.S. patent
application Ser. No. 15/003,298, filed Jan. 21, 2016, and the
contents of which are incorporated herein by reference in its
entirety.
FIELD BACKGROUND
[0002] The present invention relates generally to a sensor assembly
of a magnetic sensor.
[0003] Magnetic sensors based on a nitrogen vacancy (NV) center in
diamond are known. Diamond NV (DNV) sensors may provide good
sensitivity for magnetic field measurements. Such magnetic sensor
systems often include components such an optical excitation source,
an RF excitation source, and optical detectors. These components
are all formed on different substrates or as separate components
mechanically supported together.
SUMMARY
[0004] Systems and apparatuses are described that use multiple
radio frequency elements for providing a uniform magnetic field
over an NV diamond and also providing a magnetic bias for the NV
diamond. In one implementation, a magnetic field sensor assembly
includes four side radio frequency (RF) elements. Each side RF
element includes an RF connection. The magnetic field sensor also
includes four side RF feed cables connected to one of the four side
RF elements such that each side RF element is connected to one RF
feed cable that provides a feed signal to the side RF element. The
magnetic field sensor also includes a top RF element and a bottom
element along with a top RF element feed cable and a bottom RF feed
cable. The top and bottom feed cables provide a RF feed signal to
the top and bottom RF elements respectively. The four side RF side
elements, the top RF element, and the bottom RF element are
arranged in a cube formation. A nitrogen-vacancy (NV) center
diamond is located within the cube formation. The side RF elements,
top RF element, and bottom RF element generate a microwave signal
that is uniform over the NV center diamond, and also generate a
magnetic bias field to the NV center diamond.
[0005] In other implementations, a magnetic field sensor assembly
includes four side radio frequency (RF) elements. Each side RF
element includes an RF connection. The magnetic field sensor also
includes four side RF feed cables connected to one of the four side
RF elements such that each side RF element is connected to one RF
feed cable that provides a feed signal to the side RF element. The
magnetic field sensor also includes a top RF element and a bottom
element along with a top RF element feed cable and a bottom RF feed
cable. The top and bottom feed cables provide a RF feed signal to
the top and bottom RF elements respectively. The four side RF side
elements, the top RF element, and the bottom RF element are
arranged in a column formation. A nitrogen-vacancy (NV) center
diamond is located within the column formation. The side RF
elements, top RF element, and bottom RF element generate a
microwave signal that is uniform over the NV center diamond, and
also generate a magnetic bias field to the NV center diamond.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The foregoing and other features of the present disclosure
will become more fully apparent from the following description and
appended claims, taken in conjunction with the accompanying
drawings. Understanding that these drawings depict only several
implementations in accordance with the disclosure and are,
therefore, not to be considered limiting of its scope, the
disclosure will be described with additional specificity and detail
through use of the accompanying drawings.
[0007] FIG. 1 illustrates one orientation of an NV center in a
diamond lattice.
[0008] FIG. 2 is an energy level diagram illustrates energy levels
of spin states for the NV center.
[0009] FIG. 3 is a schematic illustrating an NV center magnetic
sensor system.
[0010] FIG. 4 is a graph illustrating the fluorescence as a
function of applied RF frequency of an NV center along a given
direction for a zero magnetic field and a non-zero magnetic
field.
[0011] FIG. 5 is a graph illustrating the fluorescence as a
function of applied RF frequency for four different NV center
orientations for a non-zero magnetic field.
[0012] FIG. 6 is a schematic illustrating an NV center magnetic
sensor system in accordance with some illustrative
implementations.
[0013] FIG. 7 is a schematic illustrating a portion of a DNV sensor
with a coil assembly in accordance with some illustrative
implementations.
[0014] FIG. 8 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations.
[0015] FIGS. 9A and 9B are schematics illustrating a coil assembly
in accordance with some illustrative implementations.
[0016] FIG. 10 is a cross section illustrating a coil assembly in
accordance with some illustrative implementations.
[0017] FIG. 11 is a schematic illustrating a side element of a coil
assembly in accordance with some illustrative implementations.
[0018] FIG. 12 is a schematic illustrating a top or bottom element
of a coil assembly in accordance with some illustrative
implementations.
[0019] FIG. 13 is a schematic illustrating a center mounting block
of a coil assembly in accordance with some illustrative
implementations.
[0020] FIG. 14 is a cross section illustrating of a portion of a
DNV sensor with a coil assembly in accordance with some
illustrative implementations.
[0021] FIG. 15 is a schematic illustrating a coil assembly in
accordance with some illustrative implementations.
[0022] FIG. 16 is a schematic illustrating a cross section of a
coil assembly in accordance with some illustrative
implementations.
[0023] FIG. 17 is a schematic illustrating a side element of a coil
assembly in accordance with some illustrative implementations.
[0024] FIG. 18 is a schematic illustrating a portion of a DNV
sensor with a coil assembly in accordance with some illustrative
implementations.
[0025] FIG. 19 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations.
[0026] FIG. 20 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations.
[0027] FIG. 21 is a schematic illustrating a coil assembly in
accordance with some illustrative implementations.
[0028] FIG. 22 is a schematic illustrating a cross section of a
coil assembly in accordance with some illustrative
implementations.
[0029] FIG. 23 is a schematic illustrating a side element of a coil
assembly in accordance with some illustrative implementations.
[0030] FIGS. 24A and 24B are schematics illustrating top and bottom
elements of a coil assembly in accordance with some illustrative
implementations.
DETAILED DESCRIPTION
[0031] Nitrogen-vacancy (NV) centers are defects in a diamond's
crystal structure. Synthetic diamonds can be created that have
these NV centers. NV centers generate red light when excited by a
light source, such as a green light source, and microwave
radiation. When an excited NV center diamond is exposed to an
external magnetic field the frequency of the microwave radiation at
which the diamond generates red light and the intensity of the
light change. By measuring this change and comparing the change to
the microwave frequency that the diamond generates red light at
when not in the presence of the external magnetic field, the
external magnetic field strength can be determined. Accordingly, NV
centers can be used as part of a magnetic field sensor.
[0032] In various implementations, microwave RF excitation is
needed in a DNV sensor. The more uniform the microwave signal is
across the NV centers in the diamond the better and more accurate
an NV sensor will perform. Uniformity, however, can be difficult to
achieve. Also, the larger the bandwidth of the element, the better
the NV sensor will perform. Large bandwidth, such as octave
bandwidth, however, can be difficult to achieve. Various NV sensors
respond to a microwave frequency that is not easily generated by RF
antenna elements that are comparable to the small size of the NV
sensor. In addition, RF elements should reduce the amount of light
within the sensor that is blocked by the RF elements. When a single
RF element is used, the RF element is offset from the NV diamond
when the RF element maximized the faces and edges of the diamond
that light can enter or leave. Moving the RF element away from the
NV diamond, however, impacts the uniformity of strength of the RF
that is applied to the NV diamond.
[0033] The present inventors have realized that a configuration of
RF elements can provide both the magnetic bias and the RF field for
a DNV magnetic system. The magnetic bias provided by various
implementations can be a uniform magnetic field along three
polarizations of the axes of the coils used in various
implementations. As described in greater detail below, using the
various configuration of RF elements in a DNV sensor can allow
greater access to the edges and faces of the diamond for light
input and egress, while also providing a relatively uniform field
in addition to a bias magnetic field. In various implementations, a
NV diamond is contained within a housing. The housing can have six
sides, each side operating as an RF element to apply a uniform RF
field to the NV diamond. In addition, the six RF elements can also
provide the magnetic bias for the NV sensor. Further, the six sides
can be configured to allow various different configurations for
light ingress and egress. The spacing and size of the RF elements
allow for all edges and faces of the diamond to be used for light
ingress and egress. The more light captured by photo-sensing
elements of a DNV senor results in an increased efficiency of the
sensor. In addition, the multiple polarization RF field of various
implementations can increase the number of NV centers that are
efficiently excited. In addition, the multiple polarization RF
field can be used to differentially control the polarizations to
achieve higher order functionality from the DNV sensor.
[0034] NV Center, its Electronic Structure, and Optical and RF
Interaction
[0035] The nitrogen vacancy (NV) center in diamond comprises a
substitutional nitrogen atom in a lattice site adjacent a carbon
vacancy as shown in FIG. 1. The NV center may have four
orientations, each corresponding to a different crystallographic
orientation of the diamond lattice.
[0036] The NV center may exist in a neutral charge state or a
negative charge state. Conventionally, the neutral charge state
uses the nomenclature NV.sup.0, while the negative charge state
uses the nomenclature NV, which is adopted in this description.
[0037] The NV center has a number of electrons including three
unpaired electrons, each one from the vacancy to a respective of
the three carbon atoms adjacent to the vacancy, and a pair of
electrons between the nitrogen and the vacancy. The NV center,
which is in the negatively charged state, also includes an extra
electron.
[0038] The NV center has rotational symmetry, and as shown in FIG.
2, has a ground state, which is a spin triplet with .sup.3A.sub.2
symmetry with one spin state m.sub.s=0, and two further spin states
m.sub.s=+1, and m.sub.s=-1. In the absence of an external magnetic
field, the m.sub.s=.+-.1 energy levels are offset from the
m.sub.s=0 due to spin-spin interactions, and the m.sub.s=.+-.1
energy levels are degenerate, i.e., they have the same energy. The
m.sub.s=0 spin state energy level is split from the m.sub.s=.+-.1
energy levels by an energy of 2.87 GHz for a zero external magnetic
field.
[0039] Introducing an external magnetic field with a component
along the NV axis lifts the degeneracy of the m.sub.s=.+-.1 energy
levels, splitting the energy levels m.sub.s=.+-.1 by an amount
2g.mu..sub.BBz, where g is the g-factor, .mu..sub.B is the Bohr
magneton, and Bz is the component of the external magnetic field
along the NV axis. This relationship is correct for a first order
and inclusion of higher order corrections is a straight forward
matter and will not affect the computational and logic steps in the
systems and methods described below.
[0040] The NV center electronic structure further includes an
excited triplet state .sup.3E with corresponding m.sub.s=0 and
m.sub.s=.+-.1 spin states. The optical transitions between the
ground state .sup.3A.sub.2 and the excited triplet .sup.3E are
predominantly spin conserving, meaning that the optical transitions
are between initial and final states which have the same spin. For
a direct transition between the excited triplet .sup.3E and the
ground state .sup.3A.sub.2, a photon of red light is emitted with a
photon energy corresponding to the energy difference between the
energy levels of the transitions.
[0041] There is, however, an alternate non-radiative decay route
from the triplet .sup.3E to the ground state .sup.3A.sub.2 via
intermediate electron states, which are thought to be intermediate
singlet states A, E with intermediate energy levels. Significantly,
the transition rate from the m.sub.s=.+-.1 spin states of the
excited triplet .sup.3E to the intermediate energy levels is
significantly greater than the transition rate from the m.sub.s=0
spin state of the excited triplet .sup.3E to the intermediate
energy levels. The transition from the singlet states A, E to the
ground state triplet .sup.3A.sub.2 predominantly decays to the
m.sub.s=0 spin state over the m.sub.s=.+-.1 spin states. These
features of the decay from the excited triplet .sup.3E state via
the intermediate singlet states A, E to the ground state triplet
.sup.3A.sub.2 allows that if optical excitation is provided to the
system, the optical excitation will eventually pump the NV center
into the m.sub.s=0 spin state of the ground state .sup.3A.sub.2. In
this way, the population of the m.sub.s=0 spin state of the ground
state .sup.3A.sub.2 may be "reset" to a maximum polarization
determined by the decay rates from the triplet .sup.3E to the
intermediate singlet states.
[0042] Another feature of the decay is that the fluorescence
intensity due to optically stimulating the excited triplet .sup.3E
state is less for the m.sub.s=.+-.1 states than for the m.sub.s=0
spin state. This is so because the decay via the intermediate
states does not result in a photon emitted in the fluorescence
band, and because of the greater probability that the m.sub.s=.+-.1
states of the excited triplet .sup.3E state will decay via the
non-radiative decay path. The lower fluorescence intensity for the
m.sub.s=.+-.1 states than for the m.sub.s=0 spin state allows the
fluorescence intensity to be used to determine the spin state. As
the population of the m.sub.s=.+-.1 states increases relative to
the m.sub.s =0 spin, the overall fluorescence intensity will be
reduced.
[0043] NV Center, or Magneto-Optical Defect Center, Magnetic Sensor
System
[0044] FIG. 3 is a schematic illustrating a NV center magnetic
sensor system 300 which uses fluorescence intensity to distinguish
the m.sub.s=.+-.1 states, and to measure the magnetic field based
on the energy difference between the m.sub.s=+1 state and the
m.sub.s=-1 state. The system 300 includes an optical excitation
source 310, which directs optical excitation to an NV diamond
material 320 with NV centers. The system 300 further includes an RF
excitation source 330 which provides RF radiation to the NV diamond
material 320. Light from the NV diamond may be directed through an
optical filter 350 to an optical detector 340.
[0045] The RF excitation source 330 may be a microwave coil, for
example. The RF excitation source 330 when emitting RF radiation
with a photon energy resonant with the transition energy between
ground m.sub.s=0 spin state and the m.sub.s=+1 spin state excites a
transition between those spin states. For such a resonance, the
spin state cycles between ground m.sub.s=0 spin state and the
m.sub.s=+1 spin state, reducing the population in the m.sub.s=0
spin state and reducing the overall fluorescence at resonance.
Similarly resonance occurs between the m.sub.s=0 spin state and the
m.sub.s=-1 spin state of the ground state when the photon energy of
the RF radiation emitted by the RF excitation source is the
difference in energies of the m.sub.s=0 spin state and the
m.sub.s=-1 spin state. At resonance between the m.sub.s=0 spin
state and the m.sub.s=-1 spin state, or between the m.sub.s=0 spin
state and the m.sub.s=+1 spin state, there is a decrease in the
fluorescence intensity.
[0046] The optical excitation source 310 may be a laser or a light
emitting diode, for example, which emits light in the green, for
example. The optical excitation source 310 induces fluorescence in
the red, which corresponds to an electronic transition from the
excited state to the ground state. Light from the NV diamond
material 320 is directed through the optical filter 350 to filter
out light in the excitation band (in the green for example), and to
pass light in the red fluorescence band, which in turn is detected
by the detector 340. The optical excitation light source 310, in
addition to exciting fluorescence in the diamond material 320, also
serves to reset the population of the m.sub.s=0 spin state of the
ground state .sup.3A.sub.2 to a maximum polarization, or other
desired polarization.
[0047] For continuous wave excitation, the optical excitation
source 310 continuously pumps the NV centers, and the RF excitation
source 330 sweeps across a frequency range which includes the zero
splitting (when the m.sub.s=.+-.1 spin states have the same energy)
photon energy of 2.87 GHz. The fluorescence for an RF sweep
corresponding to a diamond material 320 with NV centers aligned
along a single direction is shown in FIG. 4 for different magnetic
field components Bz along the NV axis, where the energy splitting
between the m.sub.s=-1 spin state and the m.sub.s=+1 spin state
increases with Bz. Thus, the component Bz may be determined.
Optical excitation schemes other than continuous wave excitation
are contemplated, such as excitation schemes involving pulsed
optical excitation, and pulsed RF excitation. Examples, of pulsed
excitation schemes include Ramsey pulse sequence, and spin echo
pulse sequence.
[0048] In general, the diamond material 320 will have NV centers
aligned along directions of four different orientation classes.
FIG. 5 illustrates fluorescence as a function of RF frequency for
the case where the diamond material 320 has NV centers aligned
along directions of four different orientation classes. In this
case, the component Bz along each of the different orientations may
be determined. These results along with the known orientation of
crystallographic planes of a diamond lattice allows not only the
magnitude of the external magnetic field to be determined, but also
the direction of the magnetic field.
[0049] While FIG. 3 illustrates an NV center magnetic sensor system
300 with NV diamond material 320 with a plurality of NV centers, in
general the magnetic sensor system may instead employ a different
magneto-optical defect center material, with a plurality of
magneto-optical defect centers. The electronic spin state energies
of the magneto-optical defect centers shift with magnetic field,
and the optical response, such as fluorescence, for the different
spin states is not the same for all of the different spin states.
In this way, the magnetic field may be determined based on optical
excitation, and possibly RF excitation, in a corresponding way to
that described above with NV diamond material.
[0050] FIG. 6 is a schematic of an NV center magnetic sensor 600,
according to an embodiment of the invention. The sensor 600
includes an optical excitation source 610, which directs optical
excitation to an NV diamond material 620 with NV centers, or
another magneto-optical defect center material with magneto-optical
defect centers. An RF excitation source 630 provides RF radiation
to the NV diamond material 620. The NV center magnetic sensor 600
may include a bias magnet 670 applying a bias magnetic field to the
NV diamond material 620. Light from the NV diamond material 620 may
be directed through an optical filter 650 and an electromagnetic
interference (EMI) filter 660, which suppresses conducted
interference, to an optical detector 640. The sensor 600 further
includes a controller 680 arranged to receive a light detection
signal from the optical detector 640 and to control the optical
excitation source 610 and the RF excitation source 630.
[0051] The RF excitation source 630 may be a microwave coil, for
example. The RF excitation source 630 is controlled to emit RF
radiation with a photon energy resonant with the transition energy
between the ground m.sub.s=0 spin state and the m.sub.s=.+-.1 spin
states as discussed above with respect to FIG. 3.
[0052] The optical excitation source 610 may be a laser or a light
emitting diode, for example, which emits light in the green, for
example. The optical excitation source 610 induces fluorescence in
the red, which corresponds to an electronic transition from the
excited state to the ground state. Light from the NV diamond
material 620 is directed through the optical filter 650 to filter
out light in the excitation band (in the green for example), and to
pass light in the red fluorescence band, which in turn is detected
by the optical detector 640. The EMI filter 660 is arranged between
the optical filter 650 and the optical detector 640 and suppresses
conducted interference. The optical excitation light source 610, in
addition to exciting fluorescence in the NV diamond material 620,
also serves to reset the population of the m.sub.s=0 spin state of
the ground state .sup.3A.sub.2 to a maximum polarization, or other
desired polarization.
[0053] The controller 680 is arranged to receive a light detection
signal from the optical detector 640 and to control the optical
excitation source 610 and the RF excitation source 630. The
controller may include a processor 682 and a memory 684, in order
to control the operation of the optical excitation source 610 and
the RF excitation source 630. The memory 684, which may include a
nontransitory computer readable medium, may store instructions to
allow the operation of the optical excitation source 610 and the RF
excitation source 630 to be controlled.
[0054] According to one embodiment of operation, the controller 680
controls the operation such that the optical excitation source 610
continuously pumps the NV centers of the NV diamond material 620.
The RF excitation source 630 is controlled to continuously sweep
across a frequency range which includes the zero splitting (when
the m.sub.s=.+-.1 spin states have the same energy) photon energy
of 2.87 GHz. When the photon energy of the RF radiation emitted by
the RF excitation source 630 is the difference in energies of the
m.sub.s=0 spin state and the m.sub.s=-1 or m.sub.s=+1 spin state,
the overall fluorescence intensity is reduced at resonance, as
discussed above with respect to FIG. 3. In this case, there is a
decrease in the fluorescence intensity when the RF energy resonates
with an energy difference of the m.sub.s=0 spin state and the
m.sub.s=-1 or m.sub.s =+1 spin states. In this way the component of
the magnetic field Bz along the NV axis may be determined by the
difference in energies between the m.sub.s=-1 and the m.sub.s=+1
spin states.
[0055] As noted above, the diamond material 620 will have NV
centers aligned along directions of four different orientation
classes, and the component Bz along each of the different
orientations may be determined based on the difference in energy
between the m.sub.s=-1 and the m.sub.s=+1 spin states for the
respective orientation classes. In certain cases, however, it may
be difficult to determine which energy splitting corresponds to
which orientation class, due to overlap of the energies, etc. The
bias magnet 670 provides a magnetic field, which is preferably
uniform on the NV diamond material 620, to separate the energies
for the different orientation classes, so that they may be more
easily identified.
[0056] FIG. 7 is a schematic illustrating a portion of a DNV sensor
with a coil assembly in accordance with some illustrative
implementations. The magnetic sensor shown in FIG. 6 used a single
RF excitation source 630 and a bias magnet 670. The DNV sensor
illustrated in FIG. 7 uses six separate RF elements that also
provide the bias field that is provided the bias magnet 670 in FIG.
6. Accordingly, in various implementations, the DNV sensor shown in
FIG. 7 does not require a separate bias magnetic. FIGS. 7-13
illustrate various components of the DNV sensor.
[0057] In FIG. 7, the portion of the illustrated DNV sensor
includes a heatsink 702 that can connect to the rest of the DNV
sensor via a mounting clamp. Not shown is a light element, such as
a laser or LED that is located within or near the heatsink 702.
Light from the light element travels through a lens tube 706
through a focusing lens tube 718 and through a coil assembly 716
that includes the NV diamond. Light passes into the coil assembly
716 through the NV diamond and exits the coil assembly. Light that
exits the coil assembly passes through a red filter to a photo
sensor assembly 714. The coil assembly 716, red filter, and photo
sensor can all be housed in a lens tube 710 that can be coupled to
lens tube 718 via a lens tube coupler 708. A lens tube rotation
mount 712 allows a rotation adjustment element to be attached that
allows the coil assembly to be rotated in relation to the light
element.
[0058] FIG. 8 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations. The portion of the DNV sensor
that is illustrated contains the coil assembly 816 and the photo
sensor 820. The coil assembly 816 includes six RF elements. Each RF
element has an RF mount that can be used to connect an RF cable
830. Thus, each RF element can have its own RF feed. In various
implementations, the each RF element is fed a unique RF signal. In
other implementations, sub-combinations of the RF elements receive
the same RF feed signal. For example, groups of two or three RF
elements can receive the same RF feed signal. Various connectors
can be used to connect an RF cable 830 to the RF elements, such as
a right angle connector 832. The coil assembly 816, red filter 826,
EMI glass 824, and photo sensor mounting plate can be held in place
using retaining rings 802. A photo sensor 820 can be secured to the
photo sensor mounting plate 822, which can be used to locate the
photo sensor 820 in the path of light that exits the coil assembly
816.
[0059] FIG. 10 is a cross section illustrating a coil assembly in
accordance with some illustrative implementations. In this
illustration, the light path 1030 is shown. The light path allows
for light from the lighting element to pass through the coil
assembly and through the NV diamond 1040. Light exits the NV
diamond and proceeds out of the coil assembly through the light
path 1030.
[0060] The coil assembly includes four RF elements 1002 and two top
and bottom elements 1020. The NV diamond 1040 is held in place via
a diamond plug 1004 that holds the diamond in the mounting block
1006. The RF elements can be held together using various means such
as element mounting screws 1032. The six total RF elements can be
seen in FIGS. 9A and 9B that illustrate a coil assembly in
accordance with some illustrative implementations. Four side RF
elements 902 are shown along with two top and bottom RF elements
920. Each RF element is attached to a center mounting block 904.
Attachment mechanisms such as screws 932 can be used to attach the
RF elements to the mounting block. In the illustrated
implementation, a light injection hole 930 is the bottom RF element
and the light exit hole 910 is in the top RF element. Accordingly,
in this implementation light passes through the coil assembly and
the diamond in a straight path. In one implementation, the light
enters a face of the NV diamond and exits through another face of
the NV diamond. As described below, in other implementation the
light path through the coil assembly is not straight and may take
on multiple paths of egress.
[0061] FIG. 11 is a schematic illustrating a side element 1100 of a
coil assembly in accordance with some illustrative implementations.
The side element 1100 can include a middle mounting hole and one
other mounting hole. In this implementation, there would be side
elements that had different mounting hole configurations. As shown
in FIG. 11, the side element 1100 has three mounting holes, but not
all mounting holes are required to be used. In one implementation,
the middle mounting hole and one of the remaining two mounting
holes are used, but all three mounting holes are not used. Each
side element 1100 includes an RF connector 1102 that is used to
provide the RF feed signal to the side element.
[0062] FIG. 12 is a schematic illustrating a top or bottom element
1200 of a coil assembly in accordance with some illustrative
implementations. Similar to the side element 1100, the top or
bottom element 1200 includes an RF connector 1202 for receiving an
RF feed signal. The top or bottom element 1200, however, has only
two mounting holes 1204. The three hole is a light path portion
1230 that allows for light to enter or exit the coil assembly.
[0063] FIG. 13 is a schematic illustrating a center mounting block
1300 of a coil assembly in accordance with some illustrative
implementations. The NV diamond is located within the mounting
block 1300. In one implementation, a diamond plug can be used to
hold the NV diamond. The mounting block 1300 can include a diamond
mounting location that provides alignment of the NV diamond. For
example, the mounting block 1300 can include a recess that fits the
NV diamond. Once positioned, the diamond plug can be inserted into
the mounting block 1300 to hold the diamond in place.
[0064] FIGS. 14-17 illustrate another implementation. FIG. 14 is a
cross section illustrating of a portion of a DNV sensor with a coil
assembly in accordance with some illustrative implementations. A
coil assembly 1416 holds an NV diamond within an NV diamond sensor.
The coil assembly 1416 can include six RF elements, four side
elements and two top and bottom elements (shown in FIGS. 15-17). RF
cables 1430 can connect to the RF elements via RF connections 1432.
The RF cables 1430 are used to provide an RF signal to one or more
of the RF elements. The RF signal can be different for each RF
element or subsets of the RF elements can receive different RF
signals. These RF feed signals are used by the RF elements to
provide a uniform microwave RF signal to the NV diamond. In
addition, the arrangement of the RF elements allows the RF elements
to also provide the magnetic bias field to the NV diamond. In the
illustrated implementation, light enters and exits through the top
and bottom elements. Light that exits the NV diamond can pass
through a red filter 1426 and through a light pipe 1450 that is
located within an attenuator 1440. In various implementations, at
least a portion of the light pipe 1450 is located within the
attenuator 1440. Such a configuration allows the photo-sensing
array 1420 to be positioned closer to the NV diamond and remain
unaffected by the EMI of the sensor. Further description of the
benefits of housing a portion of the light pipe within an
attenuator is described in U.S. patent application Ser. No.
15/003,281, entitled "Magnetometer with Light Pipe," filed on the
same day as this application, the contents of which are hereby
incorporated by reference. Retaining rings 1402 can be used to hold
the various elements together and in position.
[0065] FIG. 15 is a schematic illustrating a coil assembly in
accordance with some illustrative implementations. FIG. 16 is a
schematic illustrating a cross section of a coil assembly in
accordance with some illustrative implementations. The coil
assembly includes two bottom or top RF elements 1506 and 1606. In
the illustrated implementation, the top or bottom RF elements are
circular and are larger compared to the side elements 1502 and
1602. In between the top or bottom elements are the four side
elements 1502 and 1602. FIG. 17 is a schematic illustrating a side
element of a coil assembly in accordance with some illustrative
implementations. The side element has an RF connector 1702 used to
provide a feed RF signal to the RF element. The side RF elements do
not include any mounting holes as the side RF elements can be held
into position by the top and bottom RF elements. In various
implementations, each of the RF elements can include multiple
stacked spiral antenna coils. These stacked coils can occupy a
small footprint and can provide the needed microwave RF field in
such that the RF field is uniform over the NV diamond. Additional
details regarding RF elements and RF circuit boards that contain RF
elements are described in U.S. patent application Ser. No.
15/003,309, entitled "DIAMOND NITROGEN VACANCY SENSOR WITH DUAL RF
SOURCES," filed on the same day as this application, the contents
of which are hereby incorporated by reference. In various
implementations, each RF side element and top and bottom RF
elements can include an RF element or an RF circuit board.
[0066] The NV diamond 1622 is located within the six RF elements.
The RF elements can be held together by mounting screws 1510 and
1610. A light injection portion 1504 of the top RF element allows
light to enter the coil assembly and enter the NV diamond. The
bottom portion includes a corresponding light egress portion 1620.
The NV diamond can fit within a mounting block 1608 and be held in
position via a diamond plug 1624.
[0067] FIGS. 18-24 illustrate another implementation. In the
illustrated implementation, light enters the NV diamond through an
edge of the NV diamond and exits through multiple faces of the NV
diamond. How light enters and exits the NV diamond is based upon
the orientation of the NV diamond relative to the light source.
Thus, in various implementations the NV diamond can be repositioned
to allow light to enter and exit from edges, faces, and/or both
edges and faces.
[0068] FIG. 18 is a schematic illustrating a portion of a DNV
sensor with a coil assembly in accordance with some illustrative
implementations. Similar to other implementations, the DNV sensor
includes a light source heatsink 1802 and 1902, a mounting clamp
1804 for the heatsink 1802, a lens tube 1806, a focusing lens tube
1818, a coil assembly 1816 located, and red filters and photo
sensor assemblies 1814, and a lens tube rotation mount 1812 and
1912. FIG. 19 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations. In this implementation, the
light source is an LED 1906. In other implementations, other light
sources, such as a laser, can be used. A thermal electric cooler
1904 can be used to provide cooling for the LED 1906. Light from
the LED 1906 can be focused using lens 1918. The focused light
enters the NV diamond that is located within the coil assembly
1916.
[0069] FIG. 20 is a schematic illustrating a cross section of a
portion of a DNV sensor with a coil assembly in accordance with
some illustrative implementations. In this figure, the NV diamond
2040 within the coil assembly can be seen. Light enters the edge of
the NV diamond in this implementation and exits the NV diamond 2040
from two faces of the NV diamond 2040. The light the exits the NV
diamond 2040 travels one of two light pipes 1914. In various
implementations, at least a portion of the light pipe is located
within an attenuator. The NV diamond 2040 can be held in place
within the coil assembly via center mounting blocks 2050. The
mounting blocks and the coil assembly can be held in place using
retaining rings 2052. RF cables 2030 connect to the RF elements via
RF connectors 2032 to provide an RF feed signal to the RF elements
as described in greater detail below.
[0070] FIG. 21 is a schematic illustrating a coil assembly in
accordance with some illustrative implementations. FIG. 22 is a
schematic illustrating a cross section of a coil assembly in
accordance with some illustrative implementations. FIG. 21 shows
four side elements 2014 and 2242 located between the top and bottom
RF elements 2112 and 2212. The center mounting blocks 2108 and 2208
and retaining plate 2106 and 2206 are also shown. As describe
above, light enters the NV diamond 2240 at an edge. The light
reaches the NV diamond via a light injection opening 2101 and 2202.
Light exits the NV diamond 2240 substantially orthogonal to the
ingress path through two light exit holes 2110. A second light exit
hole is opposite of the illustrated light exit hole 2110. In FIG.
22, the second light exit hold is behind the NV diamond 2240.
[0071] FIG. 23 is a schematic illustrating a side element of a coil
assembly in accordance with some illustrative implementations. The
individual side element includes an RF connector 2304 and a light
egress portion 2302. The side element, however, does not include
any attachment holes. Rather, the side elements can be held in
place within the coil assembly using the top and bottom elements as
illustrated in FIGS. 24A and 24B.
[0072] FIGS. 24A and 24B are schematics illustrating top and bottom
elements of a coil assembly in accordance with some illustrative
implementations. The top element includes slots 2406 for aligning
and holding into position the four RF side elements. The light
injection hole 2404 is also shown. RF connectors 2404 located on
both the top RF element and the bottom RF element allow for
separate RF feeds to be separately applied to the top and bottom RF
elements.
[0073] The foregoing description is provided to enable a person
skilled in the art to practice the various configurations described
herein. While the subject technology has been particularly
described with reference to the various figures and configurations,
it should be understood that these are for illustration purposes
only and should not be taken as limiting the scope of the subject
technology. In some aspects, the subject technology may be used in
various markets, including for example and without limitation,
advanced sensors and mobile space platforms.
[0074] There may be many other ways to implement the subject
technology. Various functions and elements described herein may be
partitioned differently from those shown without departing from the
scope of the subject technology. Various modifications to these
embodiments may be readily apparent to those skilled in the art,
and generic principles defined herein may be applied to other
embodiments. Thus, many changes and modifications may be made to
the subject technology, by one having ordinary skill in the art,
without departing from the scope of the subject technology.
[0075] Phrases such as an aspect, the aspect, another aspect, some
aspects, one or more aspects, an implementation, the
implementation, another implementation, some implementations, one
or more implementations, an embodiment, the embodiment, another
embodiment, some embodiments, one or more embodiments, a
configuration, the configuration, another configuration, some
configurations, one or more configurations, the subject technology,
the disclosure, the present disclosure, other variations thereof
and alike are for convenience and do not imply that a disclosure
relating to such phrase(s) is essential to the subject technology
or that such disclosure applies to all configurations of the
subject technology. A disclosure relating to such phrase(s) may
apply to all configurations, or one or more configurations. A
disclosure relating to such phrase(s) may provide one or more
examples. A phrase such as an aspect or some aspects may refer to
one or more aspects and vice versa, and this applies similarly to
other foregoing phrases
[0076] A reference to an element in the singular is not intended to
mean "one and only one" unless specifically stated, but rather "one
or more." The term "some" refers to one or more. Underlined and/or
italicized headings and subheadings are used for convenience only,
do not limit the subject technology, and are not referred to in
connection with the interpretation of the description of the
subject technology. All structural and functional equivalents to
the elements of the various embodiments described throughout this
disclosure that are known or later come to be known to those of
ordinary skill in the art are expressly incorporated herein by
reference and intended to be encompassed by the subject technology.
Moreover, nothing disclosed herein is intended to be dedicated to
the public regardless of whether such disclosure is explicitly
recited in the above description.
* * * * *