Two-media laser threshold magnetometry - A magnetic-field-dependent laser threshold
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-08-01 |
| Journal | APL Photonics |
| Authors | Yves Rottstaedt, Lukas Lindner, Florian Schall, Felix A. Hahl, Tingpeng Luo |
| Institutions | Tohoku University, Fraunhofer Institute for Applied Solid State Physics |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Two-media Laser Threshold Magnetometry
Section titled âTechnical Documentation & Analysis: Two-media Laser Threshold MagnetometryâExecutive Summary
Section titled âExecutive SummaryâThis document analyzes the research paper detailing the first experimental realization of a magnetic-field-dependent laser threshold (LTM) using a dual-media cavity incorporating Nitrogen-Vacancy (NV) doped diamond and a Vertical External Cavity Surface Emitting Laser (VECSEL).
- Core Achievement: Successful demonstration of a magnetic-field-dependent laser threshold shift, establishing the foundation for achieving 100% ODMR contrast in future LTM magnetometers.
- Current Performance: Shot-noise-limited sensitivity of 49.07(33) pT/âHz was calculated for the current setup using a 300 ”m thick, 1.86 ppm NV diamond.
- Projected Performance: Simulations predict a potential sensitivity improvement down to 4.9 fT/âHz by utilizing optimized diamond material with significantly higher NV concentration.
- Methodology: LTM exploits stimulated emission at 750 nm, providing high magnetic-field-dependent contrast and coherent signal strength superior to traditional spontaneous emission methods.
- Material Requirements: High-quality, low-strain, [100]-oriented Single Crystal Diamond (SCD) with precise NV concentration control is critical for maximizing contrast and achieving projected sensitivity targets.
- Observed Challenges: The study noted limitations due to induced absorption at high pump powers and field inhomogeneity resulting from the relatively thick 300 ”m diamond sample.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental setup and simulation results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Projected Sensitivity (Optimized) | 4.9 | fT/âHz | Optimized NV concentration |
| Measured Sensitivity (Current) | 49.07(33) | pT/âHz | Shot-noise-limited, cw-ODMR |
| Diamond Thickness (d) | 300 | ”m | HPHT [100]-oriented sample |
| NV Concentration (NNV) | 1.86 | ppm | Estimated concentration in diamond |
| Diamond Absorption | 0.01 | cm-1 | Measured absorption coefficient |
| VECSEL Emission Wavelength (λ) | 750 | nm | Stimulated emission wavelength |
| Pump Laser Wavelength (λg) | 532 | nm | Green laser used for optical pumping |
| Fixed Diamond Pump Power (PNV) | 8 | W | Used for threshold measurement |
| Cavity Mode Radius (wa) | 100 | ”m | At the position of the diamond |
| Cavity Outcoupling Reflectivity (R) | 99.98 | % | External concave mirror (M1) |
| Cavity Loss Rate (Ksim) | 49.5 | MHz | Optimized fit parameter for simulation |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a highly specialized dual-media optical setup and precise material handling:
- Cavity Design: A linear hemispherical optical cavity was constructed, utilizing the VECSEL back mirror and an external concave mirror (M1, Radius of Curvature ROC = 50 mm).
- Diamond Preparation: A 3x3x0.3 mm commercial HPHT [100]-oriented diamond underwent Low Pressure High Temperature (LPHT) treatment, irradiation, and annealing to create NV centers (estimated 1.86 ppm concentration).
- Independent Pumping: Both the VECSEL gain structure (AlGaAs/GaAs) and the NV-doped diamond were pumped independently using focused green lasers (λg = 532 nm).
- LTM Measurement: The magnetic-field-dependent laser threshold was demonstrated by fixing the diamond pump power (8 W) and varying the VECSEL pump power, observing the cavity output shift when spin mixing was introduced via a permanent magnet.
