Diamond-on-chip magnetic field camera for mobile imaging
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-12 |
| Journal | Physical Review Applied |
| Authors | Julian M. Bopp, Hauke Conradi, Felipe Perona MartĂnez, Anil Palaci, Jonas Wollenberg |
| Institutions | Ferdinand-Braun-Institut, Leibniz Institute of Surface Engineering |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Diamond-on-Chip Magnetic Field Camera
Section titled âTechnical Documentation & Analysis: Diamond-on-Chip Magnetic Field CameraâReference Paper: Bopp et al., Diamond-on-chip magnetic field camera for mobile imaging, Phys. Rev. Applied 23, 034024 (2025).
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a miniaturized, integrated, and fiber-packaged magnetic field camera utilizing Nitrogen-Vacancy (N-V) centers in diamond, addressing the need for robust, mobile quantum sensors in applications like neuroscience.
- Core Innovation: Development of a scalable 3 x 3 pixel magnetic field camera integrated onto a diamond substrate using Infrared Absorption Optically Detected Magnetic Resonance (IRA ODMR).
- Miniaturization: The device is fiber-packaged, eliminating the need for bulky free-space optics or moving parts, enabling future hand-held applications.
- Sensing Mechanism: Exploits the N-V- $^1$A$_1 \leftrightarrow ^1$E singlet transition (1042 nm infrared absorption) mediated by 532 nm green pump light.
- Performance Achieved: Demonstrated a reference single-pixel sensitivity of 44.3 nT Hz-1/2 (excluding excess noise) under optimized free-space conditions.
- Imaging Capability: Successfully reconstructed the position of a current-driven solenoid coil, proving spatial magnetic field resolution.
- Material Requirement: Requires high-quality, (111)-oriented Single Crystal Diamond (SCD) with controlled N-V density ($3.0 \times 10^{23}$ m-3) and highly polished facets for efficient fiber coupling.
- Future Scaling: The architecture is scalable to larger N x N arrays, pending improvements in optical coupling efficiency and on-chip integration of microwave structures.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Substrate Size | 1.4 x 1.4 x 0.2 | mm3 | (111)-oriented HPHT diamond |
| N-V Density (nV) | 3.0 x 1023 | m-3 | Achieved via electron irradiation and annealing |
| Pixel Array Size | 3 x 3 | Pixels | Defined by intersecting laser beams |
| Pixel Spacing | 500 | ”m | Limited by fiber diameter and spacing |
| Beam Waist (Dpx) | 80 | ”m | Defines the camera pixel diameter |
| Pump Wavelength | 532 | nm | Green laser for N-V excitation |
| Infrared Wavelength | 1042 | nm | Used for IRA ODMR singlet transition |
| Reference Single-Pixel Sensitivity | 44.3 | nT Hz-1/2 | Optimized free-space setup (excluding excess noise) |
| Multipixel Averaged Sensitivity | 25(10) | ”Trms | Measured root-mean-square noise |
| Best Pixel Sensitivity (3,3) | 10.6 | ”Trms | Corresponds to 10.5 ”T Hz-1/2 ASD |
| ODMR Contrast (C3,3) | 5.1 x 10-6 | Unitless | Highest contrast measured for multipixel sensor |
| Spin Dephasing Time (T2*) | 520(110) | ns | Derived from PIR-dependent noise measurement |
| Microwave Frequency (D) | 2.87 | GHz | Zero-field splitting of the N-V ground state |
Key Methodologies
Section titled âKey MethodologiesâThe integrated magnetic field camera relies on precise material preparation and complex photonic integration:
- Diamond Preparation: A (111)-oriented diamond substrate (1.4 x 1.4 x 0.2 mm3) is electron irradiated and annealed to achieve a high N-V ensemble density (3.0 x 1023 m-3).
- Facet Polishing: The four side facets of the diamond are polished to facilitate efficient coupling of pump (532 nm) and infrared (1042 nm) laser beams via integrated fibers.
- Substrate Integration: The diamond is fixed with UV-curing adhesive into trenches etched into a polymer board, which is stabilized by a silicon (Si) submount.
- Fiber Packaging: Single-mode fibers terminated by Graded-Index (GRIN) lenses are integrated into the polymer trenches to collimate and inject the pump and infrared beams across the diamond volume.
- Pixel Definition: The 3 x 3 pixel matrix is defined by the perpendicular intersection points of the collimated pump and infrared laser beams inside the diamond.
- Microwave Delivery: Three impedance-matched inductor lines (rf) consisting of connected rings are fabricated on an AlN printed-circuit board and placed in close proximity to the diamond surface to drive the N-V spin transitions.
