Abstract: A device for generating and controlling a magnetic field strength and a method for generating and controlling a magnetic field strength are disclosed. The generation is very stable and precise. Preferably, reference values of physical variable can be generated relatively simply and economically. In addition, magnetic flux densities can be measured with high resolution and, in particular, highly robustly. The device and the method can also be used for transmitting information, in particular for ultra-wide band communication. The required devices can be very small, in particular miniature, and mobile.

Abstract: A optically pumped magnetometer includes a cell filled with an alkali metal; a pump light source that generates a pump light; a probe light source that generates a probe light; a signal output unit that obtains an output signal related to magnetism, which is received by the cell, based on the probe light which has passed through the cell; a coil unit that generates a static magnetic field along a pump optical axis in a region of disposition of the cell; and a computer that controls operation of the coil unit. The computer outputs a first control signal to set an intensity of the static magnetic field to a first intensity, and a second control signal to set the intensity of the static magnetic field to a second intensity different from the first intensity.

Abstract: A system for measuring magnetic field gradients comprising a multi-bay support structure with a series of raised contact shoulders separated from each other by voids. An optical fiber is spaced along the length of the multi-cell support structure and traverses all the raised contact points and voids. The optical fiber has a plurality of Fiber Bragg gratings (FBGs) spaced lengthwise, each FBG suspended in a void. In addition, a plurality of ferromagnetic members are strung onto the optical fiber, each suspended in a void. Magnetic field gradients act on the ferromagnetic member to create localized tension in the optical fiber. The FBG's refractive indices are monitored, tension is calculated therefrom, and the tension is correlated to the magnetic field gradient. This greatly simplifies mechanical, optical, electronic and computational complexity and is bay suited for any FOSS array for measuring magnetic fields using many dense measurement points.

Abstract: A magnetic field measurement system that includes at least one magnetometer; at least one magnetic field generator; a processor coupled to the at least one magnetometer and the at least one magnetic field generator and configured to: measure an ambient background magnetic field using at least one of the at least one magnetometer in a first mode selected from a scalar mode or a vector mode; generate, in response to the measurement of the ambient background magnetic field, a compensation field using the at least one magnetic field generator; and measure a target magnetic field using at least one of the at least one magnetometer in a spin exchange relaxation free (SERF) mode which is different from the first mode.

Abstract: The atomic magnetometer includes a light source device configured to output a linearly polarized irradiation light and a circularly polarized pump light, a first vapor cell including an alkali metal atom, receiving the linearly polarized irradiation light, and outputting a first transmitted light, a second vapor cell including an alkali metal atom, receiving the linearly polarized irradiation light, and outputting a second transmitted light, a magnetic field application device configured to apply a bias magnetic field in opposite directions to the first vapor cell and the second vapor cell, and a measuring device configured to obtain the magnetic field signal based on a differentiation of a first polarization rotation signal corresponding to a polarization state of the first transmitted light and a second polarization rotation signal corresponding to a polarization state of the second transmitted light.

Abstract: Systems and methods for an integrated photonics quantum vector magnetometer are provided herein. In certain embodiments, a device includes a substrate; a radio frequency emitter that emits energy in a range of radio frequencies; and a waveguide layer formed on the substrate. The waveguide layer includes a first waveguide of a first material, wherein a probe laser is propagating within the first waveguide; and a second waveguide, wherein the second waveguide is positioned proximate to the first waveguide along a coupling length such that a pump laser propagating within the second waveguide is coupled into the first waveguide along the coupling length, wherein the pump laser causes the first material to absorb the probe laser at one or more frequencies in the range of frequencies. Moreover, the device includes a processing device that calculates a magnetic field strength based on an identification of the one or more frequencies.

Abstract: An object of the present invention is to provide a power conversion device capable of reliably discharging a voltage smoothing capacitor even when a circuit unit that outputs a discharge control signal fails. The power conversion device includes a voltage smoothing capacitor that is electrically connected in parallel with an inverter circuit unit, a discharge resistor that is electrically connected in parallel with the voltage smoothing capacitor, a switching element that is connected in series with the discharge resistor, a motor controller that selectively outputs a High-level signal and a Low-level signal as a discharge control signal, a switching signal circuit unit that outputs a rectangular wave signal having a predetermined duty, and a logic circuit that outputs any one of a rectangular wave signal having the same duty as the duty of the rectangular wave signal and a rectangular wave signal having a duty to the switching element based on the discharge control signal and the rectangular wave signal.

Abstract: An optically pumped magnetometer device includes a first vapor cell having a light input window; a first light source configured to produce a first light beam; a first prism optic configured to receive the first light beam from the first light source and redirect the first light beam into the first vapor cell at a non-normal direction relative to the light input window of the first vapor cell; and a first light detector configured to receive the first light beam after passing through the first vapor cell. The device may also include additional light sources and light detectors which may share the prism optic and vapor cell (or utilize another prism optic or vapor cell or both).

Abstract: A device includes a substrate and nanoscale fin formed from a first material, a RF emitter that emits energy in a range of radio frequencies, and a waveguide formed from a second material. The device further includes a bichromatic directional coupler configured to couple pump and probe laser light into the waveguide. The waveguide is positioned proximate to the nanoscale fin along a coupling length such that the pump laser light propagating within the waveguide is coupled into the nanoscale fin from evanescent wave overlap along the coupling length. The pump laser light causes the first material to absorb the probe laser light when energy emitted by the RF emitter is at one or more frequencies dependent on a magnetic field. The device further includes a processor configured to determine a magnetic field strength of the magnetic field based on an identification of the one or more frequencies.

Abstract: Applying a bias magnetic field to a solid-state spin sensor enables vector magnetic field measurements with the solid-state spin sensor. Unfortunately, if the bias magnetic field drifts slowly, it creates noise that confounds low-frequency field measurements. Fortunately, the undesired slow drift of the magnitude of the bias magnetic field can be removed, nullified, or cancelled by reversing the direction (polarity) of the bias magnetic field at known intervals. This makes the resulting solid-state spin sensor system suitable for detecting low-frequency (mHz, for example) changes in magnetic field or other physical parameters.

Abstract: A magnetometer for magnetic detection includes a magneto-optical defect center material having at least one magneto-optical defect center; a radio frequency (RF) exciter system including a radio frequency (RF) excitation source; an optical excitation system including an optical excitation source; an optical detector configured to receive an optical signal based on light emitted by the magneto-optical defect center material due RF excitation and optical excitation provided to the magneto-optical defect center material via the RF excitation source and the optical excitation source, respectively; a magnetic field generator configured to generate a magnetic field detected at the magneto-optical defect center material; and a system controller.

Abstract: A magnetic field measurement system that includes at least one magnetometer; at least one magnetic field generator; a processor coupled to the at least one magnetometer and the at least one magnetic field generator and configured to: measure an ambient background magnetic field using at least one of the at least one magnetometer in a first mode selected from a scalar mode or a vector mode; generate, in response to the measurement of the ambient background magnetic field, a compensation field using the at least one magnetic field generator; and measure a target magnetic field using at least one of the at least one magnetometer in a spin exchange relaxation free (SERF) mode which is different from the first mode.

Abstract: An optical fiber-mounted field sensor for measuring an electric or magnetic field includes an optical fiber configured to receive light from a laser source, a polarizer, a polarization manipulator, electro-optical material or magneto-optical material adjacent to the polarization manipulator, and a high reflection coating. The polarizer is adjacent to an output of the fiber, while the polarization manipulator is adjacent to the polarizer and opposite of the optical fiber. The electro-optical material or magneto-optical material is adjacent to the polarization manipulator, and the high reflection coating is adjacent to the electro-optical material or magneto-optical material. An optical mainframe for sending and receiving optical beams to and from the optical fiber-mounted field sensor is also described.

Abstract: Provided is an electro-optic probe for detecting an electromagnetic wave, including: an electro-optic crystal; and an optical fiber optically coupled to the electro-optic crystal, wherein a direction of a unique axis of the electro-optic crystal and a polarization direction of light from the optical fiber that enters the electro-optic crystal are set to be in line with each other, or wherein a direction of a unique axis of the electro-optic crystal and a unique polarization direction of the optical fiber are set to be in line with each other.

Abstract: In a magnetic field measurement apparatus, a light source irradiates a gas cell with linearly polarized light serving as pump light and probe light in a Z axis direction, and a magnetic field generator applies, to the gas cell, a magnetic field Ax which is a time function f(t) having the amplitude A0 taking n fixed values fi (where i=1, . . . , and n), and a magnetic field Ay which is a time function g(t) having the amplitude A0 taking m fixed values gj (where j=1, . . . , and m) in each of X axis and Y axis directions. A calculation controller calculates a magnetic field C (Cx, Cy, Cz) of a measurement region using the X axis and Y axis components Ax and Ay of an artificial magnetic field A, and a spin polarization degree Mx corresponding to a measurement value W? from a magnetic sensor.

Abstract: A gradiometer system including one or more magnetic sensor(s) is disclosed. The gradiometer includes an actuation module connectable to the magnetic sensor(s) to vary one or more sensing positions at which a magnetic field is sensed thereby. The one or more sensing positions are varied according to a certain displacement function indicating a predetermined displacement between the sensing positions as a function of time.

Abstract: A method for detecting rotation of a carrier utilizes a device embedded in said carrier that comprises an enclosure containing a gaseous mixture of an alkali metal and a noble gas. The method includes a step of starting up (DEM-MEOP) the device during which the noble gas is polarised by utilizing metastability exchange optical pumping. The start-up step is followed by a step of acquisition (MES-SEOP) by the device of a signal representative of said rotation during which the noble gas is maintained polarised by utilizing spin exchange optical pumping. The invention extends to the device and to an inertial navigation unit integrating said device and to an inertial navigation method implementing the method for detecting rotation of the carrier.

Abstract: An atomic oscillator includes a light emitting element, an atomic cell, and a light receiving element that receives the light passing through the atomic cell. The atomic cell has a first chamber containing alkali metal atoms in a gas state and having a first wall through which the light from the light emitting element passes, a second chamber containing alkali metal atoms in a liquid state and having a second wall, a passage connecting the first chamber and the second chamber to each other, and a part which is disposed between the first chamber and the second chamber and has a thermal conductivity lower than the thermal conductivity of a material forming the first wall and the thermal conductivity of a material forming the second wall.

Abstract: A magnetic field measurement system that includes at least one magnetometer; at least one magnetic field generator; a processor coupled to the at least one magnetometer and the at least one magnetic field generator and configured to: measure an ambient background magnetic field using at least one of the at least one magnetometer in a first mode selected from a scalar mode or a vector mode; generate, in response to the measurement of the ambient background magnetic field, a compensation field using the at least one magnetic field generator; and measure a target magnetic field using at least one of the at least one magnetometer in a spin exchange relaxation free (SERF) mode which is different from the first mode.

Abstract: Systems for screening and health monitoring of materials are provided. The system can include a material embedded with magneto-electric nanoparticles (MENs), a laser configured to direct incident laser light waves at a target area of the material, an optical filter disposed between the laser and the material, and an analyzer configured to detect the laser light reflected from the material.

Abstract: A device for analyzing substances in a sample on the basis of a measurement of nuclear magnetic resonances including a magnetic field device configured to generate a magnetic field. The device is configured such that, in order to detect magnetic resonances induced in the sample by the generation of the magnetic field, provision is made of at least one magnetic field sensor which comprises at least one sensitive component with diamond structures. The diamond structures have nitrogen vacancy centers.

Abstract: A magneto-encephalography device including a plurality of laser threshold magnetometers for measuring a magnetic field is provided. Each laser threshold magnetometer includes an optical cavity, a laser medium which together with the optical cavity has a laser threshold; a laser pump; and a radio-frequency (RF) drive applied to the laser medium at or around a particular resonance frequency which varies depending on the magnetic field, such that depending on the value of the physical parameter, the RF drive induces transitions between at least two states of the laser medium, each state causing a different laser threshold in an intensity of a laser output, wherein the intensity of the laser output provides a measurement of the magnitude of the magnetic field; wherein the laser threshold magnetometers are configured to be placed on a head of a subject to be monitored.

Abstract: A hexagonal ferrite material includes a Y phase hexagonal ferrite material having the composition Sr2Co2Fe12O22 or Sr2-xNaxCo2-xScxFe12O22, 0<x<2, doped with a trivalent element, a tetravalent element, and/or a transition metal.

Abstract: In one embodiment, a method is provided.

Abstract: A manufacturing method for a gas cell includes disposing a holding member including a coating material in a reservoir of a cell having a main chamber, the reservoir communicating with the main chamber, and an opening provided in the reservoir, sealing the cell, heating the holding member so as to generate a vapor of the coating material in the cell, and cooling the cell so as to form a film of the coating material on an inner wall of the cell.

Abstract: A magnetometer includes a light source that provides excitation light and a magneto-optical defect center material with at least one defect center that transmits emitted light when excited by the excitation light. The magnetometer also includes a light sensor that receives the emitted light and a plurality of magnets that provide a bias magnetic field to the magneto-optical defect center material. The magnetometer further includes a ring magnet holder that has an outer ring with an outside surface and a plurality of holders extending from the ring. The plurality of holders hold the plurality of magnets in a same orientation with respect to one another. The magnetometer further includes a mount that has an inside surface. The outside surface of the outer ring slides along the inside surface of the mount.

Abstract: A system for magnetic detection, includes a magneto-optical defect center material comprising a plurality of magneto-optical defect centers, a radio frequency (RF) excitation source, an optical detector and an optical light source. The RF excitation source is configured to provide RF excitation to the material. The optical detector is configured to receive an optical signal emitted by the material. The optical light source is configured to provide optical light to the material, and includes a readout optical light source and a reset optical light source. The readout optical light source is configured to illuminate light in a first illumination volume of the material. The reset optical light source is configured to illuminate light in a second illumination volume of the material, the second illumination volume being larger than and encompassing the first illumination volume. The reset optical light source provides a higher power light than the readout optical light source.

Abstract: A system for magnetic detection includes a nitrogen vacancy (NV) diamond material, a radio frequency (RF) excitation source that provides RF excitation to the NV diamond material, an optical excitation source that provides optical excitation to the NV diamond material, an optical detector that receives an optical signal emitted by the NV diamond material, a magnetic field generator that generates a magnetic field applied to the NV diamond material, and a controller. The controller controls the RF excitation source to apply a first RF excitation having a first frequency and a second RF excitation having a second frequency. The first frequency is associated with a first slope point of a fluorescence intensity response of an NV center orientation of a first spin state, and the second frequency is associated with a second slope point of the fluorescence intensity response of the NV center orientation of the first spin state.

Abstract: An optical sensing platform with an array of sensors, a laser or broadband light source and an optical detector that utilizes surface plasmon resonance based transduction and optical detection is provided. The sensor structure of the platform has a low index support layer, a high contrast grating, a low index spacer and a thin metal film with a target recognition element. The surface plasmon resonance based sensor uses surface plasmon waves to detect changes on the surface of the sensor when a target interacts with the target recognition element. The binding of the target with a recognition element receptor will induce changes in the refractive index of the metal layer, which changes the resonance wavelength of the plasmon wave on the sensor surface, which is used to measure or observe the reaction.

Abstract: A diamond crystal according to the present invention has an NV region containing a complex (NV center) of nitrogen substituted with a carbon atom and a vacancy located adjacent to the nitrogen, on a surface or in the vicinity of the surface, wherein the NV region has a donor concentration equal to or higher than the concentration of the NV centers, or a crystal of the NV region is a {111} face or a face having an off-angle that is ±10 degrees or less against the {111} face, and a principal axis of the NV center is a <111> axis that is perpendicular to the {111} face. Such a diamond crystal enables almost 100% of the NV center to be a state (NV?) of having a negative electric charge, and spin states of the NV? centers to be aligned in one direction.

Abstract: An optical transmitting apparatus includes a variable optical attenuator of a magneto-optical effect type disposed by spatial coupling between a light source and an optical fiber, the variable optical attenuator configured to attenuate light output from the light source and coupled to the optical fiber, according to an input driving voltage; a generator configured to generate the driving voltage of the variable optical attenuator based on information to be superimposed on the light by the variable optical attenuator, the generator inputting the generated driving voltage into the variable optical attenuator; and a controller configured to control a bias of the driving voltage generated by the generator, the controller controlling an amplitude of the driving voltage generated by the generator, based on data according to characteristics between the driving voltage and an attenuation amount of the light by the variable optical attenuator.

Abstract: A microfabricated magnetic resonator is provided. The microfabricated magnetic resonator has one or more resonator portions, each of which is a magnetoelastic resonating structure having a maximum circumference or maximum linear dimension in at least one direction that is less than 1000 ?m. At least one of the resonator portions comprises an electrodeposited material comprising at least a cobalt constituent and an iron constituent.

Abstract: A method of inducing spin polarization in an analyte is provided. The method exposes 14N spin defect centers embedded within 25 nm of a diamond surface to a magnetic field while an analyte is near the surface. The 14N spin defect centers are polarized by treatment with an electromagnetic wave protocol having a visible light pulse (p0); a microwave pulse (mw1), a radio frequency pulse (rf1), a microwave pulse (mw2) and a radio frequency pulse (rf2) resulting in polarization of the nuclear spins of the 14N spin defect centers. Polarized spins in the 14N spin defect centers induce spin polarization in the analyte.

Abstract: An optical magnetometer comprising: an optical resonator having a central void; and a magnetostrictive material located in the central void such that a change in dimension of the magnetostrictive material causes a change in mechanical modes of the optical resonator. Also a method of making the optical magnetometer.

Abstract: A signal processing device is provided for acquisition of predetermined information. The signal processing device includes a light source unit configured to radiate beams of coherent light having a plurality of wavelengths; an imaging unit configured to capture a speckle image representing an interference state of reflected light caused by the light radiated from the light source unit to an object; and a processing unit configured to process, for each of the wavelengths, the speckle image captured by the imaging unit. The processing unit acquires the predetermined information by analyzing a variation amount of the speckle image acquired for each of the wavelengths. The light source unit radiates beams of light having different wavelengths to a plurality of respective objects. The present technology can be applied to a sensor.

Abstract: An optical system for optical communications includes: a signal light exit portion, a first coupler optical system that collects the signal light, a first collimator optical system that collimates the signal light into a parallel light, an optical signal-operating portion that reflects the parallel light, a second collimator optical system that collects the parallel light reflected, a second coupler optical system that collects signal light, and a signal light-receiving portion that receives the signal light incident, wherein: the first collimator optical system is defined by a decentered optical system that includes a reflective surface that tilts with respect to an optical axis of incident signal light and is capable of reflection, and the second collimator optical system is defined by a second decentered optical system that includes a reflective surface that tilts with respect to an optical axis of incident signal light and is capable of internal reflection.

Abstract: Methods and configurations are disclosed for providing band-pass magnetic filtering of signals in magnetic communications and anomaly detection using diamond nitrogen-vacancy (DNV).

Abstract: A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

Abstract: A system for magnetic detection includes a nitrogen vacancy (NV) diamond material comprising a plurality of NV centers, a radio frequency (RF) excitation source configured to provide RF excitation to the NV diamond material, an optical excitation source configured to provide optical excitation to the NV diamond material, an optical detector configured to receive an optical signal emitted by the NV diamond material, and a controller. The optical signal is based on hyperfine states of the NV diamond material. The controller is configured to detect a gradient of the optical signal based on the hyperfine states emitted by the NV diamond material.

Abstract: Described is an apparatus for locally monitoring nerve activity that may be incorporated into a nerve ablation catheter. Such a catheter is equipped with magnetic sensing for both identifying nerves and assessing the success of the ablation. The catheter is also equipped with an ablation instrument for both stimulating and destroying nerve tissue.

Abstract: Methods for forming magneto-optical films for integrated photonic devices and integrated photonic devices incorporating same are described. An optical isolator or any nonreciprocal photonic component for an integrated photonic device can be fabricated by depositing a functional garnet layer directly onto a non-garnet substrate; depositing a seed garnet layer on the functional garnet layer; and after depositing both the functional garnet layer and the seed layer performing an annealing process. Since the seed garnet layer crystalizes faster than the functional garnet layer, crystallization of the functional garnet layer can be accomplished directly on the non-garnet substrate during a single annealing step for the seed layer and the functional garnet layer.

Abstract: One example embodiment includes an atomic sensor system. The system includes a magnetic field generator configured to generate a magnetic field in a volume. The system also includes a vapor cell arranged within the volume and comprising a polarized alkali metal vapor. The system further includes at least one magnetic field trimming system configured to generate a magnetic field gradient within the vapor cell separate from the magnetic field to provide a substantially uniform collective magnetic field within the vapor cell.

Abstract: A device includes a diamond with one or more nitrogen vacancies, a light emitting diode configured to emit light that travels through the diamond, and a photo sensor configured to sense the light. The device also includes a processor operatively coupled to the photo sensor. The processor is configured to determine, based on the light sensed by the photo sensor, a magnetic field applied to the diamond.

Abstract: A device includes a diamond assembly. The diamond assembly includes a diamond with a plurality of nitrogen vacancy centers and electrical components that emit electromagnetic waves. The device also includes a light source configured to emit light toward the diamond and a photo detector configured to detect light from the light source that traveled through the diamond. The device further includes an attenuator between the diamond assembly and the photo detector. The attenuator is configured to attenuate the electromagnetic waves emitted from the electrical components of the diamond assembly.

Abstract: Long spin coherence lifetimes are realized for ensembles of electronic spin impurities in solid state spin systems, for example NV color centers in diamond, by using spin-control RF pulse sequences to provide dynamic decoupling of the ensembles of spin impurities from environmental sources of decoherence such as dipolar and hyperfine interactions with proximal spin and other paramagnetic impurities in diamond. In this way, the measurement sensitivity of the coherent evolution of ensembles of solid state spin impurities are increased. Using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, the spin coherence lifetimes of NV ensembles can be extended to more than 2 ms in room temperature diamond, and sensitivity of magnetometry that uses NV ensembles can be increased.

Abstract: A method of suppressing polarization-dependent loss in a signal. A constant-intensity, analog, optical signal with modulating polarization is transmitted through an optical communications link. The constant-intensity, analog, optical signal with modulating polarization includes an analog radio frequency signal impressed upon a polarization-modulated, laser signal. A polarization-dependent loss of the communications link is determined, the polarization-dependent loss inducing an induced phase shift in the constant-intensity, analog, optical signal with modulating polarization. The constant-intensity, analog, optical signal with modulating polarization is re-oriented using a polarization transformer so as to suppress the induced phase shift.

Abstract: In some embodiments, an apparatus and a system, as well as a method and an article, may operate to acquire a monitoring output from a first distributed feedback (DFB) fiber laser sensor at least partially bonded to a piezoelectric portion of a downhole device, to demodulate the monitoring output to determine a frequency shift in a lasing frequency of the DFB fiber laser sensor, and to correlate the frequency shift to a measure of magnetic field strength to determine a strength of a downhole magnetic field. Additional apparatus, systems, and methods are disclosed.

Abstract: A device includes a diamond assembly. The diamond assembly includes a diamond with a plurality of nitrogen vacancy centers and electrical components that emit electromagnetic waves. The device also includes a light source configured to emit light toward the diamond and a photo detector configured to detect light from the light source that traveled through the diamond. The device further includes an attenuator between the diamond assembly and the photo detector. The attenuator is configured to attenuate the electromagnetic waves emitted from the electrical components of the diamond assembly.

Abstract: An implant with magnetic field recognition, such as an implant that recognizes fields generated by a magnetic resonance imaging (MRI) device. The implant includes at least one voltage source, at least one control unit, at least one communication coil and an optical structure with a Faraday element. The optical structure includes at least one first and second polarization filters and at least one light detector.

Abstract: A method for performing sub-nanometer three-dimensional magnetic resonance imaging of a sample under ambient conditions using a diamond having at least one shallowly planted nitrogen-vacancy (NV) center. A driving radio-frequency (RF) signal and a microwave signal are applied to provide independent control of the NV spin and the target dark spins. A magnetic-field gradient is applied to the sample with a scanning magnetic tip to provide a narrow spatial volume in which the target dark electronic spins are on resonance with the driving RF field. The sample is controllably scanned by moving the magnetic tip to systematically bring non-resonant target dark spins into resonance with RF signal. The dark spins are measured and mapped by detecting magnetic resonance of said nitrogen-vacancy center at each of said different magnetic tip positions. The dark-spin point-spread-function for imaging the dark spins is directly measured by the NV center.