- ODMR Measurement: Optically Detected Magnetic Resonance (ODMR) was performed by sweeping the frequency of a resonant microwave drive (40 dBm power) delivered via a 1 mm diameter loop antenna.
- Modeling: Experimental data was supported by an analytical simulation based on a rate model, which was also used to derive a generalized formula for shot-noise-limited sensitivity relevant for high-contrast LTM systems.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical role of high-quality, customized diamond material in achieving projected femtotesla-level sensitivities. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond required to replicate and extend this LTM research.
Applicable Materials for LTM Optimization
Section titled âApplicable Materials for LTM OptimizationâTo achieve the projected 4.9 fT/âHz sensitivity, the researchers require an optimized diamond with significantly higher NV concentration and reduced thickness to improve field homogeneity.
| Requirement | 6CCVD Solution | Technical Advantage |
|---|---|---|
| High NV Concentration | Optical Grade SCD (Single Crystal Diamond) | Custom-grown SCD with tailored NV concentrations (e.g., > 5 ppm) and precise doping profiles, essential for maximizing magnetic contrast. |
| Low Loss / High Finesse | Optical Grade SCD | Superior surface quality (Ra < 1 nm) minimizes scattering losses, crucial for maintaining the high cavity finesse (R = 99.98%) required for LTM. |
| Reduced Thickness | Custom Dimensions | Plates/wafers available from 0.1 ”m up to 500 ”m. Thinner SCD (e.g., 100 ”m) reduces field inhomogeneity and improves microwave coupling efficiency. |
| Integrated Microwave Structures | Custom Metalization | In-house capability for depositing Au, Pt, Ti, and other metals allows for the creation of optimized on-diamond microwave resonators, addressing the field inhomogeneity noted in the paper. |
Customization Potential for Next-Generation LTM
Section titled âCustomization Potential for Next-Generation LTMâ6CCVDâs advanced manufacturing capabilities directly address the limitations identified in the current research:
- Precision Thickness Control: The current 300 ”m thickness contributed to field inhomogeneity. 6CCVD can supply SCD plates down to 100 ”m or less with high parallelism, enabling tighter integration with microwave structures and improved sensitivity.
- Large Area Availability: 6CCVD offers PCD plates/wafers up to 125 mm in diameter, supporting scaling efforts for multi-sensor arrays or larger cavity designs, should the research transition from SCD to PCD for specific applications.
- Integrated Electrodes: To refine the microwave implementation and enhance contrast, 6CCVD offers custom metalization services (Ti/Pt/Au) for patterning electrodes directly onto the diamond surface, eliminating the need for bulky external loop antennas.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the physics and material science of NV centers and MPCVD growth. We can assist researchers in selecting the optimal material parameters (NV concentration, crystal orientation, thickness, and surface termination) necessary to overcome the challenges of induced absorption and maximize the shot-noise-limited sensitivity for similar laser threshold magnetometry projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Nitrogen-vacancy (NV) centers in diamond are a promising platform for high-precision magnetometry. In contrast to the use of spontaneous emission in a number of NV-magnetometers, laser threshold magnetometry exploits stimulated emission of NV centers by placing an NV-doped diamond inside an optical cavity. The NV laser system is predicted to reach a high magnetic-field-dependent contrast and coherent signal strength, leading to an improved magnetic field sensitivity combined with high linearity. Here, we consider a two-media setup where the cavity additionally includes a vertical external cavity surface emitting a laser. This optically active material compensates cavity losses at 750 nm while still allowing for magnetic-field-dependent effects from the NV-diamond. We demonstrate a magnetic-field-dependent laser threshold and investigate the effects of pump laser induced absorption of the diamond. The experimental data are supported by an analytical simulation based on a rate model. Furthermore, we derive a generalized formula to compute the shot-noise-limited magnetic field sensitivity in the regime of high contrast, yielding 49.07(0.33)pT/Hz for the present setup. Simulations with an optimized NV-diamond suggest that values down to 4.9fT/Hz are possible.