- Sensing Technique: Infrared Absorption Optically Detected Magnetic Resonance (IRA ODMR) is performed by modulating the microwave frequency around the N-V resonance (2.87 GHz) and detecting the resulting change in 1042 nm infrared absorption using a balanced photodetector and lock-in amplification.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe development of next-generation, high-sensitivity, integrated quantum sensors, as demonstrated in this paper, critically depends on high-precision diamond material engineering and fabrication. 6CCVD is uniquely positioned to supply the necessary components and expertise to overcome the current limitations identified by the researchers (e.g., suboptimal polishing, non-optimal beam overlap, and integration challenges).
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, 6CCVD recommends the following materials, optimized for high-fidelity N-V ensemble creation and optical integration:
| 6CCVD Material | Specification | Relevance to Research |
|---|---|---|
| Optical Grade SCD | (111) or (100) orientation, Low [N] < 1 ppm, High Purity. | Essential for high-contrast ODMR and minimizing background absorption. (111) orientation is required for the specific offset field sensing scheme used. |
| Custom SCD Plates | Thickness: 0.1 ”m to 500 ”m. Custom dimensions up to 10 mm substrates. | Provides the necessary thin, high-quality substrate for on-chip integration and fiber coupling. |
| High-Density N-V Precursors | SCD with controlled initial Nitrogen concentration for subsequent irradiation/annealing. | Allows researchers to achieve the required N-V density ($3.0 \times 10^{23}$ m-3) necessary for ensemble sensing sensitivity. |
Customization Potential
Section titled âCustomization PotentialâThe paper highlights several limitations directly solvable by 6CCVDâs advanced fabrication services:
| Research Requirement / Limitation | 6CCVD Solution | Technical Advantage |
|---|---|---|
| Suboptimal Facet Polishing | Ultra-Precision Polishing (Ra < 1 nm) on SCD facets. | Ensures near-perfect optical interfaces for efficient fiber coupling and optimal beam overlap within the diamond volume, directly addressing the reduced contrast issue noted in the paper. |
| Microwave Inductor Integration | Custom Metalization Services (Ti/Pt/Au, W, Cu). | Enables direct fabrication of microwave inductor lines (rf) onto the diamond surface or integrated polymer platform, reducing proximity losses and facilitating true on-chip integration. |
| Scaling to Larger Arrays | Large-Area PCD/SCD Substrates (PCD up to 125 mm). | Supports the development of next-generation N x N pixel arrays for wider field-of-view imaging, overcoming the current $1.4 \times 1.4$ mm2 limitation. |
| Custom Dimensions | Precision Laser Cutting & Shaping. | Provides exact substrate dimensions and trench features required for precise alignment and integration of GRIN fibers and polymer components. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in quantum material science and can assist researchers in optimizing material selection for similar N-V Ensemble Magnetometry projects. We offer consultation on:
- N-V Creation Recipe Optimization: Tailoring irradiation and annealing protocols to achieve specific N-V densities and charge states for maximum IRA ODMR contrast.
- Optical Loss Minimization: Designing substrate dimensions and specifying polishing requirements to minimize optical losses in the infrared path, crucial for achieving shot-noise limited sensitivity (44 nT Hz-1/2 goal).
- Integration Strategy: Advising on metal stack selection and deposition parameters for robust, high-frequency microwave structures on diamond.
Global Supply Chain
Section titled âGlobal Supply Chainâ6CCVD offers reliable, global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond substrates and integrated components, supporting international research timelines.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Integrated and fiber-packaged magnetic field sensors with a sensitivity sufficient to sense electric pulses propagating along nerves and a spatial resolution fine enough to resolve their propagation directions will trigger tremendous steps ahead in medical diagnostics and research. Nitrogen-vacancy centers in diamond are best suitable for such sensing tasks under ambient conditions. Current research on uniting a good sensitivity and high spatial resolution is facilitated by scanning or imaging techniques. However, these techniques employ moving parts or bulky microscopes. Both approaches cannot be miniaturized to build robust, adjustment-free, hand-held devices. In this work, we introduce concepts for spatially resolved magnetic field sensing and two-dimensional gradiometry with an integrated magnetic field camera. The camera utilizes infrared absorption optically detected magnetic resonance (IRA ODMR) mediated by perpendicularly intersecting infrared and pump laser beams forming a pixel matrix. We demonstrate our scalable <a:math xmlns:a=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ><a:mn>3</a:mn><a:mo>Ă</a:mo><a:mn>3</a:mn></a:math> pixel sensorâs capability to reconstruct the position of an electromagnet. In a reference measurement, we show an IRA ODMR sensitivity of <d:math xmlns:d=âhttp://www.w3.org/1998/Math/MathMLâ display=âinlineâ overflow=âscrollâ><d:mn>44</d:mn><d:mspace width=â0.1emâ/><d:mi>nT</d:mi><d:mspace width=â0.1emâ/><d:msup><d:mi>Hz</d:mi><d:mrow><d:mo>â</d:mo><d:mn>1</d:mn><d:mo>/</d:mo><d:mn>2</d:mn></d:mrow></d:msup></d:math